Chitosan-based siRNA delivery systems

Purpose: Chitosan is attractive for siRNA delivery because it is cationic, biocompatible, biodegradable, mucoadhesive, and permeation-enhancing. However, native chitosan suffers from low solubility at physiological pH, poor buffering capacity, instability in biological fluids, and insufficient endosomal escape, limiting gene-silencing efficiency. This review addresses these barriers and the strategies developed to overcome them.

Hypothesis: This is a review article and does not test a single formal hypothesis. Its central premise is that rational design of chitosan-based nanoparticles — through chitosan selection, formulation optimization, chemical modification, excipient addition, and targeting-ligand grafting — can overcome siRNA delivery barriers and enable efficient local and systemic RNAi therapy.

Aims: Describe the major biological barriers that impair chitosan-based siRNA delivery. - Review parameters influencing siRNA/chitosan nanoparticle formation and biological activity. - Summarize strategies to improve chitosan-based systems, including derivatives, excipients, and targeting ligands. - Review in vivo therapeutic applications of chitosan/siRNA nanoparticles via local and systemic delivery.

Delivery system: Polymer: Chitosan, a linear polysaccharide of randomly distributed glucosamine and N-acetylglucosamine units; cationic in slightly acidic conditions. - Nanoparticle formation: Simple complexation or ionic gelation with cross-linkers such as sodium tripolyphosphate (TPP) or thiamine pyrophosphate. - Chitosan derivatives: Trimethyl chitosan (TMC), thiolated chitosan/TMC, glycol chitosan, PEGylated chitosan, guanidinylated chitosan. - Excipients: Amine-rich polymers (PEI, poly-L-arginine), cell-penetrating peptides/peptide mimics (TAT, phosphorylatable short peptide), negatively charged components (hyaluronic acid, poly(γ-glutamic acid), polyguluronate), cyclodextrin. - Targeting ligands: RGD peptide, antibodies (scFvCD7), folate, salbutamol (β2-adrenergic receptor agonist). - Payload: siRNA; also DsiRNA and polymerized siRNA. - Administration routes: Local (intratumoral, nasal, intratracheal, intraperitoneal, oral) and systemic (intravenous).

Approach: Review of in vitro and in vivo literature. In vitro cell lines include HEK293, H1299, CHO K1, HeLa, OV-3, MG-63, A549, HepG2, B16F10, MDA-MB-231, and others. In vivo models include GFP transgenic mice, tumor-bearing mice (breast, ovarian, melanoma, SCC7, B16F10), an arthritis model, and a radiation-induced fibrosis model. No new primary experiments, group sizes, or doses are reported.

Key methods: Nanoparticle size and zeta potential; gel electrophoresis for siRNA binding; in vitro gene silencing (GFP, luciferase, RFP); cellular uptake and confocal microscopy; in vivo GFP silencing; tumor volume/weight; biodistribution; safety/toxicity.

Key results: Chitosan molecular weight: High MW (114–170 kDa) yielded up to 65% GFP silencing; low MW (9–12 kDa) gave <5%. 25 kDa chitosan showed almost no silencing; 50 kDa gave 50% in OV-3 and 10% in HeLa. - N/P ratio: 50–150 was efficient but >70 was toxic. Low N/P ratios (4 and 8) gave good luciferase silencing on H1299. Ionic gelation achieved 82% luciferase silencing on CHO K1; thiamine pyrophosphate achieved 70% GFP silencing in HepG2 after 5 days. - Thiolated glycol chitosan/polymerized siRNA: Tumor growth reduced by 80% vs untreated; microvessel formation reduced; 17% RFP silencing. - RGD-chitosan/siRNA IV in orthotopic ovarian cancer: 50% target protein reduction vs 20% for non-targeted NPs; significant tumor weight decrease. - Intratumoral chitosan/VEGF siRNA: 94% reduction in tumor volume in a slow-growing breast tumor model. - Nasal administration: 37% GFP silencing in bronchiolar epithelial cells. Intratracheal aerosol: 37% GFP inhibition in alveoli/bronchiolar regions with a lower dose (0.26 µg vs 30 µg intranasal). - Intraperitoneal chitosan/anti-TNFα siRNA: Prevented radiation-induced fibrosis up to 8 months; arthritis score reduced and 100% survival. - Chitosan-g-PEI: GFP reduced 2.5-fold vs PEI; 90% cell viability vs 50% for PEI. - HA-PEG-chitosan NPs: 85% luciferase knockdown in A549; >80% cell viability. - PGA inclusion: 72% silencing vs 50% without PGA. - Chitosan-g-(PEI-β-cyclodextrin): PEGylated NPs gave 84% vs 60% non-PEGylated gene silencing. - CD7 antibody targeting: 65% CD4 protein decrease and 80% mRNA decrease vs 35% and 30% for non-targeted NPs.

Interpretation: Chitosan/siRNA nanoparticles have high therapeutic potential. Optimized systems can protect siRNA, improve stability, enhance cellular uptake, promote endosomal escape, and enable efficient gene silencing in vitro and in vivo. Advances in formulation, derivatives, excipients, and targeting ligands counteract many past pitfalls and pave the way for a new generation of siRNA nanocarriers for preclinical and clinical development.

Limitations: This is a review, not a primary study; no new experimental data or meta-analysis. - Native chitosan has low solubility at physiological pH, poor buffering capacity, and variable in vivo stability. - Many systems remain preclinical; only two polymeric nanocarriers have been or are being evaluated in clinical trials for siRNA delivery. - Lack of uniformity in transfection protocols and chitosan sources complicates comparisons. - Long-term safety, large-animal validation, pharmacokinetics, and biodistribution are not comprehensively addressed.