Search for alpha 1-adrenoceptor subtypes selective antagonists: design, synthesis and biological activity of cystazosin, an alpha 1D-adrenoceptor antagonist

Prazosin addition to fluvoxamine: A preclinical study and open clinical trial in OCD

The efficacy of selective serotonin reuptake inhibitors (SRIs) in psychiatric disorders may be "augmented" through the addition of atypical antipsychotic drugs. A synergistic increase in dopamine (DA) release in the prefrontal cortex has been suggested to underlie this augmentation effect, though the mechanism of action is not clear yet. We used in vivo microdialysis in rats to study DA release following the administration of combinations of fluvoxamine (10 mg/kg) and quetiapine (10 mg/kg) with various monoamine-related drugs. The results confirmed that the selective 5-HT1A antagonist WAY-100635 (0.05 mg/kg) partially blocked the fluvoxamine-quetiapine synergistic effect (maximum DA increase dropped from 325% to 214%). A novel finding is that the α1-adrenergic blocker prazosin (1 mg/kg), combined with fluvoxamine, partially mimicked the effect of augmentation (maximum DA increase 205%; area-under-the-curve 163%). As this suggested that prazosin augmentation might be tested in a clinical study, we performed an open clinical trial of prazosin 20 mg addition to SRI in therapy-resistant patients with obsessive-compulsive disorder applying for neurosurgery. A small, non-significant reduction in Yale Brown Obsessive Compulsive Scale (Y-BOCS) scores was observed in 10 patients and one patient was classified as a responder with a reduction in Y-BOCS scores of more than 25%. We suggest that future clinical studies augmenting SRIs with an α1-adrenergic blocker in less treatment resistant cases should be considered. The clinical trial "Prazosin in combination with a serotonin reuptake inhibitor for patients with Obsessive Compulsive disorder: an open label study" was registered at 24/05/2011 under trial number ISRCTN61562706: http://www.controlled-trials.com/ISRCTN61562706.

6-methoxy-7-benzofuranoxy and 6-methoxy-7-indolyloxy analogues of 2-[2-(2,6-Dimethoxyphenoxy)ethyl]aminomethyl-1,4-benzodioxane (WB4101):1 discovery of a potent and selective α1D-adrenoceptor antagonist

Previous results have shown that replacement of one of the two o-methoxy groups at the phenoxy residue of the potent, but not subtype-selective, α1-AR antagonist (S)-WB4101 [(S)-1] by phenyl, or by ortho,meta-fused cyclohexane, or especially by ortho,meta-fused benzene preferentially elicits α1D-AR antagonist affinity. Such observations inspired the design of four new analogues of 1 bearing, in lieu of the 2,6-dimethoxyphenoxy residue, a 6-methoxy-substituted 7-benzofuranoxy or 7-indolyloxy group or, alternatively, their corresponding 2,3-dihydro form. Of these new compounds, which maintain, rigidified, the characteristic ortho heterodisubstituted phenoxy substructure of 1, the S enantiomer of the dihydrobenzofuranoxy derivative exhibited the highest α1D-AR antagonist affinity (pA2 9.58) with significant α1D/α1A and α1D/α1B selectivity. In addition, compared both to α1D-AR antagonists structurally related to 1 and to the well-known α1D-AR antagonist BMY7378, this derivative had modest 5-HT1A affinity and neutral α1-AR antagonist behavior.

Advances in the design and synthesis of prazosin derivatives over the last ten years

INTRODUCTION

Mechanistic, translational and pharmacological studies led to the identification and discovery of the preferred localization, binding characteristics, structure and functional properties of α1-adrenoceptor (α1-AR) subtypes in the bladder neck, bladder and prostate gland. The evidence gathered on α1-ARs, provided a molecular platform for the development of subtype-selective antagonists, resulting in more effective approaches targeting those receptors for the treatment of outlet bladder obstruction and benign prostate hyperplasia.

