427P Targeting adenosine (ADO) to improve the efficacy of combinations of cetuximab (CET) and immunotherapy in EGFRvIII MSS colorectal cancer (CRC)

Abstract

The majority (∼85%) of CRCs that are microsatellite stable (MSS) are largely unresponsive to immunotherapy due to the lack of immune infiltration and low tumor mutation burden. Here, we demonstrated the value of EGFRvIII, a tumor-specific EGFR mutant, as the biomarker for patient stratification and explored therapeutic targets to convert cold tumors into responsive hot tumors. To identify EGFRvIII and assess immune infiltration, peripheral blood and tumor sections from newly diagnosed CRC patients and those receiving first-line CET-based chemotherapy were collected for circulating tumor cells (CTCs) detection and immunofluorescence (IF) staining. Sequencing data of CRC patients from TCGA was utilized for GSVA analysis to determine tumor immune microenvironment (TIME) phenotype. In total, EGFRvIII was identified in CTCs from 12% (14/115) of untreated CRC patients. Besides, 49 patients treated with CET were included in our analysis. The ORR of patients with baseline expression of EGFRvIII in CTCs (n=14) was decreased (14.3% vs 37.1%) accompanied with shorter TTP (median 5.5 vs 9.1 months, P=0.0086). CET resistance of MC38 EGFRvIII tumors diminished in immunodeficient nude mice, revealing the critical role of immune system in CET efficacy. GSVA analysis of TCGA MSS CRC cohort (n=192) showed that the TIME of EGFRvIII CRC was classified as immune-desert phenotype, characterized by the suppression of immunity. In CET treatment cohort, IF staining showed the significantly reduced infiltration of CD8+T cells and increased PD-L1 expression in EGFRvIII tumors compared with wild-type tumors. Subsequent experiments found that EGFRvIII CRC facilitated the conversion of pro-inflammatory extracellular ATP into immunosuppressive ADO, thus escaped from immunogenic cell death triggered by CET. Combined treatment of ADO pathway inhibitors restored the infiltration and anti-tumor activities of immune cells, indicating the potential application of second-line immune therapy in EGFRvIII MSS CRC. ADO-mediated suppressive TIME resulted in declined CET efficacy in EGFRvIII MSS CRC. Regulating ATP-to-ADO conversion remodeled TIME and may pave the way for immunotherapy.