The direct effects of estradiol and several xenoestrogens on cell numbers of early- vs. late-stage prostate cancer cells

Prostate cancer is the most common non-cutaneous cancer among men, and diethylstilbestrol (DES) is an estrogen that has been used clinically to combat advanced tumors. Estrogens can indirectly decrease androgen production by central negative feedback inhibition, but may also have direct tumor killing mechanisms by a less well understood mechanism. To elucidate these mechanisms and provide understanding for potential future therapies, we identified cellular pathways and rapid signaling events that act via estrogen receptors (ERs) and contribute to estradiol (E2) or DES-mediated cell killing/growth arrest. E2 was much more effective than DES at reducing cell numbers of both LAPC-4 early-stage androgen-dependent and PC-3 late-stage androgen-independent prostate cancer cells. Both E2 and DES rapidly (within minutes) activated mitogen-activated protein kinases, generated reactive oxygen species (ROS), induced apoptosis and necroptosis, and regulated the activation and levels of cell cycle proteins. Regulation of cyclin D1 played a major role in blocking cell proliferation, but extracellular signal-regulated kinase (ERK) causing ROS generation, phosphorylation of p38, apoptosis, and phosphorylation of p16INK4A also contributed. Our rapid effects suggested the participation of membrane ERs (mERs). ERα and β mediated E2’s ability to increase ROS through sustained ERK activation, and increased p-cyclin D1 levels in LAPC-4 cells. However, ERβ and GPR30 mediated these responses in PC-3 cells. Apoptosis was initiated in LAPC-4 and PC-3 cells by E2 only, and not by DES. Necroptosis was not altered by estrogens in either cell line. We showed for the first time the presence of mERs in both early and late prostate cancer cells. Then several xenoestrogens (XEs) were evaluated for their ability to increase or decrease prostate cancer cell numbers. Coumesterol and genistein unexpectedly stimulated prostate cancer cell growth, while resveratrol minimally increased cell numbers in both early and late-stage cells. Bisphenol A (BPA) slightly, though significantly, increased cell numbers in LAPC-4 cells only. Again, control of cyclin D1 protein levels was a key mediator of the growth change effects. The findings of these studies should be relevant to the clinical treatment of prostate tumors, including development of ER subtype-specific agents to control proliferation and cell death signaling pathways. Our findings regarding XEs should help establish guidelines for prostate cancer patients regarding consumption of safe dietary concentrations of phytoestrogens and acceptable exposure levels to BPA.