Investigation of the stereoselective in vitro metabolism of the chiral antiasthmatic/antiallergic drug flezelastine by high-performance liquid chromatography and capillary zone electrophoresis

An achiral HPLC method using a silica gel column as well as two independent chiral analytical methods by HPLC and capillary zone electrophoresis (CZE) were developed in order to investigate the in vitro metabolism of the racemic antiasthmatic/antiallergic drug flezelastine. The chiral HPLC analysis was performed on a Chiralpak AD column, which also allowed the simultaneous separation of the N-dephenethyl metabolite. The chiral separation by CZE was achieved by the addition of β-cyclodextrin to the run buffer. The stereoselectivity of the in vitro biotransformation of flezelastine was investigated using liver homogenates of different species. Depending on the species, diverse stereoselective aspects were demonstrated. The determination of the enantiomeric ratios of flezelastine and of N-dephenethylflezelastine after incubations of racemic flezelastine with liver microsomes revealed that porcine liver microsomes showed the greatest enantioselectivity of the biotransformation. (−)-Flezelastine was preferentially metabolized. After incubations with bovine liver microsomes the enantiomer of N-dephenethylflezelastine formed from (+)-flezelastine dominated. Incubations of the pure enantiomers of flezelastine with induced rat liver microsomes resulted in the stereoselective formation of a hitherto unknown metabolite, which was only detected in samples of (+)-flezelastine. Initial structure elucidation of the compound indicated that the new     

Azelastine potentiates the prostaglandin-induced increase of cyclic AMP content in human platelets and in guinea-pig alveolar macrophages.

The effect of azelastine on intracellular cyclic AMP concentration and on various indexes of cell activation was evaluated in guinea-pig alveolar macrophages and in human platelets. The effect of azelastine was further investigated on adenylate cyclase activity using membranes and homogenates from guinea-pig alveolar macrophages. Pretreatment of alveolar macrophages with azelastine prevented the activation induced by PAF-acether and by the chemotactic peptide fMLP as estimated by the reduced liberation of arachidonic acid metabolites formed by the cyclooxygenase and the lipoxygenase pathways. The effect of azelastine was concentration-dependent (50 to 500 microM) and reversible. Similarly, a short pretreatment with azelastine (100 microM) prevented arachidonic acid-induced platelet aggregation. This effect was also reversible after washing the platelets. In guinea-pig alveolar macrophages, azelastine induced a concentration-dependent (10 to 500 microM) increase in intracellular cyclic AMP and markedly potentiated the increase induced by PGE2. In human platelets, azelastine alone increased intracellular cyclic AMP concentration marginally only but, as in the case of macrophages, synergized with PGI2. Azelastine did not activate significantly adenylate cyclase unless a cytosolic factor was included within the membrane fraction. This effect of azelastine was not due to Ca2+ movements and was not modified by GTP. Our findings show that azelastine interferes with cell activation through a mechanism related to an increase in intracellular cyclic AMP concentration. The increase in cyclic AMP was induced by azelastine in intact cells and in homogenates but not in a crude membrane fraction. Those results indicate that azelastine modifies a cytosolic factor that may be phosphodiesterase. In addition, similarities between the effects of azelastine and those of reference phosphodiesterase inhibitors (theophylline, isobutyl-methyl-xanthine) are shown in this study, suggesting that azelastine might behave as a phosphodiesterase inhibitor.     

Inhibitory effect of azelastine hydrochloride on synthesis and release of platelet activating factor from human alveolar macrophages

