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Kamil Kuca,1,2 Jana Zdarova Karasova,2,3 Ondrej Soukup,2 Jiri Kassa,3 Eva Novotna,2 Vendula Sepsova,2,3 Anna Horova,2 Jaroslav Pejchal,3 Martina Hrabinova,2,3 Eva Vodakova,2 Daniel Jun,2,3 Eugenie Nepovimova,1,2 Martin Valis,4 Kamil Musilek1,2 1Department of Chemistry, Faculty of Science, University of Hradec Kralove, 2Biomedical Research Center, University Hospital Hradec Kralove, 3Department of Toxicology and Military Pharmacy, Faculty of Military Health Sciences, University of Defence, 4Department of Neurology, University Hospital Hradec Kralove, Hradec Kralove, Czech Republic Background: Intoxication by nerve agents could be prevented by using small acetylcholinesterase inhibitors (eg, pyridostigmine) for potentially exposed personnel. However, the serious side effects of currently used drugs led to research of novel potent molecules for prophylaxis of organophosphorus intoxication. Methods: The molecular design, molecular docking, chemical synthesis, in vitro methods (enzyme inhibition, cytotoxicity, and nicotinic receptors modulation), and in vivo methods (acute toxicity and prophylactic effect) were used to study bispyridinium, bisquinolinium, bisisoquinolinium, and pyridinium-quinolinium/isoquinolinium molecules presented in this study. Results: The studied molecules showed non-competitive inhibitory ability towards human acetylcholinesterase in vitro that was further confirmed by molecular modelling studies. Several compounds were selected for further studies. First, their cytotoxicity, nicotinic receptors modulation, and acute toxicity (lethal dose for 50% of laboratory animals [LD50]; mice and rats) were tested to evaluate their safety with promising results. Furthermore, their blood levels were measured to select the appropriate time for prophylactic administration. Finally, the protective ratio of selected compounds against soman-induced toxicity was determined when selected compounds were found similarly potent or only slightly better to standard pyridostigmine. Conclusion: The presented small bisquaternary molecules did not show overall benefit in prophylaxis of soman-induced in vivo toxicity. Keywords: AChE inhibitors, prophylaxis, pre-treatment, nerve agents, toxicity, soman

The reactivating and therapeutic efficacy of two newly developed oximes (K305, K307) was compared with the oxime K203 and trimedoxime using in vivo methods The study determining percentage of reactivation of tabun-inhibited acetylcholinesterase in the peripheral as well as central nervous system (diaphragm, brain) in tabun-poisoned rats showed that the reactivating efficacy of both newly developed oximes is lower compared to the reactivating efficacy of the oxime K203 and trimedoxime. The therapeutic efficacy of all oximes studied roughly corresponds to their reactivating efficacy. While the ability of the oxime K305 to reduce acute toxicity of tabun in mice is approaching to the therapeutic efficacy of trimedoxime, the ability of another novel bispyridinium oxime K307 to reduce acute toxicity of tabun is significantly lower compared to trimedoxime and the oxime K203. Thus, the reactivating and therapeutic efficacy of both examined newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.

The potency of two novel oximes (K920, K923) to reactivate tabun-inhibited acetylcholinesterase and to reduce acute toxicity of tabun was compared with the oxime K203 and trimedoxime using in vivo methods. The study determining percentage of reactivation of tabun-inhibited peripheral acetylcholinesterase (diaphragm) and central acetylcholinesterase (brain) in tabun-poisoned rats showed that the reactivating efficacy of both newly developed oximes is lower than the reactivating potency of the oxime K203 and trimedoxime. The therapeutic efficacy of both newly developed oximes roughly corresponds to their weak reactivating efficacy. Their potency to reduce acute toxicity of tabun in mice was lower compared to the oxime K203 and trimedoxime. All differences in reactivating efficacy of oximes and different protective ratios were found for selected doses of oximes used in this study. Based on the results obtained, we can conclude that the reactivating and therapeutic potency of both newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning. The conclusion is only relevant for the experimental animals used in this study because of remarkable species differences in reactivating properties of oximes.

