Synthesis and pharmacological evaluation of new N-phenylpiperazine derivatives designed as homologues of the antipsychotic lead compound LASSBio-579

Design, Synthesis and Pharmacological Evaluation of Novel Conformationally Restricted N-arylpiperazine Derivatives Characterized as D2/D3 Receptor Ligands, Candidates for the Treatment of Neurodegenerative Diseases

Most neurodegenerative diseases are multifactorial, and the discovery of several molecular mechanisms related to their pathogenesis is constantly advancing. Dopamine and dopaminergic receptor subtypes are involved in the pathophysiology of several neurological disorders, such as schizophrenia, depression and drug addiction. For this reason, the dopaminergic system and dopamine receptor ligands play a key role in the treatment of such disorders. In this context, a novel series of conformationally restricted N-arylpiperazine derivatives (5a–f) with a good affinity for D₂/D₃ dopamine receptors is reported herein. Compounds were designed as interphenylene analogs of the drugs aripiprazole (2) and cariprazine (3), presenting a 1,3-benzodioxolyl subunit as a ligand of the secondary binding site of these receptors. The six new N-arylpiperazine compounds were synthesized in good yields by using classical methodologies, and binding and guanosine triphosphate (GTP)-shift studies were performed. Affinity values below 1 μM for both target receptors and distinct profiles of intrinsic efficacy were found. Docking studies revealed that Compounds 5a–f present a different binding mode with dopamine D₂ and D₃ receptors, mainly as a consequence of the conformational restriction imposed on the flexible spacer groups of 2 and 3.

Synthesis of novel pancreatic lipase inhibitors: Biological investigation and in silico studies

The targeted compounds which are Schiff base derivatives were prepared by reaction of 6-(4-phenyl-piperazin-1-yl)pyridine-3-ylamine with 2-hydroxy and 2,6-dichloro benzaldehyde. These compounds were isolated, purified and then spectrally characterized via FT-IR, ¹H and ¹³C NMR, LC MS TOF, and TGA analysis where strong proofs confirmed the formation of the targeted product. The biological activity, which is pancreatic porcine lipase inhibition, of the compounds was investigated and Orlistat was used as standard drug. The compound 3 was found to be as potent as orlistat against PL enzyme with an IC₅₀ value of 0.50 μM. The molecular docking studies were performed for both obtained compounds and orlistat against active side of porcine pancreatic lipase. Also, MM/PBSA binding free energy and molecular dynamics (MD) simulation analyzes were performed for pancreatic porcine lipase with compound 3, which showed potent inhibition according to the results of in vitro studies. Furthermore, The ADME and toxicity analysis of the compounds were examined using web-based online platforms, SwissADME and pkCSM. In the light of biological activity and in silico studies, the compound 3 can be a potential drug candidate with further studies.Communicated by Ramaswamy H. Sarma.

Synthesis and Antiproliferative Activity of 2,4,6,7-Tetrasubstituted-2H-pyrazolo[4,3-c]pyridines

A library of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines was prepared from easily accessible 1-phenyl-3-(2-phenylethynyl)-1H-pyrazole-4-carbaldehyde via an iodine-mediated electrophilic cyclization of intermediate 4-(azidomethyl)-1-phenyl-3-(phenylethynyl)-1H-pyrazoles to 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridines followed by Suzuki cross-couplings with various boronic acids and alkylation reactions. The compounds were evaluated for their antiproliferative activity against K562, MV4-11, and MCF-7 cancer cell lines. The most potent compounds displayed low micromolar GI50 values. 4-(2,6-Diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol proved to be the most active, induced poly(ADP-ribose) polymerase 1 (PARP-1) cleavage, activated the initiator enzyme of apoptotic cascade caspase 9, induced a fragmentation of microtubule-associated protein 1-light chain 3 (LC3), and reduced the expression levels of proliferating cell nuclear antigen (PCNA). The obtained results suggest a complex action of 4-(2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol that combines antiproliferative effects with the induction of cell death. Moreover, investigations of the fluorescence properties of the final compounds revealed 7-(4-methoxyphenyl)-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine as the most potent pH indicator that enables both fluorescence intensity-based and ratiometric pH sensing.

