Unlike chemically synthesized drugs, protein therapeutics are a dynamic heterogeneous mix of active compounds. Due to their complexity, analytical techniques like isoelectric focusing have become indispensable tools in evaluating biologic preparations. The resulting surge in charge isoform analysis has led to major advances in instrumentation, such as Imaged Capillary Electrophoresis (iCEâ„¢)2 . However, to obtain the full benefit from improved instrumentation requires the coinciding development of robust assays.

The goal of this note is to promote the successful application of DOE tools in the assay development process by offering a stepwise example. The road map contained in the following pages has purposely captured enough technical detail to provide a comprehensive reference guide for both the statistician and analytical biochemist. The subjects that will be covered include initial factor screening, construction of a central composite DOE, response surface modeling, assay optimization, model validation and assay performance.