In vivo testing of drug-linker stability.

Antibody-drug conjugates (ADCs) are promising biotherapeutics designed to selectively deliver highly cytotoxic drugs to tumor cells while sparing normal tissues. They can be viewed as prodrugs, stable in the bloodstream in order to minimize drug release in circulation and efficiently converted into active drugs in the tumor tissues. Designing the right combination of monoclonal antibody (mAb), linker and drug, requires monitoring and understanding the behavior of all three components in the bloodstream and tumor. In particular, linkers have been shown to influence efficacy and safety profiles of ADCs, and monitoring in vivo "drug-linker stability" is therefore critical to help the linker choice and is performed by identifying the pharmacokinetics (PK) profiles. PK properties of ADCs are measured by following the profiles of three entities: (a) the conjugate (mAb entity carrying at least one drug), (b) the total antibody (mAb entity regardless of drug load), as well as (c) the free drugs and metabolites entities. This chapter focuses on the key analytical methods (ELISA immunoassays, TFC-MS/MS, and HRMS) used to support the PK profiles assessment of the three entities, allowing the characterization of ADC "drug-linker stability".