Characterizing the tumor selectivity of oncolytic adenovirus ICVB-1042: Analysis of S-phase induction, viral replication, and cytolytic activity in human primary normal cell types.

Abstract

e14503 Background: Adenoviral-based oncolytic virus (OV) therapeutics include mutations that enable activity in tumor cells and limit toxicity in normal cells. These tumor selectivity approaches often involve mutating viral E1A function or expression; however, such modifications allow viral activity in normal cells or limit anti-tumor potency. ICVB-1042 was engineered with dual modifications in E1A and E4orf6/7, resulting in superior tumor selectivity that does not compromise lytic potency in tumor cells. This improved tumor selective virus minimizes off-tumor activity and promotes robust tumor lysis. Methods: ICVB-1042 was compared to viruses with wildtype E1A and E4orf6/7 and a clinically tested virus with an E1A mutation (ICVB-2006). Viral function and killing were assessed in primary normal human renal (HRE) and bronchial (BrE) epithelial cells in the presence of the inhibitor palbociclib to pharmacologically block S-phase entry via host cell signaling. HRE and BrE were infected with virus and evaluated for indicators of viral toxicity in normal cells. Viral replication was quantified by droplet digital polymerase chain reaction (ddPCR); cell lysis was quantified by WST-1 assay. An S-phase induction assay was developed using an mCherry-Geminin reporter that allows imaging-based quantification of viral-dependent entry to S-phase. Viral activity in cells was compared with and without the CDK4/6 inhibitor using a viral-encoded fluorescent reporter to determine the requirement for host cell proliferation on viral function. Results: ICVB-1042 demonstrated superior protection in normal cells to comparator ICVB-2006 and viruses lacking tumor selectivity modifications. Palbociclib steeply reduced viral reporter gene expression (63-88% reduction), viral replication ( > 10-fold reduction), and cytolytic activity of ICVB-1042, while non-selective viruses were unaffected by this treatment. Non-selective virus infection resulted in 3.3- to 6.1-fold higher levels of S-phase entry compared to ICVB-1042. ICVB-2006 infection resembled non-selective viruses at the level of S-phase induction (3.1- to 3.3-fold above ICVB-1042) and viral reporter gene expression was modestly inhibited by palbociclib (12-31% reduction). Conclusions: The improved tumor selectivity of ICVB-1042 results in protection of normal, non-proliferative cells from viral-mediated toxicity. The conventional approach of ICVB-2006 with a single E1A mutation leaves viral replication and cell death in normal human cells mostly intact. Together, these observations support that ICVB-1042 presents normal cell protection and reduced toxicity risks associated with OV therapy.