Using yeast surface display to engineer a soluble and crystallizable construct of hematopoietic progenitor kinase 1 (HPK1)

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.

Engineering Compositionally Uniform Yeast Whole-Cell Biocatalysts with Maximized Surface Enzyme Density for Cellulosic Biofuel Production

In recent decades, whole-cell biocatalysis has played an increasingly important role in the food, pharmaceutical, and energy sector. One promising application is the use of ethanologenic yeast displaying minicellulosomes on the cell surface to combine cellulose hydrolysis and fermentation into a single step for consolidated bioprocessing. However, cellulosic ethanol production using existing yeast whole-cell biocatalysts (yWCBs) has not reached industrial feasibility due to their inefficient cellulose hydrolysis. As prior studies have demonstrated enzyme density on the yWCB surface to be one of the most important parameters for enhancing cellulose hydrolysis, we sought to maximize this parameter at both the population and single-cell levels in yWCBs displaying tetrafunctional minicellulosomes. At the population level, enzyme density is limited by the presence of a nondisplay population constituting 25-50% of all cells. In this study, we identified the cause to be plasmid loss and successfully eliminated the nondisplay population to generate compositionally uniform yWCBs. At the single-cell level, we demonstrate that enzyme density is limited by molecular crowding, which hinders minicellulosome assembly. By adjusting the integrated gene copy number, we obtained yWCBs of tunable enzyme display levels. This tunability allowed us to avoid the crowding-limited regime and achieve a maximum enzyme density per cell. As a result, the best strain showed a cellulose-to-ethanol yield of 4.92 g/g, corresponding to 96% of the theoretical maximum and near-complete conversion (∼96%) of the starting cellulose (1% PASC). Our holistic engineering strategy that combines a population and single-cell level approach is broadly applicable to enhance the WCB performance in other biocatalytic cascade schemes.

Saccharomyces cerevisiae surface display of endolysin LysKB317 for control of bacterial contamination in corn ethanol fermentations

Control of bacterial contamination in bioethanol fermentation facilities has traditionally relied on chemical-based products such as hop acids and use of antibiotics. Recent emphasis on antibiotic stewardship has prompted new research into the development of alternative approaches to microbial remediation strategies. We recently described a recombinant peptidoglycan hydrolase, endolysin LysKB317, which inhibited Limosilactobacillus fermentum strains in corn mash fermentation. Here, Saccharomyces cerevisiae EBY100 was used to anchor recombinant LysKB317 using cell surface display with the a-agglutinin proteins Aga1p–Aga2p. Immunostaining and confocal fluorescence were used for localization of the extracellular interface of the cells. Yeast surface-expressed endolysin demonstrated an 83.8% decrease in bacterial cell counts compared to a 9.5% decrease in control yeast. Recombinant S. cerevisiae expressing LysKB317 used for small-scale corn mash fermentation, when infected with L. fermentum, could proactively control bacterial infection for 72 h with at least 1-log fold reduction. Analysis of fermentation products showed improved ethanol concentrations from 3.4% to at least 5.9% compared to the infection-only control and reduced levels of lactic and acetic acid from 34.7 mM to 13.8 mM and 25.5 mM to 18.1 mM, respectively. In an optimized yeast surface display system, proactive treatment of bacterial contaminants by endolysin LysKB317 can improve fermentation efficiency in the presence of L. fermentum contamination.

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.

Yeast Surface Display: New Opportunities for a Time-Tested Protein Engineering System

Yeast surface display has proven to be a powerful tool for the discovery of antibodies and other novel binding proteins and for engineering the affinity and selectivity of existing proteins for their targets. In the decades since the first demonstrations of the approach, the range of yeast display applications has greatly expanded to include many different protein targets and has grown to encompass methods for rapid protein characterization. Here, we briefly summarize the development of yeast display methodologies and highlight several selected examples of recent applications to timely and challenging protein engineering and characterization problems.

Inhibitors of immuno-oncology target HPK1 - a patent review (2016 to 2020)

Introduction: Hematopoietic progenitor kinase (HPK1), a serine/threonine kinase, which is primarily expressed in hematopoietic cells is a negative regulator of T-cell receptor and B cell signaling. Studies using genetic disruption of HPK1 function show enhanced T-cell signaling, cytokine production, and in vivo tumor growth inhibition. This profile of enhanced immune response highlights small molecule inhibition of HPK1 as an attractive approach for the immunotherapy of cancer.Areas covered: This article summarizes the biological rationale for the inhibition of HPK1 as a potential adjunct to the current immuno-oncology (IO) therapies. The article primarily discloses the current state of development of HPK1 inhibitors.Expert Opinion: The rapid increase in the identification of small molecule inhibitors of HPK1 should translate into a fuller understanding of the role of HPK1 inhibition in the IO setting. This understanding will be of huge importance in determining whether HPK1 inhibition alone will be sufficient for tumor growth inhibition or if combination with current IO therapies will be required.

Discovery of Orally Active Isofuranones as Potent, Selective Inhibitors of Hematopoetic Progenitor Kinase 1

While the discovery of immune checkpoint inhibitors has led to robust, durable responses in a range of cancers, many patients do not respond to currently available therapeutics. Therefore, an urgent need exists to identify alternative mechanisms to augment the immune-mediated clearance of tumors. Hematopoetic progenitor kinase 1 (HPK1) is a serine-threonine kinase that acts as a negative regulator of T-cell receptor (TCR) signaling, to dampen the immune response. Herein we describe the structure-based discovery of isofuranones as inhibitors of HPK1. Optimization of the chemotype led to improvements in potency, selectivity, plasma protein binding, and metabolic stability, culminating in the identification of compound 24. Oral administration of 24, in combination with an anti-PD1 antibody, demonstrated robust enhancement of anti-PD1 efficacy in a syngeneic tumor model of colorectal cancer.