Bioassay-directed fractionation of a medicinal plant, Polygonum cuspidatum (Polygonaceae), has led to the discovery of a hydroxystilbene, resveratrol [1], as an inhibitor of a protein-tyrosine kinase (p56lck) partially purified from bovine thymus. Both trans and cis isomers of resveratrol possess comparable protein-tyrosine kinase inhibitory activity. Comparison of the IC50 values of resveratrol for protein-tyrosine kinase inhibitory activity with those of piceid (resveratrol-O3-beta-glucoside) [2] and resveratrol-O4'-beta-glucoside [3] shows the requirement of free hydroxyl groups on both phenyl rings for the protein-tyrosine kinase inhibition. Protein kinase C inhibitory analysis suggests the requirements of two free hydroxyl groups on one phenyl ring only.

No abstract

Recent advances in the chemistry of novel bioactive natural products are reported. This research is directed to the exploration of plants with confirmed activity in bioassays designed to detect potential cancer chemotherapeutic and chemopreventive agents. Structural work and chemical studies are reported for several cytotoxic agents from the plants Annona densicoma, Annona reticulata, Claopodium crispifolium, Polytrichum obioense, and Psorospermum febrifugum. Studies are also reported based on development of a mammalian cell culture benzo[a]pyrene metabolism assay for the detection of potential anticarcinogenic agents from natural products. In this study a number of isoflavonoids and flavonoids with antimutagenic activity have been discovered.

Fourteen structurally diverse Annonaceous acetogenins, representing the three main classes of bis-adjacent, bis-nonadjacent, and single-THF ring(s), were tested for their ability to inhibit the growth of adriamycin resistant human mammary adenocarcinoma (MCF-7/Adr) cells. This cell line is resistant to treatment with adriamycin, vincristine, and vinblastine and is, thus, multidrug resistant (MDR). Among a series of bis-adjacent THF ring acetogenins, those with the stereochemistry of threo-trans-threo-trans-erythro (from C-15 to C-24) were the most potent with as much as 250 times the potency of adriamycin. A spacing of 13 carbons between the flanking hydroxyl of the THF ring system and the gamma-unsaturated lactone seems to be optimum with a spacing of 11 and 9 carbons being significantly less active. Several single-THF ring compounds were also quite potent with gigantetrocin A (11) being the most potent compound tested. The acetogenins may, thus, have chemotherapeutic potential, especially with regard to MDR tumors.

Screening of crude extracts of the bark of Annona bullata showed cytotoxic and pesticidal activities. By monitoring with brine-shrimp lethality, two novel, extremely potent acetogenins, bullatacin [1] and bullatacinone [2], were isolated. Spectral and chemical methods identified bullatacin as a diastereomer of asimicin. Bullatacinone represents bullatacin with the lactone cleaved and reformed at the 4-OH. Compounds 1 and 2 show selective cytotoxicities in human tumor cell lines, and certain susceptible cells give ED50 values as low as 10(-12)-10(-15) micrograms/ml. Bullatacin was pesticidal at concentrations as low as 1 ppm, but bullatacinone lacked pesticidal activities. The known compounds liriodenine and (-)-kaur-16-en-19-oic acid were also isolated and were lethal to brine shrimp but were not significantly cytotoxic.