Anxiolytic-like effects of N,N-dialkyl-2-phenylindol-3-ylglyoxylamides by modulation of translocator protein promoting neurosteroid biosynthesis

TSPO Radioligands for Neuroinflammation: An Overview

The translocator protein (TSPO) is predominately localized on the outer mitochondrial membrane in steroidogenic cells. In the brain, TSPO expression, low under normal conditions, results upregulated in response to glial cell activation, that occurs in neuroinflammation. As a consequence, TSPO has been extensively studied as a biomarker of such conditions by means of TSPO-targeted radiotracers. Although [11C]-PK11195, the prototypical TSPO radioligand, is still widely used for in vivo studies, it is endowed with severe limitations, mainly low sensitivity and poor amenability to quantification. Consequently, several efforts have been focused on the design of new radiotracers for the in vivo imaging of TSPO. The present review will provide an outlook on the latest advances in TSPO radioligands for neuroinflammation imaging. The final goal is to pave the way for (radio)chemists in the future design and development of novel effective and sensitive radiopharmaceuticals targeting TSPO.

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.

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.

Translocator protein in the rise and fall of central nervous system neurons

Translocator protein (TSPO), a 18 kDa protein found in the outer mitochondrial membrane, has historically been associated with the transport of cholesterol in highly steroidogenic tissues though it is found in all cells throughout the mammalian body. TSPO has also been associated with molecular transport, oxidative stress, apoptosis, and energy metabolism. TSPO levels are typically low in the central nervous system (CNS), but a significant upregulation is observed in activated microglia during neuroinflammation. However, there are also a few specific regions that have been reported to have higher TSPO levels than the rest of the brain under normal conditions. These include the dentate gyrus of the hippocampus, the olfactory bulb, the subventricular zone, the choroid plexus, and the cerebellum. These areas are also all associated with adult neurogenesis, yet there is no explanation of TSPO's function in these cells. Current studies have investigated the role of TSPO in microglia during neuron degeneration, but TSPO's role in the rest of the neuron lifecycle remains to be elucidated. This review aims to discuss the known functions of TSPO and its potential role in the lifecycle of neurons within the CNS.

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.

Targeting TSPO Reduces Inflammation and Apoptosis in an In Vitro Photoreceptor-Like Model of Retinal Degeneration

The 18 kDa translocator protein (TSPO) is predominantly located in the mitochondrial outer membrane, playing an important role in steroidogenesis, inflammation, survival, and cell proliferation. Its expression in the CNS, and mainly in glial cells, is upregulated in neuropathologies and brain injury. In this study, the potential of targeting TSPO for the therapeutic treatment of inflammatory-based retinal neurodegeneration was evaluated by means of an in vitro model of lipopolysaccharide (LPS)-induced degeneration in 661 W cells, a photoreceptor-like cell line. After the assessment of the expression of TSPO in 661W cells, which, to the best of our knowledge, was never investigated so far, the anti-inflammatory and cytoprotective effects of a number of known TSPO ligands, belonging to the class of N,N-dialkyl-2-arylindol-3-ylglyoxylamides (PIGAs), were evaluated, using the classic TSPO ligand PK11195 as the reference standard. All tested PIGAs showed the ability to modulate the inflammatory and apoptotic processes in 661 W photoreceptor-like cells and to reduce LPS-driven cellular cytotoxicity. The protective effect of PIGAs was, in all cases, reduced by cotreatment with the pregnenolone synthesis inhibitor SU-10603, suggesting the involvement of neurosteroids in the protective mechanism. As inflammatory processes play a crucial role in the retinal neurodegenerative disease progression toward photoreceptors' death and complete blindness, targeting TSPO might represent a successful strategy to slow down this degenerative process that may lead to the inexorable loss of vision.

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 steroidogenesis. 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 particularly 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 the 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.

[18F]BIBD-239: 18F-Labeled ER176, a Positron Emission Tomography Tracer Specific for the Translocator Protein

[¹¹C]ER176 has adequate sensitivity to image the human brain translocator protein (TSPO) in all three genotypes by positron emission tomography (PET). However, its clinical application is limited by the short half-life of ¹¹C (20.38 min). To overcome the deficiency of [¹¹C]ER176 and keep the pharmacophore features of ER176 to the maximum extent, we designed four fluorine-labeled ER176 derivatives using the deuterium method. In vitro competition binding confirmed that the designed compounds had high affinity for TSPO. Biodistribution experiments showed that tissues with high expression of TSPO had high uptake of these compounds, as well as that the compound showed high brain penetration and mild defluorination in vivo. Therefore, [¹⁸F]BIBD-239 with simple synthesis conditions was selected for further biological evaluation. Theoretical simulations showed that BIBD-239 and ER176 have similar binding modes and sites to Ala147-TSPO and Thr147-TSPO, which indicated that the tracers may have consistent sensitivity to the three affinity genotypes. In vitro autoradiography and in vivo PET studies of the ischemic rat brain showed dramatically higher uptake of [¹⁸F]BIBD-239 on the lesion site compared to the contralateral side with good brain kinetics. Additionally, [¹⁸F]BIBD-239 provided clear tumor PET images in a GL261 glioma model. Importantly, PET imaging and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) results showed that in vivo defluorination and other metabolites of [¹⁸F]BIBD-239 did not interfere with brain imaging. Conclusively, [¹⁸F]BIBD-239, similar to ER176 with low polymorphism sensitivity, has simple labeling conditions, high labeling yield, high affinity, and high specificity for TSPO, and it is planned for further evaluation in higher species.