Experimental Serotonergic Agents for the Treatment of Schizophrenia

Schizophrenia remains one of the most chronic and highly disabling mental disorder. To date, the pathomechanism of schizophrenia is not fully understood and current treatments are characterized by some limitations. First- and second-generation antipsychotics have shown clinical efficacy in treating positive symptoms, while are poorly effective on both negative symptoms and cognitive deficits. Moreover, they can involve many metabolic and neurological side effects, leading to low therapeutic compliance. Many evidence suggested that serotonin may play a complex role in the neurobiology of schizophrenia. Therefore, new drugs targeting 5-HT receptors (5-HTRs) have become an important area of research in schizophrenia in the hope that treatment efficacy may be improved without inducing side effects observed with currently available antipsychotics. Research using the main database sources was conducted to obtain an overview of preclinical and clinical pharmacological 5-HTR-targeted therapies in patients with schizophrenia. We identified 17 experimental serotonergic agents, under study for their potential use in schizophrenia treatment. Particularly, AVN-211, LuAF-35700 and Brilaroxazine are currently under clinical development. Moreover, some compounds showed some pro-cognitive and antipsychotic-like properties in animal models, while other agents showed contradictory effects in improving symptoms and were removed from the development program. Although some serotonergic drugs seem promising for improving the treatment of schizophrenia, further studies regarding the pathophysiological mechanisms of schizophrenia and novel compounds as well as high-quality trials are necessary in order to improve schizophrenia outcomes.

Effects of Doxycycline in Swiss Mice Predictive Models of Schizophrenia

Schizophrenia patients show very complex symptoms in several psychopathological domains. Some of these symptoms remain poorly treated. Therefore, continued effort is needed to find novel pharmacological strategies for improving schizophrenia symptoms. Recently, minocycline, a second-generation tetracycline, has been suggested as an adjunctive treatment for schizophrenia. The antipsychotic-like effect of doxycycline, a minocycline analog, was investigated here. We found that both minocycline and doxycycline prevented amphetamine-induced prepulse inhibition (PPI) disruption. However, neither of them blocked MK801-induced effects, albeit doxycycline had a modest impact against ketamine-induced effects. Neither c-Fos nor nNOS expression, which was evaluated in limbic regions, were modified after acute or sub-chronic treatment with doxycycline. Therefore, apomorphine inducing either PPI disruption and climbing behavior was not prevented by doxycycline. This result discards a direct blockade of D2-like receptors, also suggested by the lack of doxycycline cataleptic-induced effect. Contrasting, doxycycline prevented SKF 38393-induced effects, suggesting a preferential doxycycline action at D1-like rather than D2-like receptors. However, doxycycline did not bind to the orthosteric sites of D1, D2, D3, D4, 5-HT2A, 5-HT1A, and A2A receptors suggesting no direct modulation of these receptors. Our data corroborate the antipsychotic-like effect of doxycycline. However, these effects are probably not mediated by doxycycline direct interaction with classical receptors enrolled in the antipsychotic effect.

Revisiting the Pharmacodynamic Uroselectivity of α 1-Adrenergic Receptor Antagonists

