Phase 1 study of safety and tolerability of an oral contraceptive containing low-dose ethinyl oestradiol combined with glecaprevir/pibrentasvir treatment in healthy premenopausal women.

Glecaprevir/pibrentasvir (GLE/PIB) is an approved guideline-recommended chronic hepatitis C virus infection treatment. GLE/PIB coadministration with ethinyl oestradiol (EE) is not recommended in current labels owing to a Phase 1 study observing Grade ≥2 alanine aminotransferase (ALT) elevation in 2 out of 12 healthy women cotreated for 11 days with GLE/PIB and oral contraceptive (OC) containing 35 µg/250 µg EE/norgestimate. No Grade ≥2 elevation was observed with low-dose (20 µg) EE (n = 14). This Phase 1 study examined safety/tolerability of GLE/PIB coadministered with an OC containing low-dose EE using a larger sample size and longer treatment duration. Healthy premenopausal women were treated with EE/levonorgestrel alone (20/100 µg, Cycles 1-2), followed by coadministration with GLE/PIB (300/120 mg; Cycles 3-4). A safety criterion of special interest was a confirmed Grade ≥2 ALT elevation (>3× upper normal limit). Adverse events (AEs) and study drugs concentrations were examined. Of 85 enrolled women, 72 initiated combined GLE/PIB + EE/levonorgestrel treatment, 66 completed the study and 19 discontinued prematurely (non-safety reason, n = 16; AE [deemed unelated to GLE/PIB], n = 3). No participant met the safety criterion of special interest of confirmed Grade ≥2 ALT elevation. No serious/Grade ≥3 AEs were reported. Study drug concentrations were within the expected ranges. GLE/PIB in combination with an OC containing low-dose EE was generally well tolerated with no confirmed Grade ≥2 ALT elevation and no evidence of drug-induced liver injury. No pattern to the reported AEs and no new safety issues were identified. This was a Phase 1 study of healthy volunteers, not a registered clinical trial.

Effects of a ritonavir-containing regimen on the pharmacokinetics of sirolimus or everolimus in healthy adult subjects.

The immunosuppressive agents sirolimus and everolimus are sensitive CYP3A4 substrates with narrow therapeutic index. Ritonavir is a strong CYP3A inhibitor. A phase 1 study was conducted to evaluate the pharmacokinetics, safety, and tolerability of the co-administration of sirolimus or everolimus with the ritonavir-containing 3D regimen of the direct-acting antiviral agents ombitasvir, ritonavir-boosted paritaprevir, and dasabuvir in healthy subjects. This study had two independent arms, each with a two-period, single-sequence, crossover study design. A single dose of sirolimus 2 mg (N = 12) or everolimus 0.75 mg (N = 12) was administered in Period 1. In Period 2, multiple doses of the 3D regimen (ombitasvir/paritaprevir/ritonavir 25/150/100 mg once daily and dasabuvir 250 mg twice daily) were administered for 34 or 28 days, with a single dose of sirolimus 0.5 mg or everolimus 0.75 mg co-administered on Day 15. Following co-administration with the 3D regimen, the sirolimus dose-normalized maximum observed blood concentration (Cmax ) and area under the blood concentration-time curve from time zero to infinity (AUCinf ) increased to 6.4-fold and 38-fold, respectively. Following co-administration with the 3D regimen, the everolimus Cmax and AUCinf increased to 4.7-fold and 27-fold, respectively. Sirolimus and everolimus half-lives increased from 96 to 249 h, and 42 to 118 h, respectively. There were no major safety or tolerability issues in this study. The ritonavir-containing 3D regimen resulted in a significant increase in sirolimus or everolimus exposure, consistent with the known strong inhibitory effect of ritonavir on CYP3A requiring dose and/or frequency modification when co-administered with each other.

Durability of sustained virological response to glecaprevir/pibrentasvir and resistance development: A long-term follow-up study.

