Pharmacological characterization of BR-A-657, a highly potent nonpeptide angiotensin II receptor antagonist

Design, synthesis and biological evaluation of novel fluoro-substituted benzimidazole derivatives with anti-hypertension activities

A series of new fluoro-substituted benzimidazole derivatives were designed, synthesized and pharmacologically evaluated. All the target compounds were characterized by ¹HNMR, ¹³CNMR, mass spectra and elemental analysis. The biological evaluation showed that most of the synthesized compounds displayed nanomolar affinity to the angiotensin II type 1 (AT₁) receptor and could decrease blood pressure efficiently in spontaneously hypertensive rats. The maximal response of mean blood pressure (MBP) lowered 74.5 ± 3.5 mmHg (1g) and 69.2 ± 0.9 mmHg (2a) at 10 g/kg after oral administration, and the antihypertensive effect lasted beyond 24 h, which performed better than both losartan and telmisartan. So, compounds 1g and 2a may be considered as potential antihypertension drug candidates.

Design, synthesis and biological evaluation of AT1 receptor blockers derived from 6-substituted aminocarbonyl benzimidazoles

A series of new 6-substituted aminocarbonyl benzimidazole derivatives with 1, 4-disubsituted or 1, 5-disubsituted indole moiety and benzoic acid moiety were designed, synthesized and pharmacologically evaluated. Most of the synthesized compounds could bind to the AT₁ receptor and decrease blood pressure significantly. Notably, 2e and 1h could obviously decrease MBP in a dose dependent manner. The maximal response lowered 57.9 ± 2.3 mmHg (2e) and 57.6 ± 1.9 mmHg (1h) of MBP at 10 mg/kg after oral administration, and the antihypertensive effect lasted beyond 24 h, which performed better than Losartan (Fig. 1). These results indicate that 2e and 1h are effective and long-lasting anti-hypertension drug candidates and deserve further investigation for therapeutic application.

Fimasartan reduces neointimal formation and inflammation after carotid arterial injury in apolipoprotein E knockout mice

BACKGROUND

The beneficial effects of angiotensin II type 1 receptor blockers (ARBs) on atherosclerosis have been demonstrated in numerous studies. We investigated the effects of fimasartan on reducing neointimal formation and systemic inflammation after carotid artery (CA) injury in Apolipoprotein E knockout (ApoE KO) mice.

METHODS

ApoE KO mice were randomly allocated to Group I (without CA injury), Group II (without CA injury + Fimasartan), Group III (CA injury), and Group IV (CA injury + Fimasartan). Fimasartan was orally administered everyday starting 3 days before iatrogenic left CA injury.

RESULTS

At 28 days, neointimal hyperplasia and the inflammatory cytokines including TNFα, IL-6, ICAM, and MMP-9 in the peripheral blood were significantly reduced in Groups II and IV compared to Groups I and III, respectively. All fimasartan-administered groups revealed significant increases of CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells with increased plasma levels of IL-10 and TGFβ. In addition, increased CD8⁺ T cells by fimasartan were correlated with reduced smooth muscle cell (SMC) proliferation in the neointima in Groups II and IV. Furthermore, the populations of Treg and CD8⁺ T cells in total splenocytes were increased in Groups II and IV compared to Groups I and III, respectively. The enlargement of spleens due to CA injury in the Group III was attenuated by fimasartan, as shown in the Group IV. These data indicate that fimasartan significantly reduced SMC proliferation in neointima and increased Treg cells in ApoE KO CA injury mice.

CONCLUSIONS

This study suggests fimasartan could be an efficient strategy for reduction of atherosclerotic progression, with a decrease in immune response and systemic inflammation.

Regional Absorption of Fimasartan in the Gastrointestinal Tract by an Improved in situ Absorption Method in Rats

