Abstract 2567: Targeting TBL1/β-catenin complex using peptides designed to competitively inhibit aberrant Wnt signaling in cancer

Abstract Purpose: Canonical Wnt signaling is a key cascade in regulating development and stemness, however it can become dysregulated and tightly associated with oncogenesis. In human cancers, Wnt/β-catenin signaling is highly activated due to mutations of members associated with the pathway such as adenomatous polyposis coli (APC) and β-catenin. Transducin β-like protein 1 (TBL1) and highly related TBLR1, form a complex with β-catenin facilitating the translocation of β-catenin to the nucleus. The formation of this complex protects β-catenin from degradation by SIAH-1 ubiquitinase and aids β-catenin binding to TCF/LEF transcription factors to transcribe downstream Wnt target genes. We recently reported that the destruction of the TBL1/β-catenin complex using a small molecule results in ubiquitination of β-catenin and inhibition of downstream signaling. As an alternative approach, we designed a series of novel peptides to interfere with binding of β-catenin with TBL1. Methods: Homologous competitive ELISA and thermal shift assays were performed to identify potential peptides that were able to displace β-catenin from TBL1. Additionally, we evaluated the ability of the peptides to disrupt the TBL1/β-catenin complex by performing pull-down assays and monitored the levels of β-catenin ubiquitination in response to peptide treatment in colon cell lines. To assess the levels of TCF/LEF transcriptional activation downstream the Wnt/β-catenin pathway, we performed TOPFlash assays in Wnt-activated cells transfected with plasmids for peptide expression. Results: Our preliminary results identified a set of peptides that efficiently displaces β-catenin from TBL1. Homologous competitive ELISA showed that the peptides were able to displace β-catenin from TBL1 in a dose dependent manner. The top five peptide hits were then tested for their ability to inhibit Wnt signaling using the TOPFlash assay. Among these, one peptide in particular showed high efficiency in inhibiting TCF/LEF transcriptional activation downstream the Wnt/β-catenin pathway. Our study suggests that β-catenin therapeutic peptides may represent a new and exciting approach for Wnt driven cancer therapy. Citation Format: Shelby Rheinschmidt, Trason Thode, Samuel Sampson, Alexis Weston, Tithi Ghosh Halder, Serina Ng, Ryan Rodriguez del Villar, Mohan Kaadige, Anton Zernov, Marcelle Machluf, Raffaella Soldi, Sunil Sharma. Targeting TBL1/β-catenin complex using peptides designed to competitively inhibit aberrant Wnt signaling in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2567.