Carbon ion irradiation induces DNA damage in melanoma and optimizes the tumor microenvironment based on the cGAS-STING pathway.

Abstract

Increased number of studies reveal the crucial role of the Cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) pathway in anti-tumor immunity. In this study, we aim to explore the effect of cGAS/STING on tumor immune microenvironment of melanoma after carbon ion radiotherapy (CIRT) and the underlying mechanism. C57BL/6 mouse tumor models were used to evaluate the efficacy of different treatments (X-ray, carbon ion, PD-L1 inhibitor and combination therapies) on tumor growth and process. Mass cytometry was performed to assess tumor-infiltrating lymphocytes (TILs). DNA damage response (DDR) and cGAS/STING pathway were investigated by immunofluorescence-co-localization assays, γ-H2AX, P53-binding protein 1 (53BP1), Breast Cancer 1 (BRCA1), and cGAS measurements. Carbon ion irradiation caused more DNA damages and cGAS-STING pathway activation compared with X-ray irradiation, and the former slowed the melanoma growth in syngeneic model. Although X-ray irradiation is not sensitive for melanoma treatment, carbon ion irradiation showed a significant anti-tumor effect for melanoma treatment. TILs analysis revealed that CIRT boosted the infiltration of natural killer (NK), CD4+, and CD8+ T cells, meanwhile increased the number of immune checkpoint (programmed death-1, PD-1, lymphocyte activation gene 3, LAG-3 and T-cell immunoglobulin and mucin domain-containing protein 3, TIM-3). Moreover, CIRT increased PD-L1 exposure on cell surface compared with X-ray group. Furthermore, CIRT combined with PD-L1 inhibitor therapy increased the number of T cells and NK cells in melanoma, and slowed the growth of melanoma compared with other therapies. Our findings showed that CIRT displayed biological effects by increasing DNA damages of tumor cells and improving immunity in melanoma, which indicated that CIRT might be a potential synergetic treatment for radiotherapy and radioimmunotherapy in melanoma patients. Our works put forward a new insight to provide an effective strategy for melanoma therapy. These findings may help in the design of strategies on melanoma in clinical studies.