In vitro and in vivo phase II metabolism of combretastatin A-4: Evidence for the formation of a sulphate conjugate metabolite

Combretastatin A-4 (CA-4), is a natural compound with a potent tubulin polymerization and cell growth inhibitor properties. For these reasons CA-4 is one of the most potent anti-vascular agents that shows strong cytotoxicity against a variety of human cancer cells, including multi-drug-resistant cancer cell lines. In order to complete the knowledge of metabolic fate of CA-4, the in vitro and in vivo phase II metabolism was investigated. Both in incubation with rat and human liver S9 preparation in the presence of 39-phosphoadenosine-5-phosphosulfate (PAPS) as a cofactor the formation of a previously no reported sulphate metabolite was demonstrated through liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) data and comparison with a synthetic reference sample. In incubation of CA-4 using rat and human liver microsomes, the formation of CA-4 glucuronide was observed and chromatographic and mass spectral properties of the metabolite were achieved and compared with those of a synthetic reference sample. Incubation of CA-4 with rat and human liver S9 preparation in the presence of uridine-5-diphosphoglucuronic acid trisodium salt (UDPGA) and an -nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-regenerating system as cofactors resulted in the formation of glucuronides arising from phase I CA-4 metabolites. When CA-4 was administered intraperitoneally to rat at a dose of 30 mg kg-1, both glucuronide and sulphate metabolites were observed in LC-ESI-MS-MS chromatograms and their mass spectral data were identical to those obtained from synthetic standards.