Hematopoietic progenitor kinase 1 negatively regulates T cell receptor signaling and T cell-mediated immune responses

Design, synthesis, and biological evaluation of 2,4-diaminopyrimidine inhibitors of hematopoietic progenitor kinase 1

Cancer immunotherapy is an emerging anti-cancer strategy that enhances immune circulation by targeting the immune system. Among the various targets, HPK1, a member of the mammalian Ste20-like protein serine/threonine kinase family, serves as a crucial negative regulator of immune-mediated mechanisms, positioning it as a promising target for immunotherapy. Herein, based on the reported HPK1 inhibitors characterized by 2,4-diaminopyrimidine components, four series of derivatives were obtained through structural optimization methods. Compound 10c demonstrates significant inhibitory effects on HPK1 kinase, with an IC50 of 0.09 nM. Additionally, it markedly inhibits the phosphorylation of the downstream adaptor protein SLP76, with an IC50 of 33.74 nM, and effectively stimulates the secretion of the T cell activation marker IL-2, exhibiting an EC50 of 84.24 nM. These findings suggest that compound 10c holds considerable promise for applications in immunotherapy.

Immunotherapy for Renal Cell Carcinoma-What More is to Come?

The treatment of renal cell carcinoma (RCC), a malignancy that is typically chemoresistant, has drastically evolved with the introduction of vascular endothelial growth factor receptor tyrosine kinase inhibitors (VEGFR TKIs) and immune checkpoint inhibitors (ICIs). The introduction of ICI-based regimens has significantly improved outcomes for patients with metastatic RCC. Currently, first-line therapy for patients with metastatic RCC involves multiple ICI-based regimens, either dual ICIs (with anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA- 4) and anti-programmed cell death- 1 (PD- 1) therapies) or anti-PD- 1 therapy in combination with VEGFR TKIs. Despite improving patient outcomes with ICI-based regimens, durable responses remain uncommon, highlighting the need for innovative treatment strategies. In this review, we highlight the current standard of care ICI-based regimens followed by ongoing clinical trials with novel combinations of existing FDA-approved agents and targets. We also discuss novel immunotherapies currently in clinical trials, which aim to improve antitumor T cell immunity either by improving T cell activation or T cell navigation to the tumor microenvironment. The incorporation of these novel therapies offers the potential to improve RCC patient outcomes, particularly by enhancing the durability of treatment responses.

Updated patent review for hematopoietic progenitor kinase (HPK1) inhibitors and degraders (2021-present)

INTRODUCTION

Hematopoietic progenitor cell kinase (HPK1) is a serine/threonine kinase of MAP4K family. It negatively regulates T cell receptor and B cell signal transduction. The loss of HPK1 kinase function increases the secretion of cytokines and enhances T cell signal transduction, virus clearance and tumor growth inhibition. Therefore, HPK1 is considered as a promising drug target for tumor immunotherapy.

AREA COVERED

This article surveys the patents published since 2021 aiming to analyze the structural features of scaffolds and the patent landscape. It also discusses the recent clinical developments and provides perspectives on the challenges and the future directions.

EXPERT OPINION

HPK1 kinase is a viable drug target, and there is an increasing number of clinical studies on HPK1 inhibitors. In the clinical research of HPK1 inhibitors, there are mainly two ways: monotherapy and combination therapy. In recent years, HPK1 degraders derived from PROTAC technology have shown promises along with HPK1 inhibitors. It is hopeful that small molecule inhibitors or degraders targeting HPK1 will gain FDA approval for treatment of human diseases in the near future.

DATABASES SEARCHED AND INCLUSIVE DATES

A rapid survey of literature reports using keyword 'HPK1' in SciFinder® search engine yielded about 180 papers since 2021.

Discovery of 1,2,4-benzotriazine derivatives as new hematopoietic progenitor kinase 1 (HPK1) inhibitors

Hematopoietic progenitor kinase 1 (HPK1), which negatively regulates immune signaling, has emerged as an attractive small-molecule drug target for tumor immunotherapy. Herein, we report the discovery of the 1,2,4-benzotriazine derivatives as new potent HPK1 inhibitors. Notably, compound A29 exhibited improved HPK1 inhibitory activity relative to compound 1 in the ADP-Glo kinase assay (IC50 = 2.70 and 13.6 nM, respectively). The pronounced inhibitory activity of A29 against downstream p-SLP76 in Jurkat T cells (IC50 = 8.1 nM) as well as the ability to induce the production of interleukin 2 (IL-2) in human peripheral blood mononuclear cells (PBMCs) confirmed its cellular target engagement and immune stimulatory effect. Consistently, this lead compound significantly enhanced T-cell killing ability against murine colon cancer cells CT26 or MC38 in a co-culture system. Furthermore, A29 was efficacious in a CT26 xenograft mouse model alone, and significantly enhanced the antitumor efficacy of an anti-PD-1 antibody. This work provides a promising lead for the development of effective HPK1 inhibitors for tumor immunotherapy.

