Gordon M. Cragg and David J. Newman
Natural Products Branch, Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, Fairview Center, Suite 206, PO Box B, Frederick, MD 21702-1201 USA.
The NCI (http://www.nci.nih.gov) was established in 1937, its mission being ‘to provide for, foster and aid in coordinating research related to cancer’. In 1955, NCI set up the Cancer Chemotherapy National Service Center to coordinate a national voluntary cooperative cancer chemotherapy program, involving the procurement of drugs, screening, preclinical studies, and clinical evaluation of new agents. The responsibility for drug discovery and preclinical development at NCI now rests with the Developmental Therapeutics Program (DTP) and the subsequent clinical development, generally up through Phase II human trials, is conducted by its companion program, the Clinical Trials Evaluation Program, both being the major components of the Division of Cancer Treatment and Diagnosis (DCTD). Thus for the past 50 years, NCI has provided resources for the preclinical screening, and if warranted by the activities found, clinical development as well, of compounds and materials submitted by scientists and institutions, public and private, worldwide, and has played a major role in the discovery and development of many of the available commercial and investigational anticancer agents.
During this period, more than 500,000 chemicals, both synthetic and pure natural products, have been screened for antitumor activity using a variety of screening methods ranging from in vivo studies against murine tumors, through human tumor xenografts in immunodeficient mice to isolated human tumor cell lines and molecular targets expressed in a variety of formats with the initial systems varying with chronological time.
At first, most of the materials screened were pure compounds of synthetic origin, but the program also recognized that natural products were an excellent source of complex chemical structures with a wide variety of biological activities so ‘samples of opportunity’ were obtained from a variety of sources both inside and outside of the USA government. Thus in the period from 1960 to 1982 (i.e., beginning more than 30 years before the United Nations Convention on Biological Diversity (CBD) was adopted, and continuing until about to 10 years before that date) over 180,000 microbial-derived, some 16,000 marine organism-derived, and over 114,000 plant-derived extracts were screened for antitumor activity, mainly by the NCI, and from these, as mentioned above, a number of clinically effective chemotherapeutic agents have been developed (Cragg and Newman 1999, 2005)
Between 1982 and 1986, the DTP revised its complete screening system moving to an initial in vitro 60 human tumor cell line assay and decided to reinvigorate the natural products collection system by instituting a systematic collection of marine invertebrates and terrestrial plants in 1986. The focus for marine organism collections was originally the Caribbean and Australasia, through collection contracts with organizations in the USA, Australia, and New Zealand, but in 1992, following a competition open to qualified worldwide organizations, the focus was expanded to the central and southern Pacific and to the Indian Ocean (off eastern and southern Africa) through a contract with the Coral Reef Research Foundation in the Federated States of Micronesia, originally based in Chuuk and from 1996 in Palau. The contract was renewed in 2002, permitting subcontractors for the first time in 10 years, and collections are now worldwide. Terrestrial plant collections were also initiated via competitive contracts and, to date, have been carried out in over 25 countries in tropical and subtropical regions worldwide through contracts with the Missouri Botanical Garden (MBG) (Africa and Madagascar), the New York Botanical Garden (Central and South America), the University of Illinois at Chicago (Southeast Asia), the Morton Arboretum and World Botanical Associates (USA mainland and territories), though these plant collection contracts expired at the end of September 2005. Reinstitution of plant collections will depend upon budgetary factors. Over 60,000 plants samples were collected during this period, and the repository of over 120,000 extracts will continue to be studied as a source of potential agents for the treatment all human diseases as discussed below in the section on distribution of extracts.
From the beginning of these systematic collections, all of the NCI collection contractors were required to obtain all the necessary permits, including visas and collecting, shipping, and export permits from the appropriate source-country government (SCG) agencies or departments. In previous collections the samples came from a variety of sources including the USA Department of Agriculture (USDA), companies (predominately the microbial extracts), and from ‘collections of opportunity’, methods that had been utilized by organizations in many countries in the years prior to the CBD.
However, it was realized by NCI from the beginning of the systematic collection processes that there should be a formal recognition of the efforts expended by the source countries in permitting such collections. Therefore concomitantly with the initiation of these collections, efforts commenced within the NCI to devise a method that could aid the source countries in the event that a successful agent was developed from a sample collected in their territories with their prior permission.
There is one very important difference between any document that may be used by a USA government agency (such as the NCI) and any other organization in the USA, including academic institutions or nonprofit organizations funded by NCI or its parent, the National Institutes of Health (NIH) and that is as follows. The NCI is not permitted to ‘encumber a future invention’ in any agreement (35 USC 200). What this means is that unless there has been an invention no formal royalty statement may be used in an agreement. Thus NCI was specifically forbidden to use phrases such as ‘royalties will be X% of sales’ in any collection agreement because the simple act of collection is not an inventive process, contrary to what is often assumed by groups unfamiliar with such operations.
Another aspect to this is that a very large number of both organizations and countries did not fully understand that the definition of an inventor in the USA is defined by national patent law and is significantly different from the criteria for authorship of a scientific paper. In fact, if a person who is not an inventor is placed on a USA patent, or a person who is, is not put on a patent, that patent can be successfully challenged (35 USC 102). Since the only way that NCI can assure that benefits can flow back to a source country is by licensing such a patent for pharmaceutical development and ultimate commercialization, requests or even demands by a country's permitting authorities that there must be a source-country scientist(s) on a patent is not feasible unless they actually participate to the extent that under USA patent law they would be recognized as an inventor. There are, however, many other ways to ensure an interest in patent royalties than being listed as an ‘inventor’.
The NCI provides the contractors with the NCI LOC (available at http://ttb.nci.nih.gov/nploc.html and reprinted here as Appendix A) for transmission to the appropriate authorities and scientific organizations (Mays et al. 1997). The LOC states NCI's willingness to collaborate with local scientists or authorities in the discovery and development of novel drugs from organisms (plants, marine invertebrates, or microbes) collected in their countries or territorial waters, and, if requested, the NCI will enter into formal agreements based on the LOC with the relevant SCG agency or source-country organization (SCO). Appendix B lists countries which have collaborated with NCI in the collection of plants and marine organisms, both countries which have signed LOCs and those which have not, as yet, signed formal agreements with the NCI. However, in the latter case, since these countries are fully aware of the terms of the LOC, they granted the necessary permits for NCI contractor activities without requiring a formal agreement. In this respect, the NCI is totally committed to the terms of the LOC irrespective of whether or not a formal agreement has been signed. This commitment was confirmed in a letter to the Editor of the Botany 2000-ASIA Newsletter from the then Deputy Director of the NCI Division of Cancer Treatment (Kaufman 1993), and has also been stated in presentations by NCI Natural Products Branch (NPB) staff in many forums worldwide.
The feasibility of conducting collection contract activities has been affected as countries have started to formulate and implement access policies. In certain instances, such as in the Philippines with the introduction of Executive Order 247 (EO247), collection programs have had to be terminated due to the complexity of the permit application process. There are, however, indications that the EO247 policies are being reconsidered and modified to simplify the process and facilitate access by bona fide organizations (Benevidez II 2004). In other instances, collections have been temporarily suspended while policies have been implemented. An example has been the case of Papua New Guinea where a regulatory body, the Papua New Guinea Institute of Biodiversity Network (PNGBIONET), has been established to review all applications for collection permits. If the applicant is considered acceptable, PNGBIONET designates a local organization to work with the applicant and formulate a collaborative agreement ensuring appropriate terms of training, technology transfer, and benefit sharing.
In 2001, the NCI signed LOC- and Memoranda of Understanding (MoU)-based agreements with the University of Papua New Guinea and collections are proceeding once more. It is interesting that NCI NPB staff have been regularly consulted, not only by the scientific and regulatory communities in Papua New Guinea, but by similar communities in other countries seeking guidance in formulating appropriate access and collaborative policies.
As stated above, several source countries have participated in the NCI contract collection programs without formally entering into LOC-based agreements with the NCI. The reasons for not requiring a formal agreement were not stated, but it is possible that the particular source country had not formulated official access policies at the time of the collections, but accepted the terms of the LOC ‘in good faith’ or, as in the case of a number of Commonwealth countries or countries whose political system evolved from the British Empire rather than from the USA or European models, there often is no formal entity that has authority over all lands and seas and therefore may sign such a document.
This absence of formal agreements has not been due to lack of effort on the part of the NCI contractors or NPB staff to solicit formal agreements from the source countries involved. Indeed, NPB staff has interacted with SCG representatives and scientists, both in their countries, or more frequently during NCI-sponsored visits to NCI and contractor USA-based home facilities. The purpose of these visits is to provide opportunities for source-country officials and scientists from SCOs to observe the NCI drug-discovery facilities and the processes to which their raw materials are subjected, and to discuss collaboration in the drug-discovery process. A list of over 65 source-country officials and scientists, who have visited NCI, to discuss either participation in NCI contract collections or direct collaboration in the drug-discovery process, is given in Appendix C. However, as mentioned earlier, it should be stressed that NCI is totally committed to the terms of the LOC irrespective of whether or not a formal agreement has been signed with a source country participating in contract collections.
The opening paragraph of the LOC states: ‘While investigating the potential of natural products in drug discovery and development, NCI wishes to promote the conservation and sustainable utility of biological diversity, ...’ (Appendix A). This commitment to conservation is also a condition of an award of an NCI collection contract. Would-be contractors receive specific instructions in the NCI Request for Proposals (RFP): ‘Endangered species listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) must not be collected, and sound environmental practices should be exercised.’