BACKGROUND AND AIMS: This study aimed to determine durability of sustained virologic response (SVR) in hepatitis C virus-infected participants treated with glecaprevir- and/or pibrentasvir-containing regimens. METHODS: M13-576, a rollover study, evaluated the durability of SVR in a follow-up period of approximately 3 years after hepatitis C virus genotype 1-6-infected participants received a glecaprevir- and/or pibrentasvir-containing regimen in previous phase 2/3 clinical trials. The primary efficacy endpoint was the percentage of participants maintaining SVR and the percentage of participants experiencing relapse or reinfections. Resistance-associated substitutions and safety outcomes related to liver progression were also assessed. RESULTS: Of 384 participants enroled, 377 participants were included in the as-observed population and 287 participants completed the study. In prior studies, 99.7% (376/377) of participants achieved SVR12; of those, an observed 99.5% (374/376) and 100% (286/286) completing the study, maintained SVR. After non-responder imputation of missing data, 286/376 participants (76%) maintained SVR. The participant previously not achieving SVR was a treatment-experienced male with compensated cirrhosis who had NS3 and NS5A substitutions at enrolment, which remained detectable for 12 months. Of the two participants not maintaining SVR, one was re-infected and one experienced late relapse at post-treatment week 60. Five participants (all with a fibrosis stage ≥F3) had hepatocellular carcinoma. No events were deemed related to glecaprevir/pibrentasvir. CONCLUSIONS: Glecaprevir/pibrentasvir demonstrated long-term durability of efficacy after SVR12 was achieved. Hepatic-related decompensation events were not seen. Owing to low incidence of virologic failure, conclusions were not drawn on persistence of resistance-associated substitutions.

Efficacy and safety of glecaprevir/pibrentasvir in patients with HCV genotype 5/6: An integrated analysis of phase 2/3 studies.

BACKGROUND & AIMS: Hepatitis C virus (HCV) has high genetic diversity with six major genotypes (GT) GT1-6 and global distribution. HCV GT5 and 6 are rare with < 10 million people infected worldwide. Data on direct-acting antiviral use in these rare HCV genotypes are limited. The study aimed to evaluate the efficacy and safety of glecaprevir/pibrentasvir (G/P) in a pooled analysis of phase 2/3 trials in HCV GT5 or 6-infected patients without cirrhosis or with compensated cirrhosis. METHODS: Patients with chronic HCV GT5 or 6 infection received oral G/P (300 mg/120 mg) once daily for 8 or 12 weeks. The primary efficacy endpoint was sustained virological response at post-treatment week 12 (SVR12) in the intention-to-treat population. RESULTS: One hundred eighty-one patients were evaluated; 56 with HCV GT5 and 125 with HCV GT6. The majority were treatment-naïve (88%) and non-cirrhotic (85%). Overall SVR12 rate with 8- or 12-week G/P treatment was 98% (178/181). Eight-week treatment with G/P yielded SVR12 rates of 95% (21/22) in HCV GT5- and 99% (69/70) in HCV GT6-infected non-cirrhotic patients. Eight- and 12-week treatment of patients with compensated cirrhosis achieved SVR12 rates of 100% (10/10) and 94% (17/18) respectively. The G/P regimen was well-tolerated; 3% (6/181) Grade 3 or higher adverse events, and no serious adverse events were attributed to G/P or led to study drug discontinuation. CONCLUSIONS: This integrated dataset demonstrates a high SVR12 rate following 8-week G/P treatment in patients with HCV GT5 (96%) or GT6 (99%) infection without cirrhosis or with compensated cirrhosis.

Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir Mini-Tabs Plus Ribavirin for Children Aged 3-11 Years with Hepatitis C Genotype 1a.

INTRODUCTION: To assess the safety, efficacy, and pharmacokinetics of mini-tablet formulations of ombitasvir (OBV), paritaprevir (PTV), ritonavir, and dasabuvir (DSV) with or without ribavirin for 12 weeks in children infected with chronic hepatitis C virus (HCV) genotype (GT) 1. METHODS: This is an ongoing, open-label, Phase 2/3 study in children 3-11 years old infected with HCV GT1 who were HCV treatment-naïve and non-cirrhotic. Pediatric mini-tablet formulations of OBV, PTV, ritonavir, and DSV plus ribavirin oral solution were administered for 12 weeks based on body weight. Endpoints included SVR12, adverse events (AEs), and pharmacokinetic parameters. RESULTS: Overall, 26 children received OBV, PTV, ritonavir, and DSV plus ribavirin; 14 were 3-8 years old and 12 were 9-11 years old; 35% were male; and all had chronic HCV GT1a infection. The SVR12 rate was 96% (25/26; 95% CI 81.1-99.3), with 1 child failing to achieve SVR12 due to non-adherence and treatment discontinuation. Treatment-emergent AEs of Grade ≥ 3 occurred in 3 children; 2 events in 1 child were considered serious; and none were considered treatment-related. No AEs led to discontinuation of study treatment. The most common AEs were headache (27%), fatigue (23%), pyrexia (19%), and vomiting (19%). Pharmacokinetic results showed mini-tablet formulations of OBV, PTV, DSV, and ritonavir drug exposures were comparable to the adult formulation. CONCLUSION: The mini-tablet combination of OBV, PTV, ritonavir, and DSV plus ribavirin to treat HCV GT1a infection for 12 weeks was highly effective and suitable in children 3-11 years of age. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT02486406.

