The lifetime of a ligand-receptor complex has been suggested to play an important role in compound activity and sustained pharmacological action. However, due to the multitude of other factors considered during optimization, this aspect is often neglected in the early stages of drug design and development. Consequently, data on ligand residence time (RT) remain limited, and the molecular determinants underlying prolonged binding are not fully understood. In this study, we focused on ritanserin, a known 5-HT2A receptor (5-HT2AR) antagonist with an RT of 68 min. By modifying its structure, we synthesized a series of derivatives with varying RT, which was determined in vitro. Comprehensive molecular modeling analyses, including docking and molecular dynamics simulations, enabled us to propose a set of key receptor-ligand contacts contributing to prolonged binding. Both conventional molecular dynamics and enhanced sampling approaches (metadynamics and random-accelerated molecular dynamics) were applied to the native and mutant receptors, providing in-depth insights into the determinants of long ligand occupancy at the 5-HT2AR. The study indicated that prolonged RT is associated with, for example, stable and geometrically optimized π-π interactions with a hydrophobic aromatic cluster (Trp3366.48 and Phe3406.52, in particular). To our knowledge, this represents the first such a comprehensive study of its kind, offering novel hypotheses that may guide the design of new 5-HT2AR ligands with prolonged duration of action.

The temporal stability of ligand-receptor complexes is increasingly acknowledged as a critical factor in drug discovery, influencing both efficacy and pharmacodynamics. Although the relationship between the duration of compound action and complex stability can be traced back to Paul Ehrlich's 19th-century doctrine Corpora non agunt nisi fixata, its significance has gained renewed attention in recent years. This review comprehensively examines the concept of residence time (RT). We first summarize key ligand binding models (lock-and-key, induced-fit, and conformational selection) and delve into various perspectives on how RT impacts functional outcomes. Furthermore, we discuss experimental methods for measuring RT, highlighting both radioligand and non-radioligand approaches. The growing interest in RT has spurred advancements in computational techniques, particularly molecular dynamics simulations, which utilize diverse strategies to observe dissociation events. We outline these molecular dynamics-based methods, their theoretical foundations, and provide examples of their application in assessing RT. Finally, we highlight molecular determinants of prolonged RT, focusing primarily on G protein-coupled receptors (GPCRs) while also incorporating relevant data from other receptor classes.

RATIONALE:Our study aimed to unravel the unknown mechanisms behind the exceptional efficacy of Psilocybin (PSI) in treating treatment-resistant depression (TRD). Focusing on Wistar-Kyoto (WKY) rats with a TRD phenotype and Wistar (WIS) rats as a normative comparison, we investigated behavioral and neuroplasticity-related responses to PSI, striving to shed light on the distinctive features of its antidepressant effects. OBJECTIVES:We set out to assess the behavioral impact of acute and prolonged PSI administration on WKY and WIS rats, employing Novel Object Recognition (NORT), Social Interaction (SI), and Forced Swimming Test (FST). Our secondary objectives involved exploring strain-specific alterations in neuroplasticity-related parameters, including brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton-associated protein (Arc). METHODS:Conducting post-acute and extended assessments after a single PSI administration, we applied behavioral tests and biochemical analyses to measure serum BDNF levels and neuroplasticity-related parameters in the prefrontal cortex. Statistical analyses were deployed to discern significant differences between the rat strains and assess the impact of PSI on behavioral and biochemical outcomes. RESULTS:Our findings uncovered significant behavioral disparities between WKY and WIS rats, indicating passive behavior and social withdrawal in the former. PSI demonstrated pronounced pro-social and antidepressant effects in both strains, each with its distinctive temporal trajectory. Notably, we identified strain-specific variations in BDNF-related signaling and observed the modulation of Arc expression in WKY rats. CONCLUSIONS:Our study delineated mood-related behavioral nuances between WKY and WIS rat strains, underscoring the antidepressant and pro-social properties of PSI in both groups. The distinct temporal patterns of observed changes and the identified strain-specific neuroplasticity alterations provide valuable insights into the TRD phenotype and the mechanisms underpinning the efficacy of PSI.

