Quantitative analysis of drug distribution in heterogeneous tissues using dual‐stacking capillary electrophoresis–mass spectrometry.

Background and Purpose: Intratumour heterogeneity frequently leads to drug resistance, which is a major issue in drug discovery. Drug distribution is one of the key factors for elucidating the resistance mechanism; however, quantitative and regional drug measurement is challenging. Here, we developed a novel ultra‐sensitive analytical method and applied it to HER3‐targeting antibody–drug conjugate patritumab deruxtecan (HER3‐DXd), aiming to explore its payload (DXd) distribution within heterogeneous tissues. Experimental Approach: The developed analytical method is named LDMS‐CE‐MS, a capillary electrophoresis‐mass spectrometry (CE‐MS) coupled with a novel sample preconcentration/separation method called "large‐volume dual‐sample stacking by micelle collapse and sweeping (LDMS)". First, the analytical performance of LDMS‐CE‐MS for DXd detection was evaluated. Subsequently, we evaluated the bystander effect of HER3‐DXd, where tumour tissues were excised from xenograft models and clinical specimens after administration of HER3‐DXd. HER3‐high expression, adjacent, and HER3‐low expression regions were then sampled by laser microdissection to quantify the released DXd. Key Results: LDMS concentrated DXd by 1000‐fold and separated it from the hydrophilic bio‐matrix through continuous capture and release by the charged micelles, allowing quantification at sub‐attomole‐level. DXd concentrations decreased in the order of antigen‐high expression > adjacent > antigen‐low expression regions in the tumour xenograft model, whereas in clinical specimens, adjacent and antigen‐high expression regions had approximately the same concentration. These distributions represent a bystander effect. Conclusions and Implications: Our LDMS‐CE‐MS successfully visualized the attomole‐level drug distributions in heterogeneous clinical specimens. This new platform opens a new era of quantitative pharmacokinetic analysis, facilitating drug discovery and development. [ABSTRACT FROM AUTHOR]