Collection contractors are requested to refer to literature on the medicinal use of plants and other organisms found in their regions of collection, and, where feasible, to consult with local healers concerning the use of medicinal plants and their method of preparation, as a guide to the collection of species of interest. This is also alluded to in the LOC (Role of SCG/SCO, clause 2), and the LOC states that all information will be kept confidential, with publication of such information being contingent on permission being granted by the traditional healer or community, and with proper acknowledgment being made for their contribution. The main goal of the NCI, however, is to collect species from as wide a variety of families and genera as possible, with avoidance of the collection of too many species from one family to the exclusion of species from other families of interest. The NCI recognizes that cancer is not likely to be a major health concern of indigenous communities which are more focused on the treatment of devastating parasitic diseases such as malaria, resulting in the predominant identification of local plants and other organisms having efficacy against these diseases.
The advanced development of a potential drug from plant or marine sources generally is going to require the re-collection of large quantities of the source raw material for production of sufficient drug for preclinical and clinical development. While the total synthesis of the drug may be possible, the structural and stereochemical complexity of most naturally derived drugs often precluded the development of economically feasible large-scale total syntheses, though with advances in methodology in the 2001-date time frame, this may well be a favorable route for some molecules. Semi-syntheses from natural precursors are applied in certain cases, e.g., the conversion of baccatin III derivatives isolated from Taxus baccata to Taxol® and the synthesis of Yondelis® from bacterially sourced cyanocycline B. The NCI requires that a thorough survey of the abundance, range and distribution of the source organism be undertaken as a prelude to any large-scale collection (LOC, Role of SCG/SCO, clause 4). Such surveys are done in close collaboration with the local authorities and populations and only in instances where sustainable harvest is assured will extensive collections be approved. Significant examples of this policy were the isolation of the potential anti-HIV agent, (-)-calanolide B, from the latex of the plant Calophyllum teysmanii and the purification of halichondrin B from large-scale harvesting of the marine sponge, Lyssodendoryx species, from New Zealand waters (see case studies, below).
Where sustainable harvest from the wild is not considered possible, the feasibility of mass propagation of the organism in the source country is explored. This was undertaken in the production of the potential anti-HIV agent, michellamine B, from the Cameroon plant Ancistrocladus korupensis (see case study, below). Again, the local authorities and population were closely involved with the project.
In carrying out these collections, the NCI contractors work closely with qualified organizations in each of the source countries. Botanists and marine biologists from SCOs collaborate in field collection activities and taxonomic identifications, and their knowledge of local species and conditions is indispensable to the success of the NCI collection operations. When necessary and relevant, SCOs provide facilities for the preparation, packaging and shipment of the samples to the NCI's Natural Products Repository (NPR) in Frederick, MD USA.
In a significant number of cases, these interactions materially aid the procurement of both the initial collection permits and most importantly, the specific export documentation required by the country of origin. There is another important point as well that needs to be emphasized here and that is that all collections are imported into the USA against specific Department of Agriculture (USDA) and Fish and Wildlife Service (FWS) permits held by the NPB as the NCI representative.
The collaboration between the SCOs and the NCI collection contractors, in turn, provides support for expanded research activities by source-country biologists. The deposition of a voucher specimen of each species collected in the national herbarium or repository is expanding source-country holdings of their biota. (See Box 1 for potential complications in identifying the source organism.) NCI contractors also provide training opportunities for local personnel through conducting workshops and presentation of lectures, both in-country and at the contractor's USA facilities. As an example, during the contract cycle from 1996 to 2001, MBG offered one-month curatorial workshops at their facilities in St. Louis, MO USA in May 1999 and March 2001. Through its contract with MBG, the NCI supported the attendance of seven botanists from Madagascar, Ghana, Tanzania, and Zambia, and participants were instructed in collections management, botanical research methodology, biodiscovery, conservation and global information systems.
In addition, through its LOC (Appendix A) and agreements based upon it, the NCI invites scientists nominated by SCOs to visit its facilities, or equivalent facilities in other approved USA organizations, for 1 to 12 months to participate in collaborative natural products research involving the screening and bioassay-directed fractionation of extracts. (LOC, Role of DTP/DCTD/NCI, clauses 4 and 5). Twenty-two such visits have been sponsored since 1990, and the scientists involved are listed in Appendix D.
The LOC also dictates benefit sharing and use of source-country resources in the event of the licensing and development of a promising drug candidate (LOC, Role of DTP/DCTD/NCI, clauses 8–10). Successful licensees are required to negotiate agreements with SCG agencies or SCOs dictating terms of collaboration and compensation. The terms apply irrespective of whether the potential drug is the actual natural isolate or a product structurally based upon the isolate, a synthetic material for which the natural product material provided a key development lead, or a method of synthesis or use of any aforementioned isolate, product, or material; though the percentage of royalties negotiated as payment might vary depending upon the relationship of the marketed drug to the originally isolated product. The first milestone in the licensing agreement is that a signed agreement must be presented to the NIH's Office of Technology Transfer (OTT; the group within NIH that formally licenses all NIH patents) within one year of the initial granting of the license.
As mentioned earlier, the original formulation of the NCI policies for collaboration and compensation embodied in the LOC predated the drafting of the CBD (http://www.biodiv.org/convention/articles.asp) by at least four years with the first agreement being one signed by the Malagasy Republic in 1990. No changes in the LOC have arisen as a result of the CBD.
One of the scientific precepts underlying the new collection program (i.e., post-1985) was that enough natural product materials should be collected in the initial collection, subject to environmental concerns, for the chemical identity of any active agent to be determined without having to perform a re-collection. This was a lesson learned from the earlier program where frequent and sometimes unsuccessful re-collections had to be made due to an inability to determine the actual structure of the active principles with the amount of materials in hand. With the advent of newer isolation and instrumental techniques, the decision was made to collect approximately 1 kilogram (dry weight) of plant materials and 1 kilogram (frozen wet weight) of marine invertebrates and algae.
A frequent question about NCI's processes is ‘what about unstable chemical compounds, aren't you worried about decomposition and loss of activity?’ The answer is that unstable chemical entities are interesting scientifically but of little-to-no value in developing drug leads. Therefore a usable and repeatable system was devised and tested by performing various extraction techniques on plant and marine organisms known to produce agents of value and adjusting our methods until they could be found.
These samples, previously shipped to the NPR in Frederick and stored at -20°C until workup, are converted to dry or wet powders prior to sequential extraction with a 1:1 mixture of methanol:dichloromethane (organic) and water (aqueous) extracts, with full details given at http://npsg.ncifcrf.gov/. All extracts are assigned unique, confidential NCI numbers and returned to the NPR for storage at -20°C until requested for screening or further investigation. After testing in the then current in vitro human cancer cell line screen (http://dtp.nci.nih.gov/branches/btb/ivclsp.html), active extracts are subjected to bioassay-guided fractionation to isolate and characterize the pure, active constituents. Agents showing significant activity in the primary in vitro screens are selected for secondary testing in several in vivo systems, starting with the ‘hollow fiber assay’ (Hollingshead et al. 1995). Those agents exhibiting significant in vivo activity are considered for advancement into preclinical and clinical development.
As a result of the initial antitumor assays that were run, it was rapidly realized that the rate-limiting step was the isolation and identification of active principles from the extracts that were produced and considered to be ‘active’. In addition, there were a very large number of extracts, both aqueous and organic, that demonstrated a range of activities from none to extremely cytotoxic but were not selective against the human cell lines. In order to maximize the potential of these extracts and also to aid the source countries, early on in the process (effectively from the end of 1991) NCI began to permit research groups in the USA and their collaborators to access samples from the NPR, initially for antitumor work since, due to the rapid progress made in the elucidation of mechanisms underlying human diseases, a proliferation of molecular targets available for potential drug treatments became candidates for assays. The adaptation of these targets to high-throughput screening processes has greatly expanded the potential for drug discovery using the NPR extracts as input to assays against any disease of interest to the NIH. However, a small subset of materials in which NCI had interests as potential sources of novel antitumor agents were reserved for antitumor work only.
In carrying out this program (http://dtp.nci.nih.gov/branches/npb/repository.html), the NCI developed policies for the distribution of extracts from the NPR to qualified organizations for testing initially in screens related to cancer and HIV and subsequently in screens related to all human diseases, subject to the signing of a legally binding material transfer agreement (MTA) which protects the rights of all parties (http://dtp.nci.nih.gov/branches/npb/agreements.html). The key term of the MTA is the requirement that the recipient organization negotiate agreements stipulating suitable terms of collaboration and compensation with the source country(ies) of any extract(s) which yields agents which are developed towards clinical trials and possible commercialization.
Such terms would follow those stipulated by the NCI LOC and would apply even if no formal LOC-based agreement had previously been signed between the source country and the NCI. This agreement relating to the agent is to be binding upon SCO, recipient, and any licensee(s) or assignees of the recipient with respect to any intellectual property rights relating to the agent, and, similarly to the LOC, if semi-synthetic or synthetic derivatives are utilized, then they would also have similar rights but the levels of royalties etc., would be lower for obvious reasons. The overall process also included a mechanism whereby the source country could receive a proportion of its samples of extracts made from materials collected within its borders/territorial waters/economic exclusion zone free of charge for purposes of in-country research or distribution to its collaborators under whatever conditions the source country might decide.
