Structure-Activity Relationships and Therapeutic Potential of Purinergic P2X7 Receptor Antagonists.

The purinergic P2X7 receptor (P2X7R), an ATP-gated non-selective cation channel, has emerged as a gatekeeper of inflammation that controls the release of proinflammatory cytokines. As a key player in initiating the inflammatory signaling cascade, the P2X7 receptor is currently under intense scrutiny as a target for the treatment of different pathologies, including chronic inflammatory disorders (rheumatoid arthritis and osteoarthritis), chronic neuropathic pain, mood disorders (depression and anxiety), neurodegenerative diseases, ischemia, cancer (leukemia), and many others. For these reasons, pharmaceutical companies have invested in discovering compounds able to modulate the P2X7R and filed many patent applications. This review article presents an account of P2X7R structure, function, and tissue distribution, emphasizing its role in inflammation. Next, we illustrate the different chemical classes of non-competitive P2X7R antagonists reported by highlighting their properties and qualities as clinical candidates for treating inflammatory disorders and neurodegenerative diseases. We also discuss the efforts to develop effective Positron Emission Tomography (PET) radioligands to progress the understanding of the pathomechanisms of neurodegenerative disorders, to provide evidence of drug-target engagement, and to assist clinical dose selection for novel drug therapies.

Development of potent isoflavone-based formyl peptide receptor 1 (FPR1) antagonists and their effects in gastric cancer cell models.

Formyl peptide receptor-1 (FPR1) is a G protein-coupled chemoattractant receptor that plays a crucial role in the trafficking of leukocytes into the sites of bacterial infection and inflammation. Recently, FPR1 was shown to be expressed in different types of tumor cells and could play a significant role in tumor growth and invasiveness. Starting from the previously reported FPR1 antagonist 4, we have designed a new series of 4H-chromen-2-one derivatives that exhibited a substantial increase in FPR1 antagonist potency. Docking studies identified the key interactions for antagonist activity. The most potent compounds in this series (24a and 25b) were selected to study the effects of the pharmacological blockade of FPR1 in NCl-N87 and AGS gastric cancer cells. Both compounds potently inhibited cell growth through a combined effect on cell proliferation and apoptosis and reduced cell migration, while inducing an increase in angiogenesis, thus suggesting that FPR1 could play a dual role as oncogene and onco-suppressor.

LC-MS/MS Analysis on Infusion Bags and Filled Syringes of Decitabine: New Data on Physicochemical Stability of an Unstable Molecule.

Many anticancer drugs are reported to have low physicochemical stability after dilution; therefore, producers impose short times from reconstitution, dilution, and the end of administration. The precariousness of cancer patients' health in real-life experience within cancer hospitals often forces delays in the drug administration with respect to the standard treatment schedule timing, because of acute toxicities or the need to postpone a control analysis before administration. The public health costs for discarded anticancer drugs due to administration interruptions can be avoided, thanks to independent analytical studies, which integrate the producer's data reported in the technical sheet, referring to the real conditions of preparation in a sterile atmosphere under a cabin in a laboratory dedicated to handling cytotoxic drugs in controlled conditions of temperature, pressure, and particulate contamination. Decitabine is apparently an unstable molecule, whose reported stability is only 3 h at 2-8 °C when diluted, while the mother solution must be immediately used or, otherwise, discarded. This study has investigated the physicochemical stability of decitabine both in diluted infusion bags and in sterile water reconstituted syringes at 4 °C for 0, 24, 48, and 72 h. In all performed studies, the stability-indicating method involves, for the first time, the use of liquid chromatography-tandem mass spectrometry analysis. Unexpectedly, both diluted and reconstituted solutions of decitabine are more stable than previously reported data, with a 48 h-long physicochemical stability at 2-8 °C and protected from light.

Multi-Target Directed Ligands (MTDLs) Binding the σ1 Receptor as Promising Therapeutics: State of the Art and Perspectives.