Efficacy and safety of glecaprevir/pibrentasvir in patients with chronic hepatitis C virus genotype 5 or 6 infection (ENDURANCE-5,6): an open-label, multicentre, phase 3b trial.

BACKGROUND: The pangenotypic direct-acting antiviral regimen of glecaprevir coformulated with pibrentasvir is approved to treat chronic hepatitis C virus (HCV) genotype 1-6 infection in adults. In registrational studies, 84 (99%) of 85 patients with HCV genotype 5 or 6 infection achieved a sustained virological response (SVR) with glecaprevir/pibrentasvir, with no virological failures. To increase the body of data for these less prevalent genotypes, ENDURANCE-5,6 evaluated the efficacy and safety of glecaprevir/pibrentasvir exclusively in patients infected with HCV genotype 5 or 6. METHODS: ENDURANCE-5,6 was a phase 3b, single-arm, open-label, multicentre trial done in 24 hospitals or clinics in Europe, Oceania, North America, South Africa, and southeast Asia. Adults with chronic HCV genotype 5 or 6 infection who were previously untreated or treatment-experienced were eligible to be enrolled. Glecaprevir/pibrentasvir (300 mg/120 mg) was given orally once daily for 8 weeks (for patients without cirrhosis) or 12 weeks (for patients with compensated cirrhosis). The primary efficacy endpoint was SVR12 (ie, HCV RNA <15 IU/mL at 12 weeks post-treatment), assessed within each HCV genotype, and analysed in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, number NCT02966795. FINDINGS: Between Feb 9, 2017, and Aug 28, 2018, 84 patients were enrolled: 23 with genotype 5 infection and 61 with genotype 6 infection. Overall, 82 (97·6%, 95% CI 94·4-100·0) of the 84 patients achieved SVR12. 22 (95·7%, 95% CI 87·3-100·0) of 23 patients with genotype 5 infection achieved SVR12, as did 60 (98·4%, CI 95·2-100·0) of 61 with genotype 6 infection. One patient with an HCV genotype 6f infection and cirrhosis had on-treatment virological failure at treatment week 12, and one patient with HCV genotype 5a without cirrhosis who had achieved SVR at post-treatment week 4 relapsed at post-treatment week 12. Five (6%) patients had serious adverse events, none of which were deemed related to glecaprevir/pibrentsavir or led to discontinuation. Fatigue (11 [13%] patients) and headache (11 [13%]) were the only adverse events that occurred in 10% or more of patients. No post-baseline grade 3 or higher increases in aminotransferase concentrations were reported. INTERPRETATION: Glecaprevir/pibrentasvir achieved high SVR12 rates, comparable with data reported in registrational studies, and was well tolerated in patients with HCV genotype 5 or 6 infection with compensated liver disease. FUNDING: AbbVie.

Ombitasvir/Paritaprevir/Ritonavir With or Without Dasabuvir and With or Without Ribavirin for Adolescents With HCV Genotype 1 or 4.

In adults, treatment of hepatitis C virus (HCV) infection with ombitasvir (OBV)/paritaprevir (PTV)/ritonavir (r) with or without dasabuvir (DSV) and ±ribavirin (RBV) results in high rates of sustained virologic response (SVR). However, these regimens have not been investigated in adolescents. This ongoing, open-label, phase 2/3 study evaluated the pharmacokinetics, safety, and efficacy of OBV/PTV/r+DSV±RBV treatment for 12 weeks in adolescents infected with HCV genotype (GT) 1 without cirrhosis (part 1) and the safety and efficacy of OBV/PTV/r±DSV±RBV treatment for 12 or 24 weeks in adolescents infected with GT1 or GT4 without cirrhosis or with compensated cirrhosis (parts 1 and 2). Patients were 12-17 years of age and treatment naive or interferon experienced. Treatment regimens were based on HCV GT and cirrhosis status. Endpoints were SVR at posttreatment week 12 (SVR12), adverse events (AEs), and pharmacokinetic parameters. Thirty-eight adolescents were enrolled, 66% were female patients, and 76% were White; 42%, 40%, and 18% of patients had HCV GT1a, GT1b, and GT4 infections, respectively. Median age was 15 years (range, 12-17 years), and 1 patient had cirrhosis. The SVR12 rate was 100% (38/38; 95% confidence interval [CI], 90.8%-100%). No treatment-emergent grade 3 or 4 laboratory abnormalities were reported. No serious AEs occurred on treatment, and no AEs led to study drug discontinuation. The most common AEs were headache (21%), fatigue (18%), nasopharyngitis (13%), pruritus (13%), and upper respiratory tract infection (11%). Intensive pharmacokinetic results showed OBV, PTV, DSV, and ritonavir drug exposures were comparable to those seen in adults. Conclusion: Treatment with OBV/PTV/r±DSV±RBV was well tolerated and highly efficacious in adolescents with HCV GT1 or GT4 infection.

