Human oligodendrocyte-like cell differentiation is promoted by TSPO-mediated endogenous steroidogenesis

Mature oligodendrocytes (OLs) arise from oligodendrocyte precursor cells that, in case of demyelination, are recruited at the lesion site to remyelinate the axons and therefore restore the transmission of nerve impulses. It has been widely documented that exogenously administered steroid molecules are potent inducers of myelination. However, little is known about how neurosteroids produced de novo by OLs can impact this process. Here, we employed a human OL precursor cell line to investigate the role of de novo neurosteroidogenesis in the regulation of OLs differentiation, paying particular attention to the 18 kDa Translocator Protein (TSPO) which controls the rate-limiting step of the neurosteroidogenic process. Our results showed that, over the time of OL maturation, the availability of cholesterol, which is the neurosteroidogenesis initial substrate, and key members of the neurosteroidogenic machinery, including TSPO, were upregulated. In addition, OLs differentiation was impaired following neurosteroidogenesis inhibition and TSPO silencing. On the contrary, TSPO pharmacological stimulation promoted neurosteroidogenic function and positively impacted differentiation. Collectively, our results suggest that de novo neurosteroidogenesis is actively involved in the autocrine and paracrine regulation of human OL differentiation. Moreover, since TSPO was able to promote OL differentiation through a positive modulation of the neurosteroid biosynthetic process, it could be exploited as a promising target to tackle demyelinating diseases.

Tyrosine kinase inhibitors (TKIs) for ovarian cancer treatment: from organic to inorganic chemotherapeutics towards selectivity-a perspective overview

Ovarian cancer (OC) is a lethal gynecologic cancer in industrialized countries. Treatments for OC include the surgical removal and chemotherapy. In the last decades, improvements have been made in the surgery technologies, drug combinations and administration protocols, and in diagnosis. However, mortality from OC is still high owing to recurrences and insurgence of drug resistance. Accordingly, it is urgent the development of novel agents capable to effectively target OC. In this respect, tyrosine kinase inhibitors (TKIs) may play an important role. Most of TKIs developed and tested so far are organic. However, owing to their chemical versatility, also metals can be exploited to design selective and potent TKIs. We provide a short and easy-to-read overview on the main organic TKIs with a summary of those that entered clinical trials. Additionally, we describe the potential of metal-based TKIs, focusing on this overlooked family of compounds that may significantly contribute towards the concept of precision-medicine.

Targeting the Translocator Protein (18 kDa) in Cardiac Diseases: State of the Art and Future Opportunities

Mitochondria dysfunctions are typical hallmarks of cardiac disorders (CDs). The multiple tasks of this energy-producing organelle are well documented, but its pathophysiologic involvement in several manifestations of heart diseases, such as altered electromechanical coupling, excitability, and arrhythmias, is still under investigation. The human 18 kDa translocator protein (TSPO) is a protein located on the outer mitochondrial membrane whose expression is altered in different pathological conditions, including CDs, making it an attractive therapeutic and diagnostic target. Currently, only a few TSPO ligands are employed in CDs and cardiac imaging. In this Perspective, we report an overview of the emerging role of TSPO at the heart level, focusing on the recent literature concerning the development of TSPO ligands used for fighting and imaging heart-related disease conditions. Accordingly, targeting TSPO might represent a successful strategy to achieve novel therapeutic and diagnostic strategies to unravel the fundamental mechanisms and to provide solutions to still unanswered questions in CDs.

Anti-Proliferative Properties of the Novel Hybrid Drug Met-ITC, Composed of the Native Drug Metformin with the Addition of an Isothiocyanate H2S Donor Moiety, in Different Cancer Cell Lines

Metformin (Met) is the first-line therapy in type 2 diabetes mellitus but, in last few years, it has also been evaluated as anti-cancer agent. Several pathways, such as AMPK or PI3K/Akt/mTOR, are likely to be involved in the anti-cancer Met activity. In addition, hydrogen sulfide (H2S) and H2S donors have been described as anti-cancer agents affecting cell-cycle and inducing apoptosis. Among H2S donors, isothiocyanates are endowed with a further anti-cancer mechanism: the inhibition of the histone deacetylase enzymes. On this basis, a hybrid molecule (Met-ITC) obtained through the addition of an isothiocyanate moiety to the Met molecule was designed and its ability to release Met has been demonstrated. Met-ITC exhibited more efficacy and potency than Met in inhibiting cancer cells (AsPC-1, MIA PaCa-2, MCF-7) viability and it was less effective on non-tumorigenic cells (MCF 10-A). The ability of Met-ITC to release H2S has been recorded both in cell-free and in cancer cells assays. Finally, its ability to affect the cell cycle and to induce both early and late apoptosis has been demonstrated on the most sensitive cell line (MCF-7). These results confirmed that Met-ITC is a new hybrid molecule endowed with potential anti-cancer properties derived both from Met and H2S.

A complex bearing TSPO PIGA ligand coordinated to the [Au(PEt3)]+ pharmacophore is highly cytotoxic against ovarian cancer cells

Auranofin ([1-(thio-κS)-β-D-glucopyranose-2,3,4,6-tetraacetato](triethylphosphine)-gold) is a leading gold-based drug clinically used to treat arthritis. In the last years, it entered various drug reprofiling programs, and it has been found promising against various forms of tumor, including ovarian cancer. Evidence showed as its antiproliferative profile mainly depends on the inhibition of thioredoxin reductase (TrxR), being this mitochondrial system its main target. In this context, we report here the synthesis and biological evaluation of a novel complex designed as auranofin analogue obtained through the conjugation of a phenylindolylglyoxylamide ligand (which belongs to the so-called PIGA TSPO ligand family) with the auranofin-derived cationic fragment [Au(PEt3)]+. This complex is characterized by two parts. The phenylindolylglyoxylamide moiety, owing to its high affinity for TSPO (in the low nM range) should drive the compound to target mitochondria, whereas the [Au(PEt3)]+ cation is the actual anticancer-active molecular fragment. Overall, we wanted to offer the proof-of-concept that by coupling PIGA ligands to anticancer gold active moieties, it is possible to preserve and even improve anticancer effects, opening the avenue to a reliable approach for targeted therapy.