As discussed above, the collections of plants and marine organisms have been carried out in over 25 countries through contracts with qualified botanical and marine biological organizations working in close collaboration with qualified SCOs, and all collections are performed subject to the terms of the LOC. Particularly in the area of plant-related studies, source-country scientists and governments are becoming increasingly committed to performing more of the drug-discovery operations in-country, as opposed to the export of raw materials. The NCI has recognized this fact for several years, and contract collections of plants have been de-emphasized in favor of establishing direct collaborations with qualified organizations in the source countries where the necessary expertise and infrastructure exist.
The NCI has negotiated MoUs (http://ttb.nci.nih.gov/npmou.html and reprinted as Appendix E) with over 20 SCOs suitably qualified to perform in-country processing (Appendix F). In establishing these agreements, NCI undertakes to abide by the same policies of collaboration and compensation as specified in the LOC. Depending on the availability of the necessary resources NCI also assists the SCOs in establishing their own drug-discovery programs through training in techniques of antitumor screening and natural product isolation. NCI has sponsored long-term visitors from 18 countries since 1988 for purposes of such collaboration and training (Appendix G).
It is anticipated that the discovery of novel anticancer drugs will be performed by SCOs at their own expense, with assistance from the NCI in terms of secondary in vitro and in vivo testing. All results from such secondary testing would be considered the sole intellectual property of the SCO (the NCI regards such testing as a routine service to the scientific community), and can be used by the SCO in the application for patents covering sufficiently promising inventions. The NCI will devote its resources to collaborating with SCOs in the preclinical and clinical development of any SCO-discovered drug which meets the NCI selection criteria and will make a sincere effort to transfer any knowledge, expertise, and technology developed during such collaboration to the SCO, subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology.
An excellent illustration of the potential benefits of such collaborations is the MoU signed with the Universidade Federal do Ceara in Fortaleza, Brazil. Through this collaborative agreement, scientists from this university (see Appendix G) received training in the methodology used by NCI in the in vitro testing of samples in the human cancer cell line prescreen and 60 cell line screen (http://dtp.nci.nih.gov/branches/btb/ivclsp.html), and a screen was established at the university with cell lines provided by NCI. The university has established collaborations with drug-discovery groups involved in both natural products isolation and synthetic studies throughout Brazil, and the potential of the immense biodiversity of Brazil is now being explored in-country. Any novel antitumor agents (pure compounds) discovered through this in-country collaborative network can be submitted to the NCI for free secondary in vitro and in vivo evaluation, and those agents meeting the NCI selection criteria may be advanced into preclinical and clinical studies using the NCI resources and involving true collaboration between the Brazilian investigators and the NCI.
Promising discoveries may be patented by the Brazilian inventors prior to advanced development, thereby ensuring that they have control over any subsequent licensing negotiations which may result should the agent advance to the stage where pharmaceutical company interest is stimulated. Such mechanisms ensure that optimum value is added to discoveries emerging from source-country genetic diversity, and that the source country derives optimal value in terms of subsequent benefits which may result, such as milestone payments, technology transfer, and royalty payments. These aspects are discussed in more detail below in the conclusions and recommendations. Through this mechanism collaborations have been established with 23 organizations in 11 countries (Appendix F).
In the second paragraph of the LOC (Appendix A) and similarly in the second paragraph of the MoU (Appendix E), the NCI states that it ‘will make sincere efforts to transfer knowledge, expertise, and technology related to drug discovery and development to the [appropriate Source Country Institution (‘SCI’)] in [Source Country] as the agent appointed by the [SCG or SCO], subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology’. This commitment is repeated in DTP/DCTD/NCI role, clause 5, of the LOC.
Through its sponsorship of visits by source-country scientists to NCI or other equivalent USA facilities mutually acceptable to NCI and the source-country authorities (see Appendices D and G for lists of long-term visiting scientists), the NCI has provided substantial training and expertise to these visiting scientists in the methodology used in the screening and bioassay-guided fractionation of extracts of organisms collected in their countries. In most instances, the NCI has covered the full expenses of such visits, including travel and subsistence, though there have been a few cases where the collaborating SCO has paid for the travel and subsistence, with the NCI covering all the laboratory and associated costs.
Where suitable infrastructure is available at source-country institutions and NCI resources are available, the NCI will provide human cancer cell lines, as well as the appropriate cell line and virus (genetically modified to be non-infectious) for a cell-based anti-HIV screen, to those institutions to enable them to set up screens for their own in-house drug-discovery programs. This has been implemented in institutions in Brazil, China, Egypt, India, Korea, Malaysia (Sarawak and Peninsular), Mexico, Pakistan, Panama, Philippines, Russia, South Africa, Thailand, and Zimbabwe. In addition, computer software for the tracking of the collection, extraction, screening, and fractionation of natural materials is available free of charge. The NCI is not permitted to provide funding for the establishment and equipping of laboratories, but institutions may apply for support from other USA government agencies such as the Agency for International Development (USAID). Through its collection contractors, however, the NCI has assisted in the renovation and equipping (computers and herbarium cabinets) of source-country herbaria in countries who have participated in some of the collection programs.
It should be noted that substantial support for source-country operations is also provided through NCI-funded USA grantee programs in instances where the grantees have collaborations with appropriate SCOs (Suffness et al. 1995). Since grantee research is regarded as independent, collaborating institutions in source countries may receive support from the grantee in the form of equipment and materials in addition to training, and in particular, grantee institutions may sign collection agreements that include royalty and other commitment statements that the USA Government is forbidden to sign. Such an example is the ‘commercial’ agreement signed by the University of Utah and the University of the Philippines permitting collection work on Philip-pines-sourced marine invertebrates.
From 1987 to 1996, the NCI tested over 30,000 plant extracts in an in vitro cell-based anti-HIV screen which determined the degree of HIV-1 replication in treated infected lymphoblastic cells versus that in untreated in fected control cells. Several natural products have shown in vitro activity (http://www.niaid.nih.gov/daids/dtpdb/natprod.html), and the development of three of them is discussed below.
Michellamine B was isolated as the main in vitro active anti-HIV agent from the leaves of this liana, collected in the Korup region of southwest Cameroon through an NCI contract with MBG (Boyd et al. 1994). Ancistrocladus korupensis is a new species (Thomas and Gereau 1993), found only in and around the Korup National Park, and vine densities are very low, on the order of one large vine per hectare. While fallen leaves do contain michellamine B, and their collection provided sufficient biomass for the isolation of enough pure compound to complete preclinical development, it was clear that extensive collections of fresh leaves could pose a possible threat to the limited and sparse wild population.
Thus far, no other Ancistrocladus species has been found to contain michellamine B. Investigation of the feasibility of cultivation of the plant as a reliable biomass source was initiated in 1993 through a contract with the Center for New Crops and Plant Products of Purdue University working in close collaboration with the University of Yaounde 1 in Cameroon, the World Wide Fund for Nature Korup Project, MBG, Oregon State University, and the NCI-Frederick contractor, Science Applications International Corporation (SAIC). Initially, an LOC-based agreement was signed with the University of Yaounde 1, but this was abrogated by the Cameroon Government when it established a special committee to oversee the collection and cultivation operations. Despite extensive interaction and collaboration between this special committee and the NCI, and the consortium of organizations involved in the cultivation project, no formal agreement was finalized between the Cameroon Government and the NCI.
An extensive botanical survey was undertaken, the range and distribution of the species were mapped, and dried leaves were analyzed for michellamine B content. Promising plants were re-sampled for confirmatory analysis, and those showing repeated high concentrations were targeted for vegetative propagation. A medicinal plant nursery was established for the A. korupensis collection near Korup Park Headquarters in Mundemba, and through selection of promising plants from the wild and their subsequent propagation and growth in the nursery, it was demonstrated that michellamine content well above the wild average could be produced routinely (J. Simon, pers. comm., 1995). In keeping with the NCI policies of collaboration with source countries, all the cultivation studies were performed in Cameroon, and involved the local population, particularly those in the Korup region where the plant was originally discovered.
Based on the observed activity and the efficient formulation of the diacetate salt, the NCI committed michellamine B to initial new drug application (INDA)-directed preclinical development, but continuous infusion studies in dogs indicated that in vivo effective anti-HIV concentrations could only be achieved at close to neurotoxic dose levels. Thus, despite in-vitro activity against an impressive range of HIV-1 and HIV-2 strains, the difference between the toxic dose level and the anticipated level required for effective antiviral activity was small, and NCI decided to discontinue further studies aimed at clinical development. However, the discovery of novel antimalarial agents, the korupensamines, from the same species (Hallock et al. 1994) adds further potential for this species. This project has been reviewed as a ‘Benefit-Sharing Case Study’ for the Executive Secretary of the CBD by Laird and Lisinge (1998).
An extract of the leaves and twigs of the tree, C. lanigerum, collected in Sarawak, Malaysia in 1987, yielded (+)- calanolide A which showed significant anti-HIV activity (Kashman et al. 1992). Efforts to relocate the original tree failed, and collections of other specimens of the same species gave only trace amounts of calanolide A. A detailed survey of C. lanigerum and related species discovered that latex of C. teysmanii yielded extracts with significant anti-HIV activity. The active constituent was found to be an isomer, (-)-calanolide B, which was isolated in yields of 20 to 30%. While (-)-calanolide B is slightly less active than (+)-calanolide A, it has the advantage of being readily available from the latex which is tapped in a sustainable manner by making small slash wounds in the bark of mature trees without causing any harm to the trees. The calanolides were licensed by NCI/NIH to Medichem Research, Inc., (now Advanced Life Sciences) which, as required by the NCI LOC (Mays et al. 1997), negotiated an agreement with the Sarawak State Government. The drugs are being developed by Sarawak Medichem Pharmaceuticals, a joint venture company formed between the Sarawak State Government and Medichem Research, Inc. Medichem Research had synthesized (+)-calanolide A and it is currently headed for Phase II clinical trials, while (-)-calanolide B is in preclinical development. Fairly recently, a report from Mexico identified a plant producing both calanolides A & B and also the closely related compound sulattrolide, thus demonstrating the potential for the production by agricultural means of both of the compounds (Huerta-Reyes et al. 2004). The earlier development of the calanolides has been reviewed as a ‘Benefit-Sharing Case Study’ for the Executive Secretary of the CBD by staff of the Royal Botanic Gardens, Kew UK (ten Kate and Wells 1998).
