Global profiling of TSEC proliferative potential by the use of a reporter mouse for proliferation

Introduction: "Tissue-selective estrogen complex" or TSEC is a novel concept of estrogen replacement therapy for the postmenopause based on the combined use of estrogens and selective estrogen receptor modulators (SERMs). The aim of this study was to exploit the potential of a novel transgenic mouse where luciferase expression is associated with cell proliferation (the MITO-luc mouse) to investigate cell proliferation in reproductive and nonreproductive tissues in mice exposed to repetitive treatments with TSEC. Material and Methods: Ovariectomized MITO-Luc mice were subjected to a daily oral treatment with bazedoxifene, conjugated estrogen (CE), TSEC, or raloxifene for 21 days. During the treatment, the proliferative effects of treatments were monitored by bioluminescence-based in vivo imaging. At the end of the treatment, mice were euthanized and cell proliferation assessed in selected tissues by quantitative analysis of luciferase activity and by immunohistochemistry (IHC). Results: In uterus treatment with CE, but not TSEC, induced a large increase in luciferase activity underlying the proliferative effect of the hormone. No accumulation of luciferase was observed in other organs and tissues target of estrogen action. We observed an increase of Ki67 immunoreactivity only in the uterus of mice treated with CE. Conclusion: Pairing of an SERM with estrogens results in a complete blockage of CE proliferative effects in uterus and the absence of any undesired proliferative effects in other organs; moreover, the MITO-Luc mouse is an efficacious tool for the global, rapid, and reliable analysis of drug-induced proliferation.