Harnessing the potential of pharmacological small molecules to amplify VSV-based oncolytic viral therapy

Abstract Malignant cutaneous melanoma is the most lethal form of all skin cancers causing 10,000 deaths annually in the United States and 200,000 globally and remains a major oncological problem. Oncolytic viruses (OVs) can selectively infect, replicate and eradicate cancer cells with defective type I interferons (IFNs) mechanisms, a

major antiviral pathway. The PI3K/AKT/mTOR signaling pathway is a crucial survival regulator of cellular stress and helps balance protein synthesis, cell cycle, and apoptosis to ensure the survival of resilient tumor cells. Vesicular stomatitis virus (VSV) is a non-pathogenic, enveloped, negative-strand RNA Rhabdovirus with a potent

vaccine and oncolytic potential across multiple human cancer. VSV is highly sensitive to type-I interferons (IFNs); therefore, it cannot initiate a productive infection in healthy cells due to IFNs mediated antiviral response. Dysregulated IFNs and PI3K/Akt/mTOR signaling cooperate in tumorigenesis related to many cancer types,

including melanoma. Moreover, PI3K or AKT inhibition diminishes cells' IFN-Is signatures. Therefore, we hypothesize that local inhibition of the PI3K/AKT/mTOR signaling pathway in the tumors will create a needful condition for the intratumoral spread of VSV and virus-induced cancer cell death resulting in tumor growth delay

and extension in survival in a mouse model of melanoma. Because of the adverse effects associated with VSVs, we have engineered a novel hybrid VSV virus (VSV-MORV-G [VMG]), where the VSV envelops protein G and is replaced with that of Morreton virus to improve their safety and potency. We recently identified fisetin, a natural

compound, and two of its potent derivatives, F019, F040 and F142, as inhibitors that competitively bind mTOR and S6K1 kinase to inhibit the mTOR/AKT/IFN pathway. Furthermore, our preliminary data show increased sensitivity and cytotoxicity of melanoma cells to oncolytic virus upon pre-therapy with fisetin while sparing normal

cells. Thus, we expect that locally turning off the type I IFN response and mTOR can serve as a novel pharmaco- virotherapy for advanced localized melanoma. Novel outcomes stemming from the proposed investigations will inform the role of local turning off of target pathways in the development/progression of melanoma, and will serve

as a catalyst to develop practical solutions for melanoma control and possibly other cancers with significant public health burdens. Our aims are designed to test this innovative hypothesis in cell lines and preclinical animal models of melanoma. Funding of this current application will enhance biomedical research, education and

infrastructure at the ULM College of Pharmacy. The proposed work will directly involve underrepresented minorities and female students, and will sharpen their communication and presentation skills, and encourage them to pursue careers as biomedical scientists in a primary undergraduate institution (PUI).