Abstract C182: Use of an oncolytic adenovirus (ONYX-015) in vitro to enhance chemotherapy
Authors: Sykelyk Alexander W. , Koropatnick James , Ferguson Peter J. 
Published: June 2012

Abstract
Oncolytic adenoviruses have been proposed as therapeutic anticancer agents. They exploit differences between normal and tumor tissues to selectively infect and/or preferentially replicate in tumor cells. ONYX-015 is a genetically modified adenovirus that replicates only in cells that are deficient in p53, a tumor suppressor gene mutated in over 50% of human cancers. ONYX-015 contains a mutation in the E1B gene resulting in production of an inactive E1B 55 kDa protein that no longer inactivates p53. Consequently, the virus replicates only in p53(−/−) cells. However, the effectiveness of ONYX-015 critically depends on its ability to enter cells. This is dependent on virus binding to the Coxsackievirus and Adenovirus Receptor (CAR) on the cell surface. ONYX-015 is a potential option for treatment of drug-resistant tumors because the mechanism underlying virus cytotoxicity should not, in theory, be blocked by tumor cell strategies that mediate resistance to chemotherapeutic drugs. In fact, acquisition of cisplatin-resistance in an ovarian carcinoma cell line conferred enhanced sensitivity to ONYX-015 in vitro (Ganly et al., Gene Therapy, 8: 369-375, 2001). Therefore, drug-resistant tumors may be a potential clinical target for ONYX-015. Our objective was to characterize relative ONYX-015 sensitivity in human tumor cell lines that are differentially resistant to platinum-based anticancer drugs (assessed by metabolism-based viability assay) with and without combined melphalan treatment, an antitumor alkylating agent. Further, we investigated CAR protein and mRNA expression by immunoblot and RT-PCR analysis, respectively. Acquired carboplatin-resistance in a head and neck squamous cell carcinoma cell line (HN-5a) resulted in ONYX-015 resistance (approximately 15-fold increase in IC-50 in carboplatin-resistant HN-5a cells) whereas cisplatin-resistance in a human colon adenocarcinoma cell line (HT-29) conferred enhanced sensitivity to ONYX-015 (approximately 90% decrease in IC-50 in cisplatin-resistant HT-29 cells). Although CAR mRNA and protein levels differ among cell lines, the acquisition of drug-resistance did not induce changes in CAR mRNA or protein expression. The cytotoxicity of the combination of ONYX-015 and melphalan was greater-than-additive when compared to the effects of two treatments alone. This phenomenon appeared to be schedule-dependent with melphalan pretreatment or combination treatment being more effective than ONYX-015 pretreatment. We hypothesized that melphalan treatment up-regulated CAR expression, resulting in enhanced virus internalization. In support of this hypothesis we observed that treatment with 50 M melphalan induced a 2.5-fold increase in CAR mRNA by 24-h in the parental HN-5a cell line. CAR protein expression was increased 2-fold after 48-h but not 24-h treatment with melphalan. Therefore, pretreatment of cells with melphalan may enhance viral entry into cells via up-regulation of CAR. Variations in CAR expression, whether or not induced by chemotherapeutic drugs, may influence and predict viral uptake and oncolytic activity.
Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C182.