Omeprazole Increases the Efficacy of Acyclovir Against Herpes Simplex Virus Type 1 and 2

Abstract

Omeprazole was shown to improve the anti-cancer effects of the nucleoside analogue 5-fluorouracil. Here, we combined omeprazole with the antiviral nucleoside analogues ribavirin and acyclovir. Omeprazole did not affect the antiviral effects of ribavirin in non-toxic concentrations up to 80 μg/mL but increased the acyclovir-mediated effects on herpes simplex virus 1 and 2 (HSV-1 and -2) replication in a dose-dependent manner. Omeprazole alone reduced HSV-1 and -2 titers [but not HSV-induced formation of cytopathogenic effects (CPE)] at concentrations ≥40 μg/mL. However, it exerted substantially stronger effects on acyclovir activity and also increased acyclovir activity at lower concentrations that did not directly interfere with HSV replication. Omeprazole 80 μg/mL caused a 10.8-fold (Vero cells) and 47.7-fold (HaCaT cells) decrease of the acyclovir concentrations that reduced HSV-1-induced CPE formation by 50% (IC₅₀). In HSV-2-infected cells, omeprazole 80 μg/mL reduced the acyclovir IC₅₀ by 7.3- (Vero cells) and 12.9-fold (HaCaT cells). In HaCaT cells, omeprazole 80 μg/mL reduced the HSV-1 titer in the presence of acyclovir 1 μg/mL by 1.6 × 10⁵-fold and the HSV-2 titer in the presence of acyclovir 2 μg/mL by 9.2 × 10³-fold. The proton pump inhibitors pantoprazole, rabeprazole, lansoprazole, and dexlansoprazole increased the antiviral effects of acyclovir in a similar fashion as omeprazole, indicating this to be a drug class effect. In conclusion, proton pump inhibitors increase the anti-HSV activity of acyclovir and are candidates for antiviral therapies in combination with acyclovir, in particular for topical preparations for the treatment of immunocompromised individuals who are more likely to suffer from severe complications.

Keywords: HSV; HSV-1; HSV-2; antiviral drugs; antiviral therapy; proton pump inhibitors; ribavirin.

FIGURE 1

Cytopathogenic effect (CPE) formation and viral gene expression in the presence of antiviral nucleoside analogues and omeprazole. (A) Effects of omeprazole (80 μg/mL) on the concentrations of antiviral nucleoside analogues that reduce CPE formation by 50% (IC₅₀) using West Nile virus (WNV)-infected Vero cells, influenza A H1N1-infected MDCK cells, and HSV-1- or HSV-2-infected Vero or HaCaT cells. Omeprazole alone did not reduce CPE formation. Numerical values are presented in Supplementary Table S1. (B) Effects of omeprazole and acyclovir on the expression of virus proteins in HSV-1- and HSV-2-infected Vero cells. HSV-1-infected cells were treated with omeprazole 80 μg/mL and/or acyclovir 0.31 μg/mL. HSV-2-infected cells were treated with omeprazole 40 μg/mL and/or acyclovir 0.6 μg/mL. (C) HSV gB levels in HSV-1-infected Vero cells treated with omeprazole 80 μg/mL and/or acyclovir 0.31 μg/mL as determined by Western blot 24 h post infection.

FIGURE 2

Concentration-dependent effects of omeprazole on the acyclovir IC₅₀ in HSV-1- or HSV-2-infected HaCaT cells as determined by cytopathogenic effect (CPE) formation. Numerical values are presented in Supplementary Table S2. The investigated drug concentrations did not affect cell viability, neither alone or in combination. ^∗P < 0.05 relative to nucleoside analogue alone.

FIGURE 3

Effect of acyclovir 1 μg/mL (HSV-1) or 2 μg/mL (HSV-2) alone or in combination with varying omeprazole (OME) concentrations (μg/mL) on HSV-1 and HSV-2 titres in HaCaT cells. Numerical values are presented in Supplementary Table S3. ^∗P < 0.05 relative to acyclovir alone, ^#P < 0.05 relative to untreated virus control; N.D. = no detectable virus titre.

FIGURE 4

Effects of different proton pump inhibitors on acyclovir activity in HSV-1-infected HaCaT cells as indicated by cytopathogenic effect (CPE) formation. Proton pump inhibitors alone did not reduce CPE formation. Numerical values are presented in Supplementary Table S4. ^∗P < 0.05 relative to acyclovir alone.