(T1230-10-68) Mechanistic Elucidation of Pharmacokinetic Effects of Target-Mediated Drug Disposition (TMDD) for Small Molecule VAP-1 Inhibitor

Purpose: While target-mediated drug disposition (TMDD) has been well recognized and characterized in biologics due to its high prevalence, TMDD in small molecule compounds has yet to be commonly observed and received much less attention. When a small molecule is a covalent inhibitor irreversibly binding to the target protein, it can exhibit the pharmacokinetic features of TMDD. Vascular Adhesion Protein 1 (VAP-1) is a membrane-bound amine oxidase that promotes leukocyte infiltration and interaction with hepatic stellate cells (HSC). Pharmacological inhibition of VAP-1 impedes the transmigration of inflammatory leukocytes from the circulation into the liver, blocks leukocyte-HSC interaction and communication, and further prevents hepatic fibrosis. Herein, VAP-1 inhibitor GS-V1, which is irreversibly bound to VAP-1, was studied as a tool compound in preclinical species PK under various conditions to attain the PK features caused by TMDD.

Methods: With single-dose and multiple-dose PK studies in rats and monkeys, GS-V1 was formulated in aqueous solutions of 0.5% methyl cellulose/0.2% Tween 80, 15% 2-hyrdoxypropyl-β-cyclodextrin, or 5% dextrose for oral administration. Each dosing group consisted of 3 animals. Blood samples were collected at specified time points over a 24 h sampling period on each dosing day via jugular vein in rats or femoral vein in monkeys. The plasma samples were then harvested and analyzed using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Noncompartmental pharmacokinetic parameters were calculated by using Phoenix™ (Certara, Princeton, NJ).

Results: The non-linear pharmacokinetics were observed following the single ascending intravenous or oral administrations in rats and monkeys. After oral administrations at 1, 5, and 30 mg/kg in rats, the AUC_0-t values were 0.92, 12.3, and 109 µM·h, respectively. The AUC_0-t values increased greater than the dose-proportional. The estimated elimination half-lives (t_1/2) were also significantly extended from the dose level of 1 mg/kg to 30 mg/kg. The t_1/2 value was 1.6 h at 1 mg/kg, 2.6 h at 5 mg/kg, and 3.7 h at 30 mg/kg. In monkeys, this phenomenon was also observed from intravenous administrations at 1, 5, and 15 mg/kg. While the plasma concentrations of GS-V1 were barely detected above the detection limit ( >1 nM) at the dose level of 1 mg/kg, the AUC_0-t values increased greater than the dose-proportional between 5 and 15 mg/kg doses. The estimated elimination t_1/2 was extended, and the calculated clearance (CL) was decreased between 5 and 15 mg/kg doses. To investigate the PK profiles when VAP-1 binding site is saturated, GS-V1 was administered in rats following the 7 days multiple-dose at two dose levels of 0.1 and 1 mg/kg/day.

Conclusion: The observed non-linear PK (t_1/2, total CL, and AUC_0-t) from the administrations of GS-V1 in rats and monkeys indicate the saturation of VAP-1 binding sites in plasma and tissues because these observations cannot be rationalized by rapid elimination of GS-V1. These results suggest that TMDD effects can occur in a small molecule, and characterizing the PK phenomenon can aid the prediction of efficacious human doses.