Discovery and Optimization of Pyrazine Carboxamide AZ3246, a Selective HPK1 Inhibitor

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of the T cell receptor signaling pathway and is therefore a target of interest for immunooncology. Nonselective HPK1 inhibitors may affect other kinase components of T cell activation, blunting the beneficial impact of enhanced T cell activity that results from HPK1 inhibition itself. Here, we report the discovery of pyrazine carboxamide HPK1 inhibitors and their optimization through structure-based drug design to afford a highly selective HPK1 inhibitor, compound 24 (AZ3246). This compound induces IL-2 secretion in T cells with an EC50 of 90 nM without inhibiting antagonistic kinases, exhibits pharmacokinetic properties consistent with oral dosing, and demonstrates antitumor activity in the EMT6 syngeneic mouse model.

HPK1 kinase inhibitor: a sufficient approach to target HPK1 to modulate T cell activation in cancer immunotherapy compared with degraders

Background

Hematopoietic progenitor kinase 1 (HPK1) is a member of the mitogen-activated protein kinase kinase kinase kinase (MAP4K) family. It has been reported that HPK1 negatively regulates the activation of T cells. Several compounds have been developed and tested in clinical trials to target HPK1 for cancer immunotherapy. However, whether kinase inhibition is sufficient to eliminate the immunosuppressive function of HPK1, particularly in T cells, remains elusive.

Methods

In this study, genetic tools were used to edit the human T lymphocyte cell line Jurkat. The activation of HPK1-null cells, HPK1-wildtype cells and HPK1-kinase-inactive cells was compared through ectopic expression of HPK1 in HPK1 knockout cells or direct HPK1 mutation. Besides genetic validation, a series of compounds that selectively target HPK1 (with or without HPK1-degradation activity) were used to assess the potential scaffold function of HPK1 in regulation of human primary T cell activation and cytotoxic activity.

Results and conclusion

Augmented T-cell receptor (TCR)-induced activation in HPK1-knockout Jurkat cells was inhibited by complementation of wildtype, but not kinase-dead HPK1. HPK1 K46E-knockin and K46*-knockin Jurkat cells showed comparable levels of enhanced TCR-induced activation compared with control HPK1-wildtype Jurkat cells. Similarly, HPK1 kinase inhibitor (Compound 1) and cereblon-based (CRBN-based) HPK1 degrader (Compound 2) elicited similar degrees of maximum TCR-induced activation in primary human peripheral blood T cells. In summary, the results of this study suggested that HPK1 kinase inhibitor may be sufficient for HPK1 targeting in T cell mediated cancer immunotherapy.

An Oral PROTAC Targeting HPK1 Degradation Potentiates Anti-Solid Tumor Immunity

Hematopoietic progenitor pinase1 (HPK1) knockout has been identified as an efficient route to enhance anti-tumor immune response. Here, this work develops an oral proteolysis targeting chimera (PROTAC) targeting HPK1 to efficiently and selectively degrade HPK1 to augment immunotherapeutic outcomes. In a postoperative tumor model of human cervical cancer in NSG mice, the orally-administrated PROTAC can reach tumors, down-regulate HPK1 levels in locally-administrated CAR-T cells, and promote their efficiency in inhibiting solid tumor recurrence, achieving 50% partial response (PR) and 50% complete response (CR). In addition, oral administration of PROTAC can amplify the suppression capability of the anti-PD-L1 antibody on the growth of CT26 solid tumors in BALB/c mice by promoting the infiltration of CD45-positive immune cells from 0.7% to 1.5% and CD3-positive T cells from 0.2% to 0.5% within the tumors.

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.

Discovery of BAY-405: An Azaindole-Based MAP4K1 Inhibitor for the Enhancement of T-Cell Immunity against Cancer

Mitogen-activated protein kinase kinase kinase kinase 1 (MAP4K1) is a serine/threonine kinase that acts as an immune checkpoint downstream of T-cell receptor stimulation. MAP4K1 activity is enhanced by prostaglandin E2 (PGE2) and transforming growth factor beta (TGFβ), immune modulators commonly present in the tumor microenvironment. Therefore, its pharmacological inhibition is an attractive immuno-oncology concept for inducing therapeutic T-cell responses in cancer patients. Here, we describe the systematic optimization of azaindole-based lead compound 1, resulting in the discovery of potent and selective MAP4K1 inhibitor 38 (BAY-405) that displays nanomolar potency in biochemical and cellular assays as well as in vivo exposure after oral dosing. BAY-405 enhances T-cell immunity and overcomes the suppressive effect of PGE2 and TGFβ. Treatment of tumor-bearing mice shows T-cell-dependent antitumor efficacy. MAP4K1 inhibition in conjunction with PD-L1 blockade results in a superior antitumor impact, illustrating the complementarity of the single agent treatments.

