The Role of Organic Synthesis in the Emergence and Development of Antibody–Drug Conjugates as Targeted Cancer Therapies

With a number of antibody–drug conjugates (ADCs) approved for clinical use as targeted cancer therapies and numerous candidates in clinical trials, the field of ADCs is emerging as one of the frontiers in biomedical research, particularly in the area of cancer treatment. Chemists, biologists and clinicians, among other scientists, are partnering their expertise to improve their design, synthesis, efficacy and precision as they strive to advance this paradigm of personalized and targeted medicine to treat cancer patients more effectively and to expand its scope to other indications. Just as Alexander Fleming's penicillin, and the myriad other bioactive natural products that followed its discovery and success in the clinic, ignited a revolution in medicine after the Second World War, so did calicheamicin γ₁^I, and other highly potent naturally occurring antitumor agents, play a pivotal role in enabling the advent of this new paradigm of “biological-small molecule hybrid” medical intervention. Today there are four clinically approved drugs from the ADC paradigm, Mylotarg, Adcetris, Kadcyla and Besponsa, in order of approval, the first and the last of which carry the same calicheamicin γ₁^I-derived payload. Covering oncological applications, and after a brief history of the emergence of the field of antibody–drug conjugates triggered more than a century ago by Paul Ehrlich's “magic bullet” concept, this Review is primarily focusing on the chemical synthesis aspects of the ADCs multidisciplinary research enterprise.