The HPK1 Inhibitor A-745 Verifies the Potential of Modulating T Cell Kinase Signaling for Immunotherapy

Design, Synthesis, and biological evaluation of 7H-Pyrrolo[2,3-d]pyrimidines as potent HPK1 kinase inhibitors

Hematopoietic progenitor kinase 1 (HPK1) has emerged as a promising target for cancer immunotherapy due to its critical role as a negative regulator of T cell receptor (TCR) signaling. Despite this potential, no HPK1 inhibitors have been approved for cancer treatment, underscoring the need for structurally novel inhibitors. Herein, we describe the design, synthesis and biological evaluation of a series of potent HPK1 inhibitors based on our previously identified hit 9. Among them, compound 24 demonstrated strong HPK1 inhibition (IC50 of 10.1 nM) and effectively suppressed phosphorylation of the downstream protein SLP76. Notably, compound 24 exhibited enhanced potency in promoting IL-2 secretion in Jurkat T cells, reduced cellular toxicity, and improved liver microsomal stability compared to hit 9. Overall, this study provides a promising lead compound for further optimization as a candidate for cancer immunotherapy.

Automated High-Throughput Affinity Capture-Mass Spectrometry Platform with Data-Independent Acquisition

Affinity capture (AC) combined with mass spectrometry (MS)-based proteomics is highly utilized throughout the drug discovery pipeline to determine small-molecule target selectivity and engagement. However, the tedious sample preparation steps and time-consuming MS acquisition process have limited its use in a high-throughput format. Here, we report an automated workflow employing biotinylated probes and streptavidin magnetic beads for small-molecule target enrichment in the 96-well plate format, ending with direct sampling from EvoSep Solid Phase Extraction tips for liquid chromatography (LC)-tandem mass spectrometry (MS/MS) analysis. The streamlined process significantly reduced both the overall and hands-on time needed for sample preparation. Additionally, we developed a data-independent acquisition-mass spectrometry (DIA-MS) method to establish an efficient label-free quantitative chemical proteomic kinome profiling workflow. DIA-MS yielded a coverage of ∼380 kinases, a > 60% increase compared to using a data-dependent acquisition (DDA)-MS method, and provided reproducible target profiling of the kinase inhibitor dasatinib. We further showcased the applicability of this AC-MS workflow for assessing the selectivity of two clinical-stage CDK9 inhibitors against ∼250 probe-enriched kinases. Our study here provides a roadmap for efficient target engagement and selectivity profiling in native cell or tissue lysates using AC-MS.

Discovery of PF-07265028, A Selective Small Molecule Inhibitor of Hematopoietic Progenitor Kinase 1 (HPK1) for the Treatment of Cancer

Hematopoietic progenitor kinase 1 (HPK1/MAP4K1) represents a high interest target for the treatment of cancer through an immune-mediated mechanism. Herein we present highlights of the drug discovery campaign within the lactam/azalactam series of inhibitors that yielded a small molecule (21, PF-07265028), which was advanced to a phase 1 clinical trial (NCT05233436). Key components of the discovery effort included optimization of potency through mitigation of ligand strain as guided by the use of cocrystal structures, mitigation of ADME liabilities (plasma instability and fraction metabolism by CYP2D6), and optimization of kinase selectivity, particularly over immune-modulating kinases with high homology to HPK1. Structure-based drug design via leveraging cocrystal structures and lipophilic efficiency analysis proved to be valuable tools that ultimately enabled the delivery of a clinical-quality small molecule inhibitor of HPK1.

