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An antibody-drug conjugate (ADC) consists of a monoclonal antibody, a cytotoxic agent, and an appropriate linker. The linker is one of the three main components of ADC because it links the cytotoxic payload to the antibody moiety. An ideal linker must be stable as the ADC circulates in the blood to avoid release of cytotoxic agent in off-target tissue. In addition, the linker should maintain the conjugate in an inactive, nontoxic state while bound to the antibody. At the same time, the linker should have the property of releasing the cytotoxic agent upon ADC internalization. ADC linkers can be classified as noncleavable and cleavable. Cleavable linkers are the main type of ADC linkers, and their main feature is that they can be cleaved by environmental differences or specific lysosomal enzymes in response to the intracellular and extracellular environment. Cleavable linker types include enzymatically-cleavable linkers (including peptide based linkers, β-glucuronide based linkers, and phosphate linkers), PH sensitive linkers, and reduction sensitive linkers. Noncleavable linkers contain stable bonds that resist proteolytic degradation, providing excellent stability in the systemic circulation.

The molecular design and properties of a linker are key characteristics that influence the efficacy, pharmacokinetics/pharmacodynamics, and therapeutic index of the ADC. The selection of a linker depends on the target, the chemical structure of the cytotoxic agent, the internalization and degradation state of the antibody-antigen complex, and the in vitro and in vivo activity of the conjugate. Amerigo Scientific offers a wide range of linkers for connecting antibodies and payloads to meet the diverse needs of ADC preparation.