A Novel Concept for Cleavable Linkers Applicable to Conjugation Chemistry - Design, Synthesis and Characterization.

Linkers with disulfide bonds are the only cleavable linkers that utilize physiological thiol gradients as a trigger to initiate the intracellular drug release cascade. Herein, we present a novel concept exploiting the thiol gradient phenomena to design a new class of cleavable linker with no disulfide bond. To support the concept, an electron-deficient sulfonamide-based cleavable linker amenable to conjugation of drug molecules with targeting agents, was developed. Modulating the electron-withdrawing nature of the aryl sulfonamide was critical to the balance between the stability and drug release. Favorable stability and payload release in human serum under physiologically relevant thiol concentrations was demonstrated with two potent cytotoxics. Intracellular payload release was further validated in cell-based assay in context of antibody-drug conjugate generated from monoclonal antibody and sulfonamide containing linker. To support the proposed release mechanism, possible downstream by-products formed from the drug-linker adduct were characterized.