The effect of N-methylation on fenfluramine's neurotoxic and pharmacologic actions

Synthesis and Structure-Activity Relationships of Imidazole-Coumarin Conjugates against Hepatitis C Virus

A series of new conjugated compounds with a -SCH₂- linkage were synthesized by chemical methods from imidazole and coumarin derivatives. The experimental results indicate that of the twenty newly synthesized imidazole-coumarin conjugates, three of them exhibited appealing EC50 values (5.1-8.4 μM) and selective indices >20 against hepatitis C virus. Their potency and selectivity were increased substantially by modification of their structure with two factors: imidazole nucleus with a hydrogen atom at the N(1) position and coumarin nucleus with a substituent, such as Cl, F, Br, Me, and OMe. These guidelines provide valuable information for further development of conjugated compounds as anti-viral agents.

Cyproheptadine resembles clozapine in vivo following both acute and chronic administration in rats

Cyproheptadine is a cheap, widely available anti-allergy drug with a broad receptor binding profile which resembles that of clozapine. In rats discriminating clozapine from vehicle cyproheptadine mimicked clozapine very closely. Acutely it induced full generalization in the absence of response suppression, as observed with clozapine. Chronic administration of clozapine and cyproheptadine induced tolerance and cross-tolerance respectively to the clozapine stimulus. This was characterized by circa 3.5-fold parallel shifts to the right in the clozapine generalization curves. Such tolerance and cross-tolerance was spontaneously reversible, suggesting that it was pharmacodynamic, and that clozapine and cyproheptadine induce similar neuroadaptations when administered chronically. Administration of chlordiazepoxide at a very high dose induced no cross-tolerance to the clozapine stimulus showing the pharmacological specificity of tolerance. The clozapine stimulus is a compound cue involving actions at various receptors, and various clozapine-like antipsychotic (APD) drugs generalize fully to it. These data demonstrate that in vivo cyproheptadine resembles clozapine both acutely and chronically. Our findings, in conjunction with other actions of cyproheptadine -- induction of weight gain, alleviation of clozapine withdrawal, anxiolytic actions, alleviation of 'typical' APD-induced motoric side effects, and some preliminary clinical findings -- suggest that further study of cyproheptadine in conjunction with a 'typical' APD for the possible treatment of schizophrenia is merited at both pre-clinical and clinical levels.

Olanzapine and JL13 induce cross-tolerance to the clozapine discriminative stimulus in rats

We have previously shown that chronic treatment with clozapine induces tolerance to the clozapine discriminative stimulus in rats. The studies reported here extended this work to assess whether chronic treatment with the clozapine-like antipsychotics olanzapine and 5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5] benzoxazepine fumarate (JL13) induced cross-tolerance to clozapine. Two groups of rats were trained to discriminate clozapine (5 mg/kg, intraperitoneal). Training was suspended and the rats were treated with either olanzapine or JL13 at high doses (5 and 20 mg/kg, respectively). These doses were administered twice daily. The clozapine generalization curve was computed three times - before chronic drug treatment, after 10 days of chronic treatment, and after 16 drug-free days. Both olanzapine and JL13 induced cross-tolerance to the clozapine stimulus, shown by significant 3.4 and 3.9 fold parallel shifts to the right in the clozapine generalization curves. Cross-tolerance was lost spontaneously during the drug-free days after treatment as clozapine sensitivity returned to baseline. We interpret these findings as indicative of the development of pharmacodynamic cross-tolerance to clozapine. Possible neuroadaptive mechanisms involved in such cross-tolerance are discussed. The paradigm outlined here allows refinement of antipsychotic drug discrimination assays to identify common chronic effects of such drugs.

Stimulus properties of the “atypical” antipsychotic zotepine in rats: comparisons with clozapine and quetiapine

The stimulus properties of the "atypical" antipsychotic zotepine were assessed in three studies in rats. In Study 1, the ability of zotepine to generalise to clozapine was studied. Two groups of rats were trained to discriminate clozapine at 2 and 5 mg/kg. Clozapine induced full generalisation in both groups, with the generalisation curves shifted significantly to the left in the low dose group. In generalisation tests clozapine did not suppress responding. Zotepine induced dose-related generalisation in both groups, with full generalisation in the low dose group and 50% maximal generalisation in the high dose group at the highest dose that could be tested. In contrast to clozapine, zotepine induced substantial (50% or more) substitution for clozapine only at doses which suppressed responding. In Study 2 zotepine was investigated in rats trained to discriminate quetiapine (10 mg/kg). Quetiapine induced full generalisation and zotepine only induced 54% generalisation at the highest dose that could be tested. Generalisation was accompanied by response suppression induced by both quetiapine and zotepine. In Study 3 an attempt was made to train a zotepine discrimination (1 mg/kg increased to 2 mg/kg). Even after 150 training sessions it proved impossible to obtain reliable discriminative responding with zotepine. These data suggest that: (i) The actions of zotepine in discrimination assays are similar to, but not identical with, those of clozapine and quetiapine; (ii) The differences among the actions of clozapine, quetiapine and zotepine may be related to either the unique ability of zotepine to block noradrenaline (NA) uptake, or to its more marked affinity for D(2) receptors; (iii) The finding that zotepine only mimicked quetiapine up to a level of 54% was unexpected, since quetiapine and clozapine generalise reciprocally and zotepine generalised fully to (low dose) clozapine. This finding may also be related either to zotepine's ability to inhibit NA uptake or its relatively high D(2) affinity; (iv) Although zotepine clearly possesses discriminative properties, it is not possible to train it as a reliable stimulus, in contrast to clozapine and quetiapine. This may be due to its more marked D(2) receptor affinity. Collectively, these data demonstrate both similarities and differences between zotepine and other novel atypical antipsychotics in drug discrimination assays.