Novel types of symmetric bis-7-methoxytacrines connected by oligoethyleneoxy chains 3–5 and nonsymmetric monomeric 7-methoxytacrines containing hydroxyl-terminated oligoethyleneoxy chains 6–8 were prepared, and their in vitro/in silico effects on human recombinant AChE (hAChE) and human plasmatic butyrylcholinesterase (hBChE) were compared, with 7-MEOTA (2) as the standard compound. The symmetric bis-7-MEOTA derivatives 3–5 showed hAChE inhibition similar to that of 2. On the other hand, their effects on hBChE revealed an increasing inhibition trend when the oligoethyleneoxy units between the two 7-MEOTA moieties became longer. Accordingly, compounds 4 and 5 showed better selectivity towards hBChE. The most effective in the inhibition hAChE and hBChE was compound 8 with the longest oligoethyleneglycol chain, whereas compounds 6 and 7 resulted in similar IC50 values. A molecular modeling study using substrates 5 and 8 showed a possible binding conformation and protein–ligand interaction between the substrates and AChE/BChE.

A series of cholinesterase inhibitors acting as dual binding site heterodimers for the management of Alzheimer’s disease were developed. The series of 7-methoxytacrine (7-MEOTA)-amantadine ureas (11–17) was designed, prepared evaluated in vitro towards human acetyl/butyryl cholinesterase (hAChE, hBChE) and compared with the series of 7-MEOTA-amantadine thioureas (4–10). The heterodimers have different length of linkers combining 7-MEOTA and amantadine moieties. In comparison with 7-MEOTA, the newly synthesized compounds were better inhibitors of both cholinesterases. The urea analogues did not have the anticipated benefit of increased inhibitory activity and have comparable IC50 values with thiourea derivatives.

A novel series of 7-methoxytacrine (7-MEOTA)–donepezil like compounds was synthesized and tested for their ability to inhibit electric eel acetylcholinesterase (EeAChE), human recombinant AChE (hAChE), equine serum butyrylcholinesterase (eqBChE) and human plasmatic BChE (hBChE). New hybrids consist of a 7-MEOTA unit, representing less toxic tacrine (THA) derivative, connected with analogues of N-benzylpiperazine moieties mimicking N-benzylpiperidine fragment from donepezil. 7-MEOTA–donepezil like compounds exerted mostly non-selective profile in inhibiting cholinesterases of different origin with IC50 ranging from micromolar to sub-micromolar concentration scale. Kinetic analysis confirmed mixed-type inhibition presuming that these inhibitors are capable to simultaneously bind peripheral anionic site (PAS) as well as catalytic anionic site (CAS) of AChE. Molecular modeling studies and QSAR studies were performed to rationalize studies from in vitro. Overall, 7-MEOTA–donepezil like derivatives can be considered as interesting candidates for Alzheimer's disease treatment.

Two series of non-symmetrical bisquaternary pyridinium–quinolinium and pyridinium–isoquinolinium compounds were prepared as molecules potentially applicable in myasthenia gravis treatment. Their inhibitory ability towards human recombinant acetylcholinesterase and human plasmatic butyrylcholinesterase was determined and the results were compared to the known effective inhibitors such as ambenonium dichloride, edrophonium bromide and experimental compound BW284C51. Two compounds, 1-(10-(pyridinium-1-yl)decyl)quinolinium dibromide and 1-(12-(pyridinium-1-yl)dodecyl)quinolinium dibromide, showed very promising affinity for acetylcholinesterase with their IC50 values reaching nM inhibition of acetylcholinesterase. These most active compounds also showed satisfactory selectivity towards acetylcholinesterase and they seem to be very promising as leading structures for further modifications and optimization. Two of the most promising compounds were examined in the molecular modelling study in order to find the possible interactions between the ligand and tested enzyme.

The potency of three newly developed bispyridinium compounds (K454, K456, K458) to reactivate tabun-inhibited acetylcholinesterase and reduce tabun-induced lethal toxic effects was compared with the oxime K203 and trimedoxime using in vivo methods. The study determining percentage of reactivation of tabun-inhibited diaphragm and brain acetylcholinesterase in poisoned rats showed that the reactivating efficacy of all newly developed oximes is comparable with K203 but lower than the reactivating potency of trimedoxime in diaphragm. In the brain, their potency to reactivate tabun-inhibited acetylcholinesterase is lower compared with trimedoxime and the oxime K203. All three newly developed oximes were also found to be relatively effective in reducing lethal toxic effects in tabun-poisoned mice. Their therapeutic efficacy is consistent with the therapeutic potency of the oxime K203. On the other hand, their potency to reduce acute toxicity of tabun is significantly lower compared with trimedoxime. In conclusion, the reactivating and therapeutic potency of all three newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.