The serotonin 5-HT5A receptor has attracted much more research attention, due to the therapeutic potential of its ligands being increasingly recognized, and the possibilities that lie ahead of these findings. There is a growing body of evidence indicating that these ligands have procognitive, pro-social, and anti-depressant properties, which offers new avenues for the development of treatments that could address socially important conditions related to the malfunctioning of the central nervous system. The aim of our study was to unravel the molecular determinants for 5-HT5AR ligands that govern their activity towards the receptor. In response to the need for identification of molecular determinants for 5-HT5AR activity, we prepared a comprehensive collection of 5-HT5AR ligands, carefully gathering literature and patent data. Leveraging molecular modeling techniques, such as pharmacophore hypothesis development, docking, and molecular dynamics simulations enables to gain valuable insights into the specific interactions of 5-HT5AR ligand groups with the receptor. The obtained comprehensive set of 2160 compounds was divided into dozens of subsets, and a pharmacophore model was developed for each group. The results from the docking and molecular dynamics simulations have enabled the identification of crucial ligand–protein interactions that are essential for the compound's activity towards 5-HT5AR. The findings from the molecular modeling study provide valuable insights that can guide medicinal chemists in the development of new 5-HT5AR ligands. Considering the pharmacological significance of these compounds, they have the potential to become impactful treatments for individuals and communities in the future. Understanding how different crystal/cryo-EM structures of 5-HT5AR affect molecular modeling experiments could have major implications for future computational studies on this receptor.

Bottled mineral and spring water constitute one of the main sources of drinking water. Relevant legal acts in each country individually regulate the highest permitted concentrations of harmful substances in these waters. However, current regulations do not take into account newly emerging contaminants such as BPA. Analysis of the chemical composition of 72 bottled waters from the Polish market showed that undesirable elements occur in quantities that do not exceed the maximum permissible concentrations. Special attention should be paid to bottled therapeutic water, which may contain elevated concentrations of some micronutrients, such as Al, B, Ba, Fe, Mn, or Sr contributing to the pattern of health risk with excessive consumption of this type of water. The presence of BPA was confirmed in 25 tested waters. The calculated hazard index values showed that the most exposed group are children up to 12 years of age. The greatest attention should be paid to waters with high mineralisation, for which the calculated risk values are the highest.

Following the glutamatergic theory of schizophrenia and based on our previous study regarding the antipsychotic-like activity of mGlu7 NAMs, we synthesized a new compound library containing 103 members, which were examined for NAM mGlu7 activity in the T-REx 293 cell line expressing a recombinant human mGlu7 receptor. Out of the twenty-two scaffolds examined, active compounds were found only within the quinazolinone chemotype. 2-(2-Chlorophenyl)-6-(2,3-dimethoxyphenyl)-3-methylquinazolin-4(3H)-one (A9-7, ALX-171, mGlu7 IC50 = 6.14 µM) was selective over other group III mGlu receptors (mGlu4 and mGlu8), exhibited satisfactory drug-like properties in preliminary DMPK profiling, and was further tested in animal models of antipsychotic-like activity, assessing the positive, negative, and cognitive symptoms. ALX-171 reversed DOI-induced head twitches and MK-801-induced disruptions of social interactions or cognition in the novel object recognition test and spatial delayed alternation test. On the other hand, the efficacy of the compound was not observed in the MK-801-induced hyperactivity test or prepulse inhibition. In summary, the observed antipsychotic activity profile of ALX-171 justifies the further development of the group of quinazolin-4-one derivatives in the search for a new drug candidate for schizophrenia treatment.

A growing body of evidence points out the involvement of the µ-opioid receptors in the modulation of stress-related behaviour. It has been suggested that µ-opioid receptor agonists may attenuate behavioural despair following animals' exposure to an acute, inescapable stressor. Moreover, morphine was shown to ameliorate fear memories caused by a traumatic experience. As typical µ-opioid receptor agonists entail a risk of serious side effects and addiction, novel, possibly safer and less addictive agonists of this receptor are currently under investigation. One of them, PZM21, preferentially acting via the G protein signalling pathway, was previously shown to be analgesic, but less addictive than morphine. Here, we aimed to further test this ligand in stress-related behavioural paradigms in mice. The study has shown that, unlike morphine, PZM21 does not decrease immobility in the forced swimming and tail suspension tests. On the other hand, we observed that both mice treated with PZM21 and those receiving morphine presented a slight attenuation of freezing across the consecutive fear memory retrievals in the fear conditioning test. Therefore, our study implies that at the range of tested doses, PZM21, a nonrewarding representative of G protein-biased µ-opioid receptor agonists, may interfere with fear memory consolidation while having no beneficial effects on behavioural despair in mice.

