Studies On Cancer Chemopreventive Activity Of 9201 From Rhus Chinensis And Its Mechanism Of Action

The cancer chemopreventive activity and mechanism of action of Chinese gallo-tannin 9201 from Rhus chinensis was studied in this thesis.Three models were used in the chemopreventive activity studies. (1) malignant transformation of Chinese hamster lung cell line (V79) induced by benzo (a) pyrene in vitro. It was shown that 9201 (10—20μg/ml) significantly inhibited benzo (a) pyrene—induced malignant transformation of V79 cells. (2) pulmonary adenomas induced by benzo(a) pyrene in A/J mice. Experiment results demonstrated that the administration of 9201 for 30 days orally effectively inhibited the occurrence of benzo (a) pyrene—induced lung adenoma in A/J mouse. (3) 7 ,12—dimethylbenz [a] anthracene (DMBA) and croton oil—induced mouse skin papilloma. It was demonstrated that 9201 could inhibit DMBA/Croton oil induced mouse skin papilloma, and prolong the latent period of tumor occurrence, decrease the incidence of papilloma and reduce tumor number per mouse in a dose—dependent manner. It was demonstrated that 9201 is a potent cancer chemopreventive agent in vitro as well as in vivo.9201 exhibited a significantly inhibitory effect on cyclophosphamide (CTX)—induced micronucleus formation of polychromatic erythrocytes (PCE) of bone marrow in mice. In Ames test, 9201 could decrease benzo(α)pyrene—induced TA97 and TA100 His⁺—revertants. It exhibited a strong antimutagenic activity. By using immuno— histochemistry method of Ki—67 antinucleus antibody, 9201 was found to inhibit the cell proliferation caused by B(α)P in 2BS cell line. It also inhibited the oncogene ex- pression of C-myc and K—ras, but enhanced the expression of tumor suppressor genes P53 and RB in V₇₉ cells transformed and treated by B(α)P.9201 exhibited a significant inhibition on hepatic microsome cytochrome P—450 from mouse and rat in vivo as well as in vitro, and prolonged sleeping time induced by pentobarbital in mice. 9201 also increased GSH content in liver, lung and skin in nor- mal mice and benzo (α) pyrene—treated mice. It showed a significant inhibition on aryl hydrocarbon hydroxylase (AHH) activity in vivo and in vitro. 9201 significantly inhibited metabolic activation of benzo (α) pyrene in a dose dependent manner. The study of mechanism of action suggests that 9201 reduced the formation of ultimate car- cinogen by inhibiting P—450IAl activity. Molecular biology studies demonstrated that 9201 also inhibited the expression of P₁—450 and the formation of B(α)P—DNA adduct. It suggests that 9201 has antimutagenic activity and inhibit B(α)P metabolism.DNA repair activity in cells is an important parameter in cancer chemoprevention studies. In DNA damage repair test, 9201 exhibited protective action against rapid DNA damage induced by benzo (α) pyrene in CHL cells and it also inhibited the stimu- lation of unscheduled DNA synthesis caused by benzo (α)pyrene. By applying a combined alkaline unwinding/Southern blot assay for measuring low level of cellular DNA breakage within some specific genomic regions, 9201 was found to alleviate DNA damage induced by benzo(α)pyrene in the regions encompassing C—myc and 17α—satellite. It strengthened the weaken signals caused by benzo (α)pyrene and alkaline unwinding. Experimental studies showed that 9201 had a protective action to DNA damage. It was proved that 9201 has an efficient anti—initiating activity.Chinese gallotannin 9201 obviously counteracted the croton oil—induced ear edema in mice, and Fe²⁺/Cysteine—induced lipid peroxidation of rat liver microsome and could efficiently scavenge DPPH, O₂^- free radicals. It suggested that 9201 has a si- milar antioxidaton activities to polyphenols from green tea. The serape-loading and dye transfer (SLDT) technique demonstrated that TPA may inhibit gap junction inter- cellular communication(GJIC). 9201 could countermine the inhibition of TPA on GJIC and enhance GJIC.In delayed hypersensitivity assay of skin (DHR), 9201 increased spleen index, thymus index and mouse ear edema. It also enhanced the cell kill of LAK cell against leukemia K₅₆₂ and hepatoma Bel₇₄₀₂ cell lines induced by IL₂. It was shown that 9201 displayed BRM like action.In summary, 9201 is an active component from Rhus chinensis in traditional Chinese medicine. It inhibits the metabolic activation of carcinogen which elicits DNA damage. 9201 can also act as a scavenger of the DNA—reactive metabolites of benzo (α) pyrene. It has a strong antiinitiation, antimutagenie, antipromotion and antiox- idant activity. The above mentioned activity of 9201 suggests that it is an attractive ag- ent for cancer chemoprevention.