Synthesis and Structure-Activity Relationships of 2,5-Dimethoxy-4-Substituted Phenethylamines and the Discovery of CYB210010: A Potent, Orally Bioavailable and Long-Acting Serotonin 5-HT2 Receptor Agonist

Structure-activity studies of 4-substituted-2,5-dimethoxyphenethylamines led to the discovery of 2,5-dimethoxy-4-thiotrifluoromethylphenethylamines, including CYB210010, a potent and long-acting serotonin 5-HT2 receptor agonist. CYB210010 exhibited high agonist potency at 5-HT2A and 5-HT2C receptors, modest selectivity over 5-HT2B, 5-HT1A, 5-HT6, and adrenergic α2A receptors, and lacked activity at monoamine transporters and over 70 other proteins. CYB210010 (0.1-3 mg/kg) elicited a head-twitch response (HTR) and could be administered subchronically at threshold doses without behavioral tolerance. CYB210010 was orally bioavailable in three species, readily and preferentially crossed into the CNS, engaged frontal cortex 5-HT2A receptors, and increased the expression of genes involved in neuroplasticity in the frontal cortex. CYB210010 represents a new tool molecule for investigating the therapeutic potential of 5-HT2 receptor activation. In addition, several other compounds with high 5-HT2A receptor potency, yet with little or no HTR activity, were discovered, providing the groundwork for the development of nonpsychedelic 5-HT2A receptor ligands.

Abstract 2006: AMX-513 polyamine depletion therapy inhibits tumor growth and reverses immunosuppression in cancers including MYC-driven neuroblastoma and pancreatic cancer

Tumorigenesis is associated with increased polyamine levels and involves the induction of ornithine decarboxylase (ODC), the initial rate-limiting enzyme in polyamine biosynthesis, and increased uptake of polyamines from the blood and diet. As well as contributing to proliferation, polyamines are reported to exert an immunosuppressive effect. Amplification of the MYC/MYCN oncogenes has been shown to directly induce ODC activity and inhibition of this enzyme by α-difluoromethylornithine (DFMO) markedly delays tumor development. Aminex Therapeutics is developing a polyamine depletion approach targeting both biosynthesis and transport of polyamines with AMX-513, a combination of the approved ODC inhibitor, DFMO, together with AMXT 1501, an alkylated polyamine mimetic which blocks polyamine uptake.

In the syngeneic CT26.CL25 mouse model of colorectal cancer, AMX-513, dosed daily for four weeks, reduced tumor growth > 75% compared to vehicle-treated control in immunocompetent Balb/C mice. There was no effect in athymic nude mice indicating that tumor growth inhibition by AMX-513 is T-cell-dependent. In the induced transgenic K6/ODC squamous tumor mouse model, stable regression was sustained 10 weeks after treatment ended and was accompanied by tumor infiltrate increases in IFNγ and in CD3+ and CD8+ T-cells. Tumor infiltrates from AMX-513-treated KPC pancreatic cancer transgenic mice with tumor regressions showed >90% reductions in myeloid-derived suppressor cells (MDSCs; CD11b+ Gr-1+) but no changes in mature myeloid cells (CD11+Gr-1neg) by FACS analysis. AMX-513 treatment did not impact the percentage or number of CD4+CD25+FoxP3+ Tregs, but did significantly increase the percentage of activated CD8+ T cells in tumors.

Neuroblastoma is an aggressive childhood cancer frequently associated with MYCN and ODC deregulation. In neuroblastoma cell lines, the AMX-513 combination was highly synergistic (CI<0.5). Prophylactic treatment of neuroblastoma-prone TH-MYCN transgenic mice with AMX-513 significantly extended survival compared to either agent alone (median survival time = 81.0±11.8 days versus DFMO alone = 57.1±7.1 days; P<0.0001). Treatment of mice with small palpable tumors with AMX-513 in combination with cyclophosphamide/topotecan significantly improved survival compared with either AMX-513 or cyclo/topo alone (5/9 long term survivors compared to 0/10 and 0/9 for cyclo/topo and AMT-513, respectively; P<0.001 in each case). Polyamine levels were significantly decreased in mice undergoing AMX-513 treatment compared to DFMO or AMXT 1501 alone.

In conclusion, AMX-513 treatment alone or in combination with other cancer therapies results in significant tumor growth reduction in multiple cancer models and demonstrates novel immunotherapeutic potential. Clinical evaluation of AMX-513 is planned in 2017.

Citation Format: Mark R. Burns, Kathy Fosnaugh, Michael G. Palfreyman, Laura Gamble, Jayne Murray, Sophie Allan, Georgina Eden, Sara Sarraf, Murray Norris, David Ziegler, Michelle Haber. AMX-513 polyamine depletion therapy inhibits tumor growth and reverses immunosuppression in cancers including MYC-driven neuroblastoma and pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2006. doi:10.1158/1538-7445.AM2017-2006

Functional Genomics Conference: From Identifying Proteins to Faster Drug Discovery

The massive effort to sequence the human, mouse, rat, nematode (Caenorhabditis elegans), fruit fly (Drosophila), zebra fish, yeast (Saccharomyces cerevisiae), fungal (Candida albicans and Aspergillus fumigatus) and several bacterial genomes has produced a flood of sequence data. Of the more than 100,000 human genes and thousands from other organisms, many partial sequences and several completed microbial genomes are available in both public and private databases. However, elucidation of function has been achieved for only a very small portion and an even smaller percentage have been validated as drug targets. Many companies interested in identifying new drug targets also see this bounty of opportunity as a major challenge. The raw sequence data say little about the importance of the gene and nothing about its potential as a target for drug discovery. Since 1994, a new term, 'functional genomics', has entered our lexicon. Functional genomics, which in effect is 'high-throughput biology', was originally focused on understanding gene function by studying the genes of simpler organisms, such as the nematode, C. elegans. As the genes from a number of organisms are highly conserved across species, it is believed that studying these basic systems can yield valuable insights for drug companies interested in targeting therapeutics for the higher organisms. More recently, the approach to functional genomics has expanded to include study of gene function in organisms to be targeted for therapeutic intervention. This new approach was the theme of the Functional Genomics Conference: From Identifying Proteins to Faster Drug Discovery held in Washington DC on March 10 and 11, 1998. The organisers (NMHCC) hoped that the breadth of the conference topics would reflect the complexities of the modern drug discovery process and covered technologies from gene chips, bioinformatics, disease models, protein discovery and expression, target validation, high-throughput screening for genes of unknown function, to integration of the drug discovery process. The two day conference placed emphasis on cutting edge technology solutions and the development of high-throughput tools to address the emerging opportunities in genome-based drug discovery.

