Pharmacologic and pharmacokinetic profile of SK&F S-106203, a potent, orally active peptidoleukotriene receptor antagonist, in guinea-pig.

In this report the pharmacologic and pharmacokinetic profile of the leukotriene receptor antagonist 3(S)-[(2-carboxyethyl)thio]-3-[2-(8-phenyloctyl)phenyl] propanoic acid (SK&F S-106203) in guinea-pigs is described. In isolated guinea-pig tracheae SK&F S-106203 was a potent, competitive antagonist of leukotriene (LT) D4-induced contractions (pA2 = 7.6). SK&F S-106203 was also a potent antagonist of LTE4-induced contractions (pKB = 7.3), but had little effect on those elicited by LTC4 (pKB = 5.5). SK&F S-106203 (10 microM) had no effect on contractions produced by histamine, carbachol, KCl, U-44069, PGF2 alpha or PGD2. In addition, SK&F S-106203 (10 microM) did not inhibit cyclic nucleotide phosphodiesterase (PDE) activity of several PDE isozymes. In guinea-pig lung membrane preparations, SK&F S-106203 was a potent antagonist of 3H-LTD4 binding with a Ki = 19.4 +/- 2.1 nM (n = 5). The pharmacokinetic profile of SK&F S-106203 was determined in unanesthetized guinea-pigs. Following an i.v. (bolus) dose (25 mg/kg), SK&F S-106203 disappeared from plasma in a biphasic fashion with half-lives of 0.1 h (50% of the area under the plasma concentration-time curve, AUC) and 11 h. The AUC obtained for SK&F S-106203 following i.v. administration was 87.3 +/- 7.5 micrograms-h/ml. Following an oral dose of SK&F S-106203 (100 mg/kg), the maximal plasma concentration (Cmax) and the time Cmax was achieved (Tmax) were 21.62 +/- 2.26 micrograms/ml and 4 +/- 1 h, respectively; the AUC was 279.9 +/- 41.8 micrograms-h/ml. Studies examining the effects of i.v. infusion of SK&F S-106203 revealed that marked inhibition of LTD4-induced bronchospasm was produced with steady-state plasma levels of SK&F S-106203 less than 1 microgram/ml (less than 2 microM). Oral (p.o.) pretreatment with 100 mumol/kg SK&F S-106203 for up to 24 h essentially abolished LTD4-induced bronchospasm; this correlated with sustained plasma concentrations of greater than 2 micrograms/ml. The results indicate that in guinea-pig airways, SK&F S-106203 is a potent and selective LT receptor antagonist that is active via aerosol, oral and i.v. routes of administration. When given orally, SK&F S-106203 is highly bioavailable and has a very long duration of action which correlates with the pharmacokinetic profile of the compound. SK&F S-106203 may be useful therapy in asthma and other disorders in which the LTs are thought to play a prominent pathophysiological role.

SK&F S-106203 inhibits leukotriene C4, leukotriene D4 and leukotriene E4 vasopressor responses in the conscious rat.

1. The purpose of these experiments was to investigate the effects of the selective peptidoleukotriene receptor antagonist, SK&F S-106203, on leukotriene C4 (LTC4), LTD4 and LTE4 vasopressor responses in the conscious, normotensive rat. SK&F S-106203 was administered as a bolus followed by a continuous infusion in order to provide information on the relationship between antagonism of leukotriene responses and steady-state plasma concentrations. 2. Infusion of SK&F S-106203 at doses of 0.2 mgkg-1 + 1 mgkg-1 h-1, 1 mgkg-1 + 3 mgkg- h-1 or 2 mgkg-1 + 10 mgkg-1 h-1 produced dose-dependent steady-state plasma drug concentrations of 1.0, 3.2 and 23.8 micrograms ml-1, respectively. Plasma SK&F S-106203 concentrations appeared to increase in a linear fashion at doses of 1 and 3 mgkg-1 h-1; at the highest dose the increment in plasma drug concentrations (i.e., 7-8 fold) was greater than the increment in dose (i.e., 3 fold), suggesting saturation of the primary clearance mechanism(s) at this dose. 3. SK&F S-106203 (2 mgkg-1 + 10 mgkg-1 h-1) had no effect on noradrenaline-, vasopressin-, isoprenaline-, or U 46619-induced responses. 4. SK&F S-106203 produced dose-dependent rightward shifts in the LTC4 and LTE4 dose-response curves. Administration of SK&F S-106203 at doses of 0.2mg kg1 + 1 mg kg1 h-, mg kg' + 3mgkg-'h-1, or 2mgkg-' + lOmgkg-1h'- produced dose-ratios of 1.0, 3.1 and 19.9, respectively, against LTC4 responses, and dose-ratios of 1.6, 3.8 and 9.1, respectively, against LTE4 responses. 5. Against LTD4 responses, SK&F S-106203 at doses of 0.2mgkg- + mgkg-1 h-, mg kg' + 3 mg kg- 1h - ', or 2 mg kg- + 10 mg kg- h- produced dose-ratios of 2.5, 2.8, and 11.4, respectively. Administration of D-penicillamine, a non-competitive LTD4 dipeptidase inhibitor, had no effect on LTD4 responses. 6. The similarity in the LTD4 dose-ratios at the two lower infusion rates, despite increases in the plasma drug concentrations, suggests the existence of pharmacologically heterogeneous LTD4 receptors. These results indicate that SK&F S-106203 is a potent, selective and apparently competitive antagonist of LTC4, LTD4 and LTE4 vascular responses in the intact rat.

