Abstract PO043: Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer
Authors: Moroney Marisa R. , Woodruff Elizabeth R. , Qamar Lubna , Bitler Benjamin G. , Corr Bradley R. 
Published: February 2021

Background: CTNNB1 mutations convey increased rates of disease recurrence in early stage, low grade endometrial cancer (EC). The role of beta-catenin transcriptional activity in CTNNB1-mutated EC recurrence is not well understood. We aim to assess the impact of Wnt/beta-catenin inhibition in EC models.

Methods: Data mining The Cancer Genome Atlas (TCGA) of endometrial carcinoma (PanCancer Atlas), we evaluated CTNNB1-mutated vs -wildtype tumors in a low-risk population. We then studied EC cell lines that are CTNNB1-wildtype (HEC1B, Ishikawa) or CTNNB1-mutated (HEC108, HEC265, HEC1B-S33Y, Ishikawa-S33Y). CTNNB1-S33Y cell lines were created via retroviral transduction. Treatment dose 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. Tumor cell proliferation and apoptosis were evaluated with immunohistochemistry for Ki67 and Cleaved Caspase 3.

Results: TCGA database analysis parallels previous findings that CTNNB1 mutations are enriched in recurrent low-risk EC. XAV939, Wnt-C59 and PyrPam all inhibit function upstream of beta-catenin transcriptional activity and were ineffective at inhibiting EC cell viability. In contrast, PRI724 and SM04690 indirectly inhibit beta-catenin transcriptional activity and significantly reduce cell viability in CTNNB1-mutated 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%, 71.4%, p&lt;0.01). Compared to control, SM04690 significantly induced apoptosis in HEC265 cells (3.98% vs. 6.91% AnnexinV/PI+, p=0.0443) and reduced TCF transcriptional activity in HEC1B-S33Y (-84%, p=0.017) and HEC108 (-74%, p=0.002) cells. In the mouse model, HEC1B, HEC1B-S33Y and HEC265 tumors treated with SM04690 had smaller mean tumor volumes than those treated with vehicle (146.4 vs 335.4cm3, p&lt;0.001; 136.4 vs. 243.1cm3, p=0.014; 105.7 vs. 321.8cm3, p=0.06). In HEC1B-S33Y tumors, SM04690 treatment significantly reduced Ki67 H-scores compared to vehicle (129.8 vs. 146.7, p=0.0351).

Conclusions: Targeting the Wnt/beta-catenin pathway in CTNNB1-mutated EC effectively inhibited proliferation and beta-catenin/TCF transcriptional activity. Further, the inhibitor SM04690 blunted tumor progression in multiple in vivo models. These studies demonstrate beta-catenin transcriptional inhibitors are effective in CTNNB1-mutated EC and have a more significant effect in CTNNB1-mutated EC than CTNNB1-wildtype EC. These findings highlight a potential therapeutic vulnerability for treatment of CTNNB1-mutated EC.

Citation Format: Marisa R. Moroney, Elizabeth R. Woodruff, Lubna Qamar, Benjamin G. Bitler, Bradley R. Corr. Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO043.