Prostratin, a previously known compound, was isolated as the active constituent from an extract of the wood of the tree, H. nutans. (Gustafson et al. 1992). The plant was identified by Dr. Paul Cox (then at Brigham Young University) as being used for the treatment of yellow fever (subsequently identified as hepatitis) based on interviews with traditional healers in Samoa conducted under terms of a covenant negotiated between Brigham Young University and the chiefs and orators in the village of Falealupo in Samoa, and with the concurrence of the Samoan Prime Minister and members of parliament (Cox 2001). Under the covenant, over $480,000 has been supplied to the village for schools, medical clinics, water supplies, trails, an aerial rain forest canopy walkway, and an endowment for the rain forest.
Subsequent studies determined that prostratin is a potent activator of HIV expression in latently infected T-cell lines, (Gulakowski et al. 1997) and its potential value in HIV therapy lies more in its possible utility as a viral activator for use in highly active anti-retroviral therapy (HAART) techniques, rather than as an anti-HIV agent. The further development of prostratin is being undertaken by the AIDS ReSearch Alliance of America (ARA; http://www.aidsresearch.org/) (supported by the NCI and the National Institute for Allergy and Infectious Diseases) which has negotiated an agreement with the government of Samoa allowing for benchmark payments to the government of Samoa, the village, and the families of the healers. In addition, ARA will endeavor to obtain prostratin from Samoan plant sources as long as it can be produced in a cost-effective manner, and will strive to ensure that the drug will be distributed at minimal profit in developing nations where use of the drug is approved.
An example from the marine area is the preclinical development of the potential anticancer agent, halichondrin B. This compound was originally reported by Japanese investigators in 1986 but the supply was extremely limited. Following work by NCI scientists using materials provided by Dr. G.R. Pettit, which demonstrated that halichondrin B was a tubulin-interactive agent binding at a nontaxoid site on tubulin (Bai et al. 1991), together with some preliminary preclinical data, NCI decided to further develop this agent. This led to a search for a source and following reports from the New Zealand marine natural product chemists, Drs. John Blunt and Murray Munro of the University of Canterbury, a Lissodendoryx sponge was identified as a potential source, found at depths in excess of 100 meters off the east coast of New Zealand's South Island.
Over the next five years, commencing with an NCI-funded environmental assessment of the potential sponge bed, performed in collaboration with the New Zealand National Institute for Water and Atmospheric Research (NIWA), the government of New Zealand issued a collection permit for up to 1 metric ton of sponge to be harvested by dredging from the estimated total of 16 metric tons on the shelf at roughly 100 to 150 meters depth. A joint venture company was set up by NIWA and the University of Canterbury to perform this work. With the prior approval of the local indigenous Iwi (Maori tribal leaders), the collections began. Following the expenditure of approximately US$250,000 by the NCI and a comparable sum (in kind) from the government of New Zealand, a sufficient quantity (300mg from 1,000kg wet sponge) for limited further development was obtained and shipped to NCI for further work.
Since NCI had had extensive prior experience of the problems associated with large-scale recovery of biomass from the beginning (particularly the search for Taxus species in the previous five or so years), methods that might lead to production of biomass without resorting to dredging were investigated. NCI therefore separately funded a considerable amount of work on the in-sea aquaculture of the Lissodendoryx sponge in various areas of New Zealand with the aim of achieving both sponge growth and production of the halichondrins. As a result of this collaborative study we demonstrated that this deep-water sponge could be successfully grown at depths as shallow as 10 meters while still producing amounts of halichondrin B comparable to those found in the wild material (Munro et al. 1999).
Following extensive preclinical work by NCI with the New Zealand sample, halichondrin B was shown to exhibit in vivo efficacy in both early- and late-stage tumor models. However, we also compared its activity against a simpler analogue made by total synthesis under current good manufacturing practice (cGMP) conditions by the American subsidiary (The Eisai Research Institute) of the Japanese pharmaceutical company, Eisai, leading to the decision by NCI in July 2001 to recommend that their analogue, E7389, should go into Phase I clinical testing in humans. Currently this compound is now in Phase III clinical trials as a potential antitumor agent in refractory breast carcinoma. We should add, however, that the basis for the work by Eisai was from a collaboration with Professor Y. Kishi, an NCI-funded investigator at Harvard, who published the total synthesis of halichondrin B in 1992 (Aicher et al. 1992). This work and Kishi's discovery that the activity resided in the macrolide ring of halichondrin B led Eisai to license the Harvard patents and then to develop further the molecule leading to more stable and less toxic analogues, one of which is E7389, now in Phase II trials.
Since halichondrin B was first reported in 1986 by Japanese scientists from an Okinawan sponge, benefits from the development of the synthetic analogue will not flow back to the New Zealand groups, but these groups have been able to capitalize on the in-sea sponge aquaculture techniques and have a variety of sponges in aquaculture, including the peloruside-producing Mycale species (M. Page, pers. comm., 2004).
The early NCI plant-collection contractors (Missouri Botanical Garden, New York Botanical Garden, and the University of Illinois at Chicago) recommended that policies for equitable collaboration and benefit sharing with source countries be considered, and the NCI, NPB, and legal staff proceeded to formulate policies which were initially incorporated in the NCI LOC. These policies were initiated in 1988, four years prior to the signing of the CBD, and were revised and improved eventually to become the LOC. For further examples of the close relationships between the NCI, its plant collection contractors in particular, and source-country representatives, the reader should consult the reports presented at a conference (http://law.wustl.edu/centeris/index.asp?id=1836) on Biodiversity and Biotechnology and the Protection of Traditional Knowledge held in 2003 at the Washington University School of Law and in particular, the paper giving the MBG experiences working with Madagascar (Miller 2003).
It should be stressed that the evolution of the current LOC has been guided by productive interaction with source-country representatives with perhaps the most significant contribution (in 1993) from the then, and still current, Attorney-General of the State Government of Sarawak, Datuk J.C. Fong, who proposed that the DTP/DCTD/NCI role, clause 8 (involving the obligations of licensees of NCI-patented drugs that were discovered from organisms collected through the contract programs) be modified to require direct negotiation of terms of collaboration and benefit sharing between the licensees and the relevant source-country authorities. Before this modification, this term had stated: ‘Should the agent eventually be licensed to a pharmaceutical company for production and marketing, DTP/NCI, in consultation with the SCO, will make its best effort to negotiate with the company for inclusion of terms in the licensing agreement requiring payment of a percentage of royalties accruing from sales of the drug to the Source Country Organization’. Constructive proposals such as this were, and continue to be, welcomed by the NCI which readily accepted Datuk Fong's proposal as being in the best interests of all parties.
The above instance of the modification of the LOC illustrates the importance of constructive interaction and discussions between source-country authorities (and scientists) and prospective users wishing to gain access to their genetic resources. Unfortunately, formulation of access policies without such consultation can lead to excessive regulation, complexity, and demands which deter potential users from even considering applying for access. On the other hand, constructive consultation also enlightens the potential users as to the legitimate claims and concerns of the source-country authorities, scientists, and indigenous communities. Failure to consider all aspects in a truly consultative, as opposed to confrontational, manner, creates a situation where all parties are the losers. As mentioned in the section on access to source-country resources, such a situation developed in the Philippines where some pharmaceutical companies refused to participate in any program which made use of materials from that country due to the demands of EO247. Unfortunately, this has also terminated the NCI collections in the Philippines despite the assurances given by an LOC-based agreement between the Philippines National Museum and the NCI, though as mentioned earlier, there are now indications that the EO247 system is undergoing revision.
The LOC effectively divides the biodiscovery (bioprospecting) process into two phases: The first phase involving the DTP/DCDT/NCI role, clauses A1–A6, can be regarded as basic research, in which many thousands of extracts are screened, and active extracts are subjected to bioassay-guided fractionation in an effort to identify lead compounds for development as a potential drug candidates. Clauses A1–A5 may involve the source-country scientists in collaborative research aimed at the discovery of novel agents through confidential exchange of results and other relevant data, training in screening, chemical isolation, purification, and structural elucidation techniques, and transfer of appropriate technology in these areas to the source country. Incorporation of clauses such as these enable source countries to enhance their drug-discovery capabilities and have been favorably received in the negotiation of agreements. This first phase, in which (at best) one in 4,000 to 5,000 extracts may yield a promising drug lead candidate, should be regarded as truly basic research, and should be subject to application for a basic research agreement (BRA), as opposed to a commercial research agreement (CRA). This would be the earliest stage at which applications for patent coverage may be filed for those leads exhibiting sufficient promise. In such instances, a BRA must include mention of the absolute requirement for negotiation of a new agreement to cover the development of any promising drug candidate lead.
