Barriers and Strategies of Cationic Liposomes for Cancer Gene Therapy

Purpose: Cationic liposomes (CLs) are promising non-viral gene-delivery vectors, but their clinical use in cancer gene therapy is limited by extracellular barriers (opsonization, RES clearance, poor tumor penetration) and intracellular barriers (endosomal/lysosomal entrapment, restricted cytoplasmic/nuclear transport). The review focuses on these barriers and how lipid composition and surface modification can be tailored to improve transfection efficiency (TE) and in vivo fate.

Hypothesis: As a review, there is no single experimental hypothesis. Central thesis: if CL properties—lipid composition, particle size, membrane charge density, and surface modification—are rationally tailored, then CLs can better overcome physiological barriers, balance transfection efficiency against pharmacokinetics, and improve cancer gene therapy outcomes.

Aims: Review the physiological barriers of CLs against cancer gene therapy, including protein corona formation, RES clearance, EPR limitations, poor tumor penetration, cellular uptake, endosomal escape, and nuclear entry. - Discuss how lipid composition governs transfection efficiency, particle size, surface charge, and membrane charge density. - Summarize the impact of particle size, charge, and surface modification (PEGylation, targeting ligands) on the in vivo fate of CLs. - Provide guidance for preclinical studies and clinical translation of cationic liposomal gene-delivery systems.

Delivery system: Platform: Cationic liposomes (CLs) and lipoplexes. - Cationic lipids: DOTAP, DOTMA, DC-Chol, DMRIE, AtuFECT01, and others. - Helper/neutral lipids: DOPE, cholesterol, DOPC, DSPE-PEG, PEG-lipid. - Payloads: plasmid DNA (pDNA), mRNA, siRNA, shRNA, antisense DNA; clinical examples include p53, RB94, PKN3 siRNA, EGFR antisense, IL-2, STMN1 shRNA, and tumor antigen mRNAs. - Targeting/surface modification: folate, transferrin, cRGD peptides, dual-targeting ligands, PEGylation, ionizable lipids, fusogenic peptides. - Clinical examples: SGT-53, SGT-94, Atu027, Lipo-MERIT, DC-Chol liposomes, pbi-shRNA STMN1 lipoplexes, IGTM-101.

Approach: Review/synthesis of preclinical and clinical studies. In vitro models include CHO, COS-7, HeLa, 4T1, dendritic cells, macrophages, and other cancer/normal cell lines. In vivo contexts include solid tumors, lung cancer, ovarian cancer, pancreatic cancer, melanoma, glioma, rheumatoid arthritis, and tumor microenvironment studies. Clinical trial tables summarize phase I/II trials, many discontinued. The review is focused rather than comprehensive.

Key methods: Headline evidence comes from analysis of protein corona composition, EPR effect and tumor penetration, endocytic pathways (CME, CavME, macropinocytosis, phagocytosis), endosomal escape mechanisms, cytoplasmic diffusion, nuclear entry, lipid composition–TE relationships, particle size/zeta potential, membrane charge density, and clinical trial outcomes.

Key results: CLs face opsonization, RES clearance, poor tumor penetration, endosomal/lysosomal entrapment, and restricted nuclear diffusion. - Protein corona alters CL fate: DOTAP-rich liposomes preferentially bind vitronectin; DC-Chol promotes Ig/complement binding; DOPE attracts dysopsonins such as apolipoproteins and serum albumin. - EPR effect is heterogeneous; size cutoffs conflict: kidney <10–15 nm, liver 50–180 nm, leaky vasculature >200 nm, ECM <20 nm. Optimal passive targeting is often 100–200 nm, with 100 nm commonly used. - Endosomal escape depends on phase transition and membrane charge density; lamellar complexes are more stable but need complete fragmentation, while hexagonal complexes release DNA more readily. - Cytoplasmic diffusion: only particles <50 nm diffuse freely; DNA <250 bp diffuses rapidly, while >2,000 bp is almost retarded. - Cholesterol effects are lipid-dependent; longer acyl chains and monounsaturated lipids improve uptake (18:1 > 18:0; 18:0 > 16:0 > 14:0). - Onpattro (patisiran) success used ionizable lipid nanoparticles: nearly neutral in blood, positively charged in endosomes, and ~50 nm size. - Clinical trials of cationic liposomal cancer gene therapy are mostly phase I/II; many are discontinued or terminated.

Interpretation: CLs remain promising due to biodegradability, biocompatibility, and high nucleic acid encapsulation, but their positive charge causes immunogenicity, toxicity, and rapid RES clearance. The authors argue that clinical success requires a compromise between high transfection efficiency and good pharmacokinetics—favoring ionizable lipids that are neutral in blood and charged in endosomes, defined size (~50 nm), and PEG-lipid incorporation, with rational design guided by delivery barriers and physicochemical properties.

Limitations: This is a review, not a primary experimental study. - Many clinical trials remain phase I/II or discontinued; clinical translation is limited. - EPR effect is heterogeneous and insufficient for all solid tumors. - Endocytosis mechanisms and size-dependent internalization are not fully resolved. - Cytoplasmic trafficking of lipoplexes remains controversial. - The review is focused rather than comprehensive, and no large-animal validation or long-term safety data are presented.