Preclinical Studies on Nalfurafine (TRK-820), a Clinically Used KOR Agonist.

Nalfurafine has been used clinically in Japan for treatment of itch in kidney dialysis patients and in patients with chronic liver diseases. A one-year post-marketing study showed nalfurafine to be safe and efficacious without producing side effects of typical KOR agonists such as anhedonia and psychotomimesis. In this chapter, we summarize in vitro characterization and in vivo preclinical studies on nalfurafine. In vitro, nalfurafine is a highly potent and moderately selective KOR full agonist; however, whether it is a biased KOR agonist is a matter of debate. In animals, nalfurafine produced anti-pruritic effects in a dose range lower than that caused side effects, including conditioned place aversion (CPA), hypolocomotion, motor incoordination, consistent with the human data. In addition, nalfurafine showed antinociceptive effects in several pain models at doses that did not cause the side effects mentioned above. It appears to be effective against inflammatory pain and mechanical pain, but less so against thermal pain, particularly high-intensity thermal pain. U50,488H and nalfurafine differentially modulated several signaling pathways in a brain region-specific manners. Notably, U50,488H, but not nalfurafine, activated the mTOR pathway, which contributed to U50,488H-induced CPA. Because of its lack of side effects associated with typical KOR agonists, nalfurafine has been investigated as a combination therapy with an MOR ligand for pain treatment and for its effects on opioid use disorder and alcohol use disorder, and results indicate potential usefulness for these indications. Thus, although in vitro data regarding uniqueness of nalfurafine in terms of signaling at the KOR are somewhat equivocal, in vivo results support the assertion that nalfurafine is an atypical KOR agonist with a significantly improved side-effect profile relative to typical KOR agonists.

Preclinical Testing of Nalfurafine as an Opioid-sparing Adjuvant that Potentiates Analgesia by the Mu Opioid Receptor-targeting Agonist Morphine.

Mu opioid receptor (MOR)-targeting analgesics are efficacious pain treatments, but notorious for their abuse potential. In preclinical animal models, coadministration of traditional kappa opioid receptor (KOR)-targeting agonists with MOR-targeting analgesics can decrease reward and potentiate analgesia. However, traditional KOR-targeting agonists are well known for inducing antitherapeutic side effects (psychotomimesis, depression, anxiety, dysphoria). Recent data suggest that some functionally selective, or biased, KOR-targeting agonists might retain the therapeutic effects of KOR activation without inducing undesirable side effects. Nalfurafine, used safely in Japan since 2009 for uremic pruritus, is one such functionally selective KOR-targeting agonist. Here, we quantify the bias of nalfurafine and several other KOR agonists relative to an unbiased reference standard (U50,488) and show that nalfurafine and EOM-salvinorin-B demonstrate marked G protein-signaling bias. While nalfurafine (0.015 mg/kg) and EOM-salvinorin-B (1 mg/kg) produced spinal antinociception equivalent to 5 mg/kg U50,488, only nalfurafine significantly enhanced the supraspinal analgesic effect of 5 mg/kg morphine. In addition, 0.015 mg/kg nalfurafine did not produce significant conditioned place aversion, yet retained the ability to reduce morphine-induced conditioned place preference in C57BL/6J mice. Nalfurafine and EOM-salvinorin-B each produced robust inhibition of both spontaneous and morphine-stimulated locomotor behavior, suggesting a persistence of sedative effects when coadministered with morphine. Taken together, these findings suggest that nalfurafine produces analgesic augmentation, while also reducing opioid-induced reward with less risk of dysphoria. Thus, adjuvant administration of G protein-biased KOR agonists like nalfurafine may be beneficial in enhancing the therapeutic potential of MOR-targeting analgesics, such as morphine.

Single Nucleotide Polymorphisms in Chemosensory Pathway Genes GNB3, TAS2R19, and TAS2R38 Are Associated with Chronic Rhinosinusitis.

