Activation of the γ-secretase/NICD-PXR/Notch pathway induces Taxol resistance in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is currently the only subtype lacking efficient targeted therapies. Taxol is the primary chemotherapeutic agent for TNBC. However, Taxol resistance often develops in the treatment of TNBC patients, which importantly contributes to high mortality and poor prognosis in TNBC patients. Recent preclinical studies have shown that the inhibition of Notch pathway by γ-secretase inhibitors can slow down the progression of TNBC. Our studies in bioinformatic analysis of breast cancer patients and TNBC/Taxol cells in vitro showed that there was high correlation between the activation of Notch pathway and Taxol resistance in TNBC. Increased γ-secretase activity (by the overexpression of catalytic core PSEN-1) significantly reduced Taxol sensitivity of TNBC cells, and enhanced biological characteristics of malignancy in vitro, and tumour growth in vivo. Mechanistically, increased γ-secretase activity led to the accumulation of NICD in the nucleus, promoting the interaction between NICD and PXR to activate PXR, which triggered the transcription of PXR downstream associated drug resistance genes. Furthermore, we showed that pharmacological inhibition of γ-secretase with γ-secretase inhibitors (Nirogacestat and DAPT) can reverse Taxol resistance in vivo and in vitro. Our results for the first time demonstrate that the activation of γ −secretase/NCD-PXR/Notch pathway is one of important mechanisms to cause Taxol resistance in TNBC, and the blockades of this pathway may represent a new therapeutic strategy for overcoming Taxol resistance in TNBC.