Antiparasitic activities of novel, orally available fumagillin analogs

Fumagillin, an irreversible inhibitor of MetAP2, has been shown to potently inhibit growth of malaria parasites in vitro. Here, we demonstrate activity of fumagillin analogs with an improved pharmacokinetic profile against malaria parasites, trypanosomes, and amoebas. A subset of the compounds showed efficacy in a murine malaria model. The observed SAR forms a basis for further optimization of fumagillin based inhibitors against parasitic targets by inhibition of MetAP2.

Evaluation of cryptolepine and huperzine derivatives as lead compounds towards new agents for the treatment of human African trypanosomiasis

The alkaloid cryptolepine (1) and eight synthetic analogues (2-8) were assessed for in vitro activities against Trypanosoma brucei. Four of the analogues were found to be highly potent with IC50 values of less than 3 nM and three of these were assessed against T. brucei brucei infection in rats. The most effective compound was 2, 7-dibromocryptolepine (7); a single oral dose of 20 mg/kg suppressed parasitaemia and increased the mean survival time to 13.6 days compared with 8.4 days for untreated controls. In addition, four huperzine derivatives (9-12) were shown to have in vitro antitrypanosomal activities with IC50 values ranging from 303-377 nM.

Evaluation of Cryptolepine and Huperzine Derivatives as Lead Compounds towards New Agents for the Treatment of Human African Trypanosomiasis

The alkaloid cryptolepine (1) and eight synthetic analogues (2-8) were assessed for in vitro activities against Trypanosoma brucei. Four of the analogues were found to be highly potent with IC50values of less than 3 nM and three of these were assessed against T. brucei brucei infection in rats. The most effective compound was 2, 7-dibromocryptolepine (7); a single oral dose of 20 mg/kg suppressed parasitaemia and increased the mean survival time to 13.6 days compared with 8.4 days for untreated controls. In addition, four huperzine derivatives (9-12) were shown to have in vitro antitrypanosomal activities with IC50values ranging from 303-377 nM.

Synthesis and anti-breast cancer activities of substituted quinolines

Promising anti-breast cancer agents derived from substituted quinolines were discovered. The quinolines were readily synthesized in a large scale from a sequence of reactions starting from 4-acetamidoanisole. The Michael addition product was isolated as the reaction intermediate in the ring closing reaction of 4-amino-5-nitro-2-(3-trifluoromethylphenyloxy)anisole with methyl vinyl ketone leading to 6-methoxy-4-methyl-8-nitro-5-(3-trifluoromethylphenyloxy)quinoline (14). The amino function of 8-amino-6-methoxy-4-methyl-5-(3-trifluoromethylphenyloxy)quinoline, prepared from 14, was connected to various side chains via alkylation with N-(3-iodopropyl)phthalimide, Michael addition with acrylonitrile, and reductive amination with various heterocycle carboxaldehydes, such as imidazole-4-carboxaldehyde, thiophene-2-carboxaldehyde, and 2-furaldehyde. Effects of the substituted quinolines on cell viability of T47D breast cancer cells using trypan blue exclusion assay were examined. The results showed that the IC(50) value of 6-methoxy-8-[(2-furanylmethyl)amino]-4-methyl-5-(3-trifluoromethylphenyloxy)quinoline is 16+/-3nM, the lowest IC(50) out of all the quinolines tested. IC(50) values of three other quinolines are in the nanomolar range, a desirable range for pharmacological testing.

Total syntheses of (+/-)-ovalicin, C4(S *)-isomer, and its C5-analogs and anti-trypanosomal activities

Total syntheses of (+/-)-ovalicin, its C4(S( *))-isomer 44, and C5-side chain intermediate 46 were accomplished via an intramolecular Heck reaction of (Z)-3-(tert-butyldimethylsilyloxy)-1-iodo-1,6-heptadiene and a catalytic amount of palladium acetate. Subsequent epoxidation, dihydroxylation, methylation, and oxidation led to (3S( *),5R( *),6R( *))-5-methoxy-6-(tert-butyldimethylsilyloxy)-1-oxaspiro[2.5]octan-4-one (2), a reported intermediate. The addition of a side chain with cis-1-lithio-1,5-dimethyl-1,4-hexadiene (27) followed by oxidation afforded (+/-)-ovalicin. The functional group manipulation afforded a number of regio- and stereoisomers, which allow the synthesis of analogs for bioevaluation. The structure of 44 was firmly established via a single-crystal X-ray analysis. The stereochemistry at C4 generated from the addition reactions of alkenyllithium with ketones 2, 40, and 45 is dictated by C6-alkoxy functionality. Anti-trypanosomal activities of various ovalicin analogs and synthetic intermediates were evaluated, and C5-side chain analog, 46, shows the strongest activity. Compound 44 shows antiproliferative effect against HL-60 tumor cells in vitro. Compounds 46 and a precursor, (3S( *),4R( *),5R( *),6R( *))-5-methoxy-4-[(E)-(1',5'-dimethylhexa-1',4'-dienyl)]-6-(tert-butyldimethylsilyloxy)-1-oxaspiro[2.5]octan-4-ol (28), may be explored for the development of anti-parasitic drugs.

Discovery of trypanocidal compounds by whole cell HTS of Trypanosoma brucei

Chemotherapy against human African trypanosomiasis relies on four drugs that cause frequent and occasionally severe side-effects. Because human African trypanosomiasis is a disease of poor people in Africa, the traditional market-driven pathways to drug development are not available. One potentially rapid and cost-effective approach to identifying and developing new trypanocidal drugs would be high throughput-screening of existing drugs already approved for other uses, as well as clinical candidates in late development. We have developed an ATP-bioluminescence assay that could be used to rapidly and efficiently screen compound libraries against trypanosomes in a high throughput-screening format to validate this notion. We screened a collection of 2160 FDA-approved drugs, bioactive compounds and natural products to identify hits that were cytotoxic to cultured Trypanosoma brucei at a concentration of 1 mum or less. This meant that any hit identified would be effective at a concentration readily achievable by standard drug dosing in humans. From the screen, 35 hits from seven different drug categories were identified. These included the two approved trypanocidal drugs, suramin and pentamidine, several other drugs suspected but never validated as trypanocidal, and 17 novel trypanocidal drugs.

Malaria: therapy, genes and vaccines

Malaria kills over 3,000 children each day. Modern molecular and biochemical approaches are being used to help understand and control Plasmodium falciparum, the parasite that causes this deadly disease. New drugs are being invented for both chemoprophylaxis and therapeutic treatments and their use is discussed along side that of the more commonly used treatments. Classical genetic crosses coupled with molecular analysis of gene loci are use to explain the genetics behind the development of specific drug resistances that the parasites have naturally developed. Rapid advances in DNA sequencing techniques have allowed the compete sequencing of the P. falciparum and several other rodent malaria parasite genomes. Proteomics and computational analysis of these vast databanks are being used to model and investigate the three-dimensional structure of many key malaria proteins in an attempt to facilitate drug design. Recombinant protein expression in bacteria and yeast coupled with cGMP purification technologies and conditions have lead to the recent availability of several dozen malaria protein antigens for human-use Phase I and Phase II vaccine trials. Drug companies, private foundations, and key government agencies have contributed to the coordinated efforts needed to test these antigens, adjuvants and delivery methods in an effort to find an effective malaria vaccine that will prevent infection and disease.

