Assessment of mazindane, a pro-drug form of mazindol, in assays used to define cocaine treatment agents.

The current studies compared mazindane (5-(4-chlorophenyl)-2,3-dihydro-5H-imidazo [2,1a] isoindole) hydrogen sulfate, a water soluble pro-drug of mazindol (5-(4-chlorophenyl-2,3-dihydro-5H-imidazo [2,1-a] isoindol-5-ol), with mazindol in assays used to define cocaine treatment agents. Both compounds enhanced motor activity (LMA) in Swiss Webster mice with ED(50) values of 2.5 mg/kg i.p. for mazindane and 3.9 mg/kg i.p. for mazindol. At 25 mg/kg mazindane displayed toxic effects and death while mazindol was effect/death free at 50 mg/kg. In Sprague-Dawley rats trained to discriminate cocaine from saline both compounds fully substituted for cocaine with mazindane being fourfold more potent in the total session (0.33 vs. 1.3 mg/kg i.p.) and first reinforcer (0.29 vs. 1.2 mg/kg i.p). Complete substitution was observed in rhesus monkeys trained to discriminate cocaine from saline with ED(50) values for mazindane (0.134 mg/kg i.m.) and mazindol (0.119 mg/kg i.m.). Mazindol exhibited little or no activity at 10(-5) M in inhibiting radioligand binding at 14 neurotransmitter sites while mazindane gave weak activity at the histamine H(1) and 5-hydroxytryptamine 5-HT(3) sites. These results demonstrate that mazindane could be a useful alternative to mazindol as a pharmacological tool because of its similar profile of activity and enhanced water solubility.

Mazindol analogues as potential inhibitors of the cocaine binding site at the dopamine transporter.

A series of mazindol (2) and homomazindol (3) analogues with a variety of electron-donating and electron-withdrawing groups in the pendant aryl group and the benzo ring C, as well as H, methoxy, and alkyl groups replacing the hydroxyl group were synthesized, and their binding affinities at the dopamine transporter (DAT) on rat or guinea pig striatal membranes were determined. Several active analogues were also evaluated for their ability to block uptake of DA, 5-HT, and NE and inhibit binding of [(125)I] RTI-55 at HEK-hDAT, HEK-hSERT, and HEK-hNET cells. Mazindane (26) was found to be a pro-drug, oxidizing (5-H --> 5-OH) to mazindol on rat striatal membranes and HEK-hDAT cells. The 4',7,8-trichloro analogue (38) of mazindol was the most potent and selective ligand for HEK-hDAT cells (DAT K(i) = 1.1 nM; SERT/DAT = 1283 and NET/DAT = 38). Experimental results strongly favor the cyclic or ol tautomers of 2 and 3 to bind more tightly at the DAT than the corresponding keto tautomers.

Three-dimensional quantitative structure-activity relationships of mazindol analogues at the dopamine transporter.

A three-dimensional quantitative structure-activity relationship (3D-QSAR) study was performed on a series of mazindol analogues using the comparative molecular field analysis (CoMFA) method with their corresponding binding affinities for the displacement of [(3)H]WIN 35 428 from rat caudate putamen tissue. The cross-validated CoMFA models were derived from a training set of 50 compounds, and the predictive ability of the resulting CoMFA models was evaluated against a test set of 21 compounds. A set of alignment rules was derived to superimpose these compounds onto a template structure, mazindol (1). These CoMFA models yielded significant cross-validated r(2)(cv) values. Inclusion of additional descriptors did not improve the significance of the CoMFA models; thus, steric and electrostatic fields are the relevant descriptors for these compounds. The best QSAR model was selected on the basis of the predictive ability of the activity on the external test set of compounds. The analysis of coefficient contour maps provided further insight into the binding interactions of mazindol analogues with the DAT. The aromatic rings C and D are involved in hydrophobic interactions in which ring D may bind in a large hydrophobic groove. The relative orientation of these two rings is also important for high binding affinity to the DAT.

Halogenated mazindol analogs as potential inhibitors of the cocaine binding site at the dopamine transporter.

