Discovery of intracellular self-assembly protein degraders driven by tumor-specific activatable bioorthogonal reaction.

Proteolysis Targeting Chimera (PROTAC) is a type of bifunctional chimeric molecule that can directly degrade the binding proteins through the ubiquitin-proteasome pathway. PROTAC has shown great potential in overcoming drug resistance and targeting undruggable targets. However, there are still many shortcomings that need to be solved urgently, including worse membrane permeability and bioavailability induced by their large molecular weight. Herein, we used intracellular self-assembly strategy to construct tumor-specific PROTACs via small molecular precursors. We developed two types of precursors incorporated with azide and alkyne as biorthogonal groups, respectively. These small precursors with improved membrane permeability could react facilely with each other under the catalysis of copper ions with high concentration in tumor tissues, affording novel PROTACs. These novel intracellular self-assembled PROTACs could effectly induce degradation of VEGFR-2 and EphB4 in U87 cells. Meanwhile, they could also promote apoptosis and block cells in S phase. These tumor-specific intracellular self-assembled PROTACs exhibited high selectivity due to the high concentration of copper content in tumor tissue. Moreover, this new strategy could reduce the molecular weight of PROTACs, as well as improve the membrane permeability. These results will greatly expand the applications of bioorthogonal reaction in discovery of novel PROTACs.