The second phase involves the preclinical development of the identified drug candidate, which if successful, permits the advancement of the drug to clinical trials after approval by the USA Food and Drug Administration (FDA) or an equivalent regulatory body in the source country. It is at this second phase that a compound may be considered to have possible commercial potential, even though commercialization is still fairly remote, and may take many years (5 to 10 or more) to achieve.
In the LOC, entry into this second phase triggers a new agreement between the licensee and appropriate SCG or SCO (DTP/DCTD/NCI role, clauses 8–11), which will determine appropriate terms of collaboration in the development process, sustainable and environmentally sound use of source-country resources in the production of the drug, and equitable sharing of benefits (e.g., milestone payments or eventual royalty payments if the drug ever reaches the commercialization stage).
The arguments favoring a two-phase process are bolstered by the NCI experience in the early years of its natural product drug and development program. From 1960 to 1982, some 35,000 plant samples (representing about 12,000 to 13,000 species) were processed to yield 114,000 extracts. Though a significant number of interesting active chemotypes were discovered, only two compounds advanced to the stage of development into commercial products. These were Taxol® (e.g., paclitaxel and its semi-synthetic analogue, docetaxel) and camptothecin, which, though it proved to be too toxic in clinical trials to become a commercial drug, has yielded commercial analogues, such as topotecan (Hycamptine®) and irinotecan (Camptosar®). One other product, homoharringtonine, remains in advanced clinical trials for treatment of refractory leukemias. Thus, 114,000 extracts derived from approximately 12,000 to 13,000 species gave only two compounds yielding products of commercial value (further derivatives and analogues of Taxol® and camptothecin are being developed, some of which will probably become commercial products).
The requirement for a CRA, incorporating terms spelling out benefits related to drug development and percentage royalty compensation, right from the start of a collaborative drug-discovery project, has a definite deterrent effect on potential users considering applying for access. Trying to address these issues for an as-yet-undiscovered product seems a pointless exercise, and could in fact result in the source country deriving lower levels of benefits in the long term.
Negotiation of such terms is best left to the second phase of the process when a promising drug candidate has been identified. At this stage, the terms of collaboration in the production and development of a fully characterized product, in particular, the breadth of any intellectual property determination (i.e., how broad a claim or claims can be made on the structure from a patent aspect?) with activity in a defined disease state having known market demands, as well as the appropriate levels of benefit sharing, can be rationally discussed, and a second agreement addressing the well-defined issues can be negotiated.
Another factor dampening the potential users' enthusiasm for applying for access is the requirement for them personally to negotiate terms of prior informed consent (PIC) with local communities and indigenous peoples. While most potential users are in complete agreement with the principles of PIC from relevant source-country stakeholders, the negotiations of the precise terms of PIC are best left to the collaborating source-country organizations and scientists. In this respect, the BRA should be required to incorporate participation of a qualified local organization which may collaborate in all aspects of the initial basic research, as is stipulated in DTP/DCTD/NCI role, clauses 1–6, of the NCI LOC.
The NCI has found that its collection contractors and their staff have excellent relationships with their source-country partners, and work with their partners to obtain all the necessary permits and PIC from the relevant government authorities and local communities. Collections are performed in collaboration with the local organizations, with the expenses of local scientists being fully covered by the NCI through the contract. As mentioned earlier in the section on source-country collaboration, the contractors also provide training and assistance in the improvement of local herbaria. (However, see Box 1 for indications that the taxonomic identification of a plant may not be an identification of the source organism of a metabolite ostensibly isolated from that plant.) This close collaboration also extends to issues involved in development of promising candidates, such as large-scale cultivation and aquaculture projects (see the sections on collection specifications and case studies).
The NCI experience outlined above leads to the recommendations presented in the next section. Before proceeding with these recommendations, however, interested readers may wish to refer to a book discussing the regulatory atmosphere of ‘bioprospecting’ recently published under the auspices of the United Nations University by Gehl-Sampath (2005). This book discusses the various aspects of bioprospecting/biodiscovery from more economic and legal perspectives as opposed to the scientific and technological aspects.
Based on the NCI experience outlined in the previous sections, we recommend a two-phase approach to the exploration of source-country genetic resources as a source of potential novel drugs and other bioactive agents. For reference, the current versions of both the LOC and the MoU are attached as appendices A and E, respectively.
The first phase of the process should involve:
Negotiation of a BRA with the relevant SCG department or agency, or with a qualified SCO selected by the government to represent its interests.
The involvement of a suitably qualified local organization, if available, should be an essential requirement.
The BRA should incorporate terms of collaboration as spelled out in DTP/DCTD/NCI role, clauses 1–6, of the NCI LOC (covering exchange of data, training, and technology transfer).
There should be requirements for adequate protection of the environment and endangered species.
Obtaining the PIC of relevant local stakeholders (e.g., indigenous peoples, local communities, and healers where appropriate) should be the responsibility of the local collaborating organization, or, if an SCO is not identified, the relevant SCG agency should assist in this process.
The BRA should clearly require the negotiation of separate agreements covering any agents which are selected for Phase II development.
The second phase of the process once a drug lead candidate for preclinical development should trigger negotiations of a new agreement (the CRA) covering the specific issues related to the development and possible commercialization of the candidate. In addition, it is probable that the selection of an agent for Phase II development will have triggered submission of an application for patent coverage. However, it must be noted right from the start that the application for a patent and any subsequent issue of a patent is far removed from the possibility of commercialization. In fact, very few patented agents ever reach the stage of commercialization. Generally, from available data we estimate that less than four percent of patented pharmaceutical drug candidates actually become commercial drugs (Adams 1999) and even this figure is probably high.) The second phase should include:
Terms of collaboration in the large-scale procurement of supplies of raw material for production of sufficient quantities of the drug candidate for preclinical and possible clinical development. Such terms should address environmental impact studies, the possibility of sustainable harvest, and the need for cultivation of the source organism. Local scientists and communities should be involved in these processes, as far as possible.
Terms of collaboration in the production of the drug candidate (extraction, isolation, analysis, etc.), depending on the facilities and expertise existent in the source country and training and technology transfer where appropriate.
Terms of collaboration and training in the preclinical aspects of the drug candidate (e.g., formulation, pharmacology).
In the last two points it must be noted that certain cGMP conditions (e.g., approved facilities) have to be met to satisfy the requirements of the FDA and equivalent regulatory bodies in other countries. These are extremely expensive conditions to fulfill, and generally these processes are best performed in the main user (developed) country.
Terms of milestone payments at certain stages of development (e.g., FDA approval for entry into Phase I clinical trials, completion of Phase I clinical trials, etc.).
Payment of percentage royalties on the sales of the drug, should it become commercialized, to an appropriate SCO or SCG agency as determined by the source country. (An attractive alternative to royalty percentage for a source country may be the provision of supplies of the drug free of charge for treatment of the local population, the provision of other drugs more useful to the source country, or the granting of a royalty-free license for production of the drug for use in the source country only.)
LETTER OF COLLECTION AGREEMENT
[Source Country Institution]
[Source Country Organization]
Developmental Therapeutics Program
Division of Cancer Treatment and Diagnosis
National Cancer Institute
The Developmental Therapeutics Program (DTP), Division of Cancer Treatment and Diagnosis (‘DCTD’), National Cancer Institute (NCI) is currently investigating plants, micro-organisms, and marine macro-organisms as potential sources of novel anticancer drugs. The DTP is the drug discovery program of the NCI which is an Institute of the National Institutes of Health (NIH), an arm of the Department of Health and Human Services (DHHS) of the United States Government. While investigating the potential of natural products in drug discovery and development, NCI wishes to promote the conservation and sustainable utility of biological diversity, and recognizes the need to compensate [Source Country, SC] organizations and peoples in the event of commercialization of a drug developed from an organism collected within their country's borders.
As part of the drug discovery program, DTP has contracts with various organizations for the collection of plants, micro-organisms and marine macro-organisms worldwide. DTP has an interest in investigating plants, micro-organisms and marine macro-organisms from [Source Country], and wishes to collaborate with the [Source Country Government (SCG) or Source Country Organization(s) (SCO)] as appropriate in this investigation. The collection of plants, micro-organisms and marine macro-organisms will be within the framework of the collection contract between the NCI and the NCI Contractor [Contractor] which will collaborate with the appropriate agency in the [SCG or SCO]. The NCI will make sincere efforts to transfer knowledge, expertise, and technology related to drug discovery and development to the [appropriate Source Country Organization (SCO] in [Source Country] as the agent appointed by the [SCG or SCO], subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology. The [SCG or SCO], in turn, desires to collaborate closely with the DTP/NCI in pursuit of the investigation of its plants, micro-organisms and marine macro-organisms, subject to the conditions and stipulations of this agreement.
DTP/NCI will screen the extracts of all plants, micro-organisms and marine macro-organisms provided from [Source Country] for anticancer activity, and will provide the test results to [SCO] on an annual basis. Such results will be channeled via Contractor.
The parties will keep the test results and subsequently-developed data confidential until approved for publication by the parties. Before either party submits a paper or abstract containing test results for publication, the other party shall have 60 days to review and, as necessary file a sole or joint patent application in accordance with Article 6.
Any extracts exhibiting significant activity will be further studied by bioassay-guided fractionation in order to isolate the pure compounds(s) responsible for the observed activity. Since the relevant bioassays are only available at DTP/NCI, such fractionation will be carried out in DTP/NCI laboratories. A suitably qualified scientist designated by [SCO] may participate in this process subject to the terms stated in Article 4. In addition, in the course of the contract period, DTP/NCI will assist the [SCO], thereby assisting the [Source Country], to develop the capacity to undertake drug discovery and development, including capabilities for the screening and isolation of active compounds from plants, micro-organisms and marine organisms.
