Tools for the analysis and characterization of therapeutic protein species

A continuously increasing number of therapeutic proteins are being released into the market, including biosimilars. In contrast to small organic drugs, therapeutic proteins require an extensive analysis of their exact chemical composition because of their complexity and proof of the absence of contaminants, such as host cell proteins and nucleic acids. Especially challenging is the detection of low abundant species of therapeutic proteins because these spe-cies are usually very similar to the target therapeutic protein. However, the detection of these species is very important for the safety of patients because a very small change of the exact chemical composition may cause serious side effects. In this review, we give a brief overview about the most important analytical approaches for characterizing therapeutic protein species and their contaminants and focus on the progress in this field during the past 3 years. Top-down mass spectrometry of intact therapeutic proteins in the future may solve many of the current problems in their analysis.