PK Assays for Antibody-Drug Conjugates (ADCs)

Antibody-drug conjugates (ADCs) are complex molecules with monoclonal antibodies covalently bound to cytotoxic small molecule compounds via a chemical linker. ADCs specifically bind to targeted cell surface antigens overexpressed on tumor cells. Upon binding, the ADCs are internalized and trafficked to lysosomes, from which the cytotoxic drug is released within the cell. The use and targeted delivery of highly potent cytotoxic drugs is designed to enhance the antitumor effects of the molecule while minimizing systemic toxicity. Due to the heterogeneity of ADCs structure and the dynamic variation of drug-to-antibody ratio (DAR) in vivo, the biological analysis of ADCs faces great challenges. Pharmacokinetics (PK) assays are used to measure the concentration of ADCs in biological samples over time. ADCs are analyzed by PK assays to determine absorption, distribution, metabolism, and excretion (ADME). These pharmacokinetic parameters are useful in optimizing dosing regimens and understanding the relationship between ADC concentrations and therapeutic effects. Therefore, PK assays are essential for understanding the PK and disposition of ADCs in preclinical and clinical studies.

Fig. 1 Schematic of ADC stucture (Lin K, et al. 2012)

The PK depends on a large number of parameters: concentrations of the mAb, of free cytotoxic agent and of ADC in the central and peripheral compartment; dissociation constant between the cytotoxic agent and the mAb outside or inside the tumour or cell; internalization constant and DAR.

• The total antibody concentration includes both the conjugated and unconjugated forms of an ADC and is usually determined using an enzyme-linked immunosorbent assay (ELISA)-based format.

Fig. 2 Typical ELISA formats for ADC analytes (Lin K, et al. 2012)

• The released drug catabolite concentration of an ADC is usually determined using affinity capture LC-MS, in which the ADC is specifically extracted from plasma and then analyzed by LC-MS/MS.

Fig. 3 DM1 catabolite LC–MS/MS assay (Dere R, et al. 2013)

Creative Diagnostics has years of experience in developing and validating PK analysis of ADC for biotech and pharma companies. Our veteran scientists are able to design scientific and appropriate assay format and optimum proposal for different products. For more detailed information, please contact our customer service.