α₁-Adrenoceptor (AR) antagonists are widely used for the relief of urinary retention secondary to benign prostatic hyperplasia (BPH). While the five Food and Drug Administration-approved α ₁-AR antagonists (terazosin, doxazosin, alfuzosin, tamsulosin, and silodosin) share similar efficacy, they differ in tolerability, with reports of ejaculatory dysfunction. The aim of the present work was to revisit their α ₁-AR subtype selectivity as well as of LDT5 (1-(2-methoxyphenyl)-4-[2-(3,4-dimethoxyphenyl) ethyl]piperazine monohydrochloride), a compound previously described as a multitarget antagonist of α _1A-/α _1D-AR and 5-HT_1A receptors, and to estimate their affinity for D₂, D₃, and 5-HT_1A receptors, which are putatively involved in ejaculatory dysfunction. Competition binding assays were performed with native (D₂, 5-HT_1A) or transfected (human α _1A-, α _1B-, α _1Dt-AR, and D₃) receptors for determination of the drug's affinities. Tamsulosin and silodosin have the highest affinities for α _1A-AR, but only silodosin is clearly a selective α _1A-AR antagonist, with K _i ratios of 25.3 and 50.2 for the α _1D- and α _1B-AR, respectively. Tamsulosin, silodosin, and LDT5 (but not terazosin, doxazosin, and alfuzosin) have high affinity for the 5-HT_1A receptor (K _i around 5-10 nM), behaving as antagonists. We conclude that the uroselectivity of tamsulosin is not explained by its too-low selectivity for the α _1A- versus α _1B-AR, and that its affinity for D₂ and D₃ receptors is probably too low for explaining the ejaculatory dysfunction reported for this drug. Present data also support the design of "better-than-LDT5" new multitarget lead compounds with pharmacokinetic selectivity based on poor brain penetration and that could prevent hyperplastic cell proliferation and BPH progression. SIGNIFICANCE STATEMENT: The present work revisits the uroselectivity of the five Food and Drug Administration-approved α₁ adrenoceptor antagonists for the treatment of benign prostatic hyperplasia (BPH). Contrary to what has been claimed by some, our results indicate that the uroselectivity of tamsulosin is probably not fully explained by its too-weak selectivity for the α_1A versus α_1B adrenoceptors. We also show that tamsulosin affinity for D₃ and 5-HT_1A receptors is probably too low for explaining the ejaculatory dysfunction reported for this drug. Based on our lead compound LDT5, present data support the search for a multitarget antagonist of α_1A-α_1D and 5-HT_1A receptors with poor brain penetration as an alternative for BPH treatment.

Evaluation of Functional Selectivity of Haloperidol, Clozapine, and LASSBio-579, an Experimental Compound With Antipsychotic-Like Actions in Rodents, at G Protein and Arrestin Signaling Downstream of the Dopamine D2 Receptor

LASSBio-579, an N-phenylpiperazine antipsychotic lead compound, has been previously reported as a D₂ receptor (D₂R) ligand with antipsychotic-like activities in rodent models of schizophrenia. In order to better understand the molecular mechanism of action of LASSBio-579 and of its main metabolite, LQFM 037, we decided to address the hypothesis of functional selectivity at the D₂R. HEK-293T cells transiently coexpressing the human long isoform of D₂ receptor (D₂LR) and bioluminescence resonance energy transfer (BRET)-based biosensors were used. The antagonist activity was evaluated using different concentrations of the compounds in the presence of a submaximal concentration of dopamine (DA), after 5 and 20 min. For both signaling pathways, haloperidol, clozapine, and our compounds act as DA antagonists in a concentration-dependent manner, with haloperidol being by far the most potent, consistent with its nanomolar D₂R affinity measured in binding assays. In our experimental conditions, only haloperidol presented a robust functional selectivity, being four- to fivefold more efficient for inhibiting translocation of β-arrestin-2 (β-arr2) than for antagonizing Gi activation. Present data are the first report on the effects of LASSBio-579 and LQFM 037 on the β-arr2 signaling pathway and further illustrate that the functional activity could vary depending on the assay conditions and approaches used.

Multi-Target Approach for Drug Discovery against Schizophrenia

Polypharmacology is nowadays considered an increasingly crucial aspect in discovering new drugs as a number of original single-target drugs have been performing far behind expectations during the last ten years. In this scenario, multi-target drugs are a promising approach against polygenic diseases with complex pathomechanisms such as schizophrenia. Indeed, second generation or atypical antipsychotics target a number of aminergic G protein-coupled receptors (GPCRs) simultaneously. Novel strategies in drug design and discovery against schizophrenia focus on targets beyond the dopaminergic hypothesis of the disease and even beyond the monoamine GPCRs. In particular these approaches concern proteins involved in glutamatergic and cholinergic neurotransmission, challenging the concept of antipsychotic activity without dopamine D₂ receptor involvement. Potentially interesting compounds include ligands interacting with glycine modulatory binding pocket on N-methyl-d-aspartate (NMDA) receptors, positive allosteric modulators of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, positive allosteric modulators of metabotropic glutamatergic receptors, agonists and positive allosteric modulators of α7 nicotinic receptors, as well as muscarinic receptor agonists. In this review we discuss classical and novel drug targets for schizophrenia, cover benefits and limitations of current strategies to design multi-target drugs and show examples of multi-target ligands as antipsychotics, including marketed drugs, substances in clinical trials, and other investigational compounds.