AREAS COVERED

Advances over the last decade in the design and optimization of Prazosin, Doxazosin and Terazosin quinazoline-based derivatives as α1-AR antagonists. Evidence on the metabolic and growth interference action by these agents, in addition to their smooth-muscle-relaxing effects. The new action recognition emerges from data on the inhibitory effect of quinazoline-based antagonists on primary tumor growth and progression to metastasis. In addition to the cellular findings in the prostate, functional validation and therapeutic effects of selected lead pharmaceutically optimized derivatives in the context of impairing vascularity and triggering tumor apoptosis.

EXPERT OPINION

Knowledge on targeting intracellular signalling pathways driving the cellular response via an α1-AR-dependent and independent antagonistic action, must be invested towards the optimization of new agents that while bypassing AR, exhibit improved pharmacological efficacy against human cancer.

Potent cardioprotective effect of the 4-anilinoquinazoline derivative PD153035: involvement of mitochondrial K(ATP) channel activation

Background

The aim of the present study was to evaluate the protective effects of the 4-anilinoquinazoline derivative PD153035 on cardiac ischemia/reperfusion and mitochondrial function.

Methodology/Principal Findings

Perfused rat hearts and cardiac HL-1 cells were used to determine cardioprotective effects of PD153035. Isolated rat heart mitochondria were studied to uncover mechanisms of cardioprotection. Nanomolar doses of PD153035 strongly protect against heart and cardiomyocyte damage induced by ischemia/reperfusion and cyanide/aglycemia. PD153035 did not alter oxidative phosphorylation, nor directly prevent Ca²⁺ induced mitochondrial membrane permeability transition. The protective effect of PD153035 on HL-1 cells was also independent of AKT phosphorylation state. Interestingly, PD153035 activated K⁺ transport in isolated mitochondria, in a manner prevented by ATP and 5-hydroxydecanoate, inhibitors of mitochondrial ATP-sensitive K⁺ channels (mitoK_ATP). 5-Hydroxydecanoate also inhibited the cardioprotective effect of PD153035 in cardiac HL-1 cells, demonstrating that this protection is dependent on mitoK_ATP activation.

Conclusions/Significance

We conclude that PD153035 is a potent cardioprotective compound and acts in a mechanism involving mitoK_ATP activation.

Synthesis and Structure−Activity Relationship of Fluoro Analogues of 8-{2-[4-(4-Methoxyphenyl)piperazin-1yl]ethyl}-8-azaspiro[4.5]decane-7,9-dione as Selective α1d-Adrenergic Receptor Antagonists

We have discovered high-affinity antagonists (exemplified by 11 and 12) that are the most selective for alpha(1d)-adrenergic receptors (alpha(1d)-AR) reported to date. In cloned receptor assay systems, 12 displays at least 95-fold selectivity for the alpha(1d)-AR over all other G-protein-coupled receptors tested, and the subtype selectivity of 11 was confirmed in pharmacologically defined isolated tissue preparations.

Prediction of selectivity of α1-adrenergic antagonists by counterpropagation neural network (CP-ANN)

A quantitative structure-selectivity relationships of series of structurally diverse alpha1-adrenergic antagonists was performed by using counter-propagation neural network (CP-ANN). The theoretical molecular descriptors have been calculated and selected using CODESSA program. The results obtained for a highly non-congeneric set of molecules have confirmed the potential of use of CP-ANN approach in prediction of relative activity (selectivity) of alpha1-adrenergic antagonists.

