Diminishing GSH-Adduct Formation of Tricyclic Diazepine-based Mutant IDH1 Inhibitors

Mutant isocitrate dehydrogenase 1 (IDH1) has been identified as an attractive oncology target for which >70% of grade II and III gliomas and ∼10% of acute myeloid leukemia (AML) harbor somatic IDH1 mutations. These mutations confer a neomorphic gain of function, leading to the production of the oncometabolite (R)-2-hydroxyglutarate (2-HG). We identified and developed a potent, selective, and orally bioavailable brain-penetrant tricyclic diazepine scaffold that inhibits mutant IDH1. During the course of in vitro metabolism studies, GSH-adduct metabolites were observed. The hypothesis for GSH-adduct formation was driven by the electron-rich nature of the tricyclic core. Herein, we describe our efforts to reduce the electron-rich nature of the core. Ultimately, a strategy focused on core modifications to block metabolic hot spots coupled with substitution pattern changes (C8 N → C linked) led to the identification of new tricyclic analogues with minimal GSH-adduct formation across species while maintaining an overall balanced profile.

Pharmacological AMPK activation induces transcriptional responses congruent to exercise in skeletal and cardiac muscle, adipose tissues and liver

Physical activity promotes metabolic and cardiovascular health benefits that derive in part from the transcriptional responses to exercise that occur within skeletal muscle and other organs. There is interest in discovering a pharmacologic exercise mimetic that could imbue wellness and alleviate disease burden. However, the molecular physiology by which exercise signals the transcriptional response is highly complex, making it challenging to identify a single target for pharmacological mimicry. The current studies evaluated the transcriptome responses in skeletal muscle, heart, liver, and white and brown adipose to novel small molecule activators of AMPK (pan-activators for all AMPK isoforms) compared to that of exercise. A striking level of congruence between exercise and pharmacological AMPK activation was observed across the induced transcriptome of these five tissues. However, differences in acute metabolic response between exercise and pharmacologic AMPK activation were observed, notably for acute glycogen balances and related to the energy expenditure induced by exercise but not pharmacologic AMPK activation. Nevertheless, intervention with repeated daily administration of short-acting activation of AMPK was found to mitigate hyperglycemia and hyperinsulinemia in four rodent models of metabolic disease and without the cardiac glycogen accretion noted with sustained pharmacologic AMPK activation. These findings affirm that activation of AMPK is a key node governing exercise mediated transcription and is an attractive target as an exercise mimetic.

Discovery of MK-8722: A Systemic, Direct Pan-Activator of AMP-Activated Protein Kinase

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a key regulator of mammalian energy homeostasis and has been implicated in mediating many of the beneficial effects of exercise and weight loss including lipid and glucose trafficking. As such, the enzyme has long been of interest as a target for the treatment of Type 2 Diabetes Mellitus. We describe the optimization of β1-selective, liver-targeted AMPK activators and their evolution into systemic pan-activators capable of acutely lowering glucose in mouse models. Identifying surrogates for the key acid moiety in early generation compounds proved essential in improving β2-activation and in balancing improvements in plasma unbound fraction while avoiding liver sequestration.

Systemic pan-AMPK activator MK-8722 improves glucose homeostasis but induces cardiac hypertrophy

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy homeostasis in eukaryotes. Despite three decades of investigation, the biological roles of AMPK and its potential as a drug target remain incompletely understood, largely because of a lack of optimized pharmacological tools. We developed MK-8722, a potent, direct, allosteric activator of all 12 mammalian AMPK complexes. In rodents and rhesus monkeys, MK-8722-mediated AMPK activation in skeletal muscle induced robust, durable, insulin-independent glucose uptake and glycogen synthesis, with resultant improvements in glycemia and no evidence of hypoglycemia. These effects translated across species, including diabetic rhesus monkeys, but manifested with concomitant cardiac hypertrophy and increased cardiac glycogen without apparent functional sequelae.

Structure-activity-relationship of amide and sulfonamide analogs of omarigliptin

A series of novel substituted-[(3R)-amino-2-(2,5-difluorophenyl)]tetrahydro-2H-pyran analogs have been prepared and evaluated as potent, selective and orally active DPP-4 inhibitors. These efforts lead to the discovery of a long acting DPP-4 inhibitor, omarigliptin (MK-3102), which recently completed phase III clinical development and has been approved in Japan.

