Pharmacokinetics, pharmacodynamics, metabolism, transport, and resistance studies of a novel histone deacetylase inhibitor FK228 (FR901228, NSC630176)

Depsipeptide FK228 (FR901228, NSC630176), a promising histone deacetylase (HDAC) inhibitor, is currently undergoing clinical evaluation against various malignancies.;Pharmacokinetic study of FK228 in the rat was first conducted with a focus on its pharmacokinetic properties and dose recovery. FK228 was found to be removed rapidly from the circulation with a total body clearance higher than the rat cardiac output, suggesting extensive metabolism in the blood. Dose recovery of FK228 was low (<15%) and there was an involvement of glutathione in FK228 elimination. Based on these results, we conducted in vitro metabolism studies, which led to identification of four glutathione conjugates and two thiols from rat and human blood incubations. Purification of these major metabolites followed by HDAC inhibition assays indicated that FK228 is a prodrug, with three major metabolites being more potent HDAC inhibitors than FK228 itself.;A clinical pharmacokinetic study in AML and CLL patients was conducted. A pharmacokinetic-pharmacodynamic correlation study showed that HDAC inhibitory activity was inversely correlated with FK228 systemic exposure. This provided the first clinical evidence that FK228 was a prodrug.;FK228 transport and uptake was investigated. It was found that FK228 is a substrate for both MDR1 and MRP1 by transport and cytotoxicity studies using specific inhibitors of the membrane transporters. In order to study the roles of MDR1 and MRP1 in acquired FK228 resistance, four FK228 resistant cell lines were established and characterized. We found that upregulation of MDR1, but not MRP1 or other ABC transporters, was responsible for the acquired resistance. The maintenance of acquired FK228 resistance depended on continuous drug exposure. No deregulation or impairment of the histone acetylation machinery was found. The MDR1 upregulation was further found to be via a reversible induction procedure, in which FK228 first inhibited HDACs and then caused hyperacetylation at the MDR1 promoter region to form the euchromatin structure ready for transcription.;Overall, the dissertation work, involving both preclinical and clinical studies, provided valuable information of pharmacokinetics, bioactivation, transport and uptake, and resistance of the novel anticancer drug FK228.