Indol-3-ylglyoxylamide as Privileged Scaffold in Medicinal Chemistry

In recent years, indolylglyoxylamide-based derivatives have received much attention due to their application in drug design and discovery, leading to the development of a wide array of compounds that have shown a variety of pharmacological activities. Combining the indole nucleus, already validated as a "privileged structure," with the glyoxylamide function allowed for an excellent template to be obtained that is suitable to a great number of structural modifications aimed at permitting interaction with specific molecular targets and producing desirable therapeutic effects. The present review provides insight into how medicinal chemists have elegantly exploited the indolylglyoxylamide moiety to obtain potentially useful drugs, with a particular focus on compounds exhibiting activity in in vivo models or reaching clinical trials. All in all, this information provides exciting new perspectives on existing data that can be useful in further design of indolylglyoxylamide-based molecules with interesting pharmacological profiles. The aim of this report is to present an update of collection data dealing with the employment of this moiety in the rational design of compounds that are able to interact with a specific target, referring to the last 20 years.

The human microglial surveillant phenotype is preserved by de novo neurosteroidogenesis through the control of cholesterol homeostasis: Crucial role of 18 kDa Translocator Protein

Neurodegenerative disease-associated microglia commonly exhibit harmful cholesterol accumulation that impairs their ability to resolve the neuroinflammatory response, contributing to disease onset and progression. Neurosteroids, whose levels have been often found significantly altered in brain diseases, are the most potent endogenous anti-inflammatory molecules exerting beneficial effects on activities of brain cells, including microglia. For the first time, the impact of neurosteroidogenesis on cholesterol homeostasis for the immune surveillance phenotype maintenance was investigated in a human microglia in vitro model. To enhance and inhibit neurosteroidogenesis, pharmacological stimulation and knock-down of 18 kDa Translocator Protein (TSPO), which is involved in the neurosteroidogenesis rate-limiting step, were used as experimental approaches, respectively. The obtained results point to an essential autocrine control of neurosteroidogenesis in orchestrating cholesterol trafficking in human microglia. TSPO pharmacological stimulation ensured cholesterol turnover by strengthening cholesterol efflux systems and preserving healthy immune surveillant phenotype. Conversely, TSPO knock-down induced an impairment of the controlled interplay among cholesterol synthesis, efflux, and metabolism mechanisms, leading to an excessive cholesterol accumulation and acquisition of a chronically activated dysfunctional phenotype. In this model, the exogenous neurosteroid administration restored proper the cholesterol clearance. The TSPO ability in promoting native neurosteroidogenesis opens the way to restore cholesterol homeostasis, and thus to maintain microglia proper functionality for the treatment of neuroinflammation-related brain diseases.

A cyanine-based NIR fluorescent Vemurafenib analog to probe BRAFV600E in cancer cells

BRAF represents one of the most frequently mutated protein kinase genes and BRAF^V600E mutation may be found in many types of cancer, including hairy cell leukemia (HCL), anaplastic thyroid cancer (ATC), colorectal cancer and melanoma. Herein, a fluorescent probe, based on the structure of the highly specific BRAF^V600E inhibitor Vemurafenib (Vem, 1) and featuring the NIR fluorophore cyanine-5 (Cy5), was straightforwardly synthesized and characterized (Vem-L-Cy5, 3), showing promising spectroscopic properties. Biological validation in BRAF^V600E-mutated cancer cells evidenced the ability of 3 to penetrate inside the cells, specifically binding to its elective target BRAF^V600E with high affinity, and inhibiting MEK phosphorylation and cell growth with a potency comparable to that of native Vem 1. Taken together, these data highlight Vem-L-Cy5 3 as a useful tool to probe BRAF^V600E mutation in cancer cells, and suitable to acquire precious insights for future developments of more informed BRAF inhibitors-centered therapeutic strategies.

Target-Based Anticancer Indole Derivatives for the Development of Anti-Glioblastoma Agents

Glioblastoma (GBM) is the most aggressive and frequent primary brain tumor, with a poor prognosis and the highest mortality rate. Currently, GBM therapy consists of surgical resection of the tumor, radiotherapy, and adjuvant chemotherapy with temozolomide. Consistently, there are poor treatment options and only modest anticancer efficacy is achieved; therefore, there is still a need for the development of new effective therapies for GBM. Indole is considered one of the most privileged scaffolds in heterocyclic chemistry, so it may serve as an effective probe for the development of new drug candidates against challenging diseases, including GBM. This review analyzes the therapeutic benefit and clinical development of novel indole-based derivatives investigated as promising anti-GBM agents. The existing indole-based compounds which are in the pre-clinical and clinical stages of development against GBM are reported, with particular reference to the most recent advances between 2013 and 2022. The main mechanisms of action underlying their anti-GBM efficacy, such as protein kinase, tubulin and p53 pathway inhibition, are also discussed. The final goal is to pave the way for medicinal chemists in the future design and development of novel effective indole-based anti-GBM agents.

New antiproliferative agents derived from tricyclic 3,4-dihydrobenzo[4,5]imidazo[1,2-a][1,3,5]triazine scaffold: Synthesis and pharmacological effects

A series of novel 3,4-dihydrobenzo[4,5]imidazo[1,2-a][1,3,5]triazine (BIT) derivatives were designed and synthesized. In vitro antiproliferative activity was detected toward two human colorectal adenocarcinoma cell lines (CaCo-2 and HT-29) and one human dermal microvascular endothelial cell line (HMVEC-d). The most active compounds, namely 2-4 and 8, were further investigated to clarify the mechanism behind their biological activity. Through immunofluorescence assay, we identified the target of these molecules to be the microtubule cytoskeleton with subsequent formation of dense microtubule accumulation, particularly at the periphery of the cancer cells, as observed in paclitaxel-treated cells. Overall, these results highlight BIT derivatives as robust and feasible candidates deserving to be further developed in the search for novel potent antiproliferative microtubule-targeting agents.

Translocator Protein 18-kDa: a promising target to treat neuroinflammation-related degenerative diseases

In the nervous system, inflammatory responses physiologically occur as defense mechanisms triggered by damaging events. If improperly regulated, neuroinflammation can contribute to the development of chronically activated states of glial cells, with the perpetuation of inflammation and neuronal damage, thus leading to neurological and neurodegenerative disorders. Interestingly, neuroinflammation is associated with the overexpression of the mitochondrial translocator protein (TSPO) in activated glia. Despite the precise role of TSPO in the immunomodulatory mechanisms during active disease states is still unclear, it has emerged as a promising target to promote neuroprotection. Indeed, TSPO ligands have been shown to exert beneficial effects in counteracting neuroinflammation and neuronal damage in several in vitro and in vivo models of neurodegenerative diseases. In particular, the regulation of neurosteroids' production, cytokine release, metabolism of radical oxidative species, and cellular bioenergetics appear to be the main cellular events that underlie the observed effects. The present review aims to illustrate and summarize recent findings on the potential effect of TSPO ligands against neuroinflammation and related neurodegenerative mechanisms, taking into consideration some pathologies of the nervous system in which inflammatory events are crucial for the onset and progression of the disease, and attempting to shed light on the immunomodulatory effects of TSPO.

