Mechanistic Analysis of Drug Linker Clearance During Ultrafiltration/Diafiltration of an Antibody–Drug Conjugate

Ultrafiltration/diafiltration (UF/DF) is a key unit operation in the manufacture of antibody-drug conjugates (ADCs), commonly utilized for post-conjugation purification to remove residual Drug Linker (DL) compounds and affect buffer exchange. The clearance of residual drug linker (DL), however, is often well below that predicted by ideal diafiltration theory. This work provides the first detailed mechanistic analysis of the factors that influence DL clearance during constant volume diafiltration, with particular emphasis on antibody concentration, membrane properties, and operating conditions. Diafiltration experiments in both stirred cell and tangential flow filtration systems demonstrate that DL sieving coefficients decrease with increasing ADC concentration and with increasing filtrate flux. These trends are quantitatively described using a newly developed diafiltration model accounting for intermolecular association between the hydrophobic DL and the ADC, with the ADC concentration at the membrane surface evaluated using the classical concentration polarization analysis. Experimental data obtained over a range of conditions are well-described using this concentration polarization-binding model. The model not only explains DL clearance data, but it also provides a framework for effective process design of UF/DF processes to ensure the required levels of DL clearance during ADC purification.