Microenvironment-Responsive Delivery of the Cas9 RNA-Guided Endonuclease for Efficient Genome Editing.

Successful and efficient delivery of Cas9 protein and gRNA into cells is critical for genome editing and its therapeutic application. In this study， we developed an improved supercharged polypeptide (SCP) mediated delivery system based on dithiocyclopeptide linker to realize the effective genome editing in tumor cells. The fusion protein Cas9-linker-SCP (Cas9-LS) forms positively charged complexes with gRNA in vitro to provide possibilities for gRNA delivery into cells. Under the microenvironment of tumor cells， the dithiocyclopeptide linker， containing matrix metalloproteinase 2 (MMP-2) sensitive sequence and an intramolecular disulfide bond， can be completely disconnected to promote the release of Cas9 protein with the nuclear localization sequence (NLS) in the cytoplasm and transfer to the cell nucleus for highly efficient genome editing， resulting in an obvious increase of indel efficiency in comparison to fusion protein without dithiocyclopeptide linker (Cas9-SCP). Furthermore， Cas9-LS shows no significant cytotoxicity and minimal hemolytic activity. We envision that the microenvironment-responsive Cas9 protein delivery system can facilitate more efficient genome editing in tumor cells.