The novel piperazine-containing compound LQFM018: Necroptosis cell death mechanisms, dopamine D4 receptor binding and toxicological assessment

Piperazine is a promising scaffold for drug development due to its broad spectrum of biological activities. Based on this, the new piperazine-containing compound LQFM018 (2) [ethyl 4-((1-(4-chlorophenyl)-1H-pyrazol-4-yl)methyl)piperazine-1-carboxylate] was synthetized and some biological activities investigated. In this work, we described its ability to bind aminergic receptors, antiproliferative effects as well as the LQFM018 (2)-triggered cell death mechanisms, in K562 leukemic cells, by flow cytometric analyses. Furthermore, acute oral systemic toxicity and potential myelotoxicity assessments of LQFM018 (2) were carried out. LQFM018 (2) was originally obtained by molecular simplification from LASSBio579 (1), an analogue compound of clozapine, with 33% of global yield. Binding profile assay to aminergic receptors showed that LQFM018 (2) has affinity for the dopamine D₄ receptor (K_i = 0.26 μM). Moreover, it showed cytotoxicity in K562 cells, in a concentration and time-dependent manner; IC₅₀ values obtained were 399, 242 and 119 μM for trypan blue assay and 427, 259 and 50 μM for MTT method at 24, 48 or 72 h, respectively. This compound (427 μM) also promoted increase in LDH release and cell cycle arrest in G2/M phase. Furthermore, it triggered necrotic morphologies in K562 cells associated with intense cell membrane rupture as confirmed by Annexin V/propidium iodide double-staining. LQFM018 (2) also triggered mitochondrial disturb through loss of ΔΨm associated with increase of ROS production. No significant accumulation of cytosolic cytochrome c was verified in treated cells. Furthermore, it was verified an increase of expression of TNF-R1 and mRNA levels of CYLD with no involviment in caspase-3 and -8 activation and NF-κB in K562 cells. LQFM018 (2) showed in vitro myelotoxicity potential, but it was orally well tolerated and classified as UN GHS category 5 (LD₅₀ > 2000-5000 mg/Kg). Thus, LQFM018 (2) seems to have a non-selective action considering hematopoietic cells. In conclusion, it is suggested LQFM018 (2) promotes cell death in K562 cells via necroptotic signaling, probably with involvement of dopamine D₄ receptor. These findings open new perspectives in cancer therapy by use of necroptosis inducing agents as a strategy of reverse cancer cell chemoresistance.

ADME studies and preliminary safety pharmacology of LDT5, a lead compound for the treatment of benign prostatic hyperplasia

This study aimed to estimate the absorption, distribution, metabolism and excretion (ADME) properties and safety of LDT5, a lead compound for oral treatment of benign prostatic hyperplasia that has previously been characterized as a multi-target antagonist of α_1A-, α_1D-adrenoceptors and 5-HT_1A receptors. The preclinical characterization of this compound comprised the evaluation of its in vitro properties, including plasma, microsomal and hepatocytes stability, cytochrome P450 metabolism and inhibition, plasma protein binding, and permeability using MDCK-MDR1 cells. De-risking and preliminary safety pharmacology assays were performed through screening of 44 off-target receptors and in vivo tests in mice (rota-rod and single dose toxicity). LDT5 is stable in rat and human plasma, human liver microsomes and hepatocytes, but unstable in rat liver microsomes and hepatocytes (half-life of 11 min). LDT5 is highly permeable across the MDCK-MDR1 monolayer (P_app ∼32×10^-6 cm/s), indicating good intestinal absorption and putative brain penetration. LDT5 is not extensively protein-bound and is a substrate of human CYP2D6 and CYP2C19 but not of CYP3A4 (half-life >60 min), and did not significantly influence the activities of any of the human cytochrome P450 isoforms screened. LDT5 was considered safe albeit new studies are necessary to rule out putative central adverse effects through D₂, 5-HT_1A and 5-HT_2B receptors, after chronic use. This work highlights the drug-likeness properties of LDT5 and supports its further preclinical development.

