{
  "abstract": "Background Myeloid-derived suppressor cells (MDSCs) are prevalent in several hard-to-treat cancers and contribute to immune escape and an immunosuppressive tumor microenvironment (TME). Despite great interest in their role in therapy responses and potential as therapeutic targets, the pathways responsible for MDSCs derivation and maintenance are incompletely defined. Activating mutations of the Wnt/b-catenin pathway are frequent oncogenic drivers in colorectal cancer (CRC) that promote immune escape, however the specific role of Wnt/b-catenin signaling in immunosuppressive cell types such as MDSCs is poorly defined. ST316 is a peptide antagonist of the interaction between b-catenin and its co-activators BCL9/BCL9L that is currently in a phase II clinical study for advanced CRC in combination with standard-of-care agents ( NCT05848739). We identified a significant decrease in polymorphonuclear (PMN)-MDSCs in peripheral blood (PB) of phase I patients following ST316 monotherapy. Here we explore the impact of ST316 on PMN-MDSC development and immunosuppressive activity in vivo and in vitro.Methods Circulating PMN-MDSCs from syngeneic CT-26 tumor-bearing Balb/c mice were assessed by flow cytometry. PMN-MDSC origin and differentiation were assessed by in vivo tracking of PMN-MDSCs collected and sorted from CT-26 tumor-bearing mice, labeled and transplanted into naïve or tumor-bearing recipients. Tumor, spleen and bone marrow isolates from recipients were analyzed by flow cytometry for MDSCs content, precursor cells and T cell infiltration and activation. Suppressor assays were performed by co-culture of T-cells with MDSCs and tumor cells exposed to control or ST316. T-cell responses were determined by CFSE dilution and IFN-γ and Granzyme B expression by flow cytometry.Results PMN-MDSC precursor populations are generated in the bone marrow in Wnt/b-catenin-driven CRC and are significantly reduced following ST316 exposure, leading to reduced PMN-MDSCs frequency. PMN-MDSC gene expression profiles indicate that ST316 modulates markers associated with neutrophil maturation, identifying a role for b-catenin/BCL9 in PMN-MDSC differentiation. Co-culture assays indicate that ST316 significantly increased T cell activation markers and proliferation, identifying an essential role for β-catenin/BCL9 in the immunosuppressive activity of PMN-MDSCs.Conclusions These data identify a critical and previously underappreciated role for β-catenin/BCL9 in the maturation, maintenance and immunosuppressive potential of MDSCs. Expression profiling and flow cytometry identified candidate markers to track PMN-MDSC levels and activity. These observations are consistent with ST316 anti-tumor activity as monotherapy and in combination with standard-of-care agents in CRC. Overall, these data help dissect the role of Wnt/b-catenin in PMN-MDSC development and further support antagonism of b-catenin/BCL9 with ST316 as a novel therapeutic approach for CRC.Ethics Approval All aspects of animal care were in accordance with the Guide for Care and Use of Laboratory Animals and all experiments were approved by the Institutional IACUC at New York Medical College (NYMC).",
  "authors": [
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Claudio Scuoppo"
    },
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Julia Diehl"
    },
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Ricardo Ramirez"
    },
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Mark Koester"
    },
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Barry Kappel"
    },
    {
      "affiliations": [
        "Sapience Therapeutics, Tarrytown, NY, USA"
      ],
      "name": "Jim A Rotolo"
    }
  ],
  "title": "1198 Antagonism of beta-catenin/Bcl9 impairs generation of immune-suppressive MDSCs and promotes enhanced immune responses",
  "uid": "2e7f8128-aaf4-5fa6-8b22-1113fec57d4e"
}