Discovery of Pyridine-2-Carboxamides Derivatives as Potent and Selective HPK1 Inhibitors for the Treatment of Cancer

Hematopoietic progenitor kinase 1 (HPK1) has emerged as an attractive target for immunotherapy due to its critical role in T cell activation and proliferation. The major challenge in developing HPK1 inhibitors lies in balancing kinase selectivity, pharmacokinetic (PK) properties, and therapeutic efficacy. In this study, we report a series of pyridine-2-carboxamide analogues demonstrating strong HPK1 inhibitory activity in enzymatic and cellular assays, along with good kinase selectivity. Among these analogues, compound 19 showed good in vitro HPK1 inhibitory activity, excellent kinase selectivity (>637-fold vs GCK-like kinase and >1022-fold vs LCK), and robust in vivo efficacy in the CT26 (tumor growth inhibition (TGI) = 94.3%, 2/6 CRs) and MC38 murine colorectal cancer models (TGI = 83.3%, 1/6 complete response) when administered in combination with anti-PD-1. Compound 19 also demonstrated adequate in vitro ADME and in vivo PK properties, displaying good oral bioavailability across multiple species (F % = 35-63). These findings summarize our compound's favorable safety and efficacy profiles, justifying its testing in future translational studies.

Discovery of 1(2H)-phthalazinone and 1(2H)-isoquinolinone derivatives as potent hematopoietic progenitor kinase 1 (HPK1) inhibitors

Although immune checkpoint inhibitors (ICIs) have been a revelation for treating several cancers, an unmet need remains to broaden ICI therapeutic scope and increase their response rates in clinical trials. Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of T cell activation and has previously been identified as a promising target for immunotherapy. Herein, we report the discovery of a series of HPK1 inhibitors with novel 1(2H)-phthalazinone and 1(2H)-isoquinolinone scaffolds. Among them, compound 24 demonstrated potent in vitro activity (HPK1 IC50 value of 10.4 nM) and cellular activity (pSLP76 EC50 = 41 nM & IL-2 EC50 = 108 nM). Compound 24 exhibited favorable mouse and rat pharmacokinetic profiles with reasonable oral exposure. Compound 24 showed potent in vivo anti-tumor activity in a CT26 syngeneic tumor model with 95 % tumor growth inhibition in combination with anti-PD-1.

An updated review of small-molecule HPK1 kinase inhibitors (2016-present)

Hematopoietic progenitor kinase 1 (HPK1) is a serine-threonine kinase specific to hematopoiesis and a member of the MAP4K family of Ste20-related protein kinases. Targeting HPK1 to ameliorate T cell exhaustion and enhance T cell functions is a promising strategy for clinical immunotherapies. Numerous studies have reported the progress in developing effective HPK1 inhibitors and elucidating their mechanisms of action. However, most inhibitors affect multiple signaling pathways, resulting in unintended side effects that limit their clinical development and application. Herein, we reviewed HPK1-related signaling pathways, clinical candidates and recent advances in small-molecule inhibitors targeting HPK1. Additionally, we present our perspectives on current challenges and potential future research field, hoping to provide inspiration for the development of novel HPK1 inhibitors.

Design, Synthesis, and Biological Evaluation of a Series of Spiro Analogues as Novel HPK1 Inhibitors

Hematopoietic progenitor kinase 1 (HPK1) negatively affects T cell activation and proliferation and is a promising target for immunotherapy. Although HPK1 inhibitors have shown promising efficacy in preclinical models, none have been approved for clinical use. One significant challenge in developing an HPK1 inhibitor is the difficulty in designing a potent inhibitor with good kinase selectivity and pharmacokinetic properties. Here, we report a series of spiro HPK1 inhibitors with good potency and selectivity. Specifically, compound 16 exhibited potent HPK1 inhibition (IC50 = 2.67 nM), adequate selectivity toward the MAP4K family (>100-fold), and good selectivity against selected kinases (>300-fold). Compound 16 demonstrated moderate in vivo clearance and reasonable oral exposure in mice and rats. Notably, compound 16 possessed good antitumor efficacy in the CT26 murine colon cancer and a synergistic effect when combined with anti-PD-1. These exciting preclinical results support the continued development of this class of HPK1 inhibitors.

