Peripheral benzodiazepine receptor ligands: mitochondrial transmembrane potential depolarization and apoptosis induction in rat C6 glioma cells

Ameliorative effect of diazepam against ethanol-induced mitochondrial disruption in brains of the mice

Brain oxidative damage and neurodegeneration by ethanol (ETH) are considered as important factors that triggered by oxidative stress. Recently, the abuse of diazepam (DZM) has increased by alcoholism-addicted patients. The present study evaluated the effects of combination treatment of ETH with DZM on oxidative damage induced in brain mitochondria of the mice. Only ETH (0.3, 0.6, and 2.5 g / kg) and ETH+ DZM (2.5 mg / kg) were administered intraperitoneally (ip) to the mice. Pathological changes and oxidative stress biomarkers including ROS, lipid peroxidation, carbonyl protein, mitochondrial function, and glutathione content were evaluated in brain mitochondria after 42 days. Results indicated that co-treatment of DZM and ETH significantly reduced mitochondrial toxicity, oxidative damage, pathological changes and increased level of glutathione. Subchronic ETH administration induced brain oxidative damage, mitochondrial disruption, and serious damage to the brain cells. Whereas, combination treatment improved oxidative damage, mitochondrial function, and pathological changes in brain cells after intoxication by ETH. These findings suggest antioxidant effect of DZM in combination with ETH and can be considered in reducing oxidative stress and mitochondrial damage attenuation in the brain. Combination therapy may be a better therapeutic candidate for prevention of brain oxidative damage induced by ETH.

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.

Diazepam's antifungal activity in fluconazole-resistant Candida spp. and biofilm inhibition in C. albicans: evaluation of the relationship with the proteins ALS3 and SAP5

The genus Candida spp. has been highlighted as one of the main etiological agents causing fungal infections, with Candida albicans being the most prominent, responsible for most cases of candidemia. Due to its capacity for invasion and tissue adhesion, it is associated with the formation of biofilms, mainly in the environment and hospital devices, decreasing the effectiveness of available treatments. The repositioning of drugs, which is characterized by the use of drugs already on the market for other purposes, together with molecular-docking methods can be used aiming at the faster development of new antifungals to combat micro-organisms. This study aimed to evaluate the antifungal effect of diazepam on mature C. albicans biofilms in vitro and its action on biofilm in formation, as well as its mechanism of action and interaction with structures related to the adhesion of C. albicans, ALS3 and SAP5. To determine the MIC, the broth microdilution test was used according to protocol M27-A3 (CLSI, 2008). In vitro biofilm formation tests were performed using 96-well plates, followed by molecular-docking protocols to analyse the binding agent interaction with ALS3 and SAP5 targets. The results indicate that diazepam has antimicrobial activity against planktonic cells of Candida spp. and C. albicans biofilms, interacting with important virulence factors related to biofilm formation (ALS3 and SAP5). In addition, treatment with diazepam triggered a series of events in C. albicans cells, such as loss of membrane integrity, mitochondrial depolarization and increased production of EROs, causing DNA damage and consequent cell apoptosis.

18-kDa translocator protein association complexes in the brain: From structure to function

The outer mitochondrial membrane 18-kDa translocator protein (TSPO) is highly conserved in organisms of different species and ubiquitously expressed throughout tissues, including the nervous system. In the healthy adult brain, TSPO expression levels are low and promptly modulated under different pathological conditions, such as cancer, inflammatory states, and neurological and psychiatric disorders. Not surprisingly, several endogenous and synthetic molecules capable of binding TSPO have been proposed as drugs or diagnostic tools for brain diseases. The most studied biochemical function of TSPO is cholesterol translocation into mitochondria, which in turn affects the synthesis of steroids in the periphery and neurosteroids in the brain. In the last 30 years, roles for TSPO have also been suggested in other cellular processes, such as heme synthesis, apoptosis, autophagy, calcium signalling and reactive oxygen species production. Herein, we provide an overview of TSPO associations with different proteins, focusing particular attention on their related functions. Furthermore, recent TSPO-targeted therapeutic interventions are explored and discussed as prospect for innovative treatments in mental and brain diseases.

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.

From the Cover: Vulnerability of C6 Astrocytoma Cells After Single-Compound and Joint Exposure to Type I and Type II Pyrethroid Insecticides

A primary mode-of-action of all pyrethroid insecticides (PYRs) is the disruption of the voltage-gated sodium channel electrophysiology in neurons of target pests and nontarget species. The neurological actions of PYRs on non-neuronal cells of the nervous system remain poorly investigated. In the present work, we used C6 astrocytoma cells to study PYR actions (0.1-50 μM) under the hypothesis that glial cells may be targeted by and vulnerable to PYRs. To this end, we characterized the effects of bifenthrin (BF), tefluthrin (TF), α-cypermethrin (α-CYP), and deltamethrin (DM) on the integrity of nuclear, mitochondrial, and lysosomal compartments. In general, 24- to 48-h exposures produced concentration-related impairment of cell viability. In single-compound, 24-h exposure experiments, effective concentration (EC)₁₅s 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT assay) were computed as follows (in μM): BF, 16.1; TF, 37.3; α-CYP, 7.8; DM, 5.0. We found concentration-related damage in several C6-cell subcellular compartments (mitochondria, nuclei, and lysosomes) at ≥ 10^-1 μM levels. Last, we examined a mixture of all PYRs (ie, Σ individual EC₁₅) using MTT assays and subcellular analyses. Our findings indicate that C6 cells are responsive to nM levels of PYRs, suggesting that astroglial susceptibility may contribute to the low-dose neurological effects caused by these insecticides. This research further suggests that C6 cells may provide relevant information as a screening platform for pesticide mixtures targeting nervous system cells by expected and unexpected toxicogenic pathways potentially contributing to clinical neurotoxicity.

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.

The Effect of Cigarette Smoke on the Translocator Protein (TSPO) in Cultured Lung Cancer Cells

Lung cancer is prevalent in cigarette smokers. The mitochondrial membrane translocator protein (TSPO), is thought to protect cells from free radical damage. We examined the effect of cigarette smoke (CS) (containing free radicals) alone and in the presence of saliva (containing redox active free iron), on survival of H1299 lung cancer cells and on their mitochondrial characteristics, and whether TSPO binding was influenced by CS and by saliva. We exposed H1299 cells to CS in the presence/absence of saliva and also characterized TSPO binding in the cells using [3H]PK 11195 as a radioligand. CS induced a significant drop in mitochondrial potential (ΔΨm), while addition of saliva did not lead to further loss of ΔΨm (42.5% vs. 39.85%). Scatchard analysis of the saturation curve of [3H]PK 11195 binding (0.2-6 nM final concentration) yielded a straight-line plot (R =  0.9). Average Bmax value was 3274 ± 787 fmol/mg of protein, and average Kd value was 9.2 ± 1.3 nM. Benzodiazepine diazepam partially prevented decrease in cell survival following exposure to CS and redox active iron containing media (saliva) while benzodiazepine clonazepam did not, indicating that this effect is TSPO-specific. Exposure of cells to CS resulted in alternation of biomolecules expressed by CLs peroxidation, reduction of TSPO binding, and depletion of the mitochondrial potential. This irreversible damage was enhanced in the presence of saliva. All these modulations may result in cellular death increase following CS exposure, enhanced in the presence of saliva.

