Mike Bayne

Abstract C184: Validation of an ELISA for the determination of Rituximab pharmacokinetics in clinical trials subjects

Rituximab is a chimeric anti‐CD20 monocolonal antibody directed against the CD20 antigen on the B cell surface. Rituximab was originally developed by IDEC Pharmaceuticals from a high affinity murine monoclonal Antibody (mAb). CD20 is expressed on mature B cells, present on 95% of B cell lymphomas and is thought to act as a calcium channel that regulates progression through the cell cycle. Cross‐linking of CD20 by anti‐CD20 mAb results in apoptosis through a caspase dependent pathway and may trigger complement dependent cytotoxicity (CDC) or antibody directed cell cytotoxicity. Rituximab has revolutionised the treatment of many B‐cell malignancies and is now increasingly being used in non‐malignant conditions such as auto‐immune disorders. Serum Rituximab levels are highly variable in patients receiving similar ‘standard’ approved doses, and little is known regarding the factors that affect serum Rituximab concentration and that in turn may influence clinical outcome. In order to provide a pharmacokinetic (PK) tool that may ultimately enable patient specific dosing of Rituximab therapy; we have generated a reliable, robust ELISA to quantitate serum Rituximab levels and to provide accurate PK data that will guide the optimisation of rituximab dosing regimes. An extensive validation of the assay was performed in order to use the assay in the clinical setting. The plate coating efficiency (within and between days) proved reliable resulting in a robust starting platform for the assay. The within day precision for the assay determined using spiked serum samples and was shown to be This assay is highly accurate and reproducible in determining the pharmacokinetic levels of Rituximab in patient serum samples. This assay represents a powerful new tool for clinical evaluation of this widely used therapeutic, it meets stringent acceptance criteria, is fit for purpose, and is currently being applied to several clinical trials incorporating Rituximab in the treatment of Lymphoma. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C184.