BACKGROUND: Chronic rhinosinusitis (CRS) is a multifaceted disease with a significant genetic component. The importance of taste receptor signaling has recently been highlighted in CRS; single nucleotide polymorphisms (SNPs) of bitter tastant-responsive G-protein-coupled receptors have been linked with CRS and with altered innate immune responses to multiple bacterially derived signals. OBJECTIVE: To determine in CRS the frequency of six SNPs in genes with known bitter tastant signaling function. METHODS: Genomic DNA was isolated from 74 CRS volunteers in West Virginia, and allele frequency was determined and compared with demographically matched data from the 1,000 Genomes database. RESULTS: For two SNPs in a gene recently associated with bitterant signaling regulation, RGS21, there were no associations with CRS (although the frequency of the minor allele of RGS21, rs7528947, was seen to increase with increasing Lund-Mackay CT staging score). Two TAS2R bitter taste receptor gene variants (TAS2R19 rs10772420 and TAS2R38 rs713598), identified in prior CRS genetics studies, were found to have similar associations in this study. CONCLUSION: Unique to our study is the establishment of an association between CRS in this patient population and GNB3 SNP rs5443, a variation in an established G protein component downstream of bitterant receptor signal transduction.

Development of Full Sweet, Umami, and Bitter Taste Responsiveness Requires Regulator of G protein Signaling-21 (RGS21).

The mammalian tastes of sweet, umami, and bitter are initiated by activation of G protein-coupled receptors (GPCRs) of the T1R and T2R families on taste receptor cells. GPCRs signal via nucleotide exchange and hydrolysis, the latter hastened by GTPase-accelerating proteins (GAPs) that include the Regulators of G protein Signaling (RGS) protein family. We previously reported that RGS21, uniquely expressed in Type II taste receptor cells, decreases the potency of bitter-stimulated T2R signaling in cultured cells, consistent with its in vitro GAP activity. However, the role of RGS21 in organismal responses to GPCR-mediated tastants was not established. Here, we characterized mice lacking the Rgs21 fifth exon. Eliminating Rgs21 expression had no effect on body mass accumulation (a measure of alimentation), fungiform papillae number and morphology, circumvallate papillae morphology, and taste bud number. Two-bottle preference tests, however, revealed that Rgs21-null mice have blunted aversion to quinine and denatonium, and blunted preference for monosodium glutamate, the sweeteners sucrose and SC45647, and (surprisingly) NaCl. Observed reductions in GPCR-mediated tastant responses upon Rgs21 loss are opposite to original expectations, given that loss of RGS21-a GPCR signaling negative regulator-should lead to increased responsiveness to tastant-mediated GPCR signaling (all else being equal). Yet, reduced organismal tastant responses are consistent with observations of reduced chorda tympani nerve recordings in Rgs21-null mice. Reduced tastant-mediated responses and behaviors exhibited by adult mice lacking Rgs21 expression since birth have thus revealed an underappreciated requirement for a GPCR GAP to establish the full character of tastant signaling.

Automated design of ligands to polypharmacological profiles.

The clinical efficacy and safety of a drug is determined by its activity profile across many proteins in the proteome. However, designing drugs with a specific multi-target profile is both complex and difficult. Therefore methods to design drugs rationally a priori against profiles of several proteins would have immense value in drug discovery. Here we describe a new approach for the automated design of ligands against profiles of multiple drug targets. The method is demonstrated by the evolution of an approved acetylcholinesterase inhibitor drug into brain-penetrable ligands with either specific polypharmacology or exquisite selectivity profiles for G-protein-coupled receptors. Overall, 800 ligand-target predictions of prospectively designed ligands were tested experimentally, of which 75% were confirmed to be correct. We also demonstrate target engagement in vivo. The approach can be a useful source of drug leads when multi-target profiles are required to achieve either selectivity over other drug targets or a desired polypharmacology.

Identification and Validation of Small Molecules That Enhance Recombinant Adeno-associated Virus Transduction following High-Throughput Screens.

