Azobenzene‐Based Linker Strategy for Selective Activation of Antibody–Drug Conjugates

Abstract Existing antibody–drug conjugate (ADC) linkers, whether cleavable or non‐cleavable, are designed to release highly toxic payloads or payload derivatives upon internalisation of the ADCs into cells. However, clinical studies have shown that only <1 % of the dosed ADCs accumulate in tumour cells. The remaining >99 % of ADCs are nonspecifically distributed in healthy tissue cells, thus inevitably leading to off‐target toxicity. Herein, we describe an intelligent tumour‐specific linker strategy to address these limitations. A tumour‐specific linker is constructed by introducing a hypoxia‐activated azobenzene group as a toxicity controller. We show that this azobenzene‐based linker is non‐cleavable in healthy tissues (O 2 >10 %), and the corresponding payload derivative, cysteine‐appended azobenzene‐linker–monomethyl auristatin E (MMAE), can serve as a safe prodrug to mask the toxicity of MMAE (switched off). Upon exposure to the hypoxic tumour microenvironment (O 2 <1 %), this linker is cleaved to release MMAE and fully restores the high cytotoxicity of the ADC (switched on). Notably, the azobenzene linker‐containing ADC exhibits satisfactory antitumour efficacy in vivo and a larger therapeutic window compared with ADCs containing traditional cleavable or non‐cleavable linkers. Thus, our azobenzene‐based linker sheds new light on the development of next‐generation ADC linkers.