The Effect of First-in-Class Small Molecule RhoA Inhibitor, HL07, on the Phenylephrine-induced Artery Contraction

The RhoA/ROCK inhibitors have emerged as a new promising treatment for cardiovascular diseases. Recently, we first reported a series of first-in-class small molecular RhoA inhibitors and a chemical compound named HL07 showed high RhoA inhibition activities. In this study, we aimed to explore the pharmacological effect and possible mechanism of HL07 on agonists-induced vasoconstriction. Results showed that 1) in rat thoracic aorta (TA) rings, HL07(0∼180µmol/L) effectively inhibited phenylephrine (PE)-induced contraction in concentration-dependent manner , whereas the half maximal inhibitory concentration (IC50) being 156.93 µmol/L, while it produced weak inhibition on high-K+ -induced contraction. Furthermore, in the presence of nifedipine and thapsigargin (Nif/TSG), HL07 had a comparable degree of inhibition on PE-induced contraction with IC50=149.52 µmol/L; especially at the concentration (0∼150 µmol/L), the inhibition was greater than the inhibition in absence of Nif/TSG (P<0.01). In addition, HL07 displayed greater inhibition on pulmonary artery (PA) rings (IC50=134.97 µmol/L) than on TA rings. 2) HL07 potently blocked RhoA activation stimulated by PE in concentration-dependent manner in human cerebrovascular smooth muscle cells (HBVSMCs), when HL07 at 10, 2, 0.25 µmol/L, the corresponding inhibition rates were 64 ± 5%, 42 ± 7%, 31 ± 5%, respectively; and at the same concentrations, HL07 had no significant effect on RhoA mRNA level. 3) In HBVSMCs, RhoA activity was increased by pre-incubating with GNP, but HL07 showed inhibitory effect on this tendency. These results indicate that HL07 produces significant inhibitory effects on PE-induced vascular smooth muscle contraction. The inhibitory effects of HL07 were mainly contributed to its inhibition on RhoA/Rho-kinase pathway through blocking RhoA activation, and the binding affinities of HL07 for RhoA preference over the GNP might be responsible for the inhibition of HL07 on RhoA activity.