Carcinogenic Metabolites Formed from Antiestrogens

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Development of the "perfect" selective estrogen receptor modulator (SERM) is of paramount importance in postmenopausal women's health. The beneficial and undesirable side effects of SERMs are directly analogous to estrogens, which are known carcinogens through a mechanism involving oxidative metabolism to redox active/electrophilic quinoids. We hypothesize that the adverse effects of SERMs are also related to their oxidative metabolism to quinoids. Whether these quinoids are detrimental are unknown at this time and it is the focus of this proposal to determine the effect of structure on these mechanisms in an effort to provide crucial information leading to the development of the "perfect" SERM. The specific aims are: 1. Effect of structure on the formation and reactivity of SERM quinoids. We have shown that classical quinone methides, di-quinone methides, and o-quinones are produced from triphenylethylene, benzothiophene, and miscellaneous SERMs. We plan to examine the relative abilities of new classes of SERMs such as bazodoxifene and lasofoxifene as well as the Lilly naphthol analogs to be oxidized to quinoids. The rate of formation, type of quinoid, as well as their reactivity will be studied in subcellular fractions and Ishikawa endometrial cells. 2. What are the protein targets of SERM quinoids? In the current proposal, we plan to use the COATag methodology and "click chemistry" or modified Staudinger ligation approaches to examine protein covalent modification in rat mammary subcellular fractions and Ishikawa cells. The targeted proteins will be isolated using avidin affinity chromatography, separated by 2D electrophoresis, digested, and analyzed by MALDI-TOF and LC-MS-MS. We predict that the reactivity of SERM quinoids will have a strong influence on which proteins are modified as well as sites of protein alkylation within the target proteins. 3. Do SERM quinoids modify DNA and induce cellular transformation? This aim will focus on how the type and reactivity of SERM quinoid formed will dictate the extent of DNA damage. Initial model studies with deoxynucleosides and DNA will allow characterization of stable DNA adducts, analysis of depurinating adducts, as well as determination of DNA oxidation. We will then analyze SERM-induced DNA damage in Ishikawa cell lines. Apurinic sites (AP) will be directly quantified using the aldehyde reactive probe assay and the transversions and transitions resulting from these mutagenic lesions will be detected by mismatch-capture methodology. Finally, transformation studies will be performed in MCF-10A cells and the transformed clones will be implanted into athymic nude mice to investigate their ability to induce tumor formation. These studies will elucidate the relative importance of quinoid formation and cellular targets for each SERM, thereby enabling correlations of reactivity with structure from which general principles influencing the behavior of SERM quinoids in cells will emerge.