Selenium Effects on Prostate Cell Growth1

Abstract

Epidemiological and clinical data suggest that selenium may prevent prostate cancer, but the biological effects of selenium on normal or malignant prostate cells are not well known. We evaluated the effects of sodium selenite (Na₂SeO₃) or l-selenomethionine (SeMet) on monolayer and anchorage-independent growth in a series of normal primary prostate cultures (epithelial, stromal, and smooth muscle) and prostate cancer cell lines (LNCaP, PC-3, and DU145). We observed differential, dose-dependent growth inhibition and apoptosis within prostate cancer cells (compared with normal prostate cells) treated with 1–500μ m of Na₂SeO₃ or SeMet. Na₂SeO₃ more potently inhibited growth at any given concentration. The androgen-responsive LNCaP cells were the most sensitive to selenium growth suppression (IC₅₀s at 72 h for Na₂SeO₃ and SeMet were 0.2 and 1.0μ m, respectively). Growth of the primary prostate cells virtually was not suppressed (IC₅₀s at 72 h for Na₂SeO₃ and SeMet were 22–38 and >500μ m, respectively). We also observed that DNA condensation and DNA fragmentation (terminal deoxynucleotidyltransferase dUTP nick end labeling/fluorescence-activated cell sorting) were elevated in selenium-treated cells and that activated caspase-3 colocalized with terminal deoxynucleotidyltransferase dUTP nick end labeling-stained cells by immunofluorescence. Higher basal poly(ADP-ribose) polymerase (PARP) expression levels and PARP cleavage (a substrate for caspase-3) were observed during apoptosis in tumor cells, compared with normal cells. Selective tumor cell death was associated with an increase in sub-G₀-G₁ cells after propidium iodide staining and fluorescence-activated cell sorting analysis. SeMet caused an increase in arrest in the G₂-M phase of the cell cycle selectively in cancer cells. Inhibition of cancer cell growth by SeMet was associated with phosphorylation of P-Tyr15-p34/cdc2, which caused growth arrest in the G₂-M phase. Anchorage-independent growth of prostate cancer cells in soft agar was sensitive to selenium. Our results suggest that Na₂SeO₃ is the more potent inducer of apoptosis in normal and cancer prostate cells. Our SeMet results involving PARP and G₂-M cell-cycle arrest (cited above) indicate that SeMet selectively induces apoptosis in cancer but not primary cells of the human prostate. Our overall findings are relevant to the molecular mechanisms of selenium actions on prostate carcinogenesis and help demonstrate the selective, dose-dependent effects of selenium (especially SeMet) on prostate cancer cell death and growth inhibition.