The document discusses antibody-drug conjugates (ADCs), which are monoclonal antibodies coupled to cytotoxic drugs. Effective ADC payloads must be highly cytotoxic, target intracellular components, be small to avoid immunogenicity, and be stable in plasma. Common intracellular targets of ADC payloads include DNA, microtubules, and transcription machinery. The payloads aim to induce DNA damage, disrupt microtubule assembly, or interfere with transcription to promote cancer cell death. Novel payloads also include nano-carriers, protein toxins, and enzymes for antibody-directed prodrug therapy.