Roberta Budriesi

1,4-Dihydropyridine Scaffold in Medicinal Chemistry, The Story So Far And Perspectives (Part 2): Action in Other Targets and Antitargets

1,4-Dihydropyridines were introduced in the last century for the treatment of coronary diseases. Then medicinal chemists decorated the 1,4-DHP nucleus, the most studied scaffold among L-type calcium channel blockers, achieving diverse activities at several receptors, channels and enzymes. We already described (Ioan et al. Curr. Med. Chem. 2011, 18, 4901-4922) the effects of 1,4-DHPs at ion channels and G-protein coupled receptors. In this paper we continue the analysis of the wide range of biological effects exerted by compounds belonging to this chemical class. In particular, focus is given to the ability of 1,4-DHPs to revert multi drug resistance that, after over 20 years of research, continues to be of great interest. We also describe activities on other targets and the action of 1,4-DHPs against several diseases. Finally, we report and review the interaction of 1,4-DHPs with the hERG channel, transporters and phase I metabolizing enzymes. This work is a starting point for further exploration of the 1,4-DHP core activities on targets, off-targets and antitargets.

1,4-Dihydropyridine Scaffold in Medicinal Chemistry, The Story so Far And Perspectives (Part 1): Action in Ion Channels and GPCRs

Since the pioneering studies of Fleckenstein and co-workers, L-Type Calcium Channel (LTCC) blockers have attracted large interest due to their effectiveness in treating several cardiovascular diseases. Medicinal chemists achieved high potency and tissue selectivity by decorating the 1-4-DHP nucleus, the most studied scaffold among LTCC blockers. Nowadays it is clear that the 1,4-DHP nucleus is a privileged scaffold since, when appropriately substituted, it can selectively modulate diverse receptors, channels and enzymes. Therefore, the 1,4-DHP scaffold could be used to treat various diseases by a single-ligand multi-target approach. In this review, we describe the structure-activity relationships of 1,4-DHPs at ion channels, G-protein coupled receptors, and outline the potential for future therapeutic applications.

Cystic Fibrosis: A New Target for 4-Imidazo[2,1-b]thiazole-1,4-dihydropyridines

The pharmacology of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl– channel has attracted significant interest in recent years with the aim to search for rational new therapies for diseases caused by CFTR malfunction. Mutations that abolish the function of CFTR cause the life-threatening genetic disease cystic fibrosis (CF). The most common cause of CF is the deletion of phenylalanine 508 (ΔF508) in the CFTR chloride channel. Felodipine, nifedipine, and other antihypertensive 1,4-dihydropyridines (1,4-DHPs) that block L-type Ca2+ channels are also effective potentiators of CFTR gating, able to correct the defective activity of ΔF508 and other CFTR mutants (Mol. Pharmacol.2005, 54, 1736). For this purpose, we evaluated the ability of the previously and newly synthesized 4-imidazo[2,1-b]thiazoles-1,4-dihydropyridines without vascular activity and inotropic and/or chronotropic cardiac effects (J. Med. Chem.2008, 54, 1592) to enhance the activity of ΔF508-CFTR. Our studies indicate compounds 17, 18, 20, 21, 38, and 39 as 1,4-DHPs with an interesting profile of activity.

THE DESIGN OF NOVEL METHOCTRAMINE-RELATED TETRAAMINES AS MUSCARINIC RECEPTOR SUBTYPE SELECTIVE ANTAGONISTS

Several novel methoctramine-related tetraamines were designed, and their biological profiles at muscarinic receptor subtypes were assessed by functional experiments in isolated guinea pig and rat atria (M2) and smooth muscle (ileum and trachea, M3) and by binding assays in rat cortex (M1), heart (M2), and submaxillary gland (M3) homogenates and NG 108-15 cells (M4). Tripitramine, a nonsymmetrical tetraamine, resulted in the most potent and the most selective muscarinic M2 receptor antagonist of the series (pA2 = 9.14-9.85; pKi = 9.54). Spirotramine (FC 15-94), a symmetrical tetraamine, was able to differentiate between muscarinic M1 receptors (pKi = 7.88) and the other subtypes (M2, pKi = 6.20; M3, pKi = 5.81; M4, pKi = 6.27). Thus, tripitramine and spirotramine could be valuable tools for the pharmacological classification and characterization of muscarinic receptor subtypes.

In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M2 receptors

1 The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea‐pig and rat and in the trachea and lung strip of guinea‐pig and compared with the effects of methoctramine.

Antiinflammatory effect of phytosterols in experimental murine colitis model: prevention, induction, remission study.

Phytosterols, besides hypocholesterolemic effect, present anti-inflammatory properties. Little information is available about their efficacy in Inflammatory Bowel Disease (IBD). Therefore, we have evaluated the effect of a mixture of phytosterols on prevention/induction/remission in a murine experimental model of colitis. Phytosterols were administered x os before, during and after colitis induction with Dextran Sodium Sulfate (DSS) in mice. Disease Activity Index (DAI), colon length, histopathology score, 18F-FDG microPET, oxidative stress in the intestinal tissue (ileum and colon) and gallbladder ileum and colon spontaneous and carbachol (CCh) induced motility, plasma lipids and plasma, liver and biliary bile acids (BA) were evaluated. A similar longitudinal study was performed in a DSS colitis control group. Mice treated with DSS developed severe colitis as shown by DAI, colon length, histopathology score, 18F-FDG microPET, oxidative stress. Both spontaneous and induced ileal and colonic motility were severely disturbed. The same was observed with gallbladder. DSS colitis resulted in an increase in plasma cholesterol, and a modification of the BA pattern. Phytosterols feeding did not prevent colitis onset but significantly reduced the severity of the disease and improved clinical and histological remission. It had strong antioxidant effects, almost restored colon, ileal and gallbladder motility. Plasmatic levels of cholesterol were also reduced. DSS induced a modification in the BA pattern consistent with an increase in the intestinal BA deconjugating bacteria, prevented by phytosterols. Phytosterols seem a potential nutraceutical tool for gastrointestinal inflammatory diseases, combining metabolic systematic and local anti-inflammatory effects.