The effect of azelastine hydrochloride (azelastine) on synthesis and release of platelet activating factor (PAF) in alveolar macrophages obtained from asthmatic and non-asthmatic subjects was examined. Alveolar macrophages (AMs) were preincubated with or without azelastine and stimulated with f-Met-Leu-Phe (fMLP, 10 μM) for 15 min. PAF activity was detected by aggregation of washed guinea pig platelets. PAF activity released from alveolar macrophages (AMs) from asthmatics without preincubation of azelastine was 15.97 [2.17] (mean [SD], ng/10⁷ cells) in supernatants and 42.52 [10.16] in cell pellets. After preincubation with 10⁻⁸, 10⁻⁶, and 10⁻⁴ M of azelastine, PAF activity reduced to 10.71 [2.73] (mean [SD], ng/10⁷ cells), 7.86 [0.94], and 3.52 [0.31] in the supernatants, and 35.58 [7.37], 21.57 [4.36], and 14.77 [0.99] (n = 15) in the cell pellets, respectively.PAF activity in non-asthmatic subjects without preincubation of azelastine was 8.55 [1.16] (mean [SD], ng/10⁷ cells) in supernatants and 32.64 [3.37] in cell pellets. After preincubation with 10⁻⁸, 10⁻⁶, and 10⁻⁴ M of azelastine, PAF activity reduced to 6.68 [0.78] (mean [SD], ng/10⁷ cells), 4.47 [0.51], and 2.97 [0.36] in the supernatants, and 29.53 [3.75], 14.78 [1.95], and 6.16 [0.55] (n = 20) in the cell pellets, respectively.Our results showed that preincubation with azelastine caused a dose-dependent inhibition of intra- and extracellular PAF activity from asthmatic and non-asthmatic macrophages in the same manner.     

Identification of selective 8-(piperidin-4-yloxy)quinoline sulfone and sulfonamide histamine H1 receptor antagonists for use in allergic rhinitis

A series of potent, selective and long-acting quinoline-based sulfonamide human H₁ histamine receptor antagonists, designed for once-daily intranasal administration for the treatment of rhinitis were developed. Sulfonamide 33b had a slightly lower affinity for the H₁ receptor than azelastine, had low oral bioavailability in the rat and dog, and was turned over to five major metabolites. Furthermore, 33b had longer duration of action than azelastine in guinea pigs, lower rat brain-penetration, and did not cause time dependent inhibition of CYP2D6 or CYP3A4. The clinical dose in humans is expected to be low (approximately 0.5 mg per day) based on the clinical dose used for azelastine and a comparison of efficacy data from animal models for 33b and azelastine.     

Efficacy and tolerability of levocabastine and azelastine nasal sprays for the treatment of allergic rhinitis

Levocabastine and azelastine are currently the only antihistamines available as nasal sprays for the topical therapy of seasonal allergic rhinitis. The present study was undertaken to compare the onset of action, efficacy and tolerability of these two agents in a total of 242 patients with this condition. This was an international, multicentre, open-label, randomized, parallel-group trial with 123 patients treated with levocabastine (0.5 mg/ml, two puffs per nostril twice daily) and 119 with azelastine (1 mg/ml, one puff per nostril twice daily). Onset of action was comparable for the two drugs with over 50% of patients in each group reporting significant symptomatic relief within 30 min of administration of the first dose of study medication. Therapeutic efficacy was also found to be comparable in the two groups with no statistically significant intergroup differences reported for any of the parameters evaluated, although assessments of global therapeutic efficacy revealed a trend favouring levocabastine. Levocabastine appeared to be better tolerated than azelastine (p = 0.06), with the incidence of the most common adverse experiences, application site reactions and taste disturbances, significantly higher on azelastine than with levocabastine (5% versus 1%; p = 0.05 and 5% versus 0%; p = 0.01, respectively). In conclusion, levocabastine nasal spray appears to be at least as effective as, but better tolerated than, azelastine nasal spray for the treatment of seasonal allergic rhinitis.     

Effect of azelastie on PGE2 production in fibroblasts in normal skin. the possibility of inhibition of inducible cyclooxygenase by azelastine

The effects of azelastine on prostaglandin E2 (PGE2) production were investigated by using cultured normal dermal fibroblasts obtained from the same traumatic region of 3 patients and the CRL-1475 cell line, lnterleukin-1 β (IL-1) enhanced PGE2 production in cultured normal fibroblasts and CRL-1475 cells. 10⁻⁶ M azelastine inhibited PGE2 production in these IL-1-stimulated fibroblasts. However, the drug did not influence spontaneous PGE2 production in cultured CRL-1475 fibroblasts not stimulated with IL-1 but slightly it increased in cultured normal dermal fibroblasts under the same conditions. These results suggest that azelastine either regulates synthesis of an inducible cyclooxygenase protein or inhibits PGE2 production as an inducible cyclooxygenase inhibitor.     

