Accelerated Endosomal Escape of Splice-Switching Oligonucleotides Enables Efficient Hepatic Splice Correction

Splice-switching oligonucleotides (SSOs) can restore protein functionality in pathologies and are promising tools for manipulating the RNA-splicing machinery. Delivery vectors can considerably improve SSO functionality in vivo and allow dose reduction, thereby addressing the challenges of RNA-targeted therapeutics. Here, we report a biocompatible SSO nanocarrier, based on redox-responsive disulfide cross-linked low-molecular-weight linear polyethylenimine (cLPEI), for overcoming multiple biological barriers from subcellular compartments to en-route serum stability and finally in vivo delivery challenges. Intracellularly responsive cross-links of cLPEI significantly accelerated the endosomal escape and offered efficient SSO release to the cell's nucleus, thereby leading to high splice correction in vitro. In vivo performance of cLPEI-SSOs was investigated in a novel transgenic mouse model for splice correction, spatiotemporal tracking of SSO delivery in wild-type mice, and biodistribution in a colorectal cancer peritoneal metastasis model. A single intravenous application of 5 mg kg^-1 cLPEI-SSOs induced splice correction in liver, lung, kidney, and bladder, giving functional protein, which was validated by RT-PCR. Near-infrared (NIR) fluorescence imaging and X-ray computed tomography revealed improved organ retention and reduced renal excretion of SSOs. NIR microscopy demonstrated the accumulation of SSOs in angiogenic tumors within the pancreas. Successful nuclear delivery of SSOs was observed in the hepatocytes. Thus, cLPEI nanocarriers resulted in highly efficient splice correction in vivo, highlighting the critical role of the enhanced SSO bioavailability.