Opportunities and challenges for targeting HPK1 in cancer immunotherapy

Hematopoietic Progenitor Kinase 1 (HPK1, also known as MAP4K1) is a hematopoiesis-specific serine/threonine kinase that belongs to the MAP4K family of Ste20-related protein kinases. HPK1 has been identified as a negative regulator of T-cell receptor signaling. Recent studies have indicated that the inhibition or knockout of HPK1 kinase function can effectively alleviate T cell exhaustion, enhance T cell functionality, and improve the therapeutic efficacy of tumor immunotherapy. In recent years, small molecule chemical drugs targeting HPK1 have made significant progress and have become a hot topic in the research and development of tumor immunotherapy drugs. However, the advancement of small molecule drugs that target HPK1 is hindered by various challenges, including the limited selectivity, insufficient immune stimulation, and the ambiguity surrounding role of non-kinase scaffold functions of HPK1 in tumor immune responses. This review briefly describes the biological structure of HPK1 and its related signaling pathways in tumor immunity, systematically discusses the latest research progress in small molecule chemical drugs targeting HPK1. Finally, we summarize and prospect the opportunities and challenges in the drug development of small molecule chemical drugs targeting HPK1 in tumor immunity.

Design, synthesis, and biological evaluation of novel HPK1 inhibitors possessing 3-cyano-quinoline moiety

Hematopoietic progenitor kinase 1 (HPK1), a negative regulator of T cell receptor signaling, plays a crucial role in multiple cellular immune responses. Emerging researches have demonstrated that inhibiting HPK1 kinase function enhances T cells' ability to recognize tumor antigens and boosts anti-tumor immune responses. As a result, HPK1 has become a promising target for tumor immunotherapy. Herein, we report the design, synthesis, and biological evaluation of a series of novel HPK1 inhibitors featuring a 3-cyano-quinoline scaffold. Among these, compound 3a was identified as the most potent HPK1 inhibitor (HPK1 IC50 = 48 nM). It effectively inhibited SLP76 phosphorylation, enhanced IL-2 cytokine secretion, and reversed PGE2-induced immunosuppression in Jurkat cells. In addition, compound 3a exhibited favorable metabolic stability in mouse liver microsomes and plasma. Overall, this work provides a structurally novel lead compound for the development of HPK1 inhibitors.

Pyrazine-based small molecule kinase inhibitors: clinical applications and patent review (2019-2023)

Protein kinases play a key role in cellular signaling pathways including proliferation, apoptosis, inflammation and immune regulation. Therefore, targeting kinases with small molecules has emerged as a therapeutic potential in cancers and other diseases including inflammatory and autoimmune disorders. The main chemical motifs of the available small molecule kinase inhibitors are heterocyclic, nitrogen-containing and six-membered rings including pyrazine. Several potent and selective pyrazine-based kinase inhibitors have been developed and progressed into clinical trials. The data of clinical application of kinase inhibitors demonstrate good clinical activity with manageable toxicity in several relapse-resistant malignancies and severe to moderate immunological disorders. All pyrazine-based kinase inhibitors are orally active. This paper reviews the most recent kinase literature (2019-2023) related to pyrazine-based small molecule inhibitors. This review includes the FDA (Food and Drug Administration)-approved and patent agents along with their targeted kinase, scaffold, potency, selectivity profile, assignee and biological results in clinical and preclinical studies.

Inhibition of MALT1 and BCL2 Induces Synergistic Antitumor Activity in Models of B-Cell Lymphoma

The activated B cell (ABC) subset of diffuse large B-cell lymphoma (DLBCL) is characterized by chronic B-cell receptor signaling and associated with poor outcomes when treated with standard therapy. In ABC-DLBCL, MALT1 is a core enzyme that is constitutively activated by stimulation of the B-cell receptor or gain-of-function mutations in upstream components of the signaling pathway, making it an attractive therapeutic target. We discovered a novel small-molecule inhibitor, ABBV-MALT1, that potently shuts down B-cell signaling selectively in ABC-DLBCL preclinical models leading to potent cell growth and xenograft inhibition. We also identified a rational combination partner for ABBV-MALT1 in the BCL2 inhibitor, venetoclax, which when combined significantly synergizes to elicit deep and durable responses in preclinical models. This work highlights the potential of ABBV-MALT1 monotherapy and combination with venetoclax as effective treatment options for patients with ABC-DLBCL.