Electroconvulsive seizures regulate gene expression of distinct neurotrophic signaling pathways

Electroconvulsive therapy (ECT) remains the treatment of choice for drug-resistant patients with depressive disorders, yet the mechanism for its efficacy remains unknown. Gene transcription changes were measured in the frontal cortex and hippocampus of rats subjected to sham seizures or to 1 or 10 electroconvulsive seizures (ECS), a model of ECT. Among the 3500-4400 RNA sequences detected in each sample, ECS increased by 1.5- to 11-fold or decreased by at least 34% the expression of 120 unique genes. The hippocampus produced more than three times the number of gene changes seen in the cortex, and many hippocampal gene changes persisted with chronic ECS, unlike in the cortex. Among the 120 genes, 77 have not been reported in previous studies of ECS or seizure responses, and 39 were confirmed among 59 studied by quantitative real time PCR. Another 19 genes, 10 previously unreported, changed by <1.5-fold but with very high significance. Multiple genes were identified within distinct pathways, including the BDNF-MAP kinase-cAMP-cAMP response element-binding protein pathway (15 genes), the arachidonic acid pathway (5 genes), and more than 10 genes in each of the immediate-early gene, neurogenesis, and exercise response gene groups. Neurogenesis, neurite outgrowth, and neuronal plasticity associated with BDNF, glutamate, and cAMP-protein kinase A signaling pathways may mediate the antidepressant effects of ECT in humans. These genes, and others that increase only with chronic ECS such as neuropeptide Y and thyrotropin-releasing hormone, may provide novel ways to select drugs for the treatment of depression and mimic the rapid effectiveness of ECT.

Psychiatric Genomics, inc

Mental illness affects millions of patients and has been shown to have multiple genetic components. The interaction of environmental factors, such as stress, with the expression of genetic susceptibilities has hampered the development of novel and effective drug treatments. A new approach is described that can discover novel classes of drugs for the treatment of the underlying causes of these diseases rather than their symptoms. This approach screens drug candidates according to their ability to alter the expression of multiple genes in a multiparameter high-throughput screening assay (MPHTS SM) that does not require a prori knowledge of the targets of screening assays. Clinical development of drug candidates will be pursued through partnerships with pharmaceutical companies and/or large biotechnology companies.

Novel directions in antipsychotic target identification using gene arrays

Schizophrenia is a major health problem that affects 2 million individuals in the United States. Antipsychotics offer considerable symptomatic relief and, although commonly discovered by screening with single biological targets, most interact with multiple receptors and signaling pathways. Considerable evidence from family and twin studies demonstrates genetic components and multiple chromosomal regions associated with schizophrenia. The polygenic nature of schizophrenia and multiple mechanisms for most effective agents indicate the need for broader approaches to target identification. Gene expression profiling of post-mortem human brain tissue simultaneously reveals the expression of many thousands of genes. A comparison of tissue from normals and patients provides a 'disease signature' of aberrantly expressed genes. 'Drug signatures' are the gene expression changes of cultured human or animal neurons treated with psychiatric drugs, and from animals chronically treated with these drugs. A selection of genes from disease and drug signatures can create a set of targets whose changes may better predict disease and its treatment by effective agents. This multi-parameter high throughput screening (MPHTS(SM)) approach evaluates the mRNA expression pattern of cultured cells exposed to candidate compounds. Compounds that normalize genes altered in schizophrenia may better address its underlying causes. Drugs that mimic gene expression changes that are consistently altered by effective antipsychotic agents provide a drug improvement strategy if efficacy is enhanced or side effects are attenuated.

The primary in vitro anticancer activity of "half-mustard type" phenothiazines in NCI's revised anticancer screening paradigm

Some new phenothiazines have been synthesized on the basis of previous studies. The anticancer activity of "half-mustard type" phenothiazines was investigated on sixty different cancer cell lines in vitro. The percentage of growth (PG), 50% inhibition of growth (GI50), the tumor growth inhibition (TGI) and the concentration required for 50% lethality of cells (IC50) were examined and calculated in the presence of various (from 10(-4) to 10(-8) M) concentrations of phenothiazine alkylurea derivatives. The following cell lines were involved in the study: 6 leukemia, 9 non-small-cell lung cancer, 7 colon cancer, 6 central nervous system cancer, 8 melanoma, 6 ovarian cancer, 8 renal cancer, 2 prostate and 8 breast cancer cell lines. The antileukemic activity of four chloroethyl-substituted phenothiazine-alkylureas was shown by considerable growth inhibition, in the 10(-5) M range, of the six different leukemia cell lines. The 50% inhibition of growth was nearly the same for the four compounds on all cell lines. Tumor growth inhibition (TGI) and IC50 value to cells varied from -4.0 to -4.66. The two derivatives with the butylene bridge were more effective than propylene linked compounds against the CCRP-CEM, HL60 (TB), K-562 and MOLT-4 cell lines. However, the anti-leukemic activity of the derivatives was nearly the same for RPMT 8226 and SR cell lines. The substituent at the 2- position of phenothiazine ring and the length of the linker between the side chain nitrogen and the phenothiazine ring system are apparently important for antileukemic activity. Four of the 9 non-small-cell lung cancer cell lines were sensitive, while the other 5 cell lines were not. The compounds had a slight growth inhibitory effect on colon cell carcinoma and melanoma cells in which case the butylene linker seemed to be more effective than the propylene linker. At the same time, all of the compounds were weak or mostly inactive on cancer cells from the central nervous system. One ovarian cancer line of the 6, the IGROVI was sensitive to butylurea phenothiazines, however, the other five were not sensitive at all. The difference in the sensitivity of various renal cell carcinomas was significant: 5 lines were not sensitive, three of them (786-0, RXF-393 and TK-10) were sensitive to only butylene-substituted phenothiazine-ureas, propylene substitution resulted in ineffective compounds. The compounds were not able to inhibit the 2 prostate and 4 breast cancer cell lines, even at 10(-4) M. It was interesting that propylene-linked ureas were more effective than butylene-linked derivatives on MCF-7, but butylene-linked derivatives were more effective than propylene-linked compounds on MDA MB-231 and MDA-N. In addition, MDA MB 435 was more sensitive to the trifluoromethyl derivatives than the compounds without this substituent. Since the phthalimido-alkyl phenothiazines were not active at the first level of prescreen, these compounds were omitted from this study. The drug sensitivity of some cancer cell lines was not uniform for the different groups, therefore we postulate that the resistance can be related to some kind of (existing) drug-efflux mechanism. Apparently, the tumor specificity of phenothiazine alkylureas is more related to the leukemia specificity of alkylureas than to any CNS or lung specificity of phenothiazines.