Translocator Protein Ligand PIGA1138 Reduces Disease Symptoms and Severity in Experimental Autoimmune Encephalomyelitis Model of Primary Progressive Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune and demyelinating disease of the central nervous system (CNS) caused by CNS infiltration of peripheral immune cells, immune-mediated attack of the myelin sheath, neuroinflammation, and/or axonal/neuronal dysfunctions. Some drugs are available to cope with relapsing-remitting MS (RRMS) but there is no therapy for the primary progressive MS (PPMS). Because growing evidence supports a regulatory role of the translocator protein (TSPO) in neuroinflammatory, demyelinating, and neurodegenerative processes, we investigated the therapeutic potential of phenylindolyilglyoxylamydes (PIGAs) TSPO ligands in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) mice mimicking the human PPMS. MOG-EAE C57Bl/6-mice were treated by TSPO ligands PIGA839, PIGA1138, or the vehicle. Several methods were combined to evaluate PIGAs-TSPO ligand effects on MOG-EAE symptoms, CNS infiltration by immune cells, demyelination, and axonal damages. PIGA1138 (15 mg/kg) drastically reduced MOG-EAE mice clinical scores, ameliorated motor dysfunctions assessed with the Catwalk device, and counteracted MOG-EAE-induced demyelination by preserving Myelin basic protein (MBP) expression in the CNS. Furthermore, PIGA1138-treatment prevented EAE-evoked decreased neurofilament-200 expression in spinal and cerebellar axons. Moreover, PIGA1138 inhibited peripheral immune-CD45 + cell infiltration in the CNS, suggesting that it may control inflammatory mechanisms involved in PPMS. Concordantly, PIGA1138 enhanced anti-inflammatory interleukin-10 serum level in MOG-EAE mice. PIGA1138-treatment, which increased neurosteroid allopregnanolone production, ameliorated all pathological biomarkers, while PIGA839, unable to activate neurosteroidogenesis in vivo, exerted only moderate/partial effects in MOG-EAE mice. Altogether, our results suggest that PIGA1138-based treatment may represent an interesting possibility to be explored for the innovation of effective therapies against PPMS.

Synthesis and pharmacological evaluation of [18F]PBR316: a novel PET ligand targeting the translocator protein 18 kDa (TSPO) with low binding sensitivity to human single nucleotide polymorphism rs6971

Radiopharmaceuticals that target the translocator protein 18 kDa (TSPO) have been investigated with positron emission tomography (PET) to study neuroinflammation, neurodegeneration and cancer. We have developed the novel, achiral, 2-phenylimidazo[1,2-a]pyridine, PBR316 that targets the translocator protein 18 kDa (TSPO) that addresses some of the limitations inherent in current TSPO ligands; namely specificity in binding, blood brain barrier permeability, metabolism and insensitivity to TSPO binding in subjects as a result of rs6971 polymorphism. PBR316 has high nanomolar affinity (4.7-6.0 nM) for the TSPO, >5000 nM for the central benzodiazepine receptor (CBR) and low sensitivity to rs6971 polymorphism with a low affinity binders (LABs) to high affinity binders (HABs) ratio of 1.5. [18F]PBR316 was prepared in 20 ± 5% radiochemical yield, >99% radiochemical purity and a molar activity of 160-400 GBq μmol-1. Biodistribution in rats showed high uptake of [18F]PBR316 in organs known to express TSPO such as heart (3.9%) and adrenal glands (7.5% ID per g) at 1 h. [18F]PBR316 entered the brain and accumulated in TSPO-expressing regions with an olfactory bulb to brain ratio of 3 at 15 min and 7 at 4 h. Radioactivity was blocked by PK11195 and Ro 5-4864 but not Flumazenil. Metabolite analysis showed that radioactivity in adrenal glands and the brain was predominantly due to the intact radiotracer. PET-CT studies in mouse-bearing prostate tumour xenografts indicated biodistribution similar to rats with radioactivity in the tumour increasing with time. [18F]PBR316 shows in vitro binding that is insensitive to human polymorphism and has specific and selective in vivo binding to the TSPO. [18F]PBR316 is suitable for further biological and clinical studies.

