Since its discovery in the 1940s in serum, the mammalian intestinal mucosa, and in the central nervous system, serotonin (5-HT) has been shown to be involved in virtually all cognitive and behavioral human functions, and alterations in its neurochemistry have been implicated in the etiology of a plethora of neuropsychiatric disorders. The cloning of 5-HT receptor subtypes has been of importance in enabling them to be classified as specific protein molecules encoded by specific genes. The 5-HT7 receptor is the most recently classified member of the serotonin receptor family. Since its identification, it has been the subject of intense research efforts driven by its presence in functionally relevant regions of the brain. The availability of some selective antagonists and agonists, in combination with genetically modified mice lacking the 5-HT7 receptor, has allowed for a better understanding of the pathophysiological role of this receptor. This paper reviews data on localization and pharmacological properties of the 5-HT7 receptor, and summarizes the results of structure-activity relationship studies aimed at the discovery of selective 5-HT7 receptor ligands. Additionally, an overview of the potential therapeutic applications of 5-HT7 receptor agonists and antagonists in central nervous system disorders is presented.

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To establish the activity of sigma ligands at sigma1 and sigma2 receptor, we chose two tumour cell lines, the human SK-N-SH neuroblastoma and the rat C6 glioma lines, which express sigma2 receptors at a high density and sigma1 receptors in their high-affinity or low-affinity state. We tested the sigma2 receptor agonist PB28 and the sigma2 antagonist AC927, and (+)-pentazocine and NE100 as agonist and antagonist, respectively, at sigma1 receptors, with regard to antiproliferative and cytotoxic effects. In addition, 1,3-di(2-tolyl)guanidine (DTG) and haloperidol were tested as reference compounds displaying nearly equipotent sigma affinity (sigma2>sigma1 and sigma1>sigma2, respectively). In both SK-N-SH and C6 cells, PB28 and NE100 displayed the most potent results both in antiproliferative and cytotoxic assay while AC927 and (+)-pentazocine were inactive in both assays. The cytotoxic and antiproliferative effects of DTG and haloperidol reflected their sigma1 antagonist activity and sigma2 agonist activity. Moreover, our results in the tumour cell lines correlated well with those for sigma2 activity found previously in a functional assay in the guinea-pig bladder. These findings establish a new model for evaluating both sigma2 and sigma1 receptor activity of sigma ligands, which could be useful for developing new ligands having mixed sigma2 agonist/sigma1 antagonist activity as potential antineoplastic agents.

S Ligands have recently been shown to have cytotoxic activity, to induce ceramide-dependent/caspase-independent apoptosis, and to down-regulate P-glycoprotein (P-gp) mRNA levels in some mouse and human models. In this study, we verified whether a mixed S 2 agonist/S 1 antagonist, PB28, was able to have antitumor activity and to enhance anthracycline efficacy in two human breast cancer cell lines, MCF7 and MCF7 ADR, both characterized by significant S 2 receptor expression, by high and low S 1 receptor expression, and low and high P-gp expression, respectively. In both cell lines, PB28 showed high S 2 receptor affinity and low S 1 receptor affinity; furthermore, it inhibited cell growth with a clear effect at 48 hours (IC 50 in nanomolar range), a consistent time exposure-independent increase of G 0 -G 1 -phase fraction (of f20% of both cell lines) and caspase-independent apoptosis (15% increased after 1-day drug exposure). PB28 also reduced P-gp expression in a concentration-and time-dependent manner (f60% in MCF7 and 90% in MCF7 ADR). We showed also a strong synergism between PB28 and doxorubicin by adopting either simultaneous or sequential schedules of the two drugs. We suggest that this synergism could depend on PB28-induced increase of intracellular accumulation of doxorubicin (f50% in MCF7 and 75% in MCF7 ADR by flow cytometry analysis). In conclusion, we suggest that the S 2 agonist PB28 could be an interesting antitumor agent either in monotherapy or in combination with conventional drugs.

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Several 1-cyclohexylpiperazine derivatives related to sigma(2) receptor ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (33, K(i) = 0.34 nM) were synthesized and tested in radioligand binding assays, to attempt a structure-affinity relationship study. Intermediate alkyl chain length and methoxyl group position on the tetralin nucleus were varied. A few naphthalene analogues were also prepared. High affinities were found in sigma(2) receptor binding for almost all compounds, some of which displayed K(i) values in subnanomolar range, but low sigma(2)/sigma(1) selectivities were found. The highest sigma(2) affinities were displayed by compounds with an intermediate alkyl chain of three (32 and 43) or five methylenes (39 and 46). Quite high sigma(1) receptor affinity was found for compounds with a four-methylene chain; 36 (K(i) = 0.036 nM) and 45 (K(i) = 0.22 nM) displaying good sigma(1)/sigma(2) selectivity (406- and 139-fold, respectively). Moreover, homologues of compound 33 displayed also satisfactory selectivities over dopamine D(2)-like, serotonin 5-HT(3), and adrenergic alpha(1) receptors. These compounds and a few others were tested in the inhibition of the electrically evoked contractions in guinea pig bladder and were demonstrated to be full sigma(2) agonists. The activity values correlated well to the affinity scale (EC(50) in microM range). 33 and related compounds are proposed as a class of potential antineoplastic and PET diagnosis agents.

