MEK1/2 Inhibitor (U0126) and PI3K Inhibitor (LY294002) Suppress Herpes Simplex Virus Type 1 Replication by Targeting MAPK/ERK1/2 and PI3K/AKT Signaling Pathways: Implications for Oral Health and Translational Control of Orolabial HSV-1 Infection.

Background: Current antivirals for orolabial Herpes simplex virus type 1 (HSV-1) often provide incomplete suppression and limited reactivation control, sustaining recurrent oral lesions and inflammation that compromise oral health. HSV-1 subverts host signaling networks to enhance its replication and trigger inflammation. Among these, the extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathways are hijacked to facilitate viral gene expression and cell survival. Objectives: In this study, we employed U0126 [a mitogen-activated protein kinase 1/2 (MEK1/2) inhibitor] and LY294002 [a phosphatidylinositol 3-kinase (PI3K) inhibitor] as targeted pharmacological tools to intercept HSV-1's exploitation of host keratinocyte signaling. Methods: Human HaCaT keratinocytes were infected with HSV-1 and treated with U0126 or LY294002. Western blotting was used to assess phosphorylation of ERK1/2 and activation of protein kinase B (AKT). MTT assays were performed to evaluate cell viability. Real-time PCR was utilized to quantify viral transcripts (ICP0, ICP4, gB, and gC) and inflammatory cytokines [interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α)]. Confocal microscopy was employed to visualize the intracellular distribution of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), phosphorylated activation of protein kinase B (p-AKT), and HSV-1 glycoprotein D (gD). Viral titers were determined using plaque assays. Results: The HSV-1 infection induced a time-dependent increase in phosphorylation of ERK1/2 and AKT, with p-ERK1/2 peaking at 12 h and p-AKT increasing 2.5-fold by 24 h. Cell viability declined from 100% at baseline to 45% at 24-hours post-infection (hpi). Treatment with U0126 and LY294002 reduced p-ERK1/2 and p-AKT levels to 25% and 30% of infected controls, respectively, restoring viability to 82 - 86%. Both inhibitors markedly suppressed viral gene expression (ICP0, ICP4, gB, gC down by 60 - 80%) and inflammatory cytokines (IL-6 and TNF-α reduced by > 50%). Plaque assays showed a strong decline in infectious titers - from 175 plaques per well in untreated infection to 60 and 45 plaques after U0126 and LY294002, respectively. Confocal imaging further revealed diminished nuclear accumulation of p-ERK1/2 and p-AKT, indicating disruption of post-entry signaling critical for viral replication. Conclusions: Targeting host signaling bottlenecks with U0126 and LY294002 offers a dual-pronged antiviral strategy against HSV-1 by dismantling the ERK/AKT axis critical for replication and inflammatory amplification. These findings position MEK1/2 and PI3K as promising therapeutic nodes for managing cutaneous HSV-1 infections. This host-directed dual-pathway inhibition may therefore help reduce recurrent orolabial HSV-1 lesions.