RAD001 (Everolimus) Improves the Efficacy of Replicating Adenoviruses that Target Colon Cancer

Abstract

Selectively replicating adenoviruses have the potential to cure cancer but have shown little efficacy in clinical trials. We have tested the ability of the mTOR kinase inhibitor RAD001 (everolimus) to enhance the response of xenografts to an oncolytic adenovirus. The virus has Tcf sites inserted in the early viral promoters and replicates selectively in cells with activation of the Wnt signaling pathway. To enhance tumor cell infection, an integrin targeting peptide (CDCRGDCFC) was inserted into the fiber gene of the virus. RAD001 combines three useful properties: it inhibits tumor cell growth directly, blocks angiogenesis, and suppresses the immune response. RAD001 does not block viral protein expression, DNA replication, or cytopathic effect in tumor cells in vitro. After 6 weeks of daily RAD001 treatment, ongoing viral DNA replication could be detected in tumor xenografts, showing that RAD001 does not inhibit virus replication in vivo. I.v. injection of virus alone produced a small delay in xenograft growth, whereas combination therapy substantially prolonged the survival of the mice. We suggest that collapsing the tumor vasculature after the initial infection traps the virus and facilitates local spread within the tumor. Unlike conventional drugs, which require continued access to the tumor through the vascular system, oncolytic viruses are in principle less sensitive to late reductions in perfusion because they are produced locally within the tumor.