Antitrypanosomal activity of 5'-deoxy-5'-(iodomethylene)adenosine and related 6-N-cyclopropyladenosine analogues

Treatment of the 6-N-cyclopropyl-2',3'-di-O-isopropylideneadenosine 5'-aldehyde with sulfone-stabilized phosphonate or fluorophosphonate reagents followed by stannyldesulfonylations and subsequent iodo- or protiodestannylation gave 6-N-cyclopropyl-5'-deoxy-5'-(iodomethylene)adenosine 8b or its 5'-fluoromethylene analogue 11. Treatment of the 5'-aldehyde with hydroxylamine or dibromomethylene- or cyanomethylene-stabilized Wittig reagents and deprotections gave the oxime 4b, 5'-cyanomethylene 5b, and 5'-dibromomethylene 13b analogues. Dehydrobromination of 13b gave acetylenic compound 14b. From the tested 6-N-cyclopropyladenosine analogues modified at the 5' carbon, the 5'-iodomethylene 8b had the most potent activity against Trypanosoma brucei in vitro with an IC50 of 12 microg/mL. The IC50 value was 19 microg/mL for both the 5'-fluoromethylene 11 and the 5'-cyanomethylene 5b compounds. The (E)-5'-deoxy-5'-(iodomethylene)adenosine 2a, a known inhibitor of AdoHcy hydrolase not modified with a cyclopropyl ring at 6-amino group, also inhibited T. brucei with an IC50 of 9 microg/mL. In contrast to some other adenosine analogues modified at C5', the 6-N-cyclopropyladenosine analogues described here do not exhibit an inhibitory effect on AdoHcy hydrolase and displayed only marginal antiviral activity.

Antiprotozoal activities of symmetrical bishydroxamic acids

Symmetrical bishydroxamic acids along with their sodium salts containing an alkyl spacer between two aromatic rings were synthesized, and their antiparasitic activities were evaluated. Bishydroxamic acids were conveniently prepared from the alkylation of methyl 4-hydroxybenzoate with various dihalo-alkane, -alkene, and -ether followed by reaction with hydroxylamine. Surprisingly, the bishydroxamic acids and their sodium salts possess strong inhibitory activities against Plasmodium falciparum parasites with IC50 values in the range of 0.26-3.2 microM. Bishydroxamic acid 3 and its sodium salt 12 also inhibit the growth of Leishmania donovani, albeit at higher concentrations. The corresponding biscarboxylic acids and bismethyl esters are inactive. Presumably, the ability of bishydroxamic acids to complex with metallic iron in hemoglobin may be responsible for antimalarial activity of these compounds.

Anti-HIV-1 activity of 3-deaza-adenosine analogs. Inhibition of S-adenosylhomocysteine hydrolase and nucleotide congeners

Eight adenosine analogs, 3-deaza-adenosine (DZA), 3-deaza-(+/-)aristeromycin (DZAri), 2',3'-dideoxy-adenosine (ddAdo), 2',3'-dideoxy-3-deaza-adenosine (ddDZA), 2',3'-dideoxy-3-deaza-(+/-)aristeromycin (ddDZAri), 3-deaza-5'-(+/-)noraristeromycin (DZNAri), 3-deaza-neplanocin A (DZNep), and neplanocin A (NepA), were tested as inhibitors of human placenta S-adenosylhomocysteine (AdoHcy) hydrolase. The order of potency for the inhibition of human placental AdoHcy hydrolase was: DZNep approximately NepA >> DZAri approximately DZNAri > DZA >> ddAdo approximately ddDZA approximately ddDZAri. These same analogs were examined for their anti-HIV-1 activities measured by the reduction in p24 antigen produced by 3'-azido-3'-deoxythymidine (AZT)-sensitive HIV-1 isolates, A012 and A018, in phytohemagglutinin-stimulated peripheral blood mononuclear (PBMCs) cells. Interestingly, DZNAri and the 2',3'-dideoxy 3-deaza-nucleosides (ddAdo, ddDZAri, and ddDZA) were only marginal inhibitors of p24 antigen production in HIV-1 infected PBMC. DZNAri is unique because it is the only DZA analog with a deleted methylene group that precludes anabolic phosphorylation. In contrast, the other analogs were potent inhibitors of p24 antigen production by both HIV-1 isolates. Thus it was postulated that these nucleoside analogs could exert their antiviral effect via a combination of anabolically generated nucleotides (with the exception of DZNAri), which could inhibit reverse transcriptase or other viral enzymes, and the inhibition of viral or cellular methylation reactions. Additionally, QSAR-like models based on the molecular mechanics (MM) were developed to predict the order of potency of eight adenosine analogs for the inhibition of human AdoHcy hydrolase. In view of the potent antiviral activities of the DZA analogs, this approach provides a promising tool for designing and screening of more potent AdoHcy hydrolase inhibitors and antiviral agents.

Structure, evolution, and inhibitor interaction of S-adenosyl-L-homocysteine hydrolase from Plasmodium falciparum

S-adenosylhomocysteine hydrolase (SAHH) is a key regulator of S-adenosylmethionine-dependent methylation reactions and an interesting pharmacologic target. We cloned the SAHH gene from Plasmodium falciparum (PfSAHH), with an amino acid sequence agreeing with that of the PlasmoDB genomic database. Even though the expressed recombinant enzyme, PfSAHH, could use 3-deaza-adenosine (DZA) as an alternative substrate in contrast to the human SAHH, it has a unique inability to substitute 3-deaza-(+/-)aristeromycin (DZAri) for adenosine. Among the analogs of DZA, including neplanocin A, DZAri was the most potent inhibitor of the PfSAHH enzyme activity, with a K(i) of about 150 nM, whether Ado or DZA was used as a substrate. When the same DZA analogs were tested for their antimalarial activity, they also inhibited the in vitro growth of P. falciparum parasites potently. Homology-modeling analysis revealed that a single substitution (Thr60-Cys59) between the human and malarial PfSAHH, in an otherwise similar SAH-binding pocket, might account for the differential interactions with the nucleoside analogs. This subtle difference in the active site may be exploited in the development of novel drugs that selectively inhibit PfSAHH. We performed a comprehensive phylogenetic analysis of the SAHH superfamily and inferred that SAHH evolved in the common ancestor of Archaea and Eukaryota, and was subsequently horizontally transferred to Bacteria. Additionally, an analysis of the unusual and uncharacterized AHCYL1 family of the SAHH paralogs extant only in animals reveals striking divergence of its SAH-binding pocket and the loss of key conserved residues, thus suggesting an evolution of novel function(s).