The primary in vitro antitumor screening of "half-mustard type" phenothiazines

The antitumor effects of "half-mustard type" phenothiazines were studied on 57 different tumor cell lines, including leukemias, non-small lung cancer, colon, central nervous system, ovarian, renal, breast, and prostate cancer, as well as melanoma cell cultures. Alkyl-urea derivatives of phenothiazines displayed in vitro antitumor activity. The phenothiazine phthalimido derivatives (1-6) were not active on the majority of cancer cell cultures. In contrast, propylureas (9, 11) were active against some leukemia cell types. Only two compounds with the butylene [(CH2)4] linker (10, 12) were active against non-small lung cancer cells. Compounds containing the propylene linker were less effective. On colon cancer lines, tumor cells from the central nervous system and on melanoma cells the same compounds were effective, however, having substituents at the 2-position of phenothiazine seems to be important. Surprisingly, the majority of ovarian cancer cell lines (except one type, IGROVI) and five of eight renal cancer lines were not sensitive to these phenothiazine derivatives. The two butylene linked phenothiazine ureas (10, 12) had moderate antiproliferative action on two renal cancer cell lines. The prostate cancer and some breast cancer cell lines were not sensitive. Nevertheless some breast cancer cell lines were apparently sensitive to CF3-substituted phenothiazine alkylureas. On the basis of these experiments one may postulate that in the case of insensitive cells an mdr-gene encoded multidrug resistance efflux pump is responsible for the resistance. The selectivity or organ cell specificity of the effective phenothiazines will be targeted for improvement in further studies, in order to avoid the general cytotoxic effects of "half mustard type" phenothiazines.

The in vitro antitumor assay of "half-mustard type" phenothiazines in screens of AIDS-related leukemia and lymphomas

Twelve different "half-mustard type" phenothiazines were newly synthesized and tested on seven AIDS-related lymphoma (ARL) tumor cell lines, one leukemia CCRF-CEM cell culture and five different lymphoma lines; RL, KD-488, AS283, PA682 and SU-DHL-7 cell lines. The alkylene-urea substituted phenothiazines affected the growth and inhibited the growth rate of AIDS-related lymphoma cells. The Cl-substituent at the 2-position was more effective than the CF3 substitution. In AIDS-related leukemia also the compounds with Cl at the 2-position with propylene or butylene linkers, -(CH2)3- and -(CH2)4-, respectively, were more effective than the CF3 substituted compounds. Two of the six phenothiazine-substituted alkyl-urea derivatives, i.e., 1-(2-chloroethyl)-3-(2-chloro-10H-phenothiazin-10-yl)propyl-l-urea (9, GI50 = -5.66, TGI = -5.04) and 1-(2-chloroethyl)- 3-(2-chloro-10H-phenothiazin-10-yl)butyl-1-urea (10, GI50 = -5.61, TGI = -5.12) exhibited antitumor activity for AIDS-related leukemia and five AIDS-related lymphomas. The trifluoromethyl-substituted derivatives were not as effective on AIDS-related tumor cell lines. Apparently, the substituent at the 2-position on the phenothiazine and the alkylene number of the linker attached to the nitrogen of the phenothiazine ring have an important role in the compound's antitumor effects on AIDS-related leukemia and lymphomas.

MDL 100,458 and MDL 102,288: two potent and selective glycine receptor antagonists with different functional profiles

Glycine receptor antagonists have been proposed to have multiple therapeutic applications, including the treatment of stroke, epilepsy, and anxiety. The present study compared the biochemical and behavioral profiles of two strychnine-insensitive glycine receptor antagonists, MDL 100,458 (3-(benzoylmethylamino)-6-chloro-1H-indole-2- carboxylic acid) and MDL 102,288 (5,7-dichloro-1,4-dihydro-4-[[[4- [(methoxycarbonyl)amino]phenyl]sulfonyl]imino]-2-quinolinecarboxylic acid monohydrate). Both compounds potently inhibited [3H]glycine binding to rat cortical/hippocampal membranes (Ki = 136, 167 nM, respectively) without showing significant activity in 18 other receptor binding assays. In an in vitro functional assay, both compounds completely antagonized N-methyl-D-aspartate (NMDA)-stimulated cGMP accumulation in rat cerebellar slices. However, in contrast to their equipotency in the glycine receptor assay, MDL 100,458 was approximately 6-fold more potent than MDL 102,288 in the cGMP assay (IC50 values = 1.25, 7.8 microM, respectively). Behavioral tests demonstrated that MDL 102,288 and MDL 100,458 exhibited strikingly different in vivo profiles. MDL 100,458 antagonized audiogenic seizures in DBA/2J mice (ED50 = 20.8 mg/kg i.p.), whereas MDL 102,288 was without effect in the dose range tested (ED50 > 300 mg/kg i.p.). Central nervous system penetration did not appear to account for this difference. For example, MDL 102,288 was not active following direct intracerebroventricular administration (ED50 > 16 micrograms; vs. 0.78 microgram for MDL 100,458). In a test of anxiolytic activity, MDL 102,288 reduced separation-induced ultrasonic vocalizations in rat pups (ED50 = 6.3 mg/kg i.p.) whereas MDL 100,458 was only weakly active (ED50 = 80.8 mg/kg i.p.). Furthermore, the anxiolytic effect of MDL 102,288 was selective in that it occurred at doses that did not produce motoric disruption as measured by an inclined-plane test (ED50 > 160 mg/kg; therapeutic index > 25.4). In contrast, the anxiolytic activity of MDL 100,458 was non-selective in that it occurred at doses that also produced motoric disruption (ED50 = 57.7 mg/kg; therapeutic index = 0.7). Thus, two glycine receptor antagonists which have similar in vitro binding profiles as selective ligands for the strychnine-insensitive glycine receptor, demonstrate different in vitro and in vivo functional profiles. The reason for these differences is not clear, though one possibility could be that the compounds may act on different NMDA receptor subtypes. These data support the possibility that different glycine receptor antagonists may have different therapeutic targets.

The role of 5-HT2A receptors in antipsychotic activity

The correlation between the clinical activity of antipsychotic agents and their affinity for the D2 dopamine receptor has been the mainstay of the hypothesis that schizophrenia is due to excessive dopaminergic function. More recently, the unique clinical profile of the atypical antipsychotic clozapine has been proposed to involve actions on additional receptor systems. In particular, the high affinity of clozapine for the 5HT2A receptor subtype has been suggested to contribute to its reduced side-effect liability, greater efficacy and its activity in therapy-resistant schizophrenia. We have used the highly selective 5-HT2A antagonist MDL 100,907 to explore the contribution of 5-HT2A receptor blockade to antipsychotic activity. Biochemical, electrophysiological and behavioral studies reveal that selective 5HT2A receptor antagonists have the preclinical profile of an atypical antipsychotic. The limited clinical evidence available also suggests that compounds producing 5-HT2A receptor blockade are effective, in particular, against the negative symptoms of schizophrenia.

The acute effect of the bioprecursor of the selective brain MAO-A inhibitor, MDL 72392, on rat pineal melatonin biosynthesis

The bioprecursor amino acid MDL 72394 is decarboxylated by aromatic L-amino acid decarboxylase (AADC) to liberate MDL 72392, an irreversible selective MAO-A inhibitor. Pretreatment with the AADC inhibitor carbidopa, which does not penetrate the brain-blood barrier, prevents the liberation of the MAO-A inhibitor outside the brain and results in exclusive inhibition of brain MAO-A. We found that systemic administration of MDL 72394 (0.5 mg/kg, i.p.) stimulated rat pineal melatonin biosynthesis. Carbidopa, in a dose-dependent manner, attenuated or completely prevented MDL-induced stimulation of melatonin biosynthesis in the pineal gland located outside the blood-brain-barrier.

