Evaluation of cancer chemopreventive activity mediated by antioxidants and modulators of tumor promotion

In order to discover new cancer chemopreventive agents from natural products, we have monitored the ability of plant extracts to inhibit a variety of in vitro biomarkers, including antioxidant activity, inhibition of phorbol ester-induced ornithine decarboxylase (ODC) activity in cell culture, and modulation of benzo(a)pyrene-DNA binding and metabolism. Using a simple 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity assay, approximately 700 plant extracts were evaluated for antioxidant potential. Approximately 30 plant extracts were shown to mediate antioxidant activity. With bioassay-guided fractionation, several flavonoids and phenolic compounds were isolated as active principles from active lead plant extracts. Further, in order to directly identify active antioxidant principles from plant extracts, an electrospray HPLC/MS dereplication method was developed and applied. {dollar}(-){dollar}-Epicatechin gallate, curcumin, floribundones 1 and 2, and 1,2,3,6-tetra-O-galloyl-{dollar}beta{dollar}- scD-glucose were identified as active principles using this method.; In addition, using inhibition of ornithine decarboxylase (ODC) induction as the target, approximately 800 plant extracts were evaluated. As a result of bioassay-guided fractionation, the rotenoids deguelin and tephrosin were isolated as potent ODC inhibitors from Mundulea sericea Willd. (Leguminosae). Further, these isolates inhibited chemically-induced preneoplastic lesions in mammary organ culture and papillomas in the two-stage mouse shin model. Since deguelin was considered a promising antitumor promoter, the mechanism has been studied by investigating effects on ODC mRNA expression, c-Myc-induced ODC activity, NADH-dehydrogenase activity, ATP formation and tubulin polymerization. In addition, 16 rotenoid derivatives were synthesized and evaluated for their chemopreventive potential to determine if a more potent and/or less toxic derivative could be found. 4{dollar}spprime{dollar}-Bromorotenoic acid also showed good inhibitory effects on TPA-induced ODC activity both in mouse epidermal cell culture and mouse skin, with decreased cytotoxicity.; Furthermore, the inhibitory potential of benzo(a)pyrene (B(a)P) -DNA binding and modulation of B(a)P metabolism were investigated with cancer chemopreventive agents using an immortalized normal human bronchial cell culture model. In general, phenolic antioxidants and sulfur-containing phase II enzyme inducers showed potent inhibitory effects with B(a)P-DNA binding assays, and also inhibited total B(a)P metabolism. Phenolic antioxidants, in addition, showed inhibitory effects on phorbol ester-induced anchorage-independent JB6 cell transformation in soft agar.