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.

HPK1 Dysregulation-Associated NK Cell Dysfunction and Defective Expansion Promotes Metastatic Melanoma Progression

Distant metastasis, the leading cause of cancer death, is efficiently kept in check by immune surveillance. Studies have uncovered peripheral natural killer (NK) cells as key antimetastatic effectors and their dysregulation during metastasis. However, the molecular mechanism governing NK cell dysfunction links to metastasis remains elusive. Herein, MAP4K1 encoding HPK1 is aberrantly overexpressed in dysfunctional NK cells in the periphery and the metastatic site. Conditional HPK1 overexpression in NK cells suffices to exacerbate melanoma lung metastasis but not primary tumor growth. Conversely, MAP4K1-deficient mice are resistant to metastasis and further protected by combined immune-checkpoint inhibitors. Mechanistically, HPK1 restrains NK cell cytotoxicity and expansion via activating receptors. Likewise, HPK1 limits human NK cell activation and associates with melanoma NK cell dysfunction couples to TGF-β1 and patient response to immune checkpoint therapy. Thus, HPK1 is an intracellular checkpoint controlling NK-target cell responses, which is dysregulated and hijacked by tumors during metastatic progression.

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.

Pharmacological inhibition of HPK1 synergizes with PD-L1 blockade to provoke antitumor immunity against tumors with low antigenicity

Immune checkpoint inhibitors have significantly transformed the landscape of cancer therapy. Nevertheless, while these inhibitors are highly effective for certain patient groups, many do not benefit due to primary or acquired resistance. Specifically, these treatments often lack sufficient therapeutic efficacy against cancers with low antigenicity. Thus, the development of an effective strategy to overcome cancers with low antigenicity is imperative for advancing next-generation cancer immunotherapy. Here, we show that small molecule inhibitor of hematopoietic progenitor kinase 1 (HPK1) combined with programmed cell death ligand 1 (PD-L1) blockade can enhance T-cell response to tumor with low antigenicity. We found that treatment of OT-1 splenocytes with HPK1 inhibitor enhanced the activation of signaling molecules downstream of T-cell receptor provoked by low-affinity-antigen stimulation. Using an in vivo OT-1 T-cell transfer model, we demonstrated that combining the HPK1 inhibitor with the anti-PD-L1 antibody significantly suppressed the growth of tumors expressing low-affinity altered peptide ligand of chicken ovalbumin, while anti-PD-L1 antibody monotherapy was ineffective. Our findings offer crucial insights into the potential for overcoming tumors with low antigenicity by combining conventional immune checkpoint inhibitors with HPK1 inhibitor.

Novel hematopoietic progenitor kinase 1 inhibitor KHK-6 enhances T-cell activation

Inhibiting the functional role of negative regulators in immune cells is an effective approach for developing immunotherapies. The serine/threonine kinase hematopoietic progenitor kinase 1 (HPK1) involved in the T-cell receptor signaling pathway attenuates T-cell activation by inducing the degradation of SLP-76 through its phosphorylation at Ser-376, reducing the immune response. Interestingly, several studies have shown that the genetic ablation or pharmacological inhibition of HPK1 kinase activity improves the immune response to cancers by enhancing T-cell activation and cytokine production; therefore, HPK1 could be a promising druggable target for T-cell-based cancer immunotherapy. To increase the immune response against cancer cells, we designed and synthesized KHK-6 and evaluated its cellular activity to inhibit HPK1 and enhance T-cell activation. KHK-6 inhibited HPK1 kinase activity with an IC50 value of 20 nM and CD3/CD28-induced phosphorylation of SLP-76 at Ser-376 Moreover, KHK-6 significantly enhanced CD3/CD28-induced production of cytokines; proportion of CD4+ and CD8+ T cells that expressed CD69, CD25, and HLA-DR markers; and T-cell-mediated killing activity of SKOV3 and A549 cells. In conclusion, KHK-6 is a novel ATP-competitive HPK1 inhibitor that blocks the phosphorylation of HPK1 downstream of SLP-76, enhancing the functional activation of T cells. In summary, our study showed the usefulness of KHK-6 in the drug discovery for the HPK1-inhibiting immunotherapy.

