Modularly Designed Peptide Nanoprodrug Augments Antitumor Immunity of PD-L1 Checkpoint Blockade by Targeting Indoleamine 2,3-Dioxygenase

The limited efficacy of single-agent immune checkpoint inhibitors in treating tumors has prompted investigations on their combination partners. Here, a tumor-homing indoleamine 2,3-dioxygenase (IDO) nanoinhibitor is reported to selectively inhibit immunosuppressive IDO pathway in the tumor microenvironment. It is self-assembled from a modularly designed peptide-drug conjugate containing a hydrophilic targeting motif (arginyl-glycyl-aspartic acid; RGD), two protonatable histidines, and an ester bond-linked hydrophobic IDO inhibitor, which exhibits pH-responsive disassembly and esterase-catalyzed drug release. Markedly, it achieved potent and persistent inhibition of intratumoral IDO activity with a reduced systemic toxicity, which greatly enhanced the therapeutic efficacy of programmed cell death-ligand 1 blockade in vivo. Overall, this study provides a promising paradigm of combinatorial normalization immunotherapy by exploiting a targeted IDO nanoinhibitor to augment the antitumor immunity of checkpoint inhibitors.