Direct cytoplasmic delivery of RNAi therapeutics through a non-lysosomal pathway for enhanced gene therapy

The first approved RNAi therapeutics, ONPATTRO, in 2017 moves the concept of RNA interference (RNAi) therapy from research to clinical reality, raising the hopes for the treatment of currently incurable diseases. However, RNAi therapeutics are still facing two main challenges-susceptibility to enzymatic degradation and low ability to escape from endo/lysosome into the cytoplasm. Therefore, we developed disulfide-based nanospheres (DBNPs) as universal vehicles to achieve efficient RNA delivery to address these problems. Notably, the DBNPs possess unique and desirable features, including improved resistance to nuclease degradation, direct cytoplasmic delivery through thiol-mediated cellular uptake, and cytosolic environment-responsive release, greatly enhancing the bioavailability of RNA therapeutics. Additionally, DBNPs are superior in terms of overcoming formidable physiological barriers, including vascular barriers and impermeable tumor tissues. Owning to these advantages, the DBNPs exhibit efficient gene silencing effect when delivering either small interfering RNA (siRNA) or microRNA in various cell lines and generate remarkable growth inhibition in the zebrafish and mouse model of pancreatic tumors as compared to traditional delivery vectors, such as PEI. Therefore, DBNPs have potential application prospect in RNAi therapy both in vitro and in vivo. STATEMENT OF SIGNIFICANCE: RNA interference (RNAi) therapeutics could target and alter any disease-related mRNA translation, thus have great potential in clinical application. Delivery efficiency of RNA modalities into cell cytoplasm is the main problem that currently limit RNAi therapeutics to release their full potential. Most of the known delivery materials suffer from the endo/lysosomal entrapment and enzymatic degradation during endocytosis-dependent uptake, resulting unsatisfied efficiency of the cytoplasmic release. Here, we developed disulfide-based nanospheres could directly transfer RNA modalities into the cytoplasm and significantly enhance the delivery efficiency, thus holding great potential in RNAi therapy.

Interest of extracellular vesicles in regards to lipid nanoparticle based systems for intracellular protein delivery

Compared to chemicals that continue to dominate the overall pharmaceutical market, protein therapeutics offer the advantages of higher specificity, greater activity, and reduced toxicity. While nearly all existing therapeutic proteins were developed against soluble or extracellular targets, the ability for proteins to enter cells and target intracellular compartments can significantly broaden their utility for a myriad of exiting targets. Given their physical, chemical, biological instability that could induce adverse effects, and their limited ability to cross cell membranes, delivery systems are required to fully reveal their biological potential. In this context, as natural protein nanocarriers, extracellular vesicles (EVs) hold great promise. Nevertheless, if not present naturally, bringing an interest protein into EV is not an easy task. In this review, we will explore methods used to load extrinsic protein into EVs and compare these natural vectors to their close synthetic counterparts, liposomes/lipid nanoparticles, to induce intracellular protein delivery.

Photo-responsive prodrug nanoparticles for efficient cytoplasmic delivery and synergistic photodynamic-chemotherapy of metastatic triple-negative breast cancer

Triple-negative breast cancer (TNBC) have been considered as the most malignant subtype of breast cancer with leading incidence and mortality among females. Herein, photo-responsive prodrug nanoparticles (AlP/CPT-NPs) were designed with efficient cytoplasmic delivery of anti-cancer agent for cooperative photodynamic-chemotherapy. AlP/CPT-NPs were prepared using photosensitizer Al(III) phthalocyanine chloride disulfonic acid (AlP) and ROS-activatable camptothecin prodrug (CPT-PD). AlP/CPT-NPs could induce intracellular ¹O₂ generation upon light exposure, which not only initiate immediate disassembly of AlP/CPT-NPs but also promote cytoplasmic delivery of CPT through ¹O₂-mediated lysosomal rupture. The released intracellular CPT could be translocated into nuclei in only 5 min post-irradiation. Consequently, AlP/CPT-NPs efficiently suppressed the tumor growth and metastasis of TNBC in a spatiotemporally controlled manner, providing a promising option for effective treatment of metastatic TNBC. STATEMENT OF SIGNIFICANCE: Breast cancer is a complex disease with leading incidence among females, in which triple-negative breast cancer (TNBC) is considered as the most malignant subtype with increased risk of resistance, recurrence and metastasis. Herein, we designed photo-responsive prodrug nanoparticles (AlP/CPT-NPs) for synergistic treatment of metastatic TNBC. Upon 660 nm light exposure, the ¹O₂ generated by AlP/CPT-NPs could initiate immediate disassembly of AlP/CPT-NPs and further promote cytoplasmic delivery of the therapeutic payloads (camptothecin, CPT). The prepared AlP/CPT-NPs induced potent in vivo phototherapeutic damage through photodynamic-chemotherapy, resulting in complete tumor ablation with metastasis suppression.

Method for Confirming Cytoplasmic Delivery of RNA Aptamers

RNA aptamers are single-stranded RNA oligos that represent a powerful emerging technology with potential for treating numerous diseases. More recently, cell-targeted RNA aptamers have been developed for delivering RNA interference (RNAi) modulators (siRNAs and miRNAs) to specific diseased cells (e.g., cancer cells or HIV infected cells) in vitro and in vivo. However, despite initial promising reports, the broad application of this aptamer delivery technology awaits the development of methods that can verify and confirm delivery of aptamers to the cytoplasm of target cells where the RNAi machinery resides. We recently developed a functional assay (RIP assay) to confirm cellular uptake and subsequent cytoplasmic release of an RNA aptamer which binds to a cell surface receptor expressed on prostate cancer cells (PSMA). To assess cytoplasmic delivery, the aptamer was chemically conjugated to saporin, a ribosome inactivating protein toxin that is toxic to cells only when delivered to the cytoplasm (where it inhibits the ribosome) by a cell-targeting ligand (e.g., aptamer). Here, we describe the chemistry used to conjugate the aptamer to saporin and discuss a gel-based method to verify conjugation efficiency. We also detail an in vitro functional assay to confirm that the aptamer retains function following conjugation to saporin and describe a cellular assay to measure aptamer-mediated saporin-induced cytotoxicity.

Efficient cell-specific uptake of binding proteins into the cytoplasm through engineered modular transport systems

Through advances in protein scaffold engineering and selection technologies, highly specific binding proteins, which fold under reducing conditions, can be generated against virtually all targets. Despite tremendous therapeutic opportunities, intracellular applications are hindered by difficulties associated with achieving cytosolic delivery, compounded by even correctly measuring it. Here, we addressed cytosolic delivery systematically through the development of a biotin ligase-based assay that objectively quantifies cytosolic delivery in a generic fashion. We developed modular transport systems that consist of a designed ankyrin repeat protein (DARPin) for receptor targeting and a different DARPin for intracellular recognition and a bacterial toxin-derived component for cytosolic translocation. We show that both anthrax pores and the translocation domain of Pseudomonas exotoxin A (ETA) efficiently deliver DARPins into the cytosol. We found that the cargo must not exceed a threshold thermodynamic stability for anthrax pores, which can be addressed by engineering, while the ETA pathway does not appear to have this restriction.