Abstract 1507: Aberrant oncolytic human adenovirus late mRNA translation causes failure of viral progeny production in murine cancer

Abstract

Abstract Introduction. Oncolytic viruses have therapeutic potential in cancer by selectively replicating within malignant cells, causing death. Adenovirus type 5(Ad5) mutant dl922-947 contains a 24 bp deletion in E1A-CR2 and selectively replicates in cells with an abnormal Rb pathway - a feature of 90% human malignancies. dl922-947 has activity in human ovarian cancer following intraperitoneal (ip) delivery. Immunocompetent models are essential to evaluate the host immunological response as adenoviruses induce robust immune responses and CD8+ T cell infiltration has prognostic importance in ovarian cancer. However, adenoviridae are species specific and Ad5 fails to produce infectious progeny in murine tissue, preventing development of such models. We have investigated why human adenovirus replication fails in murine cancer. Methods. dl922-947 lifecycle was examined in murine carcinoma cells CMT64 and MOVCAR7 and human epithelial ovarian cancer (EOC) cells OVCAR4. Results. Infectivity, qPCR and sub-fractionation assays demonstrated no deficit in virion internalisation, genome replication or mRNA nuclear export in murine cells. E1A transcription and expression were similar in murine and human cells. However, there was marked failure of late viral capsid protein expression on immunoblot, which was not reversed by proteasome inhibition. TCID50 assay confirmed minimal infectious progeny production in murine cells (0.005-0.25 pfu/cell at MOI 10 in murine cells vs 104 pfu/cell in OVCAR4 cells 48h pi). Temporal differences in late gene transcription were seen between OVCAR4 and MOVCAR7 but not CMT64 cells, whilst late mRNA processing was qualitatively normal in murine cells. dl922-947 infection failed to induce global shut-down of host protein translation in murine cells on Coomassie staining. Transcription of L4 100K, important for preferential viral mRNA translation, was 1 log lower in murine cells than human controls, which may contribute to decreased production of infectious virions. Interestingly, co-infection of MOVCAR7 cells with dl922-947 and murine adenovirus type 1 (MAV-1) partially rescued late viral protein expression and increased dl922-947 cytotoxicity by MTT assay (>50% reduction of EC50). Conclusions: Failure of late viral mRNA translation results in failure of dl922-947 replication in murine cells. Current work focuses on the importance of the 5’ UTR tripartite leader sequence (TPL) common to all adenoviral late mRNAs. Specifically, sequence differences between human Ad5 and MAV-1 TPL may prevent adequate translation. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1507.