HG-9-91-01

HG-9-91-01 is a potent and selective inhibitor of SIK. HG-9-91-01 not only targets the ATP-binding site, but also a small hydrophobic pocket adjacent to this site that is created by the presence of a small amino acid residue at this gatekeeper site. HG-9-91-01 inhibits a number of protein tyrosine kinases that possess a threonine residue at the gatekeeper site, such as Src family members (Src, Lck, and Yes), BTK, and the FGF and Ephrin receptors. HG-9-91-01 potently inhibits the SIKs and, crucially, does not inhibit any other member of the AMPK-related kinase subfamily, which all possess a large hydrophobic residue (Met or Leu) at the gatekeeper site. HG-9-91-01 increases LPS-stimulated IL-10 production and greatly suppressed proinflammatory cytokine secretion, even when cells are costimulated with IFNγ to generate fully polarized classically activated (M1) macrophages.^[1]

Macrophages are treated for 1 h with 500 nM HG-9-91-01 or an equivalent volume of DMSO for control incubations then stimulated for up to 24 h with 1 μg/mL Pam3CSK4, 2 μg/mL lipoteichoic acid (LTA), 100 ng/mL LPS, 1 μg/mL R837, or 2 μM CpG. Proteins are extracted and immunoblotted by using the indicated antibodies. RNA is extracted by using the RNeasy Micro Kit. cDNA is generated by using the iScript cDNA synthesis kit and quantified by qPCR using the SsoFast EvaGreen Supermix. The relative expression of each gene is calculated from Ct values by using the Pfaffl method and is normalized against the mRNA levels of 18S or GAPDH RNA. Fold induction for each gene is reported relative to untreated control cells, which is set to 1. The concentrations of TNFα, IL-6, IL-10, IL-12p40, and RANTES in culture supernatants were measured by using the Bio-Plex Pro Assay system from Bio-Rad.

HG-9-91-01 is > 99% serum bound and rapidly degraded by mouse liver microsomes (t1/2 = 11 min) making this compound unsuitable for direct injection into animals.^[2]