UNLABELLED: While the recent success of adeno-associated virus (AAV)-mediated gene therapy in clinical trials is promising, challenges still face the widespread applicability of recombinant AAV(rAAV). A major goal is to enhance the transduction efficiency of vectors in order to achieve therapeutic levels of gene expression at a vector dose that is below the immunological response threshold. In an attempt to identify novel compounds that enhance rAAV transduction, we performed two high-throughput screens comprising 2,396 compounds. We identified 13 compounds that were capable of enhancing transduction, of which 12 demonstrated vector-specific effects and 1 could also enhance vector-independent transgene expression. Many of these compounds had similar properties and could be categorized into five groups: epipodophyllotoxins (group 1), inducers of DNA damage (group 2), effectors of epigenetic modification (group 3), anthracyclines (group 4), and proteasome inhibitors (group 5). We optimized dosing for the identified compounds in several immortalized human cell lines as well as normal diploid cells. We found that the group 1 epipodophyllotoxins (teniposide and etoposide) consistently produced the greatest transduction enhancement. We also explored transduction enhancement among single-stranded, self-complementary, and fragment vectors and found that the compounds could impact fragmented rAAV2 transduction to an even greater extent than single-stranded vectors. In vivo analysis of rAAV2 and all of the clinically relevant compounds revealed that, consistent with our in vitro results, teniposide exhibited the greatest level of transduction enhancement. Finally, we explored the capability of teniposide to enhance transduction of fragment vectors in vivo using an AAV8 capsid that is known to exhibit robust liver tropism. Consistent with our in vitro results, teniposide coadministration greatly enhanced fragmented rAAV8 transduction at 48 h and 8 days. This study provides a foundation based on the rAAV small-molecule screen methodology, which is ideally used for more-diverse libraries of compounds that can be tested for potentiating rAAV transduction. IMPORTANCE: This study seeks to enhance the capability of adeno-associated viral vectors for therapeutic gene delivery applicable to the treatment of diverse diseases. To do this, a comprehensive panel of FDA-approved drugs were tested in human cells and in animal models to determine if they increased adeno-associated virus gene delivery. The results demonstrate that particular groups of drugs enhance adeno-associated virus gene delivery by unknown mechanisms. In particular, the enhancement of gene delivery was approximately 50 to 100 times better with than without teniposide, a compound that is also used as chemotherapy for cancer. Collectively, these results highlight the potential for FDA-approved drug enhancement of adeno-associated virus gene therapy, which could result in safe and effective treatments for diverse acquired or genetic diseases.

Photochemical activation of TRPA1 channels in neurons and animals.

Optogenetics is a powerful research tool because it enables high-resolution optical control of neuronal activity. However, current optogenetic approaches are limited to transgenic systems expressing microbial opsins and other exogenous photoreceptors. Here, we identify optovin, a small molecule that enables repeated photoactivation of motor behaviors in wild-type zebrafish and mice. To our surprise, optovin's behavioral effects are not visually mediated. Rather, photodetection is performed by sensory neurons expressing the cation channel TRPA1. TRPA1 is both necessary and sufficient for the optovin response. Optovin activates human TRPA1 via structure-dependent photochemical reactions with redox-sensitive cysteine residues. In animals with severed spinal cords, optovin treatment enables control of motor activity in the paralyzed extremities by localized illumination. These studies identify a light-based strategy for controlling endogenous TRPA1 receptors in vivo, with potential clinical and research applications in nontransgenic animals, including humans.

Predicting new molecular targets for known drugs.

