Therapeutic limitations of oncolytic VSVd51-mediated miR-199a-5p delivery in triple negative breast cancer models.

Triple-negative breast cancer (TNBC) metastasis is driven, in part, by the epithelial-to-mesenchymal transition (EMT), a process critical for cancer cell migration and invasion. Current treatment options, including immunotherapies and targeted therapies, demonstrate limited efficacy in this aggressive disease, underscoring the need for innovative therapeutic approaches. Here, we present a novel approach integrating oncolytic virotherapy with RNA interference by engineering two variants of vesicular stomatitis virus (VSVd51) expressing pri- or pre-miR-199a-5p, a microRNA implicated in the regulation of EMT. We demonstrate that both viral constructs are functional and capable of overexpressing mature miR-199a-5p. In the human TNBC cell line MDA-MB-231, both viral variants inhibited the expression of ZEB1, a transcription factor central to EMT. However, in the mouse TNBC cell line 4T1, miR-199a-5p delivered via VSVd51 failed to disrupt EMT-related gene expression. In vivo testing of VSVd51-pre-miR-199 in the syngeneic BALB/c-4T1 mouse model revealed no significant survival benefits or reduction in tumor growth, even when coupled with primary tumor resection. Additional in vivo testing in immunodeficient mice using the MDA-MB-231 xenograft model showed no effect on tumor reduction. Our study highlights the challenges of integrating miRNA-based strategies with oncolytic viruses in a cancer context-specific manner and underscores the importance of vector selection and tumor model compatibility for therapeutic synergy.