A further pocket or conformational plasticity by mapping COX-1 catalytic site through modified-mofezolac structure-inhibitory activity relationships and their antiplatelet behavior

Cyclooxygenase enzymes have distinct roles in cardiovascular,neurological, and neurodegenerative disease. They are differentlyexpressed in different type of cancers. Specific and selective COXsinhibitors are needed to be used alone or in combo -therapies. Fullyunderstand the differences at the catalytic site of the twocyclooxygenase (COX) isoforms is still opened to investigation. Thus,two series of novel compounds were designed and synthesized in fair togood yields using the highly selective COX -1 inhibitor mofezolac as thelead compound to explore a COX -1 zone formed by the polar residuesQ192, S353, H90 and Y355, as well as hydrophobic amino acids I523, F518and L352. According to the structure of the COX-1:mofezolac complex,hydrophobic amino acids appear to have free volume eventually accessibleto the more sterically hindering groups than the methoxy linked to thephenyl groups of mofezolac, in particular the methoxyphenyl atC4-mofezolac isoxazole. Mofezolac bears two methoxyphenyl groups linkedto C3 and C4 of the isoxazole core ring. Thus, in the novel compounds,one or both methoxy groups were replaced by the higher homologousethoxy, normal and isopropyl, normal and tertiary butyl, and phenyl andbenzyl. Furthermore, a major difference between the two sets ofcompounds is the presence of either a methyl or acetic moiety at the C5of the isoxazole. Among the C5 -methyl series, 12 (direct precursor ofmofezolac) (COX -1 IC50 = 0.076 mu M and COX -2 IC50 = 0.35 mu M) and15a (ethoxy replacing the two methoxy groups in 12; COX -1 IC50 = 0.23mu M and COX -2 IC50 > 50 mu M) were still active and with a SelectivityIndex (SI = COX -2 IC50/COX-1 IC50) = 5 and 217, respectively. The othersymmetrically substituted alkoxyphenyl moietis were inactive at 50 mu Mfinal concentration. Among the asymmetrically substituted, only the 16a(methoxyphenyl on C3-isoxazole and ethoxyphenyl on C4-isoxazole) and 16b(methoxyphenyl on C3-isoxazole and n-propoxyphenyl on C4-isoxazole) wereactive with SI = 1087 and 38, respectively. Among the set of compoundswith the acetic moiety, structurally more similar to mofezolac (SI =6329), SI ranged between 1.4 and 943. It is noteworthy that 17b(n-propoxyphenyl on both C3- and C4-isoxazole) were found to be a COX -2slightly selective inhibitor with SI = 0.072 (COX -1 IC50 > 50 mu M andCOX -2 IC50 = 3.6 mu M). Platelet aggregation induced by arachidonicacid (AA) can be in vitro suppressed by the synthesized compounds,without affecting of the secondary hemostasia, confirming the biologicaleffect provided by the selective inhibition of COX -1. A positiveprofile of hemocompatibility in relation to erythrocyte and platelettoxicity was observed. Additionally, these compounds exhibited apositive profile of hemocompatibility and reduced cytotoxicity.Quantitative structure activity relationship (QSAR) models and molecularmodelling (Ligand and Structure based virtual screening procedures)provide key information on the physicochemical and pharmacokineticproperties of the COX -1 inhibitors as well as new insights into themechanisms of inhibition that will be used to guide the development ofmore effective and selective compounds. X-ray analysis was used toconfirm the chemical structure of 14 (MSA17).