Among different approaches to the search for novel-safer and less addictive-opioid analgesics, biased agonism has received the most attention in recent years. Some μ-opioid receptor agonists with G protein bias, including SR compounds, were proposed to induce diminished side effects. However, in many aspects, behavioral effects of those compounds, as well as the mechanisms underlying differences in their action, remain unexplored. Here, we aimed to evaluate the effects of SR-14968 and SR-17018, highly G protein-biased opioid agonists, on antinociception, motor activity and addiction-like behaviors in C57BL/6J mice. The obtained results showed that the compounds induce strong and dose-dependent antinociception. SR-14968 causes high, and SR-17018 much lower, locomotor activity. Both agonists develop reward-associated behavior and physical dependence. The compounds also cause antinociceptive tolerance, however, developing more slowly when compared to morphine. Interestingly, SR compounds, in particular SR-17018, slow down the development of antinociceptive tolerance to morphine and inhibit some symptoms of morphine withdrawal. Therefore, our results indicate that SR agonists possess rewarding and addictive properties, but can positively modulate some symptoms of morphine dependence. Next, we have compared behavioral effects of SR-compounds and PZM21 and searched for a relationship to the substantial differences in molecular interactions that these compounds form with the µ-opioid receptor.

Currently used antidepressants do not always provide the desired results, and many patients suffer from treatment-resistant depression. Clinical studies suggest that zinc deficiency (ZnD) may be an important risk factor for depression and might blunt the effect of antidepressants. This study aimed to examine whether ZnD might blunt the effectiveness of antidepressants in the olfactory bulbectomy model (OB) of depression in rats. For this purpose, rats were subjected to the OB model, fed a zinc-deficient diet (3 mg Zn/kg) for 3 weeks, and finally treated with escitalopram (Esc), venlafaxine (Ven) 10 mg/kg, i.p., or combined Esc/Ven (1 mg/kg, i.p.) with zinc (5 mg/kg) for another 3 weeks. Open field (OFT), forced swim (FST), and sucrose intake (SIT) tests were used to evaluate depressive-like behavioral changes. In addition, serum, intracellular, and synaptic Zn concentrations and the level of zinc transporter (ZnT) proteins were analyzed. The OB + ZnD model induced hyperactivity in rats in the OFT, increased immobility time in the FST, and anhedonia in the SIT. Chronic treatment with Esc reduced immobility time in the FST in the OB + ZnD model. Esc/Ven +Zn increased sucrose intake in rats from the OB + ZnD group. The OB + ZnD decreased serum zinc levels and intracellular and synaptic Zn concentration in the prefrontal cortex (PFC) and cerebellum. These changes were normalized by chronic administration of Esc/Ven +Zn. Moreover, OB + ZnD decreased levels of the ZnT1 protein in the PFC and Hp and ZnT3 in Hp. Chronic administration of antidepressants did not alter the levels of ZnT proteins. The OB + ZnD model induces more depressive-like effects than either model alone. Our results show that ZnD may induce drug resistance in rats. Normalizing serum or brain zinc concentration is insufficient to reverse behavioral abnormalities caused by the OB + ZnD model. However, zinc supplementation might improve the effectiveness of antidepressants in reversing particular depression symptoms.

Considering the allosteric regulation of mGlu receptors for potential therapeutic applications, we developed a group of 1,2,4-oxadiazole derivatives that displayed mGlu(4) receptor positive allosteric modulatory activity (EC50 = 282-656 nM). Selectivity screening revealed that they were devoid of activity at mGlu(1), mGlu(2) and mGlu(5) receptors, but modulated mGlu(7) and mGlu(8) receptors, thus were classified as group III-preferring mGlu receptor agents. None of the compounds was active towards hERG channels or in the mini-AMES test. The most potent in vitro mGlu(4) PAM derivative 52 (N-(3-chloro-4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)phenyl)picolinamide) was readily absorbed after i.p. administration (male Albino Swiss mice) and reached a maximum brain concentration of 949.76 ng/mL. Five modulators (34, 37, 52, 60 and 62) demonstrated significant anxiolytic- and antipsychotic-like properties in the SIH and DOI-induced head twitch test, respectively. Promising data were obtained, especially for N-(4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)-3-methylphenyl)picolinamide (62), whose effects in the DOI-induced head twitch test were comparable to those of clozapine and better than those reported for the selective mGlu(4) PAM ADX88178.