Subject to the provision that suitable laboratory space and other necessary resources are available, DTP/NCI agrees to invite a senior technician or scientist designated by [SCO] to work in the laboratories of DTP/NCI or, if the parties agree, in laboratories using technology which would be useful in furthering work under this agreement. The duration of such visits would not exceed one year except by prior agreement between [SCO] and DTP/NCI. The designated visiting scientist(s) will be subject to provisions usually governing Guest Researchers at NIH. Salary and other conditions of exchange will be negotiated in good faith. Costs and other conditions of visits will also be negotiated in good faith prior to the arrival of the visiting scientist(s).
In the event of the isolation of a promising agent from a plant, micro-organism or marine macro-organism collected in [Source Country], further development of the agent will be undertaken by DTP/NCI in collaboration with [SCO]. Once an active agent is approved by the DTP/NCI for preclinical development, [SCO] and the DTP/NCI will discuss participation by SCO scientists in the development of the specific agent.
The DTP/NCI will make a sincere effort to transfer any knowledge, expertise, and technology developed during such collaboration in the discovery and development process to [SCO], subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology.
DTP/NCI/NIH will, as appropriate, seek patent protection on all inventions developed under this agreement by DTP/NCI employees alone or by DTP/NCI and [SCG or SCO] employees jointly, and will seek appropriate protection abroad, including in [Source Country], if appropriate. All resulting patent applications and patents shall be assigned to the U.S. Department of Health and Human Services and managed by NIH. Under current NIH policy, all inventors of such assigned patents may receive royalties in accordance with said NIH policy for any royalty-bearing license(s) for these patent(s).
All licenses granted on any patents resulting from this collaboration shall contain a clause referring to this agreement and shall indicate that the licensee has been apprised of this agreement.
Should an agent derived from an organism collected under the terms of this agreement eventually be licensed to a pharmaceutical company for production and marketing, DTP/NCI will request that NIH/OTT require the successful licensee to negotiate and enter into agreement(s) with the appropriate [SCG] agency(ies) or [SCO] within twelve (12) months from the execution of said license. This agreement(s) will address the concern on the part of the [SCG or SCO] that pertinent agencies, institutions and/or persons receive royalties and other forms of compensation, as appropriate.
The terms of Article 8 shall apply equally to inventions directed to a direct isolate from a natural product material, a product structurally based upon an isolate from the natural product material, a synthetic material for which the natural product material provided a key development lead, or a method of synthesis or use of any aforementioned isolate, product or material; though the percentage of royalties negotiated as payment might vary depending upon the relationship of the marketed drug to the originally isolated product. It is understood that the eventual development of a drug to the stage of marketing is a long term process which may require 1015 years.
In obtaining licensees, the DTP/NCI/NIH will require the license applicant to seek as its first source of supply the natural products from [Source Country]. If no appropriate licensee is found that will use natural products available from [Source Country], or if the [SCG] or [SCO] as appropriate, or its suppliers cannot provide adequate amounts of raw materials at a mutually agreeable fair price, the licensee will be required to pay to the [SCG] or [SCO] as appropriate, compensation (to be negotiated) to be used for expenses associated with cultivation of medicinal organisms that are endangered or for other appropriate conservation measures. These terms will also apply in the event that the licensee begins to market a synthetic material for which a material from [Source Country] provided a key development lead.
Article 10 shall not apply to organisms which are freely available from different countries (i.e., common weeds, agricultural crops, ornamental plants, fouling organisms) unless information indicating a particular use of the organism (e.g., medicinal, pesticidal) was provided by local residents to guide the collection of such an organism from [Source Country], or unless other justification acceptable to both the [SCG or SCO] and the DTP/NCI is provided. In the case where an organism is freely available from different countries, but a phenotype producing an active agent is found only in [Source Country], Article 10 shall apply.
DTP/NCI will test any pure compounds independently submitted by the [SCG or SCO] scientists for antitumor activity, provided such compounds have not been tested previously in the DTP/NCI screens. If significant antitumor activity is detected, further development of the compound may, as appropriate, be undertaken by DTP/NCI in consultation with the [SCG or SCO].
Should an NCI/NIH patent on an agent derived from the submitted compound(s) eventually be licensed to a pharmaceutical company for production and marketing, DTP/NCI will request that NIH/OTT require the successful licensee to negotiate and enter into agreement(s) with the appropriate [SCG agency(ies) or SCO] within twelve (12) months from the execution of said license. This agreement will address the concern on the part of the [SCG or SCO] that pertinent agencies, institutions and/or persons receive royalties and other forms of compensation, as appropriate.
DTP/NCI may send selected samples to other organizations for investigation of their anti-cancer, anti-HIV or other therapeutic potential. Such samples will be restricted to those collected by NCI contractors unless specifically authorized by the [SCG or SCO]. Any organization receiving samples must agree to compensate the [SCG or SCO] and individuals, as appropriate, in the same fashion as described in Articles 8–10 above, notwithstanding anything to the contrary in Article 11.
The appropriate agency in [SCG or SCO] will collaborate with Contractor in the collection of plants, microorganisms and marine macro-organisms, and will work with Contractor to arrange the necessary permits to ensure the timely collection and export of materials to DTP/NCI.
Should the appropriate agency in [SCG or SCO] have any knowledge of the medicinal use of any plants, microorganisms and marine macro-organisms by the local population or traditional healers, this information will be used to guide the collection of plants, micro-organisms or marine macro-organisms on a priority basis where possible. Details of the methods of administration (e.g., hot infusion, etc.) used by the traditional healers will be provided where applicable to enable suitable extracts to be made. All such information will be kept confidential by DTP/NCI until both parties agree to publication.
The permission of the traditional healer or community will be sought before publication of their information, and proper acknowledgment will be made of their contribution.
The appropriate agency in [SCG or SCO] and Contractor will collaborate in the provision of further quantities of active raw material if required for development studies.
In the event of large amounts of raw material being required for production, the appropriate agency of the [SCG or SCO] and Contractor will investigate the mass propagation of the material in [Source Country]. Consideration should also be given to sustainable harvest of the material while conserving the biological diversity of the region, and involvement of the local population in the planning and implementation stages.
[SCG or SCG] and SCO scientists and their collaborators may screen additional samples of the same raw materials for other biological activities and develop them for such purposes independently of this agreement.
This agreement shall be valid as of the date of the final authorized signature below for an initial period of five (5) years, after which it can be renewed by mutual agreement. It may be amended at any time subject to the written agreement of both parties. Copies of such amendments will be kept on file at both of the addresses indicated below.
|For the National Cancer Institute:||For [SCI] or [SCO]:|
|Director, National Cancer Institute||Title:|
|mailing and contact address:||mailing and contact address:|
|Technology Transfer Branch|
|National Cancer Institute at Frederick|
|Fairview Center, Suite 502|
|1003 - W. 7th Street|
|Frederick, Maryland 21701-8512 U.S.A.|
* NCI is totally committed to LOC terms of the irrespective of whether or not an official agreement has been signed.
MEMORANDUM OF UNDERSTANDING
[Source Country Organization]
THE DEVELOPMENTAL THERAPEUTICS PROGRAM
DIVISION OF CANCER TREATMENT AND DIAGNOSIS
NATIONAL CANCER INSTITUTE
The Developmental Therapeutics Program (DTP), Division of Cancer Treatment and Diagnosis (DCTD), National Cancer Institute (NCI) is currently screening synthetic compounds and natural product materials derived from plants, marine macro-organisms and micro-organisms as potential sources of novel anticancer drugs. The DTP is the drug discovery program of the NCI which is an Institute of the National Institutes of Health (NIH), an arm of the Department of Health and Human Services (DHHS) of the United States Government. While investigating the potential of natural products in drug discovery and development, NCI wishes to promote the conservation and sustainable utility of biological diversity, and recognizes the need to compensate source country organizations and peoples in the event of commercialization of a drug developed from an organism collected within their countries' borders.
DTP/NCI has an interest in investigating plants, terrestrial and marine micro-organisms and marine macro-organisms from [Source Country] and wishes to collaborate with the [Source Country Organization, SCO] in this investigation. DTP/NCI will make sincere efforts to transfer knowledge, expertise, and technology related to drug discovery and development to [SCO] in [Source Country, SC] (as the agent appointed by the [Source Country] Government), subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology. [SCO], in turn, desires to collaborate closely with the DTP/NCI in pursuit of the investigation of [Source Country] 's plants, terrestrial and marine micro-organisms and marine macro-organisms and selected synthetic compounds subject to the following conditions and stipulations of this Memorandum of Understanding (MoU). [SCO] will perform the collection and processing of terrestrial plants, marine macro-organisms or micro-organisms as appropriate. It is understood that the [SCO] will be solely responsible for abiding by all source country's access policies and requirements for prior informed consent in the performance of collections. The NCI bears no responsibility for any contravention of such policies by the [SCO].
On the basis of in-house screening results in its anticancer screens, [SCO] may select both synthetic compounds and extracts of plants, marine macro-organisms and micro-organisms (subject to previously determined limits as to numbers per year) for anticancer testing at DTP/NCI. If suitable in-house screens are not available at [SCO], a list of available materials may be sent to DTP/NCI.
Prior to submission of the materials, [SCO] will send a data sheet, to be held in confidence by DTP/NCI, on each material so that DTP/NCI may check its databases for records of prior submission to DTP/NCI.