The Ligands of Translocator Protein: Design and Biological Properties

In 2020, it is already 43 years since Braestrup and Squires discovered 18 kDa translocator protein (TSPO), known until 2006 as "peripheral benzodiazepine receptor". During this time, the functions of this receptor, which is located on the outer membrane of mitochondria, were studied in detail. One of the key functions of TSPO is the transfer of cholesterol from the outer to the inner mitochondrial membrane, which is the limiting stage in the synthesis of neurosteroids. TSPO is also involved in the transport of porphyrins, mitochondrial respiration, the opening of mitochondrial pores, apoptosis and cell proliferation. This review presents current information on the structure of TSPO, the mechanism of its participation in neurosteroidogenesis, as well as endogenous and synthetic TSPO ligands. Particular emphasis is placed on the analysis of approaches to the design of synthetic ligands and their neuropsychotropic activity in vitro and in vivo. The presented review demonstrates the promise of constructing new neuropsychotropic drugs in the series of TSPO ligands.

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.

The New Dipeptide TSPO Ligands: Design, Synthesis and Structure-Anxiolytic Activity Relationship

The translocator protein (TSPO, 18 kDa) plays an important role in the synthesis of neurosteroids by promoting the transport of cholesterol from the outer to the inner mitochondrial membrane, which is the rate-limiting step in neurosteroidogenesis. Stimulation of TSPO by appropriate ligands increases the level of neurosteroids. The present study describes the design, synthesis and investigation of anxiolytic-like effects of a series of N-acyl-tryptophanyl-containing dipeptides. These novel dipeptide TSPO ligands were designed with the original drug-based peptide design strategy using alpidem as non-peptide prototype. The anxiolytic activities were investigated in Balb/C mice using the illuminated open-field and elevated plus-maze tests in outbred laboratory mice ICR (CD-1). Dipeptide GD-102 (N-phenylpropionyl-l-tryptophanyl-l-leucine amide) in the dose range of 0.01-0.5 mg/kg intraperitoneally (i.p.) has a pronounced anxiolytic activity. The anxiolytic effect of GD-102 was abolished by PK11195, a specific TSPO antagonist. The structure-activity relationship study made it possible to identify a pharmacophore fragment for the dipeptide TSPO ligand. It was shown that l,d-diastereomer of GD-102 has no activity, and the d,l-isomer has less pronounced activity. The anxiolytic activity also disappears by replacing the C-amide group with the methyl ester, a free carboxyl group or methylamide. Consecutive replacement of each amino acid residue with glycine showed the importance of each of the amino acid residues in the structure of the ligand. The most active and technologically available compound GD-102, was selected for evaluation as a potential anxiolytic drug.

An update into the medicinal chemistry of translocator protein (TSPO) ligands

The Translocator Protein 18 kDa (TSPO) has been discovered in 1977 as an alternative binding site for the benzodiazepine diazepam. It is an evolutionary well-conserved and tryptophan-rich 169-amino acids protein with five alpha helical transmembrane domains stretching the outer mitochondrial membrane, with the carboxyl-terminus in the cytosol and a short amino-terminus in the intermembrane space of mitochondrion. At this level, together with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocase (ANT), it forms the mitochondrial permeability transition pore (MPTP). TSPO expression is ubiquitary, with higher levels in steroid producing tissues; in the central nervous system, it is mainly expressed in glial cells and in neurons. TSPO is implicated in a variety of fundamental cellular processes including steroidogenesis, heme biosynthesis, mitochondrial respiration, mitochondrial membrane potential, cell proliferation and differentiation, cell life/death balance, oxidative stress. Altered TSPO expression has been found in some pathological conditions. In particular, high TSPO expression levels have been documented in cancer, neuroinflammation, and brain injury. Conversely, low TSPO expression levels have been evidenced in anxiety disorders. Therefore, TSPO is not only an interesting drug target for therapeutic purpose (anticonvulsant, anxiolytic, etc.), but also a valid diagnostic marker of related-diseases detectable by fluorescent or radiolabeled ligands. The aim of this report is to present an update of previous reviews dealing with the medicinal chemistry of TSPO and to highlight the most outstanding advances in the development of TSPO ligands as potential therapeutic or diagnostic tools, especially referring to the last five years.

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.

Mitochondria modulatory effects of new TSPO ligands in a cellular model of tauopathies

Translocator protein 18 kDa (TSPO) is a mitochondrial protein located in the outer membrane and involved in cholesterol translocation, a prerequisite for steroid biosynthesis. TSPO modulation also appears to play a role in other mitochondrial functions, including mitochondrial respiration and cell survival. In the central nervous system, its expression is up-regulated in neuropathology such as Alzheimer's disease (AD). Previously, we demonstrated that two new TSPO ligands, named 2a and 2b, stimulated pregnenolone synthesis and ATP production in a cellular model of AD overproducing β-amyloid peptide. The present study aimed to evaluate the impact of the new TSPO ligands on mitochondrial dysfunction in a cellular model of AD-related tauopathy (human neuroblastoma cells SH-SY5Y stably overexpressing the P301L-mutant Tau) presenting mitochondrial impairments, including a decreased ATP synthesis and mitochondrial membrane potential, as well as a decrease in pregnenolone synthesis compared to control cells. The effects of our new ligands were compared with those of TSPO ligands described in the literature (XBD173, SSR-180,575 and Ro5-4864). The TSPO ligands 2a and 2b exerted beneficial mitochondrial modulatory effects by increasing ATP levels and mitochondrial membrane potential, paralleled by an increase of pregnenolone levels in mutant Tau cells, as well as in control cells. The compounds 2a and 2b showed effects on mitochondrial activity similar to those obtained with the TSPO ligands of reference. These findings indicate that the new TSPO ligands modulate the mitochondrial bioenergetic phenotype as well as the de novo synthesis of neurosteroids in a cellular model of AD-related tauopathy, suggesting that these compounds could be potential new therapeutic tools for the treatment of AD.

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.

Bridging Pharmaceutical Chemistry with Drug and Nanoparticle Targeting to Investigate the Role of the 18-kDa Translocator Protein TSPO

An interesting mitochondrial biomarker is the 18-kDa mitochondrial translocator protein (TSPO). Decades of study have shown that this protein plays an important role in a wide range of cellular functions, including opening of the mitochondrial permeability transition pore as well as programmed cell death and proliferation. Variations in TSPO expression have been correlated to different diseases, from tumors to endocrine and neurological disorders. TSPO has therefore become an appealing target for both early diagnosis and selective mitochondrial drug delivery. The number of structurally different TSPO ligands examined has increased over time, highlighting the scientific community's growing understanding of the roles of TSPO in normal and pathological conditions. However, only few TSPO ligands are characterized by the presence of groups that are potentially derivatizable; therefore only few such ligands are well suited for the preparation of targeted prodrugs or nanocarriers able to deliver therapeutics and/or diagnostic agents to mitochondria. This review provides an overview of the very few examples of drug delivery systems characterized by moieties that target TSPO.

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.

Continuous flow synthesis of indoles by Pd-catalyzed deoxygenation of 2-nitrostilbenes with carbon monoxide

The palladium-catalyzed cyclization of o-vinylnitrobenzenes employing carbon monoxide as terminal reductant is investigated. The reaction proceeds with 1 to 2 mol% of Pd(OAc)₂ and generates carbon dioxide as the only stoichiometric side-product.

The antidepressant-like activity of AC-5216, a ligand for 18KDa translocator protein (TSPO), in an animal model of diabetes mellitus

Diabetes mellitus is a chronic disease that is associated with depression. Also, depression is common in adults with type 2 diabetes mellitus (T2DM). Translocator protein (18kDa) (TSPO) and allopregnanolone play an important role in the depression treatment. However, few studies have evaluated TSPO and allopregnanolone in the treatment of depression in T2DM. AC-5216, a ligand for TSPO, produces anxiolytic- and antidepressant-like effects in animal models. The present study aimed to explore antidepressant-like effects of AC-5216 on diabetic rats. Following the development of diabetic model induced by high fat diet (HFD) feeding and streptozotocin (STZ), AC-5216 (0.3 and 1 mg/kg, i.g.) elicited the antidepressant-like effects in behavioral tests while these activities were blocked by TSPO antagonist PK11195 (3 mg/kg, i.p.). The levels of allopregnanolone in the prefrontal cortex and hippocampus were increased by AC-5216 (0.3 and 1 mg/kg, i.g.), which was antagonized by PK11195 (3 mg/kg, i.p.). The increased plasma glucose (PG) and decreased insulin (INS) in HFD-STZ rats were reversed by AC-5216 (0.3 and 1 mg/kg, i.g.). This study indicates that the antidepressant-like effects of AC-5216 on HFD-STZ rats, suggesting that TSPO may represent a novel therapeutic target for depression in T2DM.

Current status and future perspectives: TSPO in steroid neuroendocrinology

The mitochondrial translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), has received significant attention both as a diagnostic biomarker and as a therapeutic target for different neuronal disease pathologies. Recently, its functional basis believed to be mediating mitochondrial cholesterol import for steroid hormone production has been refuted by studies examining both in vivo and in vitro genetic Tspo-deficient models. As a result, there now exists a fundamental gap in the understanding of TSPO function in the nervous system, and its putative pharmacology in neurosteroid production. In this review, we discuss several recent findings in steroidogenic cells that are in direct contradiction to previous studies, and necessitate a re-examination of the purported role for TSPO in de novo neurosteroid biosynthesis. We critically examine the pharmacological effects of different TSPO-binding drugs with particular focus on studies that measure neurosteroid levels. We highlight the basis of key misconceptions regarding TSPO that continue to pervade the literature, and the need for interpretation with caution to avoid negative impacts. We also summarize the emerging perspectives that point to new directions that need to be investigated for understanding the molecular function of TSPO, only after which the true potential of this therapeutic target in medicine may be realized.

