Oxidation of Innate Immune Checkpoint CD47 on Cancer Cells with Non-Thermal Plasma

SIMPLE SUMMARY: Non-thermal plasma is being developed for cancer immunotherapy. The aim of our study was to determine the effect of non-thermal plasma on immunosuppressive immune checkpoint, CD47. The direct effect of non-thermal plasma on CD47 was measured in vitro and in vivo, and the mechanism of action was studied in silico. Non-thermal plasma immediately oxidized CD47, suggesting a dual role of non-thermal plasma therapy to simultaneously increase immunogenic signals and reduce immunosuppressive ones. ABSTRACT: Non-thermal plasma (NTP) therapy has been emerging as a promising cancer treatment strategy, and recently, its ability to locally induce immunogenic cancer cell death is being unraveled. We hypothesized that the chemical species produced by NTP reduce immunosuppressive surface proteins and checkpoints that are overexpressed on cancerous cells. Here, 3D in vitro tumor models, an in vivo mouse model, and molecular dynamics simulations are used to investigate the effect of NTP on CD47, a key innate immune checkpoint. CD47 is immediately modulated after NTP treatment and simulations reveal the potential oxidized salt-bridges responsible for conformational changes. Umbrella sampling simulations of CD47 with its receptor, signal-regulatory protein alpha (SIRPα), demonstrate that the induced-conformational changes reduce its binding affinity. Taken together, this work provides new insight into fundamental, chemical NTP-cancer cell interaction mechanisms and a previously overlooked advantage of present NTP cancer therapy: reducing immunosuppressive signals on the surface of cancer cells.