Although drugs are intended to be selective, at least some bind to several physiological targets, explaining side effects and efficacy. Because many drug-target combinations exist, it would be useful to explore possible interactions computationally. Here we compared 3,665 US Food and Drug Administration (FDA)-approved and investigational drugs against hundreds of targets, defining each target by its ligands. Chemical similarities between drugs and ligand sets predicted thousands of unanticipated associations. Thirty were tested experimentally, including the antagonism of the beta(1) receptor by the transporter inhibitor Prozac, the inhibition of the 5-hydroxytryptamine (5-HT) transporter by the ion channel drug Vadilex, and antagonism of the histamine H(4) receptor by the enzyme inhibitor Rescriptor. Overall, 23 new drug-target associations were confirmed, five of which were potent (<100 nM). The physiological relevance of one, the drug N,N-dimethyltryptamine (DMT) on serotonergic receptors, was confirmed in a knockout mouse. The chemical similarity approach is systematic and comprehensive, and may suggest side-effects and new indications for many drugs.

Identifying mechanism-of-action targets for drugs and probes.

Notwithstanding their key roles in therapy and as biological probes, 7% of approved drugs are purported to have no known primary target, and up to 18% lack a well-defined mechanism of action. Using a chemoinformatics approach, we sought to "de-orphanize" drugs that lack primary targets. Surprisingly, targets could be easily predicted for many: Whereas these targets were not known to us nor to the common databases, most could be confirmed by literature search, leaving only 13 Food and Drug Administration-approved drugs with unknown targets; the number of drugs without molecular targets likely is far fewer than reported. The number of worldwide drugs without reasonable molecular targets similarly dropped, from 352 (25%) to 44 (4%). Nevertheless, there remained at least seven drugs for which reasonable mechanism-of-action targets were unknown but could be predicted, including the antitussives clemastine, cloperastine, and nepinalone; the antiemetic benzquinamide; the muscle relaxant cyclobenzaprine; the analgesic nefopam; and the immunomodulator lobenzarit. For each, predicted targets were confirmed experimentally, with affinities within their physiological concentration ranges. Turning this question on its head, we next asked which drugs were specific enough to act as chemical probes. Over 100 drugs met the standard criteria for probes, and 40 did so by more stringent criteria. A chemical information approach to drug-target association can guide therapeutic development and reveal applications to probe biology, a focus of much current interest.

Role of the N-terminal region in G protein-coupled receptor functions: negative modulation revealed by 5-HT2B receptor polymorphisms.

The putative role of the N-terminal region of rhodopsin-like 7 transmembrane biogenic amine receptors in agonist-induced signaling has not yet been clarified despite recent advances in 7 transmembrane receptor structural biology. Given the existence of N-terminal nonsynonymous polymorphisms (R6G;E42G) within the HTR2B gene in a drug-abusing population, we assessed whether these polymorphisms affect 5-hydroxytryptamine 2B (5-HT2B) receptor in vitro pharmacologic and coupling properties in transfected COS-7 cells. Modification of the 5-HT2B receptor N terminus by the R6G;E42G polymorphisms increases such agonist signaling pathways as inositol phosphate accumulation as assessed by either classic or operational models. The N-terminal R6G;E42G mutations of the 5-HT2B receptor also increase cell proliferation and slow its desensitization kinetics compared with the wild-type receptor, further supporting a role for the N terminus in transduction efficacy. Furthermore, by coexpressing a tethered wild-type 5-HT2B receptor N terminus with a 5-HT2B receptor bearing a N-terminal deletion, we were able to restore original coupling. This reversion to normal activity of a truncated 5-HT2B receptor by coexpression of the membrane-tethered wild-type 5-HT2B receptor N terminus was not observed using a membrane-tethered 5-HT2B receptor R6G;E42G N terminus. These data suggest that the N terminus exerts a negative control over basal as well as agonist-stimulated receptor activity that is lost in the R6G;E42G mutant. Our findings reveal a new and unanticipated role of the 5-HT2B receptor N terminus as a negative modulator, affecting both constitutive and agonist-stimulated activity. Moreover, our data caution against excluding the N terminus and extracellular loops in structural studies of this 7 transmembrane receptor family.

Further evaluation of the tropane analogs of haloperidol.