Quinazoline-based tricyclic compounds that regulate programmed cell death, induce neuronal differentiation, and are curative in animal models for excitotoxicity and hereditary brain disease

Expanding on a quinazoline scaffold, we developed tricyclic compounds with biological activity. These compounds bind to the 18 kDa translocator protein (TSPO) and protect U118MG (glioblastoma cell line of glial origin) cells from glutamate-induced cell death. Fascinating, they can induce neuronal differentiation of PC12 cells (cell line of pheochromocytoma origin with neuronal characteristics) known to display neuronal characteristics, including outgrowth of neurites, tubulin expression, and NeuN (antigen known as 'neuronal nuclei', also known as Rbfox3) expression. As part of the neurodifferentiation process, they can amplify cell death induced by glutamate. Interestingly, the compound 2-phenylquinazolin-4-yl dimethylcarbamate (MGV-1) can induce expansive neurite sprouting on its own and also in synergy with nerve growth factor and with glutamate. Glycine is not required, indicating that N-methyl-D-aspartate receptors are not involved in this activity. These diverse effects on cells of glial origin and on cells with neuronal characteristics induced in culture by this one compound, MGV-1, as reported in this article, mimic the diverse events that take place during embryonic development of the brain (maintenance of glial integrity, differentiation of progenitor cells to mature neurons, and weeding out of non-differentiating progenitor cells). Such mechanisms are also important for protective, curative, and restorative processes that occur during and after brain injury and brain disease. Indeed, we found in a rat model of systemic kainic acid injection that MGV-1 can prevent seizures, counteract the process of ongoing brain damage, including edema, and restore behavior defects to normal patterns. Furthermore, in the R6-2 (transgenic mouse model for Huntington disease; Strain name: B6CBA-Tg(HDexon1)62Gpb/3J) transgenic mouse model for Huntington disease, derivatives of MGV-1 can increase lifespan by >20% and reduce incidence of abnormal movements. Also in vitro, these derivatives were more effective than MGV-1.

TSPO ligand residence time influences human glioblastoma multiforme cell death/life balance

Ligands addressed to the mitochondrial Translocator Protein (TSPO) have been suggested as cell death/life and steroidogenesis modulators. Thus, TSPO ligands have been proposed as drug candidates in several diseases; nevertheless, a correlation between their binding affinity and in vitro efficacy has not been demonstrated yet, questioning the specificity of the observed effects. Since drug-target residence time is an emerging parameter able to influence drug pharmacological features, herein, the interaction between TSPO and irDE-MPIGA, a covalent TSPO ligand, was investigated in order to explore TSPO control on death/life processes in a standardized glioblastoma cell setting. After 90 min irDE-MPIGA cell treatment, 25 nM ligand concentration saturated irreversibly all TSPO binding sites; after 24 h, TSPO de-novo synthesis occurred and about 40 % TSPO binding sites resulted covalently bound to irDE-MPIGA. During cell culture treatments, several dynamic events were observed: (a) early apoptotic markers appeared, such as mitochondrial membrane potential collapse (at 3 h) and externalization of phosphatidylserine (at 6 h); (b) cell viability was reduced (at 6 h), without cell cycle arrest. After digitonin-permeabilized cell suspension treatment, a modulation of mitochondrial permeability transition pore was evidenced. Similar effects were elicited by the reversible TSPO ligand PIGA only when applied at micromolar dose. Interestingly, after 6 h, irDE-MPIGA cell exposure restored cell survival parameters. These results highlighted the ligand-target residence time and the cellular setting are crucial parameters that should be taken into account to understand the drug binding affinity and efficacy correlation and, above all, to translate efficiently cellular drug responses from bench to bedside.

α-Lipoic acid protected cardiomyoblasts from the injury induced by sodium nitroprusside through ROS-mediated Akt/Gsk-3β activation

It has been long noted that cardiac cell apoptosis provoked by excessive production of nitric oxide (NO) plays important roles in the pathogenesis of variant cardiac diseases. Attenuation of NO-induced injury would be an alternative therapeutic approach for the development of cardiac disorders. This study investigated the effects of α-lipoic acid (LA) on the injury induced by sodium nitroprusside (SNP), a widely used NO donor, in rat cardiomyoblast H9c2 cells. SNP challenge significantly decreased cell viability and increased apoptosis, as evidenced by morphological abnormalities, nuclear condensation and decline of mitochondrial potential (ΔΨm). These changes induced by SNP were significantly attenuated by LA pretreatment. Furthermore, LA pretreatment prevented the SNP-triggered suppression of Akt and Gsk-3β activation. Blockade of Akt activation with triciribin (API) completely abolished the cytoprotection of LA against SNP challenge. In addition, LA moderately increased intracellular ROS production. Interestingly, inhibition of ROS with N-acetylcysteine abrogated Akt/Gsk-3β activation and the LA-induced cytoprotection following SNP stimulation. Taken together, the results indicate that LA protected the SNP-induced injury in cardiac H9c2 cells through, at least in part, the activation of Akt/Gsk-3β signaling in a ROS-dependent mechanism.

Diazepam potentiates the antidiabetic, antistress and anxiolytic activities of metformin in type-2 diabetes mellitus with cooccurring stress in experimental animals

Psychological stress is considered as one of the limiting factors in the management of type-2 diabetes mellitus (T2DM). Therefore, the basic objective of the present study was to evaluate the antidiabetic effect of metformin, diazepam, and their combination in cooccurring T2DM and stress condition (DMS). T2DM was induced in the male rats by administering streptozotocin (45 mg/kg, i.p.) and nicotinamide (110 mg/kg, i.p.) with time lag of 15 min. Rats were subjected to two sessions of cold restraint stress paradigm for one hour on the sixth and seventh day after streptozotocin injection. Administration of metformin (25 mg/kg, p.o.) and diazepam (1 mg/kg, p.o.) in combination from the seventh to thirteenth day after streptozotocin injection showed better improvement in glucose tolerance and insulin sensitivity compared to monotherapy of either drug. In addition, the combination significantly attenuated DMS-induced hyperglycemia, hypertriglyceridaemia, hypercorticosteronemia, anxiety-like behavior, and insulin resistance through modulating insulin signaling pathway in the liver compared to monotherapy. Further, improvement of mitochondrial function, integrity, and oxidative stress in hippocampus, hypothalamus, prefrontal cortex, striatum, amygdala, and nucleus accumbens was observed with the combination. Therefore, metformin in combination with diazepam may be a better therapeutic option in the management of T2DM with cooccurring stress condition.

Estrogen receptor β activation impairs mitochondrial oxidative metabolism and affects malignant mesothelioma cell growth in vitro and in vivo

Estrogen receptor (ER)-β has been shown to possess a tumor suppressive effect, and is a potential target for cancer therapy. Using gene-expression meta-analysis of human malignant pleural mesothelioma, we identified an ESR2 (ERβ coding gene) signature. High ESR2 expression was strongly associated with low succinate dehydrogenase B (SDHB) (which encodes a mitochondrial respiratory chain complex II subunit) expression. We demonstrate that SDHB loss induced ESR2 expression, and that activated ERβ, by over-expression or by selective agonist stimulation, negatively affected oxidative phosphorylation compromising mitochondrial complex II and IV activity. This resulted in reduced mitochondrial ATP production, increased glycolysis dependence and impaired cell proliferation. The observed in vitro effects were phenocopied in vivo using a selective ERβ agonist in a mesothelioma mouse model. On the whole, our data highlight an unforeseen interaction between ERβ-mediated tumor suppression and energy metabolism that may be exploited to improve on the therapy for clinical management of malignant mesothelioma.