The aim of the present study was to assess the regional absorption of fimasartan by an improved in situ absorption method in comparison with the conventional in situ single-pass perfusion method in rats. After each gastrointestinal segment of interest was identified, fimasartan was injected into the starting point of each segment and the unabsorbed fimasartan was discharged from the end point of the segment. Blood samples were collected from the jugular vein to evaluate the systemic absorption of the drug. The relative fraction absorbed (F_abs,relative) values in the specific gastrointestinal region calculated based on the area under the curve (AUC) values obtained after the injection of fimasartan into the gastrointestinal segment were 8.2% ± 3.2%, 23.0% ± 12.1%, 49.7% ± 11.5%, and 19.1% ± 11.9% for the stomach, duodenum, small intestine, and large intestine, respectively, which were comparable with those determined by the conventional in situ single-pass perfusion. By applying the fraction of the dose available at each gastrointestinal segment following the oral administration, the actual fraction absorbed (F′_abs) values at each gastrointestinal segment were estimated at 10.9% for the stomach, 27.1% for the duodenum, 40.7% for the small intestine, and 5.4% for the large intestine, which added up to the gastrointestinal bioavailability (F_X·F_G) of 84.1%. The present method holds great promise to assess the regional absorption of a drug and aid to design new drug formulations.

Pretreatment with low-dose fimasartan ameliorates NLRP3 inflammasome-mediated neuroinflammation and brain injury after intracerebral hemorrhage

Nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which is composed of an NLRP3 domain, the adaptor molecule apoptosis-associated speck-like protein containing a CARD (ASC) domain, and procaspase-1, plays an important role in the immune pathophysiology of the secondary damage induced by intracerebral hemorrhage (ICH). This study aims to investigate whether pre-stroke treatment with fimasartan, an angiotensin II receptor blocker, has anti-inflammatory effects on ICH by inhibiting the activation of the NLRP3 inflammasome. Sprague-Dawley rats were divided into five groups: sham, vehicle, low-dose (0.5 mg/kg) and regular-doses (1.0 and 3.0 mg/kg) fimasartan. These rats were treated for 30 days before the induction of collagenase-induced ICH and continuously 3 days after surgery. The mean blood pressure (BP) in the low-dose fimasartan group was not significantly different from that of control, and BP in the regular-dose groups was decreased in a dose-dependent manner. Pretreatment with low-dose fimasartan attenuated ICH-induced edema and improved neurological functions. Activation of the NLRP3/ASC/caspase-1 and the NF-κB pathways after ICH was markedly reduced by low-dose fimasartan. The double immunofluorescence staining of brain cells showed a significant decrease in the co-localization of NLRP3 with Iba1 (microglia marker) positive cells by fimasartan treatment. Cultured microglia cells stimulated by hemolysate demonstrated significant activation of the inflammasome, which was reduced by fimasartan. Pretreatment with a low-dose fimasartan alleviated brain damage after acute ICH by inhibiting the NLRP3 inflammasome without lowering MBP. Our study suggests pre-stroke administration of fimasartan could potentially attenuate ICH-induced secondary brain injury by targeting the inflammasome.

Pharmacological Profiles of a Highly Potent and Long-Acting Angiotensin II Receptor Antagonist, Fimasartan, in Rats and Dogs after Oral Administration

The pharmacological profile of fimasartan, [2-n-butyl-5-dimethylamino-thiocarbonyl-methyl-6-methyl-3-{[2-(1H-tetrazole-5-yl)biphenyl-4-yl]methyl}-pyrimidin-4(3H)-one, a new non-peptide angiotensin type 1 (AT₁)-selective angiotensin receptor antagonist, has been investigated in a variety of in vitro and in vivo experimental models. In the present study, fimasartan showed slow dissociation and irreversible binding to AT₁ subtype receptors in membrane fractions of HEK-293 cells with a K_d of 0.03 nM and a T_1/2 of 63.7 min. The inhibitory effect of fimasartan on angiotensin II (Ang II)-induced contraction persisted longer after washout than that of losartan or candesartan. In conscious rats, a single dose of fimasartan (0.3, 1, or 3 mg/kg; per os (p.o.)) dose-dependently antagonized Ang II-induced pressor responses. Both orally administrated fimasartan and losartan dose-dependently decreased mean arterial pressure in furosemide-treated rats and dogs, and fimasartan administered orally at 1, 3, or 10 mg/kg reduced blood pressure in conscious spontaneously hypertensive rats. Taken together, these findings indicate that fimasartan has potent and sustained binding affinity at the AT₁ receptor subtype, and reveal the molecular basis responsible for the marked lowering of blood pressure in various conscious rats and dogs models after its oral administration.

Placental transfer and mammary excretion of a novel angiotensin receptor blocker fimasartan in rats

Background

Fimasartan (FMS) is a potent angiotensin receptor blocker for the treatment of mild to moderate hypertension. This study aimed to evaluate the transfer of FMS to fetus and breast milk in rats.