Improved Stability of Proline-Derived Direct Thrombin Inhibitors through Hydroxyl to Heterocycle Replacement

Modification of the previously disclosed (S)-N-(2-(aminomethyl)-5-chlorobenzyl)-1-((R)-2-hydroxy-3,3-dimethylbutanoyl)pyrrolidine-2-carboxamide 2 by optimization of the P3 group afforded novel, low molecular weight thrombin inhibitors. Heterocycle replacement of the hydroxyl functional group helped maintain thrombin in vitro potency while improving the chemical stability and pharmacokinetic profile. These modifications led to the identification of compound 10, which showed excellent selectivity over related serine proteases as well as in vivo efficacy in the rat arteriovenous shunt. Compound 10 exhibited significantly improved chemical stability and pharmacokinetic properties over 2 and may be utilized as a structurally differentiated preclinical tool comparator to dabigatran etexilate (Pro-1) to interrogate the on- and off-target effects of oral direct thrombin inhibitors.

Omarigliptin (MK-3102): a novel long-acting DPP-4 inhibitor for once-weekly treatment of type 2 diabetes

In our effort to discover DPP-4 inhibitors with added benefits over currently commercially available DPP-4 inhibitors, MK-3102 (omarigliptin), was identified as a potent and selective dipeptidyl peptidase 4 (DPP-4) inhibitor with an excellent pharmacokinetic profile amenable for once-weekly human dosing and selected as a clinical development candidate. This manuscript summarizes the mechanism of action, scientific rationale, medicinal chemistry, pharmacokinetic properties, and human efficacy data for omarigliptin, which is currently in phase 3 clinical development.

Heterocyclic core analogs of a direct thrombin inhibitor

Thrombin is a serine protease that plays a key role in blood clotting. Pyrrolidine 1 is a potent thrombin inhibitor discovered at Merck several years ago. Seven analogs (2-8) of 1 in which the pyrrolidine core was replaced with various heterocycles were prepared and evaluated for activity against thrombin, clotting factors VIIa, IXa, Xa, and XIIa, and trypsin. The thiomorpholine analog 6 was the most active, essentially matching the thrombin inhibitory activity of 1 with slightly improved selectivity over trypsin.

Synthesis and biological activity of anticoccidial agents: 2,3-diarylindoles

Novel 2,3-diarylindoles bearing an amine substituent at the indole 5- and 6-positions have been synthesized and evaluated as anticoccidial agents in both in vitro and in vivo assays. Both subnanomolar in vitro activity and broad spectrum in vivo potency were detected for several compounds, particularly compound 27.

Modeling assisted rational design of novel, potent, and selective pyrrolopyrimidine DPP-4 inhibitors

Molecular modeling was used to improve potency of the cyclohexylamine series. In addition, a 3-D QSAR method was used to gain insight for reducing off-target DPP-8/9 activities. Compounds 3, 4, and 5 were synthesized and found to be potent DPP-4 inhibitors, in particular 4 and 5 are designed to be highly selective against off-target DASH enzymes while maintaining potency on DPP-4.

Rational design of a novel, potent, and orally bioavailable cyclohexylamine DPP-4 inhibitor by application of molecular modeling and X-ray crystallography of sitagliptin

Molecular modeling was used to design a rigid analog of sitagliptin 1. The X-ray crystal structure of sitagliptin bound to DPP-4 suggested that the central beta-amino butyl amide moiety could be replaced with a cyclohexylamine group. This was confirmed by structural analysis and the resulting analog 2a was synthesized and found to be a potent DPP-4 inhibitor (IC(50)=21 nM) with excellent in vivo activity and pharmacokinetic profile.

Optimization of 1,4-diazepan-2-one containing dipeptidyl peptidase IV inhibitors for the treatment of type 2 diabetes

Following the discovery of N-acyl-1,4-diazepan-2-one as a novel pharmacophore for potent and selective DPP-4 inhibitors, optimization of this new lead with different substitution on the seven-membered ring resulted in several highly potent and selective, orally bioavailable, and efficacious DPP-4 inhibitors, such as 3R-methyl-1-cyclopropyl-1,4-diazepan-2-one derivative 9i (DPP-4 IC(50)=8.0 nM) and 3R,6R-dimethyl-1,4-diazepan-2-one derivative 14a (DPP-4 IC(50)=9.7 nM).

