Fasudil

Fasudil (HA-1077, AT-877), the isoquinolinesulfonamide derivative of the H-series protein kinase inhibitors first described by Hidaka et al. in 1984, is the only Rho-associated coiled-coil-containing protein kinase (ROCK) inhibitor approved for systemic clinical use and the first protein kinase inhibitor to receive regulatory approval for any indication. Developed by Asahi Kasei Pharma (Tokyo, Japan) and marketed as Eril, fasudil has been approved in Japan since 1995 and in China for the treatment of cerebral vasospasm following aneurysmal subarachnoid hemorrhage, where it is standard of care in Japanese neurosurgical practice. The compound inhibits ROCK by competitive occupation of the ATP-binding domain, with a Ki of approximately 0.33 micromolar against ROCK activity and modest preferential selectivity for ROCK2 (Ki approximately 47 nanomolar) over ROCK1 (Ki approximately 76 nanomolar) in purified kinase assays. Off-target inhibition of protein kinase A, protein kinase G, protein kinase C, and myosin light chain kinase occurs at approximately 5- to 100-fold higher concentrations. The principal metabolic transformation is rapid hepatic conversion to hydroxyfasudil by aldehyde oxidase (not cytochrome P450), producing an active metabolite with ROCK inhibitory potency similar to or greater than the parent compound and a substantially longer plasma half-life (approximately 5.5 hours versus 0.55 hours for fasudil). This metabolic profile renders fasudil effectively a prodrug of hydroxyfasudil in the oral context. The clinical evidence base in cerebral vasospasm rests on a pivotal 267-patient double-blind placebo-controlled trial (Shibuya et al. 1992) demonstrating significant reductions in angiographic vasospasm (38 versus 61 percent), symptomatic vasospasm (35 versus 50 percent), and poor outcome on the Glasgow Outcome Scale (12 versus 26 percent), confirmed by a 1,462-patient postmarketing surveillance study and a meta-analysis of 8 trials (odds ratio 0.48 for symptomatic vasospasm). Head-to-head comparison with nimodipine demonstrated comparable or superior outcomes (74.5 versus 61.7 percent good clinical outcome). Expanding investigational programs span pulmonary arterial hypertension, where meta-analyses of up to 865 patients demonstrate significant reductions in pulmonary artery pressure, vascular resistance, and 6-minute walk distance with no serious adverse events; and amyotrophic lateral sclerosis, where the 120-patient ROCK-ALS Phase 2 trial confirmed safety, demonstrated significant electrophysiological biomarker preservation (motor unit number index), and confirmed cerebrospinal fluid penetration of the active metabolite at concentrations matching preclinical efficacy. This monograph reviews the chemistry, synthesis, and structure-activity relationships of fasudil; the kinase inhibition profile and downstream signaling including ROCK-mediated myosin light chain phosphorylation, NF-kappaB inflammatory signaling, PPARalpha-NOX neuroprotective axis, and microglial modulation; the comprehensive pharmacokinetics of fasudil and hydroxyfasudil from the first formal Phase I oral bioavailability study; the preclinical evidence across cerebrovascular, cardiovascular, spinal cord injury, and neurodegenerative disease models; the full clinical evidence base across cerebral vasospasm, pulmonary hypertension, amyotrophic lateral sclerosis, and coronary vasospasm indications; and a comparative assessment against four ROCK inhibitor comparators (Y-27632, ripasudil, netarsudil, belumosudil) and the calcium channel blocker nimodipine. Fasudil is approved only in Japan and China. It is available as a research-grade preparation from established chemical suppliers; investigators should obtain analytical confirmation of identity and purity on every lot.