The sigma-1 (σ1) receptor is a 'pluripotent chaperone' protein mainly expressed at the mitochondria-endoplasmic reticulum membrane interfaces where it interacts with several client proteins. This feature renders the σ1 receptor an ideal target for the development of multifunctional ligands, whose benefits are now recognized because several pathologies are multifactorial. Indeed, the current therapeutic regimens are based on the administration of different classes of drugs in order to counteract the diverse unbalanced physiological pathways associated with the pathology. Thus, the multi-targeted directed ligand (MTDL) approach, with one molecule that exerts poly-pharmacological actions, may be a winning strategy that overcomes the pharmacokinetic issues linked to the administration of diverse drugs. This review aims to point out the progress in the development of MTDLs directed toward σ1 receptors for the treatment of central nervous system (CNS) and cancer diseases, with a focus on the perspectives that are proper for this strategy. The evidence that some drugs in clinical use unintentionally bind the σ1 protein (as off-target) provides a proof of concept of the potential of this strategy, and it strongly supports the promise that the σ1 receptor holds as a target to be hit in the context of MTDLs for the therapy of multifactorial pathologies.

Mitochondrial Membranes of Human SH-SY5Y Neuroblastoma Cells Express Serotonin 5-HT7 Receptor.

Mitochondria in neurons contribute to energy supply, the regulation of synaptic transmission, Ca2+ homeostasis, neuronal excitability, and stress adaptation. In recent years, several studies have highlighted that the neurotransmitter serotonin (5-HT) plays an important role in mitochondrial biogenesis in cortical neurons, and regulates mitochondrial activity and cellular function in cardiomyocytes. 5-HT exerts its diverse actions by binding to cell surface receptors that are classified into seven distinct families (5-HT1 to 5-HT7). Recently, it was shown that 5-HT3 and 5-HT4 receptors are located on the mitochondrial membrane and participate in the regulation of mitochondrial function. Furthermore, it was observed that activation of brain 5-HT7 receptors rescued mitochondrial dysfunction in female mice from two models of Rett syndrome, a rare neurodevelopmental disorder characterized by severe behavioral and physiological symptoms. Our Western blot analyses performed on cell-lysate and purified mitochondria isolated from neuronal cell line SH-SY5Y showed that 5-HT7 receptors are also expressed into mitochondria. Maximal binding capacity (Bmax) obtained by Scatchard analysis on purified mitochondrial membranes was 0.081 pmol/mg of 5-HT7 receptor protein. Lastly, we evaluated the effect of selective 5-HT7 receptor agonist LP-211 and antagonist (inverse agonist) SB-269970 on mitochondrial respiratory chain (MRC) cytochrome c oxidase activity on mitochondria from SH-SY5Y cells. Our findings provide the first evidence that 5-HT7 receptor is also expressed in mitochondria.

High-affinity sigma-1 (σ1) receptor ligands based on the σ1 antagonist PB212.

Aim: The σ1 receptor is a druggable target involved in many physiological processes and diseases. To clarify its physiology and derive therapeutic benefit, nine analogs based on the σ1 antagonist PB212 were synthesized replacing the 4-methylpiperidine with basic moieties of varying size and degree of conformational freedom. Results & methodology: 3-Phenylpyrrolidine, 4-phenylpiperidine or granatane derivatives displayed the highest affinity (Ki.#x00A0;= 0.12, 0.31 or 1.03 nM). Calcium flux assays in MCF7σ1 cells indicated that the highest σ1 receptor affinity are σ1 antagonists. Molecular models provided a structural basis for understanding the σ1 affinity and functional activity of the analogs and incorporated Glennon's σ1 pharmacophore model. Conclusion: Herein, we identify new compounds exploitable as therapeutic drug leads or as tools to study σ1 receptor physiology.

An updated patent review on P-glycoprotein inhibitors (2011-2018).

