Abstract 1779: Selective oncolysis of multiple myeloma cells by reovirus is mediated through apoptosis

Abstract Introduction: Multiple myeloma (MM) is an incurable hematologic malignancy that accounts for 10% of hematopoietic neoplasms. Recently we have demonstrated the potential of reovirus as novel therapeutic agent for MM, however, the oncolytic mechanism has not been elucidated yet. Reovirus is known to utilize multiple signalling pathways for cancer cell destruction depending on histological origin. It is currently unknown if the apoptotic signalling pathways are involved in reovirus mediated cell death of multiple myeloma. Methods: The MM cell lines RPMI 8226, U266, NCIH929, HUNS-1, MC/CAR, and OPM2 were incubated with live or UV-inactivated reovirus at a multiplicity of infection of 40 for 24, 48, and 72 hours respectively. Apoptosis was assayed by Annexin V/7-AAD expression and DNA fragmentation using flow cytometry. RPMI 8226 was further investigated at 2, 6 12, 24 and 48 hours for the presence of Phospho -Akt and activated caspase 3 post reovirus infection. Results: RPMI 8226, U266, and NCIH929 demonstrated an apoptotic response to reovirus infection within 24 hours. All 3 cell lines showed statistically significant (all F tests, p<0.00001) increases in DNA fragmentation in response to reovirus and this increase was more pronounced as time progressed. Similarly expression of Annexin V was significantly higher (all F tests, p<0.00001) in all 3 cell lines with live reovirus treatment but the kinetics were cell line dependent where a significant (p< 0.05) time effect was seen for U266 but not for RPMI 8226 and NCIH929. In contrast, the MM cell lines HUNS-1, MC/CAR, and OPM2 appeared resistant to reovirus infection and showed no evidence of apoptosis at 72 h. Supporting the apoptotic mechanism of cell death, RPMI 8226 showed down regulation of the anti-apoptotic signalling protein, Phospho-Akt, at 24 hours of incubation with reovirus. This was accompanied by a simultaneous expression of activated caspase 3. Conclusion: Not all MM cell lines are amenable to reovirus mediated cell death. This has important implications for the future use of reovirus as a therapeutic agent for cancer and highlights the importance of understanding cell signalling mechanisms as Phase 3 clinical trials of solid tumours with reovirus are currently underway. Ongoing research utilizing pharmacologic and molecular inhibitors of Akt and caspase3 will enable us to confirm the importance of these molecules in reovirus oncolysis of haematological malignancies. Understanding these signalling pathways will help develop a more personalized approach of reovirus therapy for cancer patients in the future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1779. doi:10.1158/1538-7445.AM2011-1779