Design, synthesis, and biological evaluation of 2,4-diaminopyrimidine derivatives as potent Hematopoietic Progenitor Kinase 1 (HPK1) inhibitors

HPK1 also referred to as MAP4K1, belongs to the category of mammalian STE20-like protein serine/threonine kinases. Its physiological function involves the down-regulation of T cell signals, and it is regarded as a new immune checkpoint of tumor immunology. In this study, we commenced our investigation with the hit compounds, focusing the efforts on structural optimization and SAR exploration to identify a novel class of 2,4-diaminopyrimidine HPK1 inhibitors. Notably, compound 14g exhibited a remarkable inhibitory effect on HPK1 kinase (IC50 = 0.15 nM), significantly suppressed the phosphorylation of the downstream adaptor protein SLP76 (pSLP76 IC50 = 27.92 nM), and effectively stimulated the secretion of the T cell activation marker IL-2 (EC50 = 46.64 nM). In vitro microsomal stability assay, compound 14g showed moderate stability in HLMs with T1/2 = 38.2 min and CLint = 36.4 µL·min-1·mg-1 proteins. In vivo pharmacokinetic studies, compound 14g demonstrated heightened plasma exposure (AUC0-inf = 644 ng·h·mL-1), extended half-life (T1/2 = 9.98 h), and reduced plasma clearance (CL = 52.3 mL·min-1·kg-1) compared to the reference compound after a single intravenous dose of 2 mg/kg in rats. These results indicated that compound 14g emerged as a promising inhibitor of HPK1.

HPK1 citron homology domain regulates phosphorylation of SLP76 and modulates kinase domain interaction dynamics

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of T-cell receptor signaling and as such is an attractive target for cancer immunotherapy. Although the role of the HPK1 kinase domain (KD) has been extensively characterized, the function of its citron homology domain (CHD) remains elusive. Through a combination of structural, biochemical, and mechanistic studies, we characterize the structure-function of CHD in relationship to KD. Crystallography and hydrogen-deuterium exchange mass spectrometry reveal that CHD adopts a seven-bladed β-propellor fold that binds to KD. Mutagenesis associated with binding and functional studies show a direct correlation between domain-domain interaction and negative regulation of kinase activity. We further demonstrate that the CHD provides stability to HPK1 protein in cells as well as contributes to the docking of its substrate SLP76. Altogether, this study highlights the importance of the CHD in the direct and indirect regulation of HPK1 function.

Discovery of 5-aminopyrido[2,3-d]pyrimidin-7(8H)-one derivatives as new hematopoietic progenitor kinase 1 (HPK1) inhibitors

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of T-cell receptor signaling. While HPK1 is considered as a promising target for cancer immunotherapy, no small-molecule HPK1 inhibitors have been approved for cancer treatment. Herein, we report the discovery of a series of new HPK1 inhibitors with a 5-aminopyrido[2,3-d]pyrimidin-7(8H)-one scaffold. The most potent compound 9f inhibited HPK1 kinase activity with an IC50 of 0.32 nM in the time-resolved fluorescence resonance energy transfer (TR-FRET) assays, while displayed reasonable selectivity in a panel of 416 kinases. Cellular engagement of HPK1 by compound 9f was confirmed through the nano-bioluminescence resonance energy transfer (Nano-BRET) experiments. Compound 9f effectively reduced the phosphorylation of the downstream protein SLP-76 in primary peripheral blood mononuclear cells (PBMCs) and human T lymphocytic leukemia Jurkat cells. Compound 9f also enhanced the IL-2 and IFN-γ secretion in PBMCs. Furthermore, the binding mode of compound 9f with HPK1 was confirmed by the resolved cocrystal structure. Taken together, this study provides HPK1 inhibitors with a novel scaffold and clear binding mode for further development of HPK1-targeted therapeutic agents.

Current strategies for targeting HPK1 in cancer and the barriers to preclinical progress

INTRODUCTION

Hematopoietic progenitor kinase 1 (HPK1), a 97-kDa serine/threonine Ste20-related protein kinase, functions as an intracellular negative regulator, primarily in hematopoietic lineage cells, where it regulates T cells, B cells, dendritic cells, and other immune cells. Loss of HPK1 kinase activity results in exacerbated cytokine secretion, enhanced T cell signaling, improved viral clearance, and thus increased restraint of tumor growth. These findings highlight HPK1 as a promising target for immuno-oncology treatments, culminating in the advancement of candidate compounds targeting HPK1 to clinical trials by several biotech enterprises.

