This paper presents the current state of knowledge on chloroquine disposition, with special emphasis on stereoselectivity and microsomal metabolism. In addition, the impact of the patient's physiopathological status and ethnic origin on chloroquine pharmacokinetics is discussed. In humans, chloroquine concentrations decline multiexponentially. The drug is extensively distributed, with a volume of distribution of 200 to 800 L/kg when calculated from plasma concentrations and 200 L/kg when estimated from whole blood data (concentrations being 5 to 10 times higher). Chloroquine is 60% bound to plasma proteins and equally cleared by the kidney and liver. Following administration chloroquine is rapidly dealkylated via cytochrome P450 enzymes (CYP) into the pharmacologically active desethylchloroquine and bisdesethylchloroquine. Desethylchloroquine and bisdesethylchloroquine concentrations reach 40 and 10% of chloroquine concentrations, respectively; both chloroquine and desethylchloroquine concentrations decline slowly, with elimination half-lives of 20 to 60 days. Both parent drug and metabolite can be detected in urine months after a single dose. In vitro and in vivo, chloroquine and desethylchloroquine competitively inhibit CYP2D1/6-mediated reactions. Limited in vitro studies and preliminary data from clinical experiments and observations point to CYP3A and CYP2D6 as the 2 major isoforms affected by or involved in chloroquine metabolism. In vitro efficacy studies did not detect any difference in potency between chloroquine enantiomers but, in vivo in rats, S(+)-chloroquine had a lower dose that elicited 50% of the maximal effect (ED950) than that of R(-)-chloroquine. Stereoselectivity in chloroquine body disposition could be responsible for this discrepancy. Chloroquine binding to plasma proteins is stereoselective, favouring S(+)-chloroquine (67% vs 35% for the R-enantiomer). Hence, unbound plasma concentrations are higher for R(-)-chloroquine. Following separate administration of the individual enantiomers, R(-)-chloroquine reached higher and more sustained blood concentrations. The shorter half-life of S(+)-chloroquine appears secondary to its faster clearance. Blood concentrations of the S(+)-forms of desethylchloroquine always exceeded those of the R(-)-forms, pointing to a preferential metabolism of S(+)-chloroquine.

ABSTRACT:In humans, the antimalarial drug chloroquine (CQ) is metabolized into one major metabolite, N-desethylchloroquine (DCQ). Using human liver microsomes (HLM) and recombinant human cytochrome P450 (P450), we performed studies to identify the P450 isoform(s) involved in the N-desethylation of CQ. In HLM incubated with CQ, only DCQ could be detected. Apparent K m and V max values (mean ؎ S.D.) for metabolite formation were 444 ؎ 121 M and 617 ؎ 128 pmol/min/mg protein, respectively. In microsomes from a panel of 16 human livers phenotyped for 10 different P450 isoforms, DCQ formation was highly correlated with testosterone 6␤-hydroxylation (r ‫؍‬ 0.80; p < 0.001), a CYP3A-mediated reaction, and CYP2C8-mediated paclitaxel ␣-hydroxylation (r ‫؍‬ 0.82; p < 0.001). CQ N-desethylation was diminished when coincubated with quercetin (20-40% inhibition), ketoconazole, or troleandomycin (20-30% inhibition) and was strongly inhibited (80% inhibition) by a combination of ketoconazole and quercetin, which further corroborates the contribution of CYP2C8 and CYP3As. Of 10 cDNAexpressed human P450s examined, only CYP1A1, CYP2D6, CYP3A4, and CYP2C8 produced DCQ. CYP2C8 and CYP3A4 constituted low-affinity/high-capacity systems, whereas CYP2D6 was associated with higher affinity but a significantly lower capacity. This property may explain the ability of CQ to inhibit CYP2D6-mediated metabolism in vitro and in vivo. At therapeutically relevant concentrations (ϳ100 M CQ in the liver), CYP2C8, CYP3A4, and, to a much lesser extent, CYP2D6 are expected to account for most of the CQ N-desethylation.

The sensory neuron-specific G protein coupled receptors (SNSRs) have been described as a family of receptors whose expression in small diameter sensory neurons in the trigeminal and dorsal root ganglia suggests an implication in nociception. To date, the physiological function(s) of SNSRs remain unknown. Hence, the aim of the present study was to determine the effects of rat SNSR1 activation on nociception in rats. The pharmacological characterization of rat SNSR1 was initially performed in vitro to identify a specific ligand, which could be used subsequently in the rat for physiological testing. Among all ligands tested, ␥2-MSH was the most potent at activating rat SNSR1. Structure-activity relationship studies revealed that the active moiety recognized by rat SNSR1 was the C-terminal part of ␥2-MSH. The radiolabeled C-terminal part of ␥2-MSH, ␥2-MSH-6 -12, bound with high affinity to membranes derived from rat skin and spinal cord, demonstrating the presence of receptor protein at both the proximal and distal terminals of dorsal root ganglia. To investigate the physiological role of SNSR, specific ligands to rat SNSR1 were tested in behavioral assays of pain sensitivity in rats. Selective rat SNSR1 agonists produced spontaneous pain behavior, enhanced heat and mechanical sensitivity when injected intradermally, and heat hypersensitivity when injected centrally, consistent with the localization of rat SNSR1 protein at central and peripheral sites. Together, these results clearly indicate that the SNSR1 plays a role in nociception and may provide novel therapeutic opportunities for analgesia. Gprotein-coupled receptors constitute one of the largest gene family of proteins that have been exploited successfully as drug targets (1). With the near completion of the human genome project, bioinformatic analyses have revealed the existence of Ϸ145 orphan receptors (1, 2). In recent years, the ''reverse pharmacology approach'' has generated Ͼ40 ligand-receptor pairings (1, 3), and the subsequent investigation of these newly discovered ligand-receptor pairings should help in understanding and elucidating their potential physiological and pathophysiological roles.We cloned a previously undescribed family of G protein-coupled receptors that we named the sensory neuron-specific receptors (SNSRs) because of their unique mRNA distribution in small nociceptive sensory neurons in dorsal root (DRG) and trigeminal ganglia (4). The SNSRs are phylogenetically related to the Mas oncogene receptor and belong to the Mas-related genes or Mrg family described for mouse and human by Dong et al. (5). Based on several analyses, this subfamily of receptors is comprised of four to six members in human (MrgX1-4 or SNSR1-6) and 32 receptors in mouse classified into three major subfamilies Mrg A, B, and C (4-7). Initially, only one SNSR gene was identified in rat (4); recently, Zylka et al. (8) have demonstrated that more than one rat SNSR͞ Mrg subtype exists. These receptors have been subclassified in a similar scheme as described for human a...

