Lysosome-escape Nano-Carriers for Small Molecule Drug Delivery

Core Mechanisms of Lysosome-escape Nano-Carriers

Figure 1. Endosomal escape mechanism mediated by nanovesicle system. (Sources: Desai N, et al. 2024)

1. Proton sponge effect: Polycationic substances like polyethyleneimine (PEI) take up protons from the acidic environment inside lysosomes which leads to higher osmotic pressure and eventually causes the lysosomes to expand and burst. A graphene oxide-polyethylene glycol-polyethyleneimine nanocarrier system efficiently transported Cas9/sgRNA complexes using this mechanism.
2. Membrane instability and pore formation: The stability of the lysosomal membrane is destroyed through electrostatic interaction when cationic liposomes or fusion peptides attach to it. Nanocarriers that have been modified with diaminoethane groups manage to penetrate tumor cell membranes through perforation.
3. Polyacrylamide dendrimers which are pH-responsive materials demonstrate massive expansion hundreds of times their original size within acidic environments to rupture lysosomal membranes through physical extrusion.
4. Photochemical internalization (PCI): The exposure of photosensitizers to light produces reactive oxygen species which then cause oxidative harm to lysosomal membranes.
5. Enzyme-triggered release: The membrane destruction tool becomes active when specific enzymes like CTSB cleave its linker because these enzymes show high expression levels in tumors. For example, polyethylene glycol nanocarriers achieve tumor-specific escape through CTSB-responsive linkers.

Design Strategy and Technical Path

Material Selection and Functionalization

1. Polycationic materials: such as PEI and chitosan, which achieve escape through the proton sponge effect. However, they need to be modified to reduce cytotoxicity (such as polylactic acid-co-polyethanolamine-polyimine nanomaterials).
2. pH-sensitive materials: such as phenylboronic acid functionalized polymers, which break the boronate bond in the acidic environment of lysosomes to trigger drug release.
3. Lipid-peptide complexes: Fusion peptides (such as GALA) change conformation at low pH to promote membrane fusion.
4. Inorganic-organic hybrid materials: such as graphene oxide-based carriers, combining physical adsorption and chemical responsiveness.

Responsive Design

1. Enzyme-triggered type: The linker is designed as an enzyme-sensitive structure such as CTSB to achieve tumor-specific escape.
2. Light-controlled release: Nanocarriers modified with photosensitizers escape by local light activation.
3. Dual response system: pH and reduction-sensitive nanogels, which respond to both acidic and glutathione environments in lysosomes.

Pathway Optimization

1. Avoiding the lysosomal pathway: Avoiding entry into lysosomes through caveolin-mediated endocytic bypass or endoplasmic reticulum-Golgi transport.
2. Bionic carriers: exosomes or cell membrane-modified nanocarriers use natural membrane fusion properties to promote escape.

Challenges and Future Directions

• Efficiency improvement: The efficiency of existing escape mechanisms is generally less than 1%, and a multi-mechanism synergistic strategy needs to be developed.
• Safety optimization: The cytotoxicity of polycationic materials needs to balance function and safety through structural modification (such as PEGylation).
• Clinical transformation: In vivo research needs to be strengthened to verify the stability and targeting of the carrier in a complex physiological environment.
• Intelligent design: Combine artificial intelligence to predict the material-mechanism-efficacy relationship and accelerate carrier development.

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