molecules Article COX Inhibition Profile and Molecular Docking Studies of Some 2-(Trimethoxyphenyl)-Thiazoles Smaranda Dafina Oniga 1, Liliana Pacureanu 2,*, Cristina Ioana Stoica 1, Mariana Doina Palage 1,* ID , Alexandra Crăciun 3, Laurentiu Răzvan Rusu 3, Elena-Luminita Crisan 2 and Cătălin Araniciu 1 1 Faculty of Pharmacy, “Iuliu Hatieganu” University of Medicine and Pharmacy, 8 Victor Babes St, Cluj–Napoca 400012, Romania; [email protected] (S.D.O.); [email protected] (C.I.S.); [email protected] (C.A.) 2 Institute of Chemistry Timisoara of Romanian Academy, 24 M. Viteazul Ave., Timisoara 300223, Romania; [email protected] 3 Faculty of Medicine, “Iuliu Hatieganu” University of Medicine and Pharmacy, 8 Victor Babes St, Cluj–Napoca 400012, Romania; [email protected] (A.C.); [email protected] (L.R.R.) * Correspondence: [email protected] (L.P.); [email protected] (M.D.P.); Tel.: +40-256-491818 (L.P.); +40-264-450-528 (M.D.P.); Fax: +40-256-491824 (L.P.) Received: 24 August 2017; Accepted: 6 September 2017; Published: 9 September 2017 Abstract: Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used therapeutic agents that exhibit frequent and sometimes severe adverse effects, including gastrointestinal ulcerations and cardiovascular disorders. In an effort to obtain safer NSAIDs, we assessed the direct cyclooxygenase (COX) inhibition activity and we investigated the potential COX binding mode of some previously reported 2-(trimethoxyphenyl)-thiazoles. The in vitro COX inhibition assays were performed against ovine COX-1 and human recombinant COX-2. Molecular docking studies were performed to explain the possible interactions between the inhibitors and both COX isoforms binding pockets. Four of the tested compounds proved to be good inhibitors of both COX isoforms, but only compound A3 showed a good COX-2 selectivity index, similar to meloxicam. The plausible binding mode of compound A3 revealed hydrogen bond interactions with binding site key residues including Arg120, Tyr355, Ser530, Met522 and Trp387, whereas hydrophobic contacts were detected with Leu352, Val349, Leu359, Phe518, Gly526, and Ala527. Computationally predicted pharmacokinetic profile revealed A3 as lead candidate. The present data prove that the investigated compounds inhibit COX and thus confirm the previously reported in vivo anti-inflammatory screening results suggesting that A3 is a suitable candidate for further development as a NSAID. Keywords: 2-(trimethoxyphenyl)-thiazoles; selective COX-2 inhibition; NSAIDs; molecular docking 1. Introduction Non-steroidal anti-inflammatory drugs (NSAIDs) that act by cyclooxygenase inhibition are a major drug class. Due to their ample therapeutic use that ranges from the treatment of fever and mild pain up to severe chronic inflammatory disorders, NSAIDs are one of the most commonly used medicines. The wide scale, frequent and sometimes long-term use of these drugs has allowed for a very good characterization of their safety profile. While some adverse reactions concerning gastrointestinal manifestations (gastritis, ulcer, bleeding) are well documented and established, others, like the cardiovascular risk, are still being assessed today [1,2]. It is well established that NSAIDs act by blocking the production of pro-inflammatory prostaglandins through the inhibition of cyclooxygenase (COX). At least two isoforms of COX are known, COX-1 and COX-2. COX-1 is mainly considered a “housekeeping enzyme”. It is widely Molecules 2017, 22, 1507; doi:10.3390/molecules22091507 www.mdpi.com/journal/molecules Molecules 2017, 22, 1507 2 of 15 Molecules 2017, 22, 1507 2 of 16 stimulating thromboxane A2 (TXA2). By contrast, COX-2 is viewed primarily as responsible for the distributed in most tissues where it performs mainly physiological roles like: protecting the gastric initiation and maintenance of the inflammation process with only minor physiological roles like mucosa,stimulating kidney prostacyclin function maintenance (PGI2) production and protection, and thus orpreventing regulating platelet platelet aggregation aggregation [3–5]. via stimulating thromboxaneIt is commonly A2 (TXA2). accepted By contrast, that gastrointestinal COX-2 is viewed side-effects primarily are as mainly responsible associated for the with initiation the andinhibition maintenance of the ofcyclooxygenase-1 the inflammation (COX-1), process while with cardiovascular only minor side-effects physiological are directly roles like linked stimulating with prostacyclinthe inhibition (PGI2) of COX-2 production (possibly and by thus blocking preventing PGI2 biosynthesis platelet aggregation while not hindering [3–5]. TXA2 formation [4]).It isThe commonly withdrawal accepted from that the gastrointestinal market of most side-effects COX-2 