Human glioblastoma multiforme: p53 reactivation by a novel MDM2 inhibitor

Cancer development and chemo-resistance are often due to impaired functioning of the p53 tumor suppressor through genetic mutation or sequestration by other proteins. In glioblastoma multiforme (GBM), p53 availability is frequently reduced because it binds to the Murine Double Minute-2 (MDM2) oncoprotein, which accumulates at high concentrations in tumor cells. The use of MDM2 inhibitors that interfere with the binding of p53 and MDM2 has become a valid approach to inhibit cell growth in a number of cancers; however little is known about the efficacy of these inhibitors in GBM. We report that a new small-molecule inhibitor of MDM2 with a spirooxoindolepyrrolidine core structure, named ISA27, effectively reactivated p53 function and inhibited human GBM cell growth in vitro by inducing cell cycle arrest and apoptosis. In immunoincompetent BALB/c nude mice bearing a human GBM xenograft, the administration of ISA27 in vivo activated p53, inhibited cell proliferation and induced apoptosis in tumor tissue. Significantly, ISA27 was non-toxic in an in vitro normal human cell model and an in vivo mouse model. ISA27 administration in combination with temozolomide (TMZ) produced a synergistic inhibitory effect on GBM cell viability in vitro, suggesting the possibility of lowering the dose of TMZ used in the treatment of GBM. In conclusion, our data show that ISA27 releases the powerful antitumor capacities of p53 in GBM cells. The use of this MDM2 inhibitor could become a novel therapy for the treatment of GBM patients.

Negative modulation of mitochondrial oxidative phosphorylation by epigallocatechin-3 gallate leads to growth arrest and apoptosis in human malignant pleural mesothelioma cells

Increasing evidence reveals a large dependency of epithelial cancer cells on oxidative phosphorylation (OXPHOS) for energy production. In this study we tested the potential of epigallocatechin-3-gallate (EGCG), a natural polyphenol known to target mitochondria, in inducing OXPHOS impairment and cell energy deficit in human epitheliod (REN cells) and biphasic (MSTO-211H cells) malignant pleural mesothelioma (MMe), a rare but highly aggressive tumor with high unmet need for treatment. Due to EGCG instability that causes H2O2 formation in culture medium, the drug was added to MMe cells in the presence of exogenous superoxide dismutase and catalase, already proved to stabilize the EGCG molecule and prevent EGCG-dependent reactive oxygen species formation. We show that under these experimental conditions, EGCG causes the selective arrest of MMe cell growth with respect to normal mesothelial cells and the induction of mitochondria-mediated apoptosis, as revealed by early mitochondrial ultrastructure modification, swelling and cytochrome c release. We disclose a novel mechanism by which EGCG induces apoptosis through the impairment of mitochondrial respiratory chain complexes, particularly of complex I, II and ATP synthase. This induces a strong reduction in ATP production by OXPHOS, that is not adequately counterbalanced by glycolytic shift, resulting in cell energy deficit, cell cycle arrest and apoptosis. The EGCG-dependent negative modulation of mitochondrial energy metabolism, selective for cancer cells, gives an important input for the development of novel pharmacological strategies for MMe.

A novel reporter system for molecular imaging and high-throughput screening of anticancer drugs

Apoptosis is irreversible programmed cell death, characterized by a cellular cascade activation of caspase 3, which subsequently degrades proteins and other components of cells with a motif sequence. Here we report a novel reporter system to detect apoptosis, growth arrest, and cell death based on controlled and self-amplified protein degradation. The key element of the reporter system is an apoptotic sensor chimerical protein which consists of three components: procaspase 3, ubiquitin (Ub), and a strong consensus sequence of N-degron. Between each of these units is a DEVD (Asp-Glu-Val-Asp) sequence, which acts as the cleavage target of caspase 3. This non-conventional signal loss approach is much more sensitive than other native methods that are based on signal gain. The superior sensitivity is demonstrated by its effective application in 386-well high-throughput screening (HTS) with low drug concentrations and a short incubation time. The HTS selection process using this reporter system is very simple and economic. The simplicity eliminates potential errors introduced by multiple steps; there is no need for any substrate. Furthermore, the cells in the assay need not be disrupted, and the morphology of the cells can provide additional information on mechanisms. After HTS, the intact cells can also be used for other analytic analysis. This system thus has a potentially important role in the discovery and development of new anticancer drugs. It also appears to be very versatile, can be used both in vitro and in vivo with different linked reporter genes, and can be used for a variety of imaging applications.

The 1,4-benzodiazepine Ro5-4864 (4-chlorodiazepam) suppresses multiple pro-inflammatory mast cell effector functions

Activation of mast cells (MCs) can be achieved by the high-affinity receptor for IgE (FcεRI) as well as by additional receptors such as the lipopolysaccharide (LPS) receptor and the receptor tyrosine kinase Kit (stem cell factor [SCF] receptor). Thus, pharmacological interventions which stabilize MCs in response to different receptors would be preferable in diseases with pathological systemic MC activation such as systemic mastocytosis. 1,4-Benzodiazepines (BDZs) have been reported to suppress MC effector functions. In the present study, our aim was to analyze molecularly the effects of BDZs on MC activation by comparison of the effects of the two BDZs Ro5-4864 and clonazepam, which markedly differ in their affinities for the archetypical BDZ recognition sites, i.e., the GABA_A receptor and TSPO (previously termed peripheral-type BDZ receptor). Ro5-4864 is a selective agonist at TSPO, whereas clonazepam is a selective agonist at the GABA_A receptor. Ro5-4864 suppressed pro-inflammatory MC effector functions in response to antigen (Ag) (degranulation/cytokine production) and LPS and SCF (cytokine production), whereas clonazepam was inactive. Signaling pathway analyses revealed inhibitory effects of Ro5-4864 on Ag-triggered production of reactive oxygen species, calcium mobilization and activation of different downstream kinases. The initial activation of Src family kinases was attenuated by Ro5-4864 offering a molecular explanation for the observed impacts on various downstream signaling elements. In conclusion, BDZs structurally related to Ro5-4864 might serve as multifunctional MC stabilizers without the sedative effect of GABA_A receptor-interacting BDZs.

Toward highly potent cancer agents by modulating the C-2 group of the arylthioindole class of tubulin polymerization inhibitors

New arylthioindole derivatives having different cyclic substituents at position 2 of the indole were synthesized as anticancer agents. Several compounds inhibited tubulin polymerization at submicromolar concentration and inhibited cell growth at low nanomolar concentrations. Compounds 18 and 57 were superior to the previously synthesized 5. Compound 18 was exceptionally potent as an inhibitor of cell growth: it showed IC₅₀ = 1.0 nM in MCF-7 cells, and it was uniformly active in the whole panel of cancer cells and superior to colchicine and combretastatin A-4. Compounds 18, 20, 55, and 57 were notably more potent than vinorelbine, vinblastine, and paclitaxel in the NCI/ADR-RES and Messa/Dx5 cell lines, which overexpress P-glycoprotein. Compounds 18 and 57 showed initial vascular disrupting effects in a tumor model of liver rhabdomyosarcomas at 15 mg/kg intravenous dosage. Derivative 18 showed water solubility and higher metabolic stability than 5 in human liver microsomes.