Species comparison and pharmacological characterization of human, monkey, rat, and mouse TRPA1 channels.

The transient receptor potential ankyrin-1 (TRPA1) channel has emerged as an attractive target for development of analgesic and anti-inflammatory drugs. However, drug discovery efforts targeting TRPA1 have been hampered by differences between human and rodent species. Many compounds have been identified to have antagonist activity at human TRPA1 (hTRPA1), but when tested at rat TRPA1 (rTRPA1) and mouse TRPA1 (mTRPA1), they show reduced potency as antagonists, no effect, or agonist activity. These compounds are excluded from further drug development because they cannot be tested in preclinical studies using conventional rat/mouse models. To broaden our understanding of species-specific differences, we cloned and functionally characterized rhesus monkey TRPA1 (rhTRPA1) and compared its pharmacological profile to hTRPA1, rTRPA1, and mTRPA1 channels. The functional activities of a diverse group of TRPA1 ligands (both reactive and nonreactive) were determined in a fluorescent Ca²âº influx assay, using transiently transfected human embryonic kidney 293-F cells. 4-Methyl-N-[2,2,2-trichloro-1-(4-nitro-phenylsulfanyl)-ethyl]-benzamide, menthol, and caffeine displayed species-specific differential pharmacology at TRPA1. The pharmacological profile of the rhTRPA1 channel was found to be similar to the hTRPA1 channel. In contrast, the rTRPA1 and mTRPA1 channels closely resembled each other but were pharmacologically distinct from either hTRPA1 or rhTRPA1 channels. Our findings reveal that TRPA1 function differs between primate and rodent species and suggest that rhesus monkey could serve as a surrogate species for humans in preclinical studies.

KCNQ2/3 openers show differential selectivity and site of action across multiple KCNQ channels.

KCNQ2/3 voltage-gated potassium channels conduct low-threshold, slowly activating and non-inactivating currents to repolarize the neuronal resting membrane potential. The channels negatively regulate neuronal excitability and KCNQ2/3 openers are efficacious in hyperexcited states such as epilepsy and pain. We developed and utilized thallium influx assays to profile novel KCNQ2/3 channel openers with respect to selectivity across KCNQ subtypes and on requirement for tryptophan 236 of KCNQ2, a critical residue for activity of the KCNQ opener retigabine. Using distinct chemical series of openers, a quinazolinone series showed relatively poor selectivity across multiple KCNQ channels and lacked activity at the KCNQ2(W236L) mutant channel. In contrast, several novel benzimidazole openers showed selectivity for KCNQ2/3 and KCNQ2 and retain activity at KCNQ2(W236L). Profiling of several hundred KCNQ2/3 openers across multiple diverse chemical series revealed that openers show differential degrees of selectivity across subtypes, with selectivity most difficult to achieve against KCNQ2. In addition, we report the significant finding that KCNQ openers can pharmacologically differentiate between homomeric and heteromeric channels containing subtypes in common. Moreover, most openers assayed were dependent on the W236 for activity, whereas only a small number appear to use a distinct mechanism. Collectively, we provide novel insights into the molecular pharmacology of KCNQ channels by demonstrating differential selectivity and site of action for KCNQ2/3 openers. The high-throughput thallium influx assays should prove useful for rapid characterization of KCNQ openers and in guiding efforts to identify selective compounds for advancement towards the clinic.

Central and peripheral sites of action for CB2 receptor mediated analgesic activity in chronic inflammatory and neuropathic pain models in rats.

BACKGROUND AND PURPOSE: Cannabinoid CB2 receptor activation by selective agonists has been shown to produce analgesic effects in preclinical models of inflammatory and neuropathic pain. However, mechanisms underlying CB2-mediated analgesic effects remain largely unknown. The present study was conducted to elucidate the CB2 receptor expression in 'pain relevant' tissues and the potential sites of action of CB2 agonism in rats. EXPERIMENTAL APPROACH: Expression of cannabinoid receptor mRNA was evaluated by quantitative RT-PCR in dorsal root ganglia (DRGs), spinal cords, paws and several brain regions of sham, chronic inflammatory pain (CFA) and neuropathic pain (spinal nerve ligation, SNL) rats. The sites of CB2 mediated antinociception were evaluated in vivo following intra-DRG, intrathecal (i.t.) or intraplantar (i.paw) administration of potent CB2-selective agonists A-836339 and AM1241. KEY RESULTS: CB2 receptor gene expression was significantly up-regulated in DRGs (SNL and CFA), spinal cords (SNL) or paws (CFA) ipsilateral to injury under inflammatory and neuropathic pain conditions. Systemic A-836339 and AM1241 produced dose-dependent efficacy in both inflammatory and neuropathic pain models. Local administration of CB2 agonists also produced significant analgesic effects in SNL (intra-DRG and i.t.) and CFA (intra-DRG) pain models. In contrast to A-836339, i.paw administration of AM-1241 dose-relatedly reversed the CFA-induced thermal hyperalgesia, suggesting that different mechanisms may be contributing to its in vivo properties. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that both DRG and spinal cord are important sites contributing to CB2 receptor-mediated analgesia and that the changes in CB2 receptor expression play a crucial role for the sites of action in regulating pain perception.