Methods

In order to study the transfer to the fetus and nursing pup, pregnant and nursing maternal rats were administered with FMS by a constant intravenous infusion to reach target plasma concentrations of 200 ng/mL and 100 ng/mL. The concentrations of FMS in plasma, placenta, amniotic fluid, fetus, and milk were determined by a validated LC-MS/MS assay.

Results

Upon constant intravenous infusion, the plasma FMS concentration reached the target steady state concentrations (C_ss = 200 ng/mL and 100 ng/mL) in 24 h. The tissue-to-plasma partition coefficients (K_p) for placenta, amniotic fluid, and milk were obtained based on the observed FMS concentrations in the tissues and C_ss. The K_p values for all tissues were not different between high (C_ss = 200 ng/mL) and low (C_ss = 100 ng/mL) dose groups. While the mean K_p of the placenta was 44.6–59.0 %, the mean K_p was 1.3–1.7 % for the amniotic fluid and 14.9–17.0 % for fetus. The mean K_p of milk was 10.4–15.2 %.

Conclusions

Placental transfer and milk excretion of FMS was relatively lower compared to other angiotensin receptor blockers.

A Randomized, Double-blind, Candesartan-controlled, Parallel Group Comparison Clinical Trial to Evaluate the Antihypertensive Efficacy and Safety of Fimasartan in Patients with Mild to Moderate Essential Hypertension

PURPOSE

A new antihypertensive drug that selectively blocks angiotensin II receptor type 1, fimasartan, has a potent and rapidly acting antihypertensive effect. We investigated the antihypertensive effects of fimasartan 60 and 120 mg and its safety in comparison to 8 mg of candesartan.

METHODS

This clinical trial is a multicenter, randomized, double-blind, active comparator, and parallel group study. Three hundred sixty-two individuals were screened, and 290 patients aged 19 to 75 years with mild to moderate hypertension (diastolic blood pressure [DBP], 90-110 mm Hg) were randomly assigned to 60 to 120 mg/d of fimasartan or 8 mg/d of candesartan after a 2-week placebo run-in period. Treatments were administered for 12 weeks without dosage adjustment. The primary end point was the differences in DBP changes at week 12.

FINDINGS

After 12 weeks of treatment, DBP and systolic blood pressure (SBP) decreased significantly in all 3 groups. The decrease in DBP at week 12 was larger but not statistically significant in the fimasartan 60 mg compared with the candesartan 8 mg group with a mean (SD) difference of 1.72 (8.32) mm Hg (95% CI, -0.71 to 4.15 mm Hg; P = 0.17). The lower margin of the CI (-0.71 mm Hg) exceeded the noninferiority margin (-3.5 mm Hg). The DBP-lowering effect of fimasartan 120 mg was also nonsignificantly larger than candesartan 8 mg (difference, 1.58 [8.27] mm Hg; P = 0.20). The decrease in SBP was also nonsignificantly larger in the fimasartan 60 mg group compared with the candesartan 8 mg group (difference, 3.50 [12.63] mm Hg; P = .06). The SBP-lowering effect of fimasartan 120 mg was statistically larger than candesartan 8 mg (difference, 4.98 [13.99] mm Hg; P = .02). Response rate (DBP <90 mm Hg or DBP lowering >10 mm Hg at week 12) was also nonsignificantly greater in both fimasartan groups (Fimasartan 60 mg, 81%; fimasartan 120 mg, 72%; candesartan 8 mg, 71%). The safety profile of the fimasartan 60 mg and 120 mg was similar to candesartan 8 mg, with a slightly higher, but statistically not significant, incidence of hepatic enzyme elevation in fimasartan 120 mg.

IMPLICATIONS

The antihypertensive effect of fimasartan, a newly available angiotensin II receptor type 1 blocker, is comparable, although not superior, to candesartan with a good safety profile. ClinicalTrials.gov identifier: NCT01135212.

DL0805-2, a novel indazole derivative, relaxes angiotensin II-induced contractions of rat aortic rings by inhibiting Rho kinase and calcium fluxes

AIM

DL0805-2 [N-(1H-indazol-5-yl)-1-(4-methylbenzyl) pyrrolidine-3-carboxamide] is a DL0805 derivative with more potent vasorelaxant activity and lower toxicity. This study was conducted to investigate the vasorelaxant mechanisms of DL0805-2 on angiotensin II (Ang II)-induced contractions of rat thoracic aortic rings in vitro.

