Brucein D augments the chemosensitivity of gemcitabine in pancreatic cancer via inhibiting the Nrf2 pathway

Background: Gemcitabine (GEM) is a chemotherapeutic drug used to treat pancreatic ductal adenocarcinoma carcinoma (PDAC), but chemoresistance is often encountered clinically. Nrf2, an oxidative stress responsive transcription factor, is an important contributor to chemoresistance and is closely associated with poor prognosis of PDAC. Brucein D (BD), a natural compound has been reported to exert anti-tumor effect in several cancers including PDAC. In this study, we aimed to investigate the efficacy of the BD and Nrf2 axes on the chemosensitivity of GEM and attempted to elucidate its underlying mechanism. Methods Clinical study and GEPIA database analysis was first conducted to identify the expression of Nrf2 in PDAC. We then established cell lines with stable deletion of Nrf2 through lentivirus transfecting into PDAC cells. Quantitative real-time PCR (qRT-PCR) and Western blotting were performed to measure the expression of Nrf2. The effects of BD and Nrf2 axes on PDAC cell proliferation, colony-formation, tumor growth and chemosensitivity were determined both in vitro and in vivo . Orthotopic xenograft and genetically engineered KPC mouse models of PDAC were used to evaluate the anti-cancer effects of BD and GEM. Results Nrf2 was highly expressed in PDAC from clinical study and GEPIA analysis. Gain-and lost-function study demonstrated that Nrf2 aggravated the chemosensitivity of GEM of PDAC cells both in vitro and in vivo . We further found that BD efficiently inhibited PDAC cells proliferation and enhanced the chemosensitivity of GEM. Mechanistic studies revealed that BD sensitized the GEM in PDAC cells through the ubiquitin-proteasome-dependent degradation of Nrf2, and then downregulate the Nrf2 pathway. Silencing of Nrf2 plus BD resulted in a better inhibitory effect of GEM. In contrast, Nrf2 activation aggravated the chemosensitivity of GEM, indicating that the action of BD was Nrf2 dependent. Furthermore, the efficacy of BD alone and in combination with GEM was validated on both orthotopic xenograft and genetically engineered KPC mouse models. Conclusions BD was proven to enhance the chemosensitivity of GEM in PDAC through inhibition of the Nrf2 pathway. Our experimental findings indicate that BD, a potent Nrf2 inhibitor, holds promise for further development into a novel adjuvant therapy for PDAC.