Synthesis, reactivity, and bioactivation screening of potential carcinogenic metabolites of triphenylethylene antiestrogens

Part I. Synthesis and reactivity of potential carcinogenic{09}metabolites of triphenylethylene antiestrogens. Long term usage of tamoxifen has led to an increase in the survival of patients with breast cancer; a decrease in the risk of developing breast cancer; and a decrease in the risk of developing osteoporosis and heart disease. Despite the beneficial effects of tamoxifen treatment, reports have shown that it may increase the incidence of endometrial cancer in women; induce the formation of DNA adducts; and cause hepatocarcinoma in animal models. The exact mechanism(s) of tamoxifen carcinogenesis is still unclear. To evaluate the risk factors involved in the long term usage of tamoxifen, a full understanding of the carcinogenic mechanisms of this drug is crucial.; Several bioactivation pathways leading to the toxicity of tamoxifen has been proposed. The focus of our research targets pathways leading to the generation of reactive intermediates such as tamoxifen quinone methide, carbocation, and o-quinone. Some of them have been shown to alkylate DNA and thus have the potential to initiate the carcinogenic process.; Part II. Development of a high-throughput bioactivation screening assay. High throughput drug metabolism and toxicity screening assays have played an important role in the pharmaceutical industry because of the large number of lead compounds generated from the drug discovery programs. Pulsed ultrafiltration-mass spectrometry was developed to identify potentially toxic compounds during the initial drug development phase. Metabolizing enzymes (cytochrome P450) from rat liver microsomes were trapped inside a stirred chamber fitted to an ultrafiltration membrane. Then potential drug candidates along with the cofactor, NADPH and glutathione were introduced into the chamber. The progress of their metabolism and bioactivation was monitored on-line using electrospray mass spectrometry. The results suggest that the on-line screening method is a more accurate in vitro screening model compared to off-line incubation method because the former is a flow-through system, which mimics the passage of drugs through the liver so that product feedback inhibition is minimized.