RATIONALE:Ketamine and psilocybin belong to the rapid-acting antidepressants but they also produce psychotomimetic effects including timing distortion. It is currently debatable whether these are essential for their therapeutic actions. As depressed patients report that the "time is dragging," we hypothesized that ketamine and psilocybin-like compounds may produce an opposite effect, i.e., time underestimation, purportedly contributing to their therapeutic properties.OBJECTIVES:Timing was tested following administration of (R)- and (S)-ketamine, and psilocybin, psilocin, and norpsilocin in the discrete-trial temporal discrimination task (TDT) in male rats. Timing related to premature responses, and cognitive and unspecific effects of compounds were tested in the 5-choice serial reaction time task (5-CSRTT) in the standard 1-s, and "easier" 2-s stimulus duration conditions, as well as in the vITI variant promoting impulsive responses.RESULTS:(S)-ketamine (15 but not 3.75 or 7.5 mg/kg) shifted psychometric curve to the right in TDT and reduced premature responses in 5-CSRTT, suggesting expected time underestimation, but it also decreased the accuracy of temporal discrimination and increased response and reward latencies, decreased correct responses, and increased incorrect responses. While (R)-ketamine did not affect timing and produced no unspecific actions, it reduced incorrect responses in TDT and increased accuracy in 5-CSRTT, suggesting pro-cognitive effects. Psilocin and psilocybin produced mainly unspecific effects in both tasks, while norpsilocin showed no effects.CONCLUSIONS:Time underestimation produced by (S)-ketamine could be associated with its antidepressant effects; however, it was accompanied with severe behavioral disruption. We also hypothesize that behavioral disruption produced by psychedelics objectively reflects their psychotomimetic-like actions.

A series of N-skatyltryptamines was synthesized and their affinities for serotonin and dopamine receptors were determined. Compounds exhibited activity toward 5-HT1A, 5-HT2A, 5-HT6, and D2 receptors. Substitution patterns resulting in affinity/activity switches were identified and studied using homology modeling. Chosen hits were screened to determine their metabolism, permeability, hepatotoxicity, and CYP inhibition. Several D2 receptor antagonists with additional 5-HT6R antagonist and agonist properties were identified. The former combination resembled known antipsychotic agents, while the latter was particularly interesting due to the fact that it has not been studied before. Selective 5-HT6R antagonists have been shown previously to produce procognitive and promnesic effects in several rodent models. Administration of 5-HT6R agonists was more ambiguous-in naive animals, it did not alter memory or produce slight amnesic effects, while in rodent models of memory impairment, they ameliorated the condition just like antagonists. Using the identified hit compounds 15 and 18, we tried to sort out the difference between ligands exhibiting the D2R antagonist function combined with 5-HT6R agonism, and mixed D2/5-HT6R antagonists in murine models of psychosis.

Depression is a mental disease that affects complex cognitive and emotional functions. It is believed that depression is twice as prevalent in women as in men. This phenomenon may influence the response to various antidepressant therapies, and these differences are still underestimated in clinical treatment. Nevertheless, most of the current findings are based on studies on male animal models, and relatively few of these studies take possible gender differences into consideration. Advancements in genetic engineering over the last two decades have introduced many transgenic lines that have been screened to study the pathomechanisms of depression. In this mini-review, we provide a compendious list of genetically altered mice that underwent tests for depressive-like or antidepressant behavior and determine if and how the gender factor was analyzed in their evaluation. Furthermore, we compile the gender differences in response to antidepressant treatment. On the basis of these analyses, we conclude that in many cases, gender variability is neglected or not taken into consideration in the presented results. We note the necessity of discussing this issue in the phenotypic characterization of transgenic mice, which seems to be particularly important while modeling mental diseases.

The selective serotonin reuptake inhibitors (SSRIs), acting at the serotonin transporter (SERT), are one of the most widely prescribed antidepressant medications. All five approved SSRIs possess either fluorine or chlorine atoms, and there is a limited number of reports describing their analogs with heavier halogens, i.e., bromine and iodine. To elucidate the role of halogen atoms in the binding of SSRIs to SERT, we designed a series of 22 fluoxetine and fluvoxamine analogs substituted with fluorine, chlorine, bromine, and iodine atoms, differently arranged on the phenyl ring. The obtained biological activity data, supported by a thorough in silico binding mode analysis, allowed the identification of two partners for halogen bond interactions: the backbone carbonyl oxygen atoms of E493 and T497. Additionally, compounds with heavier halogen atoms were found to bind with the SERT via a distinctly different binding mode, a result not presented elsewhere. The subsequent analysis of the prepared XSAR sets showed that E493 and T497 participated in the largest number of formed halogen bonds. The XSAR library analysis led to the synthesis of two of the most active compounds (3,4-diCl-fluoxetine 42, SERT Ki = 5 nM and 3,4-diCl-fluvoxamine 46, SERT Ki = 9 nM, fluoxetine SERT Ki = 31 nM, fluvoxamine SERT Ki = 458 nM). We present an example of the successful use of a rational methodology to analyze binding and design more active compounds by halogen atom introduction. 'XSAR library analysis', a new tool in medicinal chemistry, was instrumental in identifying optimal halogen atom substitution.