Carbonic Anhydrase Activators for Neurodegeneration: An Overview

Carbonic anhydrases (CAs) are a family of ubiquitous metal enzymes catalyzing the reversible conversion of CO₂ and H₂O to HCO₃⁻ with the release of a proton. They play an important role in pH regulation and in the balance of body fluids and are involved in several functions such as homeostasis regulation and cellular respiration. For these reasons, they have been studied as targets for the development of agents for treating several pathologies. CA inhibitors have been used in therapy for a long time, especially as diuretics and for the treatment of glaucoma, and are being investigated for application in other pathologies including obesity, cancer, and epilepsy. On the contrary, CAs activators are still poorly studied. They are proposed to act as additional (other than histidine) proton shuttles in the rate-limiting step of the CA catalytic cycle, which is the generation of the active hydroxylated enzyme. Recent studies highlight the involvement of CAs activation in brain processes essential for the transmission of neuronal signals, suggesting CAs activation might represent a potential therapeutic approach for the treatment of Alzheimer’s disease and other conditions characterized by memory impairment and cognitive problems. Actually, some compounds able to activate CAs have been identified and proposed to potentially resolve problems related to neurodegeneration. This review reports on the primary literature regarding the potential of CA activators for treating neurodegeneration-related diseases.

Essential Principles and Recent Progress in the Development of TSPO PET Ligands for Neuroinflammation Imaging

The translocator protein 18kDa (TSPO) is expressed in the outer mitochondrial membrane and is implicated in several functions, including cholesterol transport and stereoidogenesis. Under normal physiological conditions, TSPO is present in very low concentrations in the human brain but is markedly upregulated in response to brain injury and inflammation. This upregulation is strongly associated with activated microglia. Therefore, TSPO is particulary suited for assessing active gliosis associated with brain lesions following injury or disease. For over three decades, TSPO has been studied as a biomarker. Numerous radioligands for positron emission tomography (PET) that target TSPO have been developed for imaging inflammatory progression in the brain. Although [¹¹C]PK11195, the prototypical first-generation PET radioligand, is still widely used for in vivo studies, mainly now as its single more potent R-enantiomer, it has severe limitations, including low sensitivity and poor amenability to quantification. Second-generation radioligands are characterized by higher TSPO specific signals but suffer from other drawbacks, such as sensitivity to the TSPO single nucleotide polymorphism (SNP) rs6971. Therefore, their applications in human studies have a burden of needing to genotype subjects. Consequently, recent efforts are focused on developing improved radioligands that combine the optimal features of the second-generation with the ability to overcome the differences in binding affinities across the population. This review presents essential principles in the design and development of TSPO PET ligands and discusses prominent examples among the main chemotypes.

Cancer Immunotherapy: An Overview on Small Molecules as Inhibitors of the Immune Checkpoint PD-1/PD-L1 (2015-2021)

In 2018, James Allison and Tasuku Honjo received the Nobel Prize in Physiology or Medicine for their discovery of tumor therapy inhibition of negative immune regulation. Immunotherapy stimulates T-cells to fight cancer cells by blocking different immune checkpoint pathways. The interaction between programmed cell death 1 (PD-1) and its ligand PD-L1 (Programmed cell death ligand 1), is one of the main immune checkpoints. Of note, interfering with this pathway is already exploited in clinical cancer therapy, demonstrating that it is one of the key factors involved in cancer immune escape. The development of monoclonal antibodies (mAbs) that possess the ability to inhibit the interactions between PD-1/PD-L1 has radically made the difference in cancer immunotherapy. Yet, because of the many drawbacks that this therapy possesses, the research moved its efforts towards the development of novel small molecules. This may constitute a hope, but also an arduous challenge in fighting cancer. This paper reviews the recent primary literature concerning the development of novel small molecules able to blockade the interaction between PD-1 and its ligand PD-L1.

Enriching the Arsenal of Pharmacological Tools against MICAL2

Molecule interacting with CasL 2 (MICAL2), a cytoskeleton dynamics regulator, are strongly expressed in several human cancer types, especially at the invasive front, in metastasizing cancer cells and in the neo-angiogenic vasculature. Although a plethora of data exist and stress a growing relevance of MICAL2 to human cancer, it is worth noting that only one small-molecule inhibitor, named CCG-1423 (1), is known to date. Herein, with the aim to develop novel MICAL2 inhibitors, starting from CCG-1423 (1), a small library of new compounds was synthetized and biologically evaluated on human dermal microvascular endothelial cells (HMEC-1) and on renal cell adenocarcinoma (786-O) cells. Among the novel compounds, 10 and 7 gave interesting results in terms of reduction in cell proliferation and/or motility, whereas no effects were observed in MICAL2-knocked down cells. Aside from the interesting biological activities, this work provides the first structure-activity relationships (SARs) of CCG-1423 (1), thus providing precious information for the discovery of new MICAL2 inhibitors.

Synthesis and Screening in Mice of Fluorine-Containing PET Radioligands for TSPO: Discovery of a Promising 18F-Labeled Ligand

Translocator protein 18 kDa (TSPO) is a biomarker of neuroinflammation. [¹¹C]ER176 robustly quantifies TSPO in the human brain with positron emission tomography (PET), irrespective of subject genotype. We aimed to develop an ER176 analog with potential for labeling with longer-lived fluorine-18 (t_1/2 = 109.8 min). New fluoro and trifluoromethyl analogs of ER176 were prepared through a concise synthetic strategy. These ligands showed high TSPO affinity and low human genotype sensitivity. Each ligand was initially labeled by a generic ¹¹C-methylation procedure, thereby enabling speedy screening in mice. Each radioligand was rapidly taken up and well retained in the mouse brain at baseline after intravenous injection. Preblocking of TSPO showed that high proportions of brain uptake were specifically bound to TSPO at baseline. Overall, the 3-fluoro analog of [¹¹C]ER176 ([¹¹C]3b) displayed the most promising imaging properties. Therefore, a method was developed to label 3b with [¹⁸F]fluoride ion. [¹⁸F]3b gave similarly promising PET imaging results and deserves evaluation in higher species.

Carbonic anhydrase activation profile of indole-based derivatives

Carbonic Anhydrase Activators (CAAs) could represent a novel approach for the treatment of Alzheimer’s disease, ageing, and other conditions that require remedial achievement of spatial learning and memory therapy. Within a research project aimed at developing novel CAAs selective for certain isoforms, three series of indole-based derivatives were investigated. Enzyme activation assay on human CA I, II, VA, and VII isoforms revealed several effective micromolar activators, with promising selectivity profiles towards the brain-associated cytosolic isoform hCA VII. Molecular modelling studies suggested a theoretical model of the complex between hCA VII and the new activators and provide a possible explanation for their modulating as well as selectivity properties. Preliminary biological evaluations demonstrated that one of the most potent CAA 7 is not cytotoxic and is able to increase the release of the brain-derived neurotrophic factor (BDNF) from human microglial cells, highlighting its possible application in the treatment of CNS-related disorders.

Tetrahydroquinazole-based secondary sulphonamides as carbonic anhydrase inhibitors: synthesis, biological evaluation against isoforms I, II, IV, and IX, and computational studies

A library of variously decorated N-phenyl secondary sulphonamides featuring the bicyclic tetrahydroquinazole scaffold was synthesised and biologically evaluated for their inhibitory activity against human carbonic anhydrase (hCA) I, II, IV, and IX. Of note, several compounds were identified showing submicromolar potency and excellent selectivity for the tumour-related hCA IX isoform. Structure-activity relationship data attained for various substitutions were rationalised by molecular modelling studies in terms of both inhibitory activity and selectivity.

Two mixed valence diruthenium(II,III) isomeric complexes show different anticancer properties

In this paper it is demonstrated that the nature of the ligands of two Ru2(ii,iii) paddlewheel complexes dramatically affects the overall anticancer properties in cells. Herein, the complex [Ru2(EB776)4Cl] was found to be more active against a glioblastoma model with respect to its isomer [Ru2(EB106)4Cl]. These different effects depend on the steric hindrance, on the allowed conformations of the complexes and on the presence of hydrophilic regions in [Ru2(EB776)4Cl], which overall lead to a lower "steric protection".

Novel positive allosteric modulators of A2B adenosine receptor acting as bone mineralisation promoters

Small-molecules acting as positive allosteric modulators (PAMs) of the A_2B adenosine receptor (A_2B AR) could potentially represent a novel therapeutic strategy for pathological conditions characterised by altered bone homeostasis, including osteoporosis. We investigated a library of compounds (4-13) exhibiting different degrees of chemical similarity with three indole derivatives (1-3), which have been recently identified by us as PAMs of the A_2B AR able to promote mesenchymal stem cell differentiation and bone formation. Evaluation of mineralisation activity of 4-13 in the presence and in the absence of the agonist BAY60-6583 allowed the identification of lead compounds with therapeutic potential as anti-osteoporosis agents. Further biological characterisation of one of the most performing compounds, the benzofurane derivative 9, confirmed that such a molecule behaves as PAM of the A_2B AR.

Inhibition studies on carbonic anhydrase isoforms I, II, IV and IX with N-arylsubstituted secondary sulfonamides featuring a bicyclic tetrahydroindazole scaffold

Carbonic Anhydrases (CAs) are pharmaceutically relevant targets for the treatment of several disease conditions. The ubiquitous localization of these enzymes and the high homology shared by the different isoforms represent substantial impediments for the discovery of potential drugs devoid of off-target side effects. As a consequence, substantial efforts are still needed to allow for the full realization of the pharmacological potential of CA modulators. In this contribution, starting from our previous studies, we describe the synthesis of a set of new bicyclic tetrahydroindazoles featuring a secondary sulfonamide. Biological evaluation of the inhibitory activity against the hCA I, II, IV, and IX isoforms allowed drawing a structure-activity relationship profile that was rationalized through theoretical studies. This allowed dissecting the new molecules into the single portions influencing the zinc chelation properties and the selectivity profile thereby offering a new platform for the discovery of new isotype selective CA inhibitors.

The Alpha Keto Amide Moiety as a Privileged Motif in Medicinal Chemistry: Current Insights and Emerging Opportunities

Over the years, researchers in drug discovery have taken advantage of the use of privileged structures to design innovative hit/lead molecules. The α-ketoamide motif is found in many natural products, and it has been widely exploited by medicinal chemists to develop compounds tailored to a vast range of biological targets, thus presenting clinical potential for a plethora of pathological conditions. The purpose of this perspective is to provide insights into the versatility of this chemical moiety as a privileged structure in drug discovery. After a brief analysis of its physical-chemical features and synthetic procedures to obtain it, α-ketoamide-based classes of compounds are reported according to the application of this motif as either a nonreactive or reactive moiety. The goal is to highlight those aspects that may be useful to understanding the perspectives of employing the α-ketoamide moiety in the rational design of compounds able to interact with a specific target.

Allosterism vs. Orthosterism: Recent Findings and Future Perspectives on A2B AR Physio-Pathological Implications

The development of GPCR (G-coupled protein receptor) allosteric modulators has attracted increasing interest in the last decades. The use of allosteric modulators in therapy offers several advantages with respect to orthosteric ones, as they can fine-tune the tissue responses to the endogenous agonist. Since the discovery of the first A₁ adenosine receptor (AR) allosteric modulator in 1990, several efforts have been made to develop more potent molecules as well as allosteric modulators for all adenosine receptor subtypes. There are four subtypes of AR: A₁, A_2A, A_2B, and A₃. Positive allosteric modulators of the A₁ AR have been proposed for the cure of pain. A₃ positive allosteric modulators are thought to be beneficial during inflammatory processes. More recently, A_2A and A_2B AR allosteric modulators have also been disclosed. The A_2B AR displays the lowest affinity for its endogenous ligand adenosine and is mainly activated as a consequence of tissue damage. The A_2B AR activation has been found to play a crucial role in chronic obstructive pulmonary disease, in the protection of the heart from ischemic injury, and in the process of bone formation. In this context, allosteric modulators of the A_2B AR may represent pharmacological tools useful to develop new therapeutic agents. Herein, we provide an up-to-date highlight of the recent findings and future perspectives in the field of orthosteric and allosteric A_2B AR ligands. Furthermore, we compare the use of orthosteric ligands with positive and negative allosteric modulators for the management of different pathological conditions.

A mixed-valence diruthenium(II,III) complex endowed with high stability: from experimental evidence to theoretical interpretation

We herein report the synthesis and multi-technique characterization of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4], a novel diruthenium(ii,iii) complex obtained by reacting [Ru2(μ-O2CCH3)4Cl] with a dual indolylglyoxylyl dipeptide anticancer agent. We soon realised that the compound is very stable under several different conditions including aqueous buffers or organic solvents. It is also completely unreactive toward proteins. The high stability is also suggested by cellular experiments in a glioblastoma cell line. Indeed, while the parent ligand exerts high cytotoxic effects in the low μM range, the complex is completely non-cytotoxic against the same line, most probably because of the lack of ligand release. To investigate the reasons for such high stability, we carried out DFT calculations that are fully consistent with the experimental findings. The results highlight that the stability of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4] relies on the nature of the ligand, including its steric hindrance that prevents the reaction of any nucleophilic group with the Ru2 core. Ligand displacement is the key step to allow reactivity with the biological targets of metal-based prodrugs. Accordingly, we discuss the implications of some important aspects that should be considered when active molecules are chosen as ligands for the synthesis of paddle-wheel-like complexes with medicinal applications.

Exploiting the Indole Scaffold to Design Compounds Binding to Different Pharmacological Targets

Several indole derivatives have been disclosed by our research groups that have been collaborating for nearly 25 years. The results of our investigations led to a variety of molecules binding selectively to different pharmacological targets, specifically the type A γ-aminobutyric acid (GABA_A) chloride channel, the translocator protein (TSPO), the murine double minute 2 (MDM2) protein, the A_2B adenosine receptor (A_2B AR) and the Kelch-like ECH-associated protein 1 (Keap1). Herein, we describe how these works were conceived and carried out thanks to the versatility of indole nucleus to be exploited in the design and synthesis of drug-like molecules.

Targeting the KRAS oncogene: Synthesis, physicochemical and biological evaluation of novel G-Quadruplex DNA binders

The oncogene KRAS is involved in the pathogenesis of many tumors such as pancreatic, lung and colorectal cancers, thereby representing a relevant target for the treatment of these diseases. The KRAS P1 promoter contains a nuclease hypersensitive, guanine-rich sequence able to fold into a G-quadruplex motif (G4). The stabilization of this G4 structure by small molecules is emerging as a feasible approach to downregulate KRAS expression. Here, a set of novel stabilizing molecules was identified through a virtual screening campaign on the NMR structure of the 22-mer KRAS G4. The most promising hits were then submitted to structure-activity relationships studies which allowed improving their binding affinity and selectivity over double helix DNA and different G4 topologies. The best derivative (19) underwent fluorescence titration experiments and further computational studies to disclose its binding mechanism to KRAS G4. Finally, biological assays showed that this compound is capable to reduce the viability of colorectal cancer cells in which mutated KRAS acts as a driver oncogene. Thus, 19 might represent the prototype of a new class of drugs for the treatment of tumors that, expressing mutated forms of KRAS, are refractory to current therapeutic regimens.

Novel 2-substituted-benzimidazole-6-sulfonamides as carbonic anhydrase inhibitors: synthesis, biological evaluation against isoforms I, II, IX and XII and molecular docking studies

Inhibition of Carbonic Anhydrases (CAs) has been clinically exploited for many decades for a variety of therapeutic applications. Within a research project aimed at developing novel classes of CA inhibitors (CAIs) with a proper selectivity for certain isoforms, a series of derivatives featuring the 2-substituted-benzimidazole-6-sulfonamide scaffold, conceived as frozen analogs of Schiff bases and secondary amines previously reported in the literature as CAIs, were investigated. Enzyme inhibition assays on physiologically relevant human CA I, II, IX and XII isoforms revealed a number of potent CAIs, showing promising selectivity profiles towards the transmembrane tumor-associated CA IX and XII enzymes. Computational studies were attained to clarify the structural determinants behind the activities and selectivity profiles of the novel inhibitors.

Microglial Pro-Inflammatory and Anti-Inflammatory Phenotypes Are Modulated by Translocator Protein Activation

A key role of the mitochondrial Translocator Protein 18 KDa (TSPO) in neuroinflammation has been recently proposed. However, little is known about TSPO-activated pathways underlying the modulation of reactive microglia. In the present work, the TSPO activation was explored in an in vitro human primary microglia model (immortalized C20 cells) under inflammatory stimulus. Two different approaches were used with the aim to (i) pharmacologically amplify or (ii) silence, by the lentiviral short hairpin RNA, the TSPO physiological function. In the TSPO pharmacological stimulation model, the synthetic steroidogenic selective ligand XBD-173 attenuated the activation of microglia. Indeed, it reduces and increases the release of pro-inflammatory and anti-inflammatory cytokines, respectively. Such ligand-induced effects were abolished when C20 cells were treated with the steroidogenesis inhibitor aminoglutethimide. This suggests a role for neurosteroids in modulating the interleukin production. The highly steroidogenic ligand XBD-173 attenuated the neuroinflammatory response more effectively than the poorly steroidogenic ones, which suggests that the observed modulation on the cytokine release may be influenced by the levels of produced neurosteroids. In the TSPO silencing model, the reduction of TSPO caused a more inflamed phenotype with respect to scrambled cells. Similarly, during the inflammatory response, the TSPO silencing increased and reduced the release of pro-inflammatory and anti-inflammatory cytokines, respectively. In conclusion, the obtained results are in favor of a homeostatic role for TSPO in the context of dynamic balance between anti-inflammatory and pro-inflammatory mediators in the human microglia-mediated inflammatory response. Interestingly, our preliminary results propose that the TSPO expression could be stimulated by NF-κB during activation of the inflammatory response.

Unbinding of Translocator Protein 18 kDa (TSPO) Ligands: From in Vitro Residence Time to in Vivo Efficacy via in Silico Simulations

Translocator protein 18 kDa (TSPO) is a validated pharmacological target for the development of new treatments for neurological disorders. N,N-Dialkyl-2-phenylindol-3-ylglyoxylamides (PIGAs) are effective TSPO modulators and potentially useful therapeutics for the treatment of anxiety, central nervous system pathologies featuring astrocyte loss, and inflammatory-based neuropathologies. For this class of compounds, no correlation exists between the TSPO binding affinity and the corresponding functional efficacy. Rather, their biological effectiveness correlates with the kinetics of the unbinding events and more specifically with the residence time (RT). So far, the structural reasons for the different recorded RT of congeneric PIGAs remain elusive. Here, to understand the different kinetics of PIGAs, their unbinding paths were studied by employing enhanced-sampling molecular dynamics simulations. Results of these studies revealed how subtle structural differences between PIGAs have a substantial effect on the unbinding energetics. In particular, during the egress from the TSPO binding site, slow-dissociating PIGAs find tight interactions with the protein LP1 region thereby determining a long RT. Further support to these findings was achieved by in vivo studies, which demonstrated how the anxiolytic effect observed for the inspected PIGAs correlated with their RT to TSPO.

