Evaluation of the Effect of MAGE-A3 Tumor Antigen on the Oncolytic Activity of Reovirus in Colorectal Cancer Cell Lines

Colorectal cancer (CRC) is the third most deadly and fourth most commonly diagnosed cancer in the world. Although many interventions such as surgery, radiation therapy and chemotherapy are used nowadays, researchon other methods is being carried out too. The use of tumor antigens against the tumor is a kind of treatment that in combination with the virus can better stimulate the immune system against the tumor. The use of oncolytic viruses with natural characteristics in destroying cancer cells has provided a wide field for further studies. The aim of this study was to investigate the effect of MAGE-A3 tumor antigen on the oncolytic activity of Reovirus in colorectal cancer cell lines.

In this experimental study L929, a type of mouse fibroblast cell line, was used as a host cell for Reovirus propagation. Reovirus titer was determined by CCID50 method and the appropriate titer was selected for the study. The MAGEA3- expressing plasmid was transfected into colorectal cancer cells of the mouse (CT26) and human (Caco2) origin and infected with Reovirus (MOI = 1 and MOI = 0.01). 24 hours after Reovirus inoculation and observing CPE, the cells were collected to investigate apoptosis and measured by flow cytometry.

The apoptosis rate in CT26 cells in the presence of MAGE-A3 expressing vector and inoculated with Reovirus was higher (MOI=1, 38.5 ± 3.8% / p-value < 0.02 and in MOI=0.01, 30±  2.1% / p-value < 0.005) in comparison to the absence of MAGE-A3 expressing vector (MOI=1, 22.4±  0.9 and MOI=0.01, 15.8 ± 0.3). On the other hand, the rate of apoptosis in Caco2 cells in the presence of MAGE-A3 expressing vector and inoculated with Reovirus (MOI=1, 22.5±  1.8% / p-value=ns and in MOI=0.01, 11 ± 2% / p-value=ns) was lower than in the absence of vector expressing MAGE-A3 (MOI=1, 45.5±  2.7 and MOI=0.01, 11.5±  0.9). It can be stated that according to the results of this study, the cytolysis effect of Reovirus in Caco2 cell line is higher than that of CT26 cell and also the rate of cell cytolysis in the presence of MAGE expressing vector is almost twice more than that of this vector in Caco2 cells.

Given the higher cytolysis of the virus in Caco2 cells and the status of P53 and Ras genes in these two cells, in which P53 is mutant but Ras is active, the virus has more activity and MAGE-A3 presence reduces virus activity by reducing Ras activity.