Conjugation of drugs to antibodies, either directly or via linkers, involves a consideration of a variety of factors, including the identity and location of the chemical group for conjugation of the drug, the mechanism of drug release, the structural elements providing drug release, and the structural modification to the released free drug. In addition, if the drug is to be released after antibody internalization, the mechanism of drug release must be consonant with the intracellular trafficking of the conjugate.
While a number of different drug classes have been tried for delivery via antibodies, only a few drug classes have proved efficacious as antibody drug conjugates, while having a suitable toxicity profile. One such class is the auristatins, derivatives of the natural product dolastatin 10. Representative auristatins include (N-methylvaline-valine-dolaisoleuine-dolaproine-norephedrine) and (N-methylvaline-valine-dolaisoleuine-dolaproine-phenylalanine). However, there remains a need for additional auristatins with improved properties.