Translocator protein (TSPO) ligands for the diagnosis or treatment of neurodegenerative diseases: a patent review (2010-2015; part 1)

INTRODUCTION

The translocator protein (TSPO) is an emerging target in diverse neurodegenerative diseases. Up-regulated TSPO in the central nervous system (CNS) appears to be involved in neuroinflammatory processes; therefore, the development of potent TSPO ligands is a promising method for alleviating or imaging patients with neurodegenerative diseases. Areas covered: This review will provide an overview of recently developed TSPO ligands patented from 2010 to 2015. Part 1 will present a summary focusing on TSPO ligands other than indole-based or cholesterol-like compounds, which will be discussed in part 2. Part 1 covers diverse benzodiazepine-derived analogues such as isoquinoline carboxamides and aryloxyanilides. Moreover, bicyclic ring structures such as imidazopyridine, pyrazolopyrimidine, and phenylpurine will be highlighted as promising scaffolds for TSPO ligands. A brief analysis of currently reported TSPO structures will also be covered in part 1. Expert opinion: Although the underlying pharmacological mechanism of TSPO remains to be elucidated, several TSPO ligands have shown therapeutic efficacy in experimental animal models of neurodegenerative diseases. In addition, radioactive TSPO ligands have been extensively studied for the diagnosis of neurodegenerative processes. Thus, further studies on both the basic and applied mechanisms of TSPO are warranted in the pursuit of successful pharmacological applications of TSPO ligands.

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.

TSPO PIGA Ligands Promote Neurosteroidogenesis and Human Astrocyte Well-Being

The steroidogenic 18 kDa translocator protein (TSPO) is an emerging, attractive therapeutic tool for several pathological conditions of the nervous system. Here, 13 high affinity TSPO ligands belonging to our previously described N,N-dialkyl-2-phenylindol-3-ylglyoxylamide (PIGA) class were evaluated for their potential ability to affect the cellular Oxidative Metabolism Activity/Proliferation index, which is used as a measure of astrocyte well-being. The most active PIGA ligands were also assessed for steroidogenic activity in terms of pregnenolone production, and the values were related to the metabolic index in rat and human models. The results showed a positive correlation between the increase in the Oxidative Metabolism Activity/Proliferation index and the pharmacologically induced stimulation of steroidogenesis. The specific involvement of steroid molecules in mediating the metabolic effects of the PIGA ligands was demonstrated using aminoglutethimide, a specific inhibitor of the first step of steroid biosynthesis. The most promising steroidogenic PIGA ligands were the 2-naphthyl derivatives that showed a long residence time to the target, in agreement with our previous data. In conclusion, TSPO ligand-induced neurosteroidogenesis was involved in astrocyte well-being.

Lead Optimization of 2-Phenylindolylglyoxylyldipeptide Murine Double Minute (MDM)2/Translocator Protein (TSPO) Dual Inhibitors for the Treatment of Gliomas

In glioblastoma multiforme (GBM), translocator protein (TSPO) and murine double minute (MDM)2/p53 complex represent two druggable targets. We recently reported the first dual binder 3 possessing a higher anticancer effect in GBM cells than the standards PK11195 1 or Nutlin-3 2 singularly applied. Herein, through a structure-activity relationship study, we developed derivatives 4-10 with improved potencies toward both TSPO and MDM2. As a result, compound 9: (i) reactivated the p53 functionality; (ii) inhibited the viability of two human GBM cells; (iii) impaired the proliferation of glioma cancer stem cells (CSCs), more resistant to chemotherapeutics and responsible of GBM recurrence; (iv) sensitized GBM cells and CSCs to the activity of temozolomide; (v) directed its effects preferentially toward tumor cells with respect to healthy ones. Thus, 9 may represent a promising cytotoxic agent, which is worthy of being further developed for a therapeutic approach against GBM, where the downstream p53 signaling is intact and TSPO is overexpressed.

TSPO-ligands prevent oxidative damage and inflammatory response in C6 glioma cells by neurosteroid synthesis

Translocator protein 18kDa (TSPO) is predominantly located in the mitochondrial outer membrane, playing an important role in steroidogenesis, inflammation, cell survival and proliferation. Its expression in central nervous system, mainly in glial cells, has been found to be upregulated in neuropathology, and brain injury. In this study, we investigated the anti-oxidative and anti-inflammatory effects of a group of TSPO ligands from the N,N-dialkyl-2-phenylindol-3-ylglyoxylamide class (PIGAs), highlighting the involvement of neurosteroids in their pharmacological effects. To this aim we used a well-known in vitro model of neurosteroidogenesis: the astrocytic C6 glioma cell line, where TSPO expression and localization, as well as cell response to TSPO ligand treatment, have been established. All PIGAs reduced l-buthionine-(S,R)-sulfoximine (BSO)-driven cell cytotoxicity and lipid peroxidation. Moreover, an anti-inflammatory effect was observed due to the reduction of inducible nitric oxide synthase and cyclooxygenase-2 induction in LPS/IFNγ challenged cells. Both effects were blunted by aminoglutethimide (AMG), an inhibitor of pregnenolone synthesis, suggesting neurosteroids' involvement in PIGA protective mechanism. Finally, pregnenolone evaluation in PIGA exposed cells revealed an increase in its synthesis, which was prevented by AMG pre-treatment. These findings indicate that these TSPO ligands reduce oxidative stress and pro-inflammatory enzymes in glial cells through the de novo synthesis of neurosteroids, suggesting that these compounds could be potential new therapeutic tools for the treatment of inflammatory-based neuropathologies with beneficial effects possibly comparable to steroids, but potentially avoiding the negative side effects of long-term therapies with steroid hormones.

