11th NAPRECA Symposium Book of Proceedings, Antananarivo, Madagascar Pages 56-69

Drug Discovery and Development from Natural Products: The Way

Forward
Gordon M. Cragg*1 and David J. Newman1
Abstract
It is well established that natural products have been a source of leads for the development of
many of the most effective drugs currently available for the treatment of a variety of human
diseases. Biodiversity will continue to provide novel leads for drug development, but major
obstacles limit efficient progress and result in decreased interest in the pharmaceutical sector.
These include problems with the large-scale procurement of sufficient source material for
bulk production, the potency and inherent toxicity of many natural products resulting in
narrow therapeutic indices, as well as significant problems associated with the development
of suitable vehicles and dosing schedules for the administration of the drugs to patients. The
development of the anticancer drug, taxol and related analogs, provides a good example of
how these problems can effectively be overcome. Efficient lead optimization can also be
achieved through the application of methodologies such combinatorial or parallel synthesis
and biosynthesis, as well as total synthesis. It is clear that optimizing the value of natural
products as drug leads requires multidisciplinary and international collaboration. Aspects of
these issues will be discussed.

Keywords: Biodiversity, drug development, supply, formulation, collaboration

Introduction

Throughout the ages humans have relied on Nature to cater for such basic needs as the
production of foodstuffs, shelters, clothing, means of transportation, fertilizers, flavors and
fragrances, and not least, medicines. Plants have formed the basis of sophisticated traditional
medicine systems that have been in existence for thousands of years, and their uses by many
cultures have been extensively documented (1). These plant-based systems continue to play
an essential role in healthcare, and it has been estimated by the World Health Organization
that approximately 80% of the worlds inhabitants rely mainly on traditional medicines for
their primary health care (2).

Plant products also play an important role in the health care systems of the remaining 20% of
the population, mainly residing in developed countries. A recent study using US-based
prescription data from 1993, demonstrated that natural products play a major role in drug
treatment, as over 50% of the most-prescribed drugs in the US had a natural product either as
the drug, or as a forebear in the synthesis or design of the agent (3).

The continuing valuable contributions of nature as a source of potential chemotherapeutic

agents has been reviewed by Newman et al. (4). An analysis of natural products as sources of
new drugs over the period 1981-2002 indicates that 67% of the 877 small molecule, new
chemical entities (NCEs) are formally synthetic, but 16.4% correspond to synthetic molecules
containing pharmacophores derived directly from natural products (S* and S*/NM, Fig. 1)
(5). Furthermore, 12% are actually modeled on a natural product inhibitor of the molecular

1
* Special Volunteer, Natural Products Branch, Developmental Therapeutics Program,
National Cancer Institute, NCI-Frederick, Fairview Center, Suite 206, P. O. Box B,
Frederick. Maryland, 21702-1201, USA; tel: +1-301-846-5387; e-mail: craggg@mail.nih.gov

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target of interest, or mimic (i.e., competitively inhibit) the endogenous substrate of the active
site, such as ATP (S/NM, Fig. 1). Thus, only 39% of the 877 NCEs can be classified as truly
synthetic in origin. (S, Fig.1). In the area of anti-infectives (anti-bacterial, -fungal, -parasitic
and viral), close to 70% are naturally derived or inspired, while in the cancer treatment area
67% are in this category.

Figure 1. Breakdown of New Chemical Entities 1981-2002 (see reference 5 for description
of codes)

Preclinical and Clinical Drug Development

The natural product drug discovery process generally involves the testing of extracts of
source organisms of plant, marine or microbial origin in appropriate in vitro assays (cell or
enzyme/target based), followed by bioassay-guided fractionation of the active extracts and
isolation and purification of active constituents. Those constituents showing significant in
vivo activity in appropriate animal models are considered as lead molecules which may be
selected as candidates for preclinical development. Initially, such leads may be structurally
modified through use of medicinal or combinatorial chemistry techniques to provide agents
having superior activity or decreased toxicity (optimization of the therapeutic index) and
acceptable pharmacological properties.

