Design, Synthesis And Evaluation Of Cyclooxygenase-2 Inhibitors

Cyclooxygenase-2 (COX-2) selective inhibitors belong to a new class of non-steroidal anti-inflammatory drugs (NSAIDs). Owing to their reduced gastrointestinal side effects as compared to classic NSAIDs, COX-2 selective inhibitors have experienced tremendous development during the past 10 years. The differences between the active sites of COX-2 and COX-1 enzymes are the basis for design of COX-2 selective inhibitors. The volume of the active site of COX-2 is larger than that of COX-1; moreover, an additional pocket exists in the catalytic channel of COX-2, but not in COX-1.By taking advantage of the known structure-activity relationships (SAR) of selective COX-2 inhibitors, molecular modeling techniques and information provided by structural biology, eleven groups of target compounds with different structural scaffolds were designed and synthesized. The groups I , II and III involved the modification of NSAIDs ibuprofen and naproxen. A substituted benzamide group was introduced to the 3 position of the phenyl of ibuprofen in the I group. In groups II and III, the carboxyl groups of ibuprofen and naproxen were converted into thiazol-2-yl moiety. The purposes of these modifications were to introduce a structural segment to occupy the side pocket in COX-2. In groups IV and V, the oxygen ether linkage of nimesulide was replaced by a carbonyl or oxime, so as to take advantage of conformational alteration to enhance the selectivity for COX-2. In groups VI- XI, a series of thiazole derivatives were designed as me-too analogs of new structural selective COX-2 inhibitors based on the common skeleton 2-methyl-4- [4-mesyl (or 4-sulfamic)-phenyl]-thiazole. According to the principle of bioisosterism, the 5 position of the thiazole was substituted by amide, oxygen ether, amino, carbonyl and methylene moieties respectively.All together, 112 chemical substances were prepared, in which 64 compounds were target molecules, and 97 compounds were of novelty. All the target compounds were identified by the methods of 'HNMR, MS and elemental analysis (or high resolution MS). The 'Z' configuration of GCB0346B was identified by X-ray crystallography.The target compounds were biologically evaluated in vitro and some of them were tested in vivo and structure and activity relationships were analyzed to provide valuable clues to further study. The target compounds of group III IV V X XI exhibited inhibitory activity against COX-2 in vitro, among them the IC₅₀ values for COX-2 of GCB0328, GCB0329, GCB0344 and GCB0339B reached 10^-7～10^-8mol/L. Some of the target compounds were also screened in vitro against COX-1, which indicated that GCB0339B showed a selective inhibitory activity for COX-2. GCB0344 and GCB0328 were shown to significantly delay acetic acid induced mouse writhing and reduce croton oil induced mouse ear edema in vivo. GCB0344 was shown to inhibit carrageenan induced rat but not mouse paw edema; in contrast, GCB0328 was shown to inhibit carrageenan induced mouse but not rat paw edema. Such results suggested that GCB0328 and GCB0344 had remarkable analgesic and anti-inflammatory effects. It is possible that further structural optimization of these compounds will provide novel NSAIDs with high potency, low toxicity, and independent intellectual properties.Since the COX-2 selective inhibitors have been used clinically to prevent and treat some cancers, some target compounds were evaluated for their ability to inhibit cancers in vitro and in vivo. Results showed that eleven compounds such as GCB0417 and GCB0319 exhibited inhibitory effect to some extent against six cancer cell lines such as colon, mammary and gastric cancer cell lines in the improved MTT assay. Six compounds were shown inhibitory effect on colony forming of HT-29 colon cancer cells with high expression of COX-2. GCB0417 exhibited weak inhibitory activity against the growth of HT-29 colon cancer in nude mice at the dose of 200 mg/kg orally.