Epigallocatechin-3-gallate prevents oxidative phosphorylation deficit and promotes mitochondrial biogenesis in human cells from subjects with Down's syndrome

A critical role for mitochondrial dysfunction has been proposed in the pathogenesis of Down's syndrome (DS), a human multifactorial disorder caused by trisomy of chromosome 21, associated with mental retardation and early neurodegeneration. Previous studies from our group demonstrated in DS cells a decreased capacity of the mitochondrial ATP production system and overproduction of reactive oxygen species (ROS) in mitochondria. In this study we have tested the potential of epigallocatechin-3-gallate (EGCG) - a natural polyphenol component of green tea - to counteract the mitochondrial energy deficit found in DS cells. We found that EGCG, incubated with cultured lymphoblasts and fibroblasts from DS subjects, rescued mitochondrial complex I and ATP synthase catalytic activities, restored oxidative phosphorylation efficiency and counteracted oxidative stress. These effects were associated with EGCG-induced promotion of PKA activity, related to increased cellular levels of cAMP and PKA-dependent phosphorylation of the NDUFS4 subunit of complex I. In addition, EGCG strongly promoted mitochondrial biogenesis in DS cells, as associated with increase in Sirt1-dependent PGC-1α deacetylation, NRF-1 and T-FAM protein levels and mitochondrial DNA content. In conclusion, this study shows that EGCG is a promoting effector of oxidative phosphorylation and mitochondrial biogenesis in DS cells, acting through modulation of the cAMP/PKA- and sirtuin-dependent pathways. EGCG treatment promises thus to be a therapeutic approach to counteract mitochondrial energy deficit and oxidative stress in DS.

The nitric oxide donor sodium nitroprusside requires the 18 kDa Translocator Protein to induce cell death

Various studies have shown that several lethal agents induce cell death via the mitochondrial 18 kDa Translocator Protein (TSPO). In this study we tested the possibility that nitric oxide (NO) is the signaling component inducing the TSPO to initiate cell death process. Cell viability assays included Trypan blue uptake, propidium iodide uptake, lactate dehydrogenase release, and DNA fragmentation. These assays showed that application of the specific TSPO ligand PK 11195 reduced these parameters for the lethal effects of the NO donor sodium nitroprusside (SNP) by 41, 27, 40, and 42 %, respectively. TSPO silencing by siRNA also reduced the measured lethal effects of SNP by 50 % for all of these four assays. With 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxyanilide (XTT) changes in metabolic activity were detected. PK 11195 and TSPO knockdown fully prevented the reductions in XTT signal otherwise induced by SNP. Collapse of the mitochondrial membrane potential was studied with the aid of JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolylcarbocyanine chloride). PK 11195 and TSPO knockdown reduced, respectively by 36 and 100 %, the incidence of collapse of the mitochondrial membrane potential otherwise induced by SNP. 10-N-Nonyl-Acridine Orange (NAO) was used to detect mitochondrial reactive oxygen species generation due to SNP. PK 11195 and TSPO knockdown reduced this effect of SNP by 65 and 100 %, respectively. SNP did not affect TSPO protein expression and binding characteristics, and also did not cause TSPO S-nitrosylation. However, β-actin and various other proteins (not further defined) were S-nitrosylated. In conclusion, TSPO is required for the lethal and metabolic effects of the NO donor SNP, but TSPO itself is not S-nitrosylated.

Metabolism and quantification of [(18)F]DPA-714, a new TSPO positron emission tomography radioligand

[(18)F]DPA-714 [N,N-diethyl-2-(2-(4-(2[(18)F]-fluoroethoxy)phenyl)5,7dimethylpyrazolo[1,5a]pyrimidin-3-yl)acetamide] is a new radioligand currently used for imaging the 18-kDa translocator protein in animal models of neuroinflammation and recently in humans. The biodistribution by positron emission tomography (PET) in baboons and the in vitro and in vivo metabolism of [(18)F]DPA-714 were investigated in rats, baboons, and humans. Whole-body PET experiments showed a high uptake of radioactivity in the kidneys, heart, liver, and gallbladder. The liver was a major route of elimination of [(18)F]DPA-714, and urine was a route of excretion for radiometabolites. In rat and baboon plasma, high-performance liquid chromatography (HPLC) metabolic profiles showed three major radiometabolites accounting for 85% and 89% of total radioactivity at 120 minutes after injection, respectively. Rat microsomal incubations and analyses by liquid chromatography-mass spectrometry (LC-MS) identified seven metabolites, characterized as O-deethyl, hydroxyl, and N-deethyl derivatives of nonradioactive DPA-714, two of them having the same retention times than those detected in rat and baboon plasma. The third plasma radiometabolite was suggested to be a carboxylic acid compound that accounted for 15% of the rat brain radioactivity. O-deethylation led to a nonradioactive compound and [(18)F]fluoroacetic acid. Human CYP3A4 and CYP2D6 were shown to be involved in the oxidation of the radioligand. Finally an easy, rapid, and accurate method--indispensable for PET quantitative clinical studies--for quantifying [(18)F]DPA-714 by solid-phase extraction was developed. In vivo, an extensive metabolism of [(18)F]DPA-714 was observed in rats and baboons, identified as [(18)F]deethyl, [(18)F]hydroxyl, and [(18)F]carboxylic acid derivatives of [(18)F]DPA-714. The main route of excretion of the unchanged radioligand in baboons was hepatobiliary while that of radiometabolites was the urinary system.

The expression of translocator protein in human thyroid cancer and its role in the response of thyroid cancer cells to oxidative stress

The translocator protein (TSPO), formerly known as a peripheral benzodiazepine receptor, exerts pro-apoptotic function via regulation of mitochondrial membrane potential. We examined TSPO expression in human thyroid tumors (25 follicular adenomas (FA), 15 follicular cancers (FC), and 70 papillary cancers (PC)). The role of TSPO in the regulation of cell growth, migration, and apoptosis was examined in thyroid cancer cell lines after TSPO knockdown with siRNA and after treatment with TSPO antagonist (PK11195). Compared with normal thyroid, the level of TSPO expression was increased in FA, FC, and PC in 24, 26.6, and 55.7% of cases respectively. Thyroid cancer cell lines demonstrated variable levels of TSPO expression, without specific association with thyroid oncogene mutations. Treatment with inhibitors of PI3K/AKT or MEK/ERK signaling was not associated with changes in TSPO expression. Treatment with histone deacetylase inhibitor (valproic acid) increased TSPO expression in TSPO-deficient cell lines (FTC236 cells). TSPO gene silencing or treatment with PK11195 did not affect thyroid cancer cell growth and migration but prevented depolarization of mitochondrial membranes induced by oxidative stress. Induction of TSPO expression by valproic acid was associated with increased sensitivity of FTC236 to oxidative stress-inducible apoptosis. Overall, we showed that TSPO expression is frequently increased in PC. In vitro data suggested the role of epigenetic mechanism(s) in the regulation of TSPO in thyroid cells. Implication of TSPO in the thyroid cancer cell response to oxidative stress suggested its potential role in the regulation of thyroid cancer cell response to treatment with radioiodine and warrants further investigation.

Midazolam activates the intrinsic pathway of apoptosis independent of benzodiazepine and death receptor signaling

BACKGROUND AND OBJECTIVES

Midazolam has neurotoxic properties when administered neuraxially in vivo. Furthermore, midazolam induces neurodegeneration in neonatal animal models in combination with other general anesthetics. Therefore, this study focuses on the mechanism of neurotoxicity by midazolam in neuronal and nonneuronal cells. The study aims to evaluate the apoptotic pathway and to investigate the protective effects of the benzodiazepine antagonist flumazenil and the caspase inhibitor N-(2-quinolyl)valyl-aspartyl-(2,6-difluorophenoxy)-methylketone.