Antagonism of leukotriene C4, leukotriene D4 and leukotriene E4 vasoconstrictor responses in the conscious rat with the peptidoleukotriene receptor antagonist SK&F 104353: evidence for leukotriene D4 receptor heterogeneity.

The purpose of these experiments was to investigate the effects of the selective peptidoleukotriene receptor antagonist, SK&F 104353, on leukotriene (LT)C4, LTD4 and LTE4 vasopressor responses in conscious, normotensive rats. Steady-state plasma concentrations of SK&F 104353 at infusion rates of 0.2 mg/kg + 1 mg/kg/hr, 1 mg/kg + 3 mg/kg/hr or 2 mg/kg + 10 mg/kg/hr were 0.5, 1.6 and 9.4 micrograms/ml, respectively, indicating that the plasma concentrations of SK&F 104353 were related directly to the infusion rate. LTC4, LTD4 and LTE4 (0.17-170 nmol/kg i.v.) produced dose-dependent increases in mean blood pressure. The ED20 dose (i.e., dose required to increase blood pressure 20 mm Hg) of LTC4, LTD4 or LTE4 was 2.7 +/- 0.4, 2.2 +/- 0.3 and 109 +/- 17 nmol/kg, respectively. SK&F 104353 produced dose-dependent, parallel shifts to the right in the LTC4 dose-response curve. Administration of SK&F 104353 at doses of 0.2 mg/kg + 1 mg/kg/hr, 1 mg/kg + 3 mg/kg/hr or 2 mg/kg + 10 mg/kg/hr produced dose ratios (i.e., ratio of ED20 in presence of SK&F 104353 to that of the vehicle group) of 6, 12 and 26, respectively. Against LTD4 responses, SK&F 104353 at doses of 0.1 mg/kg + 0.3 mg/kg/hr or 0.2 mg/kg + 1 mg/kg/hr produced dose ratios of 3 and 9, respectively. At a dose of 1 mg/kg + 3 mg/kg/hr, there was no further increase in the dose ratio, whereas a dose of 2 mg/kg + 10 mg/kg/hr resulted in a dose ratio of greater than 100.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective antagonism of peptidoleukotriene responses does not reduce myocardial damage or neutrophil accumulation following coronary artery occlusion with reperfusion.

This study was designed to assess the effect of a peptidoleukotriene receptor antagonist, SK&F 104353, for limiting myocardial damage and neutrophil accumulation in rats subjected to myocardial reperfusion injury (MI/R). In conscious rats, SK&F 10,4353 (25 mg/kg, i.v.) antagonized LTD4-induced vasopressor responses by 90% and 60% at 1 and 4 hr, respectively, indicating effective blockade of peptido-leukotriene responses. In another group of animals subjected to 30 min of coronary artery occlusion with reperfusion for 24 hr, myocardial injury and neutrophil infiltration were determined by measuring creatine phosphokinase (CPK) specific activity and myeloperoxidase (MPO) activity, respectively, in the left ventricular free wall (LVFW). Myocardial CPK levels were 8.1 +/- 0.2 U/mg protein in Sham-MI/R vehicle-treated animals, and were significantly decreased to 6.4 +/- 0.6 U/mg protein in MI/R-vehicle animals. Myocardial MPO values were 1.5 +/- 0.5 U/g LVFW in Sham-MI/R vehicle-treated animals, and significantly increased to 4.3 +/- 0.6 U/g LVFW in MI/R-vehicle animals. Administration of SK&F 10,4353 (25 mg/kg, i.v.) 1 min prior to coronary occlusion and 3.5 hr post reperfusion had no effect on the loss of myocardial CPK specific activity or the increase in MPO levels (p greater than 0.05, compared to the MI/R-vehicle group). Thus, at a dose that antagonized LTD4-induced vasopressor responses, SK&F 104353 did not attenuate either the extent of myocardial injury or inflammatory cell accumulation associated with myocardial ischemia/reperfusion. These results suggest that peptidoleukotrienes do not contribute to the progression of myocardial ischemic/reperfusion injury.

