Encapsulation of oxime K027 into cucurbit[7]uril: In vivo evaluation of safety, absorption, brain distribution and reactivation effectiveness

Brominated oxime nucleophiles are efficiently reactivating cholinesterases inhibited by nerve agents

Six novel brominated bis-pyridinium oximes were designed and synthesized to increase their nucleophilicity and reactivation ability of phosphorylated acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Their pKa was valuably found lower to parent non-halogenated oximes. Stability tests showed that novel brominated oximes were stable in water, but the stability of di-brominated oximes was decreased in buffer solution and their degradation products were prepared and characterized. The reactivation screening of brominated oximes was tested on AChE and BChE inhibited by organophosphorus surrogates. Two mono-brominated oximes reactivated AChE comparably to non-halogenated analogues, which was further confirmed by reactivation kinetics. The acute toxicity of two selected brominated oximes was similar to commercially available oxime reactivators and the most promising brominated oxime was tested in vivo on sarin- and VX-poisoned rats. This brominated oxime showed interesting CNS distribution and significant reactivation effectiveness in blood. The same oxime resulted with the best protective index for VX-poisoned rats.

Toxicity, pharmacokinetics, and effectiveness of the ortho-chlorinated bispyridinium oxime, K870

Oxime reactivators are causal antidotes for organophosphate intoxication. Herein, the toxicity, pharmacokinetics, and reactivation effectiveness of o-chlorinated bispyridinium oxime K870 are reported. Oxime K870 was found to have a safe profile at a dose of 30 mg/kg in rats. It exhibited rapid absorption and renal clearance similar to those of other charged oximes after intramuscular administration. Its isoxazole-pyridinium degradation product was identified in vivo. Although it showed some improvement in brain targeting, it was nevertheless rapidly effluxed from the central nervous system. Its reactivation effectiveness was evaluated in rats and mice intoxicated with sarin, tabun, VX, and paraoxon and compared with pralidoxime and asoxime. K870 was found to be less effective in reversing tabun poisoning compared to its parent unchlorinated oxime K203. However, K870 efficiently reactivated blood acetylcholinesterase for all tested organophosphates in rats. In addition, K870 significantly protected against intoxication by all tested organophosphates in mice. For these reasons, oxime K870 seems to have a broader reactivation spectrum against multiple organophosphates. It seems important to properly modulate the oximate forming properties (pK_a) to obtain more versatile oxime reactivators.

Assessment of the Biocompatibility of Cucurbiturils in Blood Cells

Currently, cucurbiturils are being actively researched all over the world. Research is focused on the ways of improving the solubility and selectivity of cucurbiturils, increasing the stability of the complexes with other particles in various media and enhancing their ability to bind and release various substances. The most significant area of our research is the assessment of safety, studying the biological properties and synergistic effects of cucurbiturils during complexation with drugs. In this article, the hemocompatibility of erythrocytes and leukocytes with cucurbiturils was investigated. We demonstrated that cucurbiturils have no cytotoxic effect, even at high concentrations (1 mM) and do not affect the viability of PBMCs. However, cucurbiturils can increase the level of the early apoptosis of lymphocytes and cucurbit[7]uril enhances hemolysis in biologically relevant media. Despite this, cucurbiturils are fairly safe organic molecules in concentrations up to 0.3 mM. Thus, we believe that it will become possible to use polymer nanostructures as drug delivery systems in clinical practice, since cucurbiturils can be modified to improve pharmacological properties.

Effect of Oxime Encapsulation on Acetylcholinesterase Reactivation: Pharmacokinetic Study of the Asoxime-Cucurbit[7]uril Complex in Mice Using Hydrophilic Interaction Liquid Chromatography-Mass Spectrometry

Oxime-based molecules are used for the treatment of patients to reactivate acetylcholinesterase (AChE) function after organophosphate intoxication. However, their efficacy is limited by low penetration through the blood-brain barrier and fast elimination. In this work, the cucurbit[7]uril (CB[7]) carrier was used for the encapsulation of the clinical agent asoxime to enhance brain bioavailability and the treatment window. We present a pharmacokinetic study of asoxime and the asoxime-CB[7] complex in an in vivo mouse model. Ultrahigh-performance liquid chromatography with electrospray ionization-mass spectrometry detection was developed to determine asoxime and CB[7] in biological fluids and tissues after thorough optimization of chromatographic conditions. The dihydroxypropane-silica stationary phase using hydrophilic interaction liquid chromatography conditions provided the best chromatographic performance. The final method was validated and applied for the pharmacokinetic study of mouse plasma, urine, bile, liver, kidney, and brain samples at different times after administration of asoxime and the asoxime-CB[7] complex. The results showed a greater than 3-fold increase in the area under the curve (AUC) in the brain for asoxime administered as a complex with CB[7] relative to that for the administration of asoxime alone. The effectiveness of the treatment strategy was evaluated using a reactivation study and a functional observatory battery. Protection of brain AChE activity is crucial for saving human lives or reducing the consequences of poisoning. The asoxime administered as a complex increased the brain activity by approximately 30% compared to that with atropine alone. CB[7] coadministration improved the AChE activity by 11%, which agrees with the higher asoxime AUC assessed in the pharmacokinetic study.

