Burcu Çalışkan

Identification of novel benzimidazole derivatives as inhibitors of leukotriene biosynthesis by virtual screening targeting 5-lipoxygenase-activating protein (FLAP).

Pharmacological suppression of leukotriene biosynthesis by 5-lipoxygenase (5-LO)-activating protein (FLAP) inhibitors is a promising strategy to intervene with inflammatory, allergic and cardiovascular diseases. Virtual screening targeting FLAP based on a combined ligand- and structure-based pharmacophore model led to the identification of 1-(2-chlorobenzyl)-2-(1-(4-isobutylphenyl)ethyl)-1H-benzimidazole (7) as developable candidate. Compound 7 potently suppressed leukotriene formation in intact neutrophils (IC(50)=0.31 μM) but essentially failed to directly inhibit 5-LO suggesting that interaction with FLAP causes inhibition of leukotriene synthesis. For structural optimization, a series of 46 benzimidazole-based derivatives of 7 were synthesized leading to more potent analogues (70-72, 82) with IC(50)=0.12-0.19 μM in intact neutrophils. Together, our results disclose the benzimidazole scaffold bearing an ibuprofen fingerprint as a new chemotype for further development of anti-leukotriene agents.

The novel benzimidazole derivative BRP-7 inhibits leukotriene biosynthesis in vitro and in vivo by targeting 5-lipoxygenase-activating protein (FLAP).

Leukotrienes (LTs) are inflammatory mediators produced via the 5‐lipoxygenase (5‐LOX) pathway and are linked to diverse disorders, including asthma, allergic rhinitis and cardiovascular diseases. We recently identified the benzimidazole derivative BRP‐7 as chemotype for anti‐LT agents by virtual screening targeting 5‐LOX‐activating protein (FLAP). Here, we aimed to reveal the in vitro and in vivo pharmacology of BRP‐7 as an inhibitor of LT biosynthesis.

Synthesis and evaluation of analgesic, anti-inflammatory, and anticancer activities of new pyrazole-3(5)-carboxylic acid derivatives

In this article, we synthesized a series of novel 1-benzyl-5(3)-p-tolyl-1H-pyrazole-3(5)-carboxylic acid derivatives and characterized by IR, 1H NMR, and mass spectroscopy. Compounds were evaluated for their in vivo analgesic and anti-inflammatory activity using the p-benzoquinone-induced writhing test and the carrageenan-induced paw edema model, respectively. Out of 14 compounds tested, 7a, 7c, 7e, 7f, 7i, 8a–b, and 8f–g exhibited potent analgesic and/or anti-inflammatory activity as compared to reference drugs aspirin and indomethacin. Anticancer activity of these compounds was assessed against five cancer cell lines with the MTT assay (HL-60, human promyelocytic leukemia cells; HeLa, human cervical cancer cells; Raji, human B lymphocyte cell line; MCF7, human breast adenocarcinoma cell line; MDA-MB-231, estrogen-independent human breast cancer cell line). Compounds 7a, 8a, and 8b with high anti-inflammatory activity, and also 7d and 7j with mild anti-inflammatory activity exhibited promising anticancer activity against some selected cell lines.

Overview of recent drug discovery approaches for new generation leukotriene A4 hydrolase inhibitors

Introduction: LTA4H is a bifunctional enzyme with hydrolase and aminopeptidase activities. The hydrolase function of this enzyme specifically catalyzes the rate-limiting step in the conversion of LTA4 to LTB4, one of the most potent chemoattractant and activator of neutrophils. The wealth of in vitro and in vivo data favors in support of LTA4H as an appealing target for the discovery and development of anti-inflammatory drugs. Areas covered: The authors provide an overview of the recent advances on LTA4H inhibitors since 2000. The review details the medicinal chemistry efforts leading to the generation of novel inhibitor chemotypes with desirable drug-like properties as well as the advantages and disadvantages of LTA4H as a desirable therapeutic target. Expert opinion: Most of the LTA4H inhibitors block pro-inflammatory LTB4 biosynthesis by concomitant inhibition of both the hydrolase and aminopeptidase activities of LTA4H. However, the degradation of another endogenous chemoattractant substrate (PGP) by aminopeptidase function of LTA4H was shown, introducing a new anti-inflammatory mission for this pro-inflammatory enzyme. LTA4H inhibitors were also shown to maintain anti-inflammatory lipoxin formation. Hence, the data on new LTA4H inhibitors should be cautiously interpreted with regard to potential repercussions of preventing PGP degradation as well as for the clinical benefits of concomitant lipoxin formation.

