Incorporating the survivin promoter in an infectivity enhanced CRAd-analysis of oncolysis and anti-tumor effects in vitro and in vivo

Conditionally replicating adenoviruses (CRAds) represent a promising new modality for the treatment of cancer. A key contribution in this regard was the introduction of tumor-selective viral replication for amplification of the initial inoculum. Specifically, following cellular infection, the virus replicates selectively in the infected tumor cells and kills the cells by cytolysis. Next, the progeny virions infect surrounding target cells, replicate and eradicate the infected tumor cells, leaving normal cells unaffected. However, to date there have been two limitations to clinical application of these CRAd agents; i.e., both infectivity and tumor specificity are poor. Survivin protein is a novel member of the inhibitor of apoptosis (IAP) protein family, which plays an important role in the survival of cancer cells and progression of malignancies. Previous data have shown the survivin promoter has high activities in multiple cancer cells with a low activity in mouse liver. In this study, we propose an improved CRAd agent to circumvent the obstacles. We constructed a novel CRAd agent, CRAd-Survivin-RGD, which contains both the survivin promoter (either the short version, S-S, or the long version, S-L) to selectively drive E1 gene expression in tumor cells and a capsid modification and RGD4C to specifically enhance the tumor infectivity of CRAd agents. Both CRAd agents (S-S and S-L) showed high replication rates in the breast cancer cell line, MDA-MB-361, and low promoter activity in both normal mouse and human liver, thus signifying the CRAd agents have the phenotype of 'tumor on/liver off'. In cytocidal experiments, the CRAd agents demonstrated a high cytocidal effect on multiple cancer cell lines, including the breast cancer cell line, MDA-MB-231; the glioma cell line, D65, the melanoma cell line, MEL-28; and mesothelioma, Meso2374. The results also showed the tumor growth was dramatically inhibited by intertumoral administration of the CRAd agents in a breast cancer (MDA-MB-361) xenograft animal model. These data clearly demonstrate that CRAd-Survivin-RGD is a potential novel therapeutic agent for treatment in many, but not all, human cancers.