Reversible drug effects on the metabolic activation of polymorphonuclear leukocytes

Polymorphonuclear leukocytes (PMNs) stimulated by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP) were effectively inhibited by chlorpromazine (10 microM) and azelastine (20 microM) in terms of superoxide generation, and restored by the addition of dodecylbenzenesulfonic acid (DBS) in a range of concentrations from 20 to 40 microM. The stimulation of superoxide generation by DBS was also inactivated by dodecylamine (DA) but was restored by the subsequent addition of DBS. A dose dependent competitive inhibition and activation of leukocytes was observed between azelastine (10 microM) and DBS (20 microM). The release of arachidonic acid from leukocytes activated by the chemotactic peptide was decreased by DA or chlorpromazine, but could be restored by DBS. The changes in membrane potential of leukocytes as monitored by cyanine dye were also decreased by DA, chlorpromazine or azelastine. These observations indicate that some cationic drugs reversibly inhibit membrane bound enzymes or receptors. The physiological responses of these inhibited PMNs can then be restored by appropriate anionic amphiphiles.     

Simultaneous enantioselective separation of azelastine and three of its metabolites for the investigation of the enantiomeric metabolism in rats. I. Liquid chromatography-ionspray tandem mass spectrometry and electrokinetic capillary chromatography

Enantioselective separation methods and the enantioselective determination of the anti-allergic drug azelastine and of three of its main phase I metabolites in a biological matrix underwent chromatographic and electrophoretic investigations. An enantioselective assay of a coupling of HPLC using a beta-cyclodextrin chiral stationary phase to ionspray tandem mass spectrometry is presented. Additionally, this assay is compared to another enantioselective assay using electrokinetic capillary chromatography with beta-cyclodextrin and carboxymethyl-beta-cyclodextrin in polyacrylamide-coated capillaries. For capillary electrophoresis (CE) the importance of polyacrylamide coating for the validation of this separation method is highlighted. Extracted rat plasma samples of enantioselective metabolism studies were measured by both validated assays. Differences in the pharmacokinetics and pharmacodynamics were evaluated for the main substance azelastine and its main metabolite demethylazelastine. So, a first hint about the enantioselectivity of biotransformation of azelastine in rats was seen after oral application of either enantiomer or the racemate to rats.     

Azelastine and suplatast shorten the distribution half-life of IgE in rats

We aim to clarify whether suplatast and azelastine (anti-allergic drugs) can shorten the half-life of imnunoglobulin E (IgE) in the circulating blood. Thirty Wistar rats were divided into six groups. Distilled water or anti-allergic drugs were given orally for 6 days after the first sensitization. Two milligrams of monoclonal dinitrophenyl (DNP)-specific rat IgE was administered to the rats, which had been given suplatast or azelastine orally. The level of DNP-specific rat IgE in the serum was estimated by IgE-capture enzyme-linked immunosorbent assay, and the turnover of IgE was analyzed from its pharmacokinetic parameters. The elimination half-life of rat IgE was about 12 h irrespective of the sensitized state. The intercompartmental rate constants (Kct and Ktc) in the suplatast-administered or azelastine-administered group were larger than those of the distilled water-administered group under non-sensitized conditions. These findings suggested that the anti-allergic drugs used in the present study facilitated the excretion of IgE from the circulation in rats.     

Inhibitory action of azelastine on cytokine production from human peripheral blood leukocytes in vitro

Effects of azelastine (AZ) on human peripheral blood leukocytes (PBL) in culture were examined. Addition of 10.0 μg/ml of AZ resulted in a marked inhibition of PBL blastic activity, but lower concentrations (1.0 and 0.5 μg/ml) had no demonstrable suppressive effects on the activation. Interleukin (IL)-2, IL-3 and IL-4 production from PBL in response to Concanavalin A stimulation was also strongly suppressed when the cells were cultured in the presence of AZ. This suppression was observed even when lower concentrations (1.0 and 0.5 μg/ml) of AZ were added to cell cultures     

Synthesis and pharmacological investigation of azaphthalazinone human histamine H1 receptor antagonists