TSPO ligand residence time: a new parameter to predict compound neurosteroidogenic efficacy

The pharmacological activation of the cholesterol-binding Translocator Protein (TSPO) leads to an increase of endogenous steroids and neurosteroids determining benefic pleiotropic effects in several pathological conditions, including anxiety disorders. The relatively poor relationship between TSPO ligand binding affinities and steroidogenic efficacies prompted us to investigate the time (Residence Time, RT) that a number of compounds with phenylindolylglyoxylamide structure (PIGAs) spends in contact with the target. Here, given the poor availability of TSPO ligand kinetic parameters, a kinetic radioligand binding assay was set up and validated for RT determination using a theoretical mathematical model successfully applied to other ligand-target systems. TSPO ligand RT was quantified and the obtained results showed a positive correlation between the period for which a drug interacts with TSPO and the compound ability to stimulate steroidogenesis. Specifically, the TSPO ligand RT significantly fitted both with steroidogenic efficacy (Emax) and with area under the dose-response curve, a parameter combining drug potency and efficacy. A positive relation between RT and anxiolytic activity of three compounds was evidenced. In conclusion, RT could be a relevant parameter to predict the steroidogenic efficacy and the in vivo anxiolytic action of new TSPO ligands.

Deepening the Topology of the Translocator Protein Binding Site by Novel N,N-Dialkyl-2-arylindol-3-ylglyoxylamides

As a continuation of our studies on 2-phenylindol-3-ylglyoxylamides as potent and selective translocator protein (TSPO) ligands, two subsets of novel derivatives, featuring hydrophilic group (OH, NH2, COOH) at the para-position of the pendent 2-phenyl ring (8-16) or different 2-aryl moieties, namely, 3-thienyl, p-biphenyl, 2-naphthyl (23-35), were synthesized and biologically evaluated, some of them showing Ki values in the subnanomolar range and the 2-naphthyl group performance being the best. The resulting SARs confirmed the key role played by interactions taking place between ligands and the lipophilic L1 pocket of the TSPO binding site. Docking simulations were performed on the most potent compound of the present series (29) exploiting the recently available 3D structures of TSPO bound to its standard ligand (PK11195). Our theoretical model was fully consistent with SARs of the newly investigated as well of the previously reported 2-phenylindol-3-ylglyoxylamide derivatives.

New Indole Tubulin Assembly Inhibitors Cause Stable Arrest of Mitotic Progression, Enhanced Stimulation of Natural Killer Cell Cytotoxic Activity, and Repression of Hedgehog-Dependent Cancer

We designed 39 new 2-phenylindole derivatives as potential anticancer agents bearing the 3,4,5-trimethoxyphenyl moiety with a sulfur, ketone, or methylene bridging group at position 3 of the indole and with halogen or methoxy substituent(s) at positions 4-7. Compounds 33 and 44 strongly inhibited the growth of the P-glycoprotein-overexpressing multi-drug-resistant cell lines NCI/ADR-RES and Messa/Dx5. At 10 nM, 33 and 44 stimulated the cytotoxic activity of NK cells. At 20-50 nM, 33 and 44 arrested >80% of HeLa cells in the G2/M phase of the cell cycle, with stable arrest of mitotic progression. Cell cycle arrest was followed by cell death. Indoles 33, 44, and 81 showed strong inhibition of the SAG-induced Hedgehog signaling activation in NIH3T3 Shh-Light II cells with IC50 values of 19, 72, and 38 nM, respectively. Compounds of this class potently inhibited tubulin polymerization and cancer cell growth, including stimulation of natural killer cell cytotoxic activity and repression of Hedgehog-dependent cancer.

Translocator protein-mediated pharmacology of cholesterol transport and steroidogenesis

Steroidogenesis begins with cholesterol transfer into mitochondria through the transduceosome, a complex composed of cytosolic proteins that include steroidogenesis acute regulatory protein (STAR), 14-3-3 adaptor proteins, and the outer mitochondrial membrane proteins Translocator Protein (TSPO) and Voltage-Dependent Anion Channel (VDAC). TSPO is a drug- and cholesterol-binding protein found at particularly high levels in steroid synthesizing cells. Its aberrant expression has been linked to cancer, neurodegeneration, neuropsychiatric disorders and primary hypogonadism. Brain steroids serve as local regulators of neural development and excitability. Reduced levels of these steroids have been linked to depression, anxiety and neurodegeneration. Reduced serum testosterone is common among subfertile young men and aging men, and is associated with depression, metabolic syndrome and reduced sexual function. Although testosterone-replacement therapy is available, there are undesired side-effects. TSPO drug ligands have been proposed as therapeutic agents to regulate steroid levels in the brain and testis.