Indol-3-ylcycloalkyl ketones: effects of N1 substituted indole side chain variations on CB(2) cannabinoid receptor activity.

Several 3-acylindoles with high affinity for the CB(2) cannabinoid receptor and selectivity over the CB(1) receptor have been prepared. A variety of 3-acyl substituents were investigated, and the tetramethylcyclopropyl group was found to lead to high affinity CB(2) agonists (5, 16). Substitution at the N1-indole position was then examined. A series of aminoalkylindoles was prepared and several substituted aminoethyl derivatives were active (23-27, 5) at the CB(2) receptor. A study of N1 nonaromatic side chain variants provided potent agonists at the CB(2) receptor (16, 35-41, 44-47, 49-54, and 57-58). Several polar side chains (alcohols, oxazolidinone) were well-tolerated for CB(2) receptor activity (41, 50), while others (amide, acid) led to weaker or inactive compounds (55 and 56). N1 aromatic side chains also afforded several high affinity CB(2) receptor agonists (61, 63, 65, and 69) but were generally less potent in an in vitro CB(2) functional assay than were nonaromatic side chain analogues.

Characterization of human cannabinoid CB2 receptor coupled to chimeric Galpha(qi5) and Galpha(qo5) proteins.

Cannabinoid CB(2) receptors may couple to a variety of G proteins and intracellular effector systems to regulate physiological and pathophysiological processes involved in inflammatory and neuropathic pain. In this study, the coupling of cannabinoid hCB(2) receptors to Galpha(qo5) and Galpha(qi5) proteins was studied and compared by investigating the pharmacological properties of HEK-293 cells co-expressing cannabinoid hCB(2) with chimeric Galpha(qo5) (HEK-hCB(2)-G(qo5)) or Galpha(qi5) (HEK-hCB(2)-G(qi5)). Both cell lines were found to be amendable for measuring cannabinoid CB(2) receptor agonist evoked Ca(2+) mobilization in a high-throughput manner. Comparison of binding affinities of ligands in homogenates prepared from both cell lines revealed similar affinities for [(3)H]CP55,940 displacement with the following rank order: CP55,940 approximately WIN55,212-2 > SR144528 > JWH015approximatelyAM1241approximately AM630 > SR141617A approximately AM251. In comparison at cannabinoid hCB(1) receptors: the rank order was: SR141617A approximately CP55,940 > AM251 > WIN55,212-2 > AM1241approximatelySR144528 > JWH015approximatelyAM630. No significant differences in cannabinoid receptor agonist (CP55,940 approximately WIN55,212-2 > JWH015) or antagonist(SR144528 approximately AM1241 > AM630 > AM251 approximately SR141617A) profiles were observed in HEK-hCB(2)-G(qo5) and HEK-hCB(2)-G(qi5) cells as determined using intracellular Ca(2+) measurements. Experiments with HEK-hCB(2)-G(qi5) cells carried out by investigating interactions among CP55,940, carbachol, thapsigargin, and U73122 revealed that the mechanism of cannabinoid hCB(2) receptor coupling via chimeric G proteins to Ca(2+) mobilization involves phospholipase C-inositol trisphosphate (PLC-IP(3)) and that it is less efficient in comparison to the endogenous muscarinic mediated PLC-IP(3)-Ca(2+) pathway. This study demonstrates that expressed cannabinoid CB(2) receptors couple equally well to Galpha(qo5) and Galpha(qi5) proteins and that receptor agonist or antagonist pharmacology is not influenced by the nature of these coupled G proteins when heterologously expressed.

Characterization of a cannabinoid CB2 receptor-selective agonist, A-836339 [2,2,3,3-tetramethyl-cyclopropanecarboxylic acid [3-(2-methoxy-ethyl)-4,5-dimethyl-3H-thiazol-(2Z)-ylidene]-amide], using in vitro pharmacological assays, in vivo pain models, and pharmacological magnetic resonance imaging.

