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Background and purpose:Agonist apparent affinities (pKI′) in histamine H3-receptor binding assays were higher than expected from apparent affinity values (pKapp) estimated in bioassay. Here, we investigate whether the degree of pKI′ overestimation is related to agonist intrinsic efficacy, by studying the effect of buffer composition on the pKI′ of ligands with varying intrinsic activity.Experimental approach:In the guinea-pig ileum bioassay, intrinsic activity (α) was determined from the maximal inhibition of the contraction produced by increasing agonist concentration. pKapp values were estimated using the method of Furchgott. The pKL of [3H]clobenpropit in guinea-pig cerebral cortex was estimated by saturation analysis in 20 mM HEPES-NaOH buffer (buffer B(0,0,0)), or buffer B(0,0,0) containing 70 mM CaCl2, 100 mM NaCl and 100 mM KCl (buffer B(0.07,0.1,0.1)). PKI values were determined in competition studies in both buffers.Key results:[3H]clobenpropit saturation isotherms had n H values of unity in both buffers. In buffer B(0.07,0.1,0.1), agonist pKI′ values were closer to pKapp values than in buffer B(0,0,0) but were associated with n H values <1. A two-site analysis of agonist data in buffer B(0.07, 0.1, 0.1) provided a better fit than a one-site fit and low affinity values (pKIL) were comparable to pKapp. Differences between the pKI′ in buffer B(0,0,0) and pKIL values in buffer B(0.07,0.1,0.1) (ΔpK) were correlated with α.Conclusions and implications:H3-receptor binding assays conducted in buffer B(0,0,0) and buffer B(0.07,0.1,0.1) can provide a measure of ligand affinity (pKapp) and intrinsic efficacy. The assay predicts that some ligands previously classified as H3-receptor antagonists may possess residual intrinsic efficacy.British Journal of Pharmacology (2007) 151, 128–143. doi:10.1038/sj.bjp.0707174; published online 12 March 2007 [ABSTRACT FROM AUTHOR]

Background and Purpose: JNJ-26070109 [(R)4-bromo-N-[1-(2,4-difluoro-phenyl)-ethyl]-2-(quinoxaline-5-sulfonylamino)-benzamide] is a novel antagonist at cholecystokinin CCK(2) receptors with good pharmacokinetic properties and represents a novel mechanism for the treatment of gastro-oesophageal reflux disease (GORD). The purpose of the present study was to determine whether chronic treatment with JNJ-26070109 could prevent, as well as treat, acid rebound in rats.Experimental Approach: A chronic fistula was surgically inserted into the stomach of rats to enable the measurement of acid secretion under basal, pentagastrin and histamine-stimulated conditions. JNJ-26070109 and omeprazole were administered separately and in combination.Key Results: Sustained administration of omeprazole alone and in combination with JNJ-26070109 inhibited gastric acid secretion by >90%. However, 3 days after withdrawing treatment, there was a rebound hypersecretion by ∼1.5-fold in omeprazole-treated animals. No such acid rebound was observed with JNJ-26070109 alone or with co-administration of JNJ-26070109 and omeprazole. The anti-trophic effects of JNJ-26070109 in the gastric mucosal paralleled the effects on acid rebound. Administration of JNJ-26070109 for 3 days after cessation of omeprazole prevented the occurrence of acid rebound. Interestingly, chronic, but not acute, treatment with JNJ-26070109 also inhibited histamine-stimulated acid secretion.Conclusions and Implications: Chronic administration of JNJ-26070109 effectively inhibited gastric acid secretion and suppressed proton pump inhibitor (PPI)-induced acid rebound in the rat. This work advances the field by demonstrating that modest doses of a competitive CCK(2) receptor antagonist have significant and functionally important anti-trophic actions in the gastric mucosa. These properties make JNJ-26070109 a suitable candidate for clinical investigation for the treatment of GORD. [ABSTRACT FROM AUTHOR]

