In vitro activity: Y-27632 2HCl is a potent and selective inhibitor of ROCK1 (p160ROCK) with IC50 of 140 nM in a cell-free assay, it exhibits>200-fold selectivity over other kinases, including PKC, cAMP-dependent protein kinase, MLCK and PAK. Y27632 prevents dimethylnitrosamine-induced hepatic fibrosis in rats, increases apoptosis and disrupts the actin cortical mat in embryonic avian corneal epithelium, affects initial heart myofibrillogenesis in cultured chick blastoderm, promotes the proliferation and cell cycle progression of cultured astrocyte from spinal cord. Y-27632 suppresses the kinase activity of both ROCK-1 and ROCK-2 in vitro, and this compound inhibits the kinases by binding to the catalytic site of ROCK-1 and ROCK-2. Thus Y-27632 function on Rho-mediated stress fiber formation, the G1-S phase progression and cytokinesis. Y-27632 2HCl inhibits ROCK-II while displaying little activity against PKC, cAMP-dependent protein kinase and myosin light-chain kinase (MLCK) with Ki of 26 μM, 25 μM and> 250 μM, respectively, as well as PKA activated by another Rho-family GTPase member, Cdc42. Y-27632 2HCl inhibits smooth-muscle contraction induces by various agonists including phenylephrine, histamine, acetylcholine, serotonin, endothelin, and thromboxane with IC50 of 0.3-1 μM, by selectively inhibiting Ca2+ sensitization. Y-27632 2HCl suppresses Rho-induced, p160ROCK-mediated formation of stress fibres in cultured cells. Y-27632 2HCl treatment blocks both Rho-mediated activation of actomyosin and LPA-stimulated invasive activity of MM1 cells in a concentration-dependent manner. Y-27632 2HCl treatment is not only sufficient to initiate formation of exuberant axonal processes but also facilitates axonal maturation during the very early stages of axonogenesis, while largely sparing axon elongation. In human embryonic stem (hES) cells, Y-27632 2HCl treatment at 10 μM markedly diminishes dissociation-induced apoptosis even in serum-free suspension (SFEB) culture, increases cloning efficiency (from ~1% to ~27%), facilitates subcloning after gene transfer, and enables SFEB-cultured hES cells to survive and differentiate into Bf1+ cortical and basal telencephalic progenitors.

Kinase Assay: Recombinant ROCK-I, ROCK-II, PKN, or citron kinase is expressed in HeLa cells as Myc-tagged proteins by transfection using Lipofectamine, and is precipitated from the cell lysates by the use of 9E10 monoclonal anti-Myc antibody coupled to G protein-Sepharose. Recovered immunocomplexes are incubated with various concentrations of [32P]ATP and 10 mg of histone type 2 as substrates in the absence or presence of various concentrations of either Y-27632 or Y-30141 at 30°C for 30 min in a total volume of 30 μL of the kinase buffer containing 50 mM HEPES-NaOH, pH 7.4, 10 mM MgCl2, 5 mM MnCl2, 0.02% Briji 35, and 2 mM dithiothreitol. PKCa is incubated with 5 μM [32P]ATP and 200 μg/mL histone type 2 as substrates in the absence or presence of various concentrations of either Y-27632 or Y-30141 at 30°C for 10 min in a kinase buffer containing 50 mM Tris-HCl, pH 7.5, 0.5 mM CaCl2, 5 mM magnesium acetate, 25 μg/mL phosphatidyl serine, 50 ng/mL 12-O-tetradecanoylphorbol-13-acetate and 0.001% leupeptin in a total volume of 30 μL. Incubation is terminated by the addition of 10 μL of 43 Laemmli sample buffer. After boiling for 5 min, the mixture is subjected to SDS-polyacrylamide gel electrophoresis on a 16% gel. The gel is stained with Coomassie Brilliant Blue, and then dried. The bands corresponding to histone type 2 are excised, and the radioactivity is measured.

Cell Assay: eLa cells are plated at a density of 3×104 cells per 3.5-cm dish. The cells are cultured in DMEM containing 10% FBS in the presence of 10 mM Thymidine for 16 h. After the cells are washed with DMEM containing 10% FBS, they are cultured for an additional 8 h, and then 40 ng/mL of Nocodazole is added. After 11.5 h of the Nocodazole treatment, various concentrations of Y-27632 (0-300 μM), Y-30141, or vehicle is added and the cells are incubated for another 30 min.