Macrocyclization strategy for improving candidate profiles in medicinal chemistry

Macrocycles are defined as cyclic compounds with 12 or more members. In medicinal chemistry, they are categorized based on their core chemistry into cyclic peptides and macrocycles. Macrocycles are advantageous because of their structural diversity and ability to achieve high affinity and selectivity towards challenging targets that are often not addressable by conventional small molecules. The potential of macrocyclization to optimize drug-like properties while maintaining adequate bioavailability and permeability has been emphasized as a key innovation in medicinal chemistry. This review provides a detailed case study of the application of macrocyclization over the past 5 years, starting from the initial analysis of acyclic active compounds to optimization of the resulting macrocycles for improved efficacy and drug-like properties. Additionally, it illustrates the strategic value of macrocyclization in contemporary drug discovery efforts.

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.

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.

Small-molecule agents for cancer immunotherapy

Cancer immunotherapy, exemplified by the remarkable clinical benefits of the immune checkpoint blockade and chimeric antigen receptor T-cell therapy, is revolutionizing cancer therapy. They induce long-term tumor regression and overall survival benefit in many types of cancer. With the advances in our knowledge about the tumor immune microenvironment, remarkable progress has been made in the development of small-molecule drugs for immunotherapy. Small molecules targeting PRR-associated pathways, immune checkpoints, oncogenic signaling, metabolic pathways, cytokine/chemokine signaling, and immune-related kinases have been extensively investigated. Monotherapy of small-molecule immunotherapeutic drugs and their combinations with other antitumor modalities are under active clinical investigations to overcome immune tolerance and circumvent immune checkpoint inhibitor resistance. Here, we review the latest development of small-molecule agents for cancer immunotherapy by targeting defined pathways and highlighting their progress in recent clinical investigations.

Unraveling the Role of the NLRP3 Inflammasome in Lymphoma: Implications in Pathogenesis and Therapeutic Strategies

Inflammasomes are multimeric protein complexes, sensors of intracellular danger signals, and crucial components of the innate immune system, with the NLRP3 inflammasome being the best characterized among them. The increasing scientific interest in the mechanisms interconnecting inflammation and tumorigenesis has led to the study of the NLRP3 inflammasome in the setting of various neoplasms. Despite a plethora of data regarding solid tumors, NLRP3 inflammasome's implication in the pathogenesis of hematological malignancies only recently gained attention. In this review, we investigate its role in normal lymphopoiesis and lymphomagenesis. Considering that lymphomas comprise a heterogeneous group of hematologic neoplasms, both tumor-promoting and tumor-suppressing properties were attributed to the NLRP3 inflammasome, affecting neoplastic cells and immune cells in the tumor microenvironment. NLRP3 inflammasome-related proteins were associated with disease characteristics, response to treatment, and prognosis. Few studies assess the efficacy of NLRP3 inflammasome therapeutic targeting with encouraging results, though most are still at the preclinical level. Further understanding of the mechanisms regulating NLRP3 inflammasome activation during lymphoma development and progression can contribute to the investigation of novel treatment approaches to cover unmet needs in lymphoma therapeutics.

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.

The phosphatase DUSP22 inhibits UBR2-mediated K63-ubiquitination and activation of Lck downstream of TCR signalling

DUSP22 is a dual-specificity phosphatase that inhibits T cell activation by inactivating the kinase Lck. Here we show that the E3 ubiquitin ligase UBR2 is a positive upstream regulator of Lck during T-cell activation. DUSP22 dephosphorylates UBR2 at specific Serine residues, leading to ubiquitin-mediated UBR2 degradation. UBR2 is also modified by the SCF E3 ubiquitin ligase complex via Lys48-linked ubiquitination at multiple Lysine residues. Single-cell RNA sequencing analysis and UBR2 loss of function experiments showed that UBR2 is a positive regulator of proinflammatory cytokine expression. Mechanistically, UBR2 induces Lys63-linked ubiquitination of Lck at Lys99 and Lys276 residues, followed by Lck Tyr394 phosphorylation and activation as part of TCR signalling. Inflammatory phenotypes induced by TCR-triggered Lck activation or knocking out DUSP22, are attenuated by genomic deletion of UBR2. UBR2-Lck interaction and Lck Lys63-linked ubiquitination are induced in the peripheral blood T cells of human SLE patients, which demonstrate the relevance of the UBR2-mediated regulation of inflammation to human pathology. In summary, we show here an important regulatory mechanism of T cell activation, which finetunes the balance between T cell response and aggravated inflammation.

