Interactions of butane, but-2-ene or xylene-like linked bispyridinium para-aldoximes with native and tabun-inhibited human cholinesterases

Kinetic parameters were evaluated for inhibition of native and reactivation of tabun-inhibited human erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7) and human plasma butyrylcholinesterase (BChE, EC 3.1.1.8) by three bispyridinium para-aldoximes with butane (K074), but-2-ene (K075) or xylene-like linker (K114). Tested aldoximes reversibly inhibited both cholinesterases with the preference for binding to the native AChE. Both cholinesterases showed the highest affinity for K114 (K(i) was 0.01mM for AChE and 0.06mM for BChE). The reactivation of tabun-inhibited AChE was efficient by K074 and K075. Their overall reactivation rate constants were around 2000min(-1)M(-1), which is seven times higher than for the classical bispyridinium para-aldoxime TMB-4. The reactivation of tabun-inhibited AChE assisted by K114 was slow and reached 90% after 20h. Since the aldoxime binding affinity of tabun-inhibited AChE was similar for all tested aldoximes (and corresponded to their K(i)), the rate of the nucleophilic displacement of the phosphoryl-moiety from the active site serine was the limiting factor for AChE reactivation. On the other hand, none of the aldoximes displayed a significant reactivation of tabun-inhibited BChE. Even after 20h, the reactivation maximum was 60% for 1mM K074 and K075, and only 20% for 1mM K114. However, lower BChE affinities for K074 and K075 compared to AChE suggest that the fast tabun-inhibited AChE reactivation by these compounds would not be obstructed by their interactions with BChE in vivo.     

Peripheral site ligand-oxime conjugates: A novel concept towards reactivation of nerve agent-inhibited human acetylcholinesterase

A conceptually novel approach to the design of reactivators of nerve agent-inhibited acetylcholinesterase (AChE) is presented. The concept comprises the linkage of a peripheral site ligand via a spacer to a reactivating moiety with the eventual goal to develop non-ionic reactivators with sufficient affinity for AChE to induce reactivation and potentially improved blood-brain barrier penetration. Herein, the first step towards that goal—the synthesis and biological evaluation of a peripheral site ligand conjugated to a charged pyridinium oxime is discussed. It was found, that the introduction of the peripheral site ligand not only increased affinity of the construct for AChE but also enhanced reactivation of nerve agent-inhibited AChE.     

Stereoselective inhibition of human, mouse, and horse cholinesterases by bambuterol enantiomers

Bambuterol is a chiral carbamate and a selective inhibitor of butyrylcholinesterase (BChE, EC 3.1.1.8). In order to relate bambuterol selectivity and stereoselectivity of BChE and acetylcholinesterase (AChE, EC 3.1.1.7) of different species, we studied the inhibition of human, mouse, and horse BChE, as well as AChE of human and mouse by (R)- and (S)-bambuterol. AChE and BChE of all studied species were progressively inhibited by both bambuterol enantiomers, with a preference for the (R)-bambuterol whose inhibition rate constants were about five times higher than that of (S)-bambuterol. We observed no significant difference between human and mouse in bambuterol enantiomer BChE inhibition. However, (R)-bambuterol inhibited horse BChE about 14 times slower than human and mouse BChE, and the inhibition rate for (S)-bambuterol was about 18 times slower. Although the primary structure of horse BChE differs from the other two species in 15 amino acids, we presumed that differences in inhibition rates could be attributed to threonine at position 69 located close to the peripheral site of BChE. Since BChE inhibition by bambuterol enantiomers was at least 8000 times faster than that of AChE, both bambuterol enantiomers proved to be selective BChE inhibitors, as was previously shown for racemate.     

