Highly selective and potent p16-CDK-RB-E2F targeted oncolytic virus therapies.

Abstract

e14543 Background: Growth factor and p16-CDK-RB-E2F pathway components are mutated in almost all cancers, resulting in oncogenic E2F transcriptional activity that drives uncontrolled proliferation. Chemotherapies indiscriminately kill all proliferating cells, resulting in limiting toxicities. CDK inhibitors are more targeted but cytostatic as opposed to tumoricidal. E2F was discovered as a factor that transcribes adenovirus (Ad) E2 and cellular genes to drive viral replication. Ad E1A binds to RB, which activates E2F. On this basis, viruses with E1A-RB binding mutations are being evaluated in the clinic as oncolytic viruses (OVs) that selectively replicate in and kill RB mutant tumor cells. However, E1A-RB mutations alone are not sufficient to prevent viral replication in normal cells. The addition of ‘tumor specific promoters’ improves tumor selectivity but drastically impacts replication and lytic activity. Therefore, a critical unmet need is the engineering of E2F addicted OVs that replicate like wildtype viruses in tumor cells, but leave normal cells unharmed. Methods: We have developed a proprietary platform that enables Ad therapeutics to be assembled from libraries of functional genomic parts that confer desirable properties. Here we describe E1 and E4 genomic modules that confer E2F dependent tumor selective replication. We assembled a panel of ̃50 viruses with combinations of mutations that ablate i) E1A interactions with RB/p107/p130 and/or EP300 ii) E4-ORF1 activation of PI3-Kinase and/or MYC iii) E4-ORF6/7 induced E2F1/DP1 dimerization. These viruses were screened in panels of primary, tumor, and CRISPR-engineered cells. Results: These studies reveal that E4-ORF6/7 functions independently of E1A to activate E2F transcriptional targets, S phase entry and viral replication. We show that viruses with both E1A and E4-ORF6/7 mutations (AdSyn-181) have the ideal tumor selectivity/efficacy profiles and outperform existing OVs. We also show that the deletion of p16 in primary cells rescues AdSyn-181 replication by ̃15 fold (̃20% wildtype virus), demonstrating the E2F dependence and tumor selectivity mechanism. Furthermore, we show that in tumor cells, which have multiple p16-CDK-RB pathway mutations, AdSyn-181 replication is rescued to 100% wildtype virus levels. ICVB-1042, which incorporates these selectivity mutations – together with other modules that enhance lytic cell death and spread, tumor tropisms and IV delivery – is in IND-enabling studies. Conclusions: Leveraging extensive research into the overlapping logic of viral and cancer pathways, we have engineered OVs, including ICVB-1042, that distinguish between tumor and normal cell proliferation. Furthermore, unlike therapies that target a single component, ICVB-1042 targets tumors with different p16-CDK-RB mutations, which all converge in activating oncogenic E2F transcription, driving exponential and tumoricidal viral replication.