Biaryl analogues of conformationally constrained tricyclic tropanes as potent and selective norepinephrine reuptake inhibitors: synthesis and evaluation of their uptake inhibition at monoamine transporter sites

Suppression of Cocaine-Evoked Hyperactivity by Self-Adjuvanting and Multivalent Peptide Nanofiber Vaccines

The development of anti-cocaine vaccines that counteract the rewarding effects of the drug are currently being investigated as adjunct therapies for prevention of relapse in abstinent users. However, cocaine is weakly immunogenic and requires conjugation to carrier proteins and coadministration with strong adjuvants, which carry the risk of local reactogenicity and systemic toxicity. Here we report synthetic and multivalent self-assembling peptide nanofibers as adjuvant-free carriers for cocaine vaccines. A novel cocaine hapten modified at the P3 site was conjugated to the N-terminus of an amphipathic self-assembling domain KFE8. In aqueous buffers the cocaine-KFE8 conjugate assembled into β-sheet rich nanofibers, which raised anti-cocaine antibodies without the need for added adjuvants in mice. Vaccinated mice were treated with cocaine and a significant negative correlation was observed between antibody levels and cocaine-evoked hyperactivity. These totally synthetic and multivalent nanofibers with well-defined chemical composition represent the first generation of adjuvant-free cocaine vaccines.

Fluorine-18 Radiolabeled PET Tracers for Imaging Monoamine Transporters: Dopamine, Serotonin, and Norepinephrine

This review focuses on the development of fluorine-18 radiolabeled PET tracers for imaging the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET). All successful DAT PET tracers reported to date are members of the 3β-phenyl tropane class and are synthesized from cocaine. Currently available carbon-11 SERT PET tracers come from both the diphenylsulfide and 3β-phenyl nortropane class, but so far only the nortropanes have found success with fluorine-18 derivatives. NET imaging has so far employed carbon-11 and fluorine-18 derivatives of reboxetine but due to defluorination of the fluorine-18 derivatives further research is still necessary.

Development of Fluorine-18 Labeled Metabolically Activated Tracers for Imaging of Drug Efflux Transporters with Positron Emission Tomography

Increased activity of efflux transporters, e.g., P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), at the blood-brain barrier is a pathological hallmark of many neurological diseases, and the resulting multiple drug resistance represents a major clinical challenge. Noninvasive imaging of transporter activity can help to clarify the underlying mechanisms of drug resistance and facilitate diagnosis, patient stratification, and treatment monitoring. We have developed a metabolically activated radiotracer for functional imaging of P-gp/BCRP activity with positron emission tomography (PET). In preclinical studies, the tracer showed excellent initial brain uptake and clean conversion to the desired metabolite, although at a sluggish rate. Blocking with P-gp/BCRP modulators led to increased levels of brain radioactivity; however, dynamic PET did not show differential clearance rates between treatment and control groups. Our results provide proof-of-concept for development of prodrug tracers for imaging of P-gp/BCRP function in vivo but also highlight some challenges associated with this strategy.

Role of serotonin transporter function in rat orbitofrontal cortex in impulsive choice

Impulsivity is a multi-faceted personality construct that plays a prominent role in drug abuse vulnerability. Dysregulation of 5-hydroxytryptamine (serotonin, 5-HT) systems in subregions of the prefrontal cortex has been implicated in impulsivity. Extracellular 5-HT concentrations are regulated by 5-HT transporters (SERTs), indicating that these transporters may be important molecular targets underlying individual differences in impulsivity and drug abuse vulnerability. The present study evaluated the role of SERT in mediating individual differences in impulsivity. Rats were tested for both impulsive action using the cued go/no-go task and for impulsive choice using a delay discounting task in a counterbalanced design. Following behavioral evaluation, Km and Vmax were obtained from kinetic analysis of [(3)H]5-HT uptake by SERT using synaptosomes prepared from both orbitofrontal cortex (OFC) and medial prefrontal cortex (mPFC) obtained from each individual rat. Vmax for SERT in OFC, but not mPFC, was negatively correlated with mean adjusted delay scores in the delay discounting task. In contrast, Vmax for SERT in OFC and mPFC was not correlated with performance in the cued go/no-go task. To further evaluate the relationship between SERT function and impulsive choice, a selective SERT inhibitor, fluoxetine (0, 15, 50 and 150pmol/side) was microinjected bilaterally into OFC and effects on the delay discounting task determined. Following stabilization of behavior, fluoxetine increased mean adjusted delay scores (decreased impulsivity) in high impulsive rats compared to saline microinjection, but had no effect in low impulsive rats. These ex vivo and in vivo results suggest that enhanced SERT function in OFC underlies high impulsive choice behavior.

