Cytolytic Properties and Genome Analysis of Rigvir® Oncolytic Virotherapy Virus and Other Echovirus 7 Isolates

Rigvir (R) is a cell-adapted, oncolytic virotherapy enterovirus, which derives from an echovirus 7 (E7) isolate. While it is claimed that Rigvir (R) causes cytolytic infection in several cancer cell lines, there is little molecular evidence for its oncolytic and oncotropic potential. Previously, we genome-sequenced Rigvir (R) and five echovirus 7 isolates, and those sequences are further analyzed in this paper. A phylogenetic analysis of the full-length data suggested that Rigvir (R) was most distant from the other E7 isolates used in this study, placing Rigvir (R) in its own Glade at the root of the phylogeny. Rigvir (R) contained nine unique mutations in the viral capsid proteins VP1-VP4 across the whole data set, with a structural analysis showing six of the mutations concerning residues with surface exposure on the cytoplasmic side of the viral capsid. One of these mutations, E/Q/N162G, was located in the region that forms the contact interface between decay-accelerating factor (DAF) and E7. Rigvir (R) and five other isolates were also subjected to cell infectivity assays performed on eight different cell lines. The used cell lines contained both cancer and non-cancer cell lines for observing Rigvir (R)'s claimed properties of being both oncolytic and oncotropic. Infectivity assays showed that Rigvir (R) had no discernable difference in the viruses' oncolytic effect when compared to the Wallace prototype or the four other E7 isolates. Rigvir (R) was also seen infecting non-cancer cell lines, bringing its claimed effect of being oncotropic into question. Thus, we conclude that Rigvir (R)'s claim of being an effective treatment against multiple different cancers is not warranted under the evidence presented here. Bioinformatic analyses do not reveal a clear mechanism that could elucidate Rigvir (R)'s function at a molecular level, and cell infectivity tests do not show a discernable difference in either the oncolytic or oncotropic effect between Rigvir (R) and other clinical E7 isolates used in the study.

Automated summary

This study analyzed the genome sequences of Rigvir (R) and other echovirus 7 isolates, and found that Rigvir (R) is genetically distinct. Structural analysis revealed multiple mutations in the viral capsid proteins of Rigvir (R), including one in the region that interacts with decay-accelerating factor (DAF). Cell infectivity assays showed no significant difference in the oncolytic or oncotropic effect between Rigvir (R) and other isolates, and Rigvir (R) was also found to infect non-cancer cell lines. Therefore, this study concludes that Rigvir (R) is not an effective treatment for multiple types of cancers.