The induction of SHP-1 degradation by TAOK3 ensures the responsiveness of T cells to TCR stimulation

Thousand-and-one-amino acid kinase 3 (TAOK3) is a serine and threonine kinase that belongs to the STE-20 family of kinases. Its absence reduces T cell receptor (TCR) signaling and increases the interaction of the tyrosine phosphatase SHP-1, a major negative regulator of proximal TCR signaling, with the kinase LCK, a component of the core TCR signaling complex. Here, we used mouse models and human cell lines to investigate the mechanism by which TAOK3 limits the interaction of SHP-1 with LCK. The loss of TAOK3 decreased the survival of naïve CD4+ T cells by dampening the transmission of tonic and ligand-dependent TCR signaling. In mouse T cells, Taok3 promoted the secretion of interleukin-2 (IL-2) in response to TCR activation in a manner that depended on Taok3 gene dosage and on Taok3 kinase activity. TCR desensitization in Taok3-/- T cells was caused by an increased abundance of Shp-1, and pharmacological inhibition of Shp-1 rescued the activation potential of these T cells. TAOK3 phosphorylated threonine-394 in the phosphatase domain of SHP-1, which promoted its ubiquitylation and proteasomal degradation. The loss of TAOK3 had no effect on the abundance of SHP-2, which lacks a residue corresponding to SHP-1 threonine-394. Modulation of SHP-1 abundance by TAOK3 thus serves as a rheostat for TCR signaling and determines the activation threshold of T lymphocytes.

Highly potent, orally active novel small-molecule HPK1 inhibitor DS21150768 induces anti-tumor responses in multiple syngeneic tumor mouse models

Augmenting T-cell activity is a promising approach to enhance the efficacy of cancer immunotherapy treatment. Hematopoietic progenitor kinase 1 (HPK1) is predominantly expressed in immune cells and negatively regulates T-cell receptor signaling. It is reported that inhibition of the kinase function of HPK1 results in tumor growth suppression by enhancing cancer immunity. Thus, developing HPK1 inhibitors has attracted considerable attention as a future cancer immunotherapy approach. However, despite recent progress in HPK1 biology and pharmacology, various challenges still remain, such as developing HPK1 inhibitors with favorable pharmacological profiles and identifying tumor characteristics that can be applied to define susceptibility to HPK1 inhibition. Here, we present the identification and pharmacological evaluation of DS21150768, a potent small-molecule HPK1 inhibitor with a novel chemical scaffold. DS21150768 shows remarkable inhibition of HPK1 kinase activity, and in vitro studies demonstrated its potent activity to enhance T-cell function. DS21150768 is orally bioavailable and shows sustained plasma exposure, which leads to enhanced cytokine responses in vivo. We conducted a comparison of the anti-tumor efficacy of DS21150768 alone or in combination with anti-PD-1 antibody in 12 different mouse cancer cell models, and observed that the treatments suppressed tumor growth in multiple models. Furthermore, Gene Set Enrichment Analysis demonstrated significant enrichment of immune-related gene signatures in the tumor models responsive to DS21150768 treatment. Our results provide a path forward for the future development of HPK1 inhibitors and fundamental insights into biomarkers of HPK1-targeted therapy.

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.

Direct immunoactivation by chemotherapeutic drugs in cancer treatment

The immune system plays a crucial role in recognizing and eliminating pathogenic substances and malignant cells in the body. For cancer treatment, immunotherapy is becoming the standard treatment for many types of cancer and is often combined with chemotherapy. Although chemotherapeutic agents are often reported to have adverse effects, including immunosuppression, they can also play a positive role in immunotherapy by directly stimulating the immune system. This has been demonstrated in preclinical and clinical studies in the past decades. Chemotherapeutics can activate immune cells through different immune receptors and signaling pathways depending on their chemical structure and formulation. In this review, we summarize and discuss the direct immunoactivation effects of chemotherapeutics and possible mechanisms behind these effects. Finally, we prospect chemo-immunotherapeutic combinations for the more effective and safer treatment of cancer.

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.

An HPK1 inhibitor enhanced the tumour response to anti-PD-1 immunotherapy in non-Hodgkin's lymphoma

Anti-PD-1 immunotherapy has been widely applied in patients with some types of lymphoma. Classical Hodgkin's lymphoma (cHL) is highly sensitive to immunotherapy, but non-Hodgkin's lymphoma (NHL) does not show a good response. Studies have indicated that haematopoietic progenitor kinase 1 (HPK1) suppresses T cells and reduces antitumour immunity. Therefore, HPK1 inhibitors may restore and elicit antitumour immune responses and are promising candidate drug targets for cancer immunotherapy. We first explored the Gene Expression Profile Interactive Analysis (GEPIA) database and predicted that HPK1 expression was increased in diffuse large B-cell lymphoma (DLBCL) and associated with Nod-like receptor protein 3 (NLRP3) expression. We investigated whether an HPK1 inhibitor could enhance the tumour response to anti-PD-1 immunotherapy in NHL and the association between HPK1 and NLRP3 expression. Employing shHPK1 and an inhibitor, we demonstrated that the HPK1 inhibitor increased anti-PD-1-mediated T-cell cytotoxicity in BJAB and WSU-DLCL2 cells cocultured with peripheral blood mononuclear cells (PBMCs). HPK1 inhibitor treatment increased PD-1, PD-L1, Bax, p53 and NK-kB expression but decreased NLRP3 expression, indicating that the HPK1 inhibitor promoted apoptosis and blocked the NLRP3 inflammasome pathway to affect anti-PD-1-mediated T-cell cytotoxicity. Moreover, the HPK1 inhibitor enhanced the efficiency of anti-PD-1 immunotherapy in vivo in a zebrafish xenograft model of NHL. In summary, this study provides evidence that an HPK1 inhibitor enhanced the tumour response to anti-PD-1 immunotherapy in NHL by promoting apoptosis and blocking the NLRP3 pathway. These findings provide a potential therapeutic option for NHL combining HPK1 inhibitor treatment and anti-PD-1 immunotherapy.