Prazosin-Related Compounds. Effect of Transforming the Piperazinylquinazoline Moiety into an Aminomethyltetrahydroacridine System on the Affinity for α1-Adrenoreceptors

In a search for structurally new alpha(1)-adrenoreceptor (alpha(1)-AR) antagonists, prazosin (1)-related compounds 2-11 were synthesized and their affinity profiles were assessed by functional experiments in isolated rat vas deferens (alpha(1A)), spleen (alpha(1B)), and aorta (alpha(1D)) and by binding assays in CHO cells expressing human cloned alpha(1)-AR subtypes. Transformation of the piperazinylquinazoline moiety of 1 into an aminomethyltetrahydroacridine system afforded compound 2, endowed with reduced affinity, in particular for the alpha(1A)-AR subtype. Then, to investigate the optimal features of the tricyclic moiety, the aliphatic ring of 2 was modified by synthesizing the lower and higher homologues 3 and 4. An analysis of the pharmacological profile, together with a molecular modeling study, indicated the tetrahydroacridine moiety as the most promising skeleton for alpha(1)-antagonism. Compounds 5-8, where the replacement of the furoyl group of 2 with a benzoyl moiety afforded the possibility to evaluate the effect of the substituent trifluoromethyl on receptor binding, resulted, except for 7, in a rather surprising selectivity toward alpha(1B)-AR, in particular vs the alpha(1A) subtype. Also the insertion of the 2,6-dimethoxyphenoxyethyl function of WB 4101 on the tetrahydroacridine skeleton of 2, and/or the replacement of the aromatic amino function with a hydroxy group, affording derivatives 9-11, resulted in alpha(1B)-AR selectivity also vs the alpha(1D) subtype. On the basis of these results, the tetrahydroacridine moiety emerged as a promising tool for the characterization of the alpha(1)-AR, owing to the receptor subtype selectivity achieved by an appropriate modification of the lateral substituents.

(+/-)-Domesticine, a novel and selective alpha1D-adrenoceptor antagonist in animal tissues and human alpha 1-adrenoceptors

The pharmacological profile of (+/-)-domesticine, a novel alpha(1)-adrenoceptor antagonist, was examined in animal tissues and Chinese hamster ovary (CHO) cells expressing cloned human alpha(1)-adrenoceptor subtypes and compared with the properties of BMY-7378 ([8-(2-[4-(2-methoxy-phenyl)-1-piperazinyl]ethyl)-8-azaspirol [4.5]decane-7,9-dione dihydrochloride], the prototypical alpha(1D)-adrenoceptor antagonist. Both (+/-)-domesticine and BMY-7378 were more potent in inhibiting the phenylephrine-induced contraction in rat thoracic aorta than tail artery or spleen. The selectivity of (+/-)-domesticine to inhibit phenylephrine-induced contraction in rat thoracic aorta was 32- and 17-fold higher than that in tail artery and spleen, respectively, while that of BMY-7378 it was 125- and 11-fold, respectively. The functional affinity profiles of these compounds for the alpha(1)-adrenoceptor subtypes in animal tissues were consistent with the respective binding affinity profiles in cloned human alpha(1)-adrenoceptor subtypes. (+/-)-Domesticine displayed a 34- and 9-fold higher selectivity for alpha(1d)-adrenoceptor than for alpha(1a)- and alpha(1b)-adrenoceptor, respectively, while BMY-7378 showed a selectivity for alpha(1d)-adrenoceptor of 102-fold higher than that of alpha(1a)-adrenoceptor and 21-fold higher than that of alpha(1b)-adrenoceptor. Interestingly, in [3H]8-OH-DPAT (8-hidroxy-2-(di-n-propyl-amino)tetraline hidrobromide) binding to 5-HT(1A) receptors of rat cerebral cortex, (+/-)-domesticine showed a 183-fold higher selectivity for alpha(1D)-adrenoceptor relative to 5-HT(1A) receptor, whereas BMY-7378 displayed a similar affinity at this receptor with respect to the alpha(1D)-adrenoceptor (0.89-fold). Both compounds, however, showed a weak affinity for 5-HT(2A)/5-HT(2C) receptors in rat frontal cortex. These results suggest that (+/-)-domesticine is more potent for alpha(1D)-adrenoceptor than for alpha(1A)- or alpha(1B)-adrenoceptor subtypes and it is highly selective compared to 5-HT(1A) and other receptors.

