SPDP (SPDP Crosslinker) is a short-chain crosslinker for amine-to-sulfhydryl conjugation via NHS-ester and pyridyldithiol reactive groups that form cleavable (reducible) disulfide bonds with cysteine sulfhydryls. It is a glutathione cleavable ADC linker used for the antibody-drug conjugates (ADCs)[1][2].