Effect of the oncolytic ECHO-7 virus Rigvir® on the viability of cell lines of human origin in vitro

Background: The role of oncolytic viruses in cancer treatment is increasingly studied. The first oncolytic virus (Rigvir (R), ECHO-7) was registered in Latvia over a decade ago. In a recent retrospective study Rigvir (R) decreased mortality 4.39-6.57-fold in stage IB-IIC melanoma patients. The aims of the present study are to test the effect of Rigvir (R) on cell line viability in vitro and to visualize the cellular presence of Rigvir (R) by immunocytochemistry. Methods: The cytolytic effect of Rigvir (R) on the viability of FM-9, RD, AGS, A549, HDFa, HPAF-II, MSC, MCF7, HaCaT, and Sk-Mel-28 cell lines was measured using live cell imaging. PBMC viability was measured using flow cytometry. The presence of ECHO-7 virus was visualized using immunocytochemistry. Statistical difference between treatment groups was calculated using two-way ANOVA. Results: Rigvir (R) (10%, volume/volume) reduced cell viability in FM-9, RD, AGS, A549, HDFa, HPAF-II and MSC cell lines by 67-100%. HaCaT cell viability was partly affected while Rigvir (R) had no effect on MCF7, Sk-Mel-28 and PBMC viability. Detection of ECHO-7 by immunocytochemistry in FM-9, RD, AGS, A549, HDFa, HPAF-II and Sk-Mel-28 cell lines suggests that the presence of Rigvir (R) in the cells preceded or coincided with the time of reduction of cell viability. Rigvir (R) (10%) had no effect on live PBMC count. Conclusions: The results suggest that Rigvir (R) in vitro reduces the viability of cells of human melanoma, rhabdomyosarcoma, gastric adenocarcinoma, lung carcinoma, pancreas adenocarcinoma but not in PBMC. The presence of Rigvir (R) in the sensitive cells was confirmed using anti-ECHO-7 antibodies. The present results suggest that a mechanism of action for the clinical benefit of Rigvir (R) is its cytolytic properties. The present results suggest that the effect of Rigvir (R) could be tested in other cancers besides melanoma. Further studies of possible Rigvir (R) entry receptors are needed.