KRAS-driven protein disulfide isomerase family A member 6 expression suppresses PRKR-like endoplasmic reticulum kinase-mediated immunogenic cell death to desensitise pancreatic ductal adenocarcinoma to immune checkpoint blockers

Background: Pancreatic ductal adenocarcinoma (PDAC) is characterised by a dismal prognosis and insensitivity to immune checkpoint blockers (ICBs); however, the underlying mechanism remains elusive. Objective: This study aimed to identify tumour cell-intrinsic regulators that promote immune evasion and ICB resistance in PDAC. Design: Multi-omics analysis and clinical cohort studies identified protein disulfide isomerase family A member 6 (PDIA6) as a regulator of the immune microenvironment. Flow cytometry, multiplex immunohistochemistry, electron microscopy and Glutathione S-Transferase (GST) pulldown assays confirmed that PDIA6 repressed PRKR-like endoplasmic reticulum kinase (PERK) activation and immunogenic cell death (ICD). Chromatin immunoprecipitation confirmed that KRASG12D and YY1 modulated PDIA6 transcription. LSL-Kras G12D/+ ;LSL-Trp53 R172H/+ ;Pdx-1-Cre (KPC) mouse models showed that PDIA6 inhibition improved ICB response. Results: Multi-omics screening identified PDIA6 as a biomarker of CD8+ T-cell paucity and poor prognosis in patients with PDAC. High PDIA6 levels predicted poor ICB response in the PDAC cohorts. PDIA6 inhibition reprogrammed the immunosuppressive tumour microenvironment and hindered mouse PDAC growth in the presence of CD8+ T-cell, which is attributed to enhanced ICD. PDIA6 interacted with cysteine 453 of PERK, abrogating the disulphide bond-mediated dimerisation and activation of PERK, an ICD inducer. Oncogenic KRASG12D potently upregulated PDIA6 via YY1-mediated transcriptional activation. We identified a small-molecule inhibitor of PDIA6, PACMA31, and demonstrated that targeting PDIA6 with PACMA31 improved ICB efficacy in a PDAC mouse model with KRAS mutations. Conclusions: PDIA6, driven by KRASG12D, alleviates ICD and promotes immune evasion, functioning as a predictive biomarker to screen ICB-sensitive patients and a therapeutic target to improve ICB efficacy in PDAC with KRAS mutations.