Analogues of prazosin that bear a benextramine-related polyamine backbone exhibit different antagonism toward alpha1-adrenoreceptor subtypes

Hybrid tetraaamine disulfides 4-9 were synthesized by combining the structural features of prazosin (1), a competitive alpha1-adrenoreceptor antagonist, and benextramine (2), an irreversible alpha1/alpha2-adrenoreceptor antagonist, and their biological profiles at alpha1-adrenoreceptor subtypes were assessed by functional experiments in isolated rat vas deferens (alpha1A), spleen (alpha1B), and aorta (alpha1D). To verify the role of the disulfide moiety on the interaction with alpha1-adrenoreceptor subtypes, carbon analogues 10-15 were included in this study. All quinazolines lacking the disulfide bridge behaved, like 1, as competitive antagonists, whereas all polyamine disulfides displayed a nonhomogeneous mechanism of inhibition at the three subtypes since they were, like 2, noncompetitive antagonists at the alpha1A and alpha1B subtypes while being, unlike 2, competitive antagonists at the alpha1D. In particular, the blocking effects were characterized by a decrease of the maximal response to noradrenaline that was affected only slightly by washings. Probably the alpha1A and alpha1B subtypes bear in the binding pocket a suitable thiol function that would suffer an interchange reaction with the disulfide moiety of the antagonist and which is missing, or not accessible, in the alpha1D subtype. Polyamines 8, 9, and 14, among others, emerged as promising tools for the characterization of alpha1-adrenoreceptors, owing to their receptor subtype selectivity. Finally, the effect of nonbasic substituents on the phenyl ring of prazosin analogues 16-28 on potency and selectivity for the different subtypes can hardly be rationalized.

Design, synthesis, and biological activity of prazosin-related antagonists. Role of the piperazine and furan units of prazosin on the selectivity for alpha1-adrenoreceptor subtypes

Prazosin-related quinazolines 4-20 were synthesized, and their biological profiles at alpha1-adrenoreceptor subtypes were assessed by functional experiments in isolated rat vas deferens (alpha1A), spleen (alpha1B), and aorta (alpha1D) and by binding assays in CHO cells expressing human cloned alpha1-adrenoreceptor subtypes. The replacement of piperazine and furan units of prazosin (1) by 1, 6-hexanediamine and phenyl moieties, respectively, affording 3-20, markedly affected both affinity and selectivity for alpha1-adrenoreceptor subtypes in functional experiments. Cystazosin (3), bearing a cystamine moiety, was a selective alpha1D-adrenoreceptor antagonist being 1 order of magnitude more potent at alpha1D-adrenoreceptors (pA2, 8.54 +/- 0.02) than at the alpha1A- (pA2, 7.53 +/- 0.01) and alpha1B-subtypes (pA2, 7.49 +/- 0. 01). The insertion of substituents on the furan ring of 3, as in compounds 4 and 5, did not improve the selectivity profile. The simultaneous replacement of both piperazine and furan rings of 1 gave 8 which resulted in a potent, selective alpha1B-adrenoreceptor antagonist (85- and 15-fold more potent than at alpha1A- and alpha1D-subtypes, respectively). The insertion of substituents on the benzene ring of 8 affected, according to the type and the position of the substituent, affinity and selectivity for alpha1-adrenoreceptors. Consequently, the insertion of appropriate substituents in the phenyl ring of 8 may represent the basis of designing new selective ligands for alpha1-adrenoreceptor subtypes. Interestingly, the finding that polyamines 11, 16, and 20, bearing a 1,6-hexanediamine moiety, retained high affinity for alpha1-adrenoreceptor subtypes suggests that the substituent did not give rise to negative interactions with the receptor. Finally, binding assays performed with selected quinazolines (2, 3, and 14) produced affinity results, which were not in agreement with the selectivity profiles obtained from functional experiments. This rather surprising and unexpected finding may be explained by considering neutral and negative antagonism.