5-Aza, 6-aza, 7-aza and 8-aza-phthalazinone, and 5,8-diazaphthalazinone templates were synthesised by stereoselective routes starting from the appropriate pyridine/pyrazine dicarboxylic acids by activation with CDI, reaction with 4-chlorophenyl acetate ester enolate to give a β?ketoester, which was hydrolysed, and decarboxylated. The resulting ketone was condensed with hydrazine to form the azaphthalazinone core. The azaphthalazinone cores were alkylated with N-Boc-D-prolinol at N-2 by Mitsunobu reaction, de-protected, and then alkylated at the pyrrolidine nitrogen to provide the target H₁ receptor antagonists. All four mono-azaphthalazinone series had higher affinity (pK_i) for the human H₁ receptor than azelastine, but were not as potent as the parent non-aza phthalazinone. The 5,8-diazaphthalazinone was equipotent with azelastine. The least potent series were the 7-azaphthalazinones, whereas the 5-azaphthalazinones were the most lipophilic. The more hydrophilic series were the 8-aza series. Replacement of the N-methyl substituent on the pyrrolidine with the n-butyl group caused an increase in potency (pA₂) and a corresponding increase in lipophilicity. Introduction of a β-ether oxygen in the n-butyl analogues (2-methoxyethyl group) decreased the H₁ pA₂ slightly, and increased the selectivity against hERG. The duration of action in vitro was longer in the 6-azaphthalazinone series. The more potent and selective 6-azaphthalazinone core was used to append an H₃ receptor antagonist fragment, and to convert the series into the long acting single-ligand, dual H₁ H₃ receptor antagonist 44. The pharmacological profile of 44 was very similar to our intranasal clinical candidate 1.     

Design and validation of a homogeneous time-resolved fluorescence cell-based assay targeting the ligand-gated ion channel 5-HT3A

Ligand-gated ion channels (LGICs) are considered as attractive protein targets in the search for new therapeutic agents. Nowadays, this strategy involves the capability to screen large chemical libraries. We present a new Tag-lite ligand binding assay targeting LGICs on living cells. This technology combines the use of suicide enzyme tags fused to channels of interest with homogeneous time-resolved fluorescence (HTRF) as the detection readout. Using the 5-HT3 receptor as system model, we showed that the pharmacology of the HALO-5HT3 receptor was identical to that of the native receptor. After validation of the assay by using 5-HT3 agonists and antagonists of reference, a pilot screen enabled us to identify azelastine, a well-known histamine H1 antagonist, as a potent 5-HT3 antagonist. This interesting result was confirmed with electrophysiological experiments. The method described here is easy to implement and could be applicable for other LGICs, opening new ways for the screening of chemical libraries.     

Application of Kinetic and Dynamic Data for Antihistamines to Risk Characterization in Sensitive Populations

A major goal of risk assessment is to protect the health of individuals who may be more sensitive than the general population. This study compared human phar-macokinetic and pharmacodynamic data in sensitive groups (i.e., children, the elderly, diseased states, and poor metabolizers) versus young, healthy adults for the antihistamines cetirizine, fexofenadine, loratadine, azelastine, ebastine, chlorpheniramine, and diphenhydramine. The default components (3.16 each for kinetic and dynamic aspects) of the intraspecies uncertainty factor were adjusted with compound specific data for the antihistamines. The majority (16 of 18) of the composite factors (kinetics X dynamics) for the sensitive groups were less than 10. Children had the lowest composite factors for antihistamines, ranging from 1.1 to 6.3. Application of kinetic and dynamic data for antihistamines to the Renwick/International Programme on Chemical Safety (IPCS) scheme can aid in characterizing the extent of variability in sensitive populations, thereby reducing the uncertainty associated with the risk assessment of sensitive populations.     

In vitro suppression of lymphocyte activation in patients with seasonal allergic rhinitis and pollen-related asthma by cetirizine or azelastine in combination with ginkgolide B or astaxanthin

Novel strategies are evaluated for management of allergic rhinitis and asthma in patients co-afflicted with both disorders. It is hypothesized that the platelet activating factor receptor antagonist ginkgolide B (GB) and the carotenoid antioxidant astaxanthin (ASX) interact with antihistamines cetirizine dihydrochloride (CTZ) and azelastine (AZE) to potentiate their ability to downregulate potentially pathological immune activation. Peripheral blood mononuclear cells from asthmatics and healthy subjects, cultured 24 hours with 50 μg/ml phytohemaglutinin (PHA) or PHA plus each drug are analyzed by flow cytometry for expression of CD25+ or HLA-DR+ by CD3+ (T cells). Results are reported as stimulation indices for CD3+CD25+ (SICD3+CD25+) and CD3+HLA-DR+ (SICD3+HLADR+) cells in cultures treated with PHA alone, versus cultures treated with both PHA and drugs. Optimal suppression of activated cells was observed in cultures stimulated with ASX 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.016; SICD3+HLADR, p = 0.012); ASX 10-6 M + AZE 10-6 M (SICD3+CD25+, p = 0.012; SICD3+HLADR, p = 0.015); GB 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.024, SICD3+HLADR+, p = 0.019). Results demonstrate improved activity of antihistamines by 2 phytochemicals, suggesting dosing strategies for animal trials of ASX- or GB-augmented formulations for seasonal allergic rhinitis and asthma.     

