Pharmacokinetic Characterization and Tissue Distribution of Fusion Protein Therapeutics by Orthogonal Bioanalytical Assays and Minimal PBPK Modeling

Characterization of pharmacokinetic (PK) properties and target tissue distribution of therapeutic fusion proteins (TFPs) are critical in supporting in vivo efficacy. We evaluated the pharmacokinetic profile of an investigational TFP consisting of human immunoglobulin G4 fused to the modified interferon alpha by orthogonal bioanalytical assays and applied minimal physiologically based pharmacokinetic (PBPK) modeling to characterize the TFP pharmacokinetics in mouse. The conventional ligand binding assay (LBA), immunocapture-liquid chromatography/tandem mass spectrometry (IC-LC/MS) detecting the human IgG4 peptide or the interferon alpha peptide were developed to measure the TFP concentrations in mouse plasma and tumor. The minimal PBPK model incorporated a tumor compartment model was used for data fitting. The plasma clearance measured by LBA and IC-LC/MS was comparable in the range of 0.5–0.6 mL/h/kg. However, the tumor exposure measured by the generic human IgG4 IC-LC/MS was significantly underestimated compared with the interferon alpha specific IC-LC/MS and LBA. Furthermore, the minimal PBPK model simultaneously captured the relationship between plasma and tissue exposure. We proposed the streamlined practical strategy to characterize the plasma exposure and tumor distribution of a TFP by both LBA and IC-LC/MS. The minimal PBPK modeling was established for better understanding of pharmacokinetic profile of investigational TFPs in the biotherapeutic discovery.

Understanding the Monoclonal Antibody Disposition after Subcutaneous Administration using a Minimal Physiologically based Pharmacokinetic Model

Purpose: Monoclonal antibodies (mAbs) are commonly administered by subcutaneous (SC) route. However, bioavailability is often reduced after SC administration. In addition, the sequential transfer of mAbs through the SC tissue and lymphatic system is not completely understood. Therefore, major objectives of this study were a) To understand absorption of mAbs via the lymphatic system after SC administration using physiologically based pharmacokinetic (PBPK) modeling, and b) to demonstrate application of the model for prediction of SC pharmacokinetics (PK) of mAbs. Methods: A minimal PBPK model was constructed using various physiological parameters related to the SC injection site and lymphatic system. The remainder of the body organs were represented using a 2-compartment model (central and peripheral compartments), with parameters derived from available intravenous (IV) PK data. The IV and SC clinical PK data of a total of 10 mAbs were obtained from literature. The SC PK data were used to estimate the lymphatic trunk-lymph node (LN) clearance. Results: The mean estimated lymphatic trunk-LN clearance obtained from 37 SC PK profiles of mAbs was 0.00213 L/h (0.001332 to 0.002928, 95% confidence intervals). The estimated lymphatic trunk-LN clearance was greater for the mAbs with higher isoelectric point (pI). In addition, the estimated clearance increased with decrease in the bioavailability. Conclusion: The minimal PBPK model identified SC injection site lymph flow, afferent and efferent lymph flows, and volumes associated with the SC injection site, lymphatic capillaries and lymphatic trunk-LN as important physiological parameters governing the absorption of mAbs after SC administration. The model may be used to predict PK of mAbs using the relationship of lymphatic trunk-LN clearance and the pI. In addition, the model can be used as a bottom platform to incorporate SC and lymphatic in vitro clearance data for mAb PK prediction in the future.