Previous work from our labs has indicated that a tropane analog of haloperidol with potent D2 binding but designed to avoid the formation of MPP(+)-like metabolites, such as 4-(4-chlorophenyl)-1-(4-(4-fluorophenyl)-4-oxobutyl)pyridin-1-ium (BCPP(+)) still produced catalepsy, suggesting a strong role for the D2 receptor in the production of catalepsy in rats, and hence EPS in humans. This study tested the hypothesis that further modifications of the tropane analog to produce compounds with less potent binding to the D2 receptor than haloperidol, would produce less catalepsy. These tests have now revealed that while haloperidol produced maximum catalepsy, these compounds produced moderate to low levels of catalepsy. Compound 9, with the least binding affinity to the D2R, produced the least catalepsy and highest Minimum Adverse Effective Dose (MAED) of the analogs tested regardless of their affinities at other receptors including the 5-HT1AR. These observations support the hypothesis that moderation of the D2 binding of the tropane analogs could reduce catalepsy potential in rats and consequently EPS in man.

Identification of a new selective dopamine D4 receptor ligand.

The dopamine D4 receptor has been shown to play key roles in certain CNS pathologies including addiction to cigarette smoking. Thus, selective D4 ligands may be useful in treating some of these conditions. Previous studies in our laboratory have indicated that the piperazine analog of haloperidol exhibits selective and increased affinity to the DAD4 receptor subtype, in comparison to its piperidine analog. This led to further exploration of the piperazine moiety to identify new agents that are selective at the D4 receptor. Compound 27 (KiD4=0.84 nM) was the most potent of the compounds tested. However, it only had moderate selectivity for the D4 receptor. Compound 28 (KiD4=3.9 nM) while not as potent, was more discriminatory for the D4 receptor subtype. In fact, compound 28 has little or no binding affinity to any of the other four DA receptor subtypes. In addition, of the 23 CNS receptors evaluated, only two, 5HT1AR and 5HT2BR, have binding affinity constants better than 100 nM (Ki <100 nM). Compound 28 is a potentially useful D4-selective ligand for probing disease treatments involving the D4 receptor, such as assisting smoking cessation, reversing cognitive deficits in schizophrenia and treating erectile dysfunction. Thus, further optimization, functional characterization and evaluation in animal models may be warranted.

Synthesis and receptor profiling of Stemona alkaloid analogues reveal a potent class of sigma ligands.

Reported biological activities of Stemona natural products, such as antitussive activity, inspired the development of synthetic methods to access several alkaloids within this family and in so doing develop a general route to the core skeleta shared by the class of natural products. The chemistry was subsequently adapted to afford a series of analogue sets bearing simplified, diverse Stemona-inspired skeleta. Over 100 of these analogues were subjected to general G protein-coupled receptor profiling along with the known antitussive compound, neostenine; this led to the identification of hit compounds targeting several receptor types. The particularly rich hit subset for sigma receptors was expanded with two focused library sets, which resulted in the discovery of a fully synthetic, potent chemotype of sigma ligands. This collaborative effort combined the development of synthetic methods with extensive, flexible screening resources and exemplifies the role of natural products in bioactivity mining.

Discovery of ß-arrestin-biased dopamine D2 ligands for probing signal transduction pathways essential for antipsychotic efficacy.

Elucidating the key signal transduction pathways essential for both antipsychotic efficacy and side-effect profiles is essential for developing safer and more effective therapies. Recent work has highlighted noncanonical modes of dopamine D(2) receptor (D(2)R) signaling via ß-arrestins as being important for the therapeutic actions of both antipsychotic and antimanic agents. We thus sought to create unique D(2)R agonists that display signaling bias via ß-arrestin-ergic signaling. Through a robust diversity-oriented modification of the scaffold represented by aripiprazole (1), we discovered UNC9975 (2), UNC0006 (3), and UNC9994 (4) as unprecedented ß-arrestin-biased D(2)R ligands. These compounds also represent unprecedented ß-arrestin-biased ligands for a G(i)-coupled G protein-coupled receptor (GPCR). Significantly, UNC9975, UNC0006, and UNC9994 are simultaneously antagonists of G(i)-regulated cAMP production and partial agonists for D(2)R/ß-arrestin-2 interactions. Importantly, UNC9975 displayed potent antipsychotic-like activity without inducing motoric side effects in inbred C57BL/6 mice in vivo. Genetic deletion of ß-arrestin-2 simultaneously attenuated the antipsychotic actions of UNC9975 and transformed it into a typical antipsychotic drug with a high propensity to induce catalepsy. Similarly, the antipsychotic-like activity displayed by UNC9994, an extremely ß-arrestin-biased D(2)R agonist, in wild-type mice was completely abolished in ß-arrestin-2 knockout mice. Taken together, our results suggest that ß-arrestin signaling and recruitment can be simultaneously a significant contributor to antipsychotic efficacy and protective against motoric side effects. These functionally selective, ß-arrestin-biased D(2)R ligands represent valuable chemical probes for further investigations of D(2)R signaling in health and disease.

