Effect of caprine herpes virus-1 (CpHV-1) on cell viability and chemosensitivity in breast cancer cells.

e13044 Background: Oncolytic viruses (OVs) are gaining recognition as therapeutic agents in oncology, functioning both as enhancers of established treatments and as direct oncolytic agents. Their mechanisms of action include lysis of neoplastic cells, induction of specific antitumor immune responses, and modification of the tumor microenvironment. CpHV-1 presents several advantages as a non-human wild-type OV, such as selective replication impairment in non-malignant human cells, tropism for human tumor cells, and the absence of pre-existing immune responses in human hosts. In previous studies, we established the CpHV-1 antitumor efficacy across several cancer cell lines. Here, we aim to assess the effects of CpHV-1 in a range of breast cancer (BC) cell lines and evaluate its potential synergistic effects in combination with FDA-approved therapies specific to BC subtypes. Methods: We assessed CpHV-1's impact on BC cell viability, cell cycle, and apoptosis using MTS assays, FACS analysis, and Western blot, respectively. We evaluated CpHV-1's effects on MCF-7, T47D, SKBR3, MDA-MB-231, and MDA-MB-468 BC cell lines representing different subtypes. We also examined CpHV-1's combination with Abemaciclib (A), Tucatinib (T), and Inavolisib (I) using MTS assays and Chou-Talalay analysis. Results: The CpHV-1 infection showed a time and dose-dependent cytotoxic effect in all BC cells without significantly affecting the normal cells. In particular, we observed that, 72h post-infection (p.i.), a multiplicity of infection (MOI) value of 5 reduced cell viability by approximately 50%. To verify whether CpHV-1 exerted long-term cell growth inhibition, we performed clonogenic assays upon infection with 5MOI and found that the OV significantly reduced colony formation in cancer cells. Our preliminary data indicate that CpHV-1 alters cell cycle regulation, inducing G0-G1 arrest or driving quiescent cells to enter the S phase. Apoptosis activation was also observed. CpHV-1 synergized with A in HR+ BC cells, T in HER2+ BC cells, and I in triple-negative BC cells. We treated the BC cell lines for 72h with the two agents, both alone and in combination, at five different concentrations in a constant ratio. The CI values revealed are < 1 for all cell lines. To exclude possible cytotoxic effects on non-neoplastic cells, we treated the MCF-10A with the three different CpHV-1 combinations and observed no significant toxic effect. Conclusions: CpHV-1 demonstrates potential as an effective therapeutic agent for cancer treatment, particularly when combined with standard targeted therapies. This combination enhances sensitivity in BC cells, including triple-negative subtypes. While further research is required to fully understand the mechanisms underlying CpHV-1’s infection, our findings underscore the promise of these combined therapies as a novel and effective strategy for BC.