Simulation-based simplification of target-mediated drug disposition model of denosumab

Target-mediated drug disposition (TMDD)model is one of the main modeling theories for studying nonlinear pharmacokinetics (PK)ofmonoclonal antibodies.However,there are too many parameters in full TMDD model to be estimated based on limited clinical data,leading to instability of the final model.In the present study,we analyzed the predictive ability and applicability of a simplified quasi-steady state (QSS)model with the assumption that the total target concentration was a constant parameter during treatment with monoelonal antibody in clinical data modeling.Based on the parameters of a published TMDD model of denosumab,simulations were performed at population and individual levels.Then,a simplified TMDD model,QSS model, was used to examine the effects of hypotheses,in which the total receptor concentration was constant or variable on model fit and stability of parameter estimation.Both simulations at the population level and model fit results of simulated individual data showed that at the therapeutic doses,the total receptor concentration had little influence on changes in drug concentration,and the model with constant total receptor concentration had the same predictive power.The validated hypothesis could be applied to clinical trial design and selection of the optimal PK model in the development of monoclonal antibodies.

Pharmacokinetics of monoclonal antibodies ]nd Fc-fusion proteins

There are many factors that can influence the pharma- cokinetics （PK） of a mAb or Fc-fusion molecule with the primary determinant being FcRn-mediatad recycling. Through Fab or Fc engineering, IgG-FcRn interaction can be used to generate a variety of therapeutic anti. bodies with significantly enhanced half-life or ability to remove unwanted antigen from circulation, Glycosyla- tion of a mAb or Fc.fusion protein can have a significant impact on the PK of these molecules, mAb charge can be important and variants with pl values of 1-2 unit difference are likely to impact PK with lower pl values being favorable for a longer half.life. Most mAbs display target mediated drug disposition （TMOO）, which can have significant consequences on the study designs of preclinical and clinical studies. The PK of mAb can also be influenced by anti-drug antibody （ADA） response and off.target binding, which require careful consideration during the discovery stage, mAbs are primarily absor- bed through the lymphatics via convection and can be conveniently administered by the subcutaneous （sc） route in large doses/volumes with co-formulation of hyaluronidase. The human PK of a mAb can be rea- sonably estimated using cynomolgus monkey data and allometric scaling methods.