Auranofin synergizes with cisplatin in reducing tumor burden of Notch-dependent ovarian cancer.

The Notch pathway regulates cell proliferation, differentiation, and stem cell maintenance. Thus, aberrant Notch activation plays a key role in cancer initiation, progression, and chemoresistance. Mutations and amplification of Notch pathway genes have been identified in high-grade serous ovarian cancers and are associated with poor clinical outcomes. Among the four Notch receptors, Notch3 alterations were strongly correlated with poor overall survival. Previously, we identified auranofin, an oral gold salt therapeutic compound, as a novel Notch pathway inhibitor that disrupts the DNA binding of RBPJ, the major downstream transcriptional effector of the Notch pathway. Here, we surveyed the response of eight ovarian cancer cell lines to auranofin and found IC50 values ranging from 1.7 to 12 µM, with Notch3-negative SKOV3 cells having the highest IC50 value. In Notch-dependent OVCAR3 cells, auranofin synergized with cisplatin to enhance cell death. Importantly, auranofin treatment led to a dose-dependent decrease in RBPJ occupancy at the Notch-dependent promoters, HES1 and HES4. Furthermore, knocking down Notch3 in OVCAR3 cells significantly decreased sensitivity to auranofin, further supporting the notion that Notch3 signaling is a major target of auranofin. Moreover, auranofin increased cisplatin efficacy in an OVCAR3-derived xenograft mouse model. Using eight patient-derived cancer organoid models, we found that auranofin increased cisplatin efficacy in killing cancer organoids generated from clinically platinum-sensitive patients but also restored platinum response in a subset of organoid models developed from platinum-resistant patients. These studies underscore the potential of auranofin to improve platinum-based cancer therapy, particularly in Notch3-expressing cancers.