Selectively enhanced radiation sensitivity in prostate cancer cells associated with proteasome inhibition

The purpose of this study is to evaluate the utility of MG-132, a broad spectrum proteasome inhibitor, to selectively enhance radiation sensitivity in prostate cancer without affecting normal surrounding urothelial tissue. PC3 prostate cancer cells and normal URO-tsa bladder epithelial cells were treated with or without MG-132 and exposed to 0, 2, 4, or 6 Gy radiation. Cell viability and clonogenic survival assays were performed, and nuclear factor kappa-B (NF-κB) activity was evaluated with electrophoretic mobility shift assay (EMSA). MG-132 was associated with decreased cell viability (between 24% and 33%) and clonogenic survival (between 71% and 88%) alone and in combination with radiation in PC3 cells. MG-132 had no effect on cell viability or clonogenic survival following radiation in URO-tsa cells. Constitutive and radiation-induced NF-κB binding activity was higher in PC3 cells compared with URO-tsa cells. Furthermore, MG-132 at concentrations associated with reductions in cell viability and clongenic survival inhibited NF-κB binding activity in PC3 cells with no effect in URO-tsa cells. These results provide strong evidence that proteasome inhibition and concomitant NF-κB inhibition can be used to selectively enhance tumor radiation sensitivity in prostate cancer without affecting normal surrounding bladder tissue.