Active site mutant acetylcholinesterase interactions with 2-PAM, HI-6, and DDVP

We used mouse recombinant wild-type acetylcholinesterase (AChE; EC 3.1.1.7), butyrylcholinesterase (BChE; EC 3.1.1.8), and AChE mutants with mutations (Y337A, F295L, F297I, Y72N, Y124Q, and W286A) that resemble residues found at structurally equivalent positions in BChE, to find the basis for divergence between AChE and BChE in following reactions: reversible inhibition by two oximes, progressive inhibition by the organophosphorus compound DDVP, and oxime-assisted reactivation of the phosphorylated enzymes. The inhibition enzyme-oxime dissociation constants of AChE w.t. were 150 and 46 microM, of BChE 340 and 27 microM for 2-PAM and HI-6, respectively. Introduced mutations lowered oxime binding affinities for both oximes. DDVP progressively inhibited cholinesterases yielding symmetrical dimethylphosphorylated enzyme conjugates at rates between 104 and 105/min/M. A high extent of oxime-assisted reactivation of all conjugates was achieved, but rates by both oximes were up to 10 times slower for phosphorylated mutants than for AChE w.t.     

Synthesis and in vitro evaluation of bis-quaternary 2-(hydroxyimino)-N-(pyridin-3-yl)acetamide derivatives as reactivators against sarin and VX inhibited human acetylcholinesterase (hAChE)

A series of bis-quaternary pyridinium derivatives 3a–3i of 2-(hydroxyimino)-N-(pyridin-3-yl)acetamide (2) have been synthesized. The synthesized pyridinium compounds have an amide group in conjugation to the oxime moiety. These compounds were evaluated in vitro for their reactivation efficacy against organophosphorus (OP) nerve agents (NAs) (sarin and VX) inhibited human erythrocyte ghost acetylcholinesterase (hAChE) and compared with the reactivation efficacy of 2-PAM and obidoxime. The pK_a values of the synthesized compounds were found closer to the pK_a values of 2- and 4-pyridinium oxime reactivators such as 2-PAM and obidoxime. Some of the compounds have shown better reactivation efficacy than 2-PAM, and obidoxime against sarin and VX inhibited AChE.     

Synthesis and in vitro reactivation study of isonicotinamide derivatives of 2-(hydroxyimino)-N-(pyridin-3-yl)acetamide as reactivators of Sarin and VX inhibited human acetylcholinesterase (hAChE)

Previously (Karade et al., 2014), we have reported the synthesis and in vitro evaluation of bis-pyridinium derivatives of pyridine-3-yl-(2-hydroxyimino acetamide), as reactivators of sarin and VX inhibited hAChE. Few of the molecules showed superior in vivo protection efficacy (mice model) (Kumar et al., 2014; Swami et al., 2016) in comparison to 2-PAM against DFP and sarin poisoning. Encouraged by these results, herein we report the synthesis and in vitro evaluation of isonicotinamide derivatives of pyridine-3-yl-(2-hydroxyimino acetamide) (4a–4d) against sarin and VX inhibited erythrocyte ghost hAChE. Reactivation kinetics of these compounds was studied and the determined kinetic parameters were compared with that of commercial reactivators viz. 2-PAM and obidoxime. In comparison to 2-PAM and obidoxime, oxime 4a and 4b exhibited enhanced reactivation efficacy toward sarin inhibited hAChE while oxime 4c showed far greater reactivation efficacy toward VX inhibited hAChE. The acid dissociation constant and IC₅₀ values of these oximes were determined and correlated with the observed reactivation potential.     