AREAS COVERED

Through searching PubMed, Espacenet-patent search, and clinicaltrials.gov, this review provides a comprehensive analysis of HPK1, encompassing its structure and roles in various downstream signaling pathways, the consequences of constitutive activation of HPK1, and potential therapeutic strategies to treat HPK1-driven malignancies. Moreover, the review outlines the patents issued for small molecule inhibitors and clinical investigations of HPK1.

EXPERT OPINION

To enhance the success of tumor immunotherapy in clinical trials, it is important to develop protein degraders, allosteric inhibitors, and antibody-drug conjugates based on the crystal structure of HPK1, and to explore combination therapy approaches. Although several challenges remain, the development of HPK1 inhibitors display promising in preclinical and clinical studies.

High HPK1+PD-1+TIM-3+CD8+ T cells infiltration predicts poor prognosis to immunotherapy in NSCLC patients

At present the efficacy of immune checkpoint inhibitors (ICIs) remains limited. The lack of responsiveness in certain patients may be attributed to CD8+ T cell exhaustion within the tumor microenvironment (TME). Hematopoietic progenitor kinase 1 (HPK1) has been identified as a mediator of T cell dysfunction, leading to our hypothesis that HPK1 positive exhausted CD8+ T cells could serve as a predictor for ICIs' efficacy in NSCLC patients, and potentially indicate key cellular subset causing ICIs resistance. Here, we retrospectively collected tumor tissue samples from 36 NSCLC patients who underwent first-line immunotherapy. Using multiplex immunohistochemistry, we visualized various PD-1+CD8+ T cell subsets and explore biomarkers for response. The analysis endpoints included overall response rate (ORR), progression free survival (PFS), and overall survival (OS), correlating them with levels of cell infiltration or effective density. We found that the proportion of PD-1+CD8+ T cell subsets did not align with predictions for ORR, PFS, and OS. Conversely, a high infiltration of HPK1+PD-1+TIM-3+CD8+ T cells was identified as an independent risk factor for both PFS (P = 0.019) and OS (P = 0.03). These cells were found to express the highest levels of Granzyme B, and the secretion of Granzyme B in CD8+ T cell subsets was related to TCF-1. In conclusion, these data suggest that a high infiltration of HPK1+PD-1+TIM-3+CD8+ T cells correlates with poor clinical outcomes in NSCLC patients receiving immunotherapy. These cells may represent terminally exhausted T cells that fail to respond to ICIs, thereby laying the groundwork for the potential integration of HPK1 inhibitors with immunotherapy to enhance treatment strategy.

Design, Synthesis, and Pharmacological Evaluation of Isoindoline Analogues as New HPK1 Inhibitors

Hematopoietic progenitor kinase 1 (HPK1) is an important negative regulator in T-cell receptor signaling and as a promising key target for immunotherapy. Herein, based on the reported HPK1 inhibitor 2 featuring an isofuranone component, a structural optimization approach was conducted leading to several series of derivatives characterized by containing an isoindoline structural motif. Compound 49 was identified as a new potent HPK1 inhibitor with an IC50 value of 0.9 nM, more potent than compound 2 (5.5 nM). It also has an improved IV profile in rats and enhanced aqueous solubility. It effectively inhibited pSLP76 and reinvigorated T-cell receptor (TCR) signaling, promoting T-cell function and cytokine production both in naïve and antigen-specific T cells. Furthermore, compound 49 reversed the inhibition on T-cell activity mediated by classic immunosuppressive factors in the tumor microenvironment (TME). In the murine CT-26 tumor model, this compound reinvigorated the T cell and synergistically enhanced the antitumor efficacy of anti-PD1 at a well-tolerant dosage.

