At the present, only four antidotes are in use in therapy for poisoning by organophosphorus compounds: 2-PAM, HI-6, obidoxime and trimedoxime. Numerous compounds have been designed and synthetized to ...be more effective reactivators than those currently in use. Many of those new compounds fail at the enzyme level because interactions formed within the AChE active site are not favourable ones that lead to a successful reactivation. The approach in which the modeling of a phosphorylated oxime (POX), a product of successful reactivation in the AChE active site, may be a way to better understand the role of active site residues during the process of formation of the Michaelis type of complex between an enzyme and oxime. After reactivation, a change in phosphorus stereochemistry occurs leading to a different spatial arrangement of attached substituents, now including an oxime. To study interactions between the AChE oxyanion hole and a phosphorylated oxime, an S203G mutant was used to avoid the steric hindrance caused by the catalytic serine. In this way, the POX could be positioned close to the oxyanion hole. In the final step, the oxime without a phosphoester moiety was transferred into the phosphorylated AChE and molecular dynamics was used to test the stability of the near-attack conformation of the oxime near the phosphorylated serine.
•Acetylcholinesterase S203G mutant simulates the near-attack conformation of an oxime.•Molecular modeling of phosphorylated oxime simulates the near-attack conformation.•Molecular dynamics corroborate the near-attack conformation of oxime.
In this study, 68 crystal structures of complexes between acetylcholinesterase (AChE, EC 3.1.1.7) and its ligands, deposited in the PDB, were analyzed by scoring the functions: LigScore1, LigScore2, ...PLP1, PLP2, Jain, PMF and PMF04. The scores derived from scoring functions were correlated with an inhibition constant for each ligand (Ki or IC50) in a broad range 10−3 – 10−12 M. The linear correlation model resulted in the highest coefficient of determination (r2) for the PLP2 function, 0.591. The LigScore1 function resulted in the lowest r2 value of 0.226. The PubChem database was the source of in silico computed ligand properties which were then correlated with an inhibition constant for each ligand. For the purposes of this study, two additional non-PubChem parameters were evaluated: total and relative number of sp2 hybridized atoms in the ligand. A high coefficient of determination (r2 > 0.5) was calculated for the following parameters: the number of heavy atoms, molecular mass, and number of atoms with sp2 hybridization. The PLP2 scoring function is a good candidate for drug discovery related to AChE, although a better scoring function could be developed with a higher number of crystal structures of AChE complexes and more reliable kinetic data.
•Scoring functions can be used for AChE ligand inhibition potency assessment.•PLP2 scoring function predicts AChE ligand affinity with the highest correlation.•In silico computed ligand properties can be used for AChE affinity assessment.
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Toxicity of organophosphorus compounds (OPs) remains a major public health concern due to their widespread use as pesticides and the existence of nerve agents. Their common mechanism of action ...involves inhibition of enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) which are crucial for neurotransmission. Both chronic and acute poisoning by OPs can leave long-lasting health effects even when the patients are treated with standard medical therapy. Therefore, an increasing urgency exists to find more effective oxime reactivators for compounds which are resistant to reactivation, especially phosphoramidates. Here, we investigated in silico and in vitro interactions and kinetics of inhibition for human cholinesterases with four organophosphate pesticides-ethoprophos, fenamiphos, methamidophos and phosalone. Overall, ethoprophos and fenamiphos displayed higher potency as inhibitors for tested cholinesterases. Our results show that methamidophos-inhibited hAChE was more susceptible to reactivation than hAChE inhibited by fenamiphos by selected oximes. Molecular modelling enabled an evaluation of interactions important for specificity and selectivity of both inhibition and reactivation of cholinesterases. Two newly developed reactivators-bispyridinium triazole oxime 14A and zwitterionic oxime RS194B possess remarkable potential for further development of antidotes directed against pesticides and related phosphoramidate exposures, such as nerve agents tabun or Novichoks.