Comparison of oxime reactivation and aging of nerve agent-inhibited monkey and human acetylcholinesterases

Non-human primates are valuable animal models that are used for the evaluation of nerve agent toxicity as well as antidotes and results from animal experiments are extrapolated to humans. It has been demonstrated that the efficacy of an oxime primarily depends on its ability to reactivate nerve agent-inhibited acetylcholinesterase (AChE). If the in vitro oxime reactivation of nerve agent-inhibited animal AChE is similar to that of human AChE, it is likely that the results of an in vivo animal study will reliably extrapolate to humans. Therefore, the goal of this study was to compare the aging and reactivation of human and different monkey (Rhesus, Cynomolgus, and African Green) AChEs inhibited by GF, GD, and VR. The oximes examined include the traditional oxime 2-PAM, two H-oximes HI-6 and HLo-7, and the new candidate oxime MMB4. Results indicate that oxime reactivation of all three monkey AChEs was very similar to human AChE. The maximum difference in the second-order reactivation rate constant between human and three monkey AChEs or between AChEs from different monkey species was 5-fold. Aging rate constants of GF-, GD-, and VR-inhibited monkey AChEs were very similar to human AChE except for GF-inhibited monkey AChEs, which aged 2-3 times faster than the human enzyme. The results of this study suggest that all three monkey species are suitable animal models for nerve agent antidote evaluation since monkey AChEs possess similar biochemical/pharmacological properties to human AChE.     

Synthesis,biological evaluation and molecular modeling of substituted 2-aminobenzimidazoles as novel inhibitors of acetylcholinesterase and butyrylcholinesterase

A series of novel 2-aminobenzimidazole derivatives were synthesized under microwave irradiation. Their biological activities were evaluated on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A number of the 2-aminobenzimidazole derivatives showed good inhibitory activities to AChE and BuChE. Among them, compounds 9, 12 and 13 were found to be >25-fold more selective for BuChE than AChE. No evidence of cytotoxicity was observed by MTT assay in PC12 cells or HepG2 cells exposed to 100 μM of the compounds. Molecular modeling studies indicate that the benzimidazole moiety of compounds 9, 12 and 13 forms a face-to-face π–π stacking interaction in a ‘sandwich’ form with the indole ring of Trp82 (4.09 Å) in the active gorge, and compounds 12 and 13 form a hydrogen bond with His438 at the catalytic site of BuChE. In addition, compounds 12 and 13 fit well into the hydrophobic pocket formed by Ala328, Trp430 and Tyr332 of BuChE. Our data suggest the 2-aminobenzimidazole drugs as promising new selective inhibitors for AChE and BuChE, potentially useful to treat neurodegenerative diseases.     

Synthesis and structures of mono and binuclear nickel(II) thiolate complexes of a dicompartmental pseudo-macrocycle with N(imine)2S2 and N(oxime)2S2 metal-binding sites

The reaction of [Ni(pftp)] [pftp = N,N-propane-1,3-diyl-(6-formyl-4-methyliminatothiophenolato)] with hydroxylamine hydrochloride in the presence potassium acetate in MeOH resulted in the formation of the complex [Ni(LH₂)] [L = N,N-propane-1,3-diyl-(4-methyl-2-methyliminato-6-methyloxime-thiophenolato)] in good yield. A single crystal X-ray diffraction structural determination showed a mononuclear nickel(II) complex with the new acyclic ligand LH₂ that had been functionalised with two oxime groups containing an empty N(oxime)₂S₂ pocket to which another metal ion could be added. A further reaction of [Ni(LH₂)] with NiCl₂·6H₂O, triethylamine and ammonium hexafluorophosphate in MeOH gave a dark red product that yielded red crystals of [Ni₂(LH)]PF₆·DMF via slow recrystallisation from a DMF/PrⁱOH solvent mixture. A single crystal X-ray diffraction study of these crystals confirmed the presence of a dinuclear nickel(II) complex linked by a dithiolato-bridge. Both nickel(II) ions exhibited square-planar geometry where the metal centres are coordinated in two distinct cis-S₂N(imine)₂ and cis-S₂N(oxime)₂ binding sites provided by the new dicompartmental oxime/thiolate-containing ligand LH.     

