Abstract B149: Anti-tumor and immunostimulatory properties of ST316, a peptide antagonist of beta-catenin for treatment of cancers with aberrant Wnt pathway activity
Authors: Ghamsari Lila , Scuoppo Claudio , Gallagher Erin , Leong Siok , Koester Mark , Ramirez Rick , Mattes Zachary , Gonzales Jerel , Merutka Gene , Kappel Barry , Vainstein Abi , Rotolo Jim 
Published: December 2023

Abstract
Beta-catenin represents a significant challenge as a therapeutic target due to its multifaceted role in tumor development as well as normal cell homeostasis. Dysregulation of the Wnt/beta-catenin signaling pathway is implicated in various cancers, including colorectal, hepatocellular, breast, ovarian, and pancreatic cancers. We developed ST316 as a peptide antagonist of the interaction of beta-catenin with BCL9, a co-activator implicated in oncogenic beta-catenin signaling. ST316 is currently being evaluated in a Phase 1-2 study (NCT05848739) that is currently enrolling patients with selected advanced solid tumors likely to harbor abnormalities of the Wnt/beta-catenin signaling pathway. In vitro studies indicate that ST316 selectively attenuates Wnt transcriptional activity in beta-catenin-dependent but not -independent cell lines. Gene expression profiling using RNA sequencing in beta-catenin mutant HCT116 cells and APC mutant Colo320DM cells demonstrates a significant downregulation of Wnt pathway target genes, oncogenic signature genes and pro-tumor immunologic gene sets within 24 hours of ST316 treatment. Consequently, ST316 induced a dose-dependent decrease in viability of beta-catenin-dependent cells while beta-catenin-independent cells were resistant, indicating that the anticancer effects of ST316 are mediated by inhibition of the Wnt/beta-catenin pathway. To evaluate the impact of ST316 in vivo, a 4T1 triple negative breast cancer orthotopic tumor model was employed. Once weekly injection of ST316 (5mg/kg SC) over eight weeks suppressed expression of Wnt target genes CDK4 and cMyc and resulted in a significant 84.3% inhibition of tumor growth compared to the control group. In addition to direct anti-tumor activity, ST316 triggers a pro-inflammatory immune microenvironment. ST316 induces polarization of human macrophages derived from peripheral blood mononuclear cells, resulting in &gt;100-fold shift from immunosuppressive M2 macrophages towards the anti-tumor M1 phenotype. Co-cultures of M2 macrophages with T cells treated with ST316 demonstrate a significant three-fold increase in T-cell activation, as indicated by intracellular IFN-γ staining. Finally, ST316 enhances the anti-tumor activity of anti-PD-1 therapy in a syngeneic orthotopic 4T1 mouse model, where combination ST316 and anti-PD-1 antibody results in enhanced tumor growth inhibition compared to either single agent alone (p&lt;0.01). These findings demonstrate the antitumor and immunostimulatory effects of ST316 and highlight its potential as a therapeutic agent for targeting cancers with aberrantly activated Wnt signaling pathways.
Citation Format: Lila Ghamsari, Claudio Scuoppo, Erin Gallagher, Siok Leong, Mark Koester, Rick Ramirez, Zachary Mattes, Jerel Gonzales, Gene Merutka, Barry Kappel, Abi Vainstein, Jim Rotolo. Anti-tumor and immunostimulatory properties of ST316, a peptide antagonist of beta-catenin for treatment of cancers with aberrant Wnt pathway activity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B149.