Antiplatelet effect of Z-335, a new orally active and long-lasting thromboxane receptor antagonist

ATP-dependent transport of a novel thromboxane A2 receptor antagonist, [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335) and its xenobiotic taurine conjugate (Z-335-Tau) by rat bile canalicular membrane vesicles

PURPOSE

The characteristics of bile canalicular transport processes for xenobiotic taurine conjugates have not yet been clarified. To elucidate the biliary excretion characteristics of xenobiotic taurine conjugates, we investigated the transport of a novel thromboxane A2 receptor antagonist, Z-335, and its taurine conjugate (Z-335-Tau) across the bile canalicular membrane.

METHODS

We examined the uptake of Z-335 and Z-335-Tau by isolated bile canalicular membrane vesicles (CMVs) from Sprague Dawley and Eisai-hyperbilirubinemic rats (EHBRs) which EHBRs have a hereditary defect of canalicular multidrug resistance-associated protein 2 (Mrp2) function. Also, the in vitro and in vivo kinetics of Z-335-Tau uptake and excretion were compared.

RESULTS

Z-335 uptake by CMVs from normal rats exhibited marked ATP-dependence, whereas ATP-dependent uptake of Z-335 into CMVs from EHBRs was not observed. In contrast, Z-335-Tau uptake into CMVs from both normal rats and EHBRs was ATP dependent. The initial uptake velocity was concentration-dependent, with an in vitro Michaelis constant for initial uptake of 189 microM, which was similar to the in vivo value.

CONCLUSIONS

The biliary excretion of Z-335 involves Mrp2, whereas that of Z-335-Tau involves active transport systems that remain intact in EHBRs and show marked ATP dependence, which ATP-dependent transport is involved in the biliary excretion of Z-335-Tau in vivo.

Newer agents in antiplatelet therapy: a review

Antiplatelet therapy remains the mainstay in preventing aberrant platelet activation in pathophysiological conditions such as myocardial infarction, ischemia, and stroke. Although there has been significant advancement in antiplatelet therapeutic approaches, aspirin still remains the gold standard treatment in the clinical setting. Limitations in safety, efficacy, and tolerability have precluded many of the antiplatelet inhibitors from use in patients. Unforeseen incidences of increased bleeding risk and recurrent arterial thrombosis observed in patients have hampered the development of superior next generation antiplatelet therapies. The pharmacokinetic and pharmacodynamic profiles have also limited the effectiveness of a number of antiplatelet inhibitors currently in use due to variability in metabolism, time to onset, and reversibility. A focused effort in the development of newer antiplatelet therapies to address some of these shortcomings has resulted in a significant number of potential antiplatelet drugs which target enzymes (phosphodiesterase, cyclooxygenase), receptors (purinergic, prostaglandins, protease-activated receptors, thromboxane), and glycoproteins (αIIbβ3, GPVI, vWF, GPIb) in the platelet. The validation and search for newer antiplatelet therapeutic approaches proven to be superior to aspirin is still ongoing and should yield a better pharmacodynamic profile with fewer untoward side-effects to what is currently in use today.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Distinct effects of z-335, a new thromboxane A2 receptor antagonist, on rabbit platelets and aortic smooth muscle

The effect of a novel thromboxane A2 receptor (TP) antagonist, (+/-)-sodium[2-(4-chlorophenylsulfonylaminomethyl)- indan-5-yl]acetate monohydrate (Z-335), on the U46619-induced responses was compared between rabbit platelets and aorta. Z-335 inhibited platelet shape change induced by U46619 with higher efficacy than SQ29548, a common TP antagonist. The U46619-induced platelet aggregation was inhibited by Z-335 in a noncompetitive manner, while it was competitively inhibited by SQ29548. Z-335 inhibited U46619-induced vasoconstriction of rabbit aorta with higher efficacy than SQ29548. The pA2 value of Z-335 in aortic vasoconstriction was significantly higher than in platelet shape change. The competitive binding study showed the higher pKi value of Z-335 against [3H]-SQ29548 binding in rabbit aortic smooth muscle cells than in platelets. These data suggest that Z-335 has useful characteristics of TP antagonism.

Mechanism of hepatobiliary transport of a novel thromboxane A2 receptor antagonist, [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335), and its xenobiotic taurine conjugate (Z-335-Tau) in rats

We investigated the mechanism of hepatobiliary transport of a novel thromboxane A(2) receptor antagonist, [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335), and its taurine conjugate (Z-335-Tau) in normal Sprague-Dawley rats (SDRs) and Eisai hyperbilirubinemic rats (EHBRs). The biliary excretion rate/unbound concentration in the cytosol (nu(bile)/C(u,cyt)) of Z-335 was markedly decreased in EHBRs, whereas nu(bile)/C(u,cyt) values for Z-335-Tau did not differ significantly between EHBRs and SDRs. These results suggest that biliary excretion of Z-335 involves mrp2, whereas Z-335-Tau is excreted by other transporters. The effects of inhibitors on the biliary excretion of Z-335 and Z-335-Tau were also examined in SDRs. After infusion of bromosulfophthalein (BSP), the nu(bile)/C(u,cyt) of Z-335 was significantly decreased, whereas that of Z-335-Tau decreased to 50% of control values by infusion of indocyanine green (ICG) or taurocholate. However, biliary excretion of Z-335-Tau was maintained at a highly concentrative. In conclusion, the biliary excretion of Z-335 involves mrp2, whereas Z-335-Tau is excreted into the bile by active transport systems that remain intact in EHBRs. The mdr2 and/or BSEP/spgp might contribute to a part of total biliary excretion of Z-335-Tau, however, these transporters have not played a major role in the biliary excretion of Z-335-Tau.