Haloallylamine inhibitors of MAO and SSAO and their therapeutic potential

Based on mechanistic understandings, molecular modeling and extensive quantitative structure-activity relationships, appropriately substituted haloallylamine derivatives were designed as potential mechanism-based inhibitors of MAO and/or SSAO. Potent inhibition of MAO-B and SSAO occurred with fluoroallylamines whereas chloroallylamines, such as MDL 72274A ((E)-2-phenyl-3-chloroallylamine hydrochloride), were selective and potent inhibitors of SSAO. MDL 72974A (E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride is a potent (IC50 = 10(-9) M) inhibitor of both MAO-B and SSAO, with 190-fold lower affinity for MAO-A. In clinical studies, oral doses as low as 100 micrograms produced substantial inhibition of platelet MAO-B. Essentially complete inhibition occurred at 1 mg with the effect lasting 6-10 days. One or 4 mg MDL 72974A given daily for 28 days to 40 Parkinson's patients treated with L-dopa produced statistically significant reductions in the Unified Parkinson's Disease Rating Scale. MAO-B inhibitors, such as MDL 72974A and L-deprenyl, offer the potential of being neuroprotective in Parkinson's Disease and other neurogenerative disorders. Concommitant inhibition of SSAO may provide additional, but as yet unproven, advantages over pure inhibitors of MAO-B.

Electrophysiological, biochemical and behavioral evidence for 5-HT2 and 5-HT3 mediated control of dopaminergic function

Several lines of evidence have suggested a link between serotonergic and dopaminergic systems in the brain. The interpretation of much of these early data needs careful reevaluation in light of the recent understanding of the plethora of serotonin receptor subtypes, their distribution in the brain and the new findings with more selective serotonin antagonists. Electrophysiological, biochemical and behavioral evidence obtained using highly selective antagonists of the 5-HT2 or 5-HT3 receptor subtypes, MDL 100,907 or MDL 73,147EF, respectively, supports the thesis that serotonin modulates the dopaminergic system. This modulation is most evident when the dopaminergic system has been activated.

MDL 27,531 reduces spontaneous hindlimb contractions in rats with chronic transections of the spinal cord

Disrupted glycinergic inhibition in the brainstem and spinal cord may contribute to some of the alterations in reflex control seen in patients with spastic disorders. MDL 27,531, which acts functionally like a glycine agonist in its capacity to selectively reverse seizures produced by the glycine antagonist strychnine, was evaluated in a model of spinal injury-induced reflex dysfunction. Rats recovering chronically from complete spinal cord transections exhibited intermittent contractions of the paralyzed hindlimbs, as measured with an automated apparatus. MDL 27,531 selectively decreased these hindlimb contractions, as did the clinically demonstrated antispastic agent clonidine. In its therapeutic dose range, clonidine, but not MDL 27,531, produced ataxia in non-transected rats. These data suggest that MDL 27,531 may be a useful therapeutic agent for the treatment of dysfunctions of reflex control seen in spastic disorders of spinal origin, with potentially fewer side effects than are seen with existing drug therapies.

Potent indole- and quinoline-containing N-methyl-D-aspartate antagonists acting at the strychnine-insensitive glycine binding site

The N-methyl-D-aspartate (NMDA)-preferring glutamate receptor subtype possesses, in addition to the recognition site for glutamate, a binding site for glycine. We report here on the pharmacological properties of 3-(4,6-dichloro-2-carboxyindol-3-yl)-propionic acid (MDL 29,951) and 4-carboxymethylamino-5,7-dichloroquinoline-2-carboxylic acid (MDL 100,748), two novel glycine antagonists of NMDA receptor activation in vitro and in vivo. We have measured in parallel the effects of two previously described glycine antagonists, 7-chlorokynurenic acid and 5,7-dichlorokynurenic acid. All were potent inhibitors of [3H]glycine binding. Ki values (microM) were 0.36 (7-chlorokynurenic acid), 0.08 (5,7-dichlorokynurenic acid), 0.07 (MDL 100,748) and 0.14 (MDL 29,951). MDL 100,748 and MDL 29,951 were approximately 2000-fold selective for the glycine binding site relative to the glutamate recognition sites. All four compounds completely inhibited the use-dependent binding of [3H]N-[1-(2-thienyl) cyclohexyl]-piperidine and were noncompetitive, glycine-reversible inhibitors of both NMDA-induced biochemical and electrophysiological responses in brain slice preparations. A competitive interaction with the glycine binding site was also evident in that MDL 29,951 and MDL 100,748 produced parallel rightward shifts in the glycine requirement for demonstration of NMDA-stimulated elevations in cytosolic calcium in cultured neuronal preparations. The glycine antagonists were potent anticonvulsants after their i.c.v. administration to audiogenic seizure-susceptible DBA/2J mice. Because the compounds chosen encompass a variety of chemical structures, the results indicate that glycine is required for NMDA receptor activation and that bioavailable glycine antagonists may form the basis of a novel therapy for epilepsy.

[3H]5,7-dichlorokynurenic acid, a novel radioligand labels NMDA receptor-associated glycine binding sites

A strychnine-insensitive glycine binding site is located on the N-methyl-D-aspartate (NMDA)-preferring glutamate receptor complex. Kynurenic acid analogs are antagonists at this binding site. A derivative of kynurenic acid, 5,7-dichlorokynurenic acid (5,7-DCKA) was radiolabeled with 3H and used to study antagonist binding to the glycine recognition site. This ligand ( [3H]5,7-DCKA) showed high affinity (Kd = 69 nM), saturable (Bmax = 14.5 pmol/mg protein) binding to rat brain membranes. A variety of agonists and antagonists inhibited the binding of [3H]5,7-DCKA and [3H]glycine in a similar fashion (r = 0.93). In addition, glutamate site agonists and antagonists exerted opposite allosteric effects on [3H]5,7-DCKA binding suggesting that [3H]5,7-DCKA preferentially binds to the agonist-activated conformation of the receptor.