Triazoles are compounds with various biological activities, including fungicidal action. They became popular through cholinesterase studies after the successful synthesis of the dual binding ...femtomolar triazole inhibitor of acetylcholinesterase (AChE, EC 3.1.1.7) by Sharpless et al. via in situ click chemistry. Here, we evaluate the anticholinesterase effect of the first isopropanol triazole fungicide mefentrifluconazole (Ravystar®), developed to overcome fungus resistance in plant disease management. Mefentrifluconazole is commercially available individually or in a binary fungicidal mixture, i.e., with pyraclostrobin (Ravycare®). Pyraclostrobin is a carbamate that contains a pyrazole ring. Carbamates are known inhibitors of cholinesterases and the carbamate rivastigmine is already in use for the treatment of Alzheimer’s disease. We tested the type and potency of anticholinesterase activity of mefentrifluconazole and pyraclostrobin. Mefentrifluconazole reversibly inhibited human AChE and BChE with a seven-fold higher potency toward AChE (Ki = 101 ± 19 μM). Pyraclostrobin (50 μM) inhibited AChE and BChE progressively with rate constants of (t1/2 = 2.1 min; ki = 6.6 × 103 M−1 min−1) and (t1/2 = 1.5 min; ki = 9.2 × 103 M−1 min−1), respectively. A molecular docking study indicated key interactions between the tested fungicides and residues of the lipophilic active site of AChE and BChE. Additionally, the physicochemical properties of the tested fungicides were compared to values for CNS-active drugs to estimate the blood–brain barrier permeability. Our results can be applied in the design of new molecules with a lesser impact on humans and the environment.
In this study, we developed several QSAR models based on simple descriptors (such as topological and constitutional) to estimate butyrylcholinesterase (BChE) inhibition potency, pKi (or pIC50), of a ...set of 297 (289 after exclusion of outliers) structurally different compounds. The models were similar to the best model that we obtained previously for acetylcholinesterase AChE and were based on the valence molecular connectivity indices of second and third order (2χv and 3χv), the number of aliphatic hydroxyl groups (nOH), AlogP Ghose–Crippen octanol–water partition coeff. (logP), and O-060–atom-centred fragments (Al-O-Ar, Ar-O-Ar, R..O..R and R-O-C=X). The best models with two and three descriptors yielded r = 0.787 and S.E. = 0.89, and r = 0.827 and S.E. = 0.81, respectively. We also correlated nine scoring functions, calculated for 20 ligands whose complexes with BChE we found in the Protein Data Bank as crystal structures to pKi (or pIC50). The best correlations yielded PLP1 and PLP2 (Piecewise Linear Pairwise potential functions) with r = 0.619 and 0.689, respectively. Correlation with certain simple topological and constitutional descriptors yielded better results, e.g., 3χv (r = 0.730), on the same set of compounds (N = 20).
With the aging of the western population, more and more people are affected by the neurodegenerative Alzheimer's and Parkinson's disease. Inhibitors of acetylcholinesterase (AChE) have proven to be ...effective in the treatment of disease symptoms. We report the QSAR regression model for the estimation of potency of a set of 94 structurally diverse compounds (oximes, N-hydroxyiminoacetamides, 4-aminoquinolines and flavonoids) to inhibit AChE, pK
(AChE). The model is based on three simple descriptors: the valence molecular connectivity index of the zero-order,
χ
, combined with the number of 10-membered rings (nR10) and number of hydroxyl groups in a molecule (nOH). QSAR model yielded r = 0.947, S.E. = 0.51 and S.E.
= 0.53; the range of pK
(exp) = 6.03. It showed its stability when the set of 94 compounds was enlarged, comprising 184 compounds in total (r = 0.886, S.E. = 0.85 and S.E.
= 0.88; the range of pK
(exp) = 10.21), resulting in regression parameters which were similar, although only for
χ
coefficients within the limits of S.E. (0.167(13) and 0.172(16) for the set with 94 and 184 compounds, respectively. The predictive power of the model was shown by the prediction of pK
values for 61 randomly chosen compounds (S.E.
= 0.86) from the calibration model made on the other 123 compounds (S.E. = 0.85), all taken from the pool of 184 compounds. QSAR descriptors
χ
, nR10 and nOH were well chosen for describing the interactions of the AChE active site (amino acid interaction) with ligands through the estimation of the inhibitory potency.
