Development of ASGR-Mediated Hepatocyte-Targeting Cytotoxic Drug Conjugates with CTSB-Cleavable Linkers Incorporating Succinimide and Succinic Acid Monoamide

The ASGR-mediated endocytosis has been successfully applied to the hepatocyte-targeted delivery of therapeutic oligonucleotides via glycoconjugates. However, few studies have explored the conjugated small molecules due to the challenge of cleaving suitable linkers for the release of active small molecules, which is especially different from GalNAc-ONs cleaved by the deoxyribonuclease II in the lysosome. In this study, GalNAc-MMAE conjugates linked by CTSB-cleavable linkers were designed and synthesized. A comprehensive approach revealed that the conjugates were endocytosed by ASGR and subsequently hydrolyzed by CTSB, releasing MMAE. The optimized conjugate with a succinic acid monoamide as the fragment of the linker demonstrated favorable plasma stability, excellent biodistribution, and significant antitumor activities <i>in vivo</i> with weight gain at the effective dose in an orthotopic hepatocellular carcinoma mouse model. This research provides a strategy for developing anti-HCC therapeutic agents using GalNAc drug conjugates with CTSB-cleavable linkers to release active small molecules.