Computational modeling and biological validation of novel non-steroidal ligands for the cholesterol recognition/interaction amino acid consensus (CRAC) motif of the mitochondrial translocator protein (TSPO)

Mitochondria play a critical role in the physiological homeostasis of the cell, contributing to numerous cellular processes, including bioenergetics, metabolism and cell life and death. Owing to their keystone role, mitochondria have gained much attention as pharmacological targets. The outer mitochondrial integral membrane translocator protein (TSPO) has attracted a significant degree of pharmacological interest owing to its ability to bind a number of classes of drugs with high affinity and specificity. In addition to its well-characterized drug binding site, TSPO possess an additional high-affinity ligand binding site, originally identified for its ability to bind the lipid cholesterol, which was named the cholesterol recognition/interaction amino acid consensus (CRAC) motif. Previous investigations from our laboratory identified additional ligands targeted to TSPO's CRAC motif which are able to potently inhibit mitochondrial cholesterol transport and steroid biosynthesis, processes for which TSPO has been well-characterized. However, all of these compounds possessed the steroidal backbone common to cholesterol and steroid hormones. In our efforts to expand our understanding of TSPO's CRAC motif, we performed studies aimed at identifying non-steroidal ligands for this motif. Molecular modeling and in silico screening of large chemical libraries identified a panel of compounds which were subsequently screened for bioactivity in a number of steroidogenic model systems. These efforts identified a family of non-steroidal CRAC ligands able to potently inhibit steroidogenesis, and at higher concentrations, promote apoptosis. In addition, the best candidate in this family was able to suppress testosterone synthesis when administered to rats, indicating that this novel family of non-steroidal CRAC ligands may serve as prototypes for the development of drugs useful for treatment of diseases of steroid overproduction, such as Cushing's syndrome and steroidogenic cell tumors in humans and animals.

Anxiolytic-like effects of translocator protein (TSPO) ligand ZBD-2 in an animal model of chronic pain

The activation of Translocator protein (18 kDa) (TSPO) has been demonstrated to mediate rapid anxiolytic efficacy in stress response and stress-related disorders. This protein is involved in the synthesis of endogenous neurosteroids that promote γ-aminobutyric acid (GABA)-mediated neurotransmission in the central neural system. However, little is known about the functions and the underlying mechanisms of TSPO in chronic pain-induced anxiety-like behaviors. The novel TSPO ligand N-benzyl-N-ethyl-2-(7,8-dihydro-7-benzyl-8-oxo-2-phenyl-9H-purin-9-yl) acetamide (ZBD-2) was used in the present study. We found that ZBD-2 (0.15 or 1.5 mg/kg) significantly attenuated anxiety-like behaviors in mice with chronic inflammatory pain induced by hindpaw injection of complete Freund’s adjuvant (CFA). However, the treatment did not alter the nociceptive threshold or inflammation in the hindpaw. Hindpaw injection of CFA induced the upregulation of TSPO, GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and NR2B-containing N-methyl-d-aspartate (NMDA) receptors in the basolateral amygdala (BLA). ZBD-2 administration reversed the alterations of the abovementioned proteins in the BLA of the CFA-injected mice. Electrophysiological recording revealed that ZBD-2 could prevent an imbalance between excitatory and inhibitory transmissions in the BLA synapses of CFA-injected mice. Therefore, as the novel ligand of TSPO, ZBD-2 induced anxiolytic effects, but did not affect the nociceptive threshold of mice under chronic pain. The anxiolytic effects of ZBD-2 were related to the regulation of the balance between excitatory and inhibitory transmissions in the BLA.

Apoptosis therapy in cancer: the first single-molecule co-activating p53 and the translocator protein in glioblastoma

In the complex scenario of cancer, treatment with compounds targeting multiple cell pathways has been emerging. In Glioblastoma Multiforme (GBM), p53 and Translocator Protein (TSPO), both acting as apoptosis inducers, represent two attractive intracellular targets. On this basis, novel indolylglyoxylyldipeptides, rationally designed to activate TSPO and p53, were synthesized and biologically characterized. The new compounds were able to bind TSPO and to reactivate p53 functionality, through the dissociation from its physiological inhibitor, murine double minute 2 (MDM2). In GBM cells, the new molecules caused Δψm dissipation and inhibition of cell viability. These effects resulted significantly higher with respect to those elicited by the single target reference standards applied alone, and coherent with the synergism resulting from the simultaneous activation of TSPO and p53. Taken together, these results suggest that TSPO/MDM2 dual-target ligands could represent a new attractive multi-modal opportunity for anti-cancer strategy in GBM.

Translocator protein (18 kDa) (TSPO) is expressed in reactive retinal microglia and modulates microglial inflammation and phagocytosis

BACKGROUND

The translocator protein (18 kDa) (TSPO) is a mitochondrial protein expressed on reactive glial cells and a biomarker for gliosis in the brain. TSPO ligands have been shown to reduce neuroinflammation in several mouse models of neurodegeneration. Here, we analyzed TSPO expression in mouse and human retinal microglia and studied the effects of the TSPO ligand XBD173 on microglial functions.

