BI-5521

BI-5521 is a highly potent (nanomolar range) and selective GSK-3a and GSK-3b ATP-competitive inhibitor, with similar potencies for the 2 isoforms. Both in vitro (radioligand binding assay) and cell activity (glycogen synthesis rate stimulation in C3A cells) validations are available, but orthogonal assays have not been performed yet. BI-5521 also significantly inhibits DYRK1A at 500 nM, but activity data at lower concentrations (e.g., 1-100 nM) is not available for this off-target. Selectivity was investigated against a panel of 62 non-kinase targets, but only 48 members of the kinome were interrogated. The compound had a >100 fold selectivity for GSK-3 over 4 kinases and >1000 fold selectivity over all other assessed targets. A cytotoxicity assay was also performed in U937 cells (IC50 = 390 nM). Orthogonal probes (competitive and non-competitive inhibitors) and a negative control (BI-4481) are also available. A crystal structure of the complex between GSK-3b and a chemically related inhibitor (BI-91BS) is available at RCSB PDB database (6GJO). BI-5521 has an acceptable in vivo pharmacokinetic profile, but the CNS distribution was not investigated. The compound showed acute and subchronic efficacies in lowering blood glucose levels in rodent strains that exhibit a type 2 diabetes-like phenotype (ZDF rats and db/db mice, respectively). No data is available regarding the use of BI-5521 in animal models of other relevant diseases (e.g., tauopathies, bipolar disorder). There is currently no in vivo toxicity data available.

BI-5521 is a potent dual inhibitor of GSK-3a and GSK-3b with biochemical potencies of 2 and 1 nM respectively against these two targets. It is a very potent inhibitor of DYRK1A, showing 99% inhibition at 500 nM. BI-5521 was also tested in an invitrogen panel of 45 additional kinases and inhibited only 2 kinases at < 50% at 500 nM (KDR, 79% inhibition, ROCK, 64% inhibition). There is no available public data on any additional kinases. BI-5521 is selective against a panel of 61 non-kinase targets. BI-5521 exhibits potent, mechanism-based activity in a cell-based assay, stimulating the rate glycogen synthesis in C3A cells with an EC50 of 3 nM, with a reported cytotoxicity value of 390 nM, suggesting an ideal range for cellular experiments of 10-100 nM. BI-5521 exhibits modest but significant oral exposure in rats with bioavailability of 17% in rats and moderate iv clearance of 32 mL/min/kg. In terms of its ADME parameters, BI-5521 shows good cellular permeability (Caco-2 assay) and is inactive against a panel of CYP450s except for CYP 2C19 (12.9 uM). This probe shows robust dose dependent lowering of plasma glucose in the OGTT ZDF model at 3 and 10 mg/kg. Finally, the utility of BI-5521 is enhanced both due to the availability of a negative structurally related probe (BI-4481) as well as several structurally unrelated chemical series that are also potent inhibitors of GSK-3.