A new model of 4-alkyl-1-arylpiperazines containing a terminal dihydronaphthalene fragment on the alkyl chain was synthesized in order to have mixed serotonergic and dopaminergic activity and to pursue the recent alternative approaches to the discovery of novel antipsychotic and anxiolytic agents. Title compounds were evaluated for in vitro activity on dopamine D-2 and serotonin ~-H T~A and 5-HTz receptors by radioreceptor binding assays. They show high nanomolar affiiity for ~-H T~A , moderate affinity for D-2, and low affinity for 5-HTz receptors, and in particular, two compounds, 4-[3-( 1,2-dihydro-6-methoxynaphthalen-4-yl)-n-propyll-1-(2-methoxyphenyl)piperazine (8) and 4-[3-( 1,2-dihydro-8-methoxynaphthalen-4-yl)-n-propyll-l-(2-pyridyl)piperazine (E), show values (nM) of ICs0 = 2.0 and 1.4 for ~-H T~A and ICs0 = 90.6 and 119.3 for D-2, respectively.Some in vivo behavioral studies show compound 8 to be an antagonist on ~-H T~A receptors. These first findings place the new arylpiperazines on the same level as that of the azaspirone class, e.g., and buspirone. 1-(2-methoxypheny1)-4-[4-(2-phthalimido)-n-butyl]piperazineCommon chlorpromazine-like antipsychotic drugs produce extrapyramidal symptoms (EPS), while antianxiety agents, such as benzodiazepines, present ataxia, sedative phenomena, and signs of drug dependence as side effects.Recent observationslJ indicate that improvement of these agents may be attained by combining dopaminergic and serotonergic activities in a single structure. Indeed, at the moment, there is considerable interest in molecules with multireceptorial activity3 as novel antipsychotic agents of potential clinical significance.Within this context, examples of compounds having both D-2 and 5-HTz receptor antagonist properties are setoperone4 and risperidone:b which have been evaluated in clinical trials, as well as new molecules which are predicted to be efficacious against negative symptoms of schizophrenia and to have fewer EPS.' Another example of an atypical neuroleptic drug with reduced side effects is clozapine which, in addition to acting on a specific subclass of dopamine receptors,8 interacts with significant affinity on a broad range of receptor types (serotonergic, adrenergic, muscarinic, a n d histaminergic).B-12Formerly, in our laboratories, we have synthesized compounds such as the l-aminoethylheterotetralin13J4 derivatives 1, which show no affinity for dopaminergic and serotonergic receptors, although they are open derivatives of active cyclic structures on DA and 5-HT receptors.In order to achieve this dual affinity for these receptors, we inserted the terminal nitrogen of the side chain of compounds 1 in an arylpiperazine structure. During the last decade, the arylpiperazine moiety has shown to be one of the templates for 5-HT activity,16 but minor Abstract published in Advance ACS Abstracts, December 15,1993. 1 : R --NE-2 : R --N 7 L N -Aryl modifications involve significant changes in affinity and selectivity, since it can also display moderate to high affinity for DA rece...

Several 4-alkyl-1-arylpiperazines that present a tetralin moiety on the terminal part of the side chain were synthesized in order to increase the selectivity on the 5-HT1A versus D-2, alpha 1, sigma, and other 5-HT receptors. Many changes have been effected on previous structures of type 3(1-aryl-4-[3-(1,2-dihydronaphthalen-4-yl)-n-propyl]piperazines). Several synthetic procedures were followed to obtain the final products, depending on the presence or absence of a double bond, as well as of a heteroatom on the side chain. In the first case versatile use of Grignard reaction was made, whereas in the second one usual synthetic ways were applied. Final compounds were evaluated for in vitro activity on dopamine D-1 and D-2, serotonin 5-HT1A, 5-HT1B, 5-HT1C, and 5-HT2, alpha 1 adrenergic, and sigma receptors by radioreceptor binding assay. For the 2-MeO-Ph, 2-pyridyl, and unsubstituted phenyl N-piperazine derivatives, low IC50 values (0.3 nM) on 5-HT1A receptors and high selectivity values were observed.