Alpha-Ammonium Carbamates Undergo Efficient Two-Step Linker Cleavage and Improve the Properties of Antibody Conjugates

Targeted payload delivery strategies, such as antibody-drug conjugates (ADCs), have emerged as useful therapeutics. Although considerable efforts have been made in the areas of antibody engineering and labeling methodology, improving the overall physicochemical properties of the linker/payload combination remains an important challenge. Here we report an approach to create an intrinsically polar linker domain. We find that -ammonium carbamates (AAC) undergo a tandem 1,6–1,2 elimination sequence to release secondary amines. Using a fluorogenic hemicyanine as a model payload component, we show that a zwitterionic AAC linker improves labeling efficiency and reduces antibody aggregation when compared to a commonly used Val-Ala linker as well as a cationic AAC. Cellular and in vivo fluorescence imaging studies demonstrate that the model payload is released in antigen-expressing cells and tumors with high specificity. Broadly, this strategy may provide a general approach to mask the hydrophobicity of payloads and improve the properties of targeted agents.