Transthyretin‐driven oncolytic adenovirus suppresses tumor growth in orthotopic and ascites models of hepatocellular carcinoma

Strategies to increase antitumor efficacy of oncolytic adenoviruses are actively investigated. We have previously shown that E1B‐55 kDa‐deleted adenovirus, designated Ad5WS1, has therapeutic potential for treating hepatocellular carcinoma (HCC). To achieve HCC‐restricted replication of oncolytic adenovirus, we generated Ad5WS2, an E1B‐55 kDa‐deleted adenovirus with its E1A gene driven by the liver‐specific transthyretin promoter. Our results showed that Ad5WS2 could replicate within tumor cells where the transthyretin gene was expressed. Mouse transthyretin promoter was active in murine and human HCC cells, but relatively quiescent in cells of non‐liver origin. Ad5WS2 caused severe cytolytic effect on HCC cells, but was much attenuated in non‐HCC cells. Peritoneal administration of Ad5WS2 into mice bearing liver tumors grown in ascites resulted in enhanced survival. In an orthotopic HCC model, Ad5WS2, when systemically administered, exerted higher antitumor effects than Ad5WS1. Lack of viral replication in normal organs and minimal hepatic toxicity was noted after Ad5WS2 treatment. Furthermore, the antitumor effect of Ad5WS2 could be enhanced when combined with chemotherapeutic agent cisplatin in the ascites tumor model. These results suggest that E1B‐55 kDa‐deleted adenovirus driven by the transthyretin promoter may be a safer and more efficacious oncolytic agent for the treatment of primary and metastatic HCC. (Cancer Sci 2009; 100: 537–545)