The key steps in the preclinical development of a potential drug involve:

The development of an adequate supply of the agent to permit preclinical and clinical
development.

Formulation studies to develop a suitable vehicle to solubilize the drug for

administration to patients, generally by intravenous injection or infusion in the case of
cancer.

Pharmacological evaluation to determine the best route and schedule of

administration to achieve optimal activity of the drug in animal models, the half-lives
and bio-availability of the drug in blood and plasma, the rates of clearance and the
routes of excretion, and the identity and rates of formation of possible metabolites.

IND-directed [directed toward application to the appropriate regulatory agency (the

Food and Drug Administration in the United States) for Investigational New Drug

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status] toxicological studies to determine the type and degree of major toxicities in
rodent and dog models. These studies help to establish the safe starting doses for
administration to human patients in clinical trials.

Once an agent has been granted IND status, it then advances to the clinical development stage
which involves the following process:

Phase I studies conducted to determine the maximum tolerated dose (MTD) of a drug
in humans, and to observe the sites and reversibility of any toxic effects. In contrast
to trials with agents directed at other diseases, all patients in Phase I cancer trials have
some form of the disease.

Once the MTD has been determined and the clinicians are satisfied that no
insurmountable problems exist with toxicities, the drug advances to Phase II clinical
trials. Phase II trials generally are conducted to test the efficacy of the drug against a
range of different cancer disease types.

In those cancers where significant responses are observed, Phase III trials are
conducted to compare the activity of the drug with that of the best chemo-therapeutic
agents currently available for the treatment of those cancers. In addition, the new
drug may be tried in combination with other effective agents to determine if the
efficacy of the combined regimen exceeds that of the individual drugs used alone.

Development of Natural Product-Derived Drugs

The development of natural product-derived drugs poses significant challenges in several

areas. Of prime concern is the supply of the drug in sufficient quantities to permit preclinical,
and hopefully clinical, development, and ultimately, if given a successful, clinical outcome,
commercial production. Another major challenge is that of formulation. Natural products
generally are highly insoluble in aqueous media, and such solubility is a prime requirement
for administration of the drug to human patients, particularly through the intravenous route
commonly used in the treatment of cancer patients.

Development of Paclitaxel (Taxol). Long-Term Commitment Yields a Successful Drug

Discovery and Preclinical Development

The development of the successful anticancer drug, paclitaxel (Taxol; 1)2 provides an
excellent example of how these challenges can be overcome, but not without considerable
ingenuity, patience and persistence. The chronology for the discovery and preclinical
development of taxol is given in Table 1. It should be noted that 15 years elapsed from the
time of the initial collection of the source plant material, the bark of Taxus brevifolia, to the
approval for preclinical development. Most of the testing in the early days of the NCI drug
discovery program (1955-1982) was performed using in vivo models, mainly mouse
leukemias, and a major reason for the considerable time lapse was the fact that the activity of
taxol in these systems was in no way superior to that observed for many other potential drug
leads. It was only when significant activity in the more resistant B16 mouse melanoma was

2
Because this account is historical in nature, the name taxol is used subsequently in the text when referring to
Taxol. No infringement of the Bristol-Myers Squibb trademark is implied.

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observed, that taxol was considered of special interest, and selected for preclinical
development. The first stage in the process was testing against a panel of human solid tumor
xenograft models, and strong activity against the MX-1 mammary and CX-1 colon models
confirmed the initial promise. The crowning moment, however, was the seminal discovery by
Horwitz et al. that taxol possessed a unique mechanism of action, whereby the
polymerization of tubulin to form microtubules was promoted, and the resultant microtubules
were stabilized, leading to inhibition of mitotic spindle formation (6). This was in direct
contrast to other tubulin-interactive agents, such as vinblastine and vincristine, which inhibit
mitosis by inhibition of the tubulin polymerization process.