The crystal structure of 1-(4-bromophenyl)-2-(4-(4-fluorophenyl)piperazin-1-yl)ethanol, C18H20BrFN2O1

C18H20BrFN2O1, monoclinic, P21/c (no. 14), a = 14.1884(10) Å, b = 5.3673(4) Å, c = 22.3768(15) Å, β = 93.293(2)°, V = 1701.3(2) Å3, Z = 4, Rgt(F) = 0.0510, wRref(F2) = 0.1384, T = 273 K.

Validation of a Na+-shift binding assay for estimation of the intrinsic efficacy of ligands at the A2A adenosine receptor

INTRODUCTION

Determination of the intrinsic efficacy of ligands at the A_2A receptor is important for selecting drug candidates, e.g. in the case of inflammatory diseases where agonists are searched for or in Parkinson disease (antagonists).

METHODS

Three functional binding assays were compared with up to seven ligands with different efficacies: the GTP-shift method based on the decrease of affinity observed with agonists when GTP is added to the competition binding assay; the K_i ratio method based on the different affinity states of the receptor when using an agonist or antagonist radioligand and the Na⁺-shift assay based on the difference of affinity of agonists when tested in a medium containing a divalent cation (50mM MgCl₂) favoring the G protein coupled agonist-receptor complex or sodium (100mM NaCl) as negative allosteric modulator.

RESULTS

The Na⁺-shift assay proposed herein successfully discriminated the full agonists CGS21680, NECA and adenosine (IC₅₀ ratio=13-14) from the weak inverse agonists ZM241385 and IBMX (IC₅₀ ratio=0.85) and the partial agonists LUF5834 and regadenoson (IC₅₀ ratios equal to 3 and 10, respectively).

DISCUSSION

We conclude that the Na⁺-shift assay proposed herein for the A_2A receptors has been validated and represents a rapid, economic and efficient functional binding assay to be used in a drug development program for early estimation of the intrinsic efficacy of hits.

LASSBio-1422: a new molecular scaffold with efficacy in animal models of schizophrenia and disorders of attention and cognition

Aiming to identify new antipsychotic lead-compounds, our group has been working on the design and synthesis of new N-phenylpiperazine derivatives. Here, we characterized LASSBio-1422 as a pharmacological prototype of this chemical series. Adult male Wistar rats and CF1 mice were used for in-vitro and in-vivo assays, respectively. LASSBio-1422 [1 and 5 mg/kg, postoperatively (p.o.)] inhibited apomorphine-induced climbing as well as ketamine-induced hyperlocomotion (1 and 5 mg/kg, p.o.), animal models predictive of efficacy on positive symptoms. Furthermore, LASSBio-1422 (5 mg/kg, p.o.) prevented the prepulse impairment induced by apomorphine, (±)-2,5-dimethoxy-4-iodoamphetamine, and ketamine, as well as the memory impairment induced by ketamine in the novel object-recognition task at the acquisition, consolidation, and retrieval phases of memory formation. Potential extrapyramidal side-effects and sedation were assessed by catatonia, rota-rod, locomotion, and barbiturate sleeping time, and LASSBio-1422 (15 mg/kg, p.o.) did not affect any of the parameters observed. Binding assays showed that LASSBio-1422 has a binding profile different from the known atypical antipsychotic drugs: it does not bind to AMPA, kainate, N-methyl-D-aspartate, glicine, and mGluR2 receptors and has low or negligible affinity for D1, D2, and 5-HT2A/C receptors, but high affinity for D4 receptors (Ki=0.076 µmol/l) and, to a lesser extent, for 5-HT1A receptors (Ki=0.493 µmol/l). The antagonist action of LASSBio-1422 at D4 receptors was assessed through the classical GTP-shift assay. In conclusion, LASSBio-1422 is effective in rodent models of positive and cognitive symptoms of schizophrenia and its ability to bind to D4 and 5-HT1A receptors may at least in part explain its effects in these animal models.

The crystal structure of bis(4-(2,4-dimethylphenyl)piperazin-1-yl)methane, C25H36N4

C25H36N4, monoclinic, P21/n (no. 14), a = 10.460(2), Å, b = 12.653(3) Å, c = 17.566(3) Å, β = 94.452(7)°, V = 2317.9(8) Å3, Z = 4, R gt (F) = 0.0548, wR ref (F 2 ) = 0.1325, T = 273 K.