Radiosynthesis and first preclinical evaluation of the novel norepinephrine transporter pet-ligand [(11)C]ME@HAPTHI

Background

The norepinephrine transporter (NET) has been demonstrated to be relevant to a multitude of neurological, psychiatric and cardiovascular pathologies. Due to the wide range of possible applications for PET imaging of the NET together with the limitations of currently available radioligands, novel PET tracers for imaging of the cerebral NET with improved pharmacological and pharmacodynamic properties are needed.

Methods

The present study addresses the radiosynthesis and first preclinical evaluation of the novel NET PET tracer [¹¹C]Me@HAPTHI by describing its affinity, selectivity, metabolic stability, plasma free fraction, blood–brain barrier (BBB) penetration and binding behaviour in in vitro autoradiography.

Results

[¹¹C]Me@HAPTHI was prepared and displayed outstanding affinity and selectivity as well as excellent in vitro metabolic stability, and it is likely to penetrate the BBB. Moreover, selective NET binding in in vitro autoradiography was observed in human brain and rat heart tissue samples.

Conclusions

All preclinical results and radiosynthetic key-parameters indicate that the novel benzothiadiazole dioxide-based PET tracer [¹¹C]Me@HAPTHI is a feasible and improved NET radioligand and might prospectively facilitate clinical NET imaging.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0113-3) contains supplementary material, which is available to authorized users.

Economical synthesis of 13C-labeled opiates, cocaine derivatives and selected urinary metabolites by derivatization of the natural products

The illegal use of opiates and cocaine is a challenge world-wide, but some derivatives are also valuable pharmaceuticals. Reference samples of the active ingredients and their metabolites are needed both for controlling administration in the clinic and to detect drugs of abuse. Especially, ¹³C-labeled compounds are useful for identification and quantification purposes by mass spectroscopic techniques, potentially increasing accuracy by minimizing ion alteration/suppression effects. Thus, the synthesis of [acetyl-¹³C₄]heroin, [acetyl-¹³C₄-methyl-¹³C]heroin, [acetyl-¹³C₂-methyl-¹³C]6-acetylmorphine, [N-methyl-¹³C-O-metyl-¹³C]codeine and phenyl-¹³C₆-labeled derivatives of cocaine, benzoylecgonine, norcocaine and cocaethylene was undertaken to provide such reference materials. The synthetic work has focused on identifying ¹³C atom-efficient routes towards these derivatives. Therefore, the ¹³C-labeled opiates and cocaine derivatives were made from the corresponding natural products.

Synthesis and characterization of a iodine-125-labeled pyrrolo[1,2-a]thieno[3,2-e]pyrazine and evaluation as a potential 5-HT4R SPECT tracer

In the aim to find new radiotracers for the in vivo imaging of 5-HT(4) receptors by ultra-high resolution quantitative SPECT, we have developed the synthesis of a radioiodinated 5-HT(4) ligand using an iododestannylation procedure. The [(125)I]-ligand was obtained in a high radiochemical yield. Preliminary autoradiographic and ex vivo studies failed to show a specific labeling of 5-HT(4) receptors.

