Chapter 3: Targeted Proteomics to Support Transporter IVIVE and PBPK

Determining the activity of transporter proteins expressed in tissues and in in vitro models is a key component for building a quantitative understanding of the impact of drug transporters on the pharmacokinetics of their substrate compounds. The abundance of a transporter protein in vivo is an important determinant of its activity. Gene expression is not always a good surrogate for corresponding protein abundance in tissues, necessitating absolute quantification of proteins to understand transporter abundance. Immunochemical methods of protein quantification are limited by the availability of specific antibodies and protein standards, thus restricting absolute quantification of drug transporters. Recent advances in MS based proteomics have, however, resulted in a rapid increase in transporter protein quantification data in the literature, which have the potential to contribute considerably to our ability to account for active transport in in vitro to in vivo extrapolation and physiologically based pharmacokinetic modelling. The aim of this chapter is to give an overview of targeted mass spectrometry proteomics methods applied to drug transporters, and to discuss the utility and limitations of the absolute protein quantification data obtained.