Y-27632

Y-27632, the trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide and prototypical selective inhibitor of Rho-associated coiled-coil containing protein kinases (ROCK1 and ROCK2), is a cell-permeable pyridine derivative that competitively occupies the ATP-binding site of both ROCK isoforms with Ki values of approximately 140 to 220 nM for ROCK1 and approximately 300 nM for ROCK2, exhibiting 20- to 30-fold selectivity over the structurally related Rho effector kinases citron kinase and protein kinase N (PKN), and substantially greater selectivity over protein kinase C, protein kinase A, and myosin light chain kinase. First described by Uehata et al. in a 1997 report in Nature demonstrating that Rho-associated protein kinase-mediated calcium sensitization of smooth muscle contributes to the pathophysiology of hypertension, Y-27632 has become the most widely cited small-molecule ROCK inhibitor in biomedical research, with applications spanning vascular smooth muscle pharmacology, stem cell biology, neuroscience, ophthalmology, cancer biology, and fibrosis research.

The compound achieved landmark status in stem cell biology following the 2007 Watanabe et al. report in Nature Biotechnology demonstrating that Y-27632 markedly diminishes dissociation-induced apoptosis (anoikis) in human embryonic stem cells, increasing single-cell cloning efficiency from approximately 1 percent to 27 percent and enabling subcloning after gene transfer. This finding transformed human pluripotent stem cell culture methodology and established ROCK inhibition as a standard protective intervention during enzymatic passaging, cryopreservation, and fluorescence-activated cell sorting of human embryonic stem cells and induced pluripotent stem cells. The compound is now a routine component of pluripotent stem cell culture protocols across essentially all academic and industrial laboratories working with human pluripotent cells.

In cardiovascular pharmacology, Y-27632 inhibits agonist-induced contraction in intact blood vessels and lowers blood pressure in multiple animal models of hypertension, including renal hypertensive rats, deoxycorticosterone acetate (DOCA)-salt hypertensive rats, and spontaneously hypertensive rats, through inhibition of Rho/ROCK-mediated calcium sensitization of vascular smooth muscle. In neuroscience, the compound promotes neurite outgrowth from neural stem cells and primary neurons, attenuates myelin-associated inhibition of axon growth, and improves functional recovery after spinal cord injury in rodent models through modulation of the RhoA/ROCK signaling axis. In ophthalmology, Y-27632 reduces intraocular pressure in rabbit models by increasing aqueous humor outflow facility through relaxation of trabecular meshwork tissue, a mechanism that informed the subsequent clinical development of the ROCK inhibitors netarsudil and ripasudil for glaucoma. The compound has also been used in the preparation of cultured human corneal endothelial cell suspensions for injection therapy, with more than 130 patients treated in clinical procedures across Japan and other sites.

Y-27632 has not been developed as a systemic therapeutic agent for human administration; it remains principally a research tool compound. However, its pharmacological characterization has informed the clinical development of several ROCK inhibitors now approved for human use, including fasudil (approved in Japan and China for cerebral vasospasm), ripasudil (approved in Japan for glaucoma), and netarsudil (approved by the United States Food and Drug Administration for glaucoma). This monograph reviews the chemistry, synthesis, and stereochemistry of Y-27632; the molecular pharmacology and kinase selectivity profile; the available pharmacokinetic data from preclinical species; the preclinical pharmacology across cardiovascular, neurological, ophthalmic, oncological, and stem cell applications; the limited clinical evidence base; sourcing and quality verification; reconstitution and handling; stack interaction considerations; the adverse-event and safety signal from preclinical and limited clinical data; and a comparative assessment of five ROCK inhibitors against Y-27632 on five competency standards.