Metformin Enhances PD ‐ L1 Inhibitor Efficacy in Ovarian Cancer by Modulating the Immune Microenvironment and RBMS3 Expression

ABSTRACT Ovarian cancer (OC) is associated with poor prognosis and immune evasion through PD‐L1 expression. While anti‐PD‐L1 therapies have shown limited efficacy, combination strategies may enhance therapeutic outcomes. This study explores the potential of metformin to modulate the immune microenvironment and improve the efficacy of PD‐L1 inhibitors in OC. An immunocompetent C57BL/6 mouse model of OC was used to evaluate the effects of metformin and PD‐L1 inhibitors on tumor progression, immune cell infiltration, and cytokine expression. Mice received daily metformin treatment for 2 weeks, with PD‐L1 inhibitors administered twice weekly. Tumor growth was monitored via volume measurements, immune cell infiltration was assessed by flow cytometry, and cytokine levels (Granzyme B, IFN‐γ) were quantified using ELISA. Metformin significantly reduced tumor growth, increased CD8 + T cell infiltration, upregulated RBMS3, and elevated Granzyme B and IFN‐γ expression. Additionally, metformin downregulated PD‐L1 expression, and its combination with PD‐L1 inhibitors further enhanced CD8 + T cell activity. Silencing RBMS3 reversed these effects, underscoring its critical role in immune modulation. These findings suggest that metformin, in combination with PD‐L1 inhibitors, may enhance antitumor immune responses and improve treatment outcomes in OC. Targeting RBMS3 could represent a novel therapeutic approach for overcoming immune evasion in OC.