antibody–drug conjugate

An antibody–drug conjugate, or ADC, is a guided missile for cancer: a potent cell-killing chemical tethered to an antibody that knows how to find tumor cells. The antibody is the guidance system, homing in on a protein that sits on the surface of the cancer cell; the attached toxin, called the payload, is the warhead that does the killing once delivered.

An ADC has three parts working together — the targeting antibody, a cytotoxic payload usually far too poisonous to give on its own, and a chemical linker joining them. The antibody binds its surface target, the cell swallows the whole conjugate, and inside the cell the linker releases the payload to attack DNA or the cell-division machinery. The goal is to concentrate the poison where it is needed and spare healthy tissue.

ADCs let chemists weaponize toxins that would be impossibly toxic as free drugs. But the design is delicate: a linker that breaks too early spills payload into the bloodstream, while one that is too stable never releases the drug. Some payload also leaks from dying tumor cells and harms neighbors, and normal cells bearing a little of the target protein can be hit too — so toxicity is not fully eliminated, just redirected.