Overcoming the radioresistance of prostate cancer cells with a novel Bcl-2 inhibitor.
Bcl-2 overexpression is an important mechanism underlying the aggressive behavior of prostate cancer cells and their resistance to radio- or chemotherapy. HA14-1, a recently discovered organic Bcl-2 inhibitor, potently induces apoptosis in various human cancer cells. Sequential exposure of radioresistant LNCaP (wild-type (wt) p53), LNCaP/Bcl-2 (wt p53) and PC3 (mutant p53) prostate cancer cells to a minimally cytotoxic concentration of 10 microM HA14-1 for 1 h followed by 1-6 Gy gamma radiation, resulted in a highly synergistic (combination index <1.0) induction of cell death as determined by an apoptosis assay at 72 h, and a clonogenicity assay at 12 days, after the initial treatment. The reverse treatment sequence did not cause a synergistic induction of cell death. When compared to individual treatments, cell death induced by the combined treatment was associated with dramatically increased reactive oxygen species (ROS) generation, c-Jun N-terminal kinase (JNK) activation, Bcl-2 phosphorylation, cytochrome c release, caspase-3 activation and DNA fragmentation. Exposure to either 200 microg/ml of the antioxidant alpha-tocopherol or 10 microM JNK inhibitor SP600125 before the combined treatment resulted in decreased activation of JNK and caspase-3 as well as decreased DNA fragmentation. However, treatment with the pancaspase inhibitor carbobenzoxyl-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone before the combined treatment inhibited apoptosis without affecting JNK activation, and this inhibitory effect was enhanced in the presence of alpha-tocopherol or SP600125. Taken together, our results indicate that HA14-1 potently sensitizes radioresistant LNCaP and PC3 cells to gamma radiation, regardless of the status of p53. ROS and JNK are important early signals that trigger both caspase-dependent and -independent cell death pathways and contribute to the apoptotic synergy induced by the combined treatments.
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Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, USA. jingan@burnham.org
Chervin
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Nie
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Ducoff
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Huang
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D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D001578:Benzopyrans / Q000494:pharmacology*; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005720:Gamma Rays; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011836:Radiation Tolerance; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D001578:Benzopyrans; D004791:Enzyme Inhibitors; D009570:Nitriles; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D016159:Tumor Suppressor Protein p53; C456800:ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate; D045304:Cytochromes c; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases