Antibody-drug conjugates (ADCs) consist of small molecules (warhead/payload) linked to antibodies. The linker between small molecule and the antibody affects the payload release mechanism via metabolic reactions. Therefore, when studying ADME properties of ADCs it´s important to identify the released metabolites, including unconjugated small molecule drug, small molecule conjugated to the linker or some parts of the linker, and small molecule conjugated to the linker and amino acid residues of the antibody. ADC catabolism is typically investigated in acidic conditions using liver S9 fraction and lysosomes. In vitro metabolite identification and profiling for payload and linker payload is conducted in neutral conditions with liver S9 fraction.
Depending on the conjugation strategy, the developed ADCs may vary in the number of payload conjugated per antibody molecule. The average number of payload in the antibody is defined as drug-antibody ratio (DAR). It is essential to define DAR since it affects the efficacy of ADCs and the metabolites. DAR can be determined by analysing intact protein using LC-HR/MS. Prior to analysis, protein is typically enzymatically deglycosylated to remove carbohydrate structures since this simplifies the analysis.
As well as studying how small molecules are released from ADCs, we can investigate rodent pharmacokinetics of ADCs in our in-house animal facilities.