Based on a medicinal-chemistry-guided approach, three novel series of druglike cycloalkyl-annelated pyrazoles were synthesized and display high affinity (pKi>8) for the sigma1 receptor. Structure-affinity relationships were established, and the different scaffolds were optimized with respect to sigma1 binding and selectivity versus the sigma2 receptor and the hERG channel, resulting in selective compounds that have Ki values (for sigma1) in the subnanomolar range. Selected compounds were screened for cytochrome P450 inhibition (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4), metabolic stability (rat and human liver microsomes), and cell-membrane permeability (Caco-2). They showed favorable in vitro ADME properties as well as favorable calculated druglike and experimental physicochemical properties. Furthermore, compounds 7 f and 17 a, for example, displayed high selectivity (affinity) for the sigma1 receptor against a wide range of other receptors (>60). With these valuable tool compounds in hand, we are further exploring the role of the sigma1 receptor in relevant animal models corresponding to such medicinal indications as drug abuse, pain, depression, anxiety, and psychosis.

Changes in the expression of brain-derived neurotrophic factor (BDNF) have been implicated in some neuropsychiatric disorders. Several antipsychotic drugs affect the expression of BDNF mRNA in different areas of the rat brain. We examined the effect of single or repeated administration of 4-[4-fluorophenyl]-1,2,3,6-tetra-hydo-1-[4-[1,-2,4-triazol-1-il]butyl]pyridine citrate) (E-5842), a sigma1 receptor ligand and putative atypical antipsychotic drug on the expression of BDNF mRNA in rats. Acute treatment with E-5842 induced a down-regulation of BDNF mRNA levels in the frontal cortex and hippocampus, while a chronic treatment had no effect. Levels of another neurotrophin, nerve growth factor (NGF), remained unaltered after either acute or chronic treatment. The effects suggest that any therapeutic properties of E-5842 are not mediated by stimulation of BDNF or NGF, whereas the regulation of these trophic factors may be part of the mechanism of action of sigma1 receptor ligands.

Fibroblast growth factor-2 (FGF-2) is a member of a large family of trophic factors whose expression is regulated under several conditions in different areas of the brain. The goal of our experiments was to determine whether the administration of 4-(4-fluorophenyl)-1,2,3,6-tetrahydro-1-[4-(1,2,4-triazol-1-il)butyl] pyridine citrate (E-5842), a sigma-1 receptor ligand and putative atypical antipsychotic, could regulate the expression of FGF-2. After chronic treatment with E-5842 (21 days, and the animals killed 24 h after the last administration), an up-regulation was observed of the expression of FGF-2 mRNA in the prefrontal cortex and the striatum, and a down-regulation of the expression of FGF-2 mRNA in the hypothalamus of the rat brain. Acute treatment with E-5842 (one single administration and animals killed 6 h later) up-regulated FGF-2 expression in the prefrontal cortex, the striatum, the hypothalamus and the hippocampus in a dose-dependent manner. The acute up-regulation was transient and disappeared 24 h after E-5842 administration. The induction of FGF-2 in the striatum after repeated administration has been described for clozapine, but our data concerning regulation in the prefrontal cortex suggest that this effect is unique to E-5852 among other antipsychotics. Given the neuroprotective activity of FGF-2, the data presented here might be relevant to the deficit in cognition and other symptoms that appear in schizophrenia.

Sigma(1) (sigma(1)) receptor mRNA expression was studied in the prefrontal cortex, striatum, hippocampus and cerebellum of rat brain by northern blot and in situ hybridization. The effects of a chronic treatment with antipsychotic drugs (haloperidol and clozapine), and with E-5842, a sigma(1) receptor ligand and putative atypical antipsychotic on sigma(1) receptor expression were examined. A significant increase in the levels of sigma(1) receptor mRNA in the prefrontal cortex and striatum after E-5842 administration was observed, while no apparent changes were seen with either haloperidol or clozapine. Our results suggest a long-term adaptation of the sigma(1) receptor at the level of mRNA expression in specific areas of the brain as a response to a sustained treatment with E-5842.

Cizolirtine citrate (E-4018) is a new analgesic agent with antinociceptive activity against phenylquinone (ED50 33.7 mg/kg) and acetic acid (ED50 24.4 mg/kg) in mice, against acetic acid in rats (ED50 21.3 mg/kg) and in the plantar test (ED50 26.8 mg/kg). It demonstrated antinociceptive activity in the tail-pinch and tail-flick tests (ED50s of 68.0 and 46.0 mg/kg, respectively), in both phases of the formalin test (ED50 13.8 and 2.31 mg/kg), and in the capsaicin test (ED50 7.14 mg/kg). Cizolirtine does not inhibit prostaglandin biosynthesis, it is not a ligand for opioid receptors, it does not have antiinflammatory or ulcerogenic activity, it has some antipyretic activity and shows no affinity for alpha 2-adrenergic receptors, but its analgesic effect was modified by idazoxan and by desipramine. Recent studies have shown that the analgesic effect of cizolirtine could be related, at least partially, to an inhibition of spinal substance P release.

The effect of chronic administration of the putative atypical antipsychotic E-5842, a preferential sigma(1) receptor ligand, on ionotropic glutamate receptor subunit levels of mRNA and protein, was studied. The repeated administration of E-5842 differentially regulated levels of the NMDA-2A and of GluR2 subunits in a regionally specific way. Levels of immunoreactivity for the NMDA-2A subunit were up-regulated in the medial prefrontal cortex, the frontoparietal cortex, the cingulate cortex, and in the dorsal striatum, while they were down-regulated in the nucleus accumbens. Levels of the GluR2 subunit of the AMPA receptor were up-regulated in the medial prefrontal cortex and the nucleus accumbens and down-regulation was observed in the dorso-lateral striatum. Regulation of the levels of mRNA for the different subunits was also observed in some cases. The results show that E-5842, through a mechanism still unknown, is able to modify levels of several glutamate receptor subunits and these changes could be related to its antipsychotic activity in pre-clinical tests.