NMDA receptor complex antagonists have potential anxiolytic effects as measured with separation-induced ultrasonic vocalizations

Pre-weaning rat pups emit ultrasonic vocalizations when removed from the litter. These 'separation-induced vocalizations' (SIV) are suppressed by classical benzodiazepine anxiolytics and by non-benzodiazepine anxiolytics which lack muscle relaxant and sedative properties. The present study used the SIV model to assess potential anxiolytic properties of compounds which target different sites associated with the NMDA receptor complex. Comparison was made to drugs which affect benzodiazepine or serotonin (5-HT) receptors. Muscle relaxant potential was assessed using 'TIP' (time on an inclined plane), the amount of time a pup was able to retain its position on a steeply inclined surface. Mephenesin, a centrally acting muscle relaxant, significantly suppressed TIP but not SIV. The benzodiazepine agonist diazepam suppressed both SIV and TIP, whereas the 5-HT1A partial agonists, buspirone and MDL 73,005EF, suppressed SIV without affecting TIP. The 5-HT2 antagonist MDL 11,939 suppressed TIP but not SIV, whereas neither measure was affected by the 5-HT3 antagonist MDL 73,147EF. SIV was suppressed by NMDA antagonists including those acting at the glutamate recognition site (D,L-amino-phosphonovaleric acid (AP5) and MDL 100,453) or at the ion channel (MK-801), or by the strychnine-insensitive glycine antagonist 5,7-dichlorokynurenic acid (5,7-DCKA). TIP was suppressed even more potently by AP5, MDL 100,453 and MK-801, whereas 5,7-DCKA was inactive on this measure. Thus, antagonists acting at different sites present on the glutamate recognition site exhibit potential anxiolytic activity, but the glycine antagonist was unusual in its lack of prominent muscle relaxant side effects.

Activity of 5,7-dichlorokynurenic acid, a potent antagonist at the N-methyl-D-aspartate receptor-associated glycine binding site

5,7-Dichlorokynurenic acid (5,7-DCKA), one of the most potent excitatory amino acid receptor antagonists yet described, binds to a strychnine-insensitive glycine binding site located on the N-methyl-D-aspartate (NMDA) receptor complex (Ki = 79 nM versus [3H]glycine). 5,7-DCKA (10 microM) antagonized the ability of NMDA to stimulate the binding of the radiolabeled ion channel blocker N-[3H][1-(2-thienyl)cyclohexyl]-piperidine ([3]TCP). Glycine was able to overcome this effect and in the presence of 5,7-DCKA enhanced [3H]TCP binding to antagonist-free levels. 5,7-DCKA completely and noncompetitively antagonized several NMDA receptor-mediated biochemical and electrophysiological responses. Thus, micromolar concentrations of 5,7-DCKA inhibited NMDA-stimulated elevation of cytosolic calcium in cultured hippocampal neurons, cGMP accumulation in cerebellar slices, and norepinephrine release from hippocampal slices. The glycine antagonist could also block the action of synaptically released agonist, as shown by its ability to inhibit the increase in the magnitude of the population spike that follows tetanic stimulation of the hippocampus in vitro (long term potentiation). Inclusion of glycine or D-serine prevented all these effects of the antagonist. 5,7-DCKA was a potent anticonvulsant when administered intracerebroventricularly to mice. As in the in vitro experiments, the dose-response curve for the antagonist was shifted rightward in a parallel fashion when D-serine was coinjected. This spectrum of activity displayed by a compound acting at the glycine binding site suggests that the therapeutic utility of glycine antagonists will be similar to those proposed for other types of glutamate receptor antagonists.

Curtatoxins. Neurotoxic insecticidal polypeptides isolated from the funnel-web spider Hololena curta

Three polypeptide neurotoxins (curtatoxins) were isolated from the venom of the spider Hololena curta by reverse-phase high performance liquid chromatography, gel permeation, and ion-exchange chromatography. The purified toxins induced an immediate paralysis in the cricket Acheta domestica that resulted in desiccation and death of the insect within 24-48 h (LD50 congruent to 4-20 micrograms/g); this toxic effect is consistent with irreversible presynaptic neuromuscular blockade. Curtatoxins are a class of sequence-related, cysteine-rich, carboxyl-terminal amidated polypeptides of 36 to 38 amino acid residues. The cysteine residues are conserved at identical sequence positions among these polypeptides and form 4 intramolecular disulfide bonds. Hydropathy calculations show that the toxins have an internal hydrophobic region flanked by hydrophilic and oppositely charged amino- and carboxyl-terminal ends. By analogy to other cysteine-rich arthropod venom proteins, the folded structure of the curtatoxins is likely important for their target specificity and mode of action at the neuromuscular junction.

MDL 72,974: a potent and selective enzyme-activated irreversible inhibitor of monoamine oxidase type B with potential for use in Parkinson's disease

MDL 72,974, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine, was designed to be a selective inhibitor of monoamine oxidase type B (MAO-B). In vitro, the compound inhibits rat brain mitochondrial MAO in a concentration and time-dependent fashion and shows marked selectivity for the B form (IC50 = 680 and 3.6 nM for MAO-A and MAO-B, respectively). After oral administration to rats, the compound shows preferential inhibition of brain MAO-B with ED50 values of 8 and 0.18 mg/kg p.o. for the A and B forms, respectively. Selectivity is retained on repeat dosing. MDL 72,974 did not significantly potentiate the cardiovascular effects of intraduodenually-administered tyramine in anaesthetized rats and had only minor indirect sympathomimatic effects in the pithed rat. At MAO-B selective doses the neurotoxic effect of MPTP in mice was blocked.

Lactamimides: a novel chemical class of calcium antagonists with diltiazem-like properties

The effects of a series of lactamimides on [3H]d-cis-diltiazem binding to rat brain membranes, on [3H]nitrendipine binding to cardiac membranes, and on calcium-induced contractions in depolarized guinea pig taenia and ileum preparations were examined. Several of the lactamimides examined displaced [3H]d-cis-diltiazem binding and antagonized, in a competitive fashion, calcium-induced contractions. Over the series of lactamimides, there was a highly significant, positive linear correlation (r = 0.87, P less than 0.001) between their potency to displace [3H]d-cis-diltiazem and their potency to antagonize calcium-induced contractions in the depolarized taenia and ileum preparations. Of the lactamimides examined, MDL 16,582A [N-(2,2-diphenylpentyl)azacyclotridecan-2-imine. hydrochloride] had potency equivalent to d-cis-diltiazem with pA2 values of 7.27 and 7.38, respectively, against calcium-induced contractions in the guinea pig ileum. These lactamimides are a novel chemical class displaying diltiazem-like calcium antagonist properties.

The effects of chronic treatment with amitriptyline and MDL 72394 on the control of 5-HT release in vivo

The purpose of the experiments reported were to determine whether chronic treatment with either a monoamine oxidase (MAO) inhibitor or an uptake inhibitor would increase extracellular levels of 5-HT in vivo and whether such treatment resulted in a down-regulation of the 5-HT1B-mediated decrease in extracellular levels of 5-HT. Rats were given either saline, (E)-beta-fluoromethyline-m-tyrosine (MDL 72394 0.25 mg/kg p.o.) or amitriptyline (10 mg/kg p.o.) once a day for 21 days. Twenty-four hr after the final injection, dialysis loops were implanted into the frontal cortices of these rats and basal extracellular levels of 5-HT were measured. The effect of the 5-HT1 receptor agonist 5-methoxy-3(1,2,3,6-tetrahydropyridin-4-yl)1H indole succinate (RU 24969 10 mg/kg i.p.) on the extracellular level of 5-HT was then studied. Basal levels of 5-HT in saline-treated rats was found to be 27.9 +/- 3.9 fmol/20 microliters perfusate. Chronic treatment with amitriptyline had no effect on extracellular levels of 5-HT but chronic treatment with MDL 72394 significantly increased extracellular levels of 5-HT. Chronic treatment with either MDL 72394 or amitriptyline had no significant effect on the ability of RU 24969 to reduce extracellular levels of 5-HT. These results suggest that 5-HT1B receptors are not down-regulated in response to chronically raised extracellular levels of 5-HT.

