Resistance to growth inhibitory and apoptotic effects of phorbol ester and UCN-01 in aggressive cancer cell lines.
7-Hydroxystaurosporine (UCN-01), a non-selective inhibitor of protein kinase C (PKC), and phorbol ester (PMA), a PKC activator, are undergoing clinical evaluations. We investigated the effects of UCN-01 and PMA on a panel of prostate cancer cell lines. While PMA induced p21WAF1/CIP1 and arrest growth of LNCaP cancer cells (IC50 = 0.5-1 nM), aggressive cancer cell lines (DU145, PC3, and PC3M) were resistant to PMA (IC50 >5000 nM). Low concentrations (25-50 nM) of UCN-01 abrogated PMA-induced p21 and growth arrest in LNCaP cells. These low doses of UCN-01 however did not inhibit proliferation of any prostate cancer cell line. PMA-sensitive LNCaP cells were resistant to clinically relevant concentrations of UCN-01 (IC50 = 1.2 microM), but UCN-01 inhibited growth of DU145 and PC3/3M with an IC50 of 200-400 nM. For comparison, PMA-sensitive HL60 leukemia cells were sensitive to UCN-01 due to rapid apoptosis caused by UCN-01. In PMA-resistant prostate cancer cells, UCN-01 downregulated cyclin D1, induced p21, caused morphological differentiation, and G1-phase arrest leading to slow cell death without caspase activation. Importantly, normal prostate epithelial cells (PrEC) were very sensitive to both PMA (IC50 = 0.2 nM) and UCN-01. In PrEC, UCN-01 downregulated cyclin D1 and arrest growth with an IC50 less than 100 nM. We conclude that loss of sensitivity to either UCN-01 or PMA accompanies progression of prostate cancer.
Medicine Branch, Division of Clinical Sciences, National Cancer Institute, NIH, Bldg 10, 12N226, Bethesda, MD 20892, USA. mikhailb@box-m.nih.gov
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D000470:Alkaloids / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D005562:Formazans / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction; D019311:Staurosporine / Q000031:analogs & derivatives; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013778:Tetrazolium Salts / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects
D000470:Alkaloids; D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004273:DNA, Neoplasm; D005562:Formazans; D013778:Tetrazolium Salts; C079782:MTT formazan; C054852:7-hydroxystaurosporine; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate