P. Yan1,2, J. Zhang1,3, K. Tan1,2, Y. Ding1,2, Y. Li1,2, J. Zhang1,2, Y. Wu1,2, and L. Zhang1,3; 1Center for Cancer Diagnosis and Treatment, The Second Af?liated Hospital of Soochow University, Suzhou, Jiangsu, China, 2Center of PRaG therapy, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China, 3Center for Cancer Diagnosis and Treatment, The Second Af?liated Hospital of Soochow University, Suzhou, China
Purpose/Objective(s): Sensitizing microsatellite stable (MSS) colorectal cancer (CRC) to immunotherapy is a major challenge in the field of CRC immunotherapy. Immunotherapy-based combination radiotherapy (RT) is an effective strategy. How to give full play to the synergistic effect of radiotherapy and immunotherapy to improve the therapeutic effect of MSS CRC is a hot problem. NLRP3 is not only involved in inflammatory response activated by both exogenous and endogenous stimuli, but also yields antitumor responses in radiotherapy and innate immune system. However, whether NLRP3 participates in the immune priming and abscopal responses induced by radiotherapy combined with immunotherapy in MSS CRC remains unknown. Therefore, we employed bilateral subcutaneous transplantation tumor model of MSS CRC to clarify the role and mechanisms of NLRP3 in above problems. Materials/
Methods: 60 female Balb/c mice aged 6-8 weeks were divided into five groups: control group, aPD-1 group, RT group, RT +aPD-1 group and RT + aPD-1 + NLRP3i group. 1×105 CT26.WT cells was inoculated subcutaneously in the right thigh root and then the left thigh root 3 days later. Right subcutaneous tumor was selected for RT of 8 Gy×2 on the 12th day and PD-1 inhibitor (3mg/kg, i.p) was simultaneously given every 3 days. NLRP3 inhibitor was given (20mg/kg, i.p) before RT and then continued for four days. The proportion of immune cells was detected by flow cytometry. Results: Compared with the RT or aPD-1group, the combination therapy demonstrated a better synergistic effect validated by both the inhibited tumor progression of abscopal tumors and increased proportion of CD8+ T cells. However, NLRP3 inhibitor reversed the synergistic effect of combination therapy accompanied by tumor progression of abscopal tumors and decreased proportion of CD8+ T cells. Moreover, NLRP3 inhibition increased G-MDSCs proportion and decreased M1/M2 ratio. Conclusion: NLRP3 inhibition restricts the immune priming and abscopal responses induced by radiotherapy combined with immunotherapy in MSS CRC, suggesting that NLRP3 is a potential target in MSS CRC treatment.