Alzheimer’s disease (AD) is a debilitating progressive neurodegenerative disorder that ultimately leads to the patient’s death. Despite the fact that novel pharmacological approaches endeavoring to block the neurodegenerative process are still emerging, none of them have reached use in clinical practice yet. Thus, palliative treatment represented by acetylcholinesterase inhibitors (AChEIs) and memantine are still the only therapeutics used. Following the multi-target directed ligands (MTDLs) strategy, herein we describe the synthesis, biological evaluation and docking studies for novel 7-methoxytacrine-p-anisidine hybrids designed to purposely target both cholinesterases and the amyloid cascade. Indeed, the novel derivatives proved to be effective non-specific cholinesterase inhibitors showing non-competitive AChE inhibition patterns. This compounds’ behavior was confirmed in the subsequent molecular modeling studies.

The treatment of organophosphorus (OP) poisoning consists of the administration of a parasympatholytic agent (e.g., atropine), an anticonvulsant (e.g., diazepam) and an acetylcholinesterase (AChE) reactivator (e.g., obidoxime). The AChE reactivator is the causal treatment of OP exposure, because it cleaves the OP moiety covalently bound to the AChE active site. In this paper, fourteen novel AChE reactivators are described. Their design originated from a former promising compound K027. These compounds were synthesized, evaluated in vitro on human AChE (hAChE) inhibited by tabun, paraoxon, methylparaoxon and DFP and then compared to commercial hAChE reactivators (pralidoxime, HI-6, trimedoxime, obidoxime, methoxime) or previously prepared compounds (K027, K203). Three of these novel compounds showed a promising ability to reactivate hAChE comparable or better than the used standards. Consequently, a molecular docking study was performed for three of these promising novel compounds. The docking results confirmed the apparent influence of π-π or cation-π interactions and hydrogen bonding for reactivator binding within the hAChE active site cleft. The SAR features concerning the non-oxime part of the reactivator molecule are also discussed.

Coupling of two distinct pharmacophores, tacrine and trolox, endowed with different biological properties, afforded 21 hybrid compounds as novel multifunctional candidates against Alzheimer's disease. Several of them showed improved inhibitory properties toward acetylcholinesterase (AChE) in relation to tacrine. These hybrids also scavenged free radicals. Molecular modeling studies in tandem with kinetic analysis exhibited that these hybrids target both catalytic active site as well as peripheral anionic site of AChE. In addition, incorporation of the moiety bearing antioxidant abilities displayed negligible toxicity on human hepatic cells. This striking effect was explained by formation of nontoxic metabolites after 1 h incubation in human liver microsomes system. Finally, tacrine-trolox hybrids exhibited low in vivo toxicity after im administration in rats and potential to penetrate across blood-brain barrier. All of these outstanding in vitro results in combination with promising in vivo outcomes highlighted derivative 7u as the lead structure worthy of further investigation.

The ability of two novel bispyridinium oximes K727 and K733 and currently available oximes (HI-6, obidoxime) to reactivate sarin-inhibited acetylcholinesterase and to reduce acute toxicity of sarin was evaluated. To investigate the reactivating efficacy of the oximes, the rats were administered intramuscularly with atropine and oximes in equitoxic doses corresponding to 5% of their LD50 values at 1 min after the intramuscular administration of sarin at a dose of 24 µg/kg (LD50). The activity of acetylcholinesterase was measured at 60 min after sarin poisoning. The LD50 value of sarin in non-treated and treated mice was assessed using probit-logarithmical analysis of death occurring within 24 h after intramuscular administration of sarin at five different doses. In vivo determined percentage of reactivation of sarin-inhibited rat blood, diaphragm and brain acetylcholinesterase showed that the potency of both novel oximes K727 and K733 to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to the reactivating efficacy of obidoxime. On the other hand, the oxime HI-6 was found to be the most efficient reactivator of sarin-inhibited acetylcholinesterase. While the oxime HI-6 was able to reduce the acute toxicity of sarin3 times, both novel oximes and obidoxime decreased the acute toxicity of sarin2 times. Based on the results, we can conclude that the reactivating and therapeutic efficacy of both novel oximes K727 and K733 is significantly lower compared to the oxime HI-6 and, therefore, they are not suitable for the replacement of the oxime HI-6 for the antidotal treatment of acute sarin poisoning.