The formulation of taxol in a suitable aqueous vehicle posed considerable challenges. Like
most complex natural products, taxol is soluble in most organic solvents, but highly insoluble
in water and aqueous-organic solvent mixtures. Extensive research led to the development of
a formulation vehicle comprised of a 1:1 mixture of the emulsifying agent, Cremophor, and
ethanol at a concentration of 6 mg/mL. For clinical purposes, 5 mL ampoules were stored at
2-80C and diluted with either 50 mL 0.9% NaCl which was stable for 3 hr, or with 1,000 mL
5% dextrose which was stable for 24 hr. As will be mentioned later, there were serious, initial
clinical problems with these formulations. Toxicology studies in rodents and dogs showed
reversible toxicities in high turnover cells (hematopoietic, lymphatic, gastrointestinal), and
sensitivity of dogs to the Cremophor in
_____________________________________________________________________
TABLE 1: CHRONOLOGY OF THE DISCOVERY AND PRECLINICAL
DEVELOPMENT OF TAXOL

1962: First collection of Taxus brevifolia by USDA botanists

1964: Confirmed KB activity
1965: Recollection of bark and assignment to Dr. Monroe Wall, RTI
1966: Confirmed in vivo activity mainly mouse leukemia models
1969: Taxol first isolated in pure form (0.01% yield from bark)
1969: Survey of plant parts and abundance by USDA
1971: Isolation and structure first reported by Wall, Wani, et al.
1974: Good in vivo activity against B16 mouse melanoma
1975: B16 activity confirmed. Increased interest
1977: Accepted as a candidate for preclinical development Tumor panel testing
started
1977: Strong activity observed against human solid tumors, the MX-1 mammary
and CX-1 colon xenograft models
1978: Recognized as a mitotic spindle poison
1979: Unique mechanism of action determined.
1980: Formulation completed. Supplies adequate for toxicology studies
1982: Toxicology studies completed.
1982: Approved for INDA filing with FDA the formulation vehicle was observed.
Application for IND status with the FDA was approved in 1982, 20 years after the
first collection of the source plant material, and taxol was advanced into clinical
trials in 1983.

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Clinical Development

The chronology of the clinical development of taxol is given in Table 2. Problems were soon
encountered in Phase I trials with severe allergic reactions, resulting in the death of some
patients. This led to a dramatic drop in clinician interest, but the observation of some positive
patient responses by one clinician led to the development of a slow intravenous infusion as
opposed to original bolus injection, which, combined with pre-medication using steroids,
overcame the allergic reactions. These reactions were determined to be caused by the large
amounts of Cremophor present in the formulation vehicle, and the development of more
water-soluble taxol analogs is an ongoing area of research. The toxicities observed in the
Phase I trials, mainly leukopenia, neuropathy, alopecia, and nausea, were found to be
reversible, and the drug was advanced to Phase II trials in 1985. The progression of the Phase
II trials was restricted by the limited quantities of drug available, but the observation of
significant activity against refractory ovarian cancer in 1989 highlighted the urgent need to
develop more abundant and reliable sources of the drug.

The Supply Issue

The supply issue related to use of drug isolated from the bark of Taxus brevifolia is
________________________________________________________________________
TABLE 2: CHRONOLOGY OF THE CLINICAL DEVELOPMENT OF TAXOL
1983: Phase I clinical trials begin.
1985: Phase II trials begin
1986-1989 - Trials limited by drug supply issues
1989: Activity observed against refractory ovarian cancer
1989: Bristol-Myers Squibb (BMS) selected as Cooperative Research and
Development Agreement (CRADA) partner.
1989: Seven year exclusivity granted to BMS for investment in development
1991: Activity observed against metastatic breast cancer
1992: NDA approved by FDA for treatment of refractory ovarian cancer
1994: FDA approval for treatment of refractory breast cancer
________________________________________________________________________