Concentration-dependent, stereoselective inhibition of the endotoxin-induced hemoconcentration in conscious rats with the peptidoleukotriene receptor antagonist SK & F 104353.

Endotoxemia is associated with increases in a number of humoral mediators including vasopressin, thromboxane and leukotrienes (LT), all of which may participate in the pathophysiologic responses to endotoxemia. Previous studies from our laboratory demonstrated that endotoxin-induced hemoconcentration was attenuated with a peptidoleukotriene receptor antagonist, SK & F 104353. The purpose of this study was to investigate further the mechanism of endotoxin-induced hemoconcentration. Injection of LTD4 (51 nmol/kg, i.v.) produced an increase in the hematocrit of conscious male Sprague-Dawley rats: administration of SK & F 104353 (2 mg/kg, i.v. + 10 mg/kg/h, i.v. infusion) blocked completely this response to exogenous LTD4. Injection of Salmonella enteritidis endotoxin (30 mg/kg, i.v.) increased the hematocrit from 41 +/- 1 vol% to 55 +/- 1 vol%. Following pretreatment with SK & F 104353 (2 mg/kg, i.v. + 10 mg/kg/h, i.v.), the hemoconcentration was attenuated to 46 +/- 1 vol% (p less than 0.01). Simultaneous determination of plasma drug concentrations over a range of doses indicated that inhibition of the hemoconcentration produced by SK & F 104353 was concentration-dependent (IC30 = 0.5 microgram/ml). The IC30 for the stereoisomer, SK & F 104373, was 50 micrograms/ml. The 5-lipoxygenase/cyclooxygenase inhibitors, SK & F 86002 and BW 775C, also attenuated the endotoxin-induced increase in hematocrit, whereas indomethacin, heparin, daltroban, or the selective V1 vasopressin receptor antagonist [d(CH2)5Tyr(Me)]AVP did not significantly affect the endotoxin-induced hemoconcentration. The endotoxin-induced hemoconcentration was inhibited in a concentration-dependent, stereoselective manner with a peptidoleukotriene receptor antagonist, and by 5-lipoxygenase inhibitors, indicating that this response is mediated by peptidoleukotrienes.

Beneficial effects of the peptidoleukotriene receptor antagonist, SK&F 104353, on the responses to experimental endotoxemia in the conscious rat.

The purpose of this study was to examine the effects of the peptidoleukotriene receptor antagonist, SK&F 104353, on the responses to endotoxin in conscious male Sprague-Dawley rats. Administration of Salmonella enteritidis endotoxin (30 mg/kg i.v.; LD90) resulted in a decrease in the number of circulating platelets, leukopenia, an increase in hematocrit, and 0% survival at 24 hr. Pretreatment with SK&F 104353 (1 mg/kg, i.v. bolus followed by 3 mg/kg/hr, i.v. infusion for 6 hr) 5 min before injection of endotoxin produced steady state plasma drug levels of 1.6 micrograms/ml in naive animals and levels of approximately 3.4 micrograms/ml in endotoxemic animals (P less than 0.05). SK&F 104353 significantly attenuated the endotoxin-induced thrombocytopenia (P less than 0.05) but had no effect on either the endotoxin-induced early leukopenia or late leukocytosis. Additionally, SK&F 104353 significantly reduced the endotoxin-induced hemoconcentration (P less than 0.05) and improved survival to 30% at 48 hr (P less than 0.05). A higher dose of SK&F 104353 (2 mg/kg, i.v. bolus followed by 10 mg/kg/hr, i.v. infusion for 6 hr) did not produce any further benefit. These data indicate clearly the pathophysiologic role of peptidoleukotrienes in endotoxemia and suggest SK&F 104353 could be useful for ameliorating some of the deleterious sequelae associated with this condition.

Determination of microsomal lauric acid hydroxylase activity by HPLC with flow-through radiochemical quantitation.