Discovery of Pyrido[3',2':5,6]thiopyrano[4,3-d]pyrimidine-Based Antiproliferative Multikinase Inhibitors

Protein kinases dysregulation is extremely common in cancer cells, and the development of new agents able to simultaneously target multiple kinase pathways involved in angiogenesis and tumor growth may offer several advantages in the treatment of cancer. Herein we report the discovery of new pyridothiopyranopyrimidine derivatives (2-4) showing high potencies in VEGFR-2 KDR inhibition as well as antiproliferative effect on a panel of human tumor cell lines. Investigation on the selectivity profile of the representative 2-anilino-substituted compounds 3b, 3i, and 3j revealed a multiplicity of kinase targets that should account for the potent antiproliferative effect produced by these pyridothiopyranopyrimidine derivatives.

Soyasaponins from Zolfino bean as aldose reductase differential inhibitors

Seven triterpenoid saponins were identified in methanolic extracts of seeds of the Zolfino bean landrace (Phaseolus vulgaris L.) by HPLC fractionation, revealing their ability to inhibit highly purified human recombinant aldose reductase (hAKR1B1). Six of these compounds were associated by MS analysis with the following saponins already reported in different Phaseolus vulgaris varieties: soyasaponin Ba (V), soyasaponin Bb, soyasaponin Bd (sandosaponin A), soyasaponin αg, 3-O-[R-l-rhamnopyranosyl(1 → 2)-α-d-glucopyranosyl(1 → 2)-α-d-glucuronopyranosyl]olean-12-en-22-oxo-3α,-24-diol, and soyasaponin βg. The inhibitory activity of the collected fractions containing the above compounds was tested for hAKR1B1-dependent reduction of both l-idose and 4-hydroxynonenal, revealing that some are able to differentially inhibit the enzyme. The present work also highlights the difficulties in the search for aldose reductase differential inhibitors (ARDIs) in mixtures due to the masking effect on ARDIs exerted by the presence of conventional aldose reductase inhibitors. The possibility of differential inhibition generated by a different inhibitory model of action of molecules on different substrates undergoing transformation is also discussed.

Benzothiopyranoindole- and pyridothiopyranoindole-based antiproliferative agents targeting topoisomerases

New benzothiopyranoindoles (5a-l) and pyridothiopyranoindoles (5m-t), featuring different combinations of substituents (H, Cl, OCH₃) at R²-R⁴ positions and protonatable R¹-dialkylaminoalkyl chains, were synthesized and biologically assayed on three human tumor cell lines, showing significant antiproliferative activity (GI₅₀ values spanning from 0.31 to 6.93 μM) and pro-apoptotic effect. Linear flow dichroism experiments indicate the ability of both chromophores to form a molecular complex with DNA, following an intercalative mode of binding. All compounds displayed a moderate ability to inhibit the relaxation activity of both topoisomerases I and II, reasonably correlated to their intercalative capacities. Cleavable assay performed with topoisomerase I revealed a significant poisoning effect for compounds 5g, 5h, 5s, and 5t. A theoretical model provided by hydrated docking calculations clarified the role of the R¹-R⁴ substituents on the topoisomerase I poison activity, revealing a crucial role of the R²-OCH₃ group.

Long lasting inhibition of Mdm2-p53 interaction potentiates mesenchymal stem cell differentiation into osteoblasts

The osteoblast generation from Mesenchymal stem cells (MSCs) is tightly coordinated by transcriptional networks and signalling pathways that control gene expression and protein stability of osteogenic "master transcription factors". Among these pathways, a great attention has been focused on p53 and its physiological negative regulator, the E3 ligase Murine double minute 2 (Mdm2). Nevertheless, the signalling that regulates Mdm2-p53 axis in osteoblasts remain to be elucidated, also considering that Mdm2 possesses numerous p53-independent activities and interacts with additional proteins. Herein, the effects of Mdm2 modulation on MSC differentiation were examined by the use of short- and long-lasting inhibitors of the Mdm2-p53 complex. The long-lasting Mdm2-p53 dissociation was demonstrated to enhance the MSC differentiation into osteoblasts. The increase of Mdm2 levels promoted its association to G protein-coupled receptors kinase (GRK) 2, one of the most relevant kinases involved in the desensitization of G protein-coupled receptors (GPCRs). In turn, the long-lasting Mdm2-p53 dissociation decreased GRK2 levels and favoured the functionality of A_2B Adenosine Receptors (A_2BARs), a GPCR dictating MSC fate. EB148 facilitated cAMP accumulation, and mediated a sustained activation of extracellular signal-regulated kinases (ERKs) and cAMP response element-binding protein (CREB). Such pro-osteogenic effects were not detectable by using the reversible Mdm2-p53 complex inhibitor, suggesting the time course of Mdm2-p53 dissociation may impact on intracellular proteins involved in cell differentiation fate. These results suggest that the long-lasting Mdm2 binding plays a key role in the mobilization of intracellular proteins that regulate the final biological outcome of MSCs.

Acid Derivatives of Pyrazolo[1,5-a]pyrimidine as Aldose Reductase Differential Inhibitors

Aldose reductase (AKR1B1), the key enzyme of the polyol pathway, plays a crucial role in the development of long-term complications affecting diabetic patients. Nevertheless, the expedience of inhibiting this enzyme to treat diabetic complications has failed, due to the emergence of side effects from compounds under development. Actually AKR1B1 is a Janus-faced enzyme which, besides ruling the polyol pathway, takes part in the antioxidant defense mechanism of the body. In this work we report the evidence that a class of compounds, characterized by a pyrazolo[1,5-a]pyrimidine core and an ionizable fragment, modulates differently the catalytic activity of the enzyme, depending on the presence of specific substrates such as sugar, toxic aldehydes, and glutathione conjugates of toxic aldehydes. The study stands out as a systematic attempt to generate aldose reductase differential inhibitors (ARDIs) intended to target long-term diabetic complications while leaving unaltered the detoxifying role of the enzyme.

4-Substituted Benzenesulfonamides Incorporating Bi/Tricyclic Moieties Act as Potent and Isoform-Selective Carbonic Anhydrase II/IX Inhibitors

As a part of our efforts to expand chemical diversity in the carbonic anhydrases inhibitors (CAIs), three small series of polyheterocyclic compounds (4-6) featuring the primary benzenesulfonamide moiety linked to bi/tricyclic scaffolds were investigated. Highly effective inhibitors against the target tumor-associated hCA IX (low nanomolar/subnanomolar potency levels) showing significant functional selectivity profile toward hCA I, II, and IV isozymes were identified. Molecular docking studies clarified the reasons behind the activity and selectivity of the new compounds.

