Direct Preparation of Site‐Specific Antibody–Drug Conjugates with Unpurified Antibodies in Culture Medium

In comparison with traditional chemotherapeutic drugs, antibody–drug conjugates (ADCs) have been extensively employed in cancer therapy due to their high selectivity and low systemic toxicity. However, the structural complexity of ADCs makes its preparation process more intricate and time‐consuming. Conventional ADC production involves multistep purification processes, which significantly increase the costs. Herein, an approach for the direct preparation of site‐specific ADCs in an antibody expression system that is derived from the reported K248 site‐specific modification technology is demonstrated. This strategy requires only a single purification step to obtain site‐specific ADCs, thereby greatly shortening the preparation cycle of ADCs. The preparation of site‐specific ADCs in the expression system of Sacituzumab is successfully achieved. The resulting ADCs exhibited comparable physicochemical properties and activities to those obtained through the conventional two‐step purification strategy. The approach demonstrates high compatibility with various linkers and antibodies, offering a streamlined methodology for the preparation of site‐specific ADCs.