Attenuated reovirus displays oncolysis with reduced host toxicity

Abstract

Background:Although the naturally occurring reovirus causes only mild symptoms in humans, it shows considerable potential as an oncolytic agent because of its innate ability to target cancer cells. In immunocompromised hosts, however, wild-type reovirus can target healthy tissues, including heart, liver, pancreas and neural structures.Methods:We characterized an attenuated form of reovirus (AV) derived from a persistently infected cell line through sequence analysis, as well as western blot and in vitro transcription and translation techniques. To examine its pathogenesis and oncolytic potential, AV reovirus was tested on healthy embryonic stem cells, various non-transformed and transformed cell lines, and in severe combined immunodeficiency (SCID) mice with tumour xenografts.Results:Sequence analysis of AV reovirus revealed a premature STOP codon in its sigma 1 attachment protein. Western blot and in vitro translation confirmed the presence of a truncated σ1. In comparison to wild-type reovirus, AV reovirus did not kill healthy stem cells or induce black tail formation in SCID mice. However, it did retain its ability to target cancer cells and reduce tumour size.Conclusion:Despite containing a truncated attachment protein, AV reovirus still preferentially targets cancer cells, and compared with wild-type reovirus it shows reduced toxicity when administered to immunodeficient hosts, suggesting the potential use of AV reovirus in combination cancer therapy.

Amino acids substitutions in σ1 and μ1 outer capsid proteins of a Vero cell-adapted mammalian orthoreovirus are required for optimal virus binding and disassembly

“…These proof of concept experiments suggest that it should be also possible to adapt the virus to different cell types in order to further optimize reovirus oncolytic ability. This idea has been previously suggested and, accordingly, novel viruses were found to be better adapted as oncolytic agents (Kim et al, 2011; Page 16 of 27 Rudd et al, 2005;Shmulevitz et al, 2012;van den Wollenberg et al, 2012). Viruses selected for their large-plaque phenotype using L929 cells, somewhat reminiscent of larger plaques formed by VeroAV on Vero cells in the absence of chymotrypsin, were shown to be better oncolytic viruses both in vitro and in animal models (Shmulevitz et al, 2012).…”

“…A recent report (van den Wollenberg et al, 2012) also suggests that the ability to infect cells independently of the JAM receptor, possibly due to increased binding to sialic acids, could be a useful strategy against cancer cell types that express low levels of JAM and are thus relatively resistant to reovirus (van den Hengel et al, 2013;van den Wollenberg et al, 2009;van Houdt et al, 2008). Furthermore, a virus harboring a deletion of the JAM binding domain and binding solely onto cell surface sialic acids, was shown to be attenuated in nontransformed cells while retaining an oncolytic potential and exhibiting reduced host toxicity (Kim et al, 2011).…”

“…This amino acid substitution is located at the surface-exposed lobe of the σ3 outer capsid protein, thus increasing the protein's sensitivity to proteases and favoring viral uncoating under conditions where proteases are present in limiting amount Wetzel et al, 1997). In more recent studies, amino acid substitutions in σ3 were again observed in viruses recovered from Raji, HT1080 and CA46 cells, at positions consistent with an increased uncoating of these viruses; substitutions in σ1 were also found in two of these viruses (Kim et al, 2011).…”

“…This has led to numerous clinical studies as reviewed by others (Black and Morris, 2012;Clements et al, 2014;Harrington et al, 2010;Kelly et al, 2009;Maitra et al, 2012). Despite the fact that reoviruses are naturally oncolytic without prior genetic modifications, there is still a significant research effort ongoing to obtain novel virus variants better adapted to infect, replicate in, and kill cancer cells while sparing non-transformed cells (van den Hengel et al, 2013;Kim et al, 2011;Rudd and Lemay, 2005;Shmulevitz et al, 2012;van den Wollenberg et al, 2009van den Wollenberg et al, , 2012. One possible approach is to take advantage of novel viral variants that could be selected during establishment of viral persistence in different cell types.…”

Addition of exogenous polypeptides on the mammalian reovirus outer capsid using reverse genetics

“…The virus was also shown to induce "black foot syndrome" in immunodeficient SCID/NOD mice (Loken et al, 2004). There are thus possibly important benefits in the development of reovirus strains that are either attenuated (Kim et al, 2011) or targeted to bind specifically onto given cancer cell types, as proposed by others (Van Den Wollenberg et al, 2009). This last approach is currently under study for various oncolytic viruses such as adenovirus, measles virus, and herpesvirus, among others (Blechacz and Russell, 2008;Mathis, Stoff-Khalili, and Curiel, 2005;CampadelliFiume et al, 2011).…”