METHODS

The apoptosis-inducing effect of preservative-free midazolam on human lymphoma and neuroblastoma cell lines was evaluated using flow cytometric analysis of early apoptotic stages (annexin V/7AAD) and caspase 3 activation. B-cell lymphoma (Bcl2) protein overexpressing and caspase 9-deficient lymphoma cells were used to determine the role of the mitochondrial (intrinsic) pathway. Caspase 8-deficient and Fas-associated protein with death domain (FADD)-deficient cells were used to evaluate the death receptor (extrinsic) pathway. The protective effects of flumazenil and the caspase inhibitor N-(2-quinolyl)valyl-aspartyl-(2,6-difluorophenoxy)-methylketone were investigated in neuroblastoma cells and primary rat neurons using metabolic activity assays (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) and immunofluorescence microscopy.

RESULTS

Midazolam induced apoptosis in all investigated cell types in a concentration-dependent manner, indicated by flow cytometry. Bcl2-overexpression and caspase 9 deficiency protected against toxicity, whereas caspase 8 or FADD deficiency had no effect. Pancaspase inhibition had a strong protective effect, whereas flumazenil did not inhibit midazolam-induced apoptosis.

CONCLUSIONS

Midazolam induces apoptosis via activation of the mitochondrial pathway in a concentration-dependent manner. The mechanism of midazolam toxicity switches from caspase-dependent apoptosis to necrosis with increasing concentrations. The induction of apoptosis and necrosis by midazolam is presumably unrelated to GABAA receptor pathway signaling.

Synthesis and biological evaluation of 4-phenylquinazoline-2-carboxamides designed as a novel class of potent ligands of the translocator protein

A series of novel 4-phenylquinazoline-2-carboxamides (1-58) were designed as aza-isosters of PK11195, the well-known 18 kDa translocator protein (TSPO) reference ligand, and synthesized by means of a very simple and efficient procedure. A number of these derivatives bind to the TSPO with K(i) values in the nanomolar/subnanomolar range, show selectivity toward the central benzodiazepine receptor (BzR) and exhibit structure-affinity relationships consistent with a previously published pharmacophore/topological model of ligand-TSPO interaction.

Mitochondrial remodeling in cancer metabolism and survival: potential for new therapies

Mitochondria are semi-autonomous organelles that play essential roles in cellular metabolism and programmed cell death pathways. Genomic, functional and structural mitochondrial alterations have been associated with cancer. Some of those alterations may provide a selective advantage to cells, allowing them to survive and grow under stresses created by oncogenesis. Due to the specific alterations that occur in cancer cell mitochondria, these organelles may provide promising targets for cancer therapy. The development of drugs that specifically target metabolic and mitochondrial alterations in tumor cells has become a matter of interest in recent years, with several molecules undergoing clinical trials. This review focuses on the most relevant mitochondrial alterations found in tumor cells, their contribution to cancer progression and survival, and potential usefulness for stratification and therapy.

Tertiary amides with a five-membered heteroaromatic ring as new probes for the translocator protein

In this study novel ligands of the translocator protein (TSPO), characterized by a five-membered aromatic heterocycle (i.e. oxazole, isoxazole, oxadiazole), a phenyl ring, and an amide side chain of carboxy or acetic type, were designed using a previously reported pharmacophore/topological model. Most of compounds showed significant TSPO binding affinity (K(i) values in the nanomolar/submicromolar range), the highest being displayed by oxazolacetamides 6. A number of compounds were tested for their ability to inhibit the proliferation/viability of human glioblastoma cell line U87MG. The dose-time dependent cell response to treatment with 6d demonstrated the specificity of the observed effect. The ability of 6d to induce mitochondrial membrane dissipation (ΔΨm) substantiates the intracellular pro-apoptotic mechanism activated by ligand binding to TSPO.

Pyrazolo[1,5-a]pyrimidine acetamides: 4-Phenyl alkyl ether derivatives as potent ligands for the 18 kDa translocator protein (TSPO)

Herein, we report the synthesis of four new phenyl alkyl ether derivatives (7, 9-11) of the pyrazolo[1,5-a]pyrimidine acetamide class, all of which showed high binding affinity and selectivity for the TSPO and, in the case of the propyl, propargyl, and butyl ether derivatives, the ability to increase pregnenolone biosynthesis by 80-175% over baseline in rat C6 glioma cells. While these compounds fit our in silico generated pharmacophore for TSPO binding the current model does not account for the observed functional activity.

TLN-4601 peripheral benzodiazepine receptor (PBR/TSPO) binding properties do not mediate apoptosis but confer tumor-specific accumulation

TLN-4601 is a farnesylated dibenzodiazepinone isolated from Micromonospora sp. with an antiproliferative effect on several human cancer cell lines. Although the mechanism of action of TLN-4601 is unknown, our earlier work indicated that TLN-4601 binds the PBR (peripheral benzodiazepine receptor; more recently known as the translocator protein or TSPO), an 18 kDa protein associated with the mitochondrial permeability transition (mPT) pore. While the exact function of the PBR remains a matter of debate, it has been implicated in heme and steroid synthesis, cellular growth and differentiation, oxygen consumption and apoptosis. Using the Jurkat immortalized T-lymphocyte cell line, documented to have negligible PBR expression, and Jurkat cells stably transfected with a human PBR cDNA, the present study demonstrates that TLN-4601 induces apoptosis independently of PBR expression. As PBRs are overexpressed in brain tumors compared to normal brain, we examined if TLN-4601 would preferentially accumulate in tumors using an intra-cerebral tumor model. Our results demonstrate the ability of TLN-4601 to effectively bind the PBR in vivo as determined by competitive binding assay and receptor occupancy. Analysis of TLN-4601 tissue and plasma indicated that TLN-4601 preferentially accumulates in the tumor. Indeed, drug levels were 200-fold higher in the tumor compared to the normal brain. TLN-4601 accumulation in the tumor (176 μg/g) was also significant compared to liver (24.8 μg/g; 7-fold) and plasma (16.2 μg/mL; 11-fold). Taken together our data indicate that while PBR binding does not mediate cell growth inhibition and apoptosis, PBR binding may allow for the specific accumulation of TLN-4601 in PBR positive tumors.

Glioma cell death: cell-cell interactions and signalling networks

The prognosis for patients with malignant gliomas is poor, but improvements may emerge from a better understanding of the pathophysiology of glioma signalling. Recent therapeutic developments have implicated lipid signalling in glioma cell death. Stress signalling in glioma cell death involves mitochondria and endoplasmic reticulum. Lipid mediators also signal via extrinsic pathways in glioma cell proliferation, migration and interaction with endothelial and microglial cells. Glioma cell death and tumour regression have been reported using polyunsaturated fatty acids in animal models, human ex vivo explants, glioma cell preparations and in clinical case reports involving intratumoral infusion. Cell death signalling was associated with generation of reactive oxygen intermediates and mitochondrial and other signalling pathways. In this review, evidence for mitochondrial responses to stress signals, including polyunsaturated fatty acids, peroxidizing agents and calcium is presented. Additionally, evidence for interaction of glioma cells with primary brain endothelial cells is described, modulating human glioma peroxidative signalling. Glioma responses to potential therapeutic agents should be analysed in systems reflecting tumour connectivity and CNS structural and functional integrity. Future insights may also be derived from studies of signalling in glioma-derived tumour stem cells.

