Abstract 964: β-catenin antagonist peptide attenuates Wnt-dependent oncogenic activity

Abstract

Abstract β-catenin is an oncogenic transcription factor that has an essential role in cell development and biology. Increased β-catenin expression or activity has been implicated in many cancers, including breast and colorectal, and is associated with poor prognosis. Despite extensive ongoing research, β-catenin is conventionally considered ‘undruggable', and there are no current drugs available to target Wnt/β-catenin signaling. B-cell CLL/lymphoma 9 protein (BCL9) is a positive regulator of β-catenin transcriptional activity that is overexpressed in tumors. Disruption of β-catenin interaction with BCL9 has been shown genetically to suppress oncogenic Wnt/β-catenin transcription and represents a powerful approach to inhibit this previously undruggable target. Here, we describe the anti-tumor activity of a β-catenin antagonist peptide (BCAP), designed to disrupt the association of β-catenin with co-activator BCL9. Target engagement of BCAP with recombinant β-catenin was demonstrated in biophysical studies by circular dichroism spectroscopy, and inhibition of the β-catenin/BCL9 interaction was demonstrated in transiently transfected A549 cells by NanoBRET assay. Administration of BCAP to HEK293 cells stably transfected with TOPFlash reporter plasmid resulted in dose-dependent inhibition with an EC50 of 1.7 µM. Further, BCAP attenuated oncogenic gene transactivation in colorectal cancer cells (HCT116 and COLO320DM) and HRPOS breast cancer cells (MCF7), significantly decreasing the expression of Axin2 and CDK4 (p<0.05), while not impacting Axin2 or CDK4 gene expression in Wnt-independent RKO and NCI-H460 cells. Administration of BCAP to 4T1-luc triple-negative breast cancer, HCT116 and COLO320DM cells resulted in dose-dependent in vitro cytotoxicity 48 hours post exposure, with EC50 values of 1.4, 4.4 and 1.2 µM, respectively. In in vivo orthotopic 4T1-luc tumor models, administration of BCAP via subcutaneous injection resulted in dose-dependent inhibition of tumor growth and significantly reduced tumor volume compared to control tumors (p<0.05). These data demonstrate the significant in vitro and in vivo anti-cancer activity of BCAP and emphasize it's potential as a potent therapeutic for Wnt/β-catenin-dependent cancers. Citation Format: Jim A. Rotolo, Erin Gallagher, Lila Ghamsari, Siok Leong, Ricardo Ramirez, Mark Koester, Gene Merutka, Barry J. Kappel. β-catenin antagonist peptide attenuates Wnt-dependent oncogenic activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 964.