KR-39038, a Novel GRK5 Inhibitor, Attenuates Cardiac Hypertrophy and Improves Cardiac Function in Heart Failure

G protein-coupled receptor kinase 5 (GRK5) has been considered as a potential target for the treatment of heart failure as it has been reported to be an important regulator of pathological cardiac hypertrophy. To discover novel scaffolds that selectively inhibit GRK5, we have identified a novel small molecule inhibitor of GRK5, KR-39038 [7-((3-((4-((3-aminopropyl)amino)butyl)amino)propyl)amino)-2-(2-chlorophenyl)-6-fluoroquinazolin-4(3H)-one]. KR-39038 exhibited potent inhibitory activity (IC 50 value=0.02 µM) against GRK5 and significantly inhibited angiotensin II-induced cellular hypertrophy and HDAC5 phosphorylation in neonatal cardiomyocytes. In the pressure overload-induced cardiac hypertrophy mouse model, the daily oral administration of KR-39038 (30 mg/kg) for 14 days showed a 43% reduction in the left ventricular weight. Besides, KR-39038 treatment (10 and 30 mg/kg/ day, p.o.) showed significant preservation of cardiac function and attenuation of myocardial remodeling in a rat model of chronic heart failure following coronary artery ligation. These results suggest that potent GRK5 inhibitor could effectively attenuate both cardiac hypertrophy and dysfunction in experimental heart failure, and KR-39038 may be useful as an effective GRK5 inhibitor for pharmaceutical applications.

A Novel Urotensin II Receptor Antagonist, KR-36996 Inhibits Smooth Muscle Proliferation through ERK/ROS Pathway

Urotensin II (UII) is a mitogenic and hypertrophic agent that can induce the proliferation of vascular cells. UII inhibition has been considered as beneficial strategy for atherosclerosis and restenosis. However, currently there is no therapeutics clinically available for atherosclerosis or restenosis. In this study, we evaluated the effects of a newly synthesized UII receptor (UT) antagonist, KR-36996, on the proliferation of SMCs in vitro and neointima formation in vivo in comparison with GSK-1440115, a known potent UT antagonist. In primary human aortic SMCs (HASMCs), UII (50 nM) induced proliferation was significantly inhibited by KR-36996 at 1, 10, and 100 nM which showed greater potency (IC₅₀: 3.5 nM) than GSK-1440115 (IC₅₀: 82.3 nM). UII-induced proliferation of HASMC cells was inhibited by U0126, an ERK1/2 inhibitor, but not by SP600125 (inhibitor of JNK) or SB202190 (inhibitor of p38 MAPK). UII increased the phosphorylation level of ERK1/2. Such increase was significantly inhibited by KR-36996. UII-induced proliferation was also inhibited by trolox, a scavenger for reactive oxygen species (ROS). UII-induced ROS generation was also decreased by KR-36996 treatment. In a carotid artery ligation mouse model, intimal thickening was dramatically suppressed by oral treatment with KR-36996 (30 mg/kg) which showed better efficacy than GSK-1440115. These results suggest that KR-36996 is a better candidate than GSK-1440115 in preventing vascular proliferation in the pathogenesis of atherosclerosis and restenosis.

Blockade of Urotensin II Receptor Prevents Vascular Dysfunction

Urotensin II (UII) is a potent vasoactive peptide and mitogenic agent to induce proliferation of various cells including vascular smooth muscle cells (VSMCs). In this study, we examined the effects of a novel UII receptor (UT) antagonist, KR-36676, on vasoconstriction of aorta and proliferation of aortic SMCs. In rat aorta, UII-induced vasoconstriction was significantly inhibited by KR-36676 in a concentration-dependent manner. In primary human aortic SMCs (hAoSMCs), UII-induced cell proliferation was significantly inhibited by KR-36676 in a concentration-dependent manner. In addition, KR-36676 decreased UII-induced phosphorylation of ERK, and UII-induced cell proliferation was also significantly inhibited by a known ERK inhibitor U0126. In mouse carotid ligation model, intimal thickening of carotid artery was dramatically suppressed by oral treatment with KR-36676 (30 mg/ kg/day) for 4 weeks compared to vehicle-treated group. From these results, it is indicated that KR-36676 suppress UII-induced proliferation of VSMCs at least partially through inhibition of ERK activation, and that it also attenuates UII-induced vasoconstriction and vascular neointima formation. Our study suggest that KR-36676 may be an attractive candidate for the pharmacological management of vascular dysfunction.

KR-31831, a new synthetic anti-ischemic agent, inhibits in vivo and in vitro angiogenesis

Angiogenesis is considered to be an integral process to the growth and spread of solid tumors. Anti-angiogenesis therapy recently has been found to be one of the most promising anti-cancer therapeutic strategies. In this study, we provide several lines of evidences showing that KR-31831, a new benzopyran derivative, has anti-angiogenic activities. KR-31831 inhibited the proliferation, migration, invasion and tube formation of bovine aortic endothelial cells (BAECs), and suppressed the release of matrix metalloproteinase-2 (MMP-2) of BAECs. KR-31831 also inhibited in vivo angiogenesis in mouse Matrigel plug assay. Furthermore, the mRNA expressions of basic fibroblast growth factor (bFGF), fibroblast growth factor receptor-2 (FGFR-2), and vascular endothelial growth factor receptor-2 (VEGFR-2) were decreased by KR-31831. Taken together, these results suggest that KR-31831 acts as a novel angiogenesis inhibitor and might be useful for treating hypervascularized cancers.