FG-3019, a Human Monoclonal Antibody Recognizing Connective Tissue Growth Factor, is Subject to Target-Mediated Drug Disposition

Abstract

Purpose: To evaluate and model the pharmacokinetic and pharmacodynamic behavior in rats of FG-3019, a human monoclonal antibody targeting connective tissue growth factor (CTGF).

Methods: FG-3019, human CTGF (rhCTGF), or the N-terminal domain of rhCTGF were administered intravenously to rats and concentrations of these proteins as well as endogenous CTGF were determined by immunoassays. FG-3019, or (125)I-labeled FG-3019, and human CTGF (rhCTGF) were co-administered to assess the impact of CTGF on the elimination rate and tissue localization of FG-3019, which was further characterized by immunohistochemical analysis. A PK/PD model for target-mediated elimination of FG-3019 was developed to fit the kinetic data.

Results: FG-3019 exhibited non-linear pharmacokinetics in rats. Circulating concentrations of the N-terminal half of CTGF increased after dosing with FG-3019, reached maximal levels after 1-5 days, and returned toward baseline levels as FG-3019 cleared from the circulation, whereas the concentration of intact CTGF was unaffected by administration of FG-3019. Co-administration of rhCTGF dramatically enhanced the rate of FG-3019 elimination, redistributing the majority of (125)I-labeled FG-3019 from the blood to the liver, kidney, spleen and adrenal gland. FG-3019 co-administered with CTGF was found along the sinusoids of the liver and adrenal glands, the capillaries of the kidney glomeruli and in the spleen. A pharmacokinetic model for target-mediated elimination of FG-3019 was used to fit the time courses of FG-3019 and endogenous CTGF plasma concentrations, as well as time courses of rhCTGF and rhCTGF N-fragment after intravenous administration of these species.

Conclusions: FG-3019 is subject to target mediated elimination in rats.

Keywords: CTGF; Connective Tissue Growth Factor; FG-3019; TMDD.

Fig. 1

Plasma concentration time courses for FG-3019 in male rats. The mean plasma concentration of FG-3019 is expressed in ng/ml (right axis) and in nanomolar binding site concentration (MW = 75,000) (left axis). FG-3019 doses administered were 0.03 mg/kg (n = 3) (open squares), 0.3 mg/kg (n = 3) (solid squares), 3 mg/kg (n = 9) (solid triangles), 10 mg/kg (n = 6) (open triangles), 30 mg/kg (n = 6) (open circles) and 100 mg/kg (n = 6) (solid circles). Error bars reflect standard deviations. Solid curves are from fits of the data using a pharmacokinetic model.

Fig. 2

Rat plasma concentrations of endogenous CTGF following administration of FG-3019. Male rats were administered FG-3019 at 10 mg/kg (diamonds), 30 mg/kg (squares) or 100 mg/kg (triangles). CTGF was measured using the N+W-CTGF assay as described in the text. Error bars are standard deviations of the means of three animals. Concentrations of intact CTGF measured with the W-CTGF assay are below 5 ng/ml and are not shown. Solid curves are fits obtained from pharmacokinetic modeling. Inset: concentrations of FG-3019 in rats dosed at 100 mg/kg (circles,right axis) are shown with the corresponding CTGF concentrations (triangles,left axis).

Fig. 3

Plasma Concentration Time Courses of Recombinant Human CTGF in Male Rats. Top panel: rhCTGF-N was administered at 0.38 mg/kg (solid triangles) and 0.8 mg/kg (open squares). CTGF was measured using the N+W-CTGF assay. Bottom panel: rhCTGF was administered at 0.76 mg/kg (solid circles) and 1.6 mg/kg (open diamonds). CTGF was measured using the W-CTGF assay. Error bars are standard deviations from 3 animals per group. Solid curves were obtained by a pharmacokinetic model.

Fig. 4

Effect of Co-administered CTGF on FG-3019 pharmacokinetics. The amount of FG-3019 (expressed as percent of initial level remaining) is shown versus time after administration of CTGF or other components. Components co-administered were: buffer (open circles); CTGF-N (solid diamonds); CTGF at 0.5:1 molar ratio with FG-3019 (solid squares); CTGF at 1:1 molar ratio with FG-3019 (solid triangles); CTGF at 2:1 molar ratio with FG-3019 (solid circles). FG-3019 was administered at −10 min. CTGF was added at time zero.Error bars reflect the standard deviation of mean values.

Fig. 5

Effect of Co-administered RAP on CTGF mediated elimination of FG-3019. The level of FG-3019 (expressed as percent of initial level) is shown versus time after administration of CTGF (squares), or RAP (9 mg) immediately followed by CTGF (triangles). CTGF was administered at a 2:1 molar ratio to FG-3019. CTGF or (RAP + CTGF) was administered at time zero, 10 min after FG-3019. Error bars reflect standard deviation of mean values.

Fig. 6

Schematic diagram of the PK model of target mediated disposition of FG-3019. The model assumes that both CTGF (W) and CTGF-N (N) are constitutively produced at zero-order rates k_W and k_N, and cleared by first-order processes CL_W and CL_N, respectively. They also distribute to peripheral tissues W_T and N_T at distributional clearance rates CL_dW and CL_dN, respectively. CTGF is cleared from the tissues at the first-order clearance rate CL_WT. The antibody, FG-3019, is cleared from the circulation at the first-order clearance rate CL_Ab and distributes to the peripheral tissue compartment Ab_T at clearance rate CL_dAb. Ab binds to the target species W and N at second-order rate constants k_onW and k_onN and forms complexes Ab_W and Ab_N, respectively. The complexes dissociate to single molecule species Ab and W, and Ab and N at first-order rates k_offW and k_offN, respectively. The complexes Ab_W and Ab_N distribute to the tissue compartments Ab_WT and Ab_NT at the first-order clearance rates CL_dAbW and CL_dAbN, respectively. The complex Ab_WT is eliminated from the tissues at the first-order clearance rate CL_AbWT. The binding and dissociation of the antibody, CTGF, and CTGF-N in the tissues were neglected.

Fig. 7

Dose-dependence of target-mediated elimination of FG-3019. The percent target-mediated elimination was estimated by modeling rates of elimination of FG-3019 from tissue and central compartments.

Fig. 8

Distribution of [¹²⁵I]-FG-3019 at 15 min after administration without or with addition of CTGF. Left panel: without administration of CTGF. Right panel: with administration of CTGF 5 min before euthanasia.

Fig. 9

Immunohistochemical Localization of FG-3019. Tissue sections stained for FG-3019 are shown at 10× (upper panel) and 60× (lower panel) magnification for adrenal gland (cortex and medulla), liver, kidney (cortex) and spleen (red pulp) 5 min after IV administration of CTGF to rats dosed 10 min previously with FG-3019. Tissue sections from animals dosed with vehicle after FG-3019 instead of CTGF exhibited no staining for FG-3019.