Gene expressions in Jurkat cells poisoned by a sulphur mustard vesicant and the induction of apoptosis

1. The sulphur mustard vesicant 2-chloroethylethyl sulphide (CEES) induced apoptosis in Jurkat cells. 2. Akt (PKB), a pivotal protein kinase which can block apoptosis and promotes cell survival, was identified to be chiefly down-regulated in a dose-dependent manner following CEES treatment. Functional analysis showed that the attendant Akt activity was simultaneously reduced. 3. PDK1, an upstream effector of Akt, was also down-regulated following CEES exposure, but two other upstream effectors of Akt, PI3-K and PDK2, remained unchanged. 4. The phosphorylation of Akt at Ser(473) and Thr(308) was significantly decreased following CEES treatment, reflecting the suppressed kinase activity of both PDK1 and PDK2. 5. Concurrently, the anti-apoptotic genes, Bcl family, were down-regulated, in sharp contrast to the striking up-regulation of some death executioner genes, caspase 3, 6, and 8. 6. Based on these findings, a model of CEES-induced apoptosis was established. These results suggest that CEES attacked the Akt pathway, directly or indirectly, by inhibiting Akt transcription, translation, and post-translation modification. 7. Taken together, upon exposure to CEES, apoptosis was induced in Jurkat cells via the down-regulation of the survival factors that normally prevent the activation of the death executioner genes, the caspases.

Syntheses and bioactivities of substituted 9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrones. Unusual reactivities with amines

A number of substituted 9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrones have been synthesized and their anticancer and antimalarial activities evaluated. A one-pot synthesis of 2,5,8-trimethoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione (4) was achieved by heating a mixture of 1,4-dimethoxyanthracene, methoxyhydroquinone, silver oxide, and zinc iodide in toluene. Regioselective bromination of 4 and 2-methoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone (7) with N-bromosuccinimide provided 2-bromo-3,5,8-trimethoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione and 2-bromo-3-methoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone (1), respectively. The reactions of 1 with aliphatic primary amines and secondary amines, respectively, produced different products, a result most likely attributed to the different basicities (or nucleophilicities) and steric effects of the two kinds of amines. The structure of the displacement product, 2-bromo-3-[2-(tert-butoxycarbonyl)ethylamino]-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone, from the reaction of 1 with tert-butyl 3-aminopropanoate was unequivocally determined by a single-crystal X-ray analysis. IC(50) values of triptycene bisquinones for the inhibition of L1210 leukemia cell viability are in the 0.11-0.27 microM range and for the inhibition of Plasmodium falciparum 3D7 are in the 4.7-8.0 microM range.

Pyridophens: binary pyridostigmine-aprophen prodrugs with differential inhibition of acetylcholinesterase, butyrylcholinesterase, and muscarinic receptors

A series of "binary prodrugs" called carbaphens,(1) carbamylated derivatives on one or both of the aromatic rings of the muscarinic receptor antagonist aprophen [(N,N-diethylamino)ethyl 2,2-diphenylpropionate], were synthesized to develop binary prophylactic agents against organophosphorus intoxication. As a group, the carbaphens retained the muscarinic receptor antagonist properties of aprophen but also preferentially inhibited butyrylcholinesterase (BChE) in contrast to acetylcholinesterase (AChE). Therefore, a new series of compounds named pyridophens were designed and synthesized to achieve binary prodrugs to preferentially inhibit AChE over BChE, while still retaining the muscarinic receptor antagonism of aprophen. The pyridophens consist of the basic pyridostigmine skeleton combined with the 2,2-diphenylpropionate portion of aprophen by replacement of the diethylamino group. Three compounds, 9 (a tertiary pyridine), 10 (a quaternary pyridine), and 12 (a tertiary tetrahydropyridine), were found to be effective inhibitors of both BChE and AChE. However, 10, N-methyl-3-[[(dimethylamino)carbonyl]oxy]-2-(2'2'-diphenylpropionoxy-methyl)pyridinium iodide, inhibited AChE selectively over BChE, with a bimolecular rate constant similar to pyridostigmine. In contrast to their potent cholinesterase inhibitory activity, all of the pyridophen analogues were less potent antagonists of the muscarinic receptor than aprophen.

Angiogenesis inhibitors specific for methionine aminopeptidase 2 as drugs for malaria and leishmaniasis

Methionine aminopeptidase 2 (MetAP2) is responsible for the hydrolysis of the initiator methionine molecule from the majority of newly synthesized proteins. We have cloned the MetAP2 gene from the malaria parasite Plasmodium falciparum (PfMetAP2; GenBank accession number AF348320). The cloned PfMetAP2 has no intron, consists of 1,544 bp and encodes a protein of 354 amino acids with a molecular mass of 40,537 D and an overall base composition of 72.54% A + T. PfMetAP2 has 40% sequence identity with human MetAP2 and 45% identity with yeast MetAP2, and is located in chromosome 14 of P. falciparum. The three-dimensional structure of Pf MetAP2 has been modeled based on the crystal structure of human MetAP2, and several amino acid side chains protruding into the binding pocket that differ between the plasmodial and human enzyme have been identified. The specific MetAP2 inhibitors, fumagillin and TNP-470, potently blocked in vitro growth of P. falciparum and Leishmania donavani, with IC(50) values similar to the prototype drugs. Furthermore, in the case of P. falciparum, the chloroquine-resistant strains are equally susceptible to these two compounds.

Molecular characterization of Plasmodium falciparum S-adenosylmethionine synthetase

S-Adenosylmethionine (AdoMet) synthetase (SAMS: EC 2.5.1.6) catalyses the formation of AdoMet from methionine and ATP. We have cloned a gene for Plasmodium falciparum AdoMet synthetase (PfSAMS) (GenBank accession no. AF097923), consisting of 1209 base pairs with no introns. The gene encodes a polypeptide (PfSAMS) of 402 amino acids with a molecular mass of 44844 Da, and has an overall base composition of 67% A+T. PfSAMS is probably a single copy gene, and was mapped to chromosome 9. The PfSAMS protein is highly homologous to all other SAMS, including a conserved motif for the phosphate-binding P-loop, HGGGAFSGKD, and the signature hexapeptide, GAGDQG. All the active-site amino acids for the binding of ADP, P(i) and metal ions are similarly preserved, matching entirely those of human hepatic SAMS and Escherichia coli SAMS. Molecular modelling of PfSAMS guided by the X-ray crystal structure of E. coli SAMS indicates that PfSAMS binds ATP/Mg(2+) in a manner similar to that seen in the E. coli SAMS structure. However, the PfSAMS model shows that it can not form tetramers as does E. coli SAMS, and is probably a dimer instead. There was a differential sensitivity towards the inhibition by cycloleucine between the expressed PfSAMS and the human hepatic SAMS with K(i) values of 17 and 10 mM, respectively. Based on phylogenetic analysis using protein parsimony and neighbour-joining algorithms, the malarial PfSAMS is closely related to SAMS of other protozoans and plants.