Studies demonstrating the antihyperalgesic and antiallodynic effects of cannabinoid CB(2) receptor activation have been largely derived from the use of receptor-selective ligands. Here, we report the identification of A-836339 [2,2,3,3-tetramethyl-cyclopropanecarboxylic acid [3-(2-methoxy-ethyl)-4,5-dimethyl-3H-thiazol-(2Z)-ylidene]-amide], a potent and selective CB(2) agonist as characterized in in vitro pharmacological assays and in in vivo models of pain and central nervous system (CNS) behavior models. In radioligand binding assays, A-836339 displays high affinities at CB(2) receptors and selectivity over CB(1) receptors in both human and rat. Likewise, A-836339 exhibits high potencies at CB(2) and selectivity over CB(1) receptors in recombinant fluorescence imaging plate reader and cyclase functional assays. In addition A-836339 exhibits a profile devoid of significant affinity at other G-protein-coupled receptors and ion channels. A-836339 was characterized extensively in various animal pain models. In the complete Freund's adjuvant model of inflammatory pain, A-836339 exhibits a potent CB(2) receptor-mediated antihyperalgesic effect that is independent of CB(1) or mu-opioid receptors. A-836339 has also demonstrated efficacies in the chronic constrain injury (CCI) model of neuropathic pain, skin incision, and capsaicin-induced secondary mechanical hyperalgesia models. Furthermore, no tolerance was developed in the CCI model after subchronic treatment with A-836339 for 5 days. In assessing CNS effects, A-836339 exhibited a CB(1) receptor-mediated decrease of spontaneous locomotor activities at a higher dose, a finding consistent with the CNS activation pattern observed by pharmacological magnetic resonance imaging. These data demonstrate that A-836339 is a useful tool for use of studying CB(2) receptor pharmacology and for investigation of the role of CB(2) receptor modulation for treatment of pain in preclinical animal models.

Cloning and characterization of the monkey histamine H3 receptor isoforms.

We have recently identified three splice isoforms of the histamine H(3) receptor in multiple brain regions of cynomolgus monkey (Macaca fascicularis). Two of the novel isoforms displayed a deletion in the third intracellular loop (H(3)(413) and H(3)(410)), the third isoform H(3)(335) displayed a deletion in the i3 intracellular loop and a complete deletion of the putative fifth transmembrane domain TM5. We have confirmed by RT-PCR the expression of full-length H(3)(445) mRNA as well as H(3)(413), H(3)(410), and H(3)(335) splice isoform mRNA in multiple monkey brain regions including the frontal, parietal and occipital cortex, parahippocampal gyrus, hippocampus, amygdala, caudate nucleus, putamen, thalamus, hypothalamus, and cerebellum. The full-length isoform H(3)(445) was predominant in all of the regions tested, followed by H(3)(335), with the H(3)(413) and H(3)(410) being of low abundance. When expressed in C6 cells, H(3)(445), H(3)(413), and H(3)(410) exhibit high affinity binding to the agonist ligand [(3)H]-(N)-alpha-methylhistamine with respective pK(D) values of 9.7, 9.7, and 9.6. As expected, the H(3)(335) isoform did not display any saturable binding with [(3)H]-(N)-alpha-methylhistamine. The histamine H(3) receptor agonists histamine, (R)-alpha-methylhistamine, imetit and proxyfan were able to activate calcium mobilization responses through H(3)(445), H(3)(413) and H(3)(410) receptors when they were co-expressed with the chimeric G alpha(qi5)-protein in HEK293 cells, while no response was elicited in cells expressing the H(3)(335) isoform. The existence of multiple H(3) receptor splice isoforms across species raises the possibility that isoform specific properties including ligand affinity, signal transduction coupling, and brain localization may differentially contribute to observed in vivo effects of histamine H(3) receptor antagonists.

Indol-3-yl-tetramethylcyclopropyl ketones: effects of indole ring substitution on CB2 cannabinoid receptor activity.

A series of potent indol-3-yl-tetramethylcyclopropyl ketones have been prepared as CB 2 cannabinoid receptor ligands. Two unsubstituted indoles ( 5, 32) were the starting points for an investigation of the effect of indole ring substitutions on CB 2 and CB 1 binding affinities and activity in a CB 2 in vitro functional assay. Indole ring substitutions had varying effects on CB 2 and CB 1 binding, but were generally detrimental to agonist activity. Substitution on the indole ring did lead to improved CB 2/CB 1 binding selectivity in some cases (i.e., 7- 9, 15- 20). All indoles with the morpholino-ethyl side chain ( 32- 43) exhibited weaker binding affinity and less agonist activity relative to that of their tetrahydropyranyl-methyl analogs ( 5- 31). Several agonists were active in the complete Freund's adjuvant model of chronic inflammatory thermal hyperalgesia ( 32, 15).

