G-5555 : ATP-competitive inhibitor of PAK1, PAK2, PAK3



Protein target names: PAK1 PAK2 PAK3

Mechanism of action: ATP-competitive inhibitor

In Vitro Validations

Uniprot ID: Q13153
Target Class: Protein kinase
Target SubClass: STE
Potency: Ki
Potency Value: 3.7 nM
Potency Assay: Measuring the phosphorylation of a FRET peptide substrate (Ser/Thr19) labeled with Coumarin and Fluorescein
PDB ID for probe-target interaction (3D structure): 5DEY
Structure-activity relationship: SAR described in "Design of Selective PAK1 Inhibitor G-5555: Improving Properties by Employing an Unorthodox Low-pKa Polar Moiety, ACS Med. Chem. Lett. 2015, 6, 1241" and Chemically diverse Group I PAK inhibitors impart acute cardiovascular toxicity with a narrow therapeutic window, J. Med. Chem. 2016, 59, 5520. SAR assay used is described above.

In Cell Validations

In Vivo Data

Reagent authentication certificate: PDF image

SERP Reviews

9 Jan 2017
In Cell Rating
In Model Organisms

This is a potent inhibitor of Group I PAK enzymes (PAK1, 2 and 3; PAK1 Ki = 4 nM) that has been screened versus 235 kinases at 100 nM, with biochemical inhibition of 5 kinases (IC50 <50 nM) observed. Expanded off-target kinase screening would be helpful to enhance the selectivity profile. Parallel use of the orthogonal PAK1-selective probe NVS-PAK1-1 is suggested to aid interpretation of cellular effects between PAK family members. The selectivity of G-5555 for Group I PAK enzymes over non-kinase targets (IC50 >10 uM for 36/42 diverse receptors, ion channels, enzymes and transporters) supports its use as a cellular probe. On-target activity in cells was demonstrated (inhibition of pMEK S298, IC50 = 69 nM) and supports the suggested concentration range for cellular studies. Compound pharmacokinetics are suitable for in vivo studies and on-target modulation of PAK-dependent pMEK S298 was demonstrated in H292 xenografts following 20 and 30 mg/kg single, oral doses. A caveat to the use of the compound in vivo for high doses or repeat dosing is the reported narrow therapeutic index due to acute cardiotoxicity of pan-PAK inhibitors (attributed to PAK2 inhibition with possible exacerbation by PAK1 inhibition) that limits tolerability and exposure (J. Med. Chem. 2016, 59, 5520).

7 Jan 2017
In Cell Rating
In Model Organisms
Starting with an advanced inhibitor, the authors optimized a PAK1-inhibitory compound for potency and selectivity. Based on analysis of their SAR tables, the authors did a good job balancing trade-offs between different types of potential liabilities, including 2 log(P) units, 7-fold better potency in vitro and 3-fold more activity in cells. Reducing hERG inhibition was a stated goal, and the reported compound has about half the activity against hERG compared with the predecessor; notably, some compounds tested were even better relative to hERG, but they were less attractive in other tested parameters. Based on a comparison of the kinase-profiling data reported by the authors, there were a handful of other kinases with IC50 values near that for PAK1, some within a few (2-3)-fold and 7 within 15-fold. On the other hand, the EC50 in cells is reported ~17-fold higher (69 nM) than the IC50 against PAK1. Based on this analysis, the recommended concentration range provided (70-250 nM) might be on the high side. While 70 nM is appropriate, if the ratio of EC50/IC50 is preserved for the "off-target" kinases, then 250 nM in cells might be above the EC50 for 2-3 of these other kinases.
12 Jun 2017
In Cell Rating
In Model Organisms

G-5555 is one of a number of quality compounds now available for the study of the function of group 1 PAKs, and its use in cells is recommended, especially if used alongside other chemotypes such as FRAX-1036 (ACS Med Chem Lett 2015, p1241), the Novartis allosteric inhibitor (ACS Med Chem Lett 2015, p776) and the AstraZeneca inhibitor (ACS Med Chem Lett 2016, p1118). Although G-5555 has pharmacokinetic properties that make it suitable for in vivo studies, caution should be exercised for acute doses >30 mg/kg or repeat dosing due to the reported narrow therapeutic index in a later J. Med. Chem. paper.