Development of an Intracellular Nitric Oxide-Donating Cell-Penetrating Polypeptide as an Immunogenic Cell Death Inducer.

Recently, nitric oxide (NO) has been shown to induce immunogenic cell death (ICD) in tumor cells through endoplasmic reticulum (ER) stress and mitochondrial outer membrane permeabilization (MOMP). However, NO is unstable, making direct delivery difficult. In this study, we developed a cell-penetrating polypeptide-based NO donor, poly(l-guanidine) (PLG). Given that the guanidine structure can be catalyzed by reactive oxygen species (ROS) to produce NO, helical PLG plays three roles: spontaneous cell penetration, intracellular ROS generation to produce NO, and induction of ICD. The results revealed that helical PLG generates NO inside the cell by self-inducible guanidine oxidation and that NO effectively elicits ICD by ER stress- and MOMP-dependent intertwined mechanisms.