Effect of acute and chronic MDL 73,147EF, a 5-HT3 receptor antagonist, on A9 and A10 dopamine neurons

MDL 73,147EF (1H-indole-3-carboxylic acid-trans-octahydro-3-oxo-2,6- methano-2H-quinolizin-8-yl-ester methanesulphonate) is a potent and selective 5-HT3 receptor antagonist (pA2 9.8, rabbit heart; pIC50 less than 5, D-2 receptor). The effects of acutely and chronically administered haloperidol and MDL 73,147EF were compared in an electrophysiologic model for antipsychotic activity. Haloperidol, but not MDL 73,147EF, given acutely increased the number of active dopamine neurons in the substantia nigra (A9). Both haloperidol and MDL 73,147EF, given chronically, decreased the number of active ventral tegmental dopamine neurons and the number of active A9 dopamine neurons. The results indicate that MDL 73,147EF may prove useful as an antipsychotic with a unique mechanism of action.

Chronic MAO A and MAO B inhibition decreases the 5-HT1A receptor-mediated inhibition of forskolin-stimulated adenylate cyclase

The effect of chronic administration of various monoamine oxidase (MAO) inhibitors on the ability of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to inhibit forskolin-stimulated adenylate cyclase activity was studied. Groups of 12 rats were given either saline, (E)-beta-fluoromethylene-m-tyrosine (MDL 72394 0.25 mg/kg p.o.), clorgyline (1 mg/kg p.o.), selegiline (1 mg/kg p.o.) or tranylcypromine (5 mg/kg p.o.) once a day for 21 days. Biochemical determinations were made 72 h after the final dose. MDL 72394 and tranylcypromine produced a nonselective inhibition of MAO but clorgyline and selegiline selectively inhibited MAO A and MAO B respectively. All treatments that inhibited MAO A also increased tissue levels of 5-HT. Chronic treatment with MDL 72394, clorgyline or tranylcypromine reduced the ability of 8-OH-DPAT to inhibit forskolin-stimulated adenylate cyclase activity. These data suggest that chronic nonselective and chronic MAO A inhibition causes a down-regulation of the 5-HT1A-mediated inhibition of forskolin-stimulated adenylate cyclase activity.

Relationship between extracellular 5-hydroxytryptamine and behaviour following monoamine oxidase inhibition and L-tryptophan

1. The present study investigates the effects of selective and a non-selective monoamine oxidase (MAO) inhibitors combined with L-tryptophan on MAO-A and -B activity, hypothalamic extracellular 5-hydroxytryptamine (5-HT) in vivo and the occurrence of the 5-HT behavioural syndrome. 2. Selective inhibition of intraneuronal MAO-A with MDL 72394 (0.5 mg kg-1, i.p.) had no effect on extracellular 5-HT and following administration of L-tryptophan (50 mg kg-1, i.p.) the 5-HT behavioural syndrome was not induced. 3. Selective inhibition of MAO-A at all sites with clorgyline (5 mg kg-1, i.p.) increased extracellular 5-HT but did not induce the 5-HT behavioural syndrome when combined with L-tryptophan administration. 4. Selective inhibition of MAO-B with selegiline (10 mg kg-1, i.p.) had no effect on extracellular 5-HT and the 5-HT behavioural syndrome was not observed after L-tryptophan administration. 5. Inhibition of MAO-A and -B with a higher and therefore non-selective, dose of MDL 72394 (2 mg kg-1) markedly increased extracellular 5-HT but failed to induce the 5-HT behavioural syndrome after L-tryptophan administration. 6. Inhibition of MAO-A and -B at all sites in the brain (tranylcypromine 20 mg kg-1, i.p. or clorgyline 5 mg kg-1 plus selegiline 10 mg kg-1) increased extracellular 5-HT and induced the behavioural syndrome on administration of L-tryptophan. 7. The results demonstrate that inhibition of MAO-A and -B both within amine neurones and elsewhere in the brain is essential for the development of the 5-HT behavioural syndrome. Whilst the syndrome is associated with increased extracellular 5-HT this does not appear necessarily to result in the syndrome and may indicate that increased extracellular 5-HT is not solely involved in the induction of the '5-HT behavioural syndrome'. Whilst the syndrome is associated with increased extracellular 5-HT this does not appear necessarily to result in the syndrome and may indicate that increased extracellular 5-HT is not solely involved in the induction of the '5-HT behavioural syndrome'.

Design and early clinical evaluation of selective inhibitors of monoamine oxidase

1. Selective inhibitors of the monoamine oxidase (MAO) isoenzymes, types A and B, are of potential therapeutic utility. Brain selectivity would overcome the risk of tyramine interactions which have been shown to occur with selective MAO-A but not MAO-B inhibitors. 2. (E)-3-Fluoroallylamines of general structure, FHC = C(R)CH2NH2 have been designed as enzyme-activated, irreversible inhibitors of these enzymes. Two compounds, MDL 72145 (R = 3,4 dimethoxyphenyl) and MDL 72974 (R = 4-fluorophenethyl), are selective and irreversible inhibitors of MAO type B which in vivo show high inhibitory potency against the rat brain enzyme (ED50 0.35 and 0.18 mg/kg p.o., respectively). In animals, these inhibitors do not potentiate the cardiovascular effects of tyramine and have no amphetamine-like effects. However, they do potentiate the central effects of L-Dopa and prevent the neurotoxic effects of MPTP in both mice and monkeys. 3. In early clinical studies, MDL 72145 has been shown to be a potent, long-acting inhibitor of MAO type B. Doses of 16 mg per patient totally inhibit platelet enzyme without potentiating the cardiovascular effects of oral tyramine. Compounds of this type should prove useful in Parkinson's disease. 4. Selective inhibition of brain MAO-A can be achieved by using the bioprecursor amino acid MDL 72394 (E-beta-fluoromethylene-m-tyrosine). This amino acid is decarboxylated by aromatic L-amino acid decarboxylase (AADC) to liberate MDL 72392 (R = 3-hydroxyphenyl), a potent irreversible inhibitor of MAO-A. Combination of MDL 72394 with a peripherally selective inhibitor of AADC (e.g., carbidopa) restricts MAO inhibition to the brain. Consequently, under these conditions, there is a greatly reduced propensity to potentiate the cardiovascular effects of tyramine. 5. This has been confirmed in human volunteers; MDL 72394 (8 mg), combined with carbidopa, substantially decreased urinary MHPG and plasma DHPG concentrations with minimal potentiation of the cardiovascular effects of i.v. tyramine. These results predict that such therapy has potential in the treatment of affective disorders.