6,7,8,9-Tetrahydro-3-methyl-1H-pyrano-[4,3-b]quinolin-1-one

The condensation reaction of 4-amino-6-methyl-2-pyrone with 1-cyclohexenecarboxaldehyde and a catalytic amount of (S)-(+)-10-camphorsulfonic acid in toluene at 358 K gave a 1:2.5 ratio of the title compound, (1) (C13H13NO2), and 7,8,9,10-tetrahydro-1H-pyrano[4,3-c]isoquinoline-1-one, (2). The formation of (2) presumably proceeds through an intermediate imine. Both (1) and (2) show inhibitory activities against acetylcholinesterase and human aldose reductase. Of the three linear-fused rings of (1), both ring A and ring B are planar and the angle between these planes is 0.46 (13) degrees. While the two C atoms of cyclohexane ring C attached to its common atoms with ring B are in the plane of the latter, as expected, the remaining two C atoms of ring C are out of this plane, by 0.342 (4) and -0.402 (3) A, respectively.

Comparing predictability between eyes after bilateral laser in situ keratomileusis: a theoretical analysis of simultaneous versus sequential procedures

OBJECTIVE

To compare the predictability of laser in situ keratomileusis (LASIK) between eyes of individuals to determine whether the refractive result of the first eye is useful in improving fellow eye outcomes.

DESIGN

Single-center case series.

PARTICIPANTS

One surgeon and 196 eyes of 98 patients.

INTERVENTION

All patients received sequential bilateral LASIK. The mean time between procedures was 11.6 days. Attempted corrections ranged from 2.30 to 12.00 diopters (D).

MAIN OUTCOME MEASURES

Predictability (achieved minus attempted correction), postoperative manifest refraction, and theoretical postoperative manifest refraction, using a proposed attempted correction on the second eye based on first eye results, were analyzed.

RESULTS

At 1 week, 1 month, and 3 months, predictability of the first operated eye was correlated with predictability of the fellow eye (1 week: mean 1st = 0.33 D, mean 2nd = 0.33 D, Pearson coefficient = 0.46, P < 0.0005; 1 month: mean 1st = 0.028 D, mean 2nd = -0.020 D, Pearson coefficient = 0.43, P < 0.0005; 3 months: mean 1st = -0.22 D, mean 2nd = -0.12 D, Pearson coefficient = 0.52, P < 0.0005). At the 3-month follow-up of the second eye, comparing the actual distance from emmetropia with that calculated using a theoretical proposed attempted correction based on the first eye refraction, distance from emmetropia was closer in the theoretical correction group. This finding was stronger in patients with preoperative myopia less than 5.5 D (P = 0.03). For this group, 93% of patients in the proposed attempted correction group would fall within 1.0 D of emmetropia compared to 80% found in the actual outcomes.

CONCLUSIONS

The refractive predictability between the two eyes of an individual after LASIK is correlated. Theoretically, therefore, one may be able to achieve correction closer to emmetropia in the second eye by applying the refractive predictability results from the first operated eye. In this study, using a theoretical proposed attempted correction in the second eye based on the first eye outcome, we have shown that better outcomes in the second eye are possible, particularly in low myopes. Thus, it may be advantageous to perform bilateral LASIK sequentially rather than simultaneously, using predictability outcomes from the first operated eye in planning fellow eye treatment. Moreover, waiting approximately 1 week was found to be potentially as effective as waiting longer periods of time between treatments. Further studies are necessary to better assess the actual clinical significance of these findings.

Encephalocoele as a complication of intranasal sinus surgery: optimal evaluation with magnetic resonance imaging

We report a case of post-operative frontal basal encephalocoele evaluated using a new magnetic resonance imaging (MRI) sequence, fast inversion recovery for myelin suppression (FIRMS). FIRMS was developed to enhance the differentiation between grey and white matter. In this case, the sequence was beneficial in distinguishing the encephalocoele from adjacent nasal mucosa and secretions.

Biological effects of inhibitors of S-adenosylhomocysteine hydrolase

S-Adenosylhomocysteine (AdoHcy), formed after the donation of the methyl group of S-adenosylmethionine to a methyl acceptor, is hydrolyzed to adenosine and homocysteine by AdoHcy hydrolase physiologically. The administration of the inhibitors of AdoHcy hydrolase to cells or animals normally results in an accumulation of cellular AdoHcy higher than those found in controls, which is often accompanied by a simultaneous rise in S-adenosylmethionine because of the feedback inhibition by AdoHcy on most methylation reactions. AdoHcy hydrolase has become a tantalizing pharmacological target for inhibition since its blockade can affect cellular methylation of phospholipids, proteins, small molecules, DNA, and RNA. Indeed, all of these different methylation reactions have been found to be inhibitable by the nucleoside inhibitors/substrates of AdoHcy hydrolase. Among the interesting effects are the activation of genes, induction of cellular differentiation, increased expression of transcription factors, and sometimes the repression of genes. Furthermore, some of the nucleosides show remarkable antiviral activities in vitro and in vivo. However, the mode of action of the inhibitors appears complex. Although the inhibition of methylation might account for some of the biological effects, the ability of some of the nucleoside inhibitors to undergo metabolic phosphorylation to nucleotides may account for part of their biological activities. The defining mode of action responsible for their biological effects still awaits biochemical elaboration, especially regarding their antiviral effects, induction of genes, or cellular differentiation.

Fast inversion recovery for myelin suppression (FIRMS). A new magnetic resonance pulse sequence

Fast inversion recovery for myelin suppression is a new magnetic resonance sequence with the ability to increase gray-white matter contrast. This can improve the definition of normal anatomical structures.

Induction of proto-oncogenes during 3-deazaadenosine-stimulated differentiation of 3T3-L1 fibroblasts to adipocytes: mimicry of insulin action

3-Deazaadenosine (DZA) mimicked the molecular action of insulin in the induction of 3T3-L1 fibroblasts to differentiate into adipocytes. The molecular effects of DZA were compared with insulin, which served as a positive control, on the expression of proto-oncogenes during the initial stage of differentiation of 3T3-L1 fibroblasts. Treatment of confluent 3T3-L1 fibroblasts with DZA or insulin produced a rapid but-transient expression of mRNA for proto-oncogenes c-fos and c-jun within 30-60 min. The mRNA of c-myc increased for 2 h and then decreased 4 h after treatment. Electrophoretic mobility shift assays showed a heightened increase in the appearance of transcription factors AP-1 and AP-2. The increase was detectable as early as 1 h after the treatment with either DZA or insulin and was maintained for 6 h. 3T3-L1 cells stably transfected with the promotor of c-fos linked to a CAT reporter gene showed an increase in CAT activity in response to DZA in a time- and dose-dependent manner. In cells stably transfected with antisense c-fos, neither DZA nor insulin was able to induce a differentiation response. The early transcription of c-fos, c-jun, and c-myc proto-oncogenes and the increased expression of transcription factors AP-1 and AP-2, induced by DZA and insulin, appear to be crucial events in the differentiation of the 3T3-L1 fibroblasts to adipocytes.

