2993 - Analyzing the Changes of Inflammation-related Cytokines by Using Olink immunoassay during Treatment of SCRT Combined with ICI in Proficient Mismatch Repair locally advanced Rectal Cancer

M. He III¹, H. Li², Y. Chen², J. Shi², W. Zhang¹, L. Feng¹, Y. Mu¹, T. Xu², Y. Tang³, D. Li⁴, J. Jin¹, and N. J. Xiao⁵; ¹Department of Radiation Oncology, National Cancer Center / National Clinical Research Center for Cancer / Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, ²State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (PUMC), Beijing, China, ³Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ⁴State Key Laboratory of Molecular Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ⁵National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, Guangdong, China

Purpose/Objective(s): Great breakthroughs with immune checkpoint inhibitors (ICIs) have been observed in the treatment of colorectal cancer with deficient mismatch repair(dMMR). However, PD-1 blockade immunotherapy in proficient mismatch repair (pMMR) rectal cancer is still ineffective.Hypofractionated Radiotherapy activates the “cold” immune environment to enhance the anti-tumor effect of PD-1 blockade, but the mechanism is still unknown. Circulating inflammation-related cytokines could reflect the systematic immune status closely related to the tumor microenvironment (TME) and PD-1 blockade response. This study aims to explore the impact of Short-Course hypofractionated Radiotherapy (SCRT) on inflammation-related cytokines in patients with pMMR/MSS LARC. Materials/

Methods: STELLAR II study is a prospective, multicenter, two-arm randomized controlled, seamless phase II/III trial for pMMR/MSS LARC(NCT05484024). Patients in both groups will receive SCRT (25 Gy/5 fx) followed by 4 cycles of CAPOX or 6 cycles of mFOLFOX, with the iTNT group receiving the same chemotherapy in combination with Sintilimab(a PD-1 inhibitor). The peripheral blood samples of pre- and post-SCRT treatment of patients with LARC from STELLAR II study were collected. In the present study, the expression levels of 48 inflammation-related proteins were measured in the plasma samples from 20 patients randomly selected from the iTNT group of STELLAR II study using the Olink inflammation panel based on the highly sensitive and specific proximity extension assay technology. Analyses were done with edgeR.The heatmap was generated by analyzing the protein expression of each group. GO term analysis suggested that DEGs are enriched in terms of cellular metabolic processes. A adjusted p-value <0.05 was considered significant.
Results: The pro-tumor neutrophil-associated cytokines Interleukin-8 (IL-8,CXCL8) (p = 0.00402) and Lectin-type oxidized LDL receptor 1 (LOX-1) (p = 0.000869) were significantly decreased after SCRT. IL-8 is a cytokine that mediates its functions through activating an immunosuppressive neutrophil-enriched TME with poor T cell responsiveness in many solid malignancies. LOX-1 encoded by OLR1 was a biomarker of pro-tumor neutrophil. Simultaneously, the ligand FTL3LG, which binds to FLT3 on dendritic cells, leading to enhanced tumor antigen cross-presentation and anti-tumor response, was significantly upregulated (p = 0.0227). The analysis of gene enrichment shows chemotaxis, activation and migration related pathways of neutrophils were regulated after SCRT.These findings suggest that SCRT may downregulate neutrophils of pro-tumor phenotype, thereby stimulating the T cell anti-tumor immune response to enhance PD-1 inhibitor immunotherapy.
Conclusion: These results suggest that SCRT can reshape the TME of LARC by downregulating neutrophils of pro-tumor phenotype, stimulating the T cell anti-tumor response and thus playing an potential important role in synergistic PD-1 blockade.