Marlon D. Cowart

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 (pKi = 8.9) and human (pKi = 9.5) H3Rs. Acute functional blockade of central H3 Rs was demonstrated by blocking the dipsogenia response to the selective H3R agonist (R)-α-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 Alzheimers disease and schizophrenia.

Pharmacological Properties of ABT-239: 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 (pKi = 8.9) and human (pKi = 9.5) H3Rs. Acute functional blockade of central H3 Rs was demonstrated by blocking the dipsogenia response to the selective H3R agonist (R)-α-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 Alzheimers disease and schizophrenia.

Discovery of Histamine H3 Antagonists for the Treatment of Cognitive Disorders and Alzheimer's Disease

H3 antagonists increase the release of brain histamine, acetylcholine, noradrenaline, and dopamine, neurotransmitters that are known to modulate cognitive processes. The ability to release brain histamine supports the effect on attention and vigilance, but histamine also modulates other cognitive domains such as short-term and long-term memory. A number of H3 antagonists, including 1-{3-[3-(4-chlorophenyl)propoxy]propyl}piperidine hydrochloride (BF2.649), (1R,3R)-N-ethyl-3-fluoro-3-[3-fluoro-4-(pyrrolidin-1-ylmethyl)phenyl]cyclobutane-1-carboxamide (PF-03654746), 6-[(3-cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-yl)oxy]-N-methyl-3-pyridinecarboxamide hydrochloride (GSK189254), MK-0249 (structure not yet disclosed), JNJ-17216498 (structure not yet disclosed), and ABT-288 (structure not yet disclosed), have advanced to the clinical area for the potential treatment of human cognitive disorders. H3 antagonists exhibited wake-promoting effects in humans and efficacy in narcoleptic patients, indicating target engagement, but some of them were not efficacious in patients suffering from attention-deficit hyperactivity disorder and schizophrenic patients. Preclinical studies have also shown that H3 antagonists activate intracellular signaling pathways that may improve cognitive efficacy and disease-modifying effects in Alzheimers disease. Ongoing clinical studies will be able to determine the utility of H3 antagonists for the treatment of cognitive disorders in humans.

Rotationally constrained 2,4-diamino-5,6-disubstituted pyrimidines: a new class of histamine H4 receptor antagonists with improved druglikeness and in vivo efficacy in pain and inflammation models.

A new structural class of histamine H 4 receptor antagonists (6-14) was designed based on rotationally restricted 2,4-diaminopyrimidines. Series compounds showed potent and selective in vitro H 4 antagonism across multiple species, good CNS penetration, improved PK properties compared to reference H 4 antagonists, functional H 4 antagonism in cellular and in vivo pharmacological assays, and in vivo anti-inflammatory and antinociceptive efficacy. One compound, 10 (A-943931), combined the best features of the series in a single molecule and is an excellent tool compound to probe H 4 pharmacology. It is a potent H 4 antagonist in functional assays across species (FLIPR Ca (2+) flux, K b < 5.7 nM), has high (>190x) selectivity for H 4, and combines good PK in rats and mice (t 1/2 of 2.6 and 1.6 h, oral bioavailability of 37% and 90%) with anti-inflammatory activity (ED 50 = 37 micromol/kg, mouse) and efficacy in pain models (thermal hyperalgesia, ED 50 = 72 micromol/kg, rat).

H4 receptor antagonism exhibits anti-nociceptive effects in inflammatory and neuropathic pain models in rats

The histamine H(4) receptor (H(4)R) is expressed primarily on cells involved in inflammation and immune responses. To determine the potential role of H(4)R in pain transmission, the effects of JNJ7777120, a potent and selective H(4) antagonist, were characterized in preclinical pain models. Administration of JNJ7777120 fully blocked neutrophil influx observed in a mouse zymosan-induced peritonitis model (ED(50)=17 mg/kg s.c., 95% CI=8.5-26) in a mast cell-dependent manner. JNJ7777120 potently reversed thermal hyperalgesia observed following intraplantar carrageenan injection of acute inflammatory pain (ED(50)=22 mg/kg i.p., 95% CI=10-35) in rats and significantly decreased the myeloperoxide activity in the carrageenan-injected paw. In contrast, no effects were produced by either H(1)R antagonist diphenhydramine, H(2)R antagonists ranitidine, or H(3)R antagonist ABT-239. JNJ7777120 also exhibited robust anti-nociceptive activity in persistent inflammatory (CFA) pain with an ED(50) of 29 mg/kg i.p. (95% CI=19-40) and effectively reversed monoiodoacetate (MIA)-induced osteoarthritic joint pain. This compound also produced dose-dependent anti-allodynic effects in the spinal nerve ligation (ED(50)=60 mg/kg) and sciatic nerve constriction injury (ED(50)=88 mg/kg) models of chronic neuropathic pain, as well as in a skin-incision model of acute post-operative pain (ED(50)=68 mg/kg). In addition, the analgesic effects of JNJ7777120 were maintained following repeated administration and were evident at the doses that did not cause neurologic deficits in rotarod test. Our results demonstrate that selective blockade of H(4) receptors in vivo produces significant anti-nociception in animal models of inflammatory and neuropathic pain.

Structure−Activity Studies on a Series of a 2-Aminopyrimidine-Containing Histamine H4 Receptor Ligands

A series of 2-aminopyrimidines was synthesized as ligands of the histamine H4 receptor (H4R). Working in part from a pyrimidine hit that was identified in an HTS campaign, SAR studies were carried out to optimize the potency, which led to compound 3, 4- tert-butyl-6-(4-methylpiperazin-1-yl)pyrimidin-2-ylamine. We further studied this compound by systematically modifying the core pyrimidine moiety, the methylpiperazine at position 4, the NH2 at position 2, and positions 5 and 6 of the pyrimidine ring. The pyrimidine 6 position benefited the most from this optimization, especially in analogs in which the 6- tert-butyl was replaced with aromatic and secondary amine moieties. The highlight of the optimization campaign was compound 4, 4-[2-amino-6-(4-methylpiperazin-1-yl)pyrimidin-4-yl]benzonitrile, which was potent in vitro and was active as an anti-inflammatory agent in an animal model and had antinociceptive activity in a pain model, which supports the potential of H 4R antagonists in pain.

cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine (A-987306), A New Histamine H4R Antagonist that Blocks Pain Responses against Carrageenan-Induced Hyperalgesia

cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine, 4 (A-987306) is a new histamine H(4) antagonist. The compound is potent in H(4) receptor binding assays (rat H(4), K(i) = 3.4 nM, human H(4) K(i) = 5.8 nM) and demonstrated potent functional antagonism in vitro at human, rat, and mouse H(4) receptors in cell-based FLIPR assays. Compound 4 also demonstrated H(4) antagonism in vivo in mice, blocking H(4)-agonist induced scratch responses, and showed anti-inflammatory activity in mice in a peritonitis model. Most interesting was the high potency and efficacy of this compound in blocking pain responses, where it showed an ED(50) of 42 mumol/kg (ip) in a rat post-carrageenan thermal hyperalgesia model of inflammatory pain.

Lack of cataleptogenic potentiation with non-imidazole H3 receptor antagonists reveals potential drug-drug interactions between imidazole-based H3 receptor antagonists and antipsychotic drugs.

Since H3 receptor (H3R) antagonists/inverse agonists can improve cognitive function in animal models, they may have the potential to be used as add-on therapy in the treatment of schizophrenia, a disease with significant cognitive deficits. However, a recent study showed potentiation of haloperidol-induced catalepsy by ciproxifan, an imidazole-containing H3R antagonist/inverse agonist, suggesting there is a potential risk of exacerbating extrapyramidal symptoms (EPS) if H3R antagonists were used as adjunctive treatment [Pillot, C., Ortiz, J., Heron, A., Ridray, S., Schwartz, J.C. and Arrang, J.M., Ciproxifan, a histamine H3-receptor antagonist/inverse agonist, potentiates neurochemical and behavioral effects of haloperidol in the rat, J Neurosci, 22 (2002) 7272-80]. In order to clarify the basis of this finding, we replicated this result and extended the work with another imidazole and two non-imidazole H3R antagonists. The results indicate that ciproxifan significantly augmented the effects of haloperidol and risperidone on catalepsy. Another imidazole H3R antagonist, thioperamide, also potentiated the effect of risperidone on catalepsy. In contrast, no catalepsy-enhancing effects were observed when selective non-imidazole H3R antagonists, ABT-239 and A-431404, were coadministered with haloperidol and/or risperidone. As ciproxifan and thioperamide are inhibitors of cytochrome P450 enzymes, responsible for metabolizing risperidone and haloperidol, the possibility that the augmentation of antipsychotics by imidazoles resulted from drug-drug interactions was tested. A drug metabolism study revealed that an imidazole, but not a non-imidazole, potently inhibited the metabolism of haloperidol and risperidone. Furthermore, ketoconazole, an imidazole-based CYP 3A4 inhibitor, significantly augmented risperidone-induced catalepsy. Together, these data suggest the potentiation of antipsychotic-induced catalepsy may result from pharmacokinetic drug-drug interactions and support the potential utility of non-imidazole H3R antagonists in treatment of cognitive impairment in schizophrenia without increased risk of increased EPS in patients.

Analgesic and anti-inflammatory effects of A-286501, a novel orally active adenosine kinase inhibitor

&NA; Adenosine (ADO) is an inhibitory neuromodulator that can increase nociceptive thresholds in response to noxious stimulation. Inhibition of the ADO‐metabolizing enzyme, adenosine kinase (AK) increases extracellular ADO concentrations at sites of tissue trauma and AK inhibitors may have therapeutic potential as analgesic and anti‐inflammatory agents. N7‐((1′R,2′S,3′R,4′S)‐2′,3′‐dihydroxy‐4′‐amino‐cyclopentyl)‐4‐amino‐5‐bromo‐pyrrolo[2,3‐a]pyrimidine (A‐286501) is a novel and potent (IC50=0.47 nM) carbocyclic nucleoside AK inhibitor that has no significant activity (IC50>100 &mgr;M) at other sites of ADO interaction (A1, A2A, A3 receptors, ADO transporter, and ADO deaminase) or other (IC50 values>10 &mgr;M) neurotransmitter and peptide receptors, ion channel proteins, neurotransmitter reuptake sites and enzymes, including cyclooxygenases‐1 and ‐2. A‐286501 showed equivalent potency to inhibit AK from several mammalian species and kinetic studies revealed that A‐286501 was a reversible and competitive inhibitor with respect to ADO and non‐competitive with respect to MgATP2−. A‐286501 was orally effective to reduce nociception in animal models of acute (thermal), inflammatory (formalin and carrageenan), and neuropathic (L5/L6 nerve ligation and streptozotocin‐induced diabetic) pain. A‐286501 was particularly potent (ED50=1 &mgr;mol/kg, p.o.) to reduce carrageenan‐induced inflammatory thermal hyperalgesia as compared to its analgesic actions in other pain models (acute and neuropathic) and its ability to alter hemodynamic function and motor performance. A‐286501 was also effective to reduce carrageenan‐induced paw edema and myeloperoxidase activity, a measure of neutrophil influx (ED50=10 &mgr;mol/kg, p.o.), in the injured paw. The anti‐nociceptive effects of A‐286501 in the L5/L6 nerve injury model of neuropathic pain (ED50=20 &mgr;mol/kg, p.o.) were not blocked by the opioid antagonist naloxone, but were blocked by the ADO receptor antagonist, theophylline. Following repeated administration, A‐286501 showed less potential to produce tolerance as compared to morphine. Thus, A‐286501 is a structurally novel AK inhibitor that effectively attenuates nociception by a non‐opioid, non‐non‐steroidal anti‐inflammatory drug ADO, receptor mediated mechanism.

An 80-Amino Acid Deletion in the Third Intracellular Loop of a Naturally Occurring Human Histamine H3 Isoform Confers Pharmacological Differences and Constitutive Activity

In this article, we pharmacologically characterized two naturally occurring human histamine H3 receptor (hH3R) isoforms, hH3R(445) and hH3R(365). These abundantly expressed splice variants differ by a deletion of 80 amino acids in the intracellular loop 3. In this report, we show that the hH3R(365) is differentially expressed compared with the hH3R(445) and has a higher affinity and potency for H3R agonists and conversely a lower potency and affinity for H3R inverse agonists. Furthermore, we show a higher constitutive signaling of the hH3R(365) compared with the hH3R(445) in both guanosine-5′-O-(3-[35S]thio) triphosphate binding and cAMP assays, likely explaining the observed differences in hH3R pharmacology of the two isoforms. Because H3R ligands are beneficial in animal models of obesity, epilepsy, and cognitive diseases such as Alzheimers disease and attention deficit hyperactivity disorder and currently entered clinical trails, these differences in H3R pharmacology of these two isoforms are of great importance for a detailed understanding of the action of H3R ligands.