Development of a generic reversed-phase liquid chromatography method for protein quantification using analytical quality-by-design principles

Biopharmaceutical drug substances are generally produced using fermentation technology and are subsequently purified in the following downstream process. For the determination of critical quality attributes (CQAs), such as target protein titer and purity, monitoring tools are required before quality control analysis. We herein present a novel reversed phase liquid chromatography method (RPLC), which enables facile and robust protein quantification during upstream and downstream processing of intracellularly produced proteins in E. coli. The overall goal was to develop a fast, robust and mass spectrometry compatible method which can baseline resolve and quantify each protein of interest. Method development consisted of three steps, oriented on an Analytical Quality by Design (AQbD) workflow: (i) the stationary phase as primary parameter was chosen based on state-of-the art technology thus minimizing protein on-column adsorption and providing high efficiency, (ii) secondary parameters (i.e. gradient conditions and column temperature) were optimized applying chromatographic modeling, and (iii) the established Method Operable Design Region (MODR) was challenged and confirmed during robustness testing, performed in-silico and experimentally by a Design of experiment (DoE) based approach. Finally, we validated the RPLC method for pivotal validation parameters (i.e. linearity, limit of quantification, and repeatability) and compared it for protein quantification against a well-established analytical methodology. The outcome of this study shows (i) a protocol for RPLC development using an AQbD principle for new method generation and (ii) a highly versatile RPLC method, suited for quick and straightforward recombinant protein titer measurement being applicable for the detection of a broad range of proteins.