Review of the National Cancer Institute's Acquisition and Screening of Plant Extracts

The National Cancer Institute's (NCI) goal is to develop the means for reducing the incidence, morbidity, and mortality of cancer. In 1972, NCI established the National Cancer Program. The Division of Cancer Treatment, the main organizational component of the cancer program, became responsible for coordinating cancer treatment research within NCI. The major emphasis in cancer treatment research is searching for antitumor drugs and developing and improving combined methods of therapy using drugs singly or in combination with other forms of therapy, including surgery and radiotherapy. The Developmental Therapeutics Program (DTP), a subdivision of the Division of Cancer Treatment, administers the search for new anticancer agents. DTP acquires various chemicals and natural products for evaluation as potential sources of new cancer treatment drugs. These may be of synthetic origin or come from microbiological, plant, and animal sources. A review of the DTP research program was undertaken which focused on the activities within two branches: (1) the Natural Products Branch (NPB), which arranges for acquiring plants; and (2) the Drug Evaluation Branch (DEB), which is responsible for screening new agents for anticancer activity. NPB arranges for worldwide collection of plants. Collections are made primarily under an interagency agreement with the Department of Agriculture (USDA) which obtains about 90 percent of its collections from contract suppliers in about 60 countries and the remainder from USDA personnel throughout the world. Other sources include a contract with the University of Hawaii and occasional submissions from research institutions, interested scientists, and universities. DEB is responsible for screening new materials to identify those that can kill cancer cells. Screening is performed in two phases: (1) a prescreen to identify any compounds with the potential to kill cancer cells; and (2) the detailed screening process which further analyzes those compounds identified in the prescreen.

In 1977, DTP found substantial duplication in the plant program because of lack of controls over activities of collection contractors. Some duplication of plants is acceptable if they are collected in different seasons or from different countries because plants' chemical composition may vary based on those factors. However, NPB determined that 60 percent of the plants being collected were identical to plant species already collected and screened. To improve this situation, NPB established a control system designed to limit the repetitive collecting of plant species. The categorization process of this system allowed NPB to categorize, as not wanted, samples which came from only one country. This process should be modified so that plants are not categorized as not wanted until samples have been screened from two or more countries. By assuring that samples are obtained from two or more countries before a plant is categorized as not wanted, the chances of missing plants with anticancer potential would be reduced. NPB should review the list of 67,000 plants categorized as not wanted and reinstate those plants collected from only one country. On the other hand, DEB believes the development and application of better in vitro test systems prescreens, which test for the cell-killing ability of an extract and uses human cells grown in culture media, would identify a greater number of compounds. These screens can be designed to detect compounds with specific biochemical activities which cannot be detected by the current screens and should also be less costly.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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