Design and synthesis of 1H-pyrazolo[3,4-d]pyrimidine derivatives as hematopoietic progenitor kinase 1 (HPK1) inhibitors

Despite immune checkpoint inhibitors' tremendous success in the treatment of tumors, the moderate response rate limits their widespread use. Hematopoietic progenitor kinase 1 (HPK1) is served as an essential negative regulator of T-cell receptor, which has been identified as a promising target for enhancing antitumor immunity. However, the development of a selective HPK1 inhibitor is still challenging. Herein, we reported a novel series of 1H-pyrazolo[3,4-d]pyrimidine derivatives as HPK1 inhibitors by structure-based rational design. The optimal compound 10n significantly inhibited HPK1 with an IC50 value of 29.0 nM and the phosphorylation of SLP76 at a concentration as low as 0.1 μM. Furthermore, compound 10n exhibited good selectivity over a panel of 25 kinases, including GLK from the same MAP4K family. Together, the current study provided a novel, potent, and selective HPK1 inhibitor, acting as a lead compound for the future development of cancer immunotherapy.

Small molecule inhibitors for cancer immunotherapy and associated biomarkers - the current status

Following the success of cancer immunotherapy using large molecules against immune checkpoint inhibitors, the concept of using small molecules to interfere with intracellular negative regulators of anti-tumor immune responses has emerged in recent years. The main targets for small molecule drugs currently include enzymes of negative feedback loops in signaling pathways of immune cells and proteins that promote immunosuppressive signals within the tumor microenvironment. In the adaptive immune system, negative regulators of T cell receptor signaling (MAP4K1, DGKα/ζ, CBL-B, PTPN2, PTPN22, SHP1), co-receptor signaling (CBL-B) and cytokine signaling (PTPN2) have been preclinically validated as promising targets and initial clinical trials with small molecule inhibitors are underway. To enhance innate anti-tumor immune responses, inhibitory immunomodulation of cGAS/STING has been in the focus, and inhibitors of ENPP1 and TREX1 have reached the clinic. In addition, immunosuppressive signals via adenosine can be counteracted by CD39 and CD73 inhibition, while suppression via intratumoral immunosuppressive prostaglandin E can be targeted by EP2/EP4 antagonists. Here, we present the status of the most promising small molecule drug candidates for cancer immunotherapy, all residing relatively early in development, and the potential of relevant biomarkers.

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.

Off-target pharmacological activity at various kinases: Potential functional and pathological side effects

In drug discovery, during the lead optimization and candidate characterization stages, novel small molecules are frequently evaluated in a battery of in vitro pharmacology assays to identify potential unintended, off-target interactions with various receptors, transporters, ion channels, and enzymes, including kinases. Furthermore, these screening panels may also provide utility at later stages of development to provide a mechanistic understanding of unexpected safety findings. Here, we present a compendium of the most likely functional and pathological outcomes associated with interaction(s) to a panel of 95 kinases based on an extensive curation of the scientific literature. This panel of kinases was designed by AbbVie based on safety-related data extracted from the literature, as well as from over 20 years of institutional knowledge generated from discovery efforts. For each kinase, the scientific literature was reviewed using online databases and the most often reported functional and pathological effects were summarized. This work should serve as a practical guide for small molecule drug discovery scientists and clinical investigators to predict and/or interpret adverse effects related to pharmacological interactions with these kinases.

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.

