Data from RNA Silencing of Checkpoint Regulators Sensitizes <i>p53</i>-Defective Prostate Cancer Cells to Chemotherapy while Sparing Normal Cells

Abstract

<div>Abstract<p><i>p53</i> is frequently mutated in patients with prostate cancer, especially in those with advanced disease. Therefore, the selective elimination of <i>p53</i> mutant cells will likely have an impact in the treatment of prostate cancer. Because <i>p53</i> has important roles in cell cycle checkpoints, it has been anticipated that modulation of checkpoint pathways should sensitize <i>p53</i>-defective cells to chemotherapy while sparing normal cells. To test this idea, we knocked down ataxia telangiectasia mutated (<i>ATM</i>) gene by RNA interference in prostate cancer cell lines and in normal human diploid fibroblasts IMR90. <i>ATM</i> knockdown in <i>p53</i>-defective PC3 prostate cancer cells accelerated their cell cycle transition, increased both E2F activity and proliferating cell nuclear antigen expression, and compromised cell cycle checkpoints, which are normally induced by DNA damage. Consequently, PC3 cells were sensitized to the killing effects of the DNA-damaging drug doxorubicin. Combining <i>ATM</i> knockdown with the Chk1 inhibitor UCN-01 further increased doxorubicin sensitivity in these cells. In contrast, the same strategy did not sensitize either IMR90 or LNCaP prostate cancer cells, both of which have normal <i>p53</i>. However, IMR90 and LNCaP cells became more sensitive to doxorubicin or doxorubicin plus UCN-01 when both <i>p53</i> and <i>ATM</i> functions were suppressed. In addition, knockdown of the G<sub>2</sub> checkpoint regulators <i>ATR</i> and <i>Chk1</i> also sensitized PC3 cells to doxorubicin and increased the expression of the E2F target gene <i>PCNA</i>. Together, our data support the concept of selective elimination of <i>p53</i> mutant cells by combining DNA damage with checkpoint inhibitors and suggest a novel mechanistic insight into how such treatment may selectively kill tumor cells.</p></div>