The Introduction Of The Inverted Repeat Sequence Of Adenovirus In Hepatocellular Carcinoma Mediated Selective Expression And Oncolytic

Adenoviral vectors have been extensively investigated in experimental and clinical research on cancer gene therapy. The selectivity of transgene expression is a major concern in their application. One strategy for improving selectivity is the use of adenovirus vector that mediates transgene expression specifically in tumor cells through Inverted Repeats (IR) sequence. We designed a study to determine whether this strategy is effective in experimental therapy of hepatocellular carcinoma and colon carcinoma metastases in the liver.We found that in contrast to regular adenovirus vector Ad BG, IR-containing vector Ad IR-BG conferred specific transgene (P-gal) expression in hepatocellular carcinoma (SMMC7721, MHCC97) and colon carcinoma (LoVo, HT29) cells, with minimal expression in normal hepatocytes cells (WB). Systemic injection of Ad IR-BG also induced a tumor specific P-gal expression in SMMC7721 and LoVo xenografts in nude mice. This occurred through viral DNA recombination in Ad IR-BG-infected tumor cells but not in normal cells. Hydroxyurea, which blocked DNA replication, inhibited DNA recombination and P-gal expression in tumor cells infected by Ad IR-BG but had no effects on Ad.BG-infected cells.Cell growth for LoVo and SMMC7721 were significantly inhibited following Ad IR-BG infection whereas no inhibition was detected in Ad IR-BG-infected WB or all Ad.BG-infected cells. Progeny viruses were detected in the culture media of Ad.IR-BG-infected LoVo and SMMC7721 cells by media re-infection and real-time PCR analysis, suggesting that viral production caused oncolysis. Injection of Ad.IR-BG into SMMC7721 and LoVo xenografts in nude mice significantly delayed tumor growth. No infectious progeny virus was detected from Ad.IR-BG-infected WB cells; despite of the presence of replicated viral DNA in cell lysate. Western blots verified that viral capsid proteins, which were present in both culture media and cell lysates for Ad.IR-BG-infected LoVo and SMMC7721 cells, were absent for Ad.IR-BG-infected WB cells. This indicated that selective activation of viral capsid protein synthesis in tumor cells could be one of the determinants for Ad IR-BG-mediated selective oncolysis.These findings demonstrated that Ad.IR-BG could mediate tumor-specific gene expression and selectively oncolysis through viral replication, which is otherwise deficient in normal cells. The potential of IR-containing adenoviral vectors both to activate gene expression and induce oncolysis selectively deserves further study.