What parameters are optimized in ADC development and how do they affect performance?

ADC optimization balances efficacy, safety, and manufacturability across multiple parameters: 1) Antibody selection - target expression (tumor-specific, internalization-competent), trafficking (lysosomal delivery for cleavable linkers), binding kinetics, and species cross-reactivity for preclinical. 2) Drug-to-Antibody Ratio (DAR) - higher DAR increases potency but may reduce stability and increase hydrophobicity; typically DAR 2-4; site-specific conjugation controls DAR precisely. 3) Linker chemistry - cleavable (valine-citrulline cleaved by cathepsins, disulfide reduction, hydrazone at low pH) vs non-cleavable (requires antibody degradation); stability in circulation vs efficient release in target. 4) Payload - potency (pM IC50), mechanism (tubulin inhibitors, DNA alkylators, RNA polymerase inhibitors), bystander effect, resistance mechanisms. 5) Conjugation site - interchain cysteines (heterogeneous), engineered cysteines (THIOMAB), unnatural amino acids, enzymatic (transglutaminase, sortase); site affects PK, stability, efficacy. 6) Biophysical properties - aggregation, viscosity for manufacturing. Integrated assessment required.