Direct estradiol and diethylstilbestrol actions on early- versus late-stage prostate cancer cells

BACKGROUND Diethylstilbestrol (DES) and other pharmaceutical estrogens have been used at ≥ μM 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. METHODS LAPC-4 (androgen-dependent) and PC-3 (androgen-independent) cell viability was measured after estradiol (E₂) or DES treatment across wide concentration ranges. We then examined multiple rapid signaling mechanisms at 0.1 nM E₂ and 1 μM DES optima including levels of: activation (phosphorylation) for mitogen-activated protein kinases, cell-cycle proteins, and caspase 3, necroptosis, and reactive oxygen species (ROS). RESULTS LAPC-4 cells were more responsive than PC-3 cells. Robust and sustained extracellular-regulated kinase activation with E₂, but not DES, correlated with ROS generation and cell death. c-Jun N-terminal kinase was only activated in E₂-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 E₂ 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. CONCLUSIONS Cyclin D1 status correlated most closely with disrupted cell cycling as a cause of reduced cell numbers, though other mechanisms also contributed. As low as 0.1 nM E₂ 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.