Raddeanin A Enhances Mitochondrial DNA‐cGAS/STING Axis‐Mediated Antitumor Immunity by Targeting Transactive Responsive DNA‐Binding Protein 43

Immune checkpoint therapies (ICT) have achieved unprecedented efficacy in multiple cancer treatments, but are still limited by low clinical response rates. Identification of immunogenic cell death (ICD)‐inducing drugs that can induce tumor cell immunogenicity and reprogram the tumor microenvironment is an attractive approach to enhance antitumor immunity. In the present study, Raddeanin A (RA), an oleanane class triterpenoid saponin isolated from Anemone raddeana Regel, is uncovered as a potent ICD inducer through an ICD reporter assay combined with a T cell activation assay. RA significantly increases high‐mobility group box 1 release in tumor cells and promotes dendritic cell (DC) maturation and CD8(+) T cell activation for tumor control. Mechanistically, RA directly binds to transactive responsive DNA‐binding protein 43 (TDP‐43) and induces TDP‐43 localization to mitochondria and mtDNA leakage, leading to cyclic GMP‐AMP synthase/stimulator of interferon gene‐dependent upregulation of nuclear factor κB and type I interferon signaling, thereby potentiating the DC‐mediated antigen cross‐presentation and T cell activation. Moreover, combining RA with anti‐programmed death 1 antibody effectively enhances the efficacy of ICT in animals. These findings highlight the importance of TDP‐43 in ICD drug‐induced antitumor immunity and reveal a potential chemo‐immunotherapeutic role of RA in enhancing the efficacy of cancer immunotherapy.