Genetically engineered oncolytic viruses (OVs) have been proven to be effective anti-cancer agents. However, the heterogeneity of tumours and obligate attenuation of OVs to achieve safety can limit their efficacy. Our lab has previously shown that diverse small molecules, which we have termed “Viral Sensitizers”, used in combination with OVs can potentiate the infection of cancer cells by OVs over 1000-fold in some cases, resulting in cancer-specific killing in both in vitro and in vivo tumour models. We observed that a subset of viral sensitizer compounds ultimately acts by reducing the expression of IFNb, thereby inhibiting antiviral signaling. Here, we aimed to further refine the mechanism of action of this class of compounds. Our results suggest that VSe1 and more stable analogs such as VSe1-28 inhibit nuclear accumulation of NF-kB p65 and expression of various antiviral cytokines including, TNFa, IL-6, IFITM1, and MX2 in multiple oncolytic VSV-resistant cancer cell lines but not in normal cells. This was also observed in vivo in CT26wt immune-competent mouse tumour models, where our group has already demonstrated the therapeutic benefit of combining VSe1-28 with oncolytic VSV. Using various biochemical methods, we have determined that VSe1 and its analog VSe1-28 lead to these effects at least in part through covalent modification of NF-kB p65. In sum, this study provides a new understanding of how these novel viral sensitizers work at the molecular level. This new understanding will not only aid in the discovery and development of improved molecules but also their clinical translation in combination with oncolytic viruses.