illustrated by the following facts (7). The yields of pure drug isolated from the bark were
generally about 1 gm per 14 Kg of dried bark, amounting to a yield of approximately 0.01%
with a 73% recovery rate; this was equivalent to harvesting about 1.5 trees per 1 gm. Patient
requirements of 500 mg/patient/course and 4 courses of treatment for ovarian cancer equated
to 2 gm/patient, and with some 12,000 patients suffering from ovarian cancer, the annual
requirements for treating this patient population alone were 24 Kg or 36,000 trees. While the
sustainable harvest of bark is theoretically possible by avoiding stripping of the bark around
the complete circumference of the trunk and not disturbing the life-preserving cambium layer
(a difficult and tedious process requiring great care), in practice the bark was collected by
felling the tree and completely stripping the bark, thereby destroying the tree. Taxus (yew)
species are notoriously slow growing, and generally trees being harvested were 100 or more
years old! The increased demand for the bark led to concerns about the continued viability of
T. brevifolia populations in the western United States and Canada, and resulted in
confrontations between environmental groups and patient advocacy groups which even
reached the halls of the U. S. Congress.

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Through grants and contracts, the NCI sponsored the performance of worldwide surveys and
assessments of alternative Taxus species, including T. baccata (Europe/Caucasus/Himalayas),
T. canadensis (eastern Canada), T. cuspidata (Japan), T. globosa (Mexico), and T.
yunnanensis (China). In addition, alternative sources were considered, including: the
cultivation of T. brevifolia, T. baccata and other species, varieties and cultivars, with the
selective propagation of best producers; hydroponics, with selective breeding of the best
producers, and optimization of the growth medium and the addition of precursors and
elicitors; plant cell suspension culture, with the cloning of the most productive cell lines, the
establishment of stable cell lines, and the optimization of growth conditions and use of
elicitors (e.g., methyl jasmonate); cultivation of endophytes which have been shown to yield
taxol in extremely low yields (8); genetic engineering, through identification of the key
enzymes involved in rate limiting biosynthetic steps, isolation of the encoding genes, and
overexpression of the genes in Taxus species or relevant endophyic fungi; semi-synthesis of
taxol and analogs from more abundant natural precursors; and total synthesis.

The cultivation of T. baccata, in particular, has been a key factor in solving the supply
problem (vide infra), while plant cell culture methodology recently has been optimized to
yield multi-Kg quantities of the commercial drug (9).

A key breakthrough in solving the supply problem came with the pioneering development of
a semi-synthetic conversion of the precursor, 10-deacetylbaccatin III (2), to taxol by Potier et
al. (10). This and other baccatins are isolated in good yields from T. baccata, and taxol and
other taxane analogs, such as the clinically-active docetaxel (Taxotere; 3) (11), are now
produced commercially by a variety of efficient semi-synthetic procedures.

Taxol: A Continuing Development Process

The development of taxol from the first collection of the source plant material to its approval
for commercial use spanned some 30 years, and it would never have reached the global
cancer population without the considerable commitment of funds and resources by the NCI.
It has been estimated that the NCI, funded by the U. S. Congress and the U. S. taxpayers,
invested over $400 million, and investment continues in the support of ongoing clinical trials.

Paclitaxel (taxol) has proven to be efficacious in the treatment of breast, ovarian and non
small cell lung cancers, as well as the AIDS-related malignancy, Kaposis sarcoma.
Docetaxel (taxotere) has a similar treatment profile to paclitaxel, but is easier to formulate
and administer due to its greater aqueous solubility. Recently, it has also been found to be
effective in the treatment of metastatic, hormone-refractory prostate cancer (12). In addition,
10 other taxanes are in Phase II or Phase I clinical trials, while 23 taxanes are in preclinical
development. Taxol has also shown potential for the treatment of multiple sclerosis,
psoriasis, and rheumatoid arthritis
(http://www.phrma.org/newmedicines/newmedsdb/drugs.cfm).

For more detailed discussions of taxol and analogs the reader is referred to the reviews by
Kingston (13), Cragg and Newman (14), and the book edited by Suffness (15).

Halichondrin B. The Importance of Organic Synthesis

The first report of the isolation of halichondrin B (4), together with other congeners from the
Japanese sponge, Halichondria okadai was by Hirata and Uemura in 1986. This was

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followed by a report by Pettit et al. in 1991 of the isolation of halichondrin B from the
Palauan sponge, Axinella sp. Testing in the NCI 60 human cancer cell line screen and
analysis of the data using the COMPARE program indicated that it was a tubulin binder (at
the Vinca site) (16), and, in 1992, the NCI approved halichondrin B for preclinical
development. In the same year, NCI grantee, Kishi, published the total synthesis, a multistep
process with low overall yields (17).