S-Adenosylmethionine and methylation

S-Adenosylmethionine (AdoMet or SAM) plays a pivotal role as a methyl donor in a myriad of biological and biochemical events. Although it has been claimed that AdoMet itself has therapeutic benefits, it remains to be established whether it can be taken up intact by cells. S-Adenosylhomocysteine (AdoHcy), formed after donation of the methyl group of AdoMet to a methyl acceptor, is then hydrolyzed to adenosine and homocysteine by AdoHcy hydrolase. This enzyme has long been a target for inhibition as its blockade can affect methylation of phospholipids, proteins, DNA, RNA, and other small molecules. Protein carboxymethylation may be involved in repair functions of aging proteins, and heat shock proteins are methylated in response to stress. Bacterial chemotaxis involves carboxymethylation and demethylation in receptor-transducer proteins, although a similar role in mammalian cells is unclear. The precise role of phospholipid methylation remains open. DNA methylation is related to mammalian gene activities, somatic inheritance, and cellular differentiation. Activation of some genes has been ascribed to the demethylation of critical mCpG loci, and silencing of some genes may be related to the methylation of specific CpG loci. Viral DNA genomes exist in cells as extrachromosomal units and are generally not methylated, although once integrated into host chromosomes, different patterns of methylation are correlated with altered paradigms of transcriptional activity. Some viral latency may be related to DNA methylation. Cellular factors have been found to interact with methylated DNA sequences. Methylation of mammalian ribosomal RNAs occurs soon after the synthesis of its 47S precursor RNA in the nucleolus before cleavage to smaller fragments. Inhibition of the methylation of rRNA affects its processing to mature 18S and 28S rRNAs. The methylation of 5'-terminal cap plays an important role in mRNA export from the nucleus, efficient translation, and protection of the integrity of mRNAs. Another important function of AdoMet is that it serves as the sole donor of an aminopropyl group that is conjugated with putrescine to form, first, the polyamine spermidine, and then spermine.

Monoclonal antibody AE-2 modulates carbamate and organophosphate inhibition of fetal bovine serum acetylcholinesterase

The monoclonal antibody AE-2, raised against the human erythrocyte acetylcholinesterase (AChE) dimer (acetylcholine acetylhydrolase, EC 3.1.1.7), binds to other mammalian AChEs, including the tetramer that occurs in fetal bovine serum (FBS). AE-2 partially inhibited the rate of hydrolysis of the charged substrate acetylthiocholine by FBS AChE, whereas it increased the rate of hydrolysis of the neutral substrate indophenyl acetate. Present results show that AE-2 decreases the rate of inhibition of FBS AChE by the positively charged organophosphate amiton-p-toluene sulfonate and the positively charged carbamates pyridostigmine and neostigmine but accelerates inhibition of FBS AChE by the neutral organophosphates paraoxon and diisopropylfluorophosphate. Results suggest that AE-2 may allosterically modulate an anionic site in the catalytic center of FBS AChE.

Stabilization of thymopentin and preservation of its pharmacological properties by 2-hydroxypropyl-beta-cyclodextrin

Thymopentin prepared in 5, 15, and 20% 2-hydroxypropyl-beta-cyclodextrin (HPCD) was able to inhibit guinea-pig ileum contraction stimulated by anatoxin-a (3 x 10(-6) M) after fourteen months of storage at room temperature. Thus, in contrast to the instability of thymopentin prepared without HPCD, the pharmacological activity was retained and could be stored in a ready-to-use solution for extended periods without refrigeration.

Synthesis and antimuscarinic activity of 2-[N-(ethyl)-(N-beta-hydroxyethyl)]aminoethyl 2,2-diphenylpropionate, a metabolite of aprophen

The preparation of 2-[N-(ethyl)-(N-beta-hydroxyethyl)]amino-ethyl 2,2-diphenylpropionate (1), a metabolite of aprophen [2-diethylaminoethyl 2,2-diphenylpropionate], is described. Hydrolysis of [2-(2-chloroethyl)ethylamino]ethyl acetate hydrochloride (2) in a basic solution, followed by acidic pH adjustment, gave the ethylcholineaziridinium ion (3) that upon treatment with 2,2-diphenylpropionic acid produced 1 in a 56% yield. Synthetic 1 was found to possess antimuscarinic activities, but was approximately 10-fold less potent than the parent compound aprophen.

Induced release of acetylcholine from guinea pig ileum longitudinal muscle-myenteric plexus by anatoxin-a

Anatoxin-a (ANTX), a nicotinic agonist, has been shown to induce contraction of guinea pig ileum, which was abrogated by the muscarinic antagonist atropine and the nicotinic antagonists tubocurarine and hexamethonium. We showed here that the ganglionic nicotinic antagonist mecamylamine was a better inhibitor of the contraction of ileum induced by ANTX. The sodium channel blocker tetrodotoxin also abolished ANTX-induced contraction. In contrast, alpha-bungarotoxin, the muscle type nicotinic receptor blocker, had no effect on ANTX-induced contraction of guinea pig ileum. Longitudinal muscle-myenteric plexus prepared from guinea pig ileum, labeled with [3H]choline and then incubated with ANTX was shown for the first time to release [3H]acetylcholine (ACh) in a dose-dependent manner. Pretreatment of longitudinal muscle-myenteric plexus with tubocurarine, hexamethonium or mecamylamine blocked ANTX-induced release of [3H]ACh. In contrast, atropine was without effect. Mecamylamine was the most potent antagonist. As observed in ileum contraction, tetrodotoxin completely and potently blocked the release of [3H]ACh induced by ANTX. Neither alpha-bungarotoxin nor the neuromuscular junction blockers conotoxin G1 or M1 could inhibit the [3H]ACh release. Taken together, these results suggested that ANTX activated nicotinic receptors on ganglionic interneurons to trigger a release of ACh, which next stimulated muscarinic receptors and induced ileum contraction.

Prejunctional muscarinic receptors in the deep muscular plexus of canine ileum: comparison with smooth muscle receptors

Prejunctional muscarinic receptors from the deep muscular plexus of canine ileum were studied, and their properties were compared with those of the postjunctional receptors of the circular smooth muscle. In the purified synaptosomal fraction (a fraction containing primarily the axonal varicosities of deep muscular plexus), the muscarinic ligand N-[3H]methylscopolamine labeled an apparently homogenous population of receptors (nH = 1) with a Kd of 2.7 nM and a Bmax of 195 +/- 44 fmol/mg protein (mean +/- S.D., n = 4). These receptors showed a high affinity for the M3/M1-selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (pKi = 7.41); in contrast, the pKi values of pirenzepine (5.60), methoctramine (5.65) and AF-DX 116 (5.21) implied little selectivity for these subtypes. The binding properties of muscarinic receptors in the synaptosomal fraction were different from the binding properties of muscarinic receptors in the purified circular smooth muscle plasma membranes. Most notably, the circular smooth muscle receptors had significantly lower affinity for N-[3H]methylscopolamine (Kd = 16 nM) with a Bmax value of 2088 +/- 276 fmol/mg. The affinities of the M2 subtype-selective muscarinic antagonists methoctramine and AF-DX 116 were similar in both membrane preparations. The receptor population associated with the deep muscular plexus synaptosomal fraction was linked to the inhibition of adenylate cyclase activity, as demonstrated by a concentration-dependent, atropine-sensitive inhibition of the forskolin-stimulated enzyme in the presence of muscarinic agonists carbachol and oxotremorine. Based on the pharmacological observations presented here, the prejunctional muscarinic receptors in the axonal varicosities of deep muscular plexus are different from the postjunctional receptors present in the circular smooth muscle.