Molecular and circuit determinants in the globus pallidus mediating control of cocaine-induced behavioral plasticity.

The globus pallidus externus (GPe) is a central component of the basal ganglia circuit, receiving strong input from the indirect pathway and regulating a variety of functions, including locomotor output and habit formation. We recently showed that it also acts as a gatekeeper of cocaine-induced behavioral plasticity, as inhibition of parvalbumin-positive cells in the GPe (GPe PV ) prevents the development of cocaine-induced reward and sensitization. However, the molecular and circuit mechanisms underlying this function are unknown. Here we show that GPe PV cells control cocaine reward and sensitization by inhibiting GABAergic neurons in the substantia nigra pars reticulata (SNr GABA ), and ultimately, selectively modulating the activity of ventral tegmental area dopamine (VTA DA ) cells projecting to the lateral shell of the nucleus accumbens (NAcLat). A major input to GPe PV cells is the indirect pathway of the dorsomedial striatum (DMS D 2 ), which receives DAergic innervation from collaterals of VTA DA →NAcLat cells, making this a closed-loop circuit. Cocaine likely facilitates reward and sensitization not directly through actions in the GPe, but rather in the upstream DMS, where the cocaine-induced elevation of DA triggers a depression in DMS D 2 cell activity. This cocaine-induced elevation in DA levels can be blocked by inhibition of GPe PV cells, closing the loop. Interestingly, the level of GPe PV cell activity prior to cocaine administration is correlated with the extent of reward and sensitization that animals experience in response to future administration of cocaine, indicating that GPe PV cell activity is a key predictor of future behavioral responses to cocaine. Single nucleus RNA-sequencing of GPe cells indicated that genes encoding voltage-gated potassium channels KCNQ3 and KCNQ5 that control intrinsic cellular excitability are downregulated in GPe PV cells following a single cocaine exposure, contributing to the elevation in GPe PV cell excitability. Acutely activating channels containing KCNQ3 and/or KCNQ5 using the small molecule carnosic acid, a key psychoactive component of Salvia rosmarinus (rosemary) extract, reduced GPe PV cell excitability and also impaired cocaine reward, sensitization, and volitional cocaine intake, indicating its potential as a therapeutic to counteract psychostimulant use disorder. Our findings illuminate the molecular and circuit mechanisms by which the GPe orchestrates brain-wide changes in response to cocaine that are required for reward, sensitization, and self-administration behaviors.

Ligand discovery from a dopamine D3 receptor homology model and crystal structure.

G protein-coupled receptors (GPCRs) are intensely studied as drug targets and for their role in signaling. With the determination of the first crystal structures, interest in structure-based ligand discovery increased. Unfortunately, for most GPCRs no experimental structures are available. The determination of the D(3) receptor structure and the challenge to the community to predict it enabled a fully prospective comparison of ligand discovery from a modeled structure versus that of the subsequently released crystal structure. Over 3.3 million molecules were docked against a homology model, and 26 of the highest ranking were tested for binding. Six had affinities ranging from 0.2 to 3.1 µM. Subsequently, the crystal structure was released and the docking screen repeated. Of the 25 compounds selected, five had affinities ranging from 0.3 to 3.0 µM. One of the new ligands from the homology model screen was optimized for affinity to 81 nM. The feasibility of docking screens against modeled GPCRs more generally is considered.