Design and synthesis of 2- and 3-substituted-3-phenylpropyl analogs of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine and 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine: role of amino, fluoro, hydroxyl, methoxyl, methyl, methylene, and oxo substituents on affinity for the dopamine and serotonin transporters

Novel derivatives of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909, 1) and 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935, 2) with various substituents in positions C2 and C3 of the phenylpropyl side chain were synthesized and evaluated for their ability to bind to the dopamine transporter (DAT) and the serotonin transporter (SERT). In the C2 series, the substituent in the S-configuration, with a lone-pair of electrons, significantly enhanced the affinity for DAT, whereas the steric effect of the substituent was detrimental to DAT binding affinity. In the C3 series, neither the lone electron pair nor the steric effect of the substituent seemed to affect DAT binding affinity, while sp (2) hybridized substituents had a detrimental effect on affinity for DAT. In the series, the 2-fluoro-substituted (S)-10 had the highest DAT binding affinity and good DAT selectivity, while the 2-amino-substituted (R)-8 showed essentially the same affinity for DAT and SERT. The oxygenated 16 and 18 possessed the best selectivity for DAT.

The promiscuity of the dopamine transporter: implications for the kinetic analysis of [3H]serotonin uptake in rat hippocampal and striatal synaptosomes

Evidence indicates that monoaminergic neurotransmitter transporters are promiscuous, transporting substrates other than their cognate neurotransmitters. For example, serotonin is transported by the dopamine transporter (DAT) under conditions in which serotonin transporter (SERT) activity is eliminated (e.g., pharmacological inhibition). We performed a kinetic analysis of [(3)H]serotonin uptake in rat striatal synaptosomes (expressing DAT and SERT) and hippocampal synaptosomes (expressing SERT, but not DAT). Nonspecific [(3)H]serotonin uptake was defined as the amount of uptake remaining in the presence of fluoxetine (10microM) or paroxetine (0.05microM). In hippocampal synaptosomes, K(m) and V(max) values for [(3)H]serotonin uptake did not differ whether fluoxetine or paroxetine was used to define nonspecific uptake. However, in striatal synaptosomes, both K(m) and V(max) values for [(3)H]serotonin uptake were greater when fluoxetine, rather than paroxetine, was used to define nonspecific uptake. These data suggest that, at the concentrations employed, fluoxetine inhibits serotonin uptake at both DAT and SERT, whereas paroxetine only inhibits serotonin uptake at SERT. Thus, when DAT is inhibited by GBR 12909, kinetic parameters for serotonin uptake via SERT in striatum are not different from those obtained in hippocampus. These findings have important implications regarding the analysis of monoaminergic reuptake in brain regions exhibiting heterogeneous transporter expression.

Synthesis and monoamine transporter affinity of front bridged tricyclic 3beta-(4'-halo or 4'-methyl)phenyltropanes bearing methylene or carbomethoxymethylene on the bridge to the 2beta-position

A series of front bridged tricyclic 3beta-(4'-halo or 4'-methyl)phenyltropanes bearing methylene or carbomethoxymethylene on the bridge to the 2beta-position was synthesized, and their binding affinities were determined in cells transfected to express human norepinephrine transporter (NET), serotonin transporter (SERT), and dopamine transporter (DAT) via competition binding assays. All compounds studied in this series exhibit a moderate to high potency at all three transporters with SERT or DAT selectivity. 3beta-(4'-iodo)phenyltropane bearing methylene on the bridge to the 2beta-position (24) presents a particularly attractive pharmacological profile, with very high SERT affinity (K(i) = 0.09 nM) and selectivity versus NET (65-fold) and DAT (94-fold).

Synthesis and monoamine transporter affinity of new 2β-carbomethoxy-3β-[aryl or heteroaryl]phenyltropanes

A series of 16 new 2beta-carbomethoxy-3beta-[aryl or heteroaryl]phenyltropane derivatives was synthesized and evaluated for binding to monoamine transporters. Most of the compounds exhibited nanomolar affinity for the serotonin transporter (SERT). Four compounds presented a particularly attractive pharmacological profile, with very high SERT affinity (K(i) 0.15-0.5 nM) and selectivity versus the dopamine transporter of 25- to 77-fold.