4,5-Diarylisoxazol-3-carboxylic acids: A new class of leukotriene biosynthesis inhibitors potentially targeting 5-lipoxygenase-activating protein (FLAP)

In this article, we report novel leukotriene (LT) biosynthesis inhibitors that may target 5-lipoxygenase-activating protein (FLAP) based on the previously identified isoxazole derivative (8). The design and synthesis was directed towards a subset of 4,5-diaryl-isoxazole-3-carboxylic acid derivatives as LT biosynthesis inhibitors. Biological evaluation disclosed a new skeleton of potential anti-inflammatory agents, exemplified by 39 and 40, which potently inhibit cellular 5-LO product synthesis (IC50 = 0.24 μM, each) seemingly by targeting FLAP with weak inhibition on 5-LO (IC50 ≥ 8 μM). Docking studies and molecular dynamic simulations with 5-LO and FLAP provide valuable insights into potential binding modes of the inhibitors. Together, these diaryl-isoxazol-3-carboxylic acids may possess potential as leads for development of effective anti-inflammatory drugs through inhibition of LT biosynthesis.

Synthesis and preliminary mechanistic evaluation of 5-(p-tolyl)-1-(quinolin-2-yl)pyrazole-3-carboxylic acid amides with potent antiproliferative activity on human cancer cell lines

We synthesized a series of novel amide derivatives of 5-(p-tolyl)-1-(quinolin-2-yl)pyrazole-3-carboxylic acid and assessed their antiproliferative activities against three human cancer cell lines (Huh7, human liver; MCF7, breast and HCT116, colon carcinoma cell lines) with the sulforhodamine B assay. Compound 4j with 2-chloro-4-pyridinyl group in the amide part exhibited promising cytotoxic activity against all cell lines with IC50 values of 1.6 μM, 3.3 μM and 1.1 μM for Huh7, MCF7 and HCT116 cells, respectively, and produced dramatic cell cycle arrest at SubG1/G1 phase as an indicator of apoptotic cell death induction. On the basis of their high potency in cellular environment, these straightforward pyrazole-3-carboxamide derivatives may possess potential in the design of more potent compounds for intervention with cancer cell proliferation.

Pyrazol-3-propanoic acid derivatives as novel inhibitors of leukotriene biosynthesis in human neutrophils.

We recently presented that compounds 4a-b moderately inhibited leukotriene (LT) formation in human neutrophils. For structural derivatization of 4a-b, novel thirty-six title compounds were synthesized and led to more potent inhibition of LT biosynthesis in activated human neutrophils exemplified by compounds 15, 27-30, 32-37, 41, 42 with IC(50) values in the range of 1.6-3.5 μM. Moreover, compounds 32, 35, 42, 43 and 44 showed a substantial inhibition of platelet COX-1 activity with IC(50) of 2.5, 0.041, 0.3, 0.9 and 0.014 μM, respectively, leading up to dual acting inhibitors. On the basis of their high potency in cellular environment, these straightforward pyrazole-3-propanoic acid derivatives may possess potential in the design of more potent compounds for intervention with inflammatory and allergic diseases.