Partial agonism and fast dissociation of LASSBio-579 at dopamine D2 receptor

In an attempt to better understand the molecular mechanism of action of the antipsychotic lead LASSBio-579 and of its main metabolite LQFM 037, the aim of this work was to evaluate their intrinsic activity and binding kinetics at the dopamine D2 receptor. In transfected HEK cells expressing the D2L receptor under an inducible promoter, LASSBio-579 and LQFM 037, but not clozapine, behaved as weak partial agonists in [(35)S]-GTPγS binding assays performed in optimized conditions previously shown to evidence the partial agonist profile of aripiprazole. Besides, data obtained in radioligand competition assays on rat striatal membranes suggested a rapid association to and dissociation from the D2-like receptors. Using the kinetic rate index based on the strategy of the dual-point competition association assay, we showed that our compounds share a similar kinetic profile with clozapine, distinct from the typical antipsychotic haloperidol. These two characteristics could contribute to the atypical-like profile observed after administration of LASSBio-579 to rodents, in models of positive and negative symptoms of schizophrenia.

Piperazine scaffold: A remarkable tool in generation of diverse pharmacological agents

Piperazine is one of the most sought heterocyclics for the development of new drug candidates. This ring can be traced in a number of well established, commercially available drugs. Wide array of pharmacological activities exhibited by piperazine derivatives have made them indispensable anchors for the development of novel therapeutic agents. The review herein highlights the therapeutic significance of piperazine derivatives. Various therapeutically active piperazine derivatives developed by several chemists are reported here.

Assessment of mechanisms involved in antinociception produced by the alkaloid caulerpine

In previous works we showed that oral administration of caulerpine, a bisindole alkaloid isolated from algae of the genus Caulerpa, produced antinociception when assessed in chemical and thermal models of nociception. In this study, we evaluated the possible mechanism of action of this alkaloid in mice, using the writhing test. The antinociceptive effect of caulerpine was not affected by intraperitoneal (i.p.) pretreatment of mice with naloxone, flumazenil, l-arginine or atropine, thus discounting the involvement of the opioid, GABAergic, l-arginine-nitric oxide and (muscarinic) cholinergic pathways, respectively. In contrast, i.p. pretreatment with yohimbine, an α2-adrenoceptor antagonist, or tropisetron, a 5-HT3 antagonist, significantly blocked caulerpine-induced antinociception. These results suggest that caulerpine exerts its antinociceptive effect in the writhing test via pathways involving α2-adrenoceptors and 5-HT3 receptors. In summary, this alkaloid could be of interest in the development of new dual-action analgesic drugs.

Functional binding assays for estimation of the intrinsic efficacy of ligands at the 5-HT1A receptor: application for screening drug candidates

INTRODUCTION

Determination of the intrinsic efficacy of ligands at the 5-HT1A receptor is important for selecting drug candidates, e.g. in the case of schizophrenia where partial agonism is a favorable property shared by different atypical antipsychotics.

METHODS

Using seven ligands with different intrinsic efficacies and rat hippocampus synaptosomes, we compared critically three "functional" binding assays based on the ternary complex model that considers that the activated conformation of the receptor is the one coupled to G-protein.

RESULTS

The Ki ratio method, based on the difference of affinity of the competing drug when using an antagonist vs. an agonist as radioligand, discriminated the ligands according to their intrinsic efficacies, with values from 77 for the full agonist 5-hydroxytryptamine to 0.09 for the inverse agonist WAY 100,635. The GTP-shift method, based on the decrease of affinity observed with agonists when GTP is added to the competition binding assay, was equally effective in classifying the drugs according to their intrinsic efficacy. The lower sensibility of the GTP-shift assay was investigated and explained by the different ionic conditions used in the two assays and the way competition curves were analyzed. Albeit more direct, the assay based on agonist-stimulated [(35)S]-GTPγS binding to G proteins was more expensive and of greater variability in our hands.

DISCUSSION

We conclude that the GTP-shift procedure described herein for 5-HT1A receptors may expedite drug discovery efforts by predicting at the same time the affinity and intrinsic efficacy of ligands through a simple, rapid and economic ligand binding assay.