O
O HO O
O OH OH

O NH O H H

O O HO O
OH O O OH O O
OH
O O O O

1. Taxol 2. 10-deacetylbaccatin III

HO O
OH OH
O H O H O
HO O
O H
O NH O H O O
O O O
H H O H
O O O H
OH O O OH O
O
OH O
O
O O
O
H

3. Taxotere 4. Halichondrin B

OH

HN

O OH
OH
H 2N H OH O
O O O
O
H
H
O
O O OH
O
O
HO
O
H
NH

OH

5. E7389 6. Michellamine B
Structures 1-6

Entry into preclinical development required the large-scale production of the compound. In
April, 1992, NCI requested help from the natural products chemistry community in order to
obtain large quantities of various natural product materials, including Halichondrin B. The
New Zealand group of Blunt and Munro contacted the NCI reporting that they had
discovered a family of halichondrin B analogs in a sponge, Lissodendoryx sp., collected from
deep water off the Kaikoura Peninsula on the east coast of South Island. Over the next 5-6

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years, the NCI worked closely with the New Zealand Halichondrin Joint Venture, led by
Blunt and Munro from the University of Canterbury and Battershill from National Institute
for Water and Atmospheric Research (NIWA), and, by 1998, 300 mg of Halichondrin B was
available (18). The NCI provided close to US$300K in direct funding, with an estimated
US$250K provided in kind by the New Zealand government.

Although the process seemed simple, it actually involved interlocking stages encompassing
an environmental assessment of the sponge bed (at 200 m. depths and lower), bathyspheric
investigations as to the actual source of the sponge, and low, medium and large-scale
collections (10 kg to 1000 kg), with permits being issued by the NZ government, and
permission granted by the local Iwi population. In addition, aquaculture experiments were
performed over multiple seasons and under a variety of water conditions, temperatures, and
times, leading to the successful aquaculture of the sponge in the Marlborough Sound between
North and South Islands. The large-scale chemical isolation of the compound, and
subsequent purification to >98% purity, proved challenging since no chromophore is present
in the molecule to aid ready detection. Nevertheless, the process was considered as
economically feasible.

Meanwhile, the total synthetic work performed by Kishi et al. had led to the synthesis of two
macrocyclic ketones which were designed to simplify the parent structure of halichondrin B,
and to overcome the lactone instability found with the single macrocyclic ring in the right
half of the molecule. Eisai Research Institute, working with Kishi, performed in vivo testing
using late stage tumors, and showed that one of these ketones, E7389 (5), had superior
activity compared to halichondrin B. Toxicological testing using myelosuppression assays
showed slight differences between the two synthetic ketones, and the therapeutic indices
observed were much better for the ketones than for halichondrin B.

Three options were now available for the development of a halichondrin B candidate for
preclinical and clinical studies. Firstly, the collection or aquaculture of the source sponge
could be undertaken to enable isolation of sufficient quantities of halichondrin B. Secondly,
halichondrin B could be prepared by total synthesis, or thirdly, the development of the
synthetic ketone analogs of the right hand portion of the halichondrin B molecule could be
considered. Based on the results mentioned above, E7389 (5) was selected for development,
and, in July, 2001, E7389 was approved for Phase I clinical trials under NCI aegis, Eisai
provided 6 grams of cGMP product for the early trials, and in May, 2005, at the meeting of
the American Society of Clinical Oncology (ASCO), the authors of abstract 3036 reported
that Phase II trials are ongoing. The details of the discovery and development of E7389 are
provided in a review by Yu, Kishi and Littlefield (19) which illustrates the power of organic
total synthesis in optimizing an important drug discovery lead from natural sources.

Michellamine B. A Promising Lead but Problems with Toxicity

Michellamine B (6) was isolated as the main in vitro active anti-HIV agent from the leaves of
the liana, Ancistrocladus korupensis, collected in the Korup region of southwest Cameroon
through an NCI contract with Missouri Botanical Garden (MBG) (20). This new species (21)
is 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 drug 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.