Structure-activity relationships of dually-acting acetylcholinesterase inhibitors derived from tacrine on N-methyl-d-Aspartate receptors

Tacrine is a classic drug whose efficacy against neurodegenerative diseases is still shrouded in mystery. It seems that besides its inhibitory effect on cholinesterases, the clinical benefit is co-determined by NMDAR-antagonizing activity. Our previous data showed that the direct inhibitory effect of tacrine, as well as its 7-methoxy derivative (7-MEOTA), is ensured via a "foot-in-the-door" open-channel blockage, and that interestingly both tacrine and 7-MEOTA are slightly more potent at the GluN1/GluN2A receptors when compared with the GluN1/GluN2B receptors. Here, we report that in a series of 30 novel tacrine derivatives, designed for assessment of structure-activity relationship, blocking efficacy differs among different compounds and receptors using electrophysiology with HEK293 cells expressing the defined types of NMDARs. Selected compounds (4 and 5) potently inhibited both GluN1/GluN2A and GluN1/GluN2B receptors; other compounds (7 and 23) more effectively inhibited the GluN1/GluN2B receptors; or the GluN1/GluN2A receptors (21 and 28). QSAR study revealed statistically significant model for the data obtained for inhibition of GluN1/Glu2B at -60 mV expressed as IC₅₀ values, and for relative inhibition of GluN1/Glu2A at +40 mV caused by a concentration of 100 μM. The models can be utilized for a ligand-based virtual screening to detect potential candidates for inhibition of GluN1/Glu2A and/or GluN1/Glu2B subtypes. Using in vivo experiments in rats we observed that unlike MK-801, the tested novel compounds did not induce hyperlocomotion in open field, and also did not impair prepulse inhibition of startle response, suggesting minimal induction of psychotomimetic side effects. We conclude that tacrine derivatives are promising compounds since they are centrally available subtype-specific inhibitors of the NMDARs without detrimental behavioral side-effects.

Development of versatile and potent monoquaternary reactivators of acetylcholinesterase

To date, the only treatments developed for poisoning by organophosphorus compounds, the most toxic chemical weapons of mass destruction, have exhibited limited efficacy and versatility. The available causal antidotes are based on reactivation of the enzyme acetylcholinesterase (AChE), which is rapidly and pseudo-irreversibly inhibited by these agents. In this study, we developed a novel series of monoquaternary reactivators combining permanently charged moieties tethered to position 6- of 3-hydroxypyridine-2-aldoxime reactivating subunit. Highlighted representatives (21, 24, and 27; also coded as K1371, K1374, and K1375, respectively) that contained 1-phenylisoquinolinium, 7-amino-1-phenylisoquinolinium and 4-carbamoylpyridinium moieties as peripheral anionic site ligands, respectively, showed efficacy superior or comparable to that of the clinically used standards. More importantly, these reactivators exhibited wide-spectrum efficacy and were minutely investigated via determination of their reactivation kinetics in parallel with molecular dynamics simulations to study their mechanisms of reactivation of the tabun-inhibited AChE conjugate. To further confirm the potential applicability of these candidates, a mouse in vivo assay was conducted. While K1375 had the lowest acute toxicity and the most suitable pharmacokinetic profile, the oxime K1374 with delayed elimination half-life was the most effective in ameliorating the signs of tabun toxicity. Moreover, both in vitro and in vivo, the versatility of the agents was substantially superior to that of clinically used standards. Their high efficacy and broad-spectrum capability make K1374 and K1375 promising candidates that should be further investigated for their potential as nerve agents and insecticide antidotes.

Interaction of Cucurbit[7]uril with Oxime K027, Atropine, and Paraoxon: Risky or Advantageous Delivery System?

Antidotes against organophosphates often possess physicochemical properties that mitigate their passage across the blood–brain barrier. Cucurbit[7]urils may be successfully used as a drug delivery system for bisquaternary oximes and improve central nervous system targeting. The main aim of these studies was to elucidate the relationship between cucurbit[7]uril, oxime K027, atropine, and paraoxon to define potential risks or advantages of this delivery system in a complex in vivo system. For this reason, in silico (molecular docking combined with umbrella sampling simulation) and in vivo (UHPLC—pharmacokinetics, toxicokinetics; acetylcholinesterase reactivation and functional observatory battery) methods were used. Based on our results, cucurbit[7]urils affect multiple factors in organophosphates poisoning and its therapy by (i) scavenging paraoxon and preventing free fraction of this toxin from entering the brain, (ii) enhancing the availability of atropine in the central nervous system and by (iii) increasing oxime passage into the brain. In conclusion, using cucurbit[7]urils with oximes might positively impact the overall treatment effectiveness and the benefits can outweigh the potential risks.

Encapsulation of oxime acetylcholinesterase reactivators: influence of physiological conditions on the stability of oxime-cucurbit[7]uril complexes

The influence of physiological conditions on the host–guest chemistry of oxime acetylcholinesterase reactivators with cucurbit[7]urile was investigated to increase their effectiveness for the treatment of organophosphate intoxication.