Investigations into the Potential Role of Metabolites on the Anti-Leukemic Activity of Imatinib, Nilotinib and Midostaurin.

The efficacy and side-effects of drugs do not just reflect the biochemical and pharmacodynamic properties of the parent compound, but often comprise of cooperative effects between the properties of the parent and active metabolites. Metabolites of imatinib, nilotinib and midostaurin have been synthesised and evaluated in assays to compare their properties as protein kinase inhibitors with the parent drugs. The -desmethyl-metabolite of imatinib is substantially less active than imatinib as a BCR-ABL1 kinase inhibitor, thus providing an explanation as to why patients producing high levels of this metabolite show a relatively low response rate in chronic myeloid leukaemia (CML) treatment. The hydroxymethylphenyl and -oxide metabolites of imatinib and nilotinib are only weakly active as BCR-ABL1 inhibitors and are unlikely to play a role in the efficacy of either drug in CML. The 3-()-HO-metabolite of midostaurin shows appreciable accumulation following chronic drug administration and, in addition to mutant forms of FLT3, potently inhibits the PDPK1 and VEGFR2 kinases (IC values <100 nM), suggesting that it might contribute to drug efficacy in acute myeloid leukaemia patients. The case studies discussed here provide further examples of how the synthesis and characterisation of metabolites can make important contributions to understanding the clinical efficacy of drugs.