Novel, potent, and selective quinoxaline-based 5-HT3 receptor ligands. 1. Further structure-activity relationships and pharmacological characterization

We investigated the pharmacological profile of a novel series of quinoxaline-based 5-HT(3) receptor ligands bearing an extra basic moiety on the piperazine N-4. High affinity and selectivity were dependent on the electronic properties of the substituents, and at cardiac level 3a and 3c modulated chronotropy but not inotropy. In von Bezold-Jarisch reflex test 3a-c were partial agonists while 3i was a full agonist. Preliminary pharmacokinetic studies indicated that 3a is a brain penetrating agent.

Cardiovascular hybrid drugs: new benzazepinone derivatives as bradycardic agents endowed with selective β1-Non-competitive antagonism

The synthesis and pharmacological profile of some hybrid compounds bearing both the benzazepinone moiety present in Zatebradine and typical beta-blocker aryloxypropanolamine groups are described. The new compounds proved to be endowed with negative chronotropic and inotropic activity and are weak vasorelaxant agents. The cardiodepressant action is probably due to selective beta(1)-noncompetitive reversible antagonism. Both enantiomers of the most active compound 5c were synthesized and they showed a different cardiovascular profile, that is (+)-(R)-enantiomer displays affinity for cardiac beta(1)-adrenoceptors, while (-)-(S)-enantiomer shows specificity for vessel smooth muscle.

Ligand based approach to L-type calcium channel by imidazo[2,1-b]thiazole-1,4-dihydropyridines: from heart activity to brain affinity.

The synthesis, characterization, and functional in vitro assay in cardiac and smooth muscle (vascular and nonvascular) of a series of 4-imidazo[2,1-b]thiazole-1,4-dihydropyridines are reported. To define the calcium blocker nature of the imidazo[2,1-b]thiazole-1,4-DHPs and their selectivity on Cav1.2 and Cav1.3 isoforms, we performed binding studies on guinea pig atrial and ventricular membranes on intact cells expressing the cloned Cav1.2a subunit and on rat brain cortex. To get major insights into the reasons for the affinity for Cav1.2 and/or Cav1.3, molecular modeling studies were also undertaken. Some physicochemical and pharmacokinetic properties of selected compounds were calculated and compared. All the biological data collected and reported herein allowed us to rationalize the structure-activity relationship of the 4-imidazo[2,1-b]thiazole-1,4-DHPs and to identify which of these enhanced the activity at the central level.

Analysis of the muscarinic receptor subtype mediating inhibition of the neurogenic contractions in rabbit isolated vas deferens by a series of polymethylene tetra-amines

The pharmacological characteristics of the presynaptic muscarinic receptor subtype, which mediates inhibition of the neurogenic contractions in the prostatic portion of rabbit vas deferens, have been investigated by using a series of polymethylene tetra‐amines, which were selected for their ability to differentiate among muscarinic receptor subtypes. It was found that all tetra‐amines antagonized McN‐A‐343‐induced inhibition in electrically stimulated rabbit vas deferens in a competitive manner and with affinity values (pA2) ranging between 6.27±0.09 (spirotramine) and 8.51±0.02 (AM170). Competition radioligand binding studies, using native muscarinic receptors from rat tissues (M1, cortex; M2, heart; M3, submaxillary gland) or from NG 108‐15 cells (M4) and human cloned muscarinic M1‐M4 receptors expressed in CHO‐K1 cells, were undertaken with the same tetra‐amines employed in functional assays. All antagonists indicated a one‐site fit. The affinity estimates (pKi) of tetra‐amines calculated in binding assays using native receptors were similar to those obtained using cloned receptors. Among these compounds some displayed selectivity between muscarinic receptor subtypes, indicating that they may be valuable tools in receptor characterization. Spirotramine was selective for M1 receptors versus all other subtypes (pKi native: M1, 7.32±0.10; M2, 6.50±0.11; M3, 6.02±0.13; M4, 6.28±0.16; pKi cloned: M1, 7.69±0.08; M2, 6.22±0.14; M3, 6.11±0.16; 6.35±0.11) whereas CC8 is highly selective for M2 receptors versus the other subtypes (pKi native: M1, 7.50±0.04; M2, 9.01±0.12; M3, 6.70±0.08; M4, 7.56±0.04; pKi cloned: M1, 7.90±0.20; M2, 9.04±0.08; M3, 6.40±0.07; M4, 7.40±0.04). Furthermore, particularly relevant for this investigation were tetra‐amines dipitramine and AM172 for their ability to significantly differentiate M1 and M4 receptors. The apparent affinity values (pA2) obtained for tetra‐amines in functional studies using the prostatic portion of rabbit vas deferens correlated most closely with the values (pKi) obtained at either native or human recombinant muscarinic M4 receptors. This supports the view that the muscarinic receptor mediating inhibition of neurogenic contractions of rabbit vas deferens may not belong to the M1 type but rather appears to be of the M4 subtype.