INTRODUCTION: P-glycoprotein is a complex ATP-ase transporter involved in physiological and pathological functions. In particular, it is involved in the onset of multidrug resistance in cancer, in ocular disease, Chronic Rhinosinusitis, CNS diseases such as Alzheimer, Parkinson, and epilepsy. One of the aims of clinicians and pharmacologists is to monitor P-gp activity through the inhibitors and to use its activity and/or expression in physiological barriers for the early diagnosis of several pathologies. Considering P-glycoprotein activity, several substrates have been characterized but the challenge is to design 'pure' P-glycoprotein inhibitors. AREAS COVERED: P-glycoprotein inhibitors display a large spectrum of activities. Here the contents of patents focused on the role of P-glycoprotein inhibitor in modulating MDR in cancer, in bioavailability, in ocular disease and Chronic Rhinosinusitis are reported. EXPERT OPINION: The use of P-glycoprotein inhibitor sic et simpliciter, or in coadministration with therapeutic agents, for ocular disease, and Chronic Rhinosinusitis is promising and could be suggested for additional trials. By contrast, the bioavailability of the coadministrated drugs, increased by P-glycoprotein inhibitor, deserves a wider discussion, in particular on the pharmacokinetic aspect of both P-glycoprotein inhibitor and the coadministered drug.

Activation of Serotonin 5-HT7 Receptors Modulates Hippocampal Synaptic Plasticity by Stimulation of Adenylate Cyclases and Rescues Learning and Behavior in a Mouse Model of Fragile X Syndrome.

We have previously demonstrated that activation of serotonin 5-HT7 receptors (5-HT7R) reverses metabotropic glutamate receptor-mediated long term depression (mGluR-LTD) in the hippocampus of wild-type (WT) and Fmr1 Knockout (KO) mice, a model of Fragile X Syndrome (FXS) in which mGluR-LTD is abnormally enhanced. Here, we have investigated intracellular mechanisms underlying the effect of 5-HT7R activation using patch clamp on hippocampal slices. Furthermore, we have tested whether in vivo administration of LP-211, a selective 5-HT7R agonist, can rescue learning and behavior in Fmr1 KO mice. In the presence of an adenylate cyclase blocker, mGluR-LTD was slightly enhanced in WT and therefore the difference between mGluR-LTD in WT and Fmr1 KO slices was no longer present. Conversely, activation of adenylate cyclase by either forskolin or Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) completely reversed mGluR-LTD in WT and Fmr1 KO. 5-HT7R activation reversed mGluR-LTD in WT and corrected exaggerated mGluR-LTD in Fmr1 KO; this effect was abolished by blockade of either adenylate cyclase or protein kinase A (PKA). Exposure of hippocampal slices to LP-211 caused an increased phosphorylation of extracellular signal regulated kinase (ERK), an intracellular effector involved in mGluR-LTD, in WT mice. Conversely, this effect was barely detectable in Fmr1 KO mice, suggesting that 5-HT7R-mediated reversal of mGluR-LTD does not require ERK stimulation. Finally, an acute in vivo administration of LP-211 improved novel object recognition (NOR) performance in WT and Fmr1 KO mice and reduced stereotyped behavior in Fmr1 KO mice. Our results indicate that mGluR-LTD in WT and Fmr1 KO slices is bidirectionally modulated in conditions of either reduced or enhanced cAMP formation. Activation of 5-HT7 receptors reverses mGluR-LTD by activation of the cAMP/PKA intracellular pathway. Importantly, a systemic administration of a 5-HT7R agonist to Fmr1 KO mice corrected learning deficits and repetitive behavior. We suggest that selective 5-HT7R agonists might become novel pharmacological tools for FXS therapy.

Structural insights into serotonin receptor ligands polypharmacology.