Background and Purpose: Cholecystokinin (CCK) stimulates the release of amylase and lipase from the normal pancreas. However, it is not clear to what extent this occurs in the early stages of pancreatitis induced by biliary tract obstruction in the rat and whether CCK initiates an inflammatory cascade in this condition.Experimental Approach: Selective CCK1 receptor antagonists, JNJ-17156516 ((S)-(3-[5-(3,4-dichloro-phenyl)-1-(4-methoxy-phenyl)-1H-pyrazol-3-yl]-2-m-tolyl-propionic acid) and dexloxiglumide, were used to assess the response of plasma amylase and lipase to a CCK analogue, CCK8S, in normal rats and in rats with bile duct ligation.Key Results: Both antagonists suppressed CCK8S-induced elevation of plasma amylase activity in normal rats. JNJ-17156516 was more potent than dexloxiglumide (ED(50)=8.2 vs >30 micromol kg(-1) p.o.) and produced a longer lived inhibition (6 vs 2 h). Plasma amylase and lipase activity were elevated in parallel to CCK plasma concentrations after bile duct ligation and both activities were suppressed in a dose-dependent manner by JNJ-17156516 and dexloxiglumide. JNJ-17156516 was approximately 5- to 10-fold more potent than dexloxiglumide. Infusion of CCK8S to naïve rats to achieve levels similar to those observed after bile duct ligation (20 pM) increased plasma amylase activity and activated nuclear factor-kappaB in the pancreas. These effects were prevented by pretreatment with JNJ-17156516.Conclusions and Implications: The elevation of plasma amylase and lipase activity in the early stages of obstruction-induced pancreatitis is largely driven by elevation of plasma CCK concentration and activation of CCK1 receptors. These data show that CCK is an initiating factor in acute pancreatitis in the rat. [ABSTRACT FROM AUTHOR]

What is already known about this subject? • Two chemically diverse CCK1 receptor antagonists have been shown clinically to inhibit CCK-evoked contraction of human gallbladder [ 2, 3 ]. These studies have not examined the relationship between plasma concentration and effect, the latter usually considered to be predictive from the free drug concentration [ 8 ]. • We wanted to examine our novel CCK1 receptor antagonist in this validated model and also to explore its PK-PD relationship. What this study adds • 2-NAP inhibited CCK-evoked human gallbladder contraction in vivo but at a plasma free concentration that was, in theory, too low to have achieved adequate CCK1 receptor occupancy. • The study serves as a caveat to the assumption that free plasma concentration can be used to predict pharmacological effect. Aims To study the pharmacokinetics and pharmacodynamics of 2-NAP (2-naphthalenesulfonyl-L-aspartyl-(2-phenethyl)amide), a selective CCK1 receptor antagonist in healthy volunteers. Methods 2-NAP was given to 12 healthy male volunteers in an ascending dose, safety and PK phase 1a study by 1 h i.v. infusion (0.6–9.6 mg kg−1 h−1). A further 12 healthy male volunteers received i.v. CCK-8S (6.25 pmol kg−1 h−1) to produce gallbladder contraction, measured by ultrasound recordings of gallbladder volume, and the effect of concurrent i.v. 2-NAP administration was studied. Plasma protein binding in vitro and ex vivo was measured by ultrafiltration and by equilibrium dialysis. Results 2-NAP was generally well tolerated, displayed linear pharmacokinetics and a very high degree of plasma protein binding (99.9%). A 105 min i.v. CCK-8S infusion induced a reduction in gallbladder volume of 14.9 (±7.0) ml during placebo co-infusion and this was reduced to 2.4 (±5.9) ml when 2-NAP was co-infused with CCK-8S ( P = 0.00024, paired t-test, mean change 12.5 ml; 95% CI For mean 7.4, 18.3 ml). This extent of inhibition was consistent with a 2-NAP total plasma concentration of 36 µm, but when protein binding corrections were made, the ‘free concentration’ of 2-NAP was only 0.04 µm, a value much less than the average equilibrium dissociation constant of 2-NAP for human CCK1 receptors (∼0.7 µm). Conclusions The pharmacological effect of a drug is usually considered to be determined by its free concentration. However, the complete inhibition of CCK-8S-evoked gallbladder contraction by a free plasma concentration of 0.04 µm 2-NAP was much greater than would have been predicted from simple drug-receptor occupancy theory and cautions against the general use of free concentration of drug for predicting pharmacological effect. [ABSTRACT FROM AUTHOR]