Hematopoietic progenitor kinase 1 inhibits the development and progression of pancreatic intraepithelial neoplasia

Ras plays an essential role in the development of acinar-to-ductal metaplasia (ADM) and pancreatic ductal adenocarcinoma (PDAC). However, mutant Kras is an inefficient driver for PDAC development. The mechanisms of the switching from low Ras activity to high Ras activity that are required for development and progression of pancreatic intraepithelial neoplasias (PanINs) are unclear. In this study, we found that hematopoietic progenitor kinase 1 (HPK1) was upregulated during pancreatic injury and ADM. HPK1 interacted with the SH3 domain and phosphorylated Ras GTPase-activating protein (RasGAP) and upregulated RasGAP activity. Using transgenic mouse models of HPK1 or M46, a kinase-dead mutant of HPK1, we showed that HPK1 inhibited Ras activity and its downstream signaling and regulated acinar cell plasticity. M46 promoted the development of ADM and PanINs. Expression of M46 in KrasG12D Bac mice promoted the infiltration of myeloid-derived suppressor cells and macrophages, inhibited the infiltration of T cells, and accelerated the progression of PanINs to invasive and metastatic PDAC, while HPK1 attenuated mutant Kras-driven PanIN progression. Our results showed that HPK1 plays an important role in ADM and the progression of PanINs by regulating Ras signaling. Loss of HPK1 kinase activity promotes an immunosuppressive tumor microenvironment and accelerates the progression of PanINs to PDAC.

Negative intracellular regulators of T-cell receptor (TCR) signaling as potential antitumor immunotherapy targets

Immunotherapy strategies aim to mobilize immune defenses against tumor cells by targeting mainly T cells. Co-inhibitory receptors or immune checkpoints (ICPs) (such as PD-1 and CTLA4) can limit T cell receptor (TCR) signal propagation in T cells. Antibody-based blocking of immune checkpoints (immune checkpoint inhibitors, ICIs) enable escape from ICP inhibition of TCR signaling. ICI therapies have significantly impacted the prognosis and survival of patients with cancer. However, many patients remain refractory to these treatments. Thus, alternative approaches for cancer immunotherapy are needed. In addition to membrane-associated inhibitory molecules, a growing number of intracellular molecules may also serve to downregulate signaling cascades triggered by TCR engagement. These molecules are known as intracellular immune checkpoints (iICPs). Blocking the expression or the activity of these intracellular negative signaling molecules is a novel field of action to boost T cell-mediated antitumor responses. This area is rapidly expanding. Indeed, more than 30 different potential iICPs have been identified. Over the past 5 years, several phase I/II clinical trials targeting iICPs in T cells have been registered. In this study, we summarize recent preclinical and clinical data demonstrating that immunotherapies targeting T cell iICPs can mediate regression of solid tumors including (membrane associated) immune-checkpoint inhibitor refractory cancers. Finally, we discuss how these iICPs are targeted and controlled. Thereby, iICP inhibition is a promising strategy opening new avenues for future cancer immunotherapy treatments.

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.

Design and Synthesis of Functionally Active 5-Amino-6-Aryl Pyrrolopyrimidine Inhibitors of Hematopoietic Progenitor Kinase 1

Immune activating agents represent a valuable class of therapeutics for the treatment of cancer. An area of active research is expanding the types of these therapeutics that are available to patients via targeting new biological mechanisms. Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of immune signaling and a target of high interest for the treatment of cancer. Herein, we present the discovery and optimization of novel amino-6-aryl pyrrolopyrimidine inhibitors of HPK1 starting from hits identified via virtual screening. Key components of this discovery effort were structure-based drug design aided by analyses of normalized B-factors and optimization of lipophilic efficiency.

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.

Theoretical Studies on Selectivity of HPK1/JAK1 Inhibitors by Molecular Dynamics Simulations and Free Energy Calculations

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of T cell receptor, which has been regarded as a potential target for immunotherapy. Yu et al. observed the off-target effect of the high-throughput screening HPK1 kinase inhibitor hits on JAK1 kinase. The off-target effect is usually due to the lack of specificity of the drug, resulting in toxic side effects. Therefore, exploring the mechanisms to selectively inhibit HPK1 is critical for developing effective and safe inhibitors. In this study, two indazole compounds as HPK1 inhibitors with different selectivity towards JAK1 were used to investigate the selectivity mechanism using multiple computational methods, including conventional molecular dynamics simulations, binding free energy calculations and umbrella sampling simulations. The results indicate that the salt bridge between the inhibitor and residue Asp101 of HPK1 favors their selectivity towards HPK1 over JAK1. Information obtained from this study can be used to discover and design more potent and selective HPK1 inhibitors for immunotherapy.

Discovery of Pyrazolopyridine Derivatives as HPK1 Inhibitors

In spite of the great success of immune checkpoint inhibitors in immune-oncology therapy, an urgent need still exists to identify alternative approaches to broaden the scope of therapeutic coverage. Hematopoietic progenitor kinase 1 (HPK1), also known as MAP4K1, functions as a negative regulator of activation signals generated by the T cell antigen receptor. Herein we report the discovery of novel pyrazolopyridine derivatives as selective inhibitors of HPK1. The structure-activity relationship campaign led to the discovery of compound 16, which has shown promising enzymatic and cellular potency with encouraging kinome selectivity. The outstanding pharmacokinetic profiles of 16 in rats and monkeys supported further evaluations of its efficacy and safety in preclinical models.