Evidence for tolerance following repeated dosing in rats with ciproxifan, but not with A-304121.

Blockade of presynaptic histamine H(3) receptors with potent and selective ligands improves cognitive function in rodents and there is significant interest in developing such drugs for long-term symptomatic treatment of CNS disorders such as attention deficit hyperactivity disorder (ADHD). Unfortunately, little is known about the effects of repeated exposure to H(3) receptor antagonists/inverse agonists. We therefore investigated the effects of acute and repeated daily administration of two potent, brain penetrating H(3) receptor antagonists/inverse agonists, ciproxifan and A-304121, on rat body weight, food and water intake, core temperature and locomotor activity, as well as H(3) receptor density and gene expression levels. Methylphenidate, used clinically for the treatment of ADHD, was included as an additional comparator. Ciproxifan, an imidazole-based compound, decreased food intake over the first 10 days and locomotor activity acutely, but these effects were lost after further repeated administration. The ex vivo binding studies revealed increased H(3) receptor density in rats following repeated administration of ciproxifan for 10 or 15 days; however, H(3) receptor gene expression was not changed. In contrast, rats treated with the non-imidazole, A-304121, did not differ from controls on any measure during the observation period, while rats treated with methylphenidate exhibited hyperthermia and hyperactivity. The implications for potential long-term treatment with H(3) receptor antagonists in CNS disorders such as ADHD are discussed.

Pharmacological properties of ABT-239 [4-(2-{2-[(2R)-2-Methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile]: II. Neurophysiological characterization and broad preclinical efficacy in cognition and schizophrenia of a potent and selective histamine H3 receptor antagonist.

Acute pharmacological blockade of central histamine H3 receptors (H3Rs) enhances arousal/attention in rodents. However, there is little information available for other behavioral domains or for repeated administration using selective compounds. ABT-239 [4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile] exemplifies such a selective, nonimidazole H3R antagonist with high affinity for rat (pK(i) = 8.9) and human (pK(i) = 9.5) H3Rs. Acute functional blockade of central H3Rs was demonstrated by blocking the dipsogenia response to the selective H3R agonist (R)-alpha-methylhistamine in mice. In cognition studies, acquisition of a five-trial, inhibitory avoidance test in rat pups was improved with ABT-239 (0.1-1.0 mg/kg), a 10- to 150-fold gain in potency, with similar efficacy, over previous antagonists such as thioperamide, ciproxifan, A-304121 [(4-(3-(4-((2R)-2-aminopropanoyl)-1-piperazinyl)propoxy)phenyl)(cyclopropyl) methanone], A-317920 [N-((1R)-2-(4-(3-(4-(cyclopropylcarbonyl) phenoxy)propyl)-1-piperazinyl)-1-methyl-2-oxoethyl)-2-furamide], and A-349821 [(4'-(3-((R,R)2,5-dimethyl-pyrrolidin-1-yl)-propoxy)-biphenyl-4-yl)-morpholin-4-yl-methanone]. Efficacy in this model was maintained for 3 to 6 h and following repeated dosing with ABT-239. Social memory was also improved in adult (0.01-0.3 mg/kg) and aged (0.3-1.0 mg/kg) rats. In schizophrenia models, ABT-239 improved gating deficits in DBA/2 mice using prepulse inhibition of startle (1.0-3.0 mg/kg) and N40 (1.0-10.0 mg/kg). Furthermore, ABT-239 (1.0 mg/kg) attenuated methamphetamine-induced hyperactivity in mice. In freely moving rat microdialysis studies, ABT-239 enhanced acetylcholine release (0.1-3.0 mg/kg) in adult rat frontal cortex and hippocampus and enhanced dopamine release in frontal cortex (3.0 mg/kg), but not striatum. In summary, broad efficacy was observed with ABT-239 across animal models such that potential clinical efficacy may extend beyond disorders such as ADHD to include Alzheimer's disease and schizophrenia.

Pharmacological properties of ABT-239 [4-(2-{2-[(2R)-2-Methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile]: I. Potent and selective histamine H3 receptor antagonist with drug-like properties.