An assay for the microsomal hydroxylation of lauric acid (LA), based on HPLC with flow-through radiochemical detection, has been developed. Conditions were optimized for resolution and quantitation of three microsomal metabolites of LA, one of which has not been reported previously as a metabolite of LA in mammalian microsomal incubations. These products, 12-(omega)-hydroxy-LA, 11-(omega-1)-hydroxy-LA, and a novel metabolite, 10-(omega-2)-hydroxy-LA, were isolated by HPLC and identified by gas chromatography/mass spectrometry. In the presence of NADPH, the formation of all three metabolites was linear with time and microsomal protein concentration. Hydrogen peroxide also supported the microsomal metabolism of LA, although the ratio of metabolites was substantially different than that produced by NADPH-supported microsomes. Several biochemical probes (metyrapone, alpha-naphthoflavone, 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride, and 10-undecynoic acid) were used to dissociate the three LA hydroxylase activities. These experiments suggest that the site-specific hydroxylation [omega-, (omega-1)-, (omega-2)-] of LA may be catalyzed by different isozymes of cytochrome P-450.

In vitro microsomal metabolism of the leukotriene receptor antagonist, 5-(2-dodecylphenyl)-4,6-dithianonanedioic acid (SK&F 102,081).

In vivo experiments indicate that the major route of metabolism of SK&F 102,081 [5-(2-dodecylphenyl)-4,6-dithianonanedioic acid] is via omega-oxidation and subsequent beta-oxidation. Therefore, in vitro experiments were designed to characterize the initial reaction of this pathway, omega-hydroxylation. SK&F 102,081 was metabolized by rat hepatic microsomes to two products; mass spectral analysis indicated that these products were the omega (omega) and omega minus one (omega-1) hydroxylated metabolites, 5-[2-(12-hydroxy)dodecylphenyl]-4,6-dithianonanedioic acid and 5-[2-(11-hydroxy)dodecylphenyl]-4,6-dithianonanedioic acid, respectively. NADPH and oxygen were required for the formation of these metabolites. Kinetic analysis of omega- and (omega-1)-hydroxylations of SK&F 102,081 indicated that the apparent Km for (omega-1)-hydroxylation (52.6 microM) was approximately 2.5-fold higher than the apparent Km for omega-hydroxylation (22.0 microM). Furthermore, the cytochrome P-450 inhibitor, metyrapone, produced differential inhibition of omega- and (omega-1)-hydroxylation. In addition, the terminal acetylenic analogue of SK&F 102,081, SK&F 103,600 (5-[2-(11-dodecynyl)phenyl]-4,6-dithianonanedioic acid), produced differential suicide inactivation of SK&F 102,081 omega- and (omega-1)-hydroxylations. These studies indicate that the omega- and (omega-1)-hydroxylations of SK&F 102,081 are probably carried out by different isozymes of hepatic cytochrome P-450 in the rat. Furthermore, the isozymes that hydroxylate SK&F 102,081 at the omega- and (omega-1)-positions may be similar to those which mediate similar reactions on endogenous compounds such as prostaglandins and leukotrienes.

Biochemical characterization of hepatic microsomal leukotriene B4 hydroxylases.

omega-Hydroxylation of leukotriene B4 (LTB4) has been reported in human and rodent polymorphonuclear leukocytes; preliminary information indicates that this metabolism is cytochrome P-450 dependent. Therefore, these studies were initiated to characterize the cytochrome P-450-dependent metabolism of LTB4 in other tissues. LTB4 was metabolized by rat hepatic microsomes to two products, 20-hydroxy(omega)-LTB4 and 19-hydroxy(omega-1)-LTB4. The formation of these metabolites was both oxygen and NADPH dependent indicating that a monooxygenase(s) was responsible for these reactions. The apparent Km and Vmax for LTB4 omega-hydroxylase were 40.28 microM and 1202 pmol/min/mg of protein, respectively. In contrast, the apparent Km and Vmax for LTB4 (omega-1)-hydroxylase were 61.52 microM and 73.50 pmol/min/mg of protein, respectively. Both LTB4 omega- and (omega-1)-hydroxylases were inhibited by metyrapone in a concentration-dependent fashion. However, SK&F 525A inhibited LTB4 (omega-1)- but not omega-hydroxylase. In contrast, alpha-naphthoflavone decreased LTB4 omega- but not (omega-1)-hydroxylase activities. The differences in the Km apparent for substrate as well as the differential inhibition by inhibitors of cytochrome P-450 suggest that the omega- and (omega-1)-hydroxylations of LTB4 in hepatic microsomes are mediated by different isozymes of P-450. Furthermore, several additional characteristics of LTB4 hydroxylases indicate that these isozymes of P-450 may be different from those which catalyze similar reactions on medium-chain fatty acids, such as laurate and prostaglandins.