Carbon Ion Radiotherapy Exerts Anti-Tumor Activity by Inducing cGAS-STING Activation and Immune Response in Prostate Cancer-Bearing Mice

Abstract

The aim of this study was to assess the influence on immune cell infiltration and T cell effector function to explore the immune response evoked by carbon ion radiotherapy (CiRT) in prostate cancer-bearing mice, and explored the mechanisms underlying CiRT-induced anti-tumor efficacy, involved in cGAS-STING signaling pathway. C57BL/6 and BALB/c nude mouse tumor models were used to evaluate the efficacy of CiRT on tumor growth. Activation of cGAS-STING signaling pathway was performed by immunofluorescence analysis of cytoplasmic double-stranded DNA, western blot analysis of key factors involved in cGAS-STING pathway, and qRT-PCR analysis of the key downstream molecules like CCL5, CXCL10 and IFNβ1. Investigation of alterations of immunophenotypes including the quantification, memory status, exhaustion marker expression, and effector function were assessed by flow cytometry. CiRT showed more powerful tumor growth control of immunocompetent syngeneic C57BL/6 mice than photon radiotherapy did at biological equivalent dose of 5Gy. CiRT induces cytoplasmic DNA and cGAS-STING activation, and is functionally responsible for the observed tumor growth suppression. CiRT exerts anti-tumor effect by triggering immune response, characterized by increased infiltration of CD4+ T cells and macrophages in tumor, enhanced frequencies of CD8+ T cells and CD8+ T effector memory cells in spleen, improved interferon (IFN)-γ production ability of CD8+ tumor-infiltrating lymphocyte cells, and reduced expression of exhausted T cells in tumor and spleen. Our findings indicate that CIRT exerts excellent anti-tumor activity, which may be attributed to the induction of cGAS-STING activation and immune response, manifested by increased immune cell infiltration, improved T cell effector function and enhanced immune memory.