Chemical informatics and target identification in a zebrafish phenotypic screen.

Target identification is a core challenge in chemical genetics. Here we use chemical similarity to computationally predict the targets of 586 compounds that were active in a zebrafish behavioral assay. Among 20 predictions tested, 11 compounds had activities ranging from 1 nM to 10,000 nM on the predicted targets. The roles of two of these targets were tested in the original zebrafish phenotype. Prediction of targets from chemotype is rapid and may be generally applicable.

An analysis of the synthetic tryptamines AMT and 5-MeO-DALT: emerging 'Novel Psychoactive Drugs'.

Novel Psychoactive Drugs (NPD) can be sold without restriction and are often synthetic analogues of controlled drugs. The tryptamines are an important class of NPD as they bind to the various serotonin (5-HT) receptor subtypes and cause psychosis and hallucinations that can lead to injury or death through misadventure. Here we report on the structure elucidation and receptor binding profiles of two widely marketed tryptamine-derived NPDs, namely alpha-methyl-tryptamine and 5-methoxy-N,N-diallyl-tryptamine.

5-HT(2B) antagonism arrests non-canonical TGF-ß1-induced valvular myofibroblast differentiation.

Transforming growth factor-ß1 (TGF-ß1) induces myofibroblast activation of quiescent aortic valve interstitial cells (AVICs), a differentiation process implicated in calcific aortic valve disease (CAVD). The ubiquity of TGF-ß1 signaling makes it difficult to target in a tissue specific manner; however, the serotonin 2B receptor (5-HT(2B)) is highly localized to cardiopulmonary tissues and agonism of this receptor displays pro-fibrotic effects in a TGF-ß1-dependent manner. Therefore, we hypothesized that antagonism of 5-HT(2B) opposes TGF-ß1-induced pathologic differentiation of AVICs and may offer a druggable target to prevent CAVD. To test this hypothesis, we assessed the interaction of 5-HT(2B) antagonism with canonical and non-canonical TGF-ß1 pathways to inhibit TGF-ß1-induced activation of isolated porcine AVICs in vitro. Here we show that AVIC activation and subsequent calcific nodule formation is completely mitigated by 5-HT(2B) antagonism. Interestingly, 5-HT(2B) antagonism does not inhibit canonical TGF-ß1 signaling as identified by Smad3 phosphorylation and activation of a partial plasminogen activator inhibitor-1 promoter (PAI-1, a transcriptional target of Smad3), but prevents non-canonical p38 MAPK phosphorylation. It was initially suspected that 5-HT(2B) antagonism prevents Src tyrosine kinase phosphorylation; however, we found that this is not the case and time-lapse microscopy indicates that 5-HT(2B) antagonism prevents non-canonical TGF-ß1 signaling by physically arresting Src tyrosine kinase. This study demonstrates the necessity of non-canonical TGF-ß1 signaling in leading to pathologic AVIC differentiation. Moreover, we believe that the results of this study suggest 5-HT(2B) antagonism as a novel therapeutic approach for CAVD that merits further investigation.

Moderate chemical modifications of WAY-100635 improve the selectivity for 5-HT1A versus D4 receptors.

The selectivity for 5-HT(1A) versus D(4) receptors is significantly increased when the basic side chain of WAY-100635 is replaced by a 4-phenylpiperazine (3e) or a 4-phenyl-1,2,3,6-tetrahydropyridine moiety (3i). The 4-phenyl-1,2,3,6-tetrahydropyridine compounds (3i-l) have a higher affinity for 5-HT(1A) receptors than do the corresponding unsubstituted phenylpiperazine analogues (3e-h). Compounds 3e and 3i appear to be selective for 5-HT(1A) receptors over other relevant receptors and still behave as neutral antagonists.