Abstract 1352: In vivo CRISPR screening identifies mediators of immune evasion in KRAS-mutant lung cancer

Oncogenic KRAS mutations drive tumourigenesis in 30% of non-small cell lung cancer (NSCLC). Despite much effort, targeted therapies that aim to directly inhibit signalling pathways downstream of KRAS have limited clinical benefits for NSCLC patients, but the recent approval of PD-1/PD-L1 antibodies has led to striking durable responses. However, only a fraction of patients respond and therefore a deeper understanding of the mechanisms that drive immune evasion are required in order to broaden the clinical efficacy of immunotherapy. Increasing evidence suggests that oncogenic signalling pathways greatly influence the tumour immune landscape to impair anti-tumour immune responses. We therefore aim to understand the mechanisms by which KRAS signalling mediates immune evasion in lung cancer. Current mouse models of KRAS-mutant lung cancer are poorly immunogenic, limiting investigations into tumour-immune interactions. To overcome this, we generated a novel transplantable KRAS-mutant lung cancer model, KPAR1.3, which triggers spontaneous anti-tumour immune responses and is sensitive to immune checkpoint blockade. To identify mechanisms of immune evasion we carried out an in vivo pooled CRISPR-Cas9 screen targeting 240 KRAS-regulated genes using this novel immunogenic model. This identified the prostaglandin synthase COX-2 as a mediator of immune evasion and its expression was driven by KRAS in multiple models of mouse and human lung cancer. Loss of COX-2 promoted a pro-inflammatory tumour microenvironment and sensitised tumours to both innate and adaptive anti-tumour immune responses. Furthermore, therapeutic COX inhibition extended the survival of tumour-bearing mice and synergised with PD-1 blockade. Together these data suggest that targeting KRAS-driven mechanisms of immune evasion could broaden the clinical efficacy of immunotherapy in KRAS-mutant NSCLC. Since the approval of immunotherapy, a novel class of mutant-specific KRAS-G12C inhibitors have recently been approved for the treatment of KRAS-mutant NSCLC, however acquired drug resistance is common. We are therefore also currently investigating whether the inhibition of the COX-2/PGE2 axis enhances the therapeutic benefit of KRAS-G12C inhibitors. Citation Format: Jesse Boumelha, Pablo Romero-Clavijo, Sophie de Carné, Miriam Molina-Arcas, Julian Downward. In vivo CRISPR screening identifies mediators of immune evasion in KRAS-mutant lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1352.