Design, synthesis and binding studies of novel CYP26 inhibitors

All-frans-retinoic acid ATRA has shown spectacular success in the treatment of cancer and leukaemia, however ATRA is rapidly metabolised by the P450 enzyme CYP26. In order to enhance endogenous levels of ATRA and/or to extend the half life of externally administered ATRA, a CYP26 inhibitor is required. Two series of CYP26 inhibitors were synthesised a series of 4-alkyl/aryl-substituted 1-joeiizofuran-2-yl-phenylmethyl-1-triazoles and a series of benzoxazol-2-yl-phenylinn lazol The triazole derivatives were prepared using methodology previously described by our group. The aminobenzoxazole derivatives were envisaged from a docking experiment using a CYP26A1 homology model based on CYP3A4 template docking experiments were performed with MOE. The molecular docking of the amino-benzooxazole imidazole derivatives indicated multiple hydrogen bonding in addition to coordination between the imidazole nitrogen and the P450 haem transition metal. The triazole derivatives were evaluated for CYP26A1 inhibitory activity using a MCF-7 cell-based assay. The 4-ethyl-l,2,4-triazole and the 4-phenyl-l,2,4-triazole derivatives displayed inhibitory activity ICso 4.5 and ICso 7 uM respectively comparable with liarozole ICso 7 uM. On the other hand the aminobenzooxazole imidazole derivatives were only moderate inhibitors of the CYP26A1 enzyme in MCF-7 cells and did not achieve the promise shown in docking studies. The most potent inhibitor was the unsubstituted derivative IC5o 0.9 uM. Studies of the interaction of some of these inhibitors with hemin and TPP were also performed using different spectroscopic techniques mass spectrometry, X-ray crystallography, H NMR and UV/VIS spectroscopy and the binding constant was determined from the UV/VIS data for the unsubstituted compound of the aminobenzoxazole derivative with both hemin Km 1-69 0.31.105 M 1 and TPP Kt2 1.08 0.18.107 M2