Inhibition of metalloproteinases derived from tumours: new insights in the treatment of human glioblastoma

Glioblastoma multiforme is the most commonly diagnosed malignant primary brain tumour in adults. Invasive behaviour is the pathological hallmark of malignant gliomas; consequently, its inhibition has been suggested as a therapeutic strategy. Tumour cell-derived gelatinases (matrix metalloproteinase-2, matrix metalloproteinase-9) can be considered prime factors in glioma invasiveness: their expression correlates with the progression and the degree of malignancy. Thus, broad spectrum matrix metalloproteinase inhibitors (MMP inhibitors) have been included in clinical trials. In the present study, the invasiveness, viability and progression of the human glioma cell line U87MG were investigated following treatment with N-O-isopropyl sulfonamido-based hydroxamates (compounds 1 and 2) as MMP-2 inhibitors used at nanomolar concentration. A standard broad spectrum MMP-inhibitor belonging to the classical tertiary sulfonamido-based hydroxamates family (CGS_27023A) was used too. The compounds 1 and 2 resulted in potent inhibition of cell invasiveness (P<0.0001) without affecting viability. In some clinical trials, the combined therapy of temozolomide (an alkylating agent used in glioma treatment) plus marimastat (a broad spectrum MMP inhibitor) has provided evidence of the importance of MMPs to tumor progression and invasiveness. On this basis, the effect on U87MG cells of a combined treatment with temozolomide, plus each of the two MMP inhibitors at nanomolar concentration, was investigated. The obtained data demonstrated the inhibition of cell invasiveness and viability after treatment. These results can help in developing clinical combined therapy using MMP inhibitors that, at low doses, increase the anticancer efficacy of chemotherapeutic drugs, probably without causing the side effects typical of broad-spectrum MMP inhibitors.

14-3-3 sigma and 14-3-3 zeta plays an opposite role in cell growth inhibition mediated by transforming growth factor-beta 1

The expression of 14-3-3 proteins is dysregulated in various types of cancer. This study was undertaken to investigate the effects of 14-3-3 zeta and 14-3-3 sigma on cell growth inhibition mediated by transforming growth factor-beta 1 (TGF-beta1). Mouse mammary epithelial cells (Eph4) that are transformed with oncogenic c-H-Ras (EpRas) and no longer sensitive to TGF-beta1-mediated growth inhibition displayed increased expression of 14-3-3 zeta and decreased expression of 14-3-3 sigma compared with parental Eph4 cells. Using small interfering RNA-mediated knockdown and overexpression of 14-3-3 sigma or 14-3-3 zeta, we showed that 14-3-3 sigma is required for TGF-beta1-mediated growth inhibition whereas 14-3-3 zeta negatively modulates this growth inhibitory response. Notably, overexpression of 14-3-3 zeta increased the level of Smad3 protein that is phosphorylated at linker regions and cannot mediate the TGF-beta1 growth inhibitory response. Consistent with this finding, mutation of the 14-3-3 zeta phosphorylation sites in Smad3 markedly reduced the 14-3-3 zeta-mediated inhibition of TGF-beta1-induced p15 promoter-reporter activity and cell cycle arrest, suggesting that these residues are critical targets of 14-3-3 zeta in the suppression of TGF-beta1-mediated growth. Taken together, our findings indicate that dysregulation of 14-3-3 sigma or 14-3-3 zeta contributes to TGF-beta1 resistance in cancer cells.

Oral cancer, cigarette smoke and mitochondrial 18kDa translocator protein (TSPO) - In vitro, in vivo, salivary analysis

Oral cancer features high rates of mortality and morbidity, and is in dire need for new approaches. In the present study we analyzed 18 kDa translocator protein (TSPO) expression in oral (tongue) cancer tumors by immunohistochemistry. We also assayed TSPO binding in human tongue cancer cell lines and in the cellular fraction of saliva from tongue cancer patients, heavy cigarette smokers, and non-smoking healthy people as controls. Concurrently, TSPO protein levels, cell viability, mitochondrial membrane potential (Deltapsi(m)), and general protein levels were analyzed. TSPO expression could be significantly enhanced in oral cancer tumors, compared to unaffected adjacent tissue. We also found that five-year survival probability dropped from 65% in patients with TSPO negative tumors to 7% in patients with highly expressed TSPO (p<0.001). TSPO binding capacity was also pronounced in the human oral cancer cell lines SCC-25 and SCC-15 (3133+/-643 fmol/mg protein and 6956+/-549 fmol/mg protein, respectively). Binding decreased by 56% and 72%, in the SCC-25 and SCC-15 cell lines, respectively (p<0.05) following CS exposure in cell culture. In the cellular fraction of saliva of heavy smokers TSPO binding was lower than in non-smokers (by 53%, p<0.05). Also the cellular fraction of saliva exposed to CS in vitro showed decreased TSPO binding compared to unexposed saliva (by 30%, p<0.001). Interestingly, oral cancer patients also displayed significantly lower TSPO binding in the cellular fraction of saliva compared to healthy controls (by 40%, p<0.01). Our results suggest that low TSPO binding found in the cellular fraction of saliva may depend on genetic background as well as result from exposure to CS. We suggest that this may be related to a predisposition for occurrence of oral cancer.

PEG-PE micelles loaded with paclitaxel and surface-modified by a PBR-ligand: synergistic anticancer effect

Selective ligands to the peripheral benzodiazepine receptor (PBR) may induce apoptosis and cell cycle arrest. An overexpression of PBR in certain cancers allowed us to consider the use of highly selective ligands to PBR for receptor-mediated drug targeting to tumors. With this in mind, we prepared PBR-targeted nanoparticulate drug delivery systems (PEG-PE micelles) loaded with the anticancer drug paclitaxel (PCL) to test possible synergistic anticancer effects. PEG2k-PE-based polymeric micelles with and without PCL were prepared in HBS, pH 7.5, and conjugated with a PBR-ligand (CB86) in 0.45% of DMSO. The cytotoxic effect of such micelles against the LN 18 human glioblastoma cell line was studied in cell culture. The micelles maintained their size and size distribution and remained intact without drug release after the PBR-ligand conjugation. The PCL-loaded PBR-targeted micelles showed a significantly enhanced toxicity against human glioblastoma LN 18 cancer cells in vitro. Thus, PBR-targeted nanopreparations may potentially serve as a new nanomedicine for targeted cancer therapy.

A sporadic Parkinson disease model via silencing of the ubiquitin-proteasome/E3 ligase component SKP1A

The aim of this study was to develop a new model of sporadic Parkinson disease (PD) based on silencing of the SKP1A gene, a component of the ubiquitin-proteasome/E3 ligase complex, Skp1, Cullin 1, F-box protein, which was found to be highly decreased in the substantia nigra of sporadic PD patients. Initially, an embryonic mouse substantia nigra-derived cell line (SN4741 cells) was infected with short hairpin RNA lentiviruses encoding the murine transcript of the SKP1A gene or with scrambled vector. SKP1A silencing resulted in increased susceptibility to neuronal damages induced by the parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium ion and serum starvation, in parallel with a decline in the expression of the dopaminergic markers, dopamine transporter and vesicular monoamine transporter-2. SKP1A-deficient cells presented a delay in completion of the cell cycle and the inability to arrest at the G(0)/G(1) phase when induced to differentiate. Instead, the cells progressed through S phase, developing rounded aggregates with characteristics of aggresomes including immunoreactivity for gamma-tubulin, alpha-synuclein, ubiquitin, tyrosine hydroxylase, Hsc-70 (70-kDa heat shock cognate protein), and proteasome subunit, and culminating in a lethal phenotype. Conversely, stably enforced expression of wild type SKP1A duplicated the survival index of naïve SN4741 cells under proteasomal inhibition injury, suggesting a new structural role of SKP1 in dopaminergic neuronal function, besides its E3 ligase activity. These results link, for the first time, SKP1 to dopamine neuronal function and survival, suggesting an essential role in sporadic PD. In summary, this new model has reproduced to a significant extent the molecular alterations described in sporadic PD at the cellular level, implicating Skp1 as a potential modifier in sporadic PD neurodegeneration.