Serotonin receptors are extensively examined by academic and industrial researchers, due to their vital roles, which they play in the organism and constituting therefore important drug targets. Up to very recently, it was assumed that the basic nitrogen in compound structure is a necessary component to make it active within this receptor system. Such nitrogen interacts in its protonated form with the aspartic acid from the third transmembrane helix (D3x32) forming a hydrogen bond tightly fitting the ligand in the protein binding site. However, there are several recent studies that report strong serotonin receptor affinity also for compounds without a basic moiety in their structures. In the study, we carried out a comprehensive in silico analysis of the low-basicity phenomenon of the selected serotonin receptor ligands. We focused on the crystallized representatives of the proteins of 5-HT1B, 5-HT2A, 5-HT2B, and 5-HT2C receptors, and examined the problem both from the ligand- and structure-based perspectives. The study was performed for the native proteins, and for D3x32A mutants. The investigation resulted in the determination of nonstandard structural requirements for activity towards serotonin receptors, which can be used in the design of new nonbasic ligands.

The present study reports for the first time the occurrence of selected pharmaceuticals and personal care products (PPCPs) in the shallow aquifer underlying the Krakow city. Urban groundwater samples were gathered from 11 wells, which can serve as the emergency water supply wells. Liquid chromatography with tandem mass spectrometry method with the previous pre-concentration of samples using an SPE technique was applied for the determination of the PPCPs selected. There were quantified concentrations of PPCPs from the groups of estrogens (17-alpha-ethinylestradiol (EE2), 2.6-18.7 ng/L), non-steroidal anti-inflammatory drugs (ketoprofen, 59.5 ng/L in 1 sample), and antimicrobial preservatives used in cosmetic production (methylparaben up to 91.5 ng/L). Triclosan was observed in all analysed water samples in concentrations above the limit of detection. The presence of the PPCPs in the shallow aquifer is an evidence that the sewer network system under the city leaks and then pollutes the urban groundwater.

Among all of the monoaminergic receptors, the 5-HT6R has the highest number of non-basic ligands (approximately 5% of compounds stored in 25th version of ChEMBL database have the strongest basic pKa below 5, calculated using the Instant JChem calculator plugin). These compounds, when devoid of a basic nitrogen, exhibit high affinity and remarkable selectivity. Despite a decade of research, no clues have been given for explanation of such an intriguing phenomenon. Here, a series of analogs of four known 5-HT6R ligands, has been rationally designed to approach this issue. For each of the synthesized 42 compounds, a binding affinity for 5-HT6R has been measured, together with a selectivity profile against 5-HT1AR, 5-HT2AR, 5-HT7R and D2R. Performed induced fit docking and molecular dynamics experiments revealed that no particular interaction was responsible for the activity of non-basic compounds. In fact, a plain N-phenylsulfonylindole (1e) was found to possess a moderate (5-HT6R, Ki = 159 nM) affinity. No other monoaminergic receptor has as simple and selective ligand as this one. Thus, it is stated that it binds to the receptor solely based on its conformation and as such, possesses a minimum amount of features, required for binding. Also, any functional group able to form an additional interaction with the receptor increase the binding affinity, like in the case of two highly active non-basic compounds 3e and 5g (5-HT6R, Ki = 65 nM and 38 nM, respectively).

In line with recent clinical trials demonstrating that ondansetron, a 5-HT3 receptor (5-HT3R) antagonist, ameliorates cognitive deficits of schizophrenia and the known procognitive effects of 5-HT6 receptor (5-HT6R) antagonists, we applied the hybridization strategy to design dual-acting 5-HT3/5-HT6R antagonists. We identified the first-in-class compound FPPQ, which behaves as a 5-HT3R antagonist and a neutral antagonist 5-HT6R of the Gs pathway. FPPQ shows selectivity over 87 targets and decent brain penetration. Likewise, FPPQ inhibits phencyclidine (PCP)-induced hyperactivity and displays procognitive properties in the novel object recognition task. In contrast to FPPQ, neither 5-HT6R inverse agonist SB399885 nor neutral 5-HT6R antagonist CPPQ reversed (PCP)-induced hyperactivity. Thus, combination of 5-HT3R antagonism and 5-HT6R antagonism, exemplified by FPPQ, contributes to alleviating the positive-like symptoms. Present findings reveal critical structural features useful in a rational polypharmacological approach to target 5-HT3/5-HT6 receptors and encourage further studies on dual-acting 5-HT3/5-HT6R antagonists for the treatment of psychiatric disorders.