B117
Characterisation of the metabolism of fenretinide in paediatric tumour types
Nicola Harris, Alan Boddy, Jane Armstrong, Gareth Veal
Northern Institute for Cancer Research, Newcastle, UK
Background
Fenretinide (4HPR) is a synthetic analogue of retinoic acid, currently used in clinical trials in children for the treatment of neuroblastoma and Ewings sarcoma. The metabolism of 4HPR is of particular interest due to production of the active metabolite 4-oxo fenretinide (4-oxo 4HPR), which is able to act synergistically with 4HPR and is also active against some 4HPR resistant cell lines. The aim of this study was to characterise the in vitro metabolism of fenretinide in a microsomal assay and in neuroblastoma and Ewings sarcoma cell lines.
Method
4HPR metabolism was investigated in human liver microsomes (HLM), supersomes over-expressing individual human cytochrome P450s (CYPs) and Ewings sarcoma and neuroblastoma cell lines. Incubations were carried out for up to 3hrs with 20M or 50M 4HPR. In additional experiments cell lines were pre-incubated with ATRA (10M) to induce CYP 26. Samples were extracted and analysed by HPLC / LCMS assays developed to separate 4HPR and metabolites.
Results
HLM were found to predominantly produce 4-oxo 4HPR, with 4-hydroxy 4HPR generated as a minor metabolite. 3 CYPs from a panel of 8 tested were found to metabolise 4HPR (2C8 >3A4 >3A5). With CYP incubations, 4-hydroxy 4HPR was produced as a major metabolite and 4-oxo 4HPR produced as a minor metabolite.
Cell lines produced an additional metabolite, 4-methoxy PR (4MPR). 4MPR could also be produced by HLM with the addition of the methylation co-factor S-Adenosyl methionine, a reaction not blocked by inhibitors of catechol-O-methyltransferases (COMT). Pre-treatment with ATRA increased metabolism in all cell lines, with some cell lines only producing the active metabolite after ATRA pre-treatment.
Conclusion
The major metabolites of fenretinide have been identified and work is ongoing to fully characterise the enzymes responsible. These investigations will enable further research into the modulation of fenretinide metabolism with a view to optimising drug efficacy.
