Duloxetine, an SNRI, Targets pSTAT3 Signaling: In-Silico, RNA-Seq and In-Vitro Evidence for a Pleiotropic Mechanism of Pain Relief.

Chronic pain is a serious health issue, often irrationally managed by conventional analgesics. Duloxetine, a serotonin-norepinephrine reuptake inhibitor (SNRI), also effective in neuropathic and musculoskeletal pain, but the molecular mechanism of its analgesic action is still unclear. Here, we examined whether Duloxetine exerts pleiotropic effects by directly targeting phosphorylated STAT3 (pSTAT3), a key regulator of neuroinflammation and pain sensitization. Molecular docking showed that Duloxetine binds with pSTAT3 with binding energy -5.83 kcal/mol. Ruxolitinib, a JAK/STAT inhibitor used as reference, showed binding energy of -6.19 kcal/mol. Molecular dynamics (MD) simulations confirmed stable Duloxetine-pSTAT3 complexes, while MM-PBSA free energy analysis revealed more favorable binding for Duloxetine (ΔG = -15.17 kJ·mol(-1)) than Ruxolitinib (ΔG = -12.98 kJ·mol(-1)) for pSTAT3. In-vitro analyses, Western blot showed that Duloxetine significantly reduced IL-6-induced STAT3 and pSTAT3 expression in C2C12 cells in a dose-dependent manner (6.4 and 12.8 μM, *** p < 0.0001), although Ruxolitinib produced a stronger suppression. Transcriptomic analysis revealed Duloxetine-specific enrichment of mitochondrial, oxidative phosphorylation, and synaptic pathways, distinct from the immune-suppressive influence of Ruxolitinib. RNA-seq further revealed that STAT3 transcript abundance remains constant under all treatment conditions, indicating that post-transcriptional or post-translational mechanisms, such as phosphorylation-dependent activation, may be involved rather than transcriptional modulation of STAT3 in action of Ruxolitinib and Duloxetine and the formation of novel STAT3 indicating enhanced transcript diversity. The rMATS splicing analysis confirmed dose-dependent modulation, with Duloxetine promoting mild exon skipping at 6.4 μM (IncLevel 0.90 → 0.80) and recovery at 12.8 μM (0.85 → 0.86), while Ruxolitinib induced stronger exon inclusion (0.85 → 1.00,0.94), with broader transcript suppression at 6.4 μM and 12.8 μM, respectively. These findings establish Duloxetine as a dual-action therapeutic that combines neurotransmitter reuptake inhibition with pSTAT3 suppression and isoform-level transcriptomic modulation. This pleiotropic mechanism provides a rationale for its durable analgesic effects and supports repurposing in STAT3-associated disorders.