For targeted
therapies, immunocapture-liquid chromatography mass spectrometry (IC-LC/MS) technology has become an important tool for determination of both drug exposures, target
antigen densities, and engagement in the systemic circulation and/or in total target tissue homogenates. Although the information collected from the circulation and tissue homogenates is useful in establishing the correlations of the exposure and target engagement with the pharmacodynamic response and efficacy of a
therapy, the measurement at the cell plasma membrane within the target tissue is preferred, since it is the primary action site for
antigen and the target drug. However, to the best of our knowledge, IC-LC/MS-based methodologies to conduct the assays at the plasma membrane from tissue sample has been quite limited. In this paper, we reported an IC-LC/MS-based assay platform for assessing the target engagement in
tumor plasma membrane prepared from the
tumor tissue samples. In addition,
tumor samples with
guanylyl cyclase C (GCC) expression after fully human
IgG1 monoclonal antibody-based
antibody-drug conjugate (ADC) treatment were used as a case study. The methodology can differentiate between the total and target-drug bound fraction of GCC with minimal potential equilibrium shift between in-
cell surface protein and organelle
protein in
tumor samples to calculate in vivo target engagement. This approach to determine in vivo target engagement in
tumor plasma membrane will provide better understanding of pharmacokinetic/pharmacodynamic relationship to achieve the desired antitumor efficacy.