Glucuronidation by UGT1A1 Is the Dominant Pathway of the Metabolic Disposition of Belinostat in Liver Cancer Patients

10.1371/journal.pone.0054522PLoS ONE81

Glucuronidation by UGT1A1 Is the Dominant Pathway of the Metabolic Disposition of Belinostat in Liver Cancer Patients

Belinostat is a hydroxamate class HDAC inhibitor that has demonstrated activity in peripheral T-cell lymphoma and is undergoing clinical trials for non-hematologic malignancies. We studied the pharmacokinetics of belinostat in hepatocellular carcinoma patients to determine the main pathway of metabolism of belinostat. The pharmacokinetics of belinostat in liver cancer patients were characterized by rapid plasma clearance of belinostat with extensive metabolism with more than 4-fold greater relative systemic exposure of major metabolite, belinostat glucuronide than that of belinostat. There was significant interindividual variability of belinostat glucuronidation. The major pathway of metabolism involves UGT1A1-mediated glucuronidation and a good correlation has been identified between belinostat glucuronide formation and glucuronidation of known UGT1A1 substrates. In addition, liver microsomes harboring UGT1A1*28 alleles have lower glucuronidation activity for belinostat compared to those with wildtype UGT1A1. The main metabolic pathway of belinostat is through glucuronidation mediated primarily by UGT1A1, a highly polymorphic enzyme. The clinical significance of this finding remains to be determined.ClinicalTrials.gov NCT00321594</p

UGT1A1 expression on belinostat glucuronidation and impact of the common UGT1A1*28 promoter polymorphism.

<p>A: Correlation of belinostat glucuronide formation with UGT1A1 expression in human liver microsomes; B: Belinostat glucuronide formation by human liver microsomes according to wild-type, heterozygous and homozygous UGT1A1*28 genotypes.</p

Pharmacokinetic parameters for belinostat after 30 min i.v. infusion in Phase I trial.

<p>Abbreviation: Cmax, maximum concentration; Tmax, time to maximum concentration; AUC_{0–24 h,} area under the curve from 0 to 24 h; T_1/2, half-life at the elimination phase; CL, clearance; Vz, volume of distribution. *Mean ± SD; AUC ratio was calculated based on AUC_{0–24 h} of Bel-G (belinostat-G) over AUC_{0–24 h} of Bel (belinostat).</p

Enzyme kinetics of glucuronidation of belinostat by UGT1A1.

<p>The apparent Km and Vmax values for the glucuronide formation were 99.6 µM and 353.1 pmol/min/mg protein, respectively.</p

Identification of belinostat metabolites in human plasma using HPLC-DAD & LC-MS/MS analyses.

<p>Identification of belinostat metabolites in human plasma using HPLC-DAD & LC-MS/MS analyses.</p

Cytotoxicity and acetylation activity on HepG2.

<p>a: belinostat incubation; b: belinostat-G incubation; (templates for concentrations added (lower) and results of 24-well dose-increasing concentrations on HepG2 Cells (upper). c: MTS results for belinostat (IC₅₀ = 6.4 µM) and belinostat-G (cannot be converged). d:Belinostat acetylation activity on HepG2 cells (western blot). A: Acetyl histone 3 increased with dose increment after 5 h incubation; B: Kinetic changes of acetyl histone 3 with time increment at 10 µM.</p

Identification of belinostat metabolites in human plasma using HPLC-UV at maximum absorption wavelength (λ = 268 nm).

<p>Chromatogram at day 5 and day 22 (A); day1(B).</p