Simultaneous Targeting of RGD-Integrins and Dual Murine Double Minute Proteins in Glioblastoma Multiforme

In the fight against Glioblastoma Multiforme, recent literature data have highlighted that integrin α5β1 and p53 are part of convergent pathways in the control of glioma apoptosis. This observation prompted us to seek a molecule able to simultaneously modulate both target families. Analyzing the results of a previous virtual screening against murine double minute 2 protein (MDM2), we envisaged that Arg-Gly-Asp (RGD)-mimetic molecules could be inhibitors of MDM2/4. Herein, we present the discovery of compound 7, which inhibits both MDM2/4 and α5β1/αvβ3 integrins. A lead optimization campaign was carried out on 7 with the aim to preserve the activities on integrins while improving those on MDM proteins. Compound 9 turned out to be a potent MDM2/4 and α5β1/αvβ3 blocker. In p53-wild type glioma cells, 9 arrested cell cycle and proliferation and strongly reduced cell invasiveness, emerging as the first molecule of a novel class of integrin/MDM inhibitors, which might be especially useful in subpopulations of patients with glioblastoma expressing a functional p53 concomitantly with a high level of α5β1 integrin.

New insights in the structure-activity relationships of 2-phenylamino-substituted benzothiopyrano[4,3-d]pyrimidines as kinase inhibitors

Inhibition of angiogenesis via blocking vascular endothelial growth factor receptor (VEGFR) signaling pathway emerged as an established approach in anticancer therapy. So far, many monoclonal antibodies and ATP-competitive small molecule inhibitors have been clinically validated and approved. In this study, structure-activity relationships (SAR) within the 2-phenylamino-substituted benzothiopyrano[4,3-d]pyrimidine class of kinase inhibitors were further refined by the synthesis and biological evaluation of new compounds 1-21 featuring different substitution patterns on the pendant phenyl moiety, combined with H, OCH₃, or Cl at 8-position. Most compounds showed a promising human kinase insert domain receptor (KDR) inhibition profile, with IC₅₀ values in the submicromolar/low micromolar range, and promising antiproliferative activity on human umbilical vein endothelial cells (HUVECs) as well as on a panel of three human tumor cell lines. The angio-kinase selectivity profile was assessed for the most promising compound 16 against a set of six human kinases. Finally, computational studies allowed clarifying at molecular level the interaction pattern established by the compounds with KDR, highlighting key stable cation-π interactions, and thus providing the basis for further designing novel inhibitors.

Bax Activation Blocks Self-Renewal and Induces Apoptosis of Human Glioblastoma Stem Cells

Glioblastoma (GBM) is characterized by a poor response to conventional chemotherapeutic agents, attributed to the insurgence of drug resistance mechanisms and to the presence of a subpopulation of glioma stem cells (GSCs). GBM cells and GSCs present, among others, an overexpression of antiapoptotic proteins and an inhibition of pro-apoptotic ones, which help to escape apoptosis. Among pro-apoptotic inducers, the Bcl-2 family protein Bax has recently emerged as a promising new target in cancer therapy along with first BAX activators (BAM7, Compound 106, and SMBA1). Herein, a derivative of BAM-7, named BTC-8, was employed to explore the effects of Bax activation in different human GBM cells and in their stem cell subpopulation. BTC-8 inhibited GBM cell proliferation, arrested the cell cycle, and induced apoptosis through the induction of mitochondrial membrane permeabilization. Most importantly, BTC-8 blocked proliferation and self-renewal of GSCs and induced their apoptosis. Notably, BTC-8 was demonstrated to sensitize both GBM cells and GSCs to the alkylating agent Temozolomide. Overall, our findings shed light on the effects and the relative molecular mechanisms related to Bax activation in GBM, and they suggest Bax-targeting compounds as promising therapeutic tools against the GSC reservoir.

Computer-Aided Identification and Lead Optimization of Dual Murine Double Minute 2 and 4 Binders: Structure-Activity Relationship Studies and Pharmacological Activity

The function of p53 protein, also known as "genome guardian", might be impaired by the overexpression of its primary cellular inhibitor, the murine double minute 2 protein (MDM2). However, the recent finding that MDM2-selective inhibitors induce high levels of its homologue MDM4, prompt us to identify, through a receptor-based virtual screening on an in house database, dual MDM2/MDM4 binders. Compound 1 turned out to possess an IC₅₀ of 93.7 and of 4.6 nM on MDM2 and MDM4, respectively. A series of compounds were synthesized to optimize its activity on MDM2. As a result, compound 12 showed low nanomolar IC₅₀ for both targets. NMR studies confirmed the pocket of binding of 12 as predicted by the Glide docking software. Notably, 12 was able to cause concentration-dependent inhibition of cell proliferation, yielding an IC₅₀ value of 356 ± 21 nM in neuroblastoma SHSY5Y cells and proved even to efficiently block cancer stem cell growth.

The Anxiolytic Etifoxine Binds to TSPO Ro5-4864 Binding Site with Long Residence Time Showing a High Neurosteroidogenic Activity

The low binding affinity of the approved anxiolytic drug etifoxine (Stresam) at the steroidogenic 18 kDa translocator protein (TSPO) has questioned the specific contribution of this protein in mediating the etifoxine neurosteroidogenic efficacy. Residence time (RT) at the binding site of the classical TSPO ligand PK11195 is emerging as a relevant neurosteroidogenic efficacy measure rather than the binding affinity. Here etifoxine was evaluated for (i) the in vitro neurosteroidogenic activity in comparison to poorly neurosteroidogenic reference TSPO ligands (PK11195 and Ro5-4864) and (ii) the affinity and RT at [³H]PK11195 and [³H]Ro5-4864 binding sites in rat kidney membranes. Etifoxine shows (i) high neurosteroidogenic efficacy and (ii) low affinity/short RT at the [³H]PK11195 site and low affinity/long RT at the [³H]Ro5-4864 site, at which etifoxine competitively bound. These findings suggest that the long RT of etifoxine at the Ro5-4864 binding site could account for its high neurosteroidogenic efficacy.

Residence Time, a New parameter to Predict Neurosteroidogenic Efficacy of Translocator Protein (TSPO) Ligands: the Case Study of N,N-Dialkyl-2-arylindol-3-ylglyoxylamides

Targeting the biosynthetic pathway of neuroactive steroids with specific 18 kDa translocator protein (TSPO) ligands may be a viable therapeutic approach for a variety of neurodegenerative and neuropsychiatric diseases. However, the lack of correlation between binding affinity and in vitro steroidogenic efficacy has limited the identification of lead compounds by traditional affinity-based drug discovery strategies. Our recent research indicates that the key factor for robust steroidogenic TSPO ligand efficacy is not the binding affinity per se, but rather the time the compound spends in the target, namely its residence time (RT). The assessment of this kinetic parameter during the in vitro characterization of compounds appears mandatory in order to obtain structure-efficacy relationships suitable for the future development of novel molecules with promising pharmacological properties.

