Heat shock factor 1 inhibition sensitizes pancreatic cancer to gemcitabine via the suppression of cancer stem cell-like properties.

Pancreatic cancer is a fatal disease with poor prognosis. Gemcitabine has been regarded as the mainstay of chemotherapy for pancreatic cancer; however, it is accompanied with a high rate of chemoresistance. Cancer stem cells (CSCs) are characterized by resistance to traditional chemo- and radiotherapies. We have previously reported that heat shock factor 1 (HSF1) is involved in the invasion and metastasis of pancreatic cancer, a highly conserved transcriptional factor that mediates the canonical proteotoxic stress response. Here, we investigate whether HSF1 contributes to the chemoresistance of pancreatic cancer cells caused by gemcitabine and explore the underlying mechanisms. Genetically engineered mice (LSL-Kras; Trp53; Pdx1-Cre mice), which spontaneously develop pancreatic cancer, were used to examine the sensitivity of pancreatic cancer to gemcitabine in vivo. We found that HSF1 was enriched in sphere-forming cancer cells. Panc-1 and MiaPaCa-2 cells treated chronically with gemcitabine displayed increased transcription and expression of CSC-associated markers. In addition, gemcitabine-surviving Panc-1 and MiaPaCa-2 cells showed an increased ability to form tumorspheres. Moreover, we observed that gemcitabine treatment increased the activity and expression of HSF1, as well as transcription of its downstream targets. Finally, HSF1 inhibition significantly suppressed the expression of CSC-associated markers, augmented the cancer-killing property of gemcitabine, and increased chemosensitivity to gemcitabine in vivo. Our study reveals a novel mechanism in which HSF1 promotes the chemoresistance of pancreatic cancer to gemcitabine by modulating CSC-like properties. Targeting HSF1 could be thus a rational strategy to improve treatment outcomes.