Novel Indoleamine-2,3-Dioxygenase-Targeted Pt(IV) Prodrugs Regulate the Tumor Immune Microenvironment to Achieve Chemoimmunotherapy <i>In Vitro</i> and <i>In Vivo</i>

Convincing evidence revealed that some platinum-based drugs could stimulate immunological recognition, thereby inducing immunogenic cell death (ICD). Indoleamine-2,3-dioxygenase (IDO) is overexpressed in tumors, which caused exhaustion of tryptophan (T-cell energy) and constructed an immunosuppressive tumor microenvironment. Herein, considering IDO inhibition to improve chemotherapy, a series of IDOi-Pt(IV) prodrugs were designed to not only target DNA and IDO but also facilitate tumor-antigen exposure and immunomodulation. The optimal IDOi-Pt(IV) prodrugs (named compound <b>10</b>) significantly enhanced intracellular accumulation 22.4-fold and cytotoxicity 61.75-fold superior to cisplatin in HeLa cells. Moreover, immunofluorescence and enzyme-linked immunosorbent assays revealed that <b>10</b> induced reactive oxygen species-mediated endoplasmic reticulum stress and secretion of damage-associated molecular patterns, thereby presenting ICD effects. Molecular docking, enzyme inhibition, and Western blot assays demonstrated that <b>10</b> could effectively inhibit IDO1 and reverse immunosuppression, as further verified by mixed leukocyte reactions. <i>In vivo</i> tests showed that <b>10</b> exhibited high-efficiency and low-toxicity antitumor effects compared to cisplatin, presenting successful chemoimmunotherapy.