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Thus far, no other Ancistrocladus species has been found to contain michellamine B, and
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, the
World Wide Fund for Nature Korup Project, MBG, Oregon State University and the NCI-
Frederick contractor, Science Applications International Corporation (SAIC). An extensive
botanical survey was undertaken, and 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 B content well above the wild average could be
produced routinely. 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 advanced preclinical development, but continuous infusion
studies in dogs indicated that in vivo effective anti-HIV concentrations could only be
achieved 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 (22), adds further promise for
this species.

Natural Product Drug Development and International Collaboration

The drug discovery and development cases discussed above clearly demonstrate that the
preclinical and clinical development processes are costly and lengthy undertakings which
require considerable international and multi-disciplinary collaboration. The discovery and
development must be carried out with the prior informed consent and the necessary collection
and export permits from the relevant Source Country Government and stakeholders, and
working in close collaboration with Source Country Organizations. Appropriate agreements
must be negotiated encompassing terms of training and technology transfer, protection of
environment and sustainable development, and plans for benefit-sharing. In the case of the
NCI, these agreements are based on the NCI Letter of Collection (LOC;
http://ttb.nci.nih.gov/nploc.html) and Memorandum of Understanding (MOU;
http://dtp.nci.nih.gov/branches/npb/agreements.html) (23).

The Need for Realistic Expectations

From 1960 to 1982, some 35,000 plant samples (representing about 12,000 to 13,000 species)
were processed by the NCI 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 the taxol (e. g., paclitaxel and its
analog, docetaxel) and camptothecin, which, though it proved to be too toxic in clinical trials
to become a commercial drug, has yielded commercial analogs, such as topotecan

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(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 species only gave two compounds yielding
products of commercial value. As noted above, further derivatives and analogs of taxol are
being developed which may become commercial products, and the same applies to
camptothecin.

The above observations are based only on screening for antitumor activity, and exposure of
extracts and compounds to a greater number of assays representing a wider range of diseases
would undoubtedly raise the level of success. The undeniable message, however, is that the
chances of developing a commercially viable drug from drug lead discoveries from any
source are extremely small, and source countries should not pin their hopes on deriving
significant royalties from the sales of drugs derived from drug leads discovered from their
natural resources.

Recommended Collaborative Process

Based on the NCI experience, a two phase approach to the exploration of source country
genetic resources as a source of potential novel drugs and other bioactive agents is
recommended.

Phase I of the process should involve negotiation of a Basic Research Agreement between
the research organization (e.g., representing pharmaceutical, agrochemical or
cosmetics/flavoring interests in developed countries) and the relevant Source Country
government department or agency, or with a qualified source country organization (SCO)
selected by the government to represent its interests. The involvement of a suitably qualified
local organization, if available, should be an essential requirement, and the Basic Research
Agreement should incorporate terms of collaboration covering exchange of data, training,
and technology transfer as spelled out in DTP/DCTD/NCI role, terms 1-6, of the NCI Letter
of Collection (see LOC; http://ttb.nci.nih.gov/nploc.html). In addition, there should be
requirements for adequate protection of the environment and endangered species.

Obtaining the Prior Informed Consent 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 Source
Country government agency should assist in this process. Most importantly, the Basic
Research Agreement should clearly require the negotiation of separate agreements (Phase II
agreements) covering any agents which are selected for preclinical or equivalent advanced
development.

Selection of an agent for advanced (e.g., preclinical) development will probably trigger
submission of an application for patent coverage, but it is most important to note that 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 (24).

Selection of a drug lead candidate for preclinical or equivalent development should trigger
negotiations of a new Phase II Commercial Development Agreement (CDA) covering the
specific issues related to the development and possible commercialization of the candidate.

