A family of QconCATs (Quantification conCATemers) for the quantification of human pharmacological target proteins

We have developed a family of QconCAT standards for the absolute quantification of pharmacological target proteins in a variety of human tissues. The QconCATs consist of concatenated proteotypic peptides, are designed in silico, and expressed in E. coli in media enriched with [13C6] arginine and [13C6] lysine to generate stable isotope-labeled multiplexed absolute quantification standards. The so-called MetCAT (used to quantify cytochrome P450 (CYP) and glucuronosyltransferase (UGT) enzymes), the liver TransCAT (used to quantify plasma-membrane drug transporters) and the brain TransCAT (used to quantify transporters expressed in the blood-brain barrier) were previously reported. We now report new QconCATs for the quantification of non-UGT non-CYP drug metabolizing enzymes (NuncCAT) and receptor tyrosine kinases (KinCAT). We have also redesigned the liver TransCAT, replacing problematic peptides and the N-terminal tag, for better characterization and expression. All these QconCATs showed high purity, high labelling efficiency with stable 13C isotope (>95%), and high sequence coverage (>88%). They represent a close-knit family of standards for quantifying pharmacokinetic targets, together with a more distant cousin, the KinCAT, used to quantify pharmacodynamic targets.