Phenoxytacrine derivatives: Low-toxicity neuroprotectants exerting affinity to ifenprodil-binding site and cholinesterase inhibition

Tacrine (THA), a long withdrawn drug, is still a popular scaffold used in medicinal chemistry, mainly for its good reactivity and multi-targeted effect. However, THA-associated hepatotoxicity is still an issue and must be considered in drug discovery based on the THA scaffold. Following our previously identified hit compound 7-phenoxytacrine (7-PhO-THA), we systematically explored the chemical space with 30 novel derivatives, with a focus on low hepatotoxicity, anticholinesterase action, and antagonism at the GluN1/GluN2B subtype of the NMDA receptor. Applying the down-selection process based on in vitro and in vivo pharmacokinetic data, two candidates, I-52 and II-52, selective GluN1/GluN2B inhibitors thanks to the interaction with the ifenprodil-binding site, have entered in vivo pharmacodynamic studies. Finally, compound I-52, showing only minor affinity to AChE, was identified as a lead candidate with favorable behavioral and neuroprotective effects using open-field and prepulse inhibition tests, along with scopolamine-based behavioral and NMDA-induced hippocampal lesion models. Our data show that compound I-52 exhibits low toxicity often associated with NMDA receptor ligands, and low hepatotoxicity, often related to THA-based compounds.

Frentizole derivatives with mTOR inhibiting and senomorphic properties

Frentizole is immunosuppressive drug with low acute toxicity and lifespan-prolonging effect. Recently, frentizole´s potential to disrupt toxic amyloid β (Aβ) - Aβ-binding alcohol dehydrogenase (ABAD) interaction in mitochondria in Alzheimer´s brains has been revealed. Another broadly studied drug with anti-aging and immunosuppressive properties is an mTOR inhibitor - rapamycin. Since we do not yet precisely know what is behind the lifespan-prolonging effect of rapamycin and frentizole, whether it is the ability to inhibit the mTOR signaling pathway, reduction in mitochondrial toxicity, immunosuppressive effect, or a combination of all of them, we have decided within our previous work to dock the entire in-house library of almost 240 Aβ-ABAD modulators into the FKBP-rapamycin-binding (FRB) domain of mTOR in order to interlink mTOR-centric and mitochondrial free radical-centric theories of aging and thus to increase the chances of success. Based on the results of the docking study, molecular dynamic simulation and MM-PBSA calculations, we have selected nine frentizole-like compounds (1 - 9). Subsequently, we have determined their real physical-chemical properties (logP, logD, pKa and solubility in water and buffer), cytotoxic/cytostatic, mTOR inhibitory, and in vitro anti-senescence (senolytic and senomorphic) effects. Finally, the three best candidates (4, 8, and 9) have been forwarded for in vivo safety studies to assess their acute toxicity and pharmacokinetic properties. Based on obtained results, only compound 4 demonstrated the best results within in vitro testing, the ability to cross the blood-brain barrier and the lowest acute toxicity (LD50 in male mice 559 mg/kg; LD50 in female mice 575 mg/kg).

Pitfalls of NMDA Receptor Modulation by Neuroactive Steroids. The Effect of Positive and Negative Modulation of NMDA Receptors in an Animal Model of Schizophrenia

Evidence from clinical and preclinical studies implicates dysfunction of N-methyl-D-aspartate receptors (NMDARs) in schizophrenia progression and symptoms. We investigated the antipsychotic effect of two neuroactive steroids in an animal model of schizophrenia induced by systemic application of MK-801. The neuroactive steroids differ in their mechanism of action at NMDARs. MS-249 is positive, while PA-Glu is a negative allosteric NMDAR modulator. We hypothesized that the positive NMDA receptor modulator would attenuate deficits caused by MK-801 co-application more effectively than PA-Glu. The rats were tested in a battery of tests assessing spontaneous locomotion, anxiety and cognition. Contrary to our expectations, PA-Glu exhibited a superior antipsychotic effect to MS-249. The performance of MS-249-treated rats in cognitive tests differed depending on the level of stress the rats were exposed to during test sessions. In particular, with the increasing severity of stress exposure, the performance of animals worsened. Our results demonstrate that enhancement of NMDAR function may result in unspecific behavioral responses. Positive NMDAR modulation can influence other neurobiological processes besides memory formation, such as anxiety and response to stress.