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The CDA should address 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 in the case of pharmaceutical agents. Such terms should
address environmental impact studies, the possibility of sustainable harvest, and the possible
need for cultivation the source organism. Local scientists and communities should be
involved in these processes, as far as possible. The CDA should also include terms of
collaboration in the production of the development candidate (extraction, isolation, analysis,
etc.) depending on the facilities and expertise existent in the source country, and training and
technology transfer where appropriate, as well as training in the preclinical aspects of a drug
candidate (e. g., formulation, pharmacology). In the above two points it must be noted that
conditions of current Good Manufacturing Practice (cGMP) (e. g., approved facilities) have
to be met to satisfy the requirements of the US Food and Drug Administration (FDA) and
equivalent regulatory bodies in other countries. These are extremely expensive conditions to
fulfill, and generally these processes will be best performed by the collaborating research
organization.

Finally, terms should be included covering milestone payments when certain stages of
development are achieved (e. g., FDA approval for entry into Phase I clinical trials,
completion of Phase I trials, etc.), and payment of a percentage royalties on the sales of the
drug, should it become commercialized. An attractive alternative to royalties that may be
considered by a source country may be the provision of supplies of the drug free of charge
for treatment of the local population, and/or provision of other drugs (e.g., antimalarial, anti-
HIV) 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.

Given the very low success rate in actually developing a product through to commercial use,
it is strongly recommended that agreements should focus on short term benefits such as
training, technology transfer and milestone payments, rather than attempting to maximize
royalty payments which in all likelihood will never materialize! There are decided
advantages to maximizing short term benefits in terms of improving the capacity of source
country organizations and personnel to perform the drug discovery and early development
steps in-country, thereby optimizing the value of their resources. In addition, discovery of
promising drug leads entirely in-country creates the opportunity for source country
organizations to gain complete control of their inventions through application for appropriate
sole source country inventorship patent coverage (composition of matter patents in the case
of novel chemical entities, or use patents in the case of novel uses for known chemical
entities).

Regional Collaborative Networks Coordination of Regional Strengths

Even with large organizations such as the NCI, experience has clearly demonstrated that the
development of effective new drugs depends on multi-institutional and international
collaboration. The developments of taxol and the halichondrin analog discussed above are
clear examples of the need for such collaboration. Source countries rich in genetic resources
(plant, marine, microbial) can optimize the opportunities for effective use of their resources
through establishing regional collaborative networks in which the skills and
capacities/facilities of different countries in the region are shared, rather than each country
trying to develop its own multiplicity of capabilities. Thus, different assays (e.g.,
antimalarial, anti-HIV, anti-TB, antitumor, etc.) and different instrumentation facilities (e. g.,
NMR, MS, HPLC-MS, etc.) can be established in different countries selected by mutual

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agreement between countries in the region. Research organizations in different countries can
submit extracts to their collaborating partner organizations in other countries for testing in a
variety of assays, with results returned on a confidential basis, and active compounds isolated
by source country organizations can be submitted to partner organizations for spectroscopic
and spectrometric examination to aid in structural elucidation.

The establishment of a close collaborative regional network requires a high level of mutual
trust and commitment to true partnership, as well as the negotiation of regional agreements
ensuring appropriate confidentiality of results and the fair sharing of benefits, including
coauthorship on papers and coinventorship of involved parties on patent applications for
promising discoveries. The NCI and NIH have promoted multi-institutional and international
research collaboration through their National Cooperative Drug Discovery Group (NCDDG)
(25) and International Cooperative Biodiversity Group (ICBG) (26) programs which have
been very effective in advancing drug discovery and development, and in many cases,
involving beneficial collaborations with source country organizations.

In the case of sub-Saharan Africa, an organization such as NAPRECA has the attributes for
successfully establishing an effective collaborative regional network incorporating already
existent strengths, and applying for international support for the establishment of centers of
excellence in various screening and structural elucidation technologies, as well as for
strengthening the natural products chemistry capacity (isolation and synthesis) of selected
organizations in all member countries. It is only through the demonstration of the will to
establish such regional collaboration that progress will be made in obtaining the support
necessary for optimizing the use and sustainable development of the regions undoubtedly
rich natural resources.

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Rodman, J., Roskoski, J., Siegel-Causey, D., Combining High Risk Science with
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