Avidin–biotin system (ABC)

The Avidin–biotin system is a high-affinity molecular recognition interface based on the non-covalent interaction between the protein avidin (or streptavidin) and the vitamin biotin. This interaction is characterized by an extremely low dissociation constant (Kd ≈ 10^-15 M), making it one of the strongest known non-covalent bonds in nature (Green, 1975). In therapeutic applications, this interface is primarily employed in pre-targeting strategies for cancer treatment and imaging (Boerman et al., 2003). A typical approach involves administering a biotinylated monoclonal antibody that localizes to tumor antigens, followed by the administration of radiolabeled avidin or streptavidin to deliver a concentrated dose of radiation to the site (Urbano et al., 2007). This separation of targeting and effector delivery helps reduce systemic toxicity and improves the therapeutic index of radionuclides. Beyond oncology, the system is used in the development of modular CAR-T cells, where biotinylated adapters allow for the universal targeting of different antigens (Jain & Cheng, 2017). However, the clinical utility of this synthetic interface is often hampered by the immunogenicity of the foreign proteins and the potential for interference from endogenous biotin in the bloodstream (Wilchek & Bayer, 1990).

Other names

Avidin–biotin complexStreptavidin–biotin systemAvidin–biotin synthetic interfaceBiotin–avidin interaction

The system functions as a molecular bridge, where one component (e.g., avidin) is localized to a target site via a primary targeting agent, and the second component (e.g., biotin) carries a therapeutic or diagnostic payload, utilizing their extreme binding affinity to ensure precise delivery and signal amplification (Jain & Cheng, 2017).