HMGB3 Contributes to Anti‐PD‐1 Resistance by Inhibiting IFN‐γ‐Driven Ferroptosis in TNBC

Our previous studies showed HMGB3 expression may correlate with immunotherapy efficacy in breast cancer patients. Here, we investigated whether HMGB3 overexpression has an impact on anti-PD-1 therapy in triple-negative breast cancer (TNBC) and its molecular mechanisms. Animal models were established to observe the effect of HMGB3 on sensitivity to anti-PD-1 treatment. Correlation of HMGB3 expression and ferroptosis preventive proteins in TNBC patients' tissues with anti-PD-1 therapy efficacy was analyzed. The impact of HMGB3 on IFN-γ (Interferon-gamma) inhibitory effects and signaling was examined in human TNBC cells where HMGB3 expression was knocked down using siRNA. Moreover, TNBC cells stably transfected with lentiviral vectors containing cDNA of HMGB3 were also used to confirm the effect of overexpression of HMGB3 on IFN-γ inhibitory effect and signaling. Effect of HMGB3 on IFN-γ-driven ferroptosis and ferroptosis-associated protein expression were also investigated. Correlation of HMGB3 and IRF1 and GPX4 expression in patient's cancer tissue were also investigated. Our results demonstrated that HMGB3 expression contributes to resistance to anti-PD-1 therapy in vivo. HMGB3 expression correlated with treatment efficacy of immunotherapy and survival in TNBC patients. HMGB3 silence decreased resistance of breast cancer cells to IFN-γ cytotoxic effect, while HMGB3 overexpression increased resistance of these cancer cells. HMGB3 silence increased STAT1 phosphorylation and IRF1 expression upon IFN-γ treatment compared with control. Overexpression of HMGB3 inhibited STAT1 phosphorylation and IFN-γ signaling in TNBC cells. Moreover, HMGB3 also increased STAT3 activation and had an effect of interaction between STAT1 and STAT3. HMGB3 overexpression decreased IFN-γ-driven ferroptosis in TNBC cells. HMGB3 increased ferroptosis-inhibitory proteins (SLC7A11, GPX4, and SLC3A2) expression in TNBC cells. Ferroptosis inhibition recovers resistance to anti-PD-1 therapy in vivo. Immunohistochemistry showed HMGB3 expression correlated with ferroptosis-associated proteins and IRF1 expression in breast cancer tissue. HMGB3 contributes to anti-PD-1 resistance by inhibiting IFN-γ-driven ferroptosis in TNBC which suggested HMGB3 is a potential co-target with anti-PD-1 therapy for TNBC.