A series of halogenated (F, Cl, Br, I), pyrimido and diazepino homologs of mazindol were prepared and evaluated for their ability to displace [3H]WIN 35,428 binding and to inhibit uptake of [3H]dopamine (DA) in rat striatal tissue. All of the compounds except for the 2'-chloro (6) and 2'-bromo (16) analogs of mazindol displaced [3H]WIN 35,428 binding and inhibited [3H]DA uptake more effectively than (R)-cocaine. Structure-activity studies indicated that best inhibition of [3H]WIN 35,428 binding occurred in the imidazo series with compounds containing one or two Cl or Br atoms in the 3'- or 4'-position of the free phenyl group. Replacement of the imidazo ring by a pyrimido or diazepino ring enhanced binding inhibition. The most potent inhibitors of [3H]WIN 35,428 binding and [3H]DA uptake were 6-(3'-chlorophenyl)-2,3,4,6-tetrahydropyrimido[2,1-alpha]isoind ol-6-ol (23; IC50 1.0 nM; 8 x mazindol) and 7-(3',4'-dichlorophenyl)-2,3,4,5-tetrahydro-7H-diazepino[2,1-alpha ]isoindol-7-ol (28; IC50 0.26 nM; 32 x mazindol), respectively. No significant differences was found between binding and uptake inhibition. Mazindol and the pyrimido and diazepino homologs 24 and 27 showed a selectivity for the DA uptake over the serotonin (5-HT) uptake site of 5-, 250-, and 465-fold, respectively, and displayed weak or no affinity for a variety of neurotransmitter receptor sites.

Unexpected differences between mazindol and its homologs on biochemical and behavioral responses.

Mazindol and two homologs of mazindol were tested for their effects as uptake inhibitors in rat tissue slices for [3H]dopamine in the neostriatum, for [3H]norepinephrine in occipital cortex and for [3H]serotonin in whole brain. All three drugs were potent inhibitors of [3H]dopamine uptake (ED50 values between 57 and 280 nM), [3H]norepinephrine uptake (ED50 values less than 19 nM) and were somewhat weaker against [3H]serotonin uptake (ED50 values between 550 and 4100 nM). All three drugs were in contrast very weak as releasing agents for previously accumulated 3H-biogenic amines. Mazindol injection resulted in a large increase in locomotor activity in mice, but its two homologs were without effect. Mazindol was able to counteract amphetamine-induced increases in activity in reserpinized mice, but its homologs were inactive. Mazindol also caused a vigorous ipsilateral rotation in rats with an unilateral 6-hydroxydopamine lesion of the nigrostriatal system, but again the homologs had no such effect. However, all three drugs were potent inhibitors of prolactin secretion in rats (ID50 values 1-2 mg/kg orally). Correlations between the capacities of the drugs to inhibit 3H-biogenic amine uptake and the various in vivo responses are made.

Pharmacological studies with several analogs of mazindol: correlation between effects on dopamine uptake and various in vivo responses.

Several structural analogs of mazindol were tested as inhibitors of the uptake of [3H] dopamine in rat neostriatum, of [3H] norepinephrine in rat occipital cortex and of [3H] serotonin in whole rat brain. A rather wide range of potencies was observed but a number of the drugs were even more potent than mazindol as uptake inhibitors. All of the drugs studied were weak releasing agents for previously accumulated [3H]amines. Several of the drugs caused large increases in motor activity in normal mice but not in reserpinized mice. However, these same drugs were able to prevent amphetamine-induced increases in activity in reserpinized mice, and were able to induce ipsilateral circling in rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal pathway. Two of these same drugs were tested and found to be potent inhibitors of prolactin secretion. Correlations will be made between the capacities of the drugs to inhibit dopamine uptake and the in vivo responses mentioned above.

The effects of mazindol and 46-034 (Sandoz) on glucose oxidation and insulin binding by rat isolated fat cells.

1. The anorexic agent mazindol and its major metabolite 46-034 (Sandoz) in high concentrations ( greater than 0-4 mM) abolished basal and insulin-stimulated conversion of 1-14C-glucose to 14CO2 by rat isolated fat cells. 2. High concentrations (1mM) also inhibited specific binding of 125 I-insulin to fat cells. 3. The observed effects appeared to be due in part to perturbation of the plasma membrane since there was a rise in the lactate dehydrogenase content of the incubation medium, increased 125I-insulin degradation and a reduction in cellular tritiated water space. 4. These effects are unlikely to be relevant to the therapeutic action of mazindol.

Analogs of the anorexic mazindol.

Mazindol, 5-(p-chlorophenyl)-2,5-dihydro-3H-imidazo[2,1-a]isoindol-5-ol, has been shown to be an effective anorexic. To explore the structure-activity relationships, several 1-ethyl-3-substituted-4-aryl-4-hydroxyindeno[1,2-c]pyrazoles were prepared and subjected to various animal screens. The 1-ethyl-3-tert-butyl-4-aryl-4-hydroxyindeno[1,2-c]pyrazoles are capable of significantly depressing forced and spontaneous motor activity in mice but have low LD50's. Two of these compounds were tested in an Ehrlich ascites tumor screen. The 1-ethyl-3-phenyl-4-aryl-4-hydroxyindeno[1,2-c]pyrazoles depressed forced and spontaneous motor activity at low doses and were relatively nontoxic.