Celecoxib prodrugs possessing a diazen-1-ium-1,2-diolate nitric oxide donor moiety: Synthesis, biological evaluation and nitric oxide release studies Khaled R. A. Abdellatif, Morshed A. Chowdhury, Carlos A. Velázquez, Zhangjian Huang, Ying Dong, Dipankar Das, Gang Yu, Mavanur R. Suresh, Edward E. Knaus * Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8 article info Article history: Received 17 May 2010 Revised 2 June 2010 Accepted 3 June 2010 Available online 8 June 2010 Keywords: Nitric oxide donors Cyclooxygenase inhibition Anti-inflammatory activity abstract A new class of anti-inflammatory (AI) cupferron prodrugs was synthesized wherein a diazen-1-ium-1,2- diolato ammonium salt, and its O 2 -methyl and O 2 -acetoxyethyl derivatives, nitric oxide (NO) donor moie- ties were attached directly to an aryl carbon on a celecoxib template. The percentage of NO released from the O 2 -methyl and O 2 -acetoxyethyl compounds was higher (18.0–37.8% of the theoretical maximal release of one molecule of NO/molecule of the parent compound) upon incubation in the presence of rat serum, rel- ative to incubation with phosphate buffer saline (PBS) at pH 7.4 (3.8–11.6% range). All compounds exhibited weak inhibition of the COX-1 isozyme (IC 50 = 5.8–17.0 lM range) in conjunction with weak or modest inhibition of the COX-2 isozyme (IC 50 = 1.6–14.4 lM range). The most potent AI agent 5-[4-(O 2 -ammonium diazen-1-ium-1,2-diolato)phenyl]-1-(4-sulfamoylphenyl)-3-trifluoromethyl-1H-pyrazole exhibited a potency that was about fourfold and twofold greater than that observed for the respective reference drugs aspirin and ibuprofen. These studies indicate that use of a cupferron template constitutes a plausible drug design approach targeted toward the development of AI drugs that do not cause gastric irritation, or elevate blood pressure and induce platelet aggregation that have been associated with the use of some selective COX-2 inhibitors. Ó 2010 Elsevier Ltd. All rights reserved. The development of celecoxib (1), 1 rofecoxib (2), 2 and valdecoxib (3) 3 validated the original concept that selective cyclooxygenase-2 (COX-2) inhibitors would be effective anti-inflammatory agents with a diminished gastrointestinal (GI) and renal toxicity (see struc- tures in Fig. 1). 4–7 Unfortunately, some selective COX-2 inhibitory drugs including rofecoxib and valdecoxib alter the natural biochem- ical balance in the COX pathway. In this regard, the amount of the desirable vasodilatory and anti-aggregtory prostacyclin (PGI 2 ) pro- duced is decreased together with a simultaneous increase in the level of the undesirable vasoconstrictory and prothrombotic throm- boxane A 2 (TxA 2 ). 8–10 These two adverse biochemical changes in the COX pathway are believed to be responsible for the increased inci- dences of high blood pressure and myocardial infarction that ulti- mately prompted the withdrawal of rofecoxib and valdecoxib. 11,12 Nitric oxide (NO) exhibits a number of useful pharmacological ac- tions that include vascular relaxation (vasodilation), and inhibition of platelet aggregation and adhesion. 13 Accordingly, attachment of a NO-donor moiety to highly selective COX-2 inhibitors (NONO-cox- ibs) offers a potential drug design concept to circumvent adverse cardiovascular events. In previous studies, we reported NONO-coxib ester prodrugs (4–6), having a NO-donor diazen-1-ium-1,2-diolate moiety, that are effectively cleaved by esterases to release NO. The spontaneous decomposition reaction of N-diazeniumdiolates 4–6, upon esterase-mediated hydrolysis, would release the active com- ponents (coxib and NO) in conjunction with 1 molecule of a second- ary amine, 1 molecule of formaldehyde, and one molecule of acetic acid for 5 and 6. 14–16 In developing drug design strategies, it is important to minimize or prevent the potential risk of exposure to contraindicated products that may be formed in vivo. 17 This concern can be addressed by preparing NO-coxib prodrugs that release only the active coxib and NO. This objective was not achieved in the case of the hybrid NO-donor diazen-1-ium-1,2-diolate derivatives (7, 8) which could not be isolated since these salts undergo spontaneous decomposition to release NO and a N-nitroso product. 18,19 It has been reported (i) that the direct attachment of a NO donor group to an aromatic carbon atom provides a class of compounds called cupferrons that are stable under protonating conditions, 20,21 and (ii) this type of cupferrons release one molecule of NO together with a nitroso product that is stated to be non-carcinogenic even though no biological data was provided to support this claim. 22–24 As part of our ongoing program, we now report the synthesis, in vitro COX-1/ COX-2 inhibitory activity, in vivo anti-inflammatory (AI) activity and NO release data for a new class of nitric oxide-releasing AI com- 0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2010.06.022 * Corresponding author. Tel.: +1 780 492 5993; fax: +1 780 492 1217. E-mail address: eknaus@pharmacy.ualberta.ca (E.E. Knaus). Bioorganic & Medicinal Chemistry Letters 20 (2010) 4544–4549 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl