thioperamide and benzonitrile--4-(2-(2-((2r)-2-methyl-1-pyrrolidinyl)ethyl)-5-benzofuranyl)-

H(3) receptor antagonists based on a 2-aminoethylbenzofuran skeleton have been discovered, which are potent in vitro at human and rat H(3) receptors, with K(i) values of 0.1-5.8 nM. Analogues were discovered with potent (0.01-1 mg/kg) cognition and attention enhancing properties in animal models. One compound in particular, 4-(2-[2-(2(R)-methylpyrrolidin-1-yl)ethyl]benzofuran-5-yl)benzonitrile (ABT-239), combined potent and selective H(3) receptor antagonism and excellent pharmacokinetic and metabolic properties across species, with full efficacy in two behavioral models: a five-trial inhibitory avoidance acquisition model in rat pups at 0.1 mg/kg and a social recognition memory model in adult rats at 0.01 mg/kg. Furthermore, this compound did not stimulate locomotor activity and showed high selectivity for the induction of behavioral efficacy versus central nervous system based side effects. The potency and selectivity of this compound and of analogues from this class support the potential of H(3) receptor antagonists for the treatment of cognitive dysfunction.

Topics: Administration, Oral; Animals; Attention; Avoidance Learning; Behavior, Animal; Benzofurans; Biological Availability; Blood Proteins; Central Nervous System; Central Nervous System Agents; Cognition; Cytochrome P-450 Enzyme System; Dogs; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Haplorhini; Histamine Antagonists; Humans; Memory; Pyrrolidines; Rats; Receptors, Histamine H3; Social Behavior; Structure-Activity Relationship

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.

Topics: Animals; Antipsychotic Agents; Benzofurans; Brain Chemistry; Cataplexy; Cytochrome P-450 Enzyme System; Drug Combinations; Drug Synergism; Haloperidol; Histamine; Histamine Antagonists; Imidazoles; Ketoconazole; Male; Metabolic Clearance Rate; Piperidines; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Histamine H3; Risperidone; Schizophrenia