Acetylcholinesterase in Mouse Neuroblastoma NB2A Cells: Analysis of Production, Secretion, and Molecular Forms

The mouse neuroblastoma cell line NB2A produces cellular and secreted acetylcholinesterase (AChE). After incubation of the cells for 4 days the ratio between AChE secreted into the medium and AChE in the cells was 1:1. The cell-associated enzyme could be subdivided into soluble AChE (25%) and detergent-soluble AChE (75%). Both extracts contained predominantly monomeric AChE (4.6S) and minor amounts of tetrameric AChE (10.6S), whereas the secreted AChE in the culture supernatant contained only the tetrameric form. All forms were partially purified by affinity chromatography. It could be demonstrated that the secretory and the intracellular soluble tetramers were hydrophilic, whereas the detergent-soluble tetramer was an amphiphilic protein. On the other hand the soluble and the detergent-soluble monomeric forms were amphiphilic and their activity depended on the presence of detergent. By digestion with proteinase K amphiphilic monomeric and tetrameric AChE could be converted to a hydrophilic form that no longer required detergent for catalytic activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [3H]diisopropylfluorophosphate-labelled AChE gave one band at 64 kilodaltons (kD) under reducing conditions and two additional bands at 120 kD and 140 kD under nonreducing conditions.     

Synthesis of 2-,4,-6-, and/or 7-substituted quinoline derivatives as human dihydroorotate dehydrogenase (hDHODH) inhibitors and anticancer agents: 3D QSAR-assisted design

Following our research for human dihydroorotate dehydrogenase (hDHODH) inhibitors as anticancer agents, herein we describe 3D QSAR-based design, synthesis and in vitro screening of 2-,4,-6-, and/or 7-substituted quinoline derivatives as hDHODH inhibitors and anticancer agents. We have designed 2-,4,-6-, and/or 7-substituted quinoline derivatives and predicted their hDHODH inhibitory activity based on 3D QSAR study on 45 substituted quinoline derivatives as hDHODH inhibitors, and also predicted toxicity. Designed compounds were docked into the binding site of hDHODH. Designed compounds which showed good predictive activity, no toxicity, and good docking score were selected for the synthesis, and in vitro screening as hDHODH inhibitors in an enzyme inhibition assay, and anticancer agents in MTT assay against cancer cell lines (HT-29 and MDA-MB-231). Synthesized compounds 7 and 14 demonstrated IC₅₀ value of 1.56?µM and 1.22?µM, against hDHODH, respectively, and these are our lead compounds for the development of new hDHODH inhibitors and anticancer agents.     

Recognition of native and/or thermally induced denatured forms of the major food allergen, ovomucoid, by human IgE and mouse monoclonal IgG antibodies

Human sera obtained from children with egg allergy reacted well with both native and heated ovomucoid (OM). Ovalbumin is present in egg white in a 5 times greater quantity than OM; however, it easily aggregates and becomes difficult to extract by heating. For accurate food allergen labeling of processed food, therefore, OM should be evaluated with the determination of egg white protein in consideration of heat denaturation. Three kinds of monoclonal antibodies and sandwich ELISA tests were established which are able to recognize the native and/or heat-denatured forms of OM. The usefulness of these characteristic mAbs and ELISA tests are discussed in relation to allergen labeling, monitoring food processing, and movement or change of dietary protein in vivo.     

Interactions of WASp, myosin-I, and verprolin with Arp2/3 complex during actin patch assembly in fission yeast

Yeast actin patches are dynamic structures that form at the sites of cell growth and are thought to play a role in endocytosis. We used biochemical analysis and live cell imaging to investigate actin patch assembly in fission yeast Schizosaccharomyces pombe. Patch assembly proceeds via two parallel pathways: one dependent on WASp Wsp1p and verprolin Vrp1p converges with another dependent on class 1 myosin Myo1p to activate the actin-related protein 2/3 (Arp2/3) complex. Wsp1p activates Arp2/3 complex via a conventional mechanism, resulting in branched filaments. Myo1p is a weaker Arp2/3 complex activator that makes unstable branches and is enhanced by verprolin. During patch assembly in vivo, Wsp1p and Vrp1p arrive first independent of Myo1p. Arp2/3 complex associates with nascent activator patches over 6-9 s while remaining stationary. After reaching a maximum concentration, Arp2/3 complex patches move centripetally as activator proteins dissociate. Genetic dependencies of patch formation suggest that patch formation involves cross talk between Myo1p and Wsp1p/Vrp1p pathways.     