Identifying desired interactions with a target receptor is often the first step when designing new active compounds. However, attention should also be focused on contacts with other proteins that result in either selective or polypharmacological compounds. Here, the search for the structural determinants of selectivity between selected serotonin receptor subtypes was carried out. Special attention was focused on 5-HT7R and the cross-interactions between its ligands and the 5-HT1AR, 5-HT1BR, 5-HT2AR, 5-HT2BR, and 5-HT6R subtypes. Selective and non-selective compounds for each pair of 5-HT7/5-HTx receptors were docked to the respective 5-HTR homology models and 5-HT1B/5-HT2BR crystal structures. The contacts present in the ligand-receptor complexes obtained by docking were characterized by the structural interaction fingerprint and statistically analyzed in terms of their frequency. The results allowed for the identification of amino acids that discriminate between selective and non-selective compounds for each 5-HT7/5-HTx receptor pair, which was further compared with available mutagenesis data. Interaction pattern characteristics for compounds with particular activity profiles can constitute the basis for the coherent selectivity theory within a considered set of proteins, supporting the ongoing development of new ligands targeting these receptors. The in silico results were used to analyze prospective virtual screening results towards the 5-HT7 receptor in which compounds of different chemotypes to known 5-HT7R ligands, with micromolar level activities were identified. The findings in this study not only confirm the legitimacy of the approach but also constitute a great starting point for further studies on 5-HT7R ligands selectivity.

Novel 64Cu Labeled RGD2-BBN Heterotrimers for PET Imaging of Prostate Cancer.

Bombesin receptor 2 (BB2) and integrin αvß3 receptor are privileged targets for molecular imaging of cancer because of their overexpression in a number of tumor tissues. The most recent developments in heterodimer-based radiopharmaceuticals concern BB2- and integrin αvß3-targeting compounds, consisting of bombesin (BBN) and cyclic arginine-glycine-aspartic acid peptides (RGD), connected through short length linkers. Molecular imaging probes based on RGD-BBN heterodimer design exhibit improved tumor targeting efficacy compared to the single-receptor targeting peptide monomers. However, their application in clinical study is restricted because of inefficient synthesis or unfavorable in vivo properties, which could depend on the short linker nature. Thus, the aim of the present study was to develop a RGD2-BBN heterotrimer, composed of (7-14)BBN-NH2 peptide (BBN) linked to the E[ c(RGDyK)]2 dimer peptide (RGD2), bearing the new linker type [Pro-Gly]12. The heterodimer E[c(RGDyK)]2-PEG3-Glu-(Pro-Gly)12-BBN(7-14)-NH2 (RGD2-PG12-BBN) was prepared through conventional solid phase synthesis, then conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid (NODA-GA). In 64Cu labeling, the NODA-GA chelator showed superior radiochemical characteristics compared to DOTA (70% vs 40% yield, respectively). Both conjugates displayed dual targeting ability, showing good αvß3 affinities and high BB2 receptor affinities which, in the case of the NODA-GA conjugate, were in the same range as the best RGD-BBN heterodimer ligands reported to date ( Ki = 24 nM). 64Cu-DOTA and 64Cu-NODA-GA probes were also found to be stable after 1 h incubation in mouse serum (>90%). In a microPET study in prostate cancer PC-3 xenograft mice, both probes showed low tumor uptake, probably due to poor pharmacokinetic properties in vivo. Overall, our study demonstrates that novel RGD-BBN heterodimer with long linker can be prepared and they preserve high binding affinities to BB2 and integrin αvß3 receptor binding ability. The present study represents a step forward in the design of effective heterodimer or heterotrimer probes for dual targeting.

Functional N-Formyl Peptide Receptor†2 (FPR2) Antagonists Based on the Ureidopropanamide Scaffold Have Potential To Protect Against Inflammation-Associated Oxidative Stress.