Estradiol modulates uterine 18 kDa translocator protein gene expression in uterus and kidney of rats

We examined the effect of ovariectomy, with and without estradiol treatment, on 18 kDa translocator protein (TSPO) gene expression and its binding density in the uterus and kidney of rats. Ovariectomy causes a significant decrease in uterine, but not renal TSPO binding density, while estradiol treatment of ovariectomized rats restored TSPO binding density in the uterus. These TSPO density levels did not correlate with steady state or new RNA transcription. Our in vivo study suggests that estradiol is responsible for the maintenance of uterine TSPO density via transcriptional mechanisms. Our in vivo study also suggests that in the kidney estradiol appears to operate via post-transcriptional mechanisms to maintain TSPO density.

Single-step high-yield radiosynthesis and evaluation of a sensitive 18F-labeled ligand for imaging brain peripheral benzodiazepine receptors with PET

Elevated levels of peripheral benzodiazepine receptors (PBR) are associated with activated microglia in their response to inflammation. Hence, PBR imaging in vivo is valuable for investigating brain inflammatory conditions. Sensitive, easily prepared, and readily available radioligands for imaging with positron emission tomography (PET) are desirable for this purpose. We describe a new 18F-labeled PBR radioligand, namely [18F]N-fluoroacetyl-N-(2,5-dimethoxybenzyl)-2-phenoxyaniline ([18F]9). [18F]9 was produced easily through a single and highly efficient step, the reaction of [18F]fluoride ion with the corresponding bromo precursor, 8. Ligand 9 exhibited high affinity for PBR in vitro. PET showed that [18F]9 was avidly taken into monkey brain and gave a high ratio of PBR-specific to nonspecific binding. [18F]9 was devoid of defluorination in rat and monkey and gave predominantly polar radiometabolite(s). In rat, a low level radiometabolite of intermediate lipophilicity was identified as [18F]2-fluoro-N-(2-phenoxyphenyl)acetamide ([18F]11). [18F]9 is a promising radioligand for future imaging of PBR in living human brain.

Drugs targeting the mitochondrial pore act as cytotoxic and cytostatic agents in temozolomide-resistant glioma cells

BACKGROUND

High grade gliomas are one of the most difficult cancers to treat and despite surgery, radiotherapy and temozolomide-based chemotherapy, the prognosis of glioma patients is poor. Resistance to temozolomide is the major barrier to effective therapy. Alternative therapeutic approaches have been shown to be ineffective for the treatment of genetically unselected glioma patients. Thus, novel therapies are needed. Mitochondria-directed chemotherapy is an emerging tool to combat cancer, and inner mitochondrial permeability transition (MPT) represents a target for the development of cytotoxic drugs. A number of agents are able to induce MPT and some of them target MPT-pore (MPTP) components that are selectively up-regulated in cancer, making these agents putative cancer cell-specific drugs.

OBJECTIVE

The aim of this paper is to report a comprehensive analysis of the effects produced by selected MPT-inducing drugs (Betulinic Acid, Lonidamine, CD437) in a temozolomide-resistant glioblastoma cell line (ADF cells).

METHODS

EGFRvIII expression has been assayed by RT-PCR. EGFR amplification and PTEN deletion have been assayed by differential-PCR. Drugs effect on cell viability has been tested by crystal violet assay. MPT has been tested by JC1 staining. Drug cytostatic effect has been tested by mitotic index analysis. Drug cytotoxic effect has been tested by calcein AM staining. Apoptosis has been assayed by Hoechst incorporation and Annexine V binding assay. Authophagy has been tested by acridine orange staining.

RESULTS

We performed a molecular and genetic characterization of ADF cells and demonstrated that this line does not express the EGFRvIII and does not show EGFR amplification. ADF cells do not show PTEN mutation but differential PCR data indicate a hemizygous deletion of PTEN gene. We analyzed the response of ADF cells to Betulinic Acid, Lonidamine, and CD437. Our data demonstrate that MPT-inducing agents produce concentration-dependent cytostatic and cytotoxic effects in parallel with MPT induction triggered through MPTP. CD437, Lonidamine and Betulinic acid trigger apoptosis as principal death modality.

CONCLUSION

The obtained data suggest that these pharmacological agents could be selected as adjuvant drugs for the treatment of high grade astrocytomas that resist conventional therapies or that do not show any peculiar genetic alteration that can be targeted by specific drugs.

PK 11195 differentially affects cell survival in human wild-type and 18 kDa translocator protein-silenced ADF astrocytoma cells

Gliomas are the most common brain tumours with a poor prognosis due to their aggressiveness and propensity for recurrence. The 18 kDa translocator protein (TSPO) has been demonstrated to be greatly expressed in glioma cells and its over-expression has been correlated with glioma malignance grades. Due to both its high density in tumours and the pro-apoptotic activity of its ligands, TSPO has been suggested as a promising target in gliomas. With the aim to evidence if the TSPO expression level alters glioma cell susceptibility to undergo to cell death, we analysed the effects of the specific TSPO ligand, PK 11195, in human astrocytoma wild-type and TSPO-silenced cell lines. As first step, TSPO was characterised in human astrocytoma cell line (ADF). Our data demonstrated the presence of a single class of TSPO binding sites highly expressed in mitochondria. PK 11195 cell treatment activated an autophagic pathway followed by apoptosis mediated by the modulation of the mitochondrial permeability transition. In TSPO-silenced cells, produced by siRNA technique, a reduced cell proliferation rate and a decreased cell susceptibility to the PK 11195-induced anti-proliferative effect and mitochondrial potential dissipation were demonstrated respect to control cells. In conclusion, for the first time, PK 11195 was demonstrated to differentially affect glioma cell survival in relation to TSPO expression levels. These results encourage the development of specific-cell strategies for the treatment of gliomas, in which TSPO is highly expressed respect to normal cells.

Effects of Vinpocetine on mitochondrial function and neuroprotection in primary cortical neurons

Vinpocetine (ethyl apovincaminate), a synthetic derivative of the Vinca minor alkaloid vincamine, is widely used for the treatment of cerebrovascular-related diseases. One of the proposed mechanisms underlying its action is to protect against the cytotoxic effects of glutamate overexposure. Glutamate excitotoxicity leads to the disregulation of mitochondrial function and neuronal metabolism. As Vinpocetine has a binding affinity to the peripheral-type benzodiazepine receptor (PBR) involved in the mitochondrial transition pore complex, we investigated whether neuroprotection can be at least partially due to Vinpocetine's effects on PBRs. Neuroprotective effects of PK11195 and Ro5-4864, two drugs with selective and high affinity to PBR, were compared to Vinpocetine in glutamate excitotoxicity assays on primary cortical neuronal cultures. Vinpocetine exerted a neuroprotective action in a 1-50microM concentration range while PK11195 and Ro5-4864 were only slightly neuroprotective, especially in high (>25microM) concentrations. Combined pretreatment of neuronal cultures with Vinpocetine and PK11195 or Ro5-4864 showed increased neuroprotection in a dose-dependent manner, indicating that the different drugs may have different targets. To test this hypothesis, mitochondrial membrane potential (MMP) of cultured neurons was measured by flow cytometry. 25microM Vinpocetine reduced the decrease of mitochondrial inner membrane potential induced by glutamate exposure, but Ro5-4864 in itself was found to be more potent to block glutamate-evoked changes in MMP. Combination of Ro5-4864 and Vinpocetine treatment was found to be even more effective. In summary, the present results indicate that the neuroprotective action of vinpocetine in culture can not be explained by its effect on neuronal PBRs alone and that additional drug targets are involved.

