Influence of p53 and bcl-2 on chemosensitivity in benign and malignant prostatic cell lines

The administration of cancer chemotherapeutic agents results in an increase in the apoptotic cells in the tumor: therefore, it has been assumed that anticancer drugs exhibit their cytotoxic effects via apoptotic signaling pathways. Characteristics that confer sensitivity to drug-induced apoptosis are, a functional p53 protein and expression of the apoptosis-promoting protein, bax. The role of p53 and bax/bcl-2 in drug-induced apoptosis was assessed in six prostate cell lines, 1532T, 1535T, 1542T, 1542N, BPH-1 and LNCaP using TD50 concentrations of etoposide, vinblastine and estramustine. Cell death was monitored morphologically by fluorescent microscopy, and by flow cytometry (Annexin-V assay). Apoptotic morphology was rather low and ranged from 0.1% to 12.1%, 3.0% to 6.0% and 0.1% to 8.5% for etoposide, estramustine and vinblastine, respectively. Annexin-V binding and flow cytometry indicated apoptotic propensities of 0% to 4%, 0% to 3% and 0% to 5%, respectively. The percentage of cells responding to drug-induced apoptosis was, on average, higher in the tumor cell lines than in the normal cell lines, but showed no correlation with p53 status. The percentage of cells showing necrosis, assessed by Annexin binding and Propidium Iodide permeability in aqueous medium, tended to be much higher, and was found to be at the level of 5% to 30%. Immunoblotting demonstrated that bax and bcl-2 proteins were expressed at a basal level in all cell lines, but did not increase after exposure to TD50 doses of the three drugs. The ratio of bax and bcl-2, measured by laser scanning densitometry, was not altered by the drug-induced DNA damage. The results suggest that apoptosis is not a major mechanism of drug-induced cell death in prostate cell lines and appears to be independent of p53 status and bax/bcl-2 expression.