METHODS

TSPO protein analyses were performed in retinoschisin-deficient mouse retinas and human retinas. Lipopolysaccharide (LPS)-challenged BV-2 microglial cells were treated with XBD173 and TSPO shRNAs in vitro and pro-inflammatory markers were determined by qRT-PCR. The migration potential of microglia was determined with wound healing assays and the proliferation was studied with Fluorescence Activated Cell Sorting (FACS) analysis. Microglial neurotoxicity was estimated by nitrite measurement and quantification of caspase 3/7 levels in 661 W photoreceptors cultured in the presence of microglia-conditioned medium. The effects of XBD173 on filopodia formation and phagocytosis were analyzed in BV-2 cells and human induced pluripotent stem (iPS) cell-derived microglia (iPSdM). The morphology of microglia was quantified in mouse retinal explants treated with XBD173.

RESULTS

TSPO was strongly up-regulated in microglial cells of the dystrophic mouse retina and also co-localized with microglia in human retinas. Constitutive TSPO expression was high in the early postnatal Day 3 mouse retina and declined to low levels in the adult tissue. TSPO mRNA and protein were also strongly induced in LPS-challenged BV-2 microglia while the TSPO ligand XBD173 efficiently suppressed transcription of the pro-inflammatory marker genes chemokine (C-C motif) ligand 2 (CCL2), interleukin 6 (IL6) and inducible nitric oxide (NO)-synthase (iNOS). Moreover, treatment with XBD173 significantly reduced the migratory capacity and proliferation of microglia, their level of NO secretion and their neurotoxic activity on 661 W photoreceptor cells. Furthermore, XBD173 treatment of murine and human microglial cells promoted the formation of filopodia and increased their phagocytic capacity to ingest latex beads or photoreceptor debris. Finally, treatment with XBD173 reversed the amoeboid alerted phenotype of microglial cells in explanted organotypic mouse retinal cultures after challenge with LPS.

CONCLUSIONS

These findings suggest that TSPO is highly expressed in reactive retinal microglia and a promising target to control microglial reactivity during retinal degeneration.

Repeated administration of AC-5216, a ligand for the 18 kDa translocator protein, improves behavioral deficits in a mouse model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a severely disabling anxiety disorder that may occur following exposure to a serious traumatic event. It is a psychiatric condition that can afflict anyone who has experienced a life-threatening or violent event. Previous studies have shown that changes in 18 kDa translocator protein (TSPO) expression (or function), a promising target for treating neurological disorders without benzodiazepine-like side effects, may correlate with PTSD. However, few studies have investigated the anti-PTSD effects of TSPO ligands. AC-5216, a ligand for TSPO, induces anxiolytic- and anti-depressant-like effects in animal models. The present study aimed to determine whether AC-5216 ameliorates PTSD behavior in mice. Following the training session consisting of exposure to inescapable electric foot shocks, animals were administered AC-5216 daily during the behavioral assessments, i.e., situational reminders (SRs), the open field (OF) test, the elevated plus-maze (EPM) test, and the staircase test (ST). The results indicated that exposure to foot shocks induced long-term behavioral deficiencies in the mice, including freezing and anxiety-like behavior, which were significantly ameliorated by repeated treatment with AC-5216 but without any effect on spontaneous locomotor activity or body weight. In summary, this study demonstrated the anti-PTSD effects of AC-5216 treatment, suggesting that TSPO may represent a therapeutic target for anti-PTSD drug discovery and that TSPO ligands may be a promising new class of drugs for the future treatment of PTSD.

Flutamide treatment induces anxiolytic-like behavior in adult castrated rats

BACKGROUND

It has previously been speculated that the androgen receptor antagonist flutamide produces behavioral effects that are not mediated by androgen receptors. These earlier studies were performed in intact rodents and thus, flutamide may have interfered with endogenous testosterone produced by the testes. The main objective of the present study was to examine whether flutamide induces anxiolytic-like behavior in castrated rats.

METHODS

Male Wistar rats (8-9 weeks old) were castrated and thereafter, in the same operation, the rats received silastic capsules subcutaneously (sc) that were filled with dihydrotestosterone (DHT) or were left empty. Three weeks later, rats were sc administered flutamide 50 mg/kg/day or vehicle for seven days. Four hours after the last injection, anxiolytic-like behavior was studied in a modified Vogel's drinking conflict model. In a separate experiment, shock threshold and drinking motivation were estimated.

RESULTS

Flutamide induced anxiolytic-like behavior in castrated rats irrespective of administration of DHT. Treatment with DHT alone did not induce a significant behavioral effect. Shock threshold and drinking motivation were not affected by flutamide and/or DHT treatment.

CONCLUSIONS

This study demonstrates that flutamide induces anxiolytic-like behavior in a modified Vogel's conflict model in castrated rats, which indicates that flutamide has anxiolytic-like properties that are not dependent on testes-produced testosterone.