Inhibition of gamma-secretase activity impedes uterine serous carcinoma growth in a human xenograft model

• Uterine serous carcinoma (USC) exhibited increased Notch pathway expression compared to endometrioid carcinoma.
• Notch inhibition leads to in vitro and in vivo activities in the majority of USC cell lines and xenografts.
• Notch inhibition with paclitaxel and carboplatin leads to synergistic anti-tumor activity in subsets of USC patient derived xenografts (PDXs).

ObjectiveUterine serous carcinoma (USC) represents an aggressive subtype of endometrial cancer. We sought to understand Notch pathway activity in USC and determine if pathway inhibition has anti-tumor activity.MethodsPatient USC tissue blocks were obtained and used to correlate clinical outcomes with Notch1 expression. Three established USC cell lines were treated with gamma-secretase inhibitor (GSI) in vitro. Mice harboring cell line derived or patient derived USC xenografts (PDXs) were treated with vehicle, GSI, paclitaxel and carboplatin (P/C), or combination GSI and P/C. Levels of cleaved Notch1 protein and Hes1 mRNA were determined in GSI treated samples. Statistical analysis was performed using the Wilcoxon rank sum and Kaplan–Meier methods.ResultsHigh nuclear Notch1 protein expression was observed in 58% of USC samples with no correlation with overall survival. GSI induced dose-dependent reductions in cell number and decreased levels of cleaved Notch1 protein and Hes1 mRNA in vitro. Treatment of mice with GSI led to decreased Hes1 mRNA expression in USC xenografts. In addition, GSI impeded tumor growth of cell line xenografts as well as UT1 USC PDXs. When GSI and P/C were combined, synergistic anti-tumor activity was observed in UT1 xenografts.ConclusionsNotch1 is expressed in a large subset of USC. GSI-mediated Notch pathway inhibition led to both reduced cell numbers in vitro and decreased tumor growth of USC some xenograft models. When combined with conventional chemotherapy, GSI augmented anti-tumor activity in one USC PDX line suggesting that targeting of the Notch signaling pathway is a potential therapeutic strategy for future investigation.