Neuroprotective effect of Ro5-4864 following brain injury

The 18 kDa translocator protein (TSPO) is a protein complex located at the outer mitochondrial membrane and interacting with the mitochondrial permeability transition pore (mPTP), indicating its involvement in the control of mPTP opening. We intended to explore the effect of TSPO ligands, PK 11195 and Ro5-4864 on apoptosis in a rat model of cortical injury. Sprague-Dawley rats received a daily intraperitoneal injection of dimethylsulfoxide (vehicle), PK 11195, or Ro5-4864, starting 2 days prior the injury and a third injection after the injury. At 6 weeks, immunohistochemistry analysis showed that Ro5-4864 resulted in a significant increase in the number of surviving neurons and in the density of the neurofilament network in the perilesional cortex in comparison with animals of the vehicle and PK 11195 groups. In tissue samples dissected from the injured area, Ro5-4864 caused a significant reduction in activation of caspases 3 and 9 but not of caspase 8 in comparison with the vehicle and PK 11195 groups. In addition, measurements of transmembrane mitochondrial potential of mitochondria (Deltapsi(M)) isolated from normal rat brain showed that loss of Deltapsi(M) induced by recombinant Bax could be significantly reduced by Ro5-4864 in a concentration-dependent manner. Our findings indicate that the neuroprotective effect shown by Ro5-4864 in the present model of brain injury involves the mitochondrial pathway of apoptosis modulation of mPTP.

Ro5-4864 promotes neonatal motor neuron survival and nerve regeneration in adult rats

The translocator protein (18 kDa; TSPO), formerly known as the peripheral benzodiazepine receptor, is an outer mitochondrial membrane protein that associates with the mitochondrial permeability transition pore to regulate both steroidogenesis and apoptosis. TSPO expression is induced in adult dorsal root ganglion (DRG) sensory neurons after peripheral nerve injury and a TSPO receptor ligand, Ro5-4864, enhances DRG neurite growth in vitro and axonal regeneration in vivo. We have now found that TSPO is induced in neonatal motor neurons after peripheral nerve injury and have evaluated its involvement in neonatal and adult sensory and motor neuron survival, and in adult motor neuron regeneration. The TSPO ligand Ro5-4864 rescued cultured neonatal DRG neurons from nerve growth factor withdrawal-induced apoptosis and protected neonatal spinal cord motor neurons from death due to sciatic nerve axotomy. However, Ro5-4864 had only a small neuroprotective effect on adult facial motor neurons after axotomy, did not delay onset or prolong survival in SOD1 mutant mice, and failed to protect adult DRG neurons from sciatic nerve injury-induced death. In contrast, Ro5-4864 substantially enhanced adult facial motor neuron nerve regeneration and restoration of function after facial nerve axotomy. These data indicate a selective sensitivity of neonatal sensory and motor neurons to survival in response to Ro5-4864, which highlights that survival in injured immature neurons cannot necessarily predict success in adults. Furthermore, although Ro5-4864 is only a very weak promoter of survival in adult neurons, it significantly enhances regeneration and functional recovery in adults.

DPA-714, a new translocator protein-specific ligand: synthesis, radiofluorination, and pharmacologic characterization

The translocator protein (18 kDa) (TSPO), formerly known as the peripheral benzodiazepine receptor, is dramatically upregulated under pathologic conditions. Activated microglia are the main cell type expressing the TSPO at sites of central nervous system pathology. Radioligands for the TSPO can therefore measure active disease in the brain. This article details the synthesis, radiofluorination, and pharmacologic evaluation of a new TSPO-specific pyrazolopyrimidine, DPA-714.

METHODS

The affinity of DPA-714 for the TSPO was measured in rat kidney membranes with (3)H-PK11195. The in vitro functional activity of DPA-714 was measured in a steroidogenic assay in which the ability of DPA-714 to increase pregnenolone synthesis was measured with rat C6 glioma cells. The radiofluorination of DPA-714 was achieved by nucleophilic (18)F-fluoride displacement of the tosylate precursor. (18)F-DPA-714 was assessed in rats harboring unilateral quinolinic acid (QA) lesions. In addition, pretreatment experiments were performed with PK11195 (5 mg/kg), DPA-714 (1 mg/kg), and DPA-713 (1 mg/kg). The in vivo binding and biodistribution of (18)F-DPA-714 were determined in a baboon with PET. Experiments involving presaturation with PK11195 (1.5 mg/kg) and displacement with DPA-714 (1 mg/kg) were conducted to evaluate the specificity of radioligand binding.

RESULTS

In vitro binding studies revealed that DPA-714 displayed a high affinity for the TSPO (dissociation constant, 7.0 nM). DPA-714 stimulated pregnenolone synthesis at levels 80% above the baseline. (18)F-DPA-714 was prepared at a 16% radiochemical yield and a specific activity of 270 GBq/mumol. In rats harboring unilateral QA lesions, an 8-fold-higher level of uptake of (18)F-DPA-714 was observed in the ipsilateral striatum than in the contralateral striatum. Uptake in the ipsilateral striatum was shown to be selective because it was inhibited to the level in the contralateral striatum in the presence of PK11195, nonlabeled DPA-714, or DPA-713. PET studies demonstrated rapid penetration and good retention of (18)F-DPA-714 in the baboon brain. Pretreatment with PK11195 effectively inhibited the uptake of (18)F-DPA-714 in the whole brain, indicating its selective binding to the TSPO. The injection of nonlabeled DPA-714 20 min after the injection of (18)F-DPA-714 resulted in radioligand washout, demonstrating the reversibility of (18)F-DPA-714 binding.

CONCLUSION

(18)F-DPA-714 is a specific radioligand for the TSPO, displaying promising in vivo properties and thus warranting further investigation.

Comparative anticancer effects of flavonoids and diazepam in cultured cancer cells

This study examined the comparative anticancer effects of flavonoids and diazepam in the cultured cancer cells. In the SNU-C4 colorectal and MDA-MB-231 breast adenocarcinoma cells, apigenin and fisetin, flavonoids, and diazepam inhibited cancer cell survival concentration and incubation-time dependently. Diazepam consistently inhibited FAS activity, a known anticancer mechanism of flavonoids, in a concentration dependent manner. Unlike diazepam, in highly aggressive breast MDA-MB-231 cells known to have a nuclear/perinuclear located PBR, PK11195, a specific PBR ligand enhanced the proliferation of cells, and the proliferative effect of PK11195 was reversed by an addition of lovastatin, a HMG-CoA reductase inhibitor. Diazepam- and flavonoids-induced cytotoxic activity in both cancer cell lines was not reduced by the addition of 5-fluorouracil (5-FU), a chemotherapeutic agent. Like flavonoids, diazepam inhibited the release of vascular endothelial growth factor (VEGF) and granulocyte-macrophage-colony stimulating factor (GM-CSF) into supernatants of cultured in the SNU-C4 and MDA-MB-231 cells. In conclusion, this study provided in vitro information on the safe use of sedative in oncologic patients.