Antibody-based immune checkpoint inhibitors remain a major focus of immuno-oncology drug research and development efforts because of their recent success in providing long-term anti-tumor responses. However, the range of response of different tumor types to these drugs is hugely varied. Small molecule kinase inhibitors that block signaling pathways involved in regulation of tumor immunity at multiple points in the “cancer immunity cycle” may provide alternate, effective therapeutics. One kinase that may be a target for such small molecule inhibitors is Hematopoietic Progenitor Kinase 1 or HPK1; the potential of this kinase as a therapeutic target was reviewed by Sawasdikosol and Burakoff (1). HPK1, also known as MAP4K1, is a member of the MAP kinase protein kinase family that negatively regulates signal transduction in T-cells, B-cells and dendritic cells of the immune system.
![Fig 4. Four point MMOA screen for tideglusib and GW8510. Time dependent inhibition was evaluated by preincubation of TbGSK3β with 60 nM tideglusib and 6 nM GW-8510 with 10μM and 100μM ATP. (A). Tideglusib [60 nM] in 10μM ATP. (B). GW8510 [60 nM] in 10μM ATP. (C.) Tideglusib [60 nM] at 100μM ATP. (D.) GW8510 [60 nM] at 100μM ATP. All reactions preincubated or not preincubated with TbGSK3β for 30 min at room temperature. Experiments run with 10μM GSM peptide, 10μM ATP, and buffer. Minute preincubation (30 min) was preincubated with inhibitor, TbGSK3β, GSM peptide, and buffer. ATP was mixed to initiate reaction. No preincubation contained inhibitor, GSM peptide, ATP, and buffer. The reaction was initiated with TbGSK3β. Reactions were run at room temperature for 5 min and stopped at 80°C. ADP formed was measured by ADP-Glo kit. Values are mean +/- standard error. N = 3 for each experiment and experiments were run in duplicates. Control reactions contained DMSO and background was determined using a zero time incubation and subtracted from all reactions. Black = 30 min preincubation Grey = No preincubation.](https://www.promegaconnections.com/wp-content/uploads/2016/04/journal.pntd_.0004506.g004-243x300.png)
