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Permanent Linkers, PEG-Based Spacer Molecules  

This class of linkers is considered non-cleavable, meaning linker cleavage and payload release do not

depend on the differential properties between plasma and cytoplasmic compartments. Instead, the release of

the cytotoxic drug is postulated to occur after internalization of the ADC via antigen-mediated endocytosis

and delivery to lysosomal compartments, where the antibody is degraded to the level of amino acids through

intracellular proteolytic degradation. This process releases a drug derivative, formed by the cytotoxic drug,

the linker, and the amino acid residue to which the linker was covalently attached.

The following section displays examples of hetero-bifunctional PEG-based spacer molecules. As payloads

are quite often rather hydrophobic, PEG fragments help to solubilize the linker-payload conjugate, which is

essential to perform successful conjugation onto the antibody. It further helps to increase the solubility in

physiological media and to improve the pharmacokinetic properties of the whole ADC construct.

H-O2Oc-OH

H-O2Oc-OH*HCl

H-O2Oc-OtBu*HCI

H-O2Oc-O2Oc-O2Oc-O2Oc-OH

H-O2Oc-O2Oc-OH