METHODS

Rat thoracic aortic rings and rat aortic vascular smooth muscle cells (VSMCs) were pretreated with DL0805-2, and then stimulated with Ang II. The tension of the aortic rings was measured through an isometric force transducer. Ang II-induced protein phosphorylation, ROS production and F-actin formation were assessed with Western blotting and immunofluorescence assays. Intracellular free Ca(2+) concentrations were detected with Fluo-3 AM.

RESULTS

Pretreatment with DL0805-2 (1-100 μmol/L) dose-dependently inhibited the constrictions of the aortic rings induced by a single dose of Ang II (10(-7) mol/L) or accumulative addition of Ang II (10(-10)-10(-7) mol/L). The vasodilatory effect of DL0805-2 was independent of endothelium. In the aortic rings, pretreatment with DL0805-2 (1, 3, and 10 μmol/L) suppressed Ang II-induced Ca(2+) influx and intracellular Ca(2+) mobilization, and Ang II-induced phosphorylation of two substrates of Rho kinase (MLC and MYPT1). In VSMCs, pretreatment with DL0805-2 (1, 3, and 10 μmol/L) also suppressed Ang II-induced Ca(2+) fluxes and phosphorylation of MLC and MYPT1. In addition, pretreatment with DL0805-2 attenuated ROS production and F-actin formation in the cells.

CONCLUSION

DL0805-2 exerts a vasodilatory action in rat aortic rings through inhibiting the Rho/ROCK pathway and calcium fluxes.

Absolute bioavailability and pharmacokinetics of the angiotensin II receptor antagonist fimasartan in healthy subjects

The present study was conducted to determine the absolute bioavailability of fimasartan (FMS; Kanarb(®) ) after the single oral administration of a 60-mg tablet or a single 30-mg intravenous (IV) infusion. This investigation was a randomized, single-dose, open-labeled, two-way crossover study of 16 healthy Korean male subjects. The subjects were divided into two groups (n = 8) and each received either the oral or IV formulation followed by one-week washout period. The Cmax (ng/ml) and AUC∞ (h · ng/ml) following oral and IV administration were 62.4 ± 48.6 and 291.1 ± 121.7; and 683.3 ± 104.3 and 782.3 ± 112.7 (mean ± SD), respectively. The Tmax (h) were 3.0 h (range: 0.5-5.0 h) and 1.0 h (range: 0.8-1.0 h) in the test and reference groups, respectively. The terminal elimination half-lives (t1/2 , h) were similar (5.8 and 5.5 h, respectively) indicating that the route of administration did not influence the absorption or elimination of FMS. The systemic clearance (CL, L/h) and the volume of distribution at steady-state (Vdss , L) were 331.3 ± 444.5 L/h and 403.3 ± 710.4 L following oral administration and 39.1 ± 5.3 L/h and 42.4 ± 25.5 L following IV administration. The absolute bioavailability of the FMS tablet was 18.6%.

Effect of Long-Term Treatment with Fimasartan on Transient Focal Ischemia in Rat Brain

Fimasartan is a newly developed angiotensin receptor blocker, which may have protective effects during myocardial infarction or atherosclerosis. In this context, we investigated the effects of long-term treatment with low-dose fimasartan on focal ischemia in rat brain. We induced focal ischemia in brain by transient intraluminal occlusion of middle cerebral artery (MCA) and administered low-dose (0.5 mg/kg) or regular doses (1 or 3 mg/kg) of fimasartan via intravenous routes. After the administration of low-dose (0.5 mg/kg) fimasartan, blood pressure did not decrease compared to the phosphate-buffered saline- (PBS-) control with MCA occlusion (MCAO) group. The infarct volume and ischemic cell death were reduced in the low-dose fimasartan-treated group (46 ± 41 mm³ for 0.5 mg/kg and 153 ± 47 mm³ for PBS-control with MCAO; P < 0.01) but not in the regular-dose groups. Low-dose fimasartan treatment improved functional recovery after ischemia and significantly decreased mortality. In our study, fimasartan reduced the degradation of IκB and the formation of an inflammatory end-product, COX-2. As a result, the recruitment of inflammatory cells in the peri-infarct area decreased in fimasartan-treated group. We have demonstrated that long-term, low-dose fimasartan treatment improved outcomes after focal ischemia in the brain via a reduction of inflammation.