Formyl peptide receptor 2 (FPR2) is a G protein coupled receptor belonging to the N-formyl peptide receptor (FPR) family that plays critical roles in peripheral and brain inflammatory responses. FPR2 has been proposed as a target for the development of drugs that could facilitate the resolution of chronic inflammatory reactions by enhancing endogenous anti-inflammation systems. Starting from lead compounds previously identified in our laboratories, we designed a new series of ureidopropanamide derivatives with the goal of converting functional activity from agonism into antagonism and to develop new FPR2 antagonists. Although none of the compounds behaved as antagonists, some of the compounds were able to induce receptor desensitization and, thus, functionally behaved as antagonists. Evaluation of these compounds in an in vitro model of neuroinflammation showed that they decreased the production of reactive oxygen species in mouse microglial N9 cells after stimulation with lipopolysaccharide. These FPR2 ligands may protect cells from damage due to inflammation-associated oxidative stress.

AM-37 and ST-36 Are Small Molecule Bombesin Receptor Antagonists.

While peptide antagonists for the gastrin-releasing peptide receptor (BB2R), neuromedin B receptor (BB1R), and bombesin (BB) receptor subtype-3 (BRS-3) exist, there is a need to develop non-peptide small molecule inhibitors for all three BBR. The BB agonist (BA)1 binds with high affinity to the BB1R, BB2R, and BRS-3. In this communication, small molecule BBR antagonists were evaluated using human lung cancer cells. AM-37 and ST-36 inhibited binding to human BB1R, BB2R, and BRS-3 with similar affinity (Ki = 1.4-10.8 µM). AM-13 and AM-14 were approximately an order of magnitude less potent than AM-37 and ST-36. The ability of BA1 to elevate cytosolic Ca2+ in human lung cancer cells transfected with BB1R, BB2R, and BRS-3 was antagonized by AM-37 and ST-36. BA1 increased tyrosine phosphorylation of the EGFR and ERK in lung cancer cells, which was blocked by AM-37 and ST-36. AM-37 and ST-36 reduced the growth of lung cancer cells that have BBR. The results indicate that AM-37 and ST-36 function as small molecule BB receptor antagonists.

Stimulation of the brain serotonin receptor 7 rescues mitochondrial dysfunction in female mice from two models of Rett syndrome.

Rett syndrome (RTT) is a rare neurodevelopmental disorder, characterized by severe behavioral and physiological symptoms. Mutations in the methyl CpG binding protein 2 gene (MECP2) cause more than 95% of classic cases, and currently there is no cure for this devastating disorder. Recently we have demonstrated that neurobehavioral and brain molecular alterations can be rescued in a RTT mouse model, by pharmacological stimulation of the brain serotonin receptor 7 (5-HT7R). This member of the serotonin receptor family, crucially involved in the regulation of brain structural plasticity and cognitive processes, can be stimulated by systemic repeated treatment with LP-211, a brain-penetrant selective agonist. The present study extends previous findings by demonstrating that LP-211 treatment (0.25 mg/kg, once per day for 7 days) rescues mitochondrial respiratory chain impairment, oxidative phosphorylation deficiency and the reduced energy status in the brain of heterozygous female mice from two highly validated mouse models of RTT (MeCP2-308 and MeCP2-Bird mice). Moreover, LP-211 treatment completely restored the radical species overproduction by brain mitochondria in the MeCP2-308 model and partially recovered the oxidative imbalance in the more severely affected MeCP2-Bird model. These results provide the first evidence that RTT brain mitochondrial dysfunction can be rescued targeting the brain 5-HT7R and add compelling preclinical evidence of the potential therapeutic value of LP-211 as a pharmacological approach for this devastating neurodevelopmental disorder.

Structure-activity relationship study towards non-peptidic positron emission tomography (PET) radiotracer for gastrin releasing peptide receptors: Development of [18F] (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide.

