Overcoming the radioresistance of prostate cancer cells with a novel Bcl-2 inhibitor

Oncogene. 2007 Feb 1;26(5):652-61. doi: 10.1038/sj.onc.1209830. Epub 2006 Aug 7.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Apoptosis / radiation effects
  • Benzopyrans / pharmacology*
  • Caspases / metabolism
  • Cytochromes c / metabolism
  • Enzyme Activation
  • Enzyme Inhibitors / pharmacology*
  • Gamma Rays
  • Humans
  • JNK Mitogen-Activated Protein Kinases / metabolism
  • Male
  • Mitogen-Activated Protein Kinases / metabolism
  • Nitriles / pharmacology*
  • Prostatic Neoplasms / metabolism
  • Prostatic Neoplasms / pathology
  • Prostatic Neoplasms / radiotherapy*
  • Proto-Oncogene Proteins c-bcl-2 / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Radiation Tolerance*
  • Reactive Oxygen Species / metabolism
  • Signal Transduction
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Benzopyrans
  • Enzyme Inhibitors
  • Nitriles
  • Proto-Oncogene Proteins c-bcl-2
  • Reactive Oxygen Species
  • Tumor Suppressor Protein p53
  • ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate
  • Cytochromes c
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinases
  • Caspases