Kinase experiment:

The 10 ?L assay mixtures contain 50 mM HEPES (pH 7.5), 0.01% Brij-35, 10 mM MgCl2, 1 mM EGTA, 2 ?M FRET peptide substrate, and PAK enzyme (20 pM PAK1; 50 pM PAK2; 90 pM PAK4). Incubations are carried out at 22℃ in black polypropylene 384-well plates. Prior to the assay, enzyme, FRET peptide substrate and serially diluted test compounds (G-5555) are preincubated together in assay buffer (7.5 ?L) for 10 minutes, and the assay is initiated by the addition of 2.5 ?L assay buffer containing 4x ATP (160 ?M PAK1; 480 ?M PAK2; 16 ?M PAK4). Following the 60-minute incubation, the assay mixtures are quenched by the addition of development reagent, and 1 hour later the emissions of Coumarin (445 nm) and Fluorescein (520 nm) are determined after excitation at 400 nm using an Envision plate reader[1].

Animal experiment:

Mice: 3 mice in each of the two groups are administered 25 mg/kg oral suspension dose twice, with the second dose given 6 hours after the first dose. The dose volumes are 5 mL/kg for the IV group and 10 mL/kg for the PO groups. Following administration of G-5555 (12), 15 ?L of blood is collected at each time point are stored at -70 to -80℃ until analysis[1].

G-5555 hydrochloride is a potent and selective p21-activated kinase 1 (PAK1) inhibitor with a Ki of 3.7 nM. PAK1|3.7 nM (Ki)|PAK2|11 nM (Ki)

G-5555 shows excellent kinase selectivity and inhibits only eight out of the 235 kinases tested other than PAK1 with inhibition >70%: PAK2, PAK3, KHS1, Lck, MST3, MST4, SIK2, and YSK1. The IC50s of G-5555 against SIK2, PAK2, KHS1, MST4, YSK1, MST3 and Lck are 9, 11, 10, 20, 34, 43, 52 nM, respectively. In general, G-5555 demonstrates high selectivity for the group I PAKs. There is negligible activity for G-5555 against the hERG channel with IC50 more than 10 μM in a patch clamp assay[1]. In an array of 23 breast cancer cell lines, G-5555 has significantly greater growth inhibitory activity in cell lines that are PAK-amplified compared to non-amplified lines[2].

G-5555 exhibits low blood clearance and an acceptable half-life. Good oral exposure (AUC=30 μM•h) and high oral bioavailability (F=80%) are achieved[1]. In an H292 non-small cell lunger cancer (NSCLC) xenograft study in mice, G-5555 inhibits phosphorylation of the PAK1/2 downstream substrate mitogen-activated protein kinase 1 (MEK1) S298 and, when administered at an oral dose of 25 mg/kg b.i.d., imparts 60% tumor growth inhibition in this model13 and a PAK1 amplified breast cancer xenograft model, MDAMB-175[2].

[1]. Ndubaku CO, et al. Design of Selective PAK1 Inhibitor G-5555: Improving Properties by Employing an Unorthodox Low-pK a Polar Moiety. ACS Med Chem Lett. 2015 Oct 31;6(12):1241-6. [2]. Rudolph J, et al. Chemically Diverse Group I p21-Activated Kinase (PAK) Inhibitors Impart Acute Cardiovascular Toxicity with a Narrow Therapeutic Window. J Med Chem. 2016 Jun 9;59(11):5520-41.