Reactions of 1-amino-n′-ferrocenemethylcarboxylate with electrophiles: A combined synthetic, electrochemical, and theoretical study

The reactivity of 1-amino-n′-ferrocenemethylcarboxylate, 1,n′-H₂N-Fc-COOCH₃ (2) toward alkylating agents is reported and MeNH-Fc-COOMe (3), EtNH-Fc-COOMe (4), EtSCH₂CH₂NH-Fc-COOMe (5), (EtO)₂P(O)NH-Fc-COOMe (6) are synthesized by reacting 2 with MeI, EtI, EtSCH₂CH₂Cl and (CN)(EtO)₂P(O), respectively. Cyclic voltammetry of these compounds shows different half-wave potential characteristics compared to aminoferrocene and is dependent on the nature of the substituents, which is rationalized by molecular orbital calculations.     

Orally active microtubule-targeting agent,MPT0B271, for the treatment of human non-small cell lung cancer,alone and in combination with erlotinib

Microtubule-binding agents, such as taxanes and vinca alkaloids, are used in the treatment of cancer. The limitations of these treatments, such as resistance to therapy and the need for intravenous administration, have encouraged the development of new agents. MPT0B271 (N-[1-(4-Methoxy-benzenesulfonyl)-2,3-dihydro-1H-indol-7-yl]-1-oxy-isonicotinamide), an orally active microtubule-targeting agent, is a completely synthetic compound that possesses potent anticancer effects in vitro and in vivo. Tubulin polymerization assay and immunofluorescence experiment showed that MPT0B271 caused depolymerization of tubulin at both molecular and cellular levels. MPT0B271 reduced cell growth and viability at nanomolar concentrations in numerous cancer cell lines, including a multidrug-resistant cancer cell line NCI/ADR-RES. Further studies indicated that MPT0B271 is not a substrate of P-glycoprotein (P-gp), as determined by flow cytometric analysis of rhodamine-123 (Rh-123) dye efflux and the calcein acetoxymethyl ester (calcein AM) assay. MPT0B271 also caused G2/M cell-cycle arrest, accompanied by the up-regulation of cyclin B1, p-Thr161 Cdc2/p34, serine/threonine kinases polo-like kinase 1, aurora kinase A and B and the downregulation of Cdc25C and p-Tyr15 Cdc2/p34 protein levels. The appearance of MPM2 and the nuclear translocation of cyclin B1 denoted M phase arrest in MPT0B271-treated cells. Moreover, MPT0B271 induced cell apoptosis in a concentration-dependent manner; it also reduced the expression of Bcl-2, Bcl-xL, and Mcl-1 and increased the cleavage of caspase-3 and -7 and poly (ADP-ribose) polymerase (PARP). Finally, this study demonstrated that MPT0B271 in combination with erlotinib significantly inhibits the growth of the human non-small cell lung cancer A549 cells as compared with erlotinib treatment alone, both in vitro and in vivo. These findings identify MPT0B271 as a promising new tubulin-binding compound for the treatment of various cancers.     