For pure compounds, the data sheet(s) will give pertinent available data as to chemical constitution, structure, available biological data including in-house screening results, solubility, toxicity and any precautions which need to be followed in handling, storage and shipping.
For crude extracts, data will be provided as to the source organism taxonomy, location and date of collection, any hazards associated with the organism, available biological data and any known medicinal uses of the organ-ism/extracts.
DTP will inform [SCO] which of the materials are new to the program, and such materials will be shipped to DTP for screening. DTP will provide a record of the accession number for the materials. Quantities of materials required for initial testing are 5 mg for pure compounds and 10 mg for crude extracts.
a) Data provided by [SCO] will be considered as confidential information of [SCO], if so labeled, and will be held confidentially by DTP/NCI, unless the data are otherwise available from public sources. No confidential information of [SCO] will be kept in files open to the public either by DTP/NCI, testing laboratories, or data processing facilities, all of which are U.S. government contractors. Only those employees directly engaged in the operation of DTP/NCI will have access to the files of information regarding the source and nature of confidential materials, unless the release of data about the materials is required under law or by court order. In the event of expiration of this agreement, the confidentiality of data provided by the [SCO] will be maintained.
b) All test results will be provided to [SCO] as soon as they are available, but not later than 270 days (nine months) from the date of receipt of the sample. If available, in vitro test results will be delivered within 90 days from receipt of the sample. [SCO] will be informed in writing of any delays beyond this period (270 days) together with an explanation of the reason(s) for delay.
c) Unless the release of test results is required under law or by court order, the parties will keep the test results and subsequently-developed data confidential until published in accordance with Article 15 or until corresponding patent applications are filed in accordance with Article 9.
Any extracts exhibiting significant activity will be further studied by bioassay-guided fractionation in order to isolate the pure compound(s) responsible for the observed activity. Such fractionation will be carried out in [SCO] laboratories. If [SCO] has no available bioassay, DTP/NCI may assist [SCO] to establish the necessary bioassay systems subject to the availability of the necessary resources. Alternatively, or in addition, suitably qualified designated [SCO] scientists may be sent to DTP/NCI for the isolation studies subject to the terms stated below in Article 7. In addition, DTP/NCI may assist the [SCO], thereby assisting the [Source Country], to develop the capacity to undertake drug discovery and development, including capabilities for the screening and isolation of active compounds from terrestrial and marine organisms.
Subject to the provision that suitable laboratory space and other necessary resources are available, DTP/NCI agrees to consider inviting senior technician(s) and/or scientist(s) designated by [SCO] to work in the laboratories of DTP/NCI or, if the parties agree, in laboratories using technology which would be useful in furthering work under this MoU. The duration of such visits would not exceed one year except by prior agreement between [SCO] and DTP/NCI. The designated visiting scientist(s) will be subject to provisions usually governing Guest Researchers at NIH. Cost-sharing and other conditions of visits will be negotiated in good faith prior to the arrival of the visiting scientist(s).
In the event that an agent isolated and purified from materials provided by [SCO], and/or a synthetic compound provided by [SCO] meets the criteria established by the Drug Development Group (DDG) of NCI's DCTD (DTP's parent organization), which would include, but not be limited to, in vivo activity in rodent models, further development of the agent may be undertaken by DTP/NCI in agreement with the [SCO]. Further development of the specific agent may include but not be limited to analog development through medicinal and/or combinatorial chemistry, formulation, pharmacology and/or toxicology studies. Once an active agent is approved by DTP/NCI for preclinical development (i.e., has passed the DDG at Stage IIA), DTP/NCI may collaborate with [SCO] scientists in the development of the specific agent.
Both [SCO] and DTP/NCI recognize that inventorship will be determined under patent law. DTP/NCI/NIH and [SCO] will, as appropriate, jointly seek patent protection on all inventions developed jointly under this MoU by DTP/NCI and [SCO] employees, and will seek appropriate protection abroad, including in [Source Country], if appropriate. Application for patent protection on inventions made by [SCO] employees alone will be the responsibility of [SCO]. Application for patent protection on inventions made by DTP/NCI employees alone will be the responsibility of DTP/NCI.
With respect only to those compounds that have been determined to possess such significant anti-cancer potential as to be scheduled for clinical trials by DCTD, the U.S. Government shall have a royalty-free, irrevocable, nonexclusive license to manufacture and/or use by or for the U.S. Government the invention(s) claimed in any patents that [SCO] may have or may obtain on such compounds or on a process for use of such compounds. However, this license will apply only to [SCO] patents that rely upon data generated by DTP/NCI or DTP/NCI testing laboratories. This license shall be only for medical research purposes related to or connected with the therapy of cancer. The term ‘medical research purposes’ as used herein shall not include treatment of patients outside of clinical trials or commercial distribution of the compounds.
DTP/NCI will make a sincere effort to transfer any knowledge, expertise, and technology developed during such collaboration in the discovery and development process to [SCO], subject to the provision of mutually acceptable guarantees for the protection of intellectual property associated with any patented technology.
All licenses granted on any patents arising from the collaboration conducted under the terms of this MoU shall contain a clause referring to this MoU and shall indicate that the licensee has been apprised of this MoU.
Should an NCI/NIH patent on an agent discovered under this collaboration eventually be licensed to a pharmaceutical company for production and marketing, DTP/NCI will request that NIH/OTT require the licensee to negotiate and enter into agreement(s) with [SCO] and/or an appropriate [Source Country] Government agency(ies) within twelve (12) months from the execution of said license. The agreement(s) will address the concern on the part of the [Source Country] government that pertinent agencies, institutions and/or persons receive royalties and other forms of compensation, as appropriate.
Such terms will apply equally to inventions directed to a direct isolate from a natural product material, a product structurally based upon an isolate from the natural product material, a synthetic material for which the natural product material provided a key development lead, a derivative of a synthetic compound provided by [Source Country] or [SCO], or a method of synthesis or use of any aforementioned isolate, product, material or derivative; though the percentage of royalties negotiated as payment might vary depending upon the relationship of the marketed drug to the originally isolated product. It is understood that the eventual development of a drug to the stage of marketing is a long term process which may require 10–15 years.
In obtaining licensees, DTP/NCI/NIH will require the applicant for license to seek as its first source of supply the natural products available from [Source Country]. If no appropriate licensee is found who will use natural products available from [Source Country], or if [SCO] or their suppliers cannot provide adequate quantities of raw materials at a mutually agreeable fair price, the licensee will be required to pay to the [Source Country] Government or [SCO] as appropriate, compensation (to be negotiated) to be used for expenses associated with cultivation of medicinal organisms that are endangered or for other appropriate conservation measures. These terms will also apply in the event that the licensee begins to market a synthetic material for which a material from [Source Country] provided a key development lead.
Article 13 shall not apply to organisms which are freely available from different countries (i.e., common weeds, agricultural crops, ornamental plants, fouling organisms) unless information indicating a particular use of the organism (e.g., medicinal, pesticidal) was provided by local residents to guide the collection of such an organism from [Source Country], or unless other justification acceptable to both [SCO] and DTP/NCI is provided.
In the case where an organism is freely available from different countries, but a phenotype producing an active agent is found only in [Source Country], Article 13 shall apply.
Publication of data resulting from the collaboration under this MoU will be undertaken at times determined by agreement between [SCO] and DTP/NCI. Before either party submits a paper or abstract for publication, the other party shall have sixty (60) days to review and as necessary, file a patent application in accordance with Article 9.
It is the intention of NCI that [SCO] not be liable to DTP/NCI for any claims or damages arising from NCI's use of the material provided by [SCO]; however, no indemnification for any loss, damage, or liability is intended or provided by any party under this MoU. Each party shall be liable for any loss, claim, damage or liability, that said party incurs, as a result of said party's activities under this MoU, except that the NCI, as an agency of the United States, assumes liability only to the extent as provided under the Federal Tort Claim Act (28 U.S.C. § 171).
DTP/NCI and its relevant contractors will not distribute materials provided by [SCO] to other organizations without written authorization from [SCO]. However, should [SCO] wish to consider collaboration with organizations selected by NCI for distribution of materials acquired through NCI collection contracts, DTP/NCI will establish contact between such organizations and [SCO].
[SCO] scientists and their collaborators may screen additional samples of the same materials for other biological activities and develop them for such purposes independently of this MoU.
With the exception of Articles 1–4 and 6, all other Articles shall survive the expiration of this Agreement or its termination by the [Source Country] or [SCO]. Subsequent compounds and/or extracts may be submitted under the appropriate DTP/NCI mechanism and agreement.
This MoU shall be valid as of the date of the final authorized signature below for an initial period of five (5) years, after which, it can be renewed by mutual agreement. It may be amended at any time subject to the written agreement of both parties. Copies of such amendments will be kept on file at both of the addresses indicated below. [SCO] and DTP/NCI are confident that this MoU will lay the basis for a mutually successful cooperation in discovering and developing new therapies in the treatment of cancer.
|For the [SCO]: For the National Cancer Institute:|
|Director, National Cancer Institute|
|mailing and contact address:||mailing and contact address:|
|Technology Transfer Branch|
|National Cancer Institute at Frederick|
|Fairview Center, Suite 500|
|1003 - W. 7th Street|
|Frederick, MD 21701-8512|
Adams S. 1999. SmithKline Beecham: Analysis of patenting 1995–1998. Expert Opinion on Therapeutic Patents 9:1173–1183. [CrossRef]
Aicher T.D., K.R. Buszek, F.G. Fang, C.J. Forsyth, S.H. Jung, Y. Kishi, M.C. Matelich, P.M. Scola, D.M. Spero, and S.K. Yoon. 1992. Total synthesis of halichondrin B and norhalichondrin B. Journal of the American Chemistry Society. 114:3162–3164. [CrossRef]
Bai R.L., K.D. Paull, C.L. Herald, L. Malspeis, G.R. Pettit, and E. Hamel. 1991. Halichondrin B and homohalichondrin B, marine natural products binding in the vinca domain of tubulin. Discovery of tubulin-based mechanism of action by analysis of differential cytotoxicity data. Journal of Biological Chemistry 266(24):15882–15889.
