A dual-locked cyclopeptide-siRNA conjugate for tumor-specific gene silencing

Strategies allowing tumor-selective siRNA delivery while minimizing off-tumor gene silencing effects are highly demanded to advance cancer gene therapy, which however still remain challenging. We herein report a dual-locking bioconjugation approach to address this challenge. A dual-locked cyclopeptide-siRNA conjugate (DPRC) was designed to simultaneously endow siRNA with tumor-targeting properties and tumor-biomarker/visible-light dually controllable action. The DPRC consisted of a programmed death-ligand 1 (PD-L1)-targeting cyclopeptide as a tumor-homing ligand and B-cell lymphoma-2 (Bcl-2)-targeting siRNA as a payload. They were conjugated via a tandem-responsive cleavable linker containing a photocleavable coumarin moiety quenched by naphthylamide through a disulfide linkage. Owing to the interaction between cell-membrane PD-L1 and the cyclopeptide, the DPRC was efficiently taken up by PD-L1-positive cancer cells. Notably, the internalized DPRC could only release and restore the gene silencing activity of siBcl-2 upon GSH-mediated disulfide bond breakage followed by visible light irradiation on the coumarin moiety to induce photo-cleavage. The released siBcl-2 further silenced the expression of anti-apoptotic Bcl-2 to suppress cancer cell growth. We demonstrated the tumor-targeting and dual-locked action of siRNA by the DPRC in both two-dimensional and three-dimensional cancer cell cultures. This study thus presents a novel strategy for precise tumor-specific gene silencing by siRNA.