A library of 14 mono-oxime quinuclidinium-based compounds with alkyl or benzyl substituent were synthesized and characterized in vitro as potential antidotes for organophosphorus compounds (OP) ...poisoning treatment. We evaluated their potency for reversible inhibition and reactivation of OP inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and evaluated interactions by molecular docking studies. The reactivation was notable for both AChE and BChE inhibited by VX, cyclosarin, sarin and paraoxon, if quinuclidinium compounds contained the benzyl group attached to the quinuclidinium moiety. Out of all 14, oxime
Q8
4-bromobenzyl-3-(hydroxyimino)quinuclidinium bromide was singled out as having the highest determined overall reactivation rate of approximately 20,000 M
−1
min
−1
for cyclosarin-inhibited BChE. Furthermore, this oxime in combination with BChE exhibited a capability to act as a bioscavenger of cyclosarin, degrading within 2 h up to 100-fold excess of cyclosarin concentration over the enzyme. Molecular modeling revealed that the position of the cyclohexyl moiety conjugated with the active site serine of BChE directs the favorable positioning of the quinuclidinium ring and the bromophenyl moiety of
Q8
, which makes phosphonylated-serine easily accessible for the nucleophilic displacement by the oxime group of
Q8
. This result presents a novel scaffold for the development of new BChE-based bioscavengers. Furthermore, a cytotoxic effect was not observed for
Q8
, which also makes it promising for further in vivo reactivation studies.
Acetylcholinesterase (AChE) has proven to be an effective drug target in the treatment of neurodegenerative diseases such as Alzheimer’s, Parkinson’s and dementia. We developed a novel QSAR ...regression model for estimating potency to inhibit AChE, pKi, on a set of 75 structurally different compounds including oximes, N-hydroxyiminoacetamides, 4-aminoquinolines and flavonoids. Although the model included only three simple descriptors, the valence molecular connectivity index of the zero-order, 0χv, the number of 10-membered rings (nR10) and the number of hydroxyl groups (nOH), it yielded excellent statistics (r = 0.937, S.E. = 0.51). The stability of the model was evaluated when an initial set of 75 compounds was broadened to 165 compounds in total, with the increase of the range of pKi (exp) from 6.0 to 10.2, yielding r = 0.882 and S.E. = 0.89. The predictive power of the model was evaluated by calculating pKi values for 55 randomly chosen compounds (S.E.test = 0.90) from the calibration model created on other 110 compounds (S.E. = 0.89), all taken from the pool of 165 compounds.
Eight derivatives of 4-aminoquinolines differing in the substituents attached to the C(4)-amino group and C(7) were synthesised and tested as inhibitors of human acetylcholinesterase (AChE) and ...butyrylcholinesterase (BChE). Both enzymes were inhibited by all of the compounds with inhibition constants (Ki) ranging from 0.50 to 50 μM exhibiting slight selectivity toward AChE over BChE. The most potent inhibitors of AChE were compounds with an n-octylamino chain or adamantyl group. The shortening of the chain length resulted in a decrease in AChE inhibition by 5–20 times. Docking studies revealed that the quinoline group within the AChE active site was positioned in the choline binding site, while the C(4)-amino group substituents, depending on their lipophilicity, could establish hydrogen bonds or π-interactions with residues of the peripheral anionic site. The most potent inhibitors of BChE were compounds with the most voluminous substituent on C(4)-amino group (adamantyl) or those with a stronger electron withdrawing substituent on C(7) (trifluormethyl group). Based on AChE inhibition, compounds with an n-octylamino chain or adamantyl substituent were shown to possess the capacity for further development as potential drugs for treatment of neurodegenerative diseases.
•Three derivatives were nanomolar selective AChE inhibitors.•The quinoline group is primarily stabilised by the choline binding site residues.•4-aminoquinoline derivatives exhibit slight selectivity toward AChE over BChE.•4-aminoquinoline derivatives have potential to penetrate the blood brain barrier.
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