LAUSR

Objectives: CTNNB1 (gene encoding for beta-catenin) mutations convey increased rates of recurrence in early stage, low grade endometrial cancer (EC). The role of beta-catenin/TCF transcriptional activity in EC recurrence is not well understood. We aim to assess the impact of Wnt/beta-catenin inhibition in in vitro and in vivo EC models. Methods: Using The Cancer Genome Atlas (TCGA) of Uterine Corpus Endometrial Carcinoma (PanCancer Atlas), we evaluated CTNNB1-mutant vs -wildtype tumors in a low-risk population. We studied CTNNB1-wildtype (HEC1B, Ishikawa) and CTNNB1-mutant (HEC108, HEC265, HEC1B-S33Y, Ishikawa-S33Y) EC cell lines. CTNNB1-S33Y cell lines were created via retroviral transduction. Dose response curves were determined for 5 Wnt/beta-catenin pathway inhibitors (Wnt-C59, XAV-939, PyrPam, PRI-724, SM04690). Cell viability was assessed with Licor Cell Staining. TCF transcriptional activity was determined via TOP/FOP reporter assay. Apoptosis following treatment with SM04690 was evaluated via Annexin V/propidium iodide (PI). HEC1B, HEC1B-S33Y and HEC265 tumor-bearing athymic nude mice were treated with vehicle or SM04690 25mg/kg. Tumor size was measured using calipers. Tumors were evaluated with immunohistochemistry for proliferation (Ki67) and apoptosis (cl-caspase 3). Results: TCGA analysis confirmed that CTNNB1 mutations are enriched in recurrent low-risk EC and showed that aberrant Wnt/beta-catenin pathway activation is associated with disease recurrence. In vitro, XAV939, Wnt-C59 and PyrPam inhibited function upstream of beta-catenin transcriptional activity and were ineffective at inhibiting EC cell viability. In contrast, PRI724 and SM04690 indirectly inhibited beta-catenin transcriptional activity and significantly reduced cell viability in CTNNB1-mutant EC cell lines. Treatment with SM04690 reduced cell viability in all EC cell lines, but was significantly lower in HEC108, HEC265 and HEC1B-S33Y compared to HEC1B (24.2%, 32.3%, 44.4%, vs. 71.4%, p Conclusions: Targeting the Wnt/beta-catenin pathway in CTNNB1-mutant EC effectively inhibited proliferation and beta-catenin/TCF transcriptional activity. Further, the inhibitor SM04690 blunted tumor progression in in vivo models. These studies suggest beta-catenin transcriptional inhibitors are effective in EC and have a more significant effect in CTNNB1-mutant than -wildtype EC. These findings highlight a potential therapeutic vulnerability for treatment of CTNNB1-mutant EC.