Inhibition of rat aorta semicarbazide-sensitive amine oxidase by 2-phenyl-3-haloallylamines and related compounds

The inhibition of semicarbazide-sensitive amine oxidase (SSAO) in rat aorta homogenates by some 2-phenyl-3-haloallylamines has been studied. Derivatives containing a fluorine atom were approximately three times more potent than the corresponding 3-chloroallylamines. These halogen-containing compounds were irreversible inhibitors of SSAO after preincubation with aorta homogenates; kinetic evidence for an initial competitive, reversible interaction (Ki around 0.4-0.6 microM) was found with two compounds (MDL 72145 and 72274). A similar Ki (approx. 0.7 microM) was obtained with 2-phenylallylamine (MDL 72200). However, this compound which lacks a halogen atom was a reversible inhibitor, even after preincubation. The use of a spectrophotometric assay to measure H2O2 production from amine metabolism demonstrated that MDL 72200 was a substrate (Km = 1.4 microM) for SSAO, with a Vmax approximately five times smaller than that of benzylamine (Km = 8.1 microM). Of particular interest in this study is the finding that (E)-2-phenyl-3-chloroallylamine (MDL 72274) is highly selective as an inhibitor of SSAO, compared with MAO-A or B activities, and may be a useful compound for investigating the importance of SSAO in animal tissues.

Monoamine receptor sensitivity changes following chronic administration of MDL 72394, a site-directed inhibitor of monoamine oxidase

(E)-beta-Fluoromethylene-m-tyrosine (MDL 72394) is not per se an inhibitor of monoamine oxidase (MAO) but is a substrate of aromatic L-amino acid decarboxylase (AADC) which liberates the potent MAO inhibitor (E)-beta-fluoromethylene-m-tyramine (MDL 72392). When co-administered to animals with the peripherally selective AADC inhibitor, carbidopa, MDL 72394 inhibited MAO selectively in the brain. Chronic (14 days plus 3 days withdrawal) administration of 0.5 mg/kg per day p.o. MDL 72394, 0.1 mg/kg per day p.o. MDL 72394 combined with 10 mg/kg per day p.o. carbidopa or 50 mg/kg per day p.o. pargyline produced equivalent inhibition of rat brain MAO and decreased the binding of [3H]clonidine and [3H]RX 781094 to the alpha 2-adrenoceptor and of [3H]dihydroalprenolol to the beta-adrenoceptor without changing binding of [3H]prazosin to the alpha 1-adrenoceptor. The locomotor depressant effect of clonidine was attenuated without attenuation of the hypotensive effect in rats treated chronically with the MAO inhibitors. Neither the sensitivity of the alpha 2-autoreceptor nor of the alpha 2-heteroreceptor was decreased in brain slices. However, the sensitivity of adenylate cyclase to activation by both noradrenaline and isoprenaline was significantly reduced. The number of 5-HT2 and 5-HT1A binding sites was decreased: the 5-HT1B binding sites remained unchanged. The effect of chronic MAO inhibitor treatment on 5-HT1A receptors was associated with a decrease in the behavioural response to 8-hydroxy-2-(di-n-propylamino)tetralin and the decrease in 5-HT2 binding was related to a small reduction in the sensitivity of the inositol phosphate system to stimulation by 5-HT. The lack of effect of chronic MAO treatment on the 5-HT autoreceptor measured in cortical slices corresponded to a lack of effect on the 5-HT1B binding site except that chronic administration of pargyline produced a small but significant decrease in 5-HT autoreceptor sensitivity. Overall, the data show that chronic administration of MDL 72394 has a profile of effects on central monoamine receptor binding and function similar to that seen following chronic administration of a number of clinically effective antidepressants.

Selective inhibition of monoamine oxidase type B by MDL 72145 increases the central effects of L-dopa without modifying its cardiovascular effects

The potential of a new, potent, irreversible and selective inhibitor of monoamine oxidase type B, (E)-2-(3,4-dimethoxyphenyl)-3-fluorallyamine (MDL 72145), to augment the effects of L-DOPA in an animal model which reproduces the biochemical defect of Parkinson's disease has been evaluated. In rats bearing unilateral 6-hydroxydopamine lesions of the nigro-striatal dopamine pathways, both MDL 72145 and clorgyline, a selective inhibitor of MAO A, augmented the contralateral turning response to L-DOPA combined with carbidopa. The potential of inhibitors of MAO to interact adversely in the periphery with L-DOPA was investigated in the pithed rat; L-DOPA was given either intravenously or intraduodenally. Clorgyline consistently potentiated L-DOPA when given 18 h before testing. Neither MDL 72145 nor the selective inhibitor of MAO B, L-deprenyl, augmented the cardiovascular effects of intraduodenally administered L-DOPA. The data provide no reason to suppose that MDL 72145 would be very different in clinical use from L-deprenyl which is both effective and well-tolerated as an adjunct to the L-DOPA-based therapy of Parkinson's disease.

Inhibition of monoamine oxidase selectively in brain monoamine nerves using the bioprecursor (E)-beta-fluoromethylene-m-tyrosine (MDL 72394), a substrate for aromatic L-amino acid decarboxylase

(E)-beta-Fluoromethylene-m-tyrosine (FMMT) is a dual-enzyme-activated inhibitor of monoamine oxidase (MAO). The compound is not an inhibitor per se but is decarboxylated by aromatic L-amino acid decarboxylase (AADC) to yield a potent enzyme-activated irreversible inhibitor of MAO, (E)-beta-fluoromethylene-m-tyramine, which shows some selectivity for inhibition of MAO type A. Decarboxylation of FMMT was demonstrated in vitro using hog kidney AADC and in vivo in rats by the ability of alpha-monofluoromethyldopa (MFMD), a potent inhibitor of AADC, to prevent MAO inhibition produced by FMMT. In isolated synaptosomes, FMMT was decarboxylated by AADC, and, furthermore, the compound was actively transported into these isolated nerve endings. An active transport into the CNS has also been demonstrated in vivo by performing competition experiments with leucine. To demonstrate that FMMT is preferentially decarboxylated within monoamine nerves of the CNS, the nigrostriatal 3,4-dihydroxyphenylethylamine (dopamine) pathway of rats was unilaterally lesioned with 6-hydroxydopamine or infused with MFMD. Under these conditions, MAO inhibition produced by orally administered FMMT in the striatum ipsilateral to the lesion or infusion was markedly attenuated. Combination of FMMT with an inhibitor of extracerebral AADC, such as carbidopa, protected peripheral organs against the MAO inhibitory effects and concomitantly enhanced MAO inhibition in the CNS. Such combinations had a greatly reduced propensity to augment the cardiovascular effects of intraduodenally administered tyramine, when compared with FMMT given alone or with clorgyline, a selective inhibitor of MAO type A. The results obtained with FMMT suggest the possibility of achieving selective inhibition of MAO within monoamine nerves of the CNS and, further, suggest that combination of FMMT with an inhibitor of extracerebral AADC will reduce the propensity of this inhibitor to produce adverse interactions with tyramine.

