Antibody Drug Conjugates (ADCs) are complex multi-domain biotherapeutics which combine, with the aid of a chemical linker, tumor-targeting antibodies with potent small molecule cytotoxicants (also called warhead or payload) for the treatment of cancer. ADCs are a rapidly growing class of pharmaceuticals with nine FDA-approved drugs already on the market and over eighty at different stages of clinical development, and also an increasing number under evaluation for non-oncological indications. Off-target toxicity and a narrow therapeutic index has been a problem with ADCs. This has driven the search for better targeting (disease models, cell surface antigens), linker stability, and payload specificity. Analysis of regulatory approval documents, scientific publications and ICH guidance shows that safety evaluation of ADCs requires novel integrated strategies different from both standard chemotherapy and antibody-based products, e.g. development and validation of ADC analytical assays. There is no ADC-specific guidance on safety evaluation; current guidance emphasises the need for an adaptive approach but more ADC-specific guidance is now arguably possible. The data now available will help to optimize primary target specificity, select appropriate combination partners, develop in silico models, and provide guidance for preclinical and clinical safety evaluation for the next generation of this class of multi-domain therapeutics.
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