Synthesis and biological activity of imidazopyridine anticoccidial agents: part I

Coccidiosis is the major cause of morbidity and mortality in the poultry industry. Protozoan parasites of the genus Eimeria invade the intestinal lining of the avian host causing tissue pathology, poor weight gain, and in some cases mortality. Resistance to current anticoccidials has prompted the search for new therapeutic agents with potent in vitro and in vivo activity against Eimeria. Antiparasitic activity is due to inhibition of a parasite specific cGMP-dependent protein kinase (PKG). In this study, we present the synthesis and biological activity of imidazo[1,2-a]pyridine anticoccidial agents. From this series, several compounds showed subnanomolar in vitro activity and commercial levels of in vivo activity. However, the potential genotoxicity of these compounds precludes them from further development.

(3R)-4-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-3-(2,2,2-trifluoroethyl)-1,4-diazepan-2-one, a selective dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes

Replacement of the triazolopiperazine ring of sitagliptin (DPP-4 IC(50)=18nM) with 3-(2,2,2-trifluoroethyl)-1,4-diazepan-2-one gave dipeptidyl peptidase IV (DPP-4) inhibitor 1 which is potent (DPP-4 IC(50)=2.6nM), selective, and efficacious in an oral glucose tolerance test in mice. It was selected for extensive preclinical development as a potential back-up candidate to sitagliptin.

Synthesis and SAR Studies of diarylpyrrole anticoccidial agents

2-(4-Fluorophenyl)-3-(4-pyridinyl)-5-substituted pyrroles were prepared and evaluated as anticoccidial agents in both in vitro and in vivo assays. Among the compounds evaluated, the dimethylamine-substituted pyrrole 19a is the most potent inhibitor of Eimeria tenella PKG (cGMP-dependent protein kinase). Further SAR studies on the side chain of the 2-pyrrolidine nitrogen did not enhance in vivo anticoccidial activity.

Synthesis and SAR studies of very potent imidazopyridine antiprotozoal agents

Compounds 10a (IC50 110 pM) and 21 (IC50 40 pM) are the most potent inhibitors of Eimeria tenella cGMP-dependent protein kinase activity reported to date and are efficacious in the in vivo antiparasitic assay when administered to chickens at 12.5 and 6.25 ppm levels in the feed. However, both compounds are positive in the Ames microbial mutagenesis assay which precludes them from further development as antiprotozoal agents in the absence of negative lifetime rodent carcinogenicity studies.

Dipeptidyl peptidase IV inhibition for the treatment of type 2 diabetes: potential importance of selectivity over dipeptidyl peptidases 8 and 9

Dipeptidyl peptidase (DPP)-IV inhibitors are a new approach to the treatment of type 2 diabetes. DPP-IV is a member of a family of serine peptidases that includes quiescent cell proline dipeptidase (QPP), DPP8, and DPP9; DPP-IV is a key regulator of incretin hormones, but the functions of other family members are unknown. To determine the importance of selective DPP-IV inhibition for the treatment of diabetes, we tested selective inhibitors of DPP-IV, DPP8/DPP9, or QPP in 2-week rat toxicity studies and in acute dog tolerability studies. In rats, the DPP8/9 inhibitor produced alopecia, thrombocytopenia, reticulocytopenia, enlarged spleen, multiorgan histopathological changes, and mortality. In dogs, the DPP8/9 inhibitor produced gastrointestinal toxicity. The QPP inhibitor produced reticulocytopenia in rats only, and no toxicities were noted in either species for the selective DPP-IV inhibitor. The DPP8/9 inhibitor was also shown to attenuate T-cell activation in human in vitro models; a selective DPP-IV inhibitor was inactive in these assays. Moreover, we found DPP-IV inhibitors that were previously reported to be active in models of immune function to be more potent inhibitors of DPP8/9. These results suggest that assessment of selectivity of potential clinical candidates may be important to an optimal safety profile for this new class of antihyperglycemic agents.

