Background: Haematopoietic Progenitor Kinase (HPK-1, MAP4K1) is a member of the STE20 family of serine/threonine kinases, expressed predominantly in hematopoietic cells. The kinase activity of HPK-1 provides an inhibitory signal that dampens immune responses1. Upon activation of T-cell and/or B-cell receptors, activated HPK-1 phosphorylates the adaptor protein SLP76 at Ser376 in T cells or BLNK at Thr152 in B-cells to trigger proteasomal degradation of the adaptors and disrupt downstream T-cell or B-cell activating signalosome complexes. Blocking HPK-1 extends immune action and since HPK-1 expression is primarily restricted to immune cells, it is a compelling drug target for immune modulation. Anti-tumor efficacy has been demonstrated in HPK-1 kinase dead knock-in mice, HPK-1 knockout mice or using small molecule pharmacological inhibitors of HPK-1 either as monotherapy or in combination regimens2.

Methods: Curadev used a pharmacophore based approach to discover novel small molecule HPK-1 inhibitors. SAR studies were carried out using a screening funnel that included efficacy assessment by monitoring in vitro enzymatic and cellular activity, anti-target cross-kinase specificity by assessing cytotoxicity in fresh murine splenocytes and effector mobilization by monitoring IL2 production and human T-cell proliferation under anti-CD3/CD28 stimulation.

Results: Curadev’s medicinal chemistry campaign yielded several highly potent HPK-1 inhibitors with sub-nanomolar to nanomolar potency in in vitro human HPK-1 enzyme assays which were active in the cellular SLP76 assay. A single dose of the lead compound CRD1600 to mice treated with an anti-CD3 antibody caused systemic enhancement of pro-inflammatory cytokines such as IL2 and reduced pSLP76 levels in the spleen. These pharmacodynamic effects correlated with plasma levels of CRD1600.

Conclusions: Inhibition of HPK-1 is a promising therapeutic modality that could augment the effects of existing anti-cancer treatments including immunotherapy. CRD1600 is a potent, selective HPK-1 inhibitor that has been selected from a rich portfolio of active compounds and shows in vivo activity against the target. Further development of the compound is ongoing.

References: 1. Sawasdikosol et al., eLife, 2020, 9, e55122 and references cited therein 2. You et al., J. Immunother. Cancer, 2021, 9, e001402

Citation Format: Ritesh Shrivastava, David C. Pryde, Dharmendra Yadav, Abhisek Chatterjee, Sandip Middya, Sameer Shaikh, Rajib Ghosh, Sabyasachi Debnath, Nagaswamy Mane, Anindita Middya, Nidhi Rawat, Anuj Gautam, Sourav Basu, Monali Banerjee, Arjun Surya. CRD1600 is a potent HPK-I inhibitor with robust immune modulatory properties [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 2122.