| Reovirus is an "oncolytic" virus which kills cancer cells, but not normal cells. Reovirus also induces apoptosis in vivo and in vitro with T3 strains inducing apoptosis to a greater extent than T1 strains. The hypothesis of this study was that T1 and T3 reovirus strains would induce apoptosis in HT-29 colon and Panc-1 pancreatic cancer cell lines. The specific aims of this project were to determine: (1) if T1L, T3D, and T3A kill HT-29 and Panc-1 cells by apoptosis, (2) whether the kinetics (rate and magnitude) of reovirus-induced cell death vary with viral dose and (3) death signaling pathways activated in infected cells. Strains T1L, T3A, and T3D killed HT-29 and Panc-1 cancer cells primarily by apoptosis at all MOIs tested and resulted in activation of both mitochondrial and death receptor apoptotic pathways in Panc-1 and HT-29 cells. Downregulation of TRAIL protein expression was observed in HT-29 cells after infection with T1 and T3 strains, but remained constant in infected Panc-1 cells. Upregulation of TRAIL-receptor 1 (DR4) protein expression was detected in T3-infected HT-29 and Panc-1, but not in T1-infected cells. Strain-specific differences in the kinetics of apoptosis, in which T3D-induced less apoptosis than T1L and T3A, were observed at MOI 50 in both HT-29 and Panc-1 cells, and correlated with the ability of virus to productively infect the majority of cells in culture. Increasing the MOI from 50 to 500 or 5000 substantially increased the kinetics of apoptosis in HT-29 cells, and to a lesser extent in Panc-1 cells, and eliminated strain-specific differences in the kinetics of cell death observed at MOI 50. These results show for the first time that reovirus T1L can effectively induce apoptosis of infected cells and that T1- and T3-induced apoptosis is mediated via the same major apoptotic pathways. Strain-specific differences in the kinetics of viral-induced apoptosis at different MOIs and in TRAIL and DR4 expression in two different cancer cell types, suggest that both T1 and T3 reovirus strains should be tested for use as cancer therapeutics and optimized with respect to strain and dose for specific cancer cell types. |