Hydroxylated N-alkyl-4-piperidinyl-2,3-diarylpyrrole derivatives as potent broad-spectrum anticoccidial agents

Diaryl-(4-piperidinyl)-pyrrole derivatives bearing hydroxylated N-alkyl substituents have been synthesized and evaluated as anticoccidial agents. High potency in Et-PKG inhibition and broad-spectrum anticoccidial activities have been observed on compounds, such as 4b and 5h, which are fully efficacious in vivo at 50 ppm in feed.

Synthesis and SAR of 2,3-diarylpyrrole inhibitors of parasite cGMP-dependent protein kinase as novel anticoccidial agents

Several analogs of 2,3-diaryl pyrroles were synthesized and evaluated as inhibitors of Eimeria tenella cGMP-dependent protein kinase and in in vivo anticoccidial assays. A 4-fluorophenyl group enhances both in vitro and in vivo activities. The most potent analogs are the 5-(N-methyl, N-ethyl, and N-methylazetidine methyl) piperidyl derivatives 12, 23, and 34. These compounds have a broad spectrum of activity. Based on the in vivo efficacy and cost of synthesis, the N-ethyl analog 23 was chosen as a novel anticoccidial agent for a field trial.

Purification and molecular characterization of cGMP-dependent protein kinase from Apicomplexan parasites. A novel chemotherapeutic target

The trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H-pyrrol-3-yl]pyridine (Compound 1) inhibits the growth of Eimeria spp. both in vitro and in vivo. The molecular target of Compound 1 was identified as cGMP-dependent protein kinase (PKG) using a tritiated analogue to purify a approximately 120-kDa protein from lysates of Eimeria tenella. This represents the first example of a protozoal PKG. Cloning of PKG from several Apicomplexan parasites has identified a parasite signature sequence of nearly 300 amino acids that is not found in mammalian or Drosophila PKG and which contains an additional, third cGMP-binding site. Nucleotide cofactor regulation of parasite PKG is remarkably different from mammalian enzymes. The activity of both native and recombinant E. tenella PKG is stimulated 1000-fold by cGMP, with significant cooperativity. Two isoforms of the parasite enzyme are expressed from a single copy gene. NH(2)-terminal sequence of the soluble isoform of PKG is consistent with alternative translation initiation within the open reading frame of the enzyme. A larger, membrane-associated isoform corresponds to the deduced full-length protein sequence. Compound 1 is a potent inhibitor of both soluble and membrane-associated isoforms of native PKG, as well as recombinant enzyme, with an IC(50) of <1 nm.

Discovery of an orally bioavailable alkyl oxadiazole beta3 adrenergic receptor agonist

5-n-Pentyl oxadiazole substituted benzenesulfonamide 8 is a potent and selective beta3 adrenergic receptor agonist (beta3 EC50 = 23 nM, beta1 IC50 = 3000 nM, beta2 IC50 = 3000 nM). The compound has high oral bioavailability in dogs (62%) and rats (36%) and is among the most orally bioavailable beta3 adrenergic receptor agonists reported to date.

Synthesis and SAR of benzyl and phenoxymethylene oxadiazole benzenesulfonamides as selective beta3 adrenergic receptor agonist antiobesity agents

Benzyl and phenoxymethylene substituted oxadiazoles are potent and orally bioavailable beta3 adrenergic receptor (AR) agonists. The 4-trifluormethoxy substituted 5-benzyl oxadiazole 5f has an EC50 of 8 nM in the beta3 AR agonist assay with 100-fold selectivity over beta1 and beta2 AR binding inhibition activity. Its oral bioavailability in dogs is 30 +/- 4%, with a half-life of 3.8 +/- 0.4 h. In the anesthetized rhesus, 5f evoked a dose-dependent glycerolemia (ED50Gly = 0.15 mg/kg). Under these conditions a heart rate increase of 15% was observed at a dose level of 10 mg/kg.

Selective protection and relative importance of the carboxylic acid groups of zaragozic acid A for squalene synthase inhibition

Chemistry that allows selective modification of the carboxylic acid groups of the squalene synthase inhibitor zaragozic acid A (1) was developed and applied to the synthesis of compounds modified at the 3-,4-,5-,3,4-,3,5-, and 4,5-positions. A key step in this procedure is the selective debenzylation by transfer hydrogenolysis in the presence of other olefinic groups. These compounds were tested in the rat squalene synthase assay and in vivo mouse model. Modification at C3 retains significant enzyme potency and enhances oral activity, indicating that C3 is not essential for squalene synthase activity. Modification at C4 and C5 results in significant loss in enzyme activity. In contrast, substitution at C3 or C4 enhances in vivo activity. Furthermore, disubstitution at the C3 and C4 positions results in additive in vivo potency.