Histamine H3 receptor antagonists are being developed to treat a variety of neurological and cognitive disorders that may be ameliorated by enhancement of central neurotransmitter release. Here, we present the in vitro pharmacological and in vivo pharmacokinetic profiles for the nonimidazole, benzofuran ligand ABT-239 [4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile] and compare it with several previously described imidazole and nonimidazole H3 receptor antagonists. ABT-239 binds to recombinant human and rat H3 receptors with high affinity, with pK(i) values of 9.4 and 8.9, respectively, and is over 1000-fold selective versus human H1, H2, and H4 histamine receptors. ABT-239 is a potent H3 receptor antagonist at recombinant human and rat receptors, reversing agonist-induced changes in cAMP formation (pK(b) = 7.9 and 7.6, respectively), guanosine 5'-O-(3-[35S]thio) triphosphate ([35S]GTPgammaS) binding (pK(b) = 9.0 and 8.3, respectively), and calcium mobilization (human pK(b) = 7.9). ABT-239 also competitively reversed histamine-mediated inhibition of [3H]histamine release from rat brain cortical synaptosomes (pK(b) = 7.7) and agonist-induced inhibition of contractile responses in electric field stimulated guinea pig ileal segments (pA2 = 8.7). Additionally, ABT-239 is a potent inverse agonist, inhibiting constitutive [35S]GTPgammaS binding at both rat and human H3 receptors with respective pEC50 values of 8.9 and 8.2. ABT-239 demonstrates good pharmacokinetic characteristics in rat, dog, and monkey with t1/2 values ranging from 4 to 29 h, corresponding with clearance values and metabolic turnover in liver microsomes from these species, and good oral bioavailability ranging from 52 to 89%. Thus, ABT-239 is a selective, nonimidazole H3 receptor antagonist/inverse agonist with similar high potency in both human and rat and favorable drug-like properties.

Pharmacological and behavioral properties of A-349821, a selective and potent human histamine H3 receptor antagonist.

Histamine H3 receptors regulate the release of a variety of central neurotransmitters involved in cognitive processes. A-349821 ((4'-(3-((R,R)2,5-dimethyl-pyrrolidin-1-yl)-propoxy)-biphenyl-4-yl)-morpholin-4-yl-methanone) is a novel, non-imidazole H3 receptor ligand, displaying high affinity for recombinant rat and human H3 receptors, with pKi values of 9.4 and 8.8, respectively, and high selectivity for the H3 receptor versus H1, H2, and H4 histamine receptors. A-349821 is a potent H3 receptor antagonist in a variety of models using recombinant human and rat receptors, reversing agonist induced changes in cyclic AMP formation (pKb= 8.2 and pKb= 8.1, respectively), [35S]-GTPgammaS binding (pKb= 9.3 and pKb= 8.6, respectively) and calcium levels (human pKb= 8.3). In native systems, A-349821 competitively reversed agonist induced inhibition of electric field stimulated guinea-pig ileum (pA2= 9.5) and histamine-mediated inhibition of [3H]-histamine release from rat brain cortical synaptosomes (pKb= 9.2). Additionally, A-349821 inhibited constitutive GTPgammaS binding at both rat and human H3 receptors with respective pEC50 values of 9.1 and 8.6, demonstrating potent inverse agonist properties. In behavioral studies, A-349821 (0.4 mg/kg-4 mg/kg) potently blocked (R)-alpha-methylhistamine-induced dipsogenia in mice. The compound also enhanced cognitive activity in a five-trial inhibitory avoidance model in spontaneously hypertensive rat (SHR) pups at doses of 1-10mg/kg, with the 1mg/kg dose showing comparable efficacy to a fully efficacious dose of ciproxifan (3mg/kg). These doses of A-349821 were without effect on spontaneous locomotor activity. Thus, A-349821 is a novel, selective non-imidazole H3 antagonist/inverse agonist with balanced high potency across species and favorable cognition enhancing effects in rats.

Antiobesity effects of A-331440, a novel non-imidazole histamine H3 receptor antagonist.

Histamine affects homeostatic mechanisms, including food and water consumption, by acting on central nervous system (CNS) receptors. Presynaptic histamine H(3) receptors regulate release of histamine and other neurotransmitters, and histamine H(3) receptor antagonists enhance neurotransmitter release. A-331440 [4'-[3-(3(R)-(dimethylamino)-pyrrolidin-1-yl)-propoxy]-biphenyl-4-carbonitrile] is a histamine H(3) receptor antagonist which binds potently and selectively to both human and rat histamine H(3) receptors (K(i)<==25 nM). Mice were stabilized on a high-fat diet (45 kcal % lard) prior to 28-day oral b.i.d. dosing for measurement of obesity-related parameters. A-331440 administered at 0.5 mg/kg had no significant effect on weight, whereas 5 mg/kg decreased weight comparably to dexfenfluramine (10 mg/kg). A-331440 administered at 15 mg/kg reduced weight to a level comparable to mice on the low-fat diet. The two higher doses reduced body fat and the highest dose also normalized an insulin tolerance test. These data show that the histamine H(3) receptor antagonist, A-331440, has potential as an antiobesity agent.