A knowledge-guided pre-training framework for improving molecular representation learning

Learning effective molecular feature representation to facilitate molecular property prediction is of great significance for drug discovery. Recently, there has been a surge of interest in pre-training graph neural networks (GNNs) via self-supervised learning techniques to overcome the challenge of data scarcity in molecular property prediction. However, current self-supervised learning-based methods suffer from two main obstacles: the lack of a well-defined self-supervised learning strategy and the limited capacity of GNNs. Here, we propose Knowledge-guided Pre-training of Graph Transformer (KPGT), a self-supervised learning framework to alleviate the aforementioned issues and provide generalizable and robust molecular representations. The KPGT framework integrates a graph transformer specifically designed for molecular graphs and a knowledge-guided pre-training strategy, to fully capture both structural and semantic knowledge of molecules. Through extensive computational tests on 63 datasets, KPGT exhibits superior performance in predicting molecular properties across various domains. Moreover, the practical applicability of KPGT in drug discovery has been validated by identifying potential inhibitors of two antitumor targets: hematopoietic progenitor kinase 1 (HPK1) and fibroblast growth factor receptor 1 (FGFR1). Overall, KPGT can provide a powerful and useful tool for advancing the artificial intelligence (AI)-aided drug discovery process.

Discovery of quinazoline HPK1 inhibitors with high cellular potency

Hematopoietic progenitor kinase 1 (HPK1) is regarded as a highly validated target in pre-clinical immune oncology. HPK1 has been described as regulating multiple critical signaling pathway in both adaptive and innate cells. In support of this role, HPK1 KO T cells show enhanced sensitivity to TCR activation and HPK1 KO mice display enhanced anti-tumor activity. Taken together, inhibition of HPK1 has the potential to induce enhanced anti-tumor immune response. Herein, we described the discovery of highly potent HPK1 inhibitors starting form a weak HTS hit. Using a structure-based drug design, HPK1 inhibitors exhibiting excellent cellular single-digit nanomolar potency in both proximal (pSLP76) and distal (IL-2) biomarkers along with sustained elevation of IL-2 cytokine secretion were discovered.

Discovery of diaminotriazine carboxamides as potent inhibitors of hematopoetic progenitor kinase 1

Hematopoietic progenitor kinase 1 (HPK1), a member of mitogen-activated protein kinase kinase kinase kinase (MAP4K) family of Ste20 serine/threonine kinases, is a negative regulator of T-cell receptor (TCR) signaling. Inactivating HPK1 kinase has been reported to be sufficient to elicit antitumor immune response. Therefore, HPK1 has attracted much attention as a promising target for tumor immunotherapy. A few of HPK1 inhibitors have been reported, and none of them have been approved for clinical applications. Hence, more effective HPK1 inhibitors are needed. Herein, a series of structurally novel diaminotriazine carboxamides were rationally designed, synthesized and evaluated for their inhibitory activity against HPK1 kinase. Most of them exhibited potent inhibitory potency against HPK1 kinase. In particular, compound 15b showed more robust HPK1 inhibitory activity than that of 11d developed by Merck in kinase activity assay (IC50 = 3.1 and 8.2 nM, respectively). The significant inhibitory potency against SLP76 phosphorylation in Jurkat T cells further confirmed the efficacy of compound 15b. In human peripheral blood mononuclear cell (PBMC) functional assays, compound 15b more significantly induced the production of interleukin 2 (IL-2) and interferon γ (IFN-γ) relative to 11d. Furthermore, 15b alone or in combination with anti-PD-1 antibodies showed potent in vivo antitumor efficacy in MC38 tumor-bearing mice. Compound 15b represents a promising lead for the development of effective HPK1 small-molecule inhibitors.

Deep Generation Model Guided by the Docking Score for Active Molecular Design

A deep generation model, as a novel drug design and discovery tool, shows obvious advantages in generating compounds with novel backbones and has been applied successfully in the field of drug discovery. However, it is still a challenge to generate molecules with expected properties, especially high activity. Here, to obtain compounds both with novelty and high activity to a target, we proposed a conditional molecular generation model COMG by considering the docking score and 3D pharmacophore matching during molecular generation. The proposed model was based on the conditional variational autoencoder architecture constrained by the pharmacophore matching score. During Bayesian optimization, the docking score was applied to enhance the target relevance of generated compounds. Furthermore, to overcome the problem of high structural similarity caused by Bayesian optimization, the idea of the scaffold memory unit was also introduced. The evaluation results of COMG show that our model not only can improve the structural diversity of generated molecules but also can effectively improve the proportion of target-related drug-active molecules. The obtained results indicate that our proposed model COMG is a useful drug design tool.