Epibatidine is a nicotinic analgesic

Epibatidine, an alkaloid isolated from skin of the poison frog, Epipedobates tricolor, has been shown to be a very potent analgesic with a non-opioid mechanism of action. We found that epibatidine was about 120 times more potent and has longer duration than nicotine in analgesia, which could be antagonized by pretreatment with mecamylamine. Furthermore, epibatidine competed with high affinity (IC50 = 70 pM, Ki = 43 pM) for [3H]cytisine binding in rat brain preparations. These results indicated that the analgesic activity of epibatidine is attributed to its unique property as the most potent nicotinic acetylcholine receptor agonist.

Development, synthesis, and biological evaluation of (-)-trans-(2S,5S)-2-[3-[(2-oxopropyl)sulfonyl]-4-n-propoxy-5-(3- hydroxypropoxy)-phenyl]-5-(3,4,5-trimethoxyphenyl)tetrahydrofuran, a potent orally active platelet-activating factor (PAF) antagonist and its water-soluble prodrug phosphate ester

(-)-trans-(2S,5S)-2-[3-[(2-Oxopropyl)sulfonyl]-4-n-propoxy-5-(3- hydroxypropoxy)phenyl]-5-(3,4,5-trimethoxyphenyl)tetrahydrofuran (10) is one of the most potent platelet-activating factor (PAF) antagonists in vitro and in vivo developed to date. This diaryltetrahydrofuran derivative evolved from modifications of MK 0287 which has been evaluated in clinical studies for asthma. Two structural modifications of MK 0287 were made: (1) elaboration of the 3'-[(hydroxyethyl)sulfonyl] group to a beta-keto propylsulfonyl, and (2) replacement of the 5'-methyl ether by a 3-hydroxypropyl ether. Compound 10 potently and specifically inhibits the binding of [3H]-C18-PAF to human platelet membranes (Ki 1.85 nM) and PMN membranes (Ki 2.89 nM). In vivo, 10 inhibits PAF-induced plasma extravasation and elevated N-acetyl-beta-D-glucosaminidase (NAGA) levels in male rats with ED50 values of 60 micrograms/kg, po and 4 micrograms/kg, iv respectively, and inhibits PAF-induced bronchoconstriction in guinea pigs with an ED50 value of 15 micrograms/kg after intraduodenal administration. Compound 15, a water-soluble phosphate ester prodrug derivative of 10 is at least equipotent to 10 in the in vivo models. Compound 19S, the primary and major metabolite of 10 and 15, is equipotent in in vitro and in vivo models.

(+/-)-trans-2-(3-Methoxy-5-methylsulfonyl-4-propoxyphenyl)-5-(3,4,5- trimethoxyphenyl)tetrahydrofuran (L-659,989), a novel, potent PAF receptor antagonist

The title compound, L-659,989, is a highly potent, competitive, and selective antagonist of the binding of [3H]PAF to its receptors in platelet membranes from rabbits and humans. It exhibits equilibrium inhibition constants for PAF binding of 1.1 nM (rabbit) to 9.0 nM (human), values that are at least 1-2 orders of magnitude lower than those of other PAF antagonists tested. L-659,989 potently inhibits PAF-induced aggregation of rabbit platelets and degranulation of rat (ED50 4.5 nM) and human (ED50 10 nM) neutrophils. L-659,989 inhibits PAF-induced extravasation and lysosomal enzyme release in rats, and is active orally in female rats (ED50 0.2 mg/kg) with an extraordinary oral duration of action of 12 to 16 hours at 1.0 mg/kg p.o.

