Direct Estradiol and Diethylstilbestrol Actions on Early-Versus Late-Stage Prostate Cancer Cells

BACKGROUNDDiethylstilbestrol (DES) and other pharmaceutical estrogens have been used at mu M concentrations to treat advanced prostate tumors, with successes primarily attributed to indirect hypothalamic-pituitary-testicular axis control mechanisms. However, estrogens also directly affect tumor cells, though the mechanisms involved are not well understood. METHODSLAPC-4 (androgen-dependent) and PC-3 (androgen-independent) cell viability was measured after estradiol (E-2) or DES treatment across wide concentration ranges. We then examined multiple rapid signaling mechanisms at 0.1nM E-2 and 1 mu M DES optima including levels of: activation (phosphorylation) for mitogen-activated protein kinases, cell-cycle proteins, and caspase 3, necroptosis, and reactive oxygen species (ROS). RESULTSLAPC-4 cells were more responsive than PC-3 cells. Robust and sustained extracellular-regulated kinase activation with E-2, but not DES, correlated with ROS generation and cell death. c-Jun N-terminal kinase was only activated in E-2-treated PC-3 cells and was not correlated with caspase 3-mediated apoptosis; necroptosis was not involved. The cell-cycle inhibitor protein p16(INK4A) was phosphorylated in both cell lines by both E-2 and DES, but to differing extents. In both cell types, both estrogens activated p38 kinase, which subsequently phosphorylated cyclin D1, tagging it for degradation, except in DES-treated PC-3 cells. CONCLUSIONSCyclin D1 status correlated most closely with disrupted cell cycling as a cause of reduced cell numbers, though other mechanisms also contributed. As low as 0.1nM E-2 effectively elicited these mechanisms, and its use could dramatically improve outcomes for both early- and late-stage prostate cancer patients, while avoiding the side effects of high-dose DES treatment. Prostate 74: 1589-1603, 2014. (c) 2014 Wiley Periodicals, Inc.