Gastrin-releasing peptide receptors (GRP-Rs, also known as bombesin 2 receptors) are overexpressed in a variety of human cancers, including prostate cancer, and therefore they represent a promising target for in vivo imaging of tumors using positron emission tomography (PET). Structural modifications of the non-peptidic GRP-R antagonist PD-176252 ((S)-1a) led to the identification of the fluorinated analog (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide ((S)-1m) that showed high affinity and antagonistic properties for GRP-R. This antagonist was stable in rat plasma and towards microsomal oxidative metabolism in vitro. (S)-1m was successfully radiolabeled with fluorine-18 through a conventional radiochemistry procedure. [18F](S)-1m showed high affinity and displaceable interaction for GRP-Rs in PC3 cells in vitro.

Selective 5-HT7 receptor agonists LP 44 and LP 211 elicit an analgesic effect on formalin-induced orofacial pain in mice

ABSTRACT The most recently identified serotonin (5-HT) receptor is the 5-HT7 receptor. The antinociceptive effects of a 5-HT7 receptor agonist have been shown in neuropathic and inflammatory animal models of pain. A recent study demonstrated the functional expression of 5-HT7 receptors in the substantia gelatinosa (SG) of the trigeminal subnucleus caudalis, which receives and processes orofacial nociceptive inputs. Objective To investigate the antinociceptive effects of pharmacological activation of 5-HT7 receptors on orofacial pain in mice. Material and Methods Nociception was evaluated by using an orofacial formalin test in male Balb-C mice. Selective 5-HT7 receptor agonists, LP 44 and LP 211 (1, 5, and 10 mg/kg), were given intraperitoneally 30 min prior to a formalin injection. A bolus of 10 µl of 4% subcutaneous formalin was injected into the upper lip of mice and facial grooming behaviors were monitored. The behavioral responses consisted of two distinct periods, the early phase corresponding to acute pain (Phase I: 0–12 min) and the late phase (Phase II: 12–30 min). Results LP 44 and LP 211 (1, 5, and 10 mg/kg) produced an analgesic effect with reductions in face rubbing time in both Phase I and Phase II of the formalin test. Conclusion Our results suggest that 5-HT7 receptor agonists may be promising analgesic drugs in the treatment of orofacial pain.

Arylpiperazine agonists of the serotonin 5-HT1A receptor preferentially activate cAMP signaling versus recruitment of ß-arrestin-2.

G protein-coupled receptors (GPCRs) mediate biological signal transduction through complex molecular pathways. Therapeutic effects of GPCR-directed drugs are typically accompanied by unwanted side effects, owing in part to the parallel engagement of multiple signaling mechanisms. The discovery of drugs that are 'functionally selective' towards therapeutic effects, based on their selective control of cellular responses through a given GPCR, is thus a major goal in pharmacology today. In the present study, we show that several arylpiperazine ligands of the serotonin 5-HT1A receptor (5-HT1AR) preferentially activate 3',5'-cyclic adenosine monophosphate (cAMP) signaling versus ß-arrestin-2 recruitment. The pharmacology of these compounds is thus qualitatively different from the endogenous agonist serotonin, indicating functional selectivity of 5-HT1AR-mediated response pathways. Preliminary evidence suggests that phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) downstream of 5-HT1AR is a substrate of functionally selective signaling by partial agonists. We propose that the compounds described in the present study are useful starting points for the development of signaling pathway-selective drugs targeting 5-HT1AR.

ML-18 is a non-peptide bombesin receptor subtype-3 antagonist which inhibits lung cancer growth.

