Despite early encouraging clinical activity and fast-track approval, Mylotarg was removed from the market because of toxicity and lack of efficacy in larger trials ( 8). The first Food and Drug Administration-approved ADC, gemtuzumab ozogamicin (Mylotarg Wyeth/Pfizer), was a conjugate of the DNA cleaving agent calicheamicin to an anti-CD33 antibody for the treatment of acute myelogenous leukemia ( 7).
Antibody-drug conjugates have had significant achievements as well as notable failures in the clinic. It is hypothesized that the ADCs are endocytosed after binding cell-surface antigens and the antibody molecule is degraded in the lysosome, releasing the cytotoxic drug into the cytosol ( 5, 6). In the past decade, antibody-drug conjugates (ADC) have shown considerable promise as anticancer agents by preferentially targeting cytotoxic drugs to cells presenting tumor-associated antigens ( 1– 4). The synthesis and characterization of homogeneous ADCs with medicinal chemistry-like control over macromolecular structure should facilitate the optimization of ADCs for a host of therapeutic uses.Ī major challenge in the development of new drugs is the ability to selectively modulate a specific target in the tissue of interest while minimizing undesirable systemic side effects. The resulting conjugates demonstrated excellent pharmacokinetics, potent in vitro cytotoxic activity against Her2 + cancer cells, and complete tumor regression in rodent xenograft treatment models. The mutant protein was selectively and efficiently conjugated to an auristatin derivative through a stable oxime linkage. p-Acetylphenylalanine was site-specifically incorporated into an anti-Her2 antibody Fab fragment and full-length IgG in Escherichia coli and mammalian cells, respectively.
Here we demonstrate the use of genetically encoded unnatural amino acids with orthogonal chemical reactivity to synthesize homogeneous ADCs with precise control of conjugation site and stoichiometry. However, these strategies often lead to heterogeneous products, which make optimization of the biological, physical, and pharmacological properties of an ADC challenging. Traditionally, the drug is conjugated nonselectively to cysteine or lysine residues in the antibody. Antibody-drug conjugates (ADCs) allow selective targeting of cytotoxic drugs to cancer cells presenting tumor-associated surface markers, thereby minimizing systemic toxicity.