Abstract 1285: Chemotherapy induces PD-L1 overexpression in CRC through NF-κBp65

Abstract Background: The programmed cell death ligand (PD-L1) is an immune-inhibitory molecule that suppresses the activation of T cells, leading to the survival and growth of tumors. Overexpression of PD-L1 on cancer cells is associated with poor clinical outcomes in many types of cancers. PD-L1 upregulation contributes to chemoresistance in several types of cancer, but little is known about the mechanisms for alterations in PD-L1 expression associated with chemotherapy, especially in patients with CRC. Therefore, a better understanding of the mechanisms underlying changes in PD-L1 levels in response to standard of care chemotherapeutics in CRC is important. In this study, we examined the effects of thechemotherapeutics that are approved for the treatment of patients with CRC (oxaliplatin, 5FU, and irinotecan whose metabolite is SN38) in inducing PD-L1 expression and determining the molecular pathwaysinvolved in PD-L1 regulation. Methods: PD-L1 expression in CRC cell lines was determined in vitro using western blotting and FACS analysis. Changes in PD-L1 transcript levels were measured using real time PCR. RPPA analyses were performed to identify proteins/pathways affected by chemotherapeutics. Pharmacological inhibitors and siRNAs were used to target specific proteins in determining their role in PD-L1 expression. Results: We observed that oxaliplatin, 5FU, and SN38, resulted in induction of PD-L1 to various degrees. Interestingly this induction was observed in KRAS or BRAF mutated CRC cells but not in CRC cells with wild-type KRAS and BRAF. Increased levels of PD-L1 were due to increased transcription of PD-L1 resulting from exposure to chemotherapeutics. Chemotherapeutics lead to the activation of the DNA damage signaling mediator Chk1 and the downstream transcription activator NF-κBp65. Inhibition of Chk1 or NF-κBp65 resulted in abrogated PD-L1 induction in response to chemotherapeutic treatment. Conclusion: PD-L1 can be induced following treatment with chemotherapy in CRC cells harboring mutations in BRAF or KRAS. Our findings provide a rationale for studies combining inhibitors of NF-κBp65 with standard of care chemotherapeutics in CRC to block PD-L1 expression and enhance the efficacy of chemotherapy damaged-tumor cell clearance by innate immunity that, in turn, should improve patient outcomes. Citation Format: Fan Fan, Susmita Ghosh, Lee Ellis, Rajat Bhattacharya. Chemotherapy induces PD-L1 overexpression in CRC through NF-κBp65 [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 1285.