Host-directed novel mechanistic insights of doxorubicin reveal its efficacy against drug-resistant HSV-1 underscoring risks with oncolytic virotherapy

BACKGROUND: Herpes simplex virus type 1 (HSV-1) infects approximately four billion people worldwide, and the emergence of drug-resistant strains has reduced the effectiveness of existing antivirals. Targeting host pathways exploited by HSV-1 represents an attractive strategy for developing resistance-refractory antivirals. METHODS: We evaluated the antiviral potential of doxorubicin, an FDA-approved anticancer drug, against HSV-1 using in vitro cell culture systems, an ex vivo porcine corneal model, and an in vivo murine ocular infection model. Viral replication, host signaling pathways, and combinatorial interactions with nucleoside analogs were systematically assessed. RESULTS: Doxorubicin potently inhibited HSV-1 replication at sub-cytotoxic concentrations by suppressing the host PI3K-AKT-mTOR signaling axis, a pathway required for viral entry and productive replication. Antiviral activity was observed against laboratory-adapted strains as well as clinical acyclovir-resistant HSV-1 isolates. Pharmacological modulation of PI3K-AKT signaling, pathway activation kinetics, and studies in doxorubicin-resistant cells confirmed a host-directed mechanism. Doxorubicin exhibited strong synergy with nucleoside analog antivirals, enabling dose reduction without loss of efficacy. While inhibition of PI3K-AKT signaling constrained productive replication of both wild-type and oncolytic HSV-1, these effects were context-dependent and relevant to therapeutic settings that rely on robust viral replication. CONCLUSIONS: This study identifies PI3K-AKT pathway inhibition as a novel host-directed antiviral mechanism underlying doxorubicin's activity against HSV-1, demonstrates its synergistic potential with nucleoside analogs, and provides mechanistic insight into raising concerns over oncolytic HSV-based therapies. Collectively, these findings highlight the potential of localized, host-targeted strategies for managing drug-resistant HSV-1 infections.