specific are mainly inhibitors, associated coxibs with (valdecoxib, the inhibition ofrofecoxib), the cyclooxygenase-1 has proven that (COX-1), the intent while to decrease cardiovascular gastrointestinal side-effects side-effects are directly by creating linked specific with the inhibitionCOX-2 inhibitors of COX-2 has (possibly turned by out blocking to be unfavorable, PGI2 biosynthesis as they are while characterized not hindering by significantly TXA2 formation higher [ 4]). Thecardiovascular withdrawal from risks the[6]. marketIt seems of that most the COX-2 higher specificthe specificity inhibitors, towards coxibs COX-2 (valdecoxib, inhibition, rofecoxib), the higher has proventhe risk that of the CV intent undesirable to decrease effects. gastrointestinal This observation side-effects is supported by creating by the fact specific that celecoxib, COX-2 inhibitors the only has turnedcoxib out that to is be still unfavorable, approved by as the they US areFood characterized and Drug Administration by significantly (FDA), higher is actually cardiovascular the least COX- risks [6]. It seems2 specific that of the all higher coxibs theand specificity thus shows towards a higher COX-2 percentage inhibition, of COX-1 the inhibition higher the than risk other of CV coxibs undesirable [7]. effects.Considering This observation this, we is supported aimed to obtain by the molecules fact that celecoxib,that act only the as only selective coxib COX-2 that is stillinhibitors, approved but by are not specific COX-2 inhibitors and still maintain some degree of COX-1 inhibition. To this effect, the US Food and Drug Administration (FDA), is actually the least COX-2 specific of all coxibs and thus we set out to mimic the pharmacological profile of meloxicam, which is only slightly COX-2 selective shows a higher percentage of COX-1 inhibition than other coxibs [7]. and not COX-2 specific. Optimally, the new derivatives should have a COX-1/COX-2 selectivity ratio Considering this, we aimed to obtain molecules that act only as selective COX-2 inhibitors, but are higher than meloxicam but lower than celecoxib [7]. not specific COX-2 inhibitors and still maintain some degree of COX-1 inhibition. To this effect, we set Thus, inspired by the classical NSAIDs, molecules which contain methoxy groups (nabumetone, outindomethacin, to mimic the pharmacologicalnaproxen) and also profile recent of re meloxicam,search undertaken which isby only Abdel–Aziz slightly COX-2et al. [8], selective as shown and innot COX-2Figure specific. 1, we previously Optimally, designed the new and derivatives synthesized should a series have of a COX-1/COX-24,5-substituted 2-(trimethoxyphenyl) selectivity ratio higher thanthiazoles meloxicam [9] (A1 but–13 lower, Figure than 2). celecoxibThe thiazole [7]. nucleus is a well established component of many drugs [10–12]Thus, and inspired was chosen by the as classical a key moiety NSAIDs, because molecules it is present which in known contain NSAIDs methoxy (meloxicam, groups (nabumetone, fentiazac) indomethacin,and also in many naproxen) lead anti-inflammatory and also recent molecules research undertaken that are under by development: Abdel–Aziz 2-aryl-thiazole et al. [8], as shown [13], in Figurefuro[2,3-d]thiazole1, we previously [14], designed coumarin-thiazoles and synthesized [15], diarylthiazoles a series of 4,5-substituted [16]. 2-(trimethoxyphenyl) thiazolesIn order [9](A1 to –assess13, Figure the importance2). The thiazoleof the diaryl-het nucleuserocyclic is a well structures established of coxibs component on selective of COX- many drugs2 inhibition, [10–12] and we was previously chosen asdesigned a key moiety and becausetested molecules it is present with in knowntwo, three NSAIDs or even (meloxicam, four fentiazac)(hetero)aromatic and also rings in [9,17,18]. many lead In our anti-inflammatory previous papers, we molecules also described that the are preliminary under development: evaluation 2-aryl-thiazoleof the anti-inflammatory [13], furo[2,3-d]thiazole potential of the [14 compound], coumarin-thiazoless by determining [15], diarylthiazolestheir effects using [16 an]. induced acute inflammation experimental model [9,18]. FigureFigure 1. 1.The The inspiration inspiration for for the thedesign design of the 2-(t 2-(trimethoxyphenyl)-4-R1-5R2-thiazolerimethoxyphenyl)-4-R1-5R2-thiazole scaffold. scaffold. In order to assess the importance of the diaryl-heterocyclic structures of coxibs on selective COX-2 inhibition, we previously designed and tested molecules with two, three or even four Molecules 2017, 22, 1507 3 of 15 (hetero)aromatic rings [9,17,18]. In our previous papers, we also described the preliminary evaluation of the anti-inflammatory potential of the compounds by determining