Inhibition of the platelet activating factor (PAF)-induced in vivo responses in rats by trans-2,5-(3,4,5-trimethoxyphenyl) tetrahydrofuran (L-652,731), a PAF receptor antagonist

Trans-2,5-bis-(3,4,5-trimethoxyphenyl)tetrahydrofuran (L652, 731), a potent and specific receptor antagonist of platelet activating factor (PAF) (Hwang et al., J. Biol. Chem. 260: 15639-15645, 1985), potently inhibits several PAF-induced in vivo responses in rats. Intravenously and p.o. administered L-652,731 gave a dose-response inhibition of PAF-induced lysosomal hydrolase secretion and extravasation with ED50 values of 1 and 3 mg/kg, respectively. Inhibitions of 87% were achieved with 50 mg/kg p.o. After a single 5-mg/kg p.o. dose, L-652,731 achieved 50 to 60% inhibition of PAF-induced lysosomal hydrolase secretion and extravasation by 0.5 to 1.5 hr with near maximum inhibition lasting through 6 hr. A 20-mg/kg p.o. dose of L-652,731 inhibited PAF-induced leukopenia and neutropenia by 96 and 73%, respectively. The most substantial inhibitions of the extravasation and lysosomal hydrolase secretion induced by PAF or soluble immune complexes were achieved by p.o. L-652,731 (20 mg/kg) with moderate inhibition by dexamethasone and little or no inhibition by antagonists/inhibitors of histamine H1 or H2 or serotonin receptors or cyclooxygenase. Intravenous infusion of a 0.4 mg of L-652,731 bolus inhibited the hypotensive responses from subsequent PAF infusions by a maximum of 72% and with a half-life duration of action of 2.5 hr. Intravenous infusion of L-652,731 results in an immediate 87% reversal of the extreme hypotension induced by a previous endotoxin injection. Thus, with its good p.o. activity, long duration of action and specificity in inhibiting PAF-induced responses in vivo, L-652,731 is a very useful tool in determining the role of PAF in mediating different pathophysiological processes.

Conformation and activity of tetrahydrofuran lignans and analogues as specific platelet activating factor antagonists

The six (racemic or meso) isomers of 3,4-dimethyl-2,5-bis(3,4-dimethoxyphenyl)tetrahydrofuran and four corresponding desmethyl analogues were prepared and assayed as inhibitors of platelet activating factor (PAF) receptor binding to rabbit platelet plasma membranes. The inhibition by these isomers is stereodependent and varies with the gross shape of the molecules as determined by the molecular mechanics program MM2. The most potent PAF antagonist in this group of compounds is trans-2,5-bis(3,4,5-trimethoxyphenyl)tetrahydrofuran (L-652,731, 14) with an IC50 of 0.02 microM.

Platelet-activating factor (PAF) mediation of rat anaphylactic responses to soluble immune complexes. Studies with PAF receptor antagonist L-652,731

A new synthetic compound, L-652,731 (trans-2,5-(3,4,5-trimethoxyphenyl) tetrahydrofuran), which has been demonstrated by Hwang et al. to be a potent and specific platelet-activating factor (PAF) receptor antagonist causes 100% inhibition of 1 microM PAF-induced neutrophil degranulation at 50 microM, but has no effect on neutrophil degranulation induced by precipitating immune complexes (323 micrograms/ml), fMet-Leu-Phe (10(-7) M), or the calcium ionophore A23187 (10(-5) M). Intravenous infusion of 1 mumol L-652,731 results in almost 100% inhibition of hypotension induced by PAF but not that induced by isoproterenol, histamine, bradykinin, or acetylcholine. With the use of this novel PAF receptor antagonist, the in vivo mediator role of PAF in the soluble immune complex-induced hypotension, extravasation, vascular lysosomal hydrolase secretion, and neutropenia in rats was determined. The hypotension, extravasation, and lysosomal hydrolase release induced by immune complex infusion take 2 to 10 min longer to occur than the same responses elicited by PAF infusion. The neutropenia response is immediate with both stimuli. L-652,731 when orally administered to rats (20 mg/kg, 1.5 hr before PAF infusion) inhibited PAF-induced hypotension (69%), extravasation (76%), vascular lysosomal hydrolase release (79%), and neutropenia (73%). The same L-652,731-dosing regimen inhibited immune complex-stimulated hypotension (87%), extravasation (77%), and vascular lysosomal hydrolase release (31%). The initial and complete neutropenia induced by immune complex infusion was not inhibited in L-652,731-pretreated rats, but the rate of return of neutrophils to the blood was faster in the latter rats. Rats with blocked circulation to the liver still exhibited extensive extravasation and vascular lysosomal hydrolase release in response to PAF, but there was no extravasation and greatly reduced hydrolase release in response to immune complexes. Thus PAF is indicated to be a major mediator of soluble immune complex-induced hypotension and vascular permeability and a minor mediator of immune complex-induced lysosomal hydrolase release in rats. PAF probably does not mediate the initial and complete neutropenia stimulated by immune complexes. The liver is probably the major site for PAF production in response to circulating immune complexes.

