Abstract 1816: β-catenin antagonist peptide attenuates oncogenic gene transactivation and promotes antitumor activity in breast cancer models

Abstract

Abstract Aberrant activation of the canonical Wnt signaling pathway occurs in a variety of cancers, resulting in overactivation of β-catenin-mediated transcriptional activity and increased expression of genes that promote tumor survival, proliferation and inhibit differentiation. Disruption of the β-catenin transcription complex, by inhibiting protein-protein interactions required for its formation, represents a powerful approach to inhibit this previously ‘undruggable' target. The goal of these experiments is to characterize the anti-tumor activity of β-catenin antagonist peptides, BCA1 and BCA2, designed to disrupt the β-catenin transcription complex, in breast cancer models. In in vitro experiments, MCF7 (HER2neg/HRpos) breast adenocarcinoma cells were exposed to β-catenin antagonist peptides, and the impact on β-catenin-mediated gene transactivation was determined by quantitative polymerase chain reaction (qPCR). Results indicate that β-catenin antagonist peptide attenuated oncogenic gene transactivation in MCF7 cells, significantly decreasing the expression of direct β-catenin target genes including Myc, Cyclin D1 and Cyclin-dependent kinase 4 (p<0.05). The impact of β-catenin antagonist peptides on cancer cell viability was quantified by annexin V/PI flow cytometry analysis, indicating a dose-dependent decrease in overall cell viability 48 hours post peptide exposure. Additionally, BCA1 was administered to primary breast cancer tumoroids (HER2pos/HRneg or HER2neg/ HRneg), and the impact on tumoroid viability was quantified by histology and immunofluorescence microscopy. β-catenin antagonist peptide BCA1 resulted in dose-dependent decrease in surviving HER2pos/HRneg and HER2neg/ HRneg breast cancer tumoroids, with EC50 values of 5.2 and 6.9 µM, respectively. Finally, the impact of BCA2, an analogue of BCA1 with an additional N-terminal modification, on subcutaneous MCF7 xenograft tumors was determined in vivo. Administration of 5 mg/kg BCA2 via subcutaneous injection at a dosing frequency of 3x/week for 3 weeks resulted in 18-day tumor regression from the start of treatment and a 63.1% tumor growth inhibition compared to vehicle-treated controls (p<0.05). Taken together, these data demonstrate the significant anti-breast cancer activity of β-catenin antagonist peptides in vitro and in vivo. Citation Format: Jim A. Rotolo, Lila Ghamsari, Erin Gallagher, Rick Ramirez, Mark Koester, Siok Leong, Gene Merutka, Barry J. Kappel. β-catenin antagonist peptide attenuates oncogenic gene transactivation and promotes antitumor activity in breast cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1816.