Chromatographic separation and biological evaluation of benzimidazole derivative enantiomers as inhibitors of leukotriene biosynthesis

For an explicit analysis of the chirality on the effectiveness of a recently identified racemic benzimidazole derivative (BRP7) as inhibitor of leukotriene biosynthesis, we optimized a HPLC-based chiral chromatographic method enabling the quantitative isolation of its enantiomers in sufficient amount to carry out biological investigations. The use of a Lux Amylose-2 column revealed especially profitable to fulfil our task. Indeed, the employment of the amylose-based chiral stationary phase (CSP) in combination with a n-hexane/EtOH/DEA - 99/1/02 (v/v/v) mobile phase allowed getting the enantiomeric peaks fully resolved (α=1.80, RS=2.39). Four consecutive injections repeated at 1-min intervals produced overloaded peaks with a very limited level of isomeric contamination. This procedure allowed the isolation of ca. 20mg of each enantiomer, with enantiomeric excess higher than 99% and 95% for the (S)- and the (R)-isomer, respectively. The enantiomeric elution order was established using synthetic reference compounds of lower enantiomeric excess values. The biological evaluation of the purified individual enantiomers revealed no significant difference in terms of their IC50 values with respect to the previously investigated racemic BRP7: 0.18μM for the (R)-enantiomer (R(2)=0.999) and 0.26μM for the (S)-enantiomer (R(2)=0.986).

BRP-187: A potent inhibitor of leukotriene biosynthesis that acts through impeding the dynamic 5-lipoxygenase/5-lipoxygenase-activating protein (FLAP) complex assembly

The pro-inflammatory leukotrienes (LTs) are formed from arachidonic acid (AA) in activated leukocytes, where 5-lipoxygenase (5-LO) translocates to the nuclear envelope to assemble a functional complex with the integral nuclear membrane protein 5-LO-activating protein (FLAP). FLAP, a MAPEG family member, facilitates AA transfer to 5-LO for efficient conversion, and LT biosynthesis critically depends on FLAP. Here we show that the novel LT biosynthesis inhibitor BRP-187 prevents the 5-LO/FLAP interaction at the nuclear envelope of human leukocytes without blocking 5-LO nuclear redistribution. BRP-187 inhibited 5-LO product formation in human monocytes and polymorphonuclear leukocytes stimulated by lipopolysaccharide plus N-formyl-methionyl-leucyl-phenylalanine (IC50=7-10nM), and upon activation by ionophore A23187 (IC50=10-60nM). Excess of exogenous AA markedly impaired the potency of BRP-187. Direct 5-LO inhibition in cell-free assays was evident only at >35-fold higher concentrations, which was reversible and not improved under reducing conditions. BRP-187 prevented A23187-induced 5-LO/FLAP complex assembly in leukocytes but failed to block 5-LO nuclear translocation, features that were shared with the FLAP inhibitor MK886. Whereas AA release, cyclooxygenases and related LOs were unaffected, BRP-187 also potently inhibited microsomal prostaglandin E2 synthase-1 (IC50=0.2μM), another MAPEG member. In vivo, BRP-187 (10mg/kg) exhibited significant effectiveness in zymosan-induced murine peritonitis, suppressing LT levels in peritoneal exudates as well as vascular permeability and neutrophil infiltration. Together, BRP-187 potently inhibits LT biosynthesis in vitro and in vivo, which seemingly is caused by preventing the 5-LO/FLAP complex assembly and warrants further preclinical evaluation.

Pyrazole derivatives as inhibitors of arachidonic acid-induced platelet aggregation.

Antiplatelet drugs are promising therapeutics to intervene with platelet aggregation in arterial thrombosis, most prominently in myocardial infarction and ischemic stroke. Here, we describe the synthesis and structure-activity relationships of potent inhibitors of platelet aggregation based on the 1,5-diarylpyrazol-3-carboxamide scaffold. Analogs from this series demonstrated potent anti-aggregatory activities against arachidonic acid-induced platelet aggregation, as measured by turbidimetric method of Born. 1,5-Diarylpyrazole-3-carboxamides obtained with small-basic amines (7, 8, 50, 51, 61, 62) displayed the strongest activity with IC50 values in low nanomolar range (5.7-83 nM). On the basis of their high potency in cellular environment, these straightforward pyrazole derivatives may possess potential in the design of more potent compounds for intervention with cardiovascular diseases.