NAAG peptidase inhibitors and their potential for diagnosis and therapy

Modulation of N-acetyl-L-aspartyl-L-glutamate peptidase activity with small-molecule inhibitors holds promise for a wide variety of diseases that involve glutamatergic transmission, and has implications for the diagnosis and therapy of cancer. This new class of compounds, of which at least one has entered clinical trials and proven to be well tolerated, has demonstrated efficacy in experimental models of pain, schizophrenia, amyotrophic lateral sclerosis, traumatic brain injury and, when appropriately functionalized, can image prostate cancer. Further investigation of these promising drug candidates will be needed to bring them to the marketplace. The recent publication of the X-ray crystal structure for the enzymatic target of these compounds should facilitate the development of other new agents with enhanced activity that could improve both the diagnosis and treatment of neurological disorders.

Discovery of novel conformationally constrained tropane-based biaryl and arylacetylene ligands as potent and selective norepinephrine transporter inhibitors and potential antidepressants

To further explore the structure-activity relationships of conformationally constrained tropanes, a number of new biaryl and arylacetylene analogs were designed and synthesized. Some of these compounds such as 3a-b, 3d, 3f-h, 5b, and 7g were found to be highly potent and selective or mixed norepinephrine transporter (NET) inhibitors with Ki values of 0.8-9.4 nM. Moreover, all of these compounds display weak to extremely weak muscarinic receptor binding affinity, indicating that as potential antidepressants, they may overcome certain side effects that are of concern with other antidepressants, which are thought to be mediated by their anticholinergic properties.

Synthesis, receptor binding and functional studies of mesoridazine stereoisomers

The four stereoisomers of mesoridazine were synthesized and evaluated in D2, 5-HT1A, 5-HT2A, 5-HT2C, D1, and D3 receptor binding and functional assays. Two isomers demonstrated potent D2 receptor binding (Ki < 3 nM) and functional antagonism (IC50 < or = 10 nM) activities. These two isomers also showed moderate affinity for the 5-HT2A and D3 receptors. A third isomer was devoid of significant D2 receptor binding, but did have moderate affinity for the 5-HT2A and D3 receptors. The fourth isomer demonstrated poor affinity for all the receptors tested. Most significantly, the stereochemistry of the sulfoxide moiety played a dominant role in the observed structure-activity relationship (SAR).

Piperidine-based nocaine/modafinil hybrid ligands as highly potent monoamine transporter inhibitors: efficient drug discovery by rational lead hybridization

Some piperidine-based nocaine/modafinil hybrid ligands have been designed, synthesized, and found to display an improved potency at all three monoamine transporters and particularly for DAT and/or NET. Some highly active and selective monoamine transporter inhibitors with low nanomolar to subnanomolar potency were identified. Ligands of this type may find important applications as positron emission tomography imaging tools and in the treatment of central nervous system disorders such as depression and sleep apnea.

Synthesis and pharmacological evaluation of ( Z )-9-(Heteroarylmethylene)-7-azatricyclo[4.3.1.0 3,7 ]decanes: thiophene analogues as potent norepinephrine transporter inhibitors

To further explore the structure-activity relationships (SARs) of certain tropanes, and to gain insights into the structural features required for high activity and selectivity at norepinephrine transporters (NET), we have introduced both five- and six-membered heteroaromatic moieties such as substituted pyridyl, pyrazinyl, pyrimidyl, thiazolyl, and mono- or disubstituted thienyl groups into conformationally constrained, tricyclic tropane analogues. A number of (Z)-9-(heteroarylmethylene)-7-azatricyclo[4.3.1.0(3,7)]decanes were synthesized, and their abilities to block dopamine, serotonin, and norepinephrine reuptake by their respective transporters were evaluated. It was found that the five- or six-membered N-containing aromatics are too basic to display high NET activity, while some of the thiophene analogues were identified as potent and selective NET inhibitors.