Benevidez II P.J. 2004. Implementation pathways. p. 153–176 in S. Carrizosa, S.B. Brush, B.D. Wright, and P.E. McGuire (eds.) Accessing biodiversity and sharing the benefits: Lessons from implementing the Convention on Biological Diversity, IUCN Environmental Policy and Law Paper No. 54, Cambridge, UK.
Bok, J.W, D. Hiffmeister, L.A. Maggio-Hall, R. Murillo, J.D. Glasner, and N.P. Keller. 2006. Genomic mining fo Aspergillus natural products. Chemistry & Biology 13:31–37. [CrossRef]
Boyd M.R., Y.F. Hallock, J.H. Cardellina Ii, K.P. Manfredi, J.W. Blunt, J.B. Mcmahon, R.W. Buckheit Jr., G. Bringmann, M. Schaffer, G.M. Cragg, D.W. Thomas, and J.G. Jato. 1994. Anti-HIV michellamines from Ancistrocladus korupensis. Journal of Medical Chemistry 37:1740–1745. [CrossRef]
Cox P.A. 2001. Ensuring equitable benefits: The Falealupo Covenant and the anti-HIV drug Prostratin from a Samoan medicinal plant. Pharmaceutical Biology 39:S33–S40. [CrossRef]
Cragg G.M. and D.J. Newman. 1999. Discovery and development of antineoplastic agents from natural sources. Cancer Investigation 17:153–163. [CrossRef]
Cragg G.M. and D.J. Newman. 2005. Plants as a source of anti-cancer agents. Journal of Ethnopharmacology 100(1–2):72–79. [CrossRef]
Eyberger, A.L., R. Dondapati, and J.R. Porter. 2006. Endophyte fungal isolates from Podophyllum peltatum produce podophyllotoxin. Journal of Natural Products 69:1121–1124. [CrossRef]
Gehl Sampath P. 2005. Regulating bioprospecting: Institutions for drug research, access, and benefit-sharing. United Nations University Press. New York, NY USA.
Gulakowski R.J., J.B. McMahon, R.W. Buckheit Jr., K.R. Gustafson, and M.R. Boyd. 1997. Antireplicative and anticytopathic activities of prostratin, a non-tumor promoting phorbol ester, against human immunodeficiency virus (HIV). Antiviral Research 33(2):87–97. [CrossRef]
Gustafson K.R., J.H. Cardellina Ii, J.B. McMahon, R.J. Gulakowski, J. Ishitoya, Z. Szallasi, N.E. Lewin, P.M. Blumberg, O.S. Weislow, J.A. Beutler, R.W. Buckheit Jr., G.M. Cragg, P.A. Cox, J.P. Bader, and M.R. Boyd. 1992. A non-promoting phorbol from the Samaon medicinal plant Homalanthus nutans inhibits cell killing by HIV-1. Journal of Medical Chemisty 35:1978–1986. [CrossRef]
Hallock Y.F., K.P. Manfredi, J.W. Blunt, J.H. Cardellina Ii, M. Schaffer, K.P. Gulden, G. Bringmann, A.Y. Lee, J. Clardy, G. Francois, and M.R. Boyd. 1994. Korupensamines A-D, novel antimalarial alkaloids from Ancistrocladus korupensis. Journal of Organic Chemistry 59:6349–6355. [CrossRef]
Hollingshead M.G., M.C. Alley, R.F. Camalier, B.J. Abbott, J.G. Mayo, L. Malspeis, and M.R. Grever. 1995. In vivo cultivation of tumor cells in hollow fibers. Life Sciences 57(2):131–141. [CrossRef]
Huerta-Reyes M., M.C. Basualdo, F. Abe, M. Jimenez-Estrada, C. Soler, and R. Reyes-Chilpa. 2004. HIV-1 inhibitory compounds from Calophyllum brasiliense leaves. Biological and Pharmaceutical Bulletin 27(9):1471–1475. [CrossRef]
Kashman Y., K.R. Gustafson, R.W. Fuller, J.H. Cardellina Ii, J.B. McMpahon, M.J. Currens, R.W. Buckheit, S.H. Hughes, G.M. Cragg, and M.R. Boyd. 1992. The calanolides, a novel HIV-inhibitory class of coumarin derivatives from the tropical rainforest tree, Calophyllum lanigerum. Journal of Medical Chemistry 35:2735–2743. [CrossRef]
Kaufman D. 1993. Letter to the editor. A reaction from Dwight Kaufman M.D., Ph.D., Deputy Director, Division of Cancer Treatment. Botany 2000-ASIA Newsletter 2:6.
Laird S. and E. Lisinge. 1998. Benefit-sharing case studies: Aristocladus [sic] korupensis and Prunus africana. Fourth Meeting of the Conference of The Parties to the Convention on Biological Diversity, Bratislava, Slovakia, 4–15 May 1998. Agenda Item 16.3. (http://www.biodiv.org/doc/case-studies/abs/cs-abs-aristo.pdf)
Long, P.F., W.C. Dunlap, C.N. Battershill, and M. Jaspars. 2005. Shotgun cloning and heterologous expression of the patellamide gene cluster as a strategy to achieving sustained metabolite production. Chembiochem 6:1760–1765. [CrossRef]
Mays T.D., K.D. Mazan, G.M. Cragg, and M.R. Boyd. 1997. Triangular privity – A working paradigm for the equitable sharing of benefits from biodiversity research and development. p. 279–298 in K.E. Hoagland and A.Y. Rossman (eds.) Global genetic resources: Access, ownership, and intellectual property rights. Association of Systematics Collections. Washington, DC USA.
McAlpine, J.B, B.O. Bachmann, M. Piraee, S. Tremblay, A.-M. Alarco, E. Zazopoulos, and C.M. Farnet. 2005. Microbial genomics as a guide to drug discovery and structural elucidation: ECO-02301, a novel anitfungal agent, as an example. Journal of Natural Products 68:493–496. [CrossRef]
Miller J. 2003. Impact of the Convention on Biological Diversity: The lessons of ten years of experience with models for equitable sharing of benefits. Conference Papers: Biodiversity and Biotechnology and the Protection of Traditional Knowledge – April 4–6, 2003. Available on line at the Washington University Law website. (http://law.wustl.edu/centeris/Papers/Biodiversity/PDFWrdDoc/miller.pdf)
Munro M.H.G., J.W. Blunt, and E.J. Dumdei. 1999. The discovery and development of marine compounds with pharmaceutical potential. Journal of Biotechnology 70:15–25. [CrossRef]
Piel, J., D. Hui, G. Wen, D. Butzke, M. Platzer, N. Fusetani, and S. Matsunaga. 2004. Antitumor polyketide biosynthesis by an uncultivated bacterial symbiont of the marine sponge Theonella swinhoei. Proceedings of the National Academy of Sciences, USA 101:16222–16227. [CrossRef]
Puri, S.C, V. Verma, T. Amna, G.N. Qazi, and M. Spiteller. 2005. An endophytic fungus from Nothapodytes foetida that produces camptothecin. Journal of Natural Products 68:1717–1719. [CrossRef]
Schmidt, E.W, J.T. Nelson, D.A. Rasko, S. Sudek, J.A. Eisen, M.G. Haygood, and J. Ravel. 2005. Patellamide A and C biosynthesis by a microcin-like pathway in Prochloron didemni, the cyanobacterial symbiont of Lissoclinum patella. Proceedings of the National Academy of Sciences, USA 102:7315–7320. [CrossRef]
Strobel, G., B. Daisy, U. Castillo, and J. Harper. 2004. Natural products from endophytic microorganisms. Journal of Natural Products 67:257–268. [CrossRef]
Suffness M., G.M. Cragg, M.R. Grever, F.J. Grifo, G. Johnson, J.A.R. Mead, S.A. Schepartz, and J.M. Venditti. 1995. The National Cooperative Natural Products Drug Discovery Group (NCNPDDG) and International Cooperative Biodiversity Group (ICBG) Programs. International Journal of Pharmacognosy 33:5–16. [CrossRef]
ten Kate K. and A. Wells. 1998. Benefit-sharing case study: The access and benefit-sharing policies of the United States National Cancer Institute: A comparative account of the discovery and development of the drugs Calanolide and Topotecan. Executive Secretary of the Convention on Biological Diversity. http://www.biodiv.org/doc/case-studies/abs/cs-abs-nci.pdf.
Thomas D.W. and R.E. Gereau. 1993. Ancistrocladus korupensis (Ancistrocladaceae): A new species of liana from Cameroon. Novon 3:494–498. [CrossRef]
Yu, T.-.W and H.G. Floss. 2005. Ansamitocins (maytansinoids). p. 321–337 in G.M. Cragg, D.G.I. Kingston, and D.J. Newman (eds.) Anticancer agents from natural products. Taylor and Francis. Boca Raton, FL USA.
1 This chapter reflects the opinions of the authors, and not necessarily those of the USA Government.
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