The functional consequences of inhibition of monoamine oxidase type B: comparison of the pharmacological properties of L-deprenyl and MDL 72145

The pharmacological properties of two selective inhibitors of monoamine oxidase (MAO) type B, L-deprenyl and MDL 72145 [(E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine, HCl], have been investigated in rats and mice in relation to their effects on MAO. Selective inhibition of MAO B achieved following 18 h pretreatment with L-deprenyl and/or MDL 72145 did not per se lead to prominent pharmacological activity; no effects were seen in the mouse "Behavioural Despair" test, hypothermia induced by reserpine in mice was neither prevented nor reversed and there was no change in the cardiovascular responsiveness of the pithed rat to tyramine, noradrenaline or stimulation of the spinal sympathetic outflow. L-Deprenyl differed from MDL 72145 in that short term treatment with this drug caused positive effects in the "Behavioural Despair" test, reversal of reserpine hypothermia, indirect sympathomimetic stimulation of blood pressure and heart rate in the pithed rat and ipsilateral rotation in rats with unilateral nigro-striatal lesions. Qualitatively similar effects were seen with dexamphetamine. The marked difference between the pharmacological effects of MDL 72145 and L-deprenyl despite equivalent inhibition of MAO B suggests that many of the pharmacological actions of L-deprenyl result from its amphetamine-like sympathomimetic properties. MDL 72145 can, therefore, be considered a more reliable tool with which to explore the functional importance of MAO B inhibition in experimental animals and man.

Effect of chronic apomorphine on the development of denervation supersensitivity

We hypothesised that it would be possible to prevent the development of post-synaptic dopamine receptor supersensitivity to 6-hydroxydopamine lesions of the nigro-striatal tract in rats if they were constantly infused with the dopamine agonist apomorphine. Using osmotic minipumps to infuse apomorphine for 15 days in unilaterally lesioned rats, it was possible to delay the development of supersensitivity of the lesioned side for 9 days but not to prevent its eventual appearance. At the same time, evidence for the development of subsensitivity of presynaptic dopamine receptors of the intact side following chronic infusion of apomorphine was inferred from the production of rotations directed towards the lesioned side.

Enzyme-activated irreversible inhibitors of monoamine oxidase: phenylallylamine structure-activity relationships

Seventeen 2-aryl-3-haloallylamine derivatives were prepared and evaluated as inhibitors of monoamine oxidase (MAO, EC 1.4.3.4). The synthesis of these compounds was achieved from either alpha-methylstyrene or ring-substituted phenylacetic acid derivatives. With one exception, these 2-arylallylamines were found to be enzyme-activated, irreversible inhibitors of MAO. The most potent inhibitors were ring-substituted derivatives of (E)-2-phenyl-3-fluoroallylamine with IC50 values ranging from 10(-6) to 10(-8) M. Selectivity for the A and B form of MAO was found to depend on the nature of aromatic ring substitution. In general, hydroxyl substitution favored the inactivation of the A form of MAO, while very selective B inhibitors were obtained when the aromatic ring was substituted with a 4-methoxy group. (E)-2-(4-Methoxyphenyl)-3-fluoroallylamine and (E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine proved to be in vitro as selective for the B form of MAO as deprenyl.

MDL 72145, an enzyme-activated irreversible inhibitor with selectivity for monoamine oxidase type B

MDL 72145, (E)-2-(3',4'-dimethoxyphenyl)-3-fluoroallylamine hydrochloride, was designed and synthesised as a potential enzyme-activated irreversible inhibitor of monoamine oxidase (MAO). In vitro, the compound displayed time-dependent pseudo-first-order irreversible inhibitory characteristics with high selectivity for the B form of rat brain mitochondrial MAO. At 10 degrees C the Ki and tau 50 values for the B enzyme were 40 microM and 1.7 min, respectively, while these same kinetic constants for the A enzyme were 131 microM and 14.5 min, respectively. Selective protection against inactivation of the two forms of MAO by MDL 72145 was obtained by preincubating the enzyme with suitable concentrations of the selective A and B substrates, 5-hydroxytryptamine and benzylamine.

A method for measuring monoamine turnover in animals using an irreversible inhibitor of aromatic L-amino acid decarboxylase, DL-alpha-mono fluoromethyldopa

DL-alpha-monofluoromethyldopa (MFMD) is a potent enzyme-activated irreversible inhibitor of aromatic L-amino acid decarboxylase which, when given to rats or mice at 100 and 250 mg/kg i.p., respectively, causes a linear accumulation of L-DOPA and 5HTP and an exponential decline of noradrenaline, dopamine, and 5HT concentrations in the brain. Rates of change of these parameters can be used to calculate the turnover of the three principle monoamine neurotransmitters. Experiments with haloperidol (1 mg/kg s.c.) and the central 5HT agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (0.25 mg/kg s.c.), have been performed to validate the use of MFMD to measure monoamine turnover. MFMD has several advantages over classical methods for the determination of comparative turnovers using enzyme inhibitors.

High-performance liquid chromatographic analysis of S-adenosylmethionine and its metabolites in rat tissues: interrelationship with changes in biogenic catechol levels following treatment with L-dopa

A method is described for the simultaneous analysis of S-adenosylmethionine (SAM) and its metabolites, S-adenosylhomocysteine (SAH) and decarboxylated S-adenosylmethionine along with the natural polyamines, putrescine, spermidine and spermine. The separation is obtained by a reversed-phase ion-pair liquid chromatographic procedure with gradient elution followed by dual detection. The UV absorbance at 254 nm is used for the analysis of SAM and of the SAM metabolites, whereas the polyamines and some major amino acids, e.g., methionine, tyrosine and tryptophan, are analyzed by fluorescence detection after UV-cell derivatization with o-phthalaldehyde. A separate ion-pair reversed-phase high-performance liquid chromatographic (HPLC) procedure using isocratic elution and electrochemical detection is employed to analyse in the same tissue extracts the catechols and 5-hydroxyindoles, 3,4-dihydroxyphenylalanine (DOPA), dopamine, norepinephrine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 4-hydroxy-3- methoxyphenylalanine , tryptophan, 5-hydroxytryptophan, serotonin and 5- hydroxyindolacetic acid. The sample preparation for the two HPLC procedures requires only homogenization of the tissues in perchloric acid and centrifugation before injection onto the column. The two chromatographic procedures have been applied to study the interrelationship, in various tissues of rats, between the SAM and SAH levels and the biogenic catechols after different treatments with L-DOPA alone or in combination with alpha- monofluoromethyl -DOPA, a potent enzyme-activated irreversible inhibitor of aromatic L-amino acid decarboxylase.