Muscarinic receptor subtype specificity of (N,N-dialkylamino)alkyl 2-cyclohexyl-2-phenylpropionates: cylexphenes (cyclohexyl-substituted aprophen analogues)

A series of aprophen [(N,N-diethylamino)ethyl 2,2-diphenylpropionate] analogues, called cylexphenes, were synthesized with alterations in (1) the chain length of the amine portion of the ester, (2) the alkyl groups on the amino alcohol, and (3) a cyclohexyl group replacing one of the phenyl rings. The antimuscarinic activities of these analogues were assessed in two pharmacological assays: the inhibition of acetylcholine-induced contraction of guinea pig ileum, and the blocking of carbachol-stimulated release of alpha-amylase from rat pancreatic acinar cells. These two tissues represent the M3(ileum) and M3(pancreas) muscarinic receptor subtypes. In addition, the analogues were also evaluated for their competitive inhibition of the binding of [3H]NMS to selected cell membranes, each containing only one of the m1, M2, m3, or M4 muscarinic receptor subtypes. The m1 and m3 receptors were stably transfected into A9 L cells. The replacement of one phenyl group of aprophen with a cyclohexyl group increased the selectivity of all the analogues for the pancreatic acinar muscarinic receptor subtype over the ileum subtype by more than 10-fold, with the (N,N-dimethylamino)propyl analogue exhibiting the greatest selectivity for the pancreas receptor subtype, over 30-fold. The cylexphenes also showed a decrease in potency in comparison to the parent compound when examined for the binding of [3H]NMS to the M2 subtype. In agreement with the pharmacological data obtained from the pancreas, the (N,N-dimethylamino)propyl cylexphene 3 demonstrated the greatest selectivity for the m3 subtype, and additionally showed a preference for the m1 and M4 receptor subtypes over the M2 receptor subtype in the binding assay. Thus, this compound showed a potent selectivity according to the pharmacological and binding assays between the muscarinic receptor subtypes of the pancreas and ileum. In both the pharmacological and binding assays, the potency of the analogues decreased markedly when the chain length and the bond distance between the carbonyl oxygen and protonated nitrogen were increased beyond three methylene groups. When the structures of these analogues were analyzed using a molecular modeling program, the bond distance between the carbonyl oxygen and protonated nitrogen was deduced to be more important for the antagonist activity than subtype specificity.

Relationship of three-dimensional structure of muscarinic antagonists to antimuscarinic activity: structure of thiodeacylaprophen hydrochloride

C20H28NS+.Cl-, 2-(diethylamino)ethyl 1,1-diphenylethyl sulfide hydrochloride (thiodeacylaprophen hydrochloride), M(r) = 349.9, orthorhombic, P2(1)2(1)2(1), a = 8.933 (2), b = 11.710 (3), c = 18.934 (4) A, V = 1980.6 (7) A3, Z = 4, Dx = 1.173 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 26.70 cm-1, F(000) = 752, room temperature, final R = 4.1% for 1417 reflections with /Fo/ greater than 3 sigma (F). Thiodeacylaprophen crystallized as a tertiary amine hydrochloride salt. The S--C--C--N+ segment adopts a trans configuration as does one of the Cphenyl--C--S--C segments. A comparison of the structure of thiodeacylaprophen with the crystal structures of potent antimuscarinic agents suggests that the relatively weak antimuscarinic activity of thiodeacylaprophen compared to atropine and aprophen may be substantially due to the short intramolecular S...N+ distance of 4.106 (6) A. Other contributing structural factors may include the direction of the N+--H bond and restricted accessibility of the sulfur atom for interatomic interactions.

Activation of collagen IV gene expression in F9 teratocarcinoma cells by 3-deazaadenosine analogs. Indirect inhibitors of methylation

3-Deazaadenosine analogs can function as inhibitors and also as alternative substrates of S-adenosylhomocysteine (AdoHcy) hydrolase. In cells treated with the analogs, AdoHcy invariably accumulates, leading to inhibition of cellular methylation. F9 teratocarcinoma cells, stably transfected with two collagen (IV) promoter-enhancer-CAT constructs and treated with 10 microM 3-deazaadenosine, 3-deaza-(+-)-aristeromycin or 3-deazaneplanocin, showed a strong induction of CAT activities without affecting differentiation. In comparison, the same 3-deaza analogs did not affect the CAT activity in F9 cells transfected with the beta-actin promoter-CAT construct. Furthermore, Northern blot analysis of endogenous mRNA from wild-type F9 cells treated with the 3-deaza nucleosides all showed an induction of the collagen alpha 1(IV) chain mRNA. Thus, the 3-deaza analogs most likely affect DNA methylation because their results are consistent with the previous observation that the integrated collagen alpha 1(IV) promoter-enhancer constructs were activated with 5-azacytidine.

Behavioral effects of some diphenyl-substituted antimuscarinics: comparison with cocaine and atropine

To more fully characterize the behavioral excitatory effects observed with certain diphenyl-substituted antimuscarinics, various behavioral effects of benactyzine, a prototype excitatory antimuscarinic, was evaluated in rats. These effects were compared to those of cocaine, atropine, and azaprophen, a muscarinic antagonist that contains both the diphenyl substituents of benactyzine and a ring isomeric with the tropane ring of atropine. Under a fixed-interval 5-min schedule of food presentation, cocaine and benactyzine increased response rates. Atropine and azaprophen only decreased responding. The muscarinic agonist oxotremorine attenuated the rate-increasing effects but did not alter the disruptions in the temporal patterning produced by benactyzine or shift the dose-effect function to the right. In rats discriminating 10 mg/kg cocaine from saline, benactyzine partially substituted for cocaine, producing a maximum of 50% cocaine-appropriate responses. Benactyzine fully substituted for scopolamine in rats discriminating 0.056 mg/kg scopolamine from saline. All antimuscarinics increased locomotor activity when activity levels were low in control animals, but the increases were less than those produced by cocaine. Cocaine increased both locomotor activity and fixed-interval responding at comparable doses, whereas 10-fold higher doses of benactyzine were required to increase locomotor activity. These results support the following conclusions: 1) In addition to its classical antimuscarinic behavioral profile, benactyzine has behavioral excitatory actions similar in some respects to those of cocaine; 2) the behavioral excitatory effects of benactyzine do not appear to be due solely to antagonism of muscarinic receptors; and 3) the alkyl-ester may be an important structural feature of diphenyl-substituted antimuscarinics for the induction of behavioral stimulation.

