Oncolytic bovine herpesvirus type 1 infects and kills breast tumor cells and breast cancer-initiating cells irrespective of tumor subtype

Abstract

Oncolytic viruses are attractive cancer therapeutics because of their unique mechanisms of tumor cell targeting and the absence of toxic side effects associated with current treatments. Bovine herpesvirus type 1 (BHV-1) is a species-specific herpesvirus that fails to induce cytopathic effects in normal human cells, but is capable of infecting and killing a variety of immortalized and transformed human cell types, including human breast tumor cell lines from luminal, basal A and basal B subtypes, representing a variety of receptor expression profiles. BHV-1 is capable of initiating replication in and killing both bulk and side population cells, the latter of which have enhanced tumor-initiating capacity. Despite the lack of a productive infection or secretion of cytotoxic factors, BHV-1 infection decreases cellular viability in long-term culture following low multiplicity of infection. Moreover, BHV-1-infected MCF7 cells are significantly diminished in their capacity to form tumors in vivo. Overall, these studies suggest that oncolytic BHV-1 targets bulk breast cancer cells and cancer-initiating cells from luminal and basal subtypes by a novel mechanism that is not contingent upon cellular receptor expression status.

Permissiveness of Human Cancer Cells to Oncolytic Bovine Herpesvirus 1 Is Mediated in Part by KRAS Activity

“…BHV-1 constructs expressing green fluorescent protein (GFP) under the control of an endogenous immediate early (IE) promoter were a kind gift from Guenther Keil (Friedrich Loeffler Institut, Germany). Viral stocks were propagated and titrated on MDBK cells, followed by sucrose cushion purification (23). The oncolytic HSV-1 vector KM100 (ICP0 n212 VP16 in1814 ), expressing GFP under the control of an IE cytomegalovirus promoter, was propagated and titrated on U2OS cells.…”

“…The oncolytic HSV-1 vector KM100 (ICP0 n212 VP16 in1814 ), expressing GFP under the control of an IE cytomegalovirus promoter, was propagated and titrated on U2OS cells. Stocks of this virus were also prepared by sucrose cushion purification (23).…”

“…Genes expressed by BHV-1 are generally named after the coinciding HSV-1 genes, which often have similar functions (8,20,21). While BHV-1 is unable to productively infect normal human cells (14,22), human immortalized, transformed, and breast cancer-initiating cells are permissive to infection (22,23). Interestingly, the ability of BHV-1 to kill human breast tumor cells and breast cancer-initiating cells is not contingent upon virus replication or the production of a viral burst (23).…”

“…While BHV-1 is unable to productively infect normal human cells (14,22), human immortalized, transformed, and breast cancer-initiating cells are permissive to infection (22,23). Interestingly, the ability of BHV-1 to kill human breast tumor cells and breast cancer-initiating cells is not contingent upon virus replication or the production of a viral burst (23). Furthermore, in contrast to other species-specific viruses, sensitivity to BHV-1 does not correlate with type I IFN signaling (22).…”

Handling of the Cotton Rat in Studies for the Pre-clinical Evaluation of Oncolytic Viruses

“…The oncolytic capacity of BHV-1 has been demonstrated in vitro 11,12 . BHV-1 has been shown to initiate replication in and kill human tumor cells from a variety of histological origins, including breast cancer cells and breast cancer initiating cells 11,12 . However, the antitumor capacity of BHV-1 must be evaluated in vivo within the context of an immunocompetent host.…”