Abstract LB045: β-catenin antagonist peptide, ST316, attenuates Wnt-dependent oncogenic activity

Abstract

Abstract Constitutive activation of the Wnt/β-catenin signaling pathway underlines many breast and colorectal cancers, promoting cancer cell survival, proliferation and migration. B-cell CLL/lymphoma 9 protein (BCL9), a co-activator of β-catenin transcriptional activity, is overexpressed in many tumors and facilitates β-catenin nuclear localization. Disruption of the β-catenin and BCL9 interaction has been shown genetically to suppress oncogenic Wnt/β-catenin transcription, without impacting β-catenin homeostatic functions, and represents a powerful approach to inhibit this previously ‘undruggable’ target. Here, we investigate the impact of ST316, a peptide antagonist of β-catenin that inhibits its interaction with BCL9, on cells displaying hyperactivation of the Wnt/β-catenin pathway. Administration of ST316 to HCT116 human colorectal carcinoma cells, which carry a degradation-escape, gain-of-function mutation in β-catenin, dramatically reduced nuclear β-catenin localization. Furthermore, ST316-mediated loss of nuclear β-catenin was associated with a significant decrease in the expression of Wnt/β-catenin target genes in HCT116 cells stimulated with Wnt3a, including Axin2, hTCF7, Fox01 and CDK4. ST316 reduced β-catenin target gene expression by up to ∼70%, whereas no impact was observed following administration of a negative control peptide. A significant anti-proliferative and dose-dependent cytotoxic effect was observed on HCT116 cells 48 hours post ST316 exposure, with an EC50 of 4.4 µM, and on patient-derived, APC-mutant colorectal adenocarcinoma and breast carcinoma cells 72 hours post ST316 exposure, with EC50 values ranging from 1.5 to 2.6 µM. To extend these findings, we investigated the impact of ST316 on HCT116 tumors in vivo. ST316 (5 mg/kg) administered three times weekly by subcutaneous injection resulted in 99.6% tumor growth inhibition vs. vehicle controls (p<0.05), while a negative control peptide had no significant impact on tumor growth. These data demonstrate the potential of ST316 as a potent therapeutic candidate for Wnt/β-catenin-dependent cancers. Citation Format: Lila Ghamsari, Erin Gallagher, Emad Darvishi, Siok Leong, Mark Koester, Rick Ramirez, Jerel Gonzales, Gene Merutka, Barry Kappel, Jim A. Rotolo. β-catenin antagonist peptide, ST316, attenuates Wnt-dependent oncogenic activity [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 LB045.