Tumor treating fields (TTFields) enhance chemotherapy-induced proteotoxic stress in pancreatic cancer cells

Tumor Treating Fields (TTFields) have recently demonstrated a clinically meaningful survival benefit when added to first-line gemcitabine and nab-paclitaxel for unresectable, locally advanced pancreatic cancer (PANOVA-3). Pancreatic tumors are highly dependent on the unfolded protein response (UPR) to survive endoplasmic reticulum (ER) stress induced by hypoxia, nutrient deprivation, and cytotoxic chemotherapy. TTFields along with gemcitabine, nab-paclitaxel, and cisplatin (the Triple regimen) is under clinical investigation (NCT04605913) and may enhance antitumor efficacy by overwhelming the tumor's proteostasis mechanisms. In this study, we examined whether TTFields synergize with the Triple regimen to amplify ER stress and UPR signaling to trigger cell death in pancreatic cancer cells. TTFields showed frequency-dependent inhibition of cell proliferation (100-200 kHz) and significantly enhanced chemotherapy-induced cytotoxicity, with maximal effects at 150 kHz with a treatment duration of 72 hours. Western blot analysis revealed that both TTFields and the Triple regimen increased GRP78 expression, with significant greater induction observed when applied together, indicating augmented UPR activation. Immunofluorescence staining further demonstrated that TTFields elevated phospho-PERK and total PERK protein levels. In addition, RT-PCR analysis showed significant enhancement of XBP1 mRNA splicing by TTFields and chemotherapy. Collectively, these findings suggest that TTFields potentiate the antiproliferative effects of the Triple chemotherapy by amplifying UPR signaling through the IRE1alpha/XBP1 and PERK/eIF2 pathways. These results provide mechanistic insight into how TTFields may enhance the efficacy of chemotherapy in pancreatic cancer and support further clinical evaluation of this concomitant treatment approach.