Long lasting MDM2/Translocator protein modulator: a new strategy for irreversible apoptosis of human glioblastoma cells

The development of multi-target drugs and irreversible modulators of deregulated signalling proteins is the major challenge for improving glioblastoma multiforme (GBM) treatment. Reversible single-target drugs are not sufficient to sustain a therapeutic effect over time and may favour the activation of alternative signalling pathways and the onset of resistance phenomena. Thus, a multi-target compound that has a long-lasting mechanism of action might have a greater and longer life span of anti-proliferative activity. Recently, a dual-target indol-3ylglyoxyldipeptide derivative, designed to bind to the Translocator Protein (TSPO) and reactivate p53 function via dissociation from its physiological inhibitor, murine double minute 2 (MDM2), has been developed as a potent GBM pro-apoptotic agent. In this study, this derivative was chemically modified to irreversibly bind MDM2 and TSPO. The new compound elicited a TSPO-mediated mitochondrial membrane dissipation and restored p53 activity, triggering a long-lasting apoptosis of GBM cells. These effects were sustained over time, involved a stable activation of extracellular signal regulated kinases and were specifically observed in cancer cells, in which these protein kinases are deregulated. Dual-targeting and irreversible binding properties combined in the same molecule may represent a useful strategy to overcome the time-limited effects elicited by classical chemotherapies.

11C-ER176, a Radioligand for 18-kDa Translocator Protein, Has Adequate Sensitivity to Robustly Image All Three Affinity Genotypes in Human Brain

For PET imaging of 18-kDa translocator protein (TSPO), a biomarker of neuroinflammation, most second-generation radioligands are sensitive to the single nucleotide polymorphism rs6971; however, this is probably not the case for the prototypical agent ¹¹C-PK11195 (¹¹C-labeled N-butan-2-yl-1-(2-chlorophenyl)-N-methylisoquinoline-3-carboxamide), which has a relatively lower signal-to-noise ratio. We recently found that ¹¹C-ER176 (¹¹C-(R)-N-sec-butyl-4-(2-chlorophenyl)-N-methylquinazoline-2-carboxamide), a new analog of ¹¹C-(R)-PK11195, showed little sensitivity to rs6971 when tested in vitro and had high specific binding in monkey brain. This study sought, first, to determine whether the sensitivity of ¹¹C-ER176 in humans is similar to the low sensitivity measured in vitro and, second, to measure the nondisplaceable binding potential (BP_ND, or the ratio of specific-to-nondisplaceable uptake) of ¹¹C-ER176 in human brain.

METHODS

Nine healthy volunteers-3 high-affinity binders (HABs), 3 mixed-affinity binders (MABs), and 3 low-affinity binders (LABs)-were studied with whole-body ¹¹C-ER176 PET imaging. SUVs from 60 to 120 min after injection derived from each organ were compared between genotypes. Eight separate healthy volunteers-3 HABs, 3 MABs, and 2 LABs-underwent brain PET imaging. The 3 HABs underwent a repeated brain scan after TSPO blockade with XBD173 (N-benzyl-N-ethyl-2-(7-methyl-8-oxo-2-phenylpurin-9-yl)acetamide) to determine nondisplaceable distribution volume (V_ND) via Lassen occupancy plotting and thereby estimate BP_ND in brain.

RESULTS

Regional SUV averaged from 60 to 120 min after injection in brain and peripheral organs with high TSPO densities such as lung and spleen were greater in HABs than in LABs. On the basis of V_ND determined via the occupancy plot, the whole-brain BP_ND for LABs was estimated to be 1.4 ± 0.8, which was much lower than that for HABs (4.2 ± 1.3) but about the same as that for HABs with ¹¹C-PBR28 ([methyl-¹¹C]N-acetyl-N-(2-methoxybenzyl)-2-phenoxy-5-pyridinamine)) (∼1.2).

CONCLUSION

Obvious in vivo sensitivity to rs6971 was observed in ¹¹C-ER176 that had not been expected from in vitro studies, suggesting that the future development of any improved radioligand for TSPO should consider the possibility that in vitro properties will not be reflected in vivo. We also found that ¹¹C-ER176 has adequately high BP_ND for all rs6971 genotypes. Thus, the new radioligand would likely have greater sensitivity in detecting abnormalities in patients.

Long Residence Time at the Neurosteroidogenic 18 kDa Translocator Protein Characterizes the Anxiolytic Ligand XBD173

Recent data have demonstrated a positive correlation between the residence time (RT) and neurosteroidogenic efficacy of a ligand at the translocator protein (TSPO), an attractive anxyolitic target. To explore the potential impact of RT on TSPO ligand anxiolytic activity, the RT and the steroidogenic activity of XBD173, a ligand exerting anxiolytic activity in humans, were retrospectively evaluated. To this aim, XBD173 association and dissociation rate constants were measured (1.23 × 10(7) M(-1) min(-1) and 0.0079 min(-1), respectively). XBD173 resulted to have a long RT (127 min) and to stimulate efficaciously neurosteroidogenesis, in terms of pregnenolone production. The present findings corroborate the importance of TSPO ligand RT to predict their effective neurosteroidogenic activity and promising anxiolytic action. These positive results prompted us to set up a fast and high-throughput kinetic method to improve the efficiency of RT-based TSPO drug-discovery process.

4-amino-6-alkyloxy-2-alkylthiopyrimidine derivatives as novel non-nucleoside agonists for the adenosine A1 receptor

Three 4-amino-6-alkyloxy-2-alkylthiopyrimidine derivatives (4-6) were investigated as potential non-nucleoside agonists at human adenosine receptors (ARs). When tested in competition binding experiments, these compounds exhibited low micromolar affinity (K_i values comprised between 1.2 and 1.9 μm) for the A₁ AR and no appreciable affinity for the A_2A and A₃ ARs. Evaluation of their efficacy profiles by measurement of intracellular cAMP levels revealed that 4 and 5 behave as non-nucleoside agonists of the A₁ AR with EC₅₀ values of 0.47 and 0.87 μm, respectively. No clear concentration-response curves could be instead obtained for 6, probably because this compound modulates one or more additional targets, thus masking the putative effects exerted by its activation of A₁ AR. The three compounds were not able to modulate A_2B AR-mediated cAMP accumulation induced by the non-selective AR agonist NECA, thus demonstrating no affinity toward this receptor.