A Target-Mediated Drug Disposition model to quantify the relationship between Otelixizumab in vitro concentration and TCR/CD3 engagement.
Objectives: Otelixizumab is a monoclonal antibody (mAb) directed against CD3ε, a protein forming part of the CD3/T-cell receptor (TCR) complex on T lymphocytes . An in vitro culture system was proposed to investigate Otelixizumab binding characteristics in a static situation. Specifically, the objective of this work was to quantify the relationship between Otelixizumab in vitro concentration and TCR/CD3 engagement. Within this framework, the Target Mediated Drug Disposition (TMDD) hypothesis  was investigated for Otelixizumab disposition.
Methods: A wide range of doses was proposed in order to detect and properly quantify nonlinearities in Otelixizumab PK. For this purpose, peripheral blood mononuclear cells (PBMCs) from two donors were incubated with titrated Otelixizumab initial concentrations in the range 0.001-10 μg/ml. To investigate the kinetics of CD3/TCR re-expression, cells were washed on day 2 to remove exogenous Otelixizumab and thereby allow CD3/TCR complex re-expression to be monitored. At each time point free, bound and total TCR/CD3 expression on both CD4+ and CD8+ T cells and the amount of free antibody in the supernatant were measured. A TMDD model  accounting for Otelixizumab binding on both CD4+ and CD8+ lymphocytes was proposed with the intent to describe in vitro experimental data. Analyses were conducted using NONMEM version 7.2. Final models were selected based upon change in OFV, precision of estimates and diagnostic goodness-of-fit plots.
Results: All parameters were estimated with reasonable precision (
Conclusions: The TCR/CD3 receptor has been shown to have a major role in determining the non-linear PK of Otelixizumab. A TMDD model accounting for Otelixizumab binding to TCR/CD3 on both CD4+ and CD8+ lymphocytes successfully captured the PK and PD in vitro data, confirming that the assumptions of this model are reasonable for Otelixizumab.
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Full Reference: E. Mezzalana, K. Page, A. van Maurik, A. McDonald, G. De Nicolao, S. Zamuner. A Target-Mediated Drug Disposition model to quantify the relationship between Otelixizumab in vitro concentration and TCR/CD3 engagement. PAGE 23 (2014) Abstr 3063 [www.page-meeting.org/?abstract=3063]
Link to full text: https://www.page-meeting.org/?abstract=3063