The unique ability of oncolytic viruses (OVs) to replicate in and destroy malignant cells while leaving healthy cells intact and activating the host immune response makes them powerful targeted anti-cancer therapeutic agents. Vesicular stomatitis virus (VSV) only causes mild and asymptomatic infection, lacks pre-existing immunity, can be genetically engineered for enhanced efficiency and improved safety, and has a broad cell tropism. VSV can facilitate targeted delivery of immunostimulatory cytokines for an enhanced immune response against cancer cells, thus decreasing the possible toxicity frequently observed as a result of systemic delivery. In this study, the oncolytic potency of the two rVSV versions, rVSV-dM51-GFP, delivering green fluorescent protein (GFP), and rVSV-dM51-mIL12-mGMCSF, delivering mouse interleukin-12 (mIL-12) and granulocyte-macrophage colony-stimulating factor (mGMCSF), was compared on the four murine cancer cell lines of different origin and healthy mesenchymal stem cells (MSCs) at 24 h post-infection by flow cytometry. Lewis lung carcinoma (LL/2) cells were demonstrated to be more susceptible to the lytic effects of both rVSV versions compared to melanoma (B16-F10) cells. Detection of expression levels of antiviral and pro-apoptotic genes in response to the rVSV-dM51-GFP infection by quantitative PCR (qPCR) showed lower levels of IFIT, RIG-I, and N-cadherin and higher levels of IFNβ and p53 in LL/2 cells. Subsequently, C57BL/6 mice, infused subcutaneously with the LL/2 cells, were injected intratumorally with the rVSV-dM51-mIL12-mGMCSF 7 days later to assess the synergistic effect of rVSV and immunostimulatory factors. The in vivo study demonstrated that treatment with two rVSV-dM51-mIL12-mGMCSF doses 3 days apart resulted in a tumor growth inhibition index (TGII) of over 50%.

Background: Oncolytic viruses (OVs), a promising anti-cancer therapeutic, replicate more efficiently in cancer cells rather than in healthy cells due to the alterations in antiviral response mechanisms and dysregulation of signaling pathways. Vesicular stomatitis virus (VSV) is known for low pathogenicity, tropism to various cancer cells, and the ability to lyse cells in the hypoxic tumor microenvironment (TME). Targeted delivery of immune checkpoint and co-stimulatory molecules can enhance the anti-tumor immune response and remodel the immunosuppressive TME. The aim of this study was to compare the activity of rVSV-GFP with rVSV, encoding the programmed cell death protein 1 (PD-1) and tumor necrosis factor ligand superfamily member 9 (4-1BBL). Methods: The oncolytic efficacy of these rVSV variants used at 10⁵, 10⁶, and 10⁷ TCID50 was evaluated at 24 and 48 h post-infection by flow cytometry in a panel of mouse and human cancer cell lines. Quantitative real-time polymerase chain reaction (qPCR) was used to evaluate mRNA expression levels of certain genes at 12 and 48 h post-infection. Results: Murine hepatocellular carcinoma (H22) and human melanoma (A375) or human lung carcinoma (A549) were the most sensitive to rVSV therapy cell lines. The higher relative expression of the antiviral response genes RIG-I and IFIT1 within each biological species (mouse or human) correlated with lower sensitivity to rVSV. No such effect was observed for the type I interferons (IFNs), despite their proposed key role in resistance to OV therapy. Conclusions: H22, A375, and A549 are more susceptible to the oncolytic activity of the novel rVSV-PD-1-4-1BBL.