Conjugation of Anticancer Drugs Through Endogenous Monoclonal Antibody Cysteine Residues

Many methods have been described for the conjugation of drugs to monoclonal antibodies. The presence of a discrete number of readily reducible disulfides in the common IgG subtypes presents a convenient opportunity for conjugation to cysteine residues with thiol-reactive drug-linkers. Such conjugates can be prepared by a straightforward two-step reaction scheme involving the reduction of the antibody disulfides to the desired number of average thiols per antibody, followed by addition of the drug-linker, ideally with a maleimido functionality for rapid, selective reaction. In a discovery setting, this basic method can be scaled down to produce microgram quantities of conjugate for early screening, and in a manufacturing setting can be scaled up to produce grams or kilograms of conjugate for clinical trials and commercialization. The resulting conjugates are readily characterized using common HPLC methods.