The ability of oncolytic viruses to replicate in and lyse cancer cells offers a potential therapeutic approach. However, selectivity and efficacy of adenovirus replication need to be improved. In this study, we present that loss of p21Waf1 promotes adenovirus replication and more effective cell killing compared to cells expressing p21Waf1. To test our hypothesis, we infected different cancer cell lines with wild-type adenovirus (WtD) and the oncolytic adenoviruses, ONYX-015 and Delta-24. Our results showed that WtD and ONYX-015 induce stronger cytopathic effects on HCT116 p21-/- cells compared to HCT116-WT cells, although the timing of the oncolytic effect varied slightly between the adenoviruses. Delta-24 also showed a more potent cell killing effect on cells lacking p21Waf1 at lower MOIs, however, at high MOIs there are no difference on cell killing effect regardless of the presence or absence of the p21Waf1. Using HCT116 p21-/- cells, we demonstrated that wild-type adenovirus and ONYX-015 replicate 2.6 and 2.5 times, respectively, more efficiently compared to HCT116-WT. We showed that p21Waf1 expression is responsible for the virus replication by using p21 siRNA in HCT116-WT. Also, although modest, p27Kip1 demonstrated to play a role in enhancing virus replication and cell killing. MiaPaCa-2 is a pancreatic cancer cell that does not express p21Waf1. Cell viability analysis after WtD infection resulted in reduction of the number of viable cells by about 40% in MiaPaCa-2 cells, suggesting that p21 may play a role in virus replication. We found that TE7, an esophageal carcinoma cell line, also showed strong cell killing effect when p21Waf1 expression was suppressed by siRNA prior to wild-type adenovirus infection. These observations suggest the importance of p21Waf1 in virus replication with potential implications for gene therapy of cancer.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA