Selective replicating viral vectors : potential for use in cancer gene therapy

Targeting Gene-ViroTherapy for prostate cancer by DD3-driven oncolytic virus-harboring interleukin-24 gene

Prostate cancer (PCa) is the second leading cause of cancer-related deaths in Western male population. Previous studies have demonstrated that differential display code 3 (DD3 or DD3(PCA3)) is one of the most PCa-specific genes; therefore, it has been used as a clinical diagnostic marker for PCa. In this study, we constructed an oncolytic adenovirus Ad.DD3-E1A by using the minimal DD3 promoter to replace the native viral promoter of E1A gene. In addition, Ad.DD3-E1A was armed with therapeutic gene IL-24 to enhance its antitumor activity. The resulting adenovirus, Ad.DD3-E1A-IL-24, demonstrated PCa specificity and excellent antitumor effect. Further analyses on its antitumor mechanism revealed that it has the capacity to induce apoptosis in PCa cells and inhibit angiogenesis. These results suggest that Ad.DD3-E1A-IL-24 is a promising antitumor agent that may be able to be used in the future as a treatment for PCa.

Oncolytic adenovirus that overproduces ADP and replicates selectively in tumors due to hTERT promoter-regulated E4 gene expression

We have constructed a novel oncolytic adenovirus (Ad) vector, named VRX-011, in which the replication of the vector is targeted to cancer cells by the replacement of the wild-type Ad E4 promoter with the human telomerase reverse transcriptase (hTERT) promoter. Genes in the Ad E4 transcription unit are essential for Ad replication; therefore, VRX-011 will grow efficiently only in cells in which the hTERT promoter is active, that is, in a wide range of cancer and immortalized cells but not in most somatic cells. Consistent with these expectations, VRX-011 replicated efficiently in all cancer cell lines examined, while its growth was restricted in various primary and normal cells. VRX-011 overexpresses ADP (also known as E3-11.6K), an Ad protein required for efficient cell lysis and release of virions from cells at late stages of infection. This overexpression enhances cell-to-cell spread and could significantly increase antitumor efficacy. In a xenograft model in nude mice, both intratumoral and intravenous administration of VRX-011 effectively suppressed the growth of subcutaneous Hep3B human liver tumors. Also, intravenous delivery of VRX-011 greatly reduced the number and size of A549 human lung cancer cell nodules in a disseminated lung tumor model in nude mice. Importantly, tail vein administration of different doses of VRX-011 in C57BL/6 mice showed minimal liver toxicity. Considering its broad range of lytic replication in cancer cells, its attenuated phenotype in primary cells, its efficacy in suppressing xenografts, and its low toxicity in mouse liver, VRX-011 is a promising candidate for further evaluation as an anticancer therapeutic.