Lipid Nanoparticles as Carriers for RNAi against Viral Infections Current Status and Future Perspectives

Purpose: Naked RNAi molecules are rapidly degraded by serum nucleases and cannot readily cross cell membranes because of their negative charge. Effective delivery systems are therefore required to exploit RNAi for antiviral therapy. Lipid nanoparticles (LNPs) are attractive because they are relatively safe, simple to produce, protect encapsulated RNA, and can be functionalized for targeting or combined with conventional drugs.

Hypothesis: If RNAi molecules—siRNA, shRNA, or miRNA—are encapsulated in or complexed with lipid nanoparticles, then they can be protected from degradation, delivered to target cells and tissues, escape the endosome, and silence viral or host genes to treat or prevent viral infections.

Aims: Review RNAi mechanisms and the main RNAi molecule types: siRNA, shRNA, and miRNA. - Describe lipid-based delivery systems: solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), lipid drug conjugates (LDCs), cationic emulsions, and liposomes. - Summarize preclinical applications of LNP-RNAi against HCV, HBV, HIV, HSV-2, Ebola, HPV, rabies, influenza, and RSV. - Discuss clinical development and future perspectives for LNP-RNAi antiviral therapy.

Delivery system: Platform: lipid nanoparticles and related lipid-based carriers. - Types covered: SLNs, NLCs, LDCs, cationic emulsions, liposomes, SNALPs (stable nucleic acid lipid particles), cationic nanosomes, immunoliposomes. - Key lipids: DOTAP, DDAB, DODAG, DC-chol, DOPE, cholesterol, PEG-lipids, Compritol ATO 888, Pluronic F68. - Payloads: siRNA, shRNA, miRNA, antimiRNA, self-amplifying RNA vaccine. - Targeting/functionalization: lactosylated-PE, apolipoprotein A-I, recombinant human apo A-I, galactose, LFA-1 antibody, HA-targeting scFv, luteinizing hormone-releasing hormone analog. - Administration routes: intravenous, subcutaneous, intravaginal, intranasal, intradermal, intratumoral, inhalation.

Approach: Review and synthesis of preclinical and clinical literature. In vitro models include Huh7, Huh7.5, HepG2, FLR3-1, R6FLR-N, PC3, MDA-MB435, BHK-21, MDCK, Sf9, and others. In vivo models include HCV transgenic mice, HBV transgenic/hydrodynamic-injection mice, HCC xenografts, HIV humanized mice, HSV-2 mice, Ebola guinea pigs and nonhuman primates, HPV mouse tumors, rabies mice, influenza mice, and RSV cotton rats/mice. Clinical trials include ALN-RSV01, Miravirsen, TT-034, ARC-520, CCR5-negative cells, and TKM-Ebola. As a review, it reports no primary experimental groups, n values, doses, or controls.

Key methods: No primary methods. The review discusses data generated by cited studies using: - qPCR, Western blotting, immunofluorescence, and viral titer measurements. - ELISA and cytokine assays. - Reporter gene and luciferase silencing assays. - Histology and survival analysis. - Pharmacokinetics, biodistribution, and toxicity assessments. - Clinical safety, tolerability, and antiviral activity endpoints.

Key results: Up to January 2014, infectious diseases ranked third among gene therapy clinical trial indications, with 164 trials (8.2%). - HCV: apo A-I cationic liposomes with HCV-core siRNA inhibited viral expression by 65–75% in mouse liver on day 2; chemically modified siRNA increased silencing to up to 95% for at least 6 days. Cationic nanosomes achieved ~85% HCV inhibition with ~90% cell viability. - HBV: SNALPs produced sustained HBV titer reduction for up to 7 days. Apo A-I lipoplexes reduced viral protein expression for at least 8 days after a single treatment. - HIV: LFA-1-targeted liposomes carrying anti-CCR5 siRNA silenced leukocyte genes for 10 days in humanized mice and reduced plasma viral load and CD4 T-cell loss after challenge. - HSV-2: siRNA lipoplexes silenced gene expression in mouse vagina/ectocervix for at least 9 days and protected against lethal HSV-2 challenge. - Ebola: SNALP-delivered siRNAs completely protected guinea pigs against viremia and death when given shortly after ZEBOV challenge; 2/3 rhesus monkeys were protected with four postexposure treatments, and all macaques were protected with seven treatments. - HPV: E7 mRNA levels were reduced to 20–40% in vitro and 45–50% in tumor models after three intratumoral injections. - Clinical: ALN-RSV01 showed >50% reduction in new or progressive BOS at days 90 and 180; Miravirsen was well tolerated with prolonged antiviral activity; ARC-520 was well tolerated in 36 healthy volunteers; TT-034 and TKM-Ebola entered early clinical trials.

Interpretation: The authors conclude that RNAi is a promising antiviral strategy but is limited by delivery. LNPs are good candidates because they are safe, scalable, protect RNA, and can be functionalized for tissue tropism or combined with conventional antivirals. They suggest that LNP-delivered RNAi could become a first-line treatment for several viral infections in the future.

Limitations: Review article; no primary data, effect sizes, n values, doses, or controls. - RNAi therapy still faces toxicity, instability, off-target effects, immune stimulation, and viral escape mutants. - Delivery to target tissues and cells remains inefficient. - Clinical data are early-stage and limited. - Long-term safety, repeated dosing, and manufacturing scalability require further study. - Optimal targets and combination strategies for avoiding resistance are not fully established.