Platelet-activating factor (PAF) mediation of rat anaphylactic responses to soluble immune complexes. Studies with PAF receptor antagonist L-652,731

A new synthetic compound, L-652,731 (trans-2,5-(3,4,5-trimethoxyphenyl) tetrahydrofuran), which has been demonstrated by Hwang et al. to be a potent and specific platelet-activating factor (PAF) receptor antagonist causes 100% inhibition of 1 microM PAF-induced neutrophil degranulation at 50 microM, but has no effect on neutrophil degranulation induced by precipitating immune complexes (323 micrograms/ml), fMet-Leu-Phe (10(-7) M), or the calcium ionophore A23187 (10(-5) M). Intravenous infusion of 1 mumol L-652,731 results in almost 100% inhibition of hypotension induced by PAF but not that induced by isoproterenol, histamine, bradykinin, or acetylcholine. With the use of this novel PAF receptor antagonist, the in vivo mediator role of PAF in the soluble immune complex-induced hypotension, extravasation, vascular lysosomal hydrolase secretion, and neutropenia in rats was determined. The hypotension, extravasation, and lysosomal hydrolase release induced by immune complex infusion take 2 to 10 min longer to occur than the same responses elicited by PAF infusion. The neutropenia response is immediate with both stimuli. L-652,731 when orally administered to rats (20 mg/kg, 1.5 hr before PAF infusion) inhibited PAF-induced hypotension (69%), extravasation (76%), vascular lysosomal hydrolase release (79%), and neutropenia (73%). The same L-652,731-dosing regimen inhibited immune complex-stimulated hypotension (87%), extravasation (77%), and vascular lysosomal hydrolase release (31%). The initial and complete neutropenia induced by immune complex infusion was not inhibited in L-652,731-pretreated rats, but the rate of return of neutrophils to the blood was faster in the latter rats. Rats with blocked circulation to the liver still exhibited extensive extravasation and vascular lysosomal hydrolase release in response to PAF, but there was no extravasation and greatly reduced hydrolase release in response to immune complexes. Thus PAF is indicated to be a major mediator of soluble immune complex-induced hypotension and vascular permeability and a minor mediator of immune complex-induced lysosomal hydrolase release in rats. PAF probably does not mediate the initial and complete neutropenia stimulated by immune complexes. The liver is probably the major site for PAF production in response to circulating immune complexes.

trans-2,5-Bis-(3,4,5-trimethoxyphenyl)tetrahydrofuran. An orally active specific and competitive receptor antagonist of platelet activating factor

trans-2,5-Bis(3,4,5-trimethoxyphenyl)tetrahydrofuran (L-652,731) is found to be a potent and orally active platelet activating factor (PAF)-specific and competitive receptor antagonist. It potently inhibits [3H]PAF (1 nM) binding to receptor sites on rabbit platelet membranes with an ED50 of 2 X 10(-8) M under the assay condition without the addition of mono- or divalent cations. In a comparative study, it is more potent than CV-3988, kadsurenone, and ginkgolide B as a receptor antagonist. The equilibrium dissociation constants (KB) of L-652,731 obtained either from the inhibition of receptor binding or from the inhibition of PAF-induced aggregation of gel-filtered rabbit platelet are 2.7 X 10(-8) and 2.1 X 10(-8) M, respectively. The agreement of these KB determinations based on receptor and cellular function suggests that L-652,731 does not inhibit other steps following PAF-receptor binding. L-652,731 does not antagonize the binding of several radioligands to their respective receptor. It shows no inhibitory effect on platelet aggregation induced by other aggregating agents including thrombin, collagen, A-23187, arachidonic acid, epinephrine, and ADP. L-652,731 is orally active; it inhibits PAF-induced rat cutaneous vascular permeability with an ED50 of 30 mg/kg orally. Significant inhibitory results of L-652,731 suggest that PAF may be partially involved in cutaneous vascular permeability induced by histamine and bradykinin.