Abstract C065: Hematopoietic Progenitor Kinase 1 (HPK1) inhibition enhances antibody secretion, pro-inflammatory cytokine production and proliferation of primary human B cells
Authors: Ciccone David 
Published: December 2023

Abstract
Introduction Immune checkpoint blockade (ICB) therapies have revolutionized cancer treatment, although most approaches have focused solely on enhancing T cell responses. In recent years, it has become clear that augmentation of other immune cell subsets is critical to the overall success of cancer immunotherapy. Recent data show that tumors from patients responding to ICB are infiltrated by B cells and strongly correlated with the formation of tertiary lymphoid structures, highlighting the importance of B cells in promoting and coordinating immunotherapy responses [1,2]. Here, we demonstrate that NDI-101150, a potent and highly selective HPK1 small molecule inhibitor, can enhance B cell activation with the tumor.
Experimental Procedures Biochemical and cell-based assays were used to characterize the potency and selectivity of NDI-101150, respectively. Mouse splenocytes and/or human blood collections were used to characterize the effects of NDI-101150 on antibody secretion, cytokine production, and proliferation in purified B cells. CT-26 and EMT-6 syngeneic tumor models were used to study tumor-associated B cell responses in vivo, as well as immunization response to Keyhole Limpet Hemocyanin (KLH) in mice receiving daily oral dosing of NDI-101150.
Results In CD19+ human B cells and donor PBMCs (peripheral blood mononuclear cells), NDI-101150 treatment inhibited (&gt;90%) phosphorylation of BLNK, a B cell adapter protein phosphorylated by HPK1 downstream of B cell receptor signaling. In vitro NDI-101150 treatment dose-dependently activated primary human and mouse B cells as evidenced by increased pro-inflammatory cytokine production, enhanced IgG antibody secretion, and increased proliferation. Once daily oral administration of NDI-101150 significantly increased KLH antigen-specific IgM and IgG antibody production upon KLH immunization, increased total circulating antibody levels, and induced significant tumor growth inhibition (TGI) in CT-26 and EMT-6 murine syngeneic models (50% and 85% TGI, respectively). Immunophenotyping of tumor bearing animals treated with NDI-101150 revealed an increase in infiltrating CD19+ B cells and an increased tumor B cell transcriptional signature.
Conclusions Pharmacological inhibition of HPK1 with NDI-101150 represents a novel immunomodulatory approach for engaging and enhancing B cell activation within the tumor microenvironment. NDI-101150 is currently being tested in a Phase 1 trial in patients with advanced recurrent or metastatic solid tumors. References Helmink, B.A., et al., Nature 2020. v577: 549-55. Cabrita, R., et al., Nature 2020. v577: 561-5.
Citation Format: David Ciccone. Hematopoietic Progenitor Kinase 1 (HPK1) inhibition enhances antibody secretion, pro-inflammatory cytokine production and proliferation of primary human B cells [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 C065.