The reactivating and therapeutic efficacy of three original bispyridinium oximes (K727, K733 and K203) and one currently available oxime (trimedoxime) was evaluated in tabun-poisoned rats and mice. The oxime-induced reactivation of tabun-inhibited acetylcholinesterase was measured in diaphragm and brain of tabun-poisoned rats. The results showed that the reactivating efficacy of two recently developed oximes (K727 and K733) does not achieve the level of the reactivation of tabun-inhibited acetylcholinesterase induced by oxime K203 and trimedoxime. While all oximes studied were able to increase the activity of tabun-inhibited acetylcholinesterase in diaphragm, oxime K733 was not able to reactivate tabun-inhibited acetylcholinesterase in the brain. The therapeutic efficacy of all oximes studied roughly corresponds to their reactivating efficacy. While both recently developed oximes were able to reduce acute toxicity of tabun less than 1.5-fold, another original oxime K203 and commonly used trimedoxime reduced the acute toxicity of tabun almost two times. In conclusion, the reactivating and therapeutic potency of both newly developed oximes does not prevail the effectiveness of oxime K203 and trimedoxime, and therefore, they are not suitable for their replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning.

The potency of two newly developed oximes (K361 and K378) to reactivate tabun-inhibited cholinesterase and to reduce acute toxicity of tabun was compared with the oxime K203 and trimedoxime using in vivo methods. The study determining percentage of reactivation of tabun-inhibited diaphragm cholinesterase in poisoned rats showed that the reactivating efficacy of the oxime K378 is slightly lower than the reactivating potency of the oxime K203 and trimedoxime while the ability of the oxime K361 to reactivate tabun-inhibited cholinesterase is markedly lower compared with the oxime K203 and trimedoxime. In the brain, the potency of both newly developed oximes to reactivate tabun-inhibited cholinesterase was negligible. The therapeutic efficacy of both newly developed oximes roughly corresponds to their weak reactivating efficacy. Their potency to reduce acute toxicity of tabun was significantly lower compared with the oxime K203 as well as trimedoxime. In conclusion, the reactivating and therapeutic potency of both newly developed oximes does not prevail the effectiveness of the oxime K203 and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.

Myasthenia gravis is very rare autoimmune disease of neuromuscular junction, which presents as a weakness and increased fatiquability of striated muscles. Formerly, myasthenia was largely constraining disease and often ended by death. Recently, advanced diagnostic methods and variety of therapeutic options allow the full compensation of the disease and the quality of patient life is restored. In this review, the methods used during the myasthenia treatment along with the description of the disease itself were detailed.

Cholinesterase inhibitors are, so far, the only successful strategy for the symptomatic treatment of Alzheimer’s disease. Tacrine (THA) is a potent acetylcholinesterase inhibitor that was used in the treatment of Alzheimer’s disease for a long time. However, the clinical use of THA was hampered by its low therapeutic index, short half-life and liver toxicity. 7-Methoxytacrine (7-MEOTA) is equally pharmacological active compound with lower toxicity compared to THA. In this Letter, the synthesis, biological activity and molecular modelling of elimination by-product isolated during synthesis of 7-MEOTA based bis-alkylene linked compound is described.

This paper describes the preparation and in vitro evaluation of 18 newly prepared bis-quinolinium inhibitors on human recombinant acetylcholinesterase (AChE) and human plasmatic butyrylcholinesterase (BChE). Their inhibitory (IC50) and was compared to the chosen standards ambenonium dichloride, edrophonium chloride, BW284c51 and ethopropazine hydrochloride. One novel compound was found to be a promising inhibitor of hAChE (in nM range) and was better than edrophonium chloride or BW284c51, but was worse than ambenonium chloride. This compound also showed selectivity towards hAChE and it was confirmed as a non-competitive inhibitor of hAChE by kinetic analysis. A molecular modelling study further confirmed its binding to the peripheral active site of hAChE via apparent π–π or π–cationic interactions.

This paper describes preparation and in vitro evaluation of 19 compounds related to the selective experimental cholinesterase inhibitor BW284c51. The novel compounds were prepared as fragments of parent molecule BW284c51 and evaluated on the model of human recombinant acetylcholinesterase and human plasmatic butyrylcholinesterase. The IC₅₀ values of the prepared compounds were compared to the parent molecule BW284c51. None of the compounds was superior to the parent drug, but two BW284c51 fragments showed promising hAChE inhibition in µM scale and improved selectivity. These two fragments were further subjected to the molecular modelling study and their enzyme interactions were rationalized. The structure-activity relationship of the prepared series was stated.