Oncolytic tanapoxvirus expressing FliC causes regression of human colorectal cancer xenografts in nude mice

Abstract

Colorectal cancers are significant causes of morbidity and mortality and existing therapies often perform poorly for individuals afflicted with advanced disease. Oncolytic virotherapy is an emerging therapeutic modality with great promise for addressing this medical need. Herein we describe the in vivo testing of recombinant variants of the tanapoxvirus (TPV). Recombinant viruses were made ablated for either the 66R gene (encoding a thymidine kinase), the 2L gene (encoding a TNF-binding protein), or both. Some of the recombinants were armed to express mouse chemotactic protein 1 (mCCL2/mMCP-1), mouse granulocyte-monocyte colony stimulating factor (mGM-CSF), or bacterial flagellin (FliC). Tumors were induced in athymic nude mice by implantation of HCT 116 cells and subsequently treated by a single intratumoral injection of one of the recombinant TPVs. Histological examination showed a common neoplastic cell type and a range of immune cell infiltration, necrosis, and tumor cell organization. Significant regression was seen in tumors treated with virus TPV/Δ2L/Δ66R/fliC, and to a lesser extent the recombinants TPV/Δ2L and TPV/Δ66R. Our results suggest that oncolytic recombinants of the TPV armed with activators of the innate immune response may be effective virotherapeutic agents for colorectal cancers in humans and should be explored further to fully realize their potential.

Oncolytic Virotherapy: A Brief Overview

“…The most common target for this is the thymidine kinase genes, as the normal cellular levels are usually low. The inverse is true in cancer cells [8,9]. This selectivity, in the case of the thymidine knockouts, is present because normal cells that are not undergoing rapid division will not have an excess of thymidine or thymidine kinase and will therefore hinder viral replication long enough for the host to defend itself against infection [10].…”

“…This selectivity, in the case of the thymidine knockouts, is present because normal cells that are not undergoing rapid division will not have an excess of thymidine or thymidine kinase and will therefore hinder viral replication long enough for the host to defend itself against infection [10]. Cancer cells, which are always mitotic, more often than not have an excess of thymidine which the virus can use to successfully replicate its genome [8]. Current research using thymidine kinase knock-outs for Herpesvirus, Adenovirus, Picornaviruses, and Tanapox virus is ongoing and showing various degrees of success [8,11].…”

“…Cancer cells, which are always mitotic, more often than not have an excess of thymidine which the virus can use to successfully replicate its genome [8]. Current research using thymidine kinase knock-outs for Herpesvirus, Adenovirus, Picornaviruses, and Tanapox virus is ongoing and showing various degrees of success [8,11].…”

“…Tanapox virus contains a gene, 2L, which has been shown to down regulate TNF-alpha function in healthy cells. Current research is being done to determine the efficacy of this knock-out in colorectal cancer models both in vitro and in vivo [8].…”

“…Infiltration of the tumor is one result of cytokine/ chemokine production, which draws immune cells to the tumor microenvironment where they can assert their effects through direct interaction of cancer cells. Differentiation of immune cells occurs as a result of certain stimulatory genes, such as GMCSF seen in Tanapox virus and Herpes simplex virus models, to prompt phagocytic and cytotoxic activities [6][7][8]. Once localization and infiltration of the tumor have occurred, additional signaling mechanisms may be activated to work synergistically toward tumor reduction.…”