Inhibition of substrate oxidation in mitochondria by the peripheral-type benzodiazepine receptor ligand AHN 086

The effects, of the benzodiazepines RO5-4864, AHN 086, PK 11195 and clonazepam on respiration of mitochondria from heart, kidney, and liver were studied. ADP-stimulated respiration of heart mitochondria was the most sensitive to inhibition by AHN 086; clonazepam was not inhibitory. Several respiratory chain segment activities of submitochondrial particles were insensitive to AHN 086, except for NADH oxidase which was partially inhibited. However, in contrast to submitochondrial particles, the succinate-cytochrome c oxidoreductase activity in intact mitochondria was inhibited by AHN 086, suggesting an effect at the substrate transport level. Phosphate-induced, succinate-dependent swelling was also inhibited by AHN 086 it was not affected by clonazepam. Uncoupled ATP hydrolysis was partially inhibited by RO5-4864, AHN 086, and clonazepam. It is suggested that there is an unspecific inhibition of NADH oxidase and ATP hydrolysis by these benzodiazepines and a specific inhibition on oxidizable substrate transport by the peripheral-type benzodiazepine AHN 086.

Isolation and identification of beta-hydroxyethylaprophen: a urinary metabolite of aprophen in rats

The metabolism of the anticholinergic drug aprophen was studied in rats after oral administration via stomach intubation. beta-Hydroxyethylaprophen, a major urinary metabolite of aprophen, was isolated and identified by normal-phase high-performance liquid chromatography and electron ionization mass spectrometry. More than 22% of the parent drug was recovered and quantified over a 72-h collection period. Results show that 2,2-diphenylpropionic acid, another major metabolite of aprophen which lacks anticholinergic properties, was also isolated and identified in this study. Experiments are currently underway to synthesize and test the anticholinergic properties of beta-hydroxyethylaprophen in mammals.

Release of Ca2+ from heart and kidney mitochondria by peripheral-type benzodiazepine receptor ligands

1. The effect of the benzodiazepines Ro5-4864, AHN 086 and clonazepam on the release of Ca2+ from rat heart and kidney mitochondria was studied. 2. The peripheral-type benzodiazepines Ro5-4864 and AHN 086 induced Ca2+ release which was blocked by Mg2+ whereas the central-type benzodiazepine clonazepam was ineffective. 3. An associated collapse of membrane potential and swelling were also induced by AHN 086 in the presence of Ca2+. 4. However, no oxidation of pyridine nucleotides or increased rate or respiration were observed. 5. Release of Sr2+ was induced by AHN 086 in the absence of inorganic phosphate but not in its presence. 6. These data are discussed in the context of the current hypotheses on the mechanism of mitochondrial Ca2+ release.

Nicotinic action of anatoxin-a on guinea pig ileum antagonized by thymopentin

(+)-Anatoxin-a (ANTX) stimulated guinea pig ileum contraction with a potency similar to that of acetylcholine (ACh); the stimulation was blocked by tubocurarine, hexamethonium, or atropine. Although the contraction stimulated by ANTX was blocked by atropine, no specific inhibition of the binding of [3H]N-methylscopolamine to ileum membranes was observed in the presence of ANTX. Furthermore, ANTX failed to stimulate the secretion of alpha-amylase from pancreatic acinar cells, a process that is activated by cholinergic agonists at the muscarinic receptors. When the ileum itself was stimulated by ACh, the contraction was not blocked by either hexamethonium or tubocurarine. Preincubation of the ileum with hemicholinium caused a 50% reduction in the ability of ANTX to stimulate contraction. Based upon these data, it was inferred that ANTX binds to postganglionic synaptic nicotinic receptors in the ileum, thus releasing endogenous ACh, which in turn causes ileum contraction by interacting with the postsynaptic muscarinic receptors. It was also observed that thymopentin (TP-5), a pentapeptide corresponding to positions 32-36 of thymopoietin, blocked the stimulation of ileum contraction by ANTX.

Aprophit: an irreversible antagonist for muscarinic receptors

The development of selective irreversible ligands has proven to be an invaluable technique for the isolation, purification and characterization of many receptor proteins. An isothiocyanato-derivative of the muscarinic antagonist aprophen was synthesized and evaluated as a potential irreversible ligand for muscarinic receptors. This compound (aprophit) displaced [3H]N-methylscopolamine binding from rat cerebral cortex with a Ki of 3.1 x 10(-7) M. The inhibition was concentration-dependent and could not be reversed by extensive washing. Aprophit inhibited the acetylcholine-stimulated release of catecholamines from isolated, perfused guinea pig adrenal glands in a concentration-dependent manner. This inhibition was not reversed by perfusing the tissue with Locke's solution and was not due to a non-selective acylation by the isothiocyanate function. The data suggest that aprophit is selectively acylating muscarinic receptor proteins and thus may be useful in their further characterization.

Vasoactive intestinal polypeptides induce guinea-pig ileum contraction by causing release of endogenous acetylcholine

Two vasoactive intestinal polypeptide (VIP) analogues were observed to induce a concentration-dependent contraction of guinea-pig ileum, which was blocked by atropine but not by tubocurarine. The analogue from guinea-pig, VIP [VIP(gp)], was the most potent inducer of ileum contraction, followed by human-porcine-rat VIP [VIP(hpr)], which differs from VIP(gp) by 4 nonpolar amino acid substitutions. VIP(1-15), composed of only the first 15 of the 28 amino acids of VIP(hpr), was without effect. The relative potency of VIP(gp), VIP(hpr), and acetylcholine was 50 to 100 times more potent in inducing contraction in ileums of which the acetylcholinesterase was inactivated by paraoxon than in the controls. The VIP analogues which induced contraction of ileum also induced secretion of endogenous acetylcholine. The secreted acetylcholine was quantified by high-performance liquid chromatography using electrochemical detection and an immobilized-enzyme column consisting of choline oxidase and acetylcholinesterase. The induction of ileum contraction by VIP(gp), from 10nM to 1 microM VIP, was correlated with the amounts of ACh secreted from ileum. VIP(hpr) induced less acetylcholine secretion than VIP(gp), and was also less potent in causing ileum contraction. VIP(1-15), even at 10 microM, caused neither acetylcholine release nor ileum contraction.

Structural comparison of the potent antimuscarinic agent azaprophen hydrochloride with aprophen hydrochloride and structurally related antimuscarinic agents

