Natural Inhibitors of Carcinogenesis

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Chemoprevention is a therapeutic method wherein human cancer is prevented or delayed through oral consumption of nontoxic agents capable of inhibiting the process of carcinogenesis. As an integral component of the national effort to defeat cancer, the merit of this approach is intuitively obvious. A variety of potential cancer chemopreventive agents are known, most of which were discovered on an empirical basis. With the cooperation of three separate institutions, we have assembled a multidisciplinary team focused on the discovery and characterization of new cancer chemopreventive agents that are natural products or natural product derivatives. As established by ample precedent, nature provides broad chemical diversity. As in the past, we will continue to work with terrestrial plant materials (edible and nonedible), but we will also concentrate on obtaining lead compounds from a novel source that has not been adequately explored in the area of cancer chemoprevention, i.e., deep ocean sediment-derived microorganisms. Some unique constituents, useful for the treatment of human ailments, cannot be anticipated aside from the experimental process of natural product drug discovery. Starting with well-characterized plant materials or deep sea microorganisms, extracts are prepared and evaluated for activity in a panel of in vitro bioassays indicative of inhibiting major stages of carcinogenesis. These assays have been explicitly designed for this purpose, and some of the methodology, such as pulsed-ultrafiltration utilizing LC/MS, is highly original. Active materials are evaluated in secondary assay systems of greater physiologic complexity, and those judged to be active with a secondary discriminator are subjected to bioassay-guided fractionation. Active principles are structurally-defined by physical and spectroscopic methods, or by X-ray crystallography. The leads are then evaluated in a broader array of bioassay systems, and considered as candidates for development. As part of this program project, development involves chemical synthesis or large-scale isolation, detailed mechanistic studies, establishment of structure-activity relationships, lead optimization, definition of molecular interactions with target molecules using state-of-the-art methods of structural biology, and determination of cancer chemopreventive potential in short- or long-term studies conducted with laboratory animals. Biostatistical and analytical (LC/MS/MS) support is provided throughout. The scope of the program project thereby entails promoting new cancer chemopreventive agents from the level of the field or sea, to the level of structurally- and mechanistically-defined chemical entities of proven therapeutic efficacy. These undertakings require the coordinated effort of four separate projects that are assisted by two core components, and an External Advisory Board. To facilitate utilization of the newly discovered agents for the prevention of human cancers, which is the long-term objective of this program project, partnerships will be fostered with the NCI (e.g, through the RAPID program) or the private sector. All elements of the program project have proven effective, and we anticipate unabated progress in the future.