Host cell factors in ovarian cancer influencing efficacy of oncolytic aenovirus dl922-947

Abstract

Adenoviral gene therapy holds great potential for cancer treatment, but is limited by a lack of efficient vectors. dl922-947, an E1A CR2-deleted adenovirus, replicates selectively within and lyses cancer cells. It is believed that its selectivity depends upon abnormalities in the cell cycle regulatory Rb pathway and subsequent G1/S checkpoint, observed in 90% of human cancers. The cytotoxic efficacy of dl922-947 is greater than that of wild-type adenovirus and dl1520 (Onyx-015). Nevertheless, sensitivity to dl922-947 varies widely among ovarian cancer cell lines, despite similar infectivity. My work aimed to identify host cell factors that influence cytotoxicity and which could be potential biomarkers in clinical trials. Surprisingly, comparison of ovarian cancer lines indicated that cytotoxicity correlated poorly with infectivity, replication and virion production. Immunoblotting suggested correlation between sensitivity to dl922-947 and overexpression of p21, p27, Cyclin D, cdk4 and p16. Subsequent experiments confirmed a role for p21 in dl922-947 cytotoxic activity. In vitro and in vivo, Hct116 p21+/+ cells were significantly more sensitive to dl922-947 than matched p21-/- cells. p21 knock-down by siRNA in TOV21G and IGROV-1 cells reduced dl922-947 cytotoxicity, whilst re-expression in ACP-WAF1 cells increased activity. p21 expression was also greater in sensitive transformed TOSE cells compared to resistant normal IOSE25 cells. Results suggest that p21 promotes dl922-947 activity by stabilising Cyclin D thus promoting cell cycle progression. Comparative microarray analysis in TOSE1, 4 and IOSE25 cells and in MRC5 and MRC5-VA cells suggested determinants of dl922-947 activity beyond the Rb pathway, which may also prove valuable biomarkers. Moreover, pathways and processes emerged, correlating with sensitivity, and meriting future investigation. Together, my results suggest that a cellular environment conducive for dl922-947 function includes mediators of proliferative capacity, amongst which p21 plays a role in enhancing activity of the virus