Preclinical Pharmacokinetics Study of R- and S-Enantiomers of the Histone Deacetylase Inhibitor, AR-42 (NSC 731438), in Rodents

Abstract

AR-42, a new orally bioavailable, potent, hydroxamate-tethered phenylbutyrate class I/IIB histone deacetylase inhibitor currently is under evaluation in phase 1 and 2 clinical trials and has demonstrated activity in both hematologic and solid tumor malignancies. This report focuses on the preclinical characterization of the pharmacokinetics of AR-42 in mice and rats. A high-performance liquid chromatography-tandem mass spectrometry assay has been developed and applied to the pharmacokinetic study of the more active stereoisomer, S-AR-42, when administered via intravenous and oral routes in rodents, including plasma, bone marrow, and spleen pharmacokinetics (PK) in CD2F1 mice and plasma PK in F344 rats. Oral bioavailability was estimated to be 26 and 100% in mice and rats, respectively. R-AR-42 was also evaluated intravenously in rats and was shown to display different pharmacokinetics with a much shorter terminal half-life compared to that of S-AR-42. Renal clearance was a minor elimination pathway for parental S-AR-42. Oral administration of S-AR-42 to tumor-bearing mice demonstrated high uptake and exposure of the parent drug in the lymphoid tissues, spleen, and bone marrow. This is the first report of the pharmacokinetics of this novel agent, which is now in early phase clinical trials.

Trial registration: ClinicalTrials.gov NCT02282917 NCT01129193 NCT01798901 NCT02569320.

Keywords: AR-42; histone deacetylase inhibitor; mouse; pharmacokinetics; rat.

Fig. 1

MS/MS spectra of 10 μg/mL AR-42 (left) and internal standard, hesperetin (right). Chemical structures display potential fragmentation of each compound

Fig. 2

Ion chromatograms of extracts from blank mouse plasma (top) or mouse plasma spiked with 1000 ng/mL hesperetin (IS, middle) and 2 ng/mL S-AR-42 (bottom)

Fig. 3

Plasma concentration-time profile of S-AR-42 in the mouse following i.v. (a) and p.o. (b) administration at 20 and 50 mg/kg, respectively. Data points represent means of six replicates at each time point, and lines are fitted data using a two-compartment model

Fig. 4

Concentration of AR-42 in mouse bone marrow following the last of eight oral doses at 40 mg/kg. Data represent mean of n = 3 measurements per time point. The line was generated from fitting to a two-compartment model with extravascular input and weighting = 1/year²

Fig. 5

miR-29b expression vs. time profiles for bone marrow (top, circles) and spleen (bottom, squares) in AML-induced NGS mice. Data are fold change in expression relative to the pre-dose measurement (mice not dosed with AR-42). Data are presented as means of n = 3 measurements ± standard deviations

Fig. 6

Plasma concentration-time profiles of S-AR-42 in rat #1 following an i.v. bolus administration at 20 mg/kg (a) and p.o. administration at 50 mg/kg (b). Data points are means of n = 6 measurements. The line for the i.v. dosing data was generated from fitting to a two-compartment model