Pharmacokinetic and pharmacodynamic properties of a new thromboxane receptor antagonist (Z-335) after single and multiple oral administrations to healthy volunteers

The pharmacokinetics and pharmacodynamics of a new oral thromboxane (TX) A2 receptor antagonist, Z-335, were studied in healthy male volunteers following single doses (0.5-40 mg, PO) in a dose-escalating manner and multiple doses (40 mg, PO, once daily for 7 consecutive days) with a single-blind, placebo-controlled design. Serial blood and urine samples were analyzed for Z-335 and its metabolites to obtain key pharmacokinetic parameters. In the single-dose (10, 20, and 40 mg) study, the maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve (AUC) increased in proportion to the dose when administered afterfasting, while the mean elimination half-life (t1/2beta) was essentially unchanged (7.79-7.93 h). Recovery of the unchanged and taurine-conjugated drugs in the urine within 24 hours was 6.5% to 8.4% and 11.9% to 14.2%, respectively. These parameters essentially remained unchanged when the effect of meal intake was evaluated at the dose of 20 mg with a crossover design. Ex vivo platelet aggregation in the plasma by a TXA2 analogue, U46619, was completely inhibited within 2 hours after all doses, and complete inhibition was maintained for 12 to 14 hours, depending on the dose. The aggregation induced by collagen was also inhibited to a lesser extent, whereas that by adenosine diphosphate was hardly influenced. In the multiple-dose study, Cmax and AUC0-24 were increased by 34% after the last dose compared with the first dose. Z-335 afforded extensive inhibition of platelet aggregation by U46619 throughout the administration period, which returned, however, almost to the control level 48 hours after the last dose. The agent was well tolerated without any abnormalities in subjective and objective symptoms, blood biochemistry, hematology, and urinalysis definitely attributable to the agent, except for the changes expected from its TXA2 receptor-antagonizing actions. Z-335 was concluded to be safe and to provide long-lasting blockade of TXA2 receptors on the basis of a once-daily regimen, promoting further clinical evaluation.

Carrier-mediated active transport of a novel thromboxane A(2) receptor antagonist [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335) into rat liver

To elucidate the transport system by which [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335) is taken up into the liver, we investigated the uptake characteristics of Z-335 in isolated rat hepatocytes. In addition, we estimated the hepatic uptake of Z-335 in intact rats under steady-state conditions and compared it with the in vitro uptake clearance. Uptake of Z-335 is highly concentrative (cell-to-medium concentration ratios were 21.2 at 0.5 min and 71.7 at 5 min), temperature-dependent, and sensitive to metabolic inhibitors, indicating that uptake is mediated by energy-dependent uphill transport. In the presence of metabolic inhibitors [carbonyl cyanide p-trifluoromethoxyphenylhydrazone and rotenone], uptake remained at 37 and 49% of the control value, respectively, suggesting that ATP-independent uptake contributes to the total uptake of Z-335. The concentration dependence of the initial uptake velocity indicated a two-component process, one saturable component, with a K(m) value of 45.6 microM and a V(max) value of 4.1 nmol/min/mg of protein, and a nonspecific diffusion clearance, with a P(dif) value of 8.3 microl/min/mg of protein. The contribution of the carrier-mediated uptake to the total uptake in a linear range was estimated as 91%. The in vivo hepatic intrinsic clearance (CL(int, app)) was comparable with that in vitro uptake clearance (PS(influx)) and indicated that the CL(int, app) of Z-335 at steady state is rate-limited by the uptake process. In conclusion, hepatic intrinsic clearance of Z-335 at steady state is rate-limited by the uptake process since Z-335 is efficiently taken up by an active transport mechanism, followed by metabolism or biliary excretion.

Z-335, a new thromboxane A(2) receptor antagonist, prevents arterial thrombosis induced by ferric chloride in rats

We examined the antithrombotic effect of Z-335 ((+/-)-sodium [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate monohydrate), an orally active thromboxane A(2) receptor (TP-receptor) antagonist that ameliorates experimental gangrene, using a rat arterial thrombosis model. The thrombi were induced by topical application of 50% ferric chloride solution to the rats abdominal artery. Z-335 (0.3-3 mg/kg, p.o.) inhibited thrombus formation in a dose-dependent manner. The antithrombotic effect of Z-335 (1 and 3 mg/kg, p.o.) was almost equivalent with that of cilostazol (100 mg/kg, p.o.), a selective phosphodiesterase type III inhibitor. The effect of Z-335 (3 mg/kg, p.o.), but not cilostazol, persisted for 16 h. Z-335, but not cilostazol, inhibited platelet aggregation induced by U-46619 (a TP-receptor agonist, 9, 11-dideoxy-9alpha,11alpha-methanoepoxy prostaglandin F(2alpha)) for 16 h in rat whole blood. Histopathological examination also revealed that Z-335 prevented ferric chloride-induced thrombus formation. These results suggest that Z-335 may prevent ferric chloride-induced arterial thrombosis through its antiplatelet action by blocking TP-receptor activation.