Drug repurposing: omeprazole increases the efficacy of acyclovir against herpes simplex virus type 1 and 2

ObjectivesOmeprazole was shown to improve the anti-cancer effect of the nucleoside-analogue 5-fluorouracil. Here, we investigated the effects of omeprazole on the activities of the antiviral nucleoside analogues ribavirin and acyclovir.\n\nMethodsWest Nile virus-infected Vero cells and influenza A H1N1-infected MDCK cells were treated with omeprazole and/ or ribavirin. Herpes simplex virus 1 (HSV-1)- or HSV-2-infected Vero or HaCat cells were treated with omeprazole and/ or acyclovir. Antiviral effects were determined by examination of cytopathogenic effects (CPE), immune staining, and virus yield assay. Cell viability was investigated by MTT assay.\n\nResultsOmeprazole concentrations up to 80g/mL did not affect the antiviral effects of ribavirin. In contrast, omeprazole increased the acyclovir-mediated effects on HSV-1- and HSV-2-induced CPE formation in a dose-dependent manner in Vero and HaCat cells. Addition of omeprazole 80g/mL resulted in a 10.8-fold reduction of the acyclovir concentration that reduces CPE formation by 50% (IC50) in HSV-1-infected Vero cells and in a 47.7-fold acyclovir IC50 reduction in HSV-1-infected HaCat cells. In HSV-2-infected cells, omeprazole reduced the acyclovir IC50 by 7.3-fold (Vero cells) or by 12.9-fold (HaCat cells). Omeprazole also enhanced the acyclovir-mediated effects on viral antigen expression and virus replication in HSV-1- and HSV-2-infected cells. In HSV-1-infected HaCat cells, omeprazole 80g/mL reduced the virus titre in the presence of acyclovir 1g/mL by 1.6x105-fold. In HSV-2-infected HaCat cells omeprazole 80g/mL reduced the virus titre in the presence of acyclovir 2g/mL by 9.2x103-fold. The investigated drug concentrations did not affect cell viability, neither alone nor in combination.\n\nConclusionsOmeprazole increases the anti-HSV activity of acyclovir. As clinically well-established and tolerated drug, it is a candidate drug for antiviral therapies in combination with acyclovir.