7-phenoxytacrine is a dually acting drug with neuroprotective efficacy in vivo

N-methyl-D-aspartaterecepro receptor (NMDARs) are a subclass of glutamate receptors, which play an essential role in excitatory neurotransmission, but their excessive overactivation by glutamate leads to excitotoxicity. NMDARs are hence a valid pharmacological target for the treatment of neurodegenerative disorders; however, novel drugs targeting NMDARs are often associated with specific psychotic side effects and abuse potential. Motivated by currently available treatment against neurodegenerative diseases involving the inhibitors of acetylcholinesterase (AChE) and NMDARs, administered also in combination, we developed a dually-acting compound 7-phenoxytacrine (7-PhO-THA) and evaluated its neuropsychopharmacological and drug-like properties for potential therapeutic use. Indeed, we have confirmed the dual potency of 7-PhO-THA, i.e. potent and balanced inhibition of both AChE and NMDARs. We discovered that it selectively inhibits the GluN1/GluN2B subtype of NMDARs via an ifenprodil-binding site, in addition to its voltage-dependent inhibitory effect at both GluN1/GluN2A and GluN1/GluN2B subtypes of NMDARs. Furthermore, whereas NMDA-induced lesion of the dorsal hippocampus confirmed potent anti-excitotoxic and neuroprotective efficacy, behavioral observations showed also a cholinergic component manifesting mainly in decreased hyperlocomotion. From the point of view of behavioral side effects, 7-PhO-THA managed to avoid these, notably those analogous to symptoms of schizophrenia. Thus, CNS availability and the overall behavioral profile are promising for subsequent investigation of therapeutic use.

Tacrine - Benzothiazoles: Novel class of potential multitarget anti-Alzheimeŕs drugs dealing with cholinergic, amyloid and mitochondrial systems

A series of tacrine - benzothiazole hybrids incorporate inhibitors of acetylcholinesterase (AChE), amyloid β (Aβ) aggregation and mitochondrial enzyme ABAD, whose interaction with Aβ leads to mitochondrial dysfunction, into a single molecule. In vitro, several of 25 final compounds exerted excellent anti-AChE properties and interesting capabilities to block Aβ aggregation. The best derivative of the series could be considered 10w that was found to be highly potent and selective towards AChE with the IC₅₀ value in nanomolar range. Moreover, the same drug candidate exerted absolutely the best results of the series against ABAD, decreasing its activity by 23% at 100 µM concentration. Regarding the cytotoxicity profile of highlighted compound, it roughly matched that of its parent compound - 6-chlorotacrine. Finally, 10w was forwarded for in vivo scopolamine-induced amnesia experiment consisting of Morris Water Maze test, where it demonstrated mild procognitive effect. Taking into account all in vitro and in vivo data, highlighted derivative 10w could be considered as the lead structure worthy of further investigation.

Synthetic structural modifications of neurosteroid pregnanolone sulfate: Assessment of neuroprotective effects in vivo

Neuroactive steroid 20-oxo-5β-pregnan-3α-yl L-glutamyl 1-ester (PA-Glu), a synthetic analogue of naturally occurring 20-oxo-5β-pregnan-3α-yl sulfate (pregnanolone sulfate, PA-S), inhibits N-methyl-D-aspartate (NMDA) receptors and possesses neuroprotective properties and minimal adverse effects. Herein, we report in vivo effects of new structural modifications of the PA-S molecule: a nonpolar modification of the steroid D-ring (5β-androstan-3α-yl L-glutamyl 1-ester, AND-Glu), attachment of a positively charged group to C3 (20-oxo-5β-pregnan-3α-yl L-argininate dihydrochloride salt, PA-Arg) and their combination (5β-androstan-3α-yl L-argininate dihydrochloride salt, AND-Arg). The first aim of this study was to determine the structure-activity relationship for neuroprotective effects in a model of excitotoxic hippocampal damage in rats, based on its behavioral correlate in Carousel maze. The second aim was to explore side effects of neuroprotective steroids on motor functions, anxiety (elevated plus maze) and locomotor activity (open field) and the effect of their high doses in mice. The neuroprotective properties of PA-Glu and AND-Glu were proven, with the effect of the latter appearing to be more pronounced. In contrast, neuroprotective efficacy failed when positively charged molecules (PA-Arg, AND-Arg) were used. AND-Glu and PA-Glu at the neuroprotective dose (1 mg/kg) did not unfavorably influence motor functions of intact mice. Moreover, anxiolytic effects of AND-Glu and PA-Glu were ascertained. These findings corroborate the value of research of steroidal inhibitors of NMDA receptors as potential neuroprotectants with slight anxiolytic effect and devoid of behavioral adverse effects. Taken together, the results suggest the benefit of the nonpolar D-ring modification, but not of the attachment of a positively charged group to C3.