Delivery of therapeutic nucleic acids via transferrin and transferrin receptors lipoplexes and other carriers

Purpose: The transferrin receptor (TfR) is overexpressed on many cancer cells and is efficiently internalized, making it a useful target for delivering small-molecule drugs and nucleic acid therapeutics while reducing non-target effects. The review summarizes TfR biology, Tf-lipoplex development, and therapeutic applications.

Hypothesis: As a review, there is no single experimental hypothesis. Central thesis: TfR-targeted carriers—especially Tf-lipoplexes and anti-TfR antibody-lipoplexes/immunoliposomes—can enhance delivery and transfection of therapeutic nucleic acids to cancer cells and improve efficacy over non-targeted carriers, though specificity, safety, and clinical translation remain unresolved.

Aims: Outline the function of the Tf receptor and rationale for TfR targeting. - Describe the development of Tf–lipid–DNA complexes (Tf-lipoplexes). - Review therapeutic use of lipoplexes, polyplexes, Tf-lipoplexes, and anti-TfR antibody-lipoplexes. - Provide expert opinion on clinical translation, limitations, and future directions. Literature search terms included lipoplexes, lipopolyplexes, transferrin, transferrin receptor, and gene therapy; the review was not intended to be comprehensive.

Delivery system: Tf-lipoplexes: ternary complexes of cationic liposomes, transferrin, and DNA/RNA. Cationic lipids include DOTAP/DOPE, Lipofectin, LipofectACE, Lipofectamine, and DC-cholesterol. - Targeting ligands: transferrin, anti-TfR antibodies, anti-TfR scFv/Fv; PEGylated immunolipoplexes also described. - Other carriers: polyplexes and lipopolyplexes using PEI, PAMAM dendrimers, cationic polymers plus liposomes. - Payloads: plasmid DNA encoding p53, IL-12, HSV-tk, cytosine deaminase, BikDD, Bax, FUS1, HLA-B7/β2-microglobulin; siRNA against bcr-abl, RRM2, c-Jun; antisense oligodeoxynucleotides against R2 and Bcl-2/G3139. - Additional platforms: Tf–drug conjugates and Tf-conjugated liposomal/nanoparticle drugs.

Approach: Review/synthesis of in vitro and in vivo studies. Models include HeLa, COS-7, lymphocyte cell lines, macrophages, K562/LAMA84 leukemia, DU145 prostate cancer, JSQ-3 nasal vestibule tumor, CT26 colon carcinoma, orthotopic head and neck squamous cell carcinoma, pancreatic/prostate xenografts, lung/liver/pancreatic tumor models, and mouse hippocampus. Clinical mentions include Phase I/II MBP-426, Phase I SGT-53, Phase I siRNA nanoparticle melanoma trial, and glioblastoma HSV-tk/GCV lipoplex studies. Not comprehensive.

Key methods: Review; headline techniques in cited studies included zeta potential measurements, luciferase expression/transfection efficiency, cytokine measurements (IL-12, IFN-γ), tumor volume and survival analysis, fluorescence microscopy proposed for carrier fate, and clinical safety/efficacy assessment.

Key results: Tf-lipoplexes increased the percentage of transfected cells and transfection activity versus plain lipoplexes; ternary DOTAP/DOPE/Tf/DNA complexes were resistant to serum inhibition. In COS-7 cells, 250-fold excess free Tf did not inhibit transfection, and cytochalasin B inhibited it, suggesting non-classical endocytosis. - In CT26 colon cancer, Tf-lipoplexes carrying IL-12 caused complete tumor regression in 75% of treated mice without recurrence; survival was 88% at 23 days, with high serum IL-12 and IFN-γ. - In glioblastoma patients treated with HSV-tk/GCV lipoplexes, 2 of 8 had >50% tumor volume reduction and 6 of 8 showed local treatment effects. - TfRscFv-targeted p53 lipoplexes plus gemcitabine increased survival in metastatic pancreatic cancer models; anti-TfR scFv immunoliposomes targeted prostate xenografts. - A Phase I melanoma siRNA nanoparticle trial showed reduced RRM2 protein/mRNA and dose-dependent tumor accumulation. - Two TfR-targeting systems reached clinical evaluation: MBP-426 (Phase Ib/II) and SGT-53 (Phase I).

Interpretation: Targeting TfR via Tf or anti-TfR antibodies is a viable approach and generally enhances intracellular nucleic acid delivery compared with non-targeted controls. Successes at cell-culture and animal-model levels should be translated into clinical applications, initially using localized delivery into accessible tissues to avoid systemic side effects and non-target delivery; systemic delivery may still work in selected metastatic settings.

Limitations: The review is not comprehensive. Potential immunogenicity of targeting antibodies is a concern. TfR is expressed on some normal tissues, including immature erythroid cells, placental tissue, and rapidly dividing cells, and soluble TfR fragments circulate in plasma, raising non-target delivery concerns. Many findings remain preclinical. Multifunctional nanoparticles may face mutually exclusive design requirements. Detailed intracellular/tissue fate and nonmalignant localization studies are needed, and funding barriers for translation are noted.