Antibody-Drug Conjugates (ADCs) represent one of the most advanced classes of targeted therapies in
oncology, combining the specificity of monoclonal antibodies with the potency of cytotoxic agents. Yet
their development remains highly complex, particularly during bioconjugation, where both efficacy and safety are
defined. Through two case studies, this article illustrates how a combination of process optimisation and tailored
purification strategies enabled precise control of Drug-to-Antibody Ratio (DAR) and efficient removal of residual
free payload. Despite tight timelines and stringent specifications, robust and scalable solutions were
implemented, demonstrating how integrated expertise can accelerate ADC development.

Bioconjugation: A Critical Step in ADC Development
ADCs are sophisticated constructs built from three components: a monoclonal antibody, a linker and a cytotoxic payload. Each plays a distinct role, but it is the bioconjugation step that ultimately determines how effectively these components work together. By controlling how many payload molecules are attached to each antibody molecule, bioconjugation directly impacts the Drug-to-Antibody Ratio (DAR), a key driver of therapeutic efficacy. At the same time, it must ensure that any unreacted payload, highly cytotoxic by nature, is reduced to trace levels to guarantee patient safety. Balancing these two dimensions is not straightforward. Increasing payload loading can improve potency but often comes at the cost of higher levels of residual free drug or linker-payload species. Conversely, aggressive purification can affect yield or product quality. In practice, success depends on the ability to align conjugation efficiency with an effective and scalable purification strategy. The following case studies highlight how these challenges were addressed in real development programs.