Myxoma Virus Oncolytic Efficiency Can Be Enhanced Through Chemical or Genetic Disruption of the Actin Cytoskeleton

Chad R Irwin,Nicole A Favis,David H Evans,Kate C Agopsowicz,Mary M Hitt,Irina V Lebedeva

doi:10.1371/journal.pone.0084134

Abstract

Myxoma virus (MYXV) is one of many animal viruses that exhibit oncolytic properties in transformed human cells. Compared to orthopoxviruses like vaccinia (VACV), MYXV spreads inefficiently, which could compromise its use in treating tumors and their associated metastases. The VACV F11 protein promotes virus exit and rapid spread by inhibiting Rho signalling, which results in a disruption of cortical actin. We have previously shown that although MYXV lacks an F11 homolog, the F11L gene can be introduced into MYXV promoting the spread of this Leporipoxvirus in natural host cells. Here we show that the F11-encoding (F11L+) MYXV strain replicates to higher levels in a number of human cancer cells. We also show that F11L+ MYXV induces better tumor control and prolonged survival of mice bearing MDA-MB-231 cancer cells. Furthermore, we show that this virus also spreads more efficiently from the site of growth in one injected tumor, to a second untreated tumor.While we focused mostly on the use of a modified MYXV we were able to show that the effects of F11 on MYXV growth in cancer cells could be mimicked through the use of pharmacological inhibition or siRNA-mediated silencing of key regulators of cortical actin (RhoA, RhoC, mDia1, or LIMK2). These data suggest that it may be possible to increase the oncolytic efficacy of wild-type MYXV using chemical inhibitors of RhoA/C or their downstream targets. Furthermore, since all viruses must overcome barriers to exit posed by structures like cortical actin, these findings suggest that the oncolytic activity of other viruses may be enhanced through similar strategies.

Highlights

An ideal oncolytic virus would spread efficiently throughout a tumor, and travel rapidly to distant metastases, all while selectively killing cancer cells
Growth In a previous study, we showed that a strain of Myxoma virus (MYXV) encoding the VACV F11L gene (F11L-mCh) spreads faster on rabbit and monkey cells in culture when compared with a control virus bearing the same mCherry insert in the non-essential MYXV M127L photolyase gene [30] but lacking F11L (DM127L-mCh)
We used MDA-MB-231 mammary adenocarcinoma cells. These cells support an intermediate level of MYXV growth relative to other human cell types, and our lab previously used these cells in an siRNA-screen to identify cellular factors that facilitate MYXV growth [9]

Summary

Introduction

An ideal oncolytic virus would spread efficiently throughout a tumor, and travel rapidly to distant metastases, all while selectively killing cancer cells. MYXV normally exhibits a very narrow host range limited to rabbits and hares and does not cause disease in humans. It has been known for over 50 years that MYXV can replicate in cancerous human cells [1,2] and over the past decade the molecular bases for this alteration in host tropism has begun to be understood. Genome-wide siRNA screens have further identified many additional human genes that collectively exert more subtle effects on MYXV growth [9]

Methods

Results

Conclusion