Discovery of 7H-Pyrrolo[2,3-d]pyrimidine Derivatives as potent hematopoietic progenitor kinase 1 (HPK1) inhibitors

Hematopoietic progenitor kinase 1 (HPK1) is predominantly expressed in hematopoietic cells and is a negative regulator of T cell receptor (TCR) signaling. Recent studies have demonstrated that HPK1 is a promising therapeutic target for cancer immunotherapy. However, despite significant progress in the development of HPK1 inhibitors, none of them has been approved for cancer therapy. Development of HPK1 inhibitors with a structurally distinct scaffold is still needed. Herein, we describe the design and synthesis of a series of HPK1 inhibitors with a 7H-pyrrolo[2,3-d]pyrimidine scaffold, exemplified by 31. Compound 31 showed potent inhibitory activity against HPK1 with an IC₅₀ value of 3.5 nM and favorable selectivity within a panel of kinases. It also potently inhibited the phosphorylation level of SLP76, a substrate of HPK1, and enhanced the IL-2 secretion in Jurkat cells (human T cell leukemia). Our findings provide new clues for further optimization and development to generate HPK1 inhibitors for cancer immunotherapy.

Development of a series of quinazoline-2,5-diamine derivatives as potent hematopoietic progenitor kinase 1 (HPK1) inhibitors

Hematopoietic progenitor kinase 1 (HPK1) is a serine/threonine kinase that serves as the negative regulator of multiple immune signaling pathways. Genetic studies using HPK1 knockout and kinase-dead mice suggested that inhibiting HPK1 either alone or in combination with immune checkpoint blockade could be a promising strategy in cancer immunotherapy. Herein, we report the design, synthesis and structure-activity relationship (SAR) study of a series of potent HPK1 inhibitors bearing quinazoline-2,5-diamine scaffold. Three rounds of SAR exploration led to the identification of 9h, the most potent compound in this series which harbors a 2-methyl-1,2,3,4-tetrahydroisoquinolin-7-yl substituent. Further biological assessments using human immune cells demonstrated that 9h could strongly inhibit downstream phosphorylation, augment interleukin-2 (IL-2) production and reverse prostaglandin E2 (PGE2)-induced immune suppression. Overall, our study on these quinazoline-2,5-diamine derivatives provided not only a tool compound for the community to help with elucidating the HPK1 pharmacology, but also a reliable reference for subsequent development of HPK1 inhibitors.

Potent and Selective Biaryl Amide Inhibitors of Hematopoietic Progenitor Kinase 1 (HPK1)

Herein we report the discovery of a novel biaryl amide series as selective inhibitors of hematopoietic protein kinase 1 (HPK1). Structure-activity relationship development, aided by molecular modeling, identified indazole 5b as a core for further exploration because of its outstanding enzymatic and cellular potency coupled with encouraging kinome selectivity. Late-stage manipulation of the right-hand aryl and amine moieties surmounted issues of selectivity over TRKA, MAP4K2, and STK4 as well as generating compounds with balanced in vitro ADME profiles and promising pharmacokinetics.

Hematopoietic Progenitor Kinase 1 in Tumor Immunology: A Medicinal Chemistry Perspective

Hematopoietic progenitor kinase 1 (HPK1), a hematopoietic cell-restricted member of the serine/threonine Ste20-related protein kinases, is a negative regulator of the T cell receptor, B cell receptor, and dendritic cells. Loss of HPK1 kinase function increases cytokine secretion and enhances T cell signaling, virus clearance, and tumor growth inhibition. Therefore, HPK1 is considered a promising target for tumor immunotherapy. Several HPK1 inhibitors have been reported to regulate T cell function. In addition, HPK1-targeting PROTACs, which can induce the degradation of HPK1, have also been developed. Here, we provide an overview of research concerning HPK1 protein structure, function, and inhibitors and propose perspectives and insights for the future development of agents targeting HPK1.