Design, synthesis, and antitumor mechanism investigation of iridium(III)/ruthenium(II)-vadimezan conjugates towards 4T1 cells.

Transition metal iridium(III) and ruthenium(II) complexes exhibit significant anti-tumor potential. Vadimezan (VDA) is a potent non-nucleotide stimulator of interferon genes (STING) agonist that enhances the efficacy of tumor immunotherapy. Herein, we designed and synthesized three iridium(III) (Ir-VDA-1-3, C^N = 2-phenylpyridine (ppy, in Ir-VDA-1), 2-(2-thienyl)pyridine (thpy, in Ir-VDA-2), and 2-(2,4-difluorophenyl)pyridine (dfppy, in Ir-VDA-3)) and three ruthenium(II) (Ru-VDA-1-3, N^N = 4,7-diphenyl-1,10-phenanthroline (DIP, in Ru-VDA-1), 1,10-phenanthroline (phen, in Ru-VDA-2), and 2,2'-bipyridine (bpy, in Ru-VDA-3)) complexes by incorporating VDA with iridium(III) and ruthenium(II) complexes. Among of these, Ir-VDA-1-3 exhibited potent antitumor activity. Ir-VDA-1-3 were effectively internalized by mouse triple negative breast cancer (TNBC) 4T1 cells and localized to mitochondria, inducing mitochondrial pathway-mediated apoptosis. Western blot analysis revealed that Ir-VDA-1-3 activated and cleaved caspase 3, subsequently cleaving GSDME to induce pyroptosis. Notably, Ir-VDA-1-3 treatment significantly upregulated the expression of key proteins (cyclic GMP-AMP synthase (cGAS) and phosphorylated STING (p-STING)) in the cGAS-STING signaling pathway. Furthermore, Ir-VDA-1-3 functioned as the immunogenic cell death (ICD) inducers, promoting damage-associated molecular patterns (DAMPs) release, including calreticulin (CRT), high mobility group protein 1 (HMGB1), and adenosine triphosphate (ATP). This strategy provides a novel design concept for multimodal synergistic cancer therapy.