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.

Discovery of Macrocycle-Based HPK1 Inhibitors for T-Cell-Based Immunotherapy

Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of T-cell activation, and targeting HPK1 is considered a promising strategy for improving responses to antitumor immune therapies. The biggest challenge of HPK1 inhibitor design is to achieve a higher selectivity to GLK, an HPK1 homology protein as a positive regulator of T-cell activation. Herein, we report the design of a series of macrocycle-based HPK1 inhibitors via a conformational constraint strategy. The identified candidate compound 5i exhibited HPK1 inhibition with an IC₅₀ value of 0.8 nM and 101.3-fold selectivity against GLK. Compound 5i also displayed good oral bioavailability (F = 27-49%) in mice and beagles and favorable metabolic stability (T_1/2 > 186.4 min) in human liver microsomes. More importantly, compound 5i demonstrated a clear synergistic effect with anti-PD-1 in both MC38 (MSI) and CT26 (MSS) syngeneic tumor mouse models. These results showed that compound 5i has a great potential in immunotherapy.

Genome Editing for Engineering the Next Generation of Advanced Immune Cell Therapies

Our current genetic engineering capacity through synthetic biology and genome editing is the foundation of a revolution in biomedical science: the use of genetically programmed cells as therapeutics. The prime example of this paradigm is the adoptive transfer of genetically engineered T cells to express tumor-specific receptors, such as chimeric antigen receptors (CARs) or engineered T-cell receptors (TCR). This approach has led to unprecedented complete remission rates in patients with otherwise incurable hematological malignancies. However, this approach is still largely ineffective against solid tumors, which comprise the vast majority of neoplasms. Also, limitations associated with the autologous nature of this therapy and shared markers between cancer cells and T cells further restrict the access to these therapies. Here, we described how cutting-edge genome editing approaches have been applied to unlock the full potential of these revolutionary therapies, thereby increasing therapeutic efficacy and patient accessibility.

The expanding role for small molecules in immuno-oncology

The advent of immune checkpoint inhibition (ICI) using antibodies against PD1 and its ligand PDL1 has prompted substantial efforts to develop complementary drugs. Although many of these are antibodies directed against additional checkpoint proteins, there is an increasing interest in small-molecule immuno-oncology drugs that address intracellular pathways, some of which have recently entered clinical trials. In parallel, small molecules that target pro-tumorigenic pathways in cancer cells and the tumour microenvironment have been found to have immunostimulatory effects that synergize with the action of ICI antibodies, leading to the approval of an increasing number of regimens that combine such drugs. Combinations with small molecules targeting cancer metabolism, cytokine/chemokine and innate immune pathways, and T cell checkpoints are now under investigation. This Review discusses the recent milestones and hurdles encountered in this area of drug development, as well as our views on the best path forward.

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.

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

Hematopoietic progenitor kinase 1 (HPK1) is an MAP4K family member within the Ste20-like serine/threonine branch of the kinome. HPK1 expression is limited to hematopoietic cells and has a predominant role as a negative regulator of T cell function. Because of the central/dominant role in negatively regulating T cell function, HPK1 has long been in the center of interest as a potential pharmacological target for immune therapy. The development of a small molecule HPK1 inhibitor remains challenging because of the need for high specificity relative to other kinases, including additional MAP4K family members, that are required for efficient immune cell activation. Here, we report the identification of the selective and potent HPK1 chemical probe, A-745. In unbiased cellular kinase-binding assays, A-745 demonstrates an excellent cellular selectivity binding profile within pharmacologically relevant concentrations. This HPK1 selectivity translates to an in vitro immune cell activation phenotype reminiscent of Hpk1-deficient and Hpk1-kinase-dead T cells, including augmented proliferation and cytokine production. The results from this work give a path forward for further developmental efforts to generate additional selective and potent small molecule HPK1 inhibitors with the pharmacological properties for immunotherapy.

Discovery of Novel HPK1 Inhibitors Through Structure-Based Virtual Screening

Hematopoietic progenitor kinase (HPK1) is a negative regulator of T-cell receptor and B-cell signaling, which has been recognized as a novel antitumor target for immunotherapy. In this work, Glide docking-based virtual screening and kinase inhibition assay were performed to identify novel HPK1 inhibitors. The kinase inhibition assay results demonstrated five compounds with IC50 values below 20 μM, and the most potent one (compound M074-2865) had an IC50 value of 2.93 ± 0.09 μM. Molecular dynamics (MD) simulations were performed to delve into the interaction of sunitinib and the identified compound M074-2865 with the kinase domain of HPK1. The five compounds identified in this work could be considered promising hit compounds for further development of HPK1 inhibitors for immunotherapy.