The design, synthesis, and pharmacological evaluation of a novel class of delta opioid receptor agonists, N, N-diethyl-4-(phenylpiperidin-4-ylidenemethyl)benzamide (6a) and its analogues, are described. These compounds, formally derived from SNC-80 (2) by replacing the piperazine ring with a piperidine ring containing an exocyclic carbon carbon double bond, were found to bind with high affinity and exhibit excellent selectivity for the delta opioid receptor as full agonists. 6a, the simplest structure in the class, exhibited an IC(50) = 0.87 nM for the delta opioid receptors and extremely high selectivity over the mu receptors (mu/delta = 4370) and the kappa receptors (kappa/delta = 8590). Rat liver microsome studies on a selected number of compounds show these olefinic piperidine compounds (6) to be considerably more stable than SNC-80. This novel series of compounds appear to interact with delta opioid receptors in a similar way to SNC-80 since they demonstrate similar SAR. Two general approaches have been established for the synthesis of these compounds, based on dehydration of benzhydryl alcohols (7) and Suzuki coupling reactions of vinyl bromide (8), and are herewith reported.

Nonpeptide delta opioid agonists are analgesics with a potentially improved side-effect and abuse liability profile, compared to classical opioids. Andrews analysis of the NIH nonpeptide lead SNC-80 suggested the removal of substituents not predicted to contribute to binding. This approach led to a simplified lead, N, N-diethyl-4-[phenyl(1-piperazinyl)methyl]benzamide (1), which retained potent binding affinity and selectivity to the human delta receptor (IC(50) = 11 nM, mu/delta = 740, kappa/delta > 900) and potency as a full agonist (EC(50) = 36 nM) but had a markedly reduced molecular weight, only one chiral center, and increased in vitro metabolic stability. From this lead, the key pharmacophore groups for delta receptor affinity and activation were more clearly defined by SAR and mutagenesis studies. Further structural modifications on the basis of 1 confirmed the importance of the N, N-diethylbenzamide group and the piperazine lower basic nitrogen for delta binding, in agreement with mutagenesis data. A number of piperazine N-alkyl substituents were tolerated. In contrast, modifications of the phenyl group led to the discovery of a series of diarylmethylpiperazines exemplified by N, N-diethyl-4-[1-piperazinyl(8-quinolinyl)methyl]benzamide (56) which had an improved in vitro binding profile (IC(50) = 0.5 nM, mu/delta = 1239, EC(50) = 3.6 nM) and increased in vitro metabolic stability compared to SNC-80.

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1 Stereoselectivity in the disposition of hydroxychloroquine was investigated in 23 healthy males following a single oral dose of 200 mg racemic HCQ (rac-HCQ) sulphate. Total concentrations (R+S) and R/S ratios of HCQ and its metabolites were measured by stereoselective h.p.l.c. 2 HCQ was detected in whole blood and urine, up to 91 and 85 days after dosing, respectively. Metabolites could not be detected in whole blood while in urine detectable concentrations were still present after 85 days. The blood concentrations of HCQ enantiomers were measurable until 168 h post-dose. 3 R(-)-HCQ accounted for 62 ± 3% (mean ± s.d.) of the AUC of rac-HCQ AUC.The elimination half-life of S(+)-HCQ (457 ± 122 h) was significantly shorter than that of R(-)-HCQ (526 ± 140 h), partly due to its faster urinary excretion and hepatic metabolism. Its renal clearance was twice that of R(-)-HCQ (4.61 ± 4.01 vs 1.79 ± 1.30 1 h-1), and metabolites derived from the S-isomer represented 80-90% of the urinary recovery of the dose. 4 Over 85 days, 4.4 ± 2.9 and 3.3 ± 1.8% of the dose was recovered in urine as unchanged S(+)-HCQ and R(-)-HCQ, respectively. For the first 2 weeks, S(+)-HCQ excretion rate clearly surpassed that of R(-)-HCQ whereas afterwards the inverse was observed. However, since the first 2 weeks account for 95% of rac-HCQ renal excretion, the total urinary excretion of S(+)-HCQ clearly surpassed that of R(-)-HCQ. 5 In urine, the R/S ratios of desethylhydroxychloroquine (DHCQ) were stable while those of desethylchloroquine (DCQ) increased over time. Since both desethylations display a different enantioselectivity, different enzymes appear to be responsible for HCQ metabolism into DCQ and DHCQ.