Release of Neuropeptide FF, an Anti-Opioid Peptide, in Rat Spinal Cord Slices Is Voltage- and Ca2+-Sensitive: Possible Involvement of P-Type Ca2+ Channels

Abstract: Neuropeptide FF (NPFF), an FMRFamide-like peptide with antiopioid properties, inhibits morphine-induced analgesia but also produces hyperalgesia. In the present study, the mechanisms of NPFF release were investigated in an in vitro superfusion system with rat spinal cord slices. The opening of voltage-sensitive Na⁺ channels with veratridine (20 µ M ) induced calcium-dependent NPFF release, which was abolished by tetrodotoxin (1 µ M ), suggesting that NPFF release depends on nerve impulse activity. We also showed that NPFF release was a function of the extent of depolarization and was calcium dependent. The 30 m M K⁺-induced release was blocked by Co²⁺ or Ni²⁺ (2.5 m M ) but was unaffected by Ca²⁺ channel blockers of the L type—Cd²⁺ (100 µ M ), nifedipine or nimodipine (10 µ M ), diltiazem (20 µ M ), or verapamil (50 µ M )—or the N type—ω-conotoxin GVIA (1 µ M ). In contrast, ω-agatoxin IVA (1 µ M ) led to a 65% reduction in NPFF release, suggesting that P-type Ca²⁺ channels play a prominent role. The 35% remaining release resulted from activation of an unknown subtype. The NPFF-like material in superfusates recognized spinal NPFF receptors, suggesting that NPFF release in the spinal cord has a physiological role.     

Interactions of polysaccharides extracted by mild acid hydrolysis from the leaves of Sphagnum papillosum with either phenylhydrazine, o-phenylenediamine and its oxidation products or collagen

The purpose of this research was to evaluate if pectin-like polysaccharides, collectively known as sphagnan, extracted by acid hydrolysis from the leaves of Sphagnum moss have a unique ability to react with phenylhydrazine, o-phenylenediamine or collagen. A previous assay for determination of carbonyl groups in sphagnan by reaction with phenylhydrazine was disproved due to spectrophotometric interference from furans. The actual carbonyl content of sphagnan is estimated to be much less than previously thought. NMR spectroscopy showed that small amounts of o-phenylenediamine and/or its oxidation products bind to sphagnan probably via imine formation, but evidence of quinoxaline formation was inconclusive. Sphagnan–gelatin mixtures formed complex coacervates at pH 2.0–4.8 at low ionic strength, which is typical of electrostatic polyelectrolyte interactions, rather than covalent carbonyl-amine reactions. Measurements of hydrothermal stability and collagenase-degradation of sphagnan-treated hide powder collagen suggest that sphagnan is a poor tanning agent. The results indicate the suggested preservative properties of sphagnan are not related to tanning.     

Interactions of prostaglandins with subpopulations of ovine luteal cells. I. Stimulatory effects of prostaglandins E1, E2 and I2

Preparations of small and large steroidogenic cells from enzymatically dispersed ovine corpora lutea were utilized to study the effects of luteinizing hormone (LH) and prostaglandins (PG) E₁, E₂ and I₂. Cells were allowed to attach to culture dishes overnight and were incubated with either LH (100 ng/ml), PGE₂, PGE₂, or PGI₂ (250 ng/ml each). The secretion of progesterone by large cells was stimulated by all prostaglandins tested (P < 0.05) while the moderate stimulation observed after LH treatment was attributable to contamination of the large cell population with small cells. Prostaglandins E₁ and E₂ had no effect on progesterone secretion by small cells, while LH was stimulatory at all times (0.5 to 4 hr) and PGI₂ was stimulatory by 4 hr. Additional studies were conducted to determine if the effects of PGE₂ upon steroidogenesis in large cells were correlated with stimulated activity of adenylate cyclase. In both plated and suspended cells PGE₂ caused an increase (P < 0.05) in the rate of progesterone secretion but had no effect upon the activity of adenylate cyclase or cAMP concentrations within cells or in the incubation media. Exposure of luteal cells to forskolin, a nonhormonal stimulator of adenylate cyclase, resulted in marked increases in all parameters of cyclase activity but had no effect on progesterone secretion. These data suggest that the actions of prostaglandins E₁, E₂ and I₂ are directed primarily toward the large cells of the ovine corpus luteum and cast doubt upon the role of adenylate cyclase as the sole intermediary in regulation of progesterone secretion in this cell type.