Effect of a peptide leukotriene antagonist, ONO-1078 on antigen-induced airway microvascular leakage in actively sensitized guinea pigs.

We examined the effect of ONO-1078, a peptide leukotriene antagonist, on antigen-induced airway microvascular leakage in ovalbumin-sensitized guinea pigs. When guinea pigs were pretreated with mepyramine, ovalbumin challenge increased vascular permeability to Evans blue dye in trachea, main bronchi and intrapulmonary airways. Oral administration of ONO-1078 significantly reduced microvascular leakage in intrapulmonary airways at doses more than 3 mg/kg, but not in trachea. Moreover, oral administration of ONO-1078 significantly reduced SRS-A mediated microvascular leakage into all airway tissues and was more effective in intrapulmonary airways at 3 mg/kg. Simultaneously, ONO-1078 also inhibited SRS-A mediated bronchoconstriction. On the other hand, azelastine (10 mg/kg, p.o.), an anti-asthma agent, failed to inhibit microvascular leakage into the airways. These results suggest that peptide leukotrienes may be important mediators of airway microvascular leakage, and that the inhibitory effect of ONO-1078 on antigen-induced airway microvascular leakage in addition to the blockade of bronchoconstriction may have therapeutic implications for bronchial asthma.     

Effects of tannins and related polyphenols on superoxide-induced histamine release from rat peritoneal mast cells.

The effects of tannins and related polyphenols on KO2- and compound 48/80-induced histamine release from rat peritoneal mast cells were examined. Pretreatment with hydrolyzable tannins (1-100 microM) significantly inhibited KO2-induced histamine release. Dimeric ellagitannins, which have hexahydroxydiphenoyl (HHDP) and valoneoyl residues and/or a valoneoyl-related acyl unit in the molecule, showed more potent inhibitory effects than monomeric hydrolyzable tannins. The most effective inhibition was exhibited by agrimoniin and euphorbin C (IC50 0.68 and 0.80 microM), which have dehydrodigalloyl and euphorbinoyl groups, respectively, as well as the HHDP group. However, procyanidins, flavonoids and related polyphenols with small molecular weights, except for epigallocatechin gallate, exhibited negligible effects. Although clinically used antiallergic drugs, azelastine, astemizole, ketotifen and epinastine have been shown to prevent KO2-induced histamine release, their potencies were all less than those of ellagitannins. An inhibitory effect on compound 48/80-induced histamine release was also exhibited by higher molecular weight tannins. The inhibitory effect on histamine release caused by different stimulants suggested that ellagitannins act as cell membrane stabilizers as well as radical scavengers.     

Computational and experimental investigation of DNA repair protein photolyase interactions with low molecular weight drugs

This paper reports the previously unknown interactions between eight low molecular weight commercially available drugs (130–800 Da) and DNA repair protein photolyase using computational docking simulations and surface plasmon resonance (SPR) experiments. Theoretical dissociation constants, K_d, obtained from molecular docking simulations were compared with the values found from SPR experiments. Among the eight drugs analyzed, computational and experimental values showed similar binding affinities between selected drug and protein pairs. We found no significant differences in binding interactions between pure and commercial forms of the drug lornoxicam and DNA photolyase. Among the eight drugs studied, prednisone, desloratadine, and azelastine exhibited the highest binding affinity (K_d = 1.65, 2.05, and 8.47 μM, respectively) toward DNA photolyase. Results obtained in this study are promising for use in the prediction of unknown interactions of common drugs with specific proteins such as human clock protein cryptochrome. Copyright © 2013 John Wiley & Sons, Ltd.     