Bombesin receptor subtype (BRS)-3 is a G protein coupled receptor (GPCR) for the bombesin (BB)-family of peptides. BRS-3 is an orphan GPCR and little is known of its physiological role due to the lack of specific agonists and antagonists. PD168368 is a nonpeptide antagonist for the neuromedin B (NMB) receptor (R) whereas PD176252 is a nonpeptide antagonist for the gastrin releasing peptide (GRP) R and NMBR but not BRS-3. Here nonpeptide analogs of PD176252 e.g. the S-enantiomer ML-18, and the R-enantiomer, EMY-98, were investigated as BRS-3 antagonists using lung cancer cells. ML-18 and EMY-98 inhibited specific (125)I-BA1 (DTyr-Gln-Trp-Ala-Val-ßAla-His-Phe-Nle-NH2)BB(6-14) binding to NCI-H1299 lung cancer cells stably transfected with BRS-3 with IC50 values of 4.8 and >100µM, respectively. In contrast, ML-18 bound with lower affinity to the GRPR and NMBR with IC50 values of 16 and >100µM, respectively. ML-18 (16µM), but not its enantiomer EMY-98, inhibited the ability of 10nM BA1 to elevate cytosolic Ca(2+) in a reversible manner using lung cancer cells loaded with FURA2-AM. ML-18 (16µM), but not EMY-98, inhibited the ability of 100nM BA1 to cause tyrosine phosphorylation of the EGFR and ERK in lung cancer cells. ML-18 but not EMY-98 inhibited the proliferation of lung cancer cells. The results indicate that ML-18 is a nonpeptide BRS-3 antagonist that should serve as a template to improve potency and selectivity.

ABC transporters in CSCs membranes as a novel target for treating tumor relapse.

CSCs are responsible for the high rate of recurrence and chemoresistance of different types of cancer. The current antineoplastic agents able to inhibit bulk replicating cancer cells and radiation treatment are not efficacious toward CSCs since this subpopulation has several intrinsic mechanisms of resistance. Among these mechanisms, the expression of ATP-Binding Cassette (ABC) transporters family and the activation of different signaling pathways (such as Wnt/ß-catenin signaling, Hedgehog, Notch, Akt/PKB) are reported. Therefore, considering ABC transporters expression on CSCs membranes, compounds able to modulate MDR could induce cytotoxicity in these cells disclosing an exciting and alternative strategy for targeting CSCs in tumor therapy. The next challenge in the cure of cancer relapse may be a multimodal strategy, an approach where specific CSCs targeting drugs exert simultaneously the ability to circumvent tumor drug resistance (ABC transporters modulation) and cytotoxic activity toward CSCs and the corresponding differentiated tumor cells. The efficacy of suggested multimodal strategy could be probed by using several scaffolds active toward MDR pumps on CSCs isolated by tumor specimens.

Synthesis, radiolabeling and in vivo evaluation of [(11)C](R)-1-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]-3-(2-pyrazinyloxy)-2-propanol, a potential PET radioligand for the 5-HT(7) receptor.

In the search for a novel serotonin 7 (5-HT7) receptor PET radioligand we synthesized and evaluated a new series of biphenylpiperazine derivatives in vitro. Among the studied compounds, (R)-1-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]-3-(2-pyrazinyloxy)-2-propanol ((R)-16), showed the best combination of affinity, selectivity, and lipophilicity, and was thus chosen for carbon-11 labelling and evaluation in pigs. After intravenous injection, [(11)C](R)-16 entered the pig brain and displayed reversible tracer kinetics. Pretreatment with the 5-HT7 receptor selective antagonist SB-269970 (1) resulted in limited decrease in the binding of [(11)C](R)-16, suggesting that this radioligand is not optimal for imaging the brain 5-HT7 receptor in vivo but it may serve as a lead compound for the design of novel 5-HT7 receptor PET radioligands.

Design, synthesis, lipophilic properties, and binding affinities of potential ligands in positron emission tomography (PET) for visualization of brain dopamine D4 receptors.

We report the synthesis of compounds structurally related to the high-affinity dopamine D4 receptor ligand N-{2-[4-(3-cyanopyridin-2-yl)piperazin-1-yl]ethyl}-3-methoxybenzamide (1e). All compounds were specifically designed as potential PET radioligands for brain D4 receptor visualization, having lipophilicity within a range for brain uptake and weak non-specific binding (0.75100-fold), but its D4 receptor affinity was suboptimal for imaging of brain D4 receptors (Ki =30 nM).