A comparison of the crystalline structure of the potent azaprophen with the crystalline structures of aprophen and four other structurally related antimuscarinic agents reveals the potential for an ionic interaction of the cationic nitrogen atom and the carbonyl oxygen atom with the muscarinic receptor and an aromatic interaction with a phenyl group. 6-Methyl-6-azabicyclo[3.2.1]octan-3 alpha-ol 2,2-diphenylpropionate hydrochloride (azaprophen hydrochloride), C23H28NO2+.Cl-, Mr = 385.9, monoclinic, P2(1)/c, a = 8.490 (1), b = 14.335 (2), c = 16.847 (2) A, beta = 93.63 (1) degree, V = 2046.2 A3, Z = 4, Dx = 1.253 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 17.86 cm-1, F(000) = 824, room temperature, final R = 4.25% for 2460 reflections with [Fo[ greater than 3 sigma. 2-Diethylaminoethyl 2,2-diphenylpropionate hydrochloride (aprophen hydrochloride), C21H28NO2+.Cl-, Mr = 361.9, orthorhombic, Pbca, a = 15.118 (3), b = 7.488 (2), c = 36.306 (10) A, V = 4110.8 A3, Z = 8, Dx = 1.316 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 17.45 cm-1, F(000) = 1552, room temperature, final R = 7.96% for 1846 reflections with [Fo[ greater than 3 sigma. Both azaprophen and aprophen were crystallized as tertiary amine salts. The overall conformation of both molecules is similar as demonstrated by space-filling models and superimposed stick drawings. Although the interatomic distance between the nitrogen atom and the carbonyl oxygen atom of azaprophen and aprophen is comparable at 5.41 and 5.07 A, respectively, the nitrogen atoms of azaprophen and aprophen are 1.16 A apart when the acyloxy portion (--O--C = O) of both molecules is superimposed. A conformational analysis of azaprophen, aprophen and the structurally similar antimuscarinic agents reveals a buried ether oxygen atom and an exposed carbonyl oxygen atom as well as the common placement of a phenyl group on the same side of the acyloxy plane as the cationic nitrogen atom.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between nitrogen oxide-containing compounds and peripheral benzodiazepine receptors

Nitrogen oxide-containing compounds displaced the peripheral benzodiazepine ligand [3H]Ro5-4864 from guinea pig membrane preparations. Sodium nitroprusside (SNP) was the most potent (IC50 = 5.61 +/- 1.72 x 10(-5) M). Moreover, its ability to bind to these receptors showed marked tissue variability (heart greater than kidney much greater than cerebral cortex). When tested on rat atrium, SNP by itself had no effect on basal inotropy or the increase in inotropy induced by (-)-S-BAY K 8644. In contrast, Ro5-4864 potentiated the marked increase in inotropy induced by (-)-S-Bay K 8644, and SNP completely abolished the potentiation of inotropy observed with Ro5-4864. Since peripheral benzodiazepine receptors are associated with calcium mobilization in the heart, these findings may indicate that some of the clinical effects of nitric oxide-generating drugs could be mediated by these receptors.

Differential allosteric effects of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate-HCl (TMB-8) on muscarinic receptor subtypes

TMB-8, a putative inhibitor of intracellular calcium mobilization, prevents the binding of the muscarinic ligand N-[3H]methylscopolamine. The inhibition was observed in four tissues from guinea pig; cortex, heart, pancreas, and ileum, representing M1, cardiac M2, glandular M2, and heterogeneous M2 subtypes of muscarinic receptors, respectively. The Ki values for all four tissues were approx. 4 microM. However, dissociation kinetics revealed that TMB-8 interacted with an allosteric site of three muscarinic receptor subtypes but not the subtype from pancreas. These results indicate that TMB-8 interacts with muscarinic receptors, and therefore would disrupt calcium mobilization or any second messenger system coupled to these receptors.

Distance geometry of alpha-substituted 2,2-diphenylpropionate antimuscarinics

Quantitative structure-activity relationships between pharmacological activities and physical properties of a series of 2,2-diphenylpropionate compounds were used to define the topography of the antagonist binding site of muscarinic receptors. XICAMM, a computer molecular modeling program, was used to calculate geometrical and topological values of the compounds. The compounds were tested for their antimuscarinic activities by: (a) inhibition of [N-methyl-3H]scopolamine binding to the muscarinic receptors of N4TG1 neuroblastoma cells, (b) inhibition of carbachol-induced alpha-amylase release from rat pancreas acini, and (c) blocking of acetylcholine-induced contraction of guinea pig ileum. To evaluate as clearly as possible only the effect of the bond distance on the potency of the synthesized antimuscarinics, the compounds contained as many constant features as possible. Neither the hydrophobic nor the ester moieties of the compounds were changed, and the rings containing the protonated nitrogen were saturated and restricted. The antimuscarinic activities obtained from the three assays were significantly correlated with each other, with the exception of two compounds, 9 and 13. The latter two compounds demonstrated specificity for the m3 muscarinic receptor subtype expressed in the pancreas. Furthermore, it was demonstrated that the antimuscarinic activities were significantly related to the bond distances between the carbonyl oxygen (constant electronegative locus) and the protonated nitrogen (center of cationic charge) of the 2,2-diphenylpropionate compounds. Parabolic relationships between the pharmacological activities and bond distances were empirically established. The shortest calculated bond distance of these compounds was approximately 4.4 A, whereas the longest was about 5.9 A. The maximum antimuscarinic potency was observed with a calculated bond distance of about 5.2 A in all three assays.

Binary antidotes for organophosphate poisoning: aprophen analogues that are both antimuscarinics and carbamates

Prophylaxis against organophosphate poisoning can be achieved by pretreatment with physostigmine or pyridostigmine, which are carbamates, and aprophen, which is an anticholinergic agent. Thus, a series of aprophen analogues was synthesized with carbamyl substitutions on the phenyl rings (carbaphens). The rationale behind this design is that such compounds might exhibit most of the therapeutic characteristics of aprophen, as well as the ability to protect prophylactically by chemically masking cholinesterase enzymes. Compounds 4 (dimethylhydroxycarbaphen), 15 (dimethylcarbaphen), and 16 (monomethylcarbaphen) were found to inactivate human butyrylcholinesterase in a time-dependent manner with potencies similar to those of physostigmine or pyridostigmine, and the latter two exhibited almost the same antimuscarinic profile as aprophen. In contrast to the potent inactivation of butyrylcholinesterase by these compounds, marginal inactivation of acetylcholinesterase activity was observed, and only at much higher drug concentrations. The noncarbamylated analogues had no effect on the activity of either cholinesterase. The carbaphen compounds are hence prototype drugs that can interact with either muscarinic receptors or butyrylcholinesterase. Furthermore, these compounds are prodrugs, since after carbamylation of the cholinesterase, the leaving group 14 (hydroxyaprophen) is a potent antimuscarinic itself.

Muscarinic receptor subtype specificity of 5'-(isobutylthio)-adenosine (SIBA) and its analogs

1. 5'(Isobutylthio)-adenosine (SIBA) and its analogs, at 100 microM, inhibited [3H]N-methyl-scopolamine binding to homogenates of whole brain and cortex (mainly M1 subtype receptors) by 11-30% and to cerebellum (mainly M2 subtype receptors) by 20-39%. 2. At 0.01-1.0 microM, stimulation of [3H]QNB and NMS-inaccessible [3H]QNB binding was observed, with the most induced by 1 microM 3-deaza-SIBA. 3. In contrast, [3H]pirenzepine ([3H]PZ) binding to whole brain and cortex was inhibited in a dose-dependent manner with Ki values in the microM range. 4. As antagonists of acetylcholine-induced contraction of guinea pig ileum (mainly M2 subtype receptors), the analogs were slightly more potent than pirenzepine, but several orders of magnitude less than atropine; the order of potency was opposite that determined for the binding of [3H]PZ to cortex. 5. Thus, SIBA and its analogs may have differential effects on muscarinic receptor subtypes and show some specificity for the M1 receptor subtype.