Virtual screening using the ligand ZINC database for novel lipoxygenase-3 inhibitors

The leukotrienes constitute a group of arachidonic acid-derived compounds with biologic activities suggesting important roles in inflammation and immediate hypersensitivity. Epidermis-type lipoxygenase-3 (ALOXE3), a distinct subclass within the multigene family of mammalian lipoxygenases, is a novel isoenzyme involved in the metabolism of leukotrienes and plays a very important role in skin barrier functions. Lipoxygenase selective inhibitors such as azelastine and zileuton are currently used to reduce inflammatory response. Nausea, pharyngolaryngeal pain, headache, nasal burning and somnolence are the most frequently reported adverse effects of these drugs. Therefore, there is still a need to develop more potent lipoxygenase inhibitors. In this paper, we report the screening of various compounds from the ZINC database (contains over 21 million compounds) using the Molegro Virtual Docker software against the ALOXE3 protein. Screening was performed using molecular constraints tool to filter compounds with physico-chemical properties similar to the 1N8Q bound ligand protocatechuic acid. The analysis resulted in 4319 Lipinski compliant hits which are docked and scored to identify structurally novel ligands that make similar interactions to those of known ligands or may have different interactions with other parts of the binding site. Our screening approach identified four molecules ZINC84299674; ZINC76643455; ZINC84299122 & ZINC75626957 with MolDock score of -128.901, -120.22, -116.873 & - 102.116 kcal/mol, respectively. Their energy scores were better than the 1N8Q bound co-crystallized ligand protocatechuic acid (with MolDock score of -77.225 kcal/mol). All the ligands were docked within the binding pocket forming interactions with amino acid residues.     

Validated sensitive spectrofluorimetric method for determination of antihistaminic drug azelastine HCl in pure form and in pharmaceutical dosage forms: application to stability study

A highly sensitive, simple and rapid spectrofluorimetric method was developed for the determination of azelastine HCl (AZL) in either its pure state or pharmaceutical dosage form. The proposed method was based on measuring the native fluorescence of the studied drug in 0.2 M H₂SO₄ at λ_em = 364 nm after excitation at λ_ex = 275 nm. Different experimental parameters were studied and optimized carefully to obtain the highest fluorescence intensity. The proposed method showed a linear dependence of the fluorescence intensity on drug concentration over a concentration range of 10–250 ng/mL, with a limit of detection of 1.52 ng/mL and limit of quantitation of 4.61 ng/mL. Moreover, the method was successfully applied to pharmaceutical preparations, with percent recovery values (± SD) of 99.96 (± 0.4) and 100.1 (± 0.52) for nasal spray and eye drops, respectively. The results were in good agreement with those obtained by the comparison method, as revealed by Student's t‐test and the variance ratio F‐test. The method was extended to study the stability of AZL under stress conditions, where the drug was exposed to neutral, acidic, alkaline, oxidative and photolytic degradation according to International Conference on Harmonization (ICH) guidelines. Copyright © 2016 John Wiley & Sons, Ltd.     

Structure investigation,enrichment analysis and structure-based repurposing of FDA-approved drugs as inhibitors of BET-BRD4

We report herein detailed structural insights into the ligand recognition modes guiding bromodomain selectivity, enrichment analysis and docking-based database screening for the identification of the FDA-approved drugs that have potential to be the human BRD4 inhibitors. Analysis of multiple X-ray structures prevailed that the lysine-recognition sites are highly conserved, and apparently, the dynamic ZA loop guides the specific ligand-recognition. The protein–ligand interaction profiling revealed that both BRD2 and BRD4 shared hydrophobic interaction of bound ligands with PRO-98/PRO-82, PHE-99/PHE-83, LEU-108/LEU-92 and direct H-bonding with ASN-156/ASN-140 (BRD2/BRD4), while on the other hand the water-mediated H-bonding of bound ligands with PRO-82, GLN-85, PRO-86, VAL-87, ASP-88, LEU-92, TYR-97 and MET-132, and aromatic π–π stacking with TRP-81 prevailed as unique interaction in BRD4, and were not observed in BRD2. Subsequently, through ROC curve analysis, the best enrichment was found with PDB-ID 4QZS of BRD4 structures. Finally, through docking-based database screening study, we found that several drugs have better binding affinity than the control candidate lead (+)-JQ1 (Binding affinity?=?-7.9?kcal/mol), a well-known BRD4 inhibitor. Among the top-ranked drugs, azelastine, a selective histamine H1 receptor antagonist, showed the best binding affinity of –9.3?kcal/mol and showed interactions with several key residues of the acetyl lysine binding pocket. Azelastine may serve as a promising template for further medicinal chemistry. These insights may serve as basis for structure-based drug design, drug repurposing and the discovery of novel BRD4 inhibitors.

Communicated by Ramaswamy H. Sarma