Dendrigraft poly-l-lysine (DGL), including its central core, consists entirely of lysine, hence it is completely biodegradable. We applied DGL in a small interfering RNA (siRNA) delivery system. Binary complexes with siRNA and DGL had particle sizes of 23–73 nm and ζ-potentials of 34–42 mV. The siRNA-DGL complexes showed significant silencing effects in a mouse colon carcinoma cell line expressing luciferase (Colon26/Luc cells). The siRNA-DGL complexes induced slight cytotoxicity and hematological toxicity at a high charge ratio of DGL to siRNA, probably because of their cationic charges. Therefore, we recharged the siRNA-DGL complexes with γ-polyglutamic acid (γ-PGA), a biodegradable anionic compound, which was reported to reduce the cytotoxicity of cationic complexes. The ternary complexes showed particle sizes of 35–47 nm at a charge ratio of greater than 14 to siRNA with negative charges. Strong silencing effects of the ternary complexes were observed in Colon26/Luc cells without cytotoxicity or hematological toxicity. The cellular uptake and degradation of the binary and ternary complexes were confirmed by fluorescence microscopy. The ternary complexes suppressed luciferase activity in the tumor after direct injection into the tumors of mice bearing Colon26/Luc cells. Thus, a potentially important siRNA delivery system was constructed using biodegradable DGL.

In this experiment, we developed a novel safe and effective gene delivery vector coated with γ-polyglutamic acid (γ-PGA-coated complexes). The γ-PGA-coated complex was composed of chiseled spherical nano-particles with anionic charges. The plasmid DNA/polyethyleneimine complex (non-coated complex) showed high transgene efficiency in the spleen and lung after intravenous administration in mice, with high liver toxicity and lethality. On the other hand, γ-PGA-coated complex selectively showed high transgene efficiency in the spleen without such toxicity. Furthermore, the γ-PGA-coated complex highly accumulated and showed high gene expression in the marginal zone of the spleen. Those results strongly indicated that γ-PGA-coated complex was suitable as a DNA vaccine vector. We therefore applied γ-PGA-coated complex to melanoma DNA vaccine, pUb-M. The γ-PGA-coated complex containing pUb-M significantly inhibited the growth and metastasis of a melanoma cell line, B16-F10 cells. In conclusion, we developed a splenic gene vector, γ-PGA-coated complex, as a novel technology for clinical vaccination.

We previously found that a complex comprising plasmid DNA (pDNA), polyethylenimine (PEI), and γ-polyglutamic acid (γ-PGA) had high transgene efficiency without cytotoxicity in vitro and in vivo. However, messenger RNA (mRNA) remains an attractive alternative to pDNA. In this study, we developed a safe and effective delivery system for mRNA to prevent its degradation and efficiently deliver it into target cells. Various cationic and anionic complexes were produced containing PEI, γ-PGA, and an mRNA encoding firefly luciferase. Their physicochemical properties and cytotoxicities were analyzed and the in vitro and in vivo protein expression were determined. The cationic mRNA/PEI complex showed high in vitro protein expression with strong cytotoxicity. The anionic complex was constructed as mRNA/PEI8/γ-PGA12 complex with a theoretical charge ratio of 1:8:12 based on the phosphate groups of the mRNA, nitrogen groups of PEI, and carboxylate groups of γ-PGA. It was stable and showed high in vitro protein expression without cytotoxicity. After intravenous administration of mRNA/PEI8/γ-PGA12 complex to mice, high protein expression was observed in the spleen and liver and slight expression was observed in the lung over 24 h. Thus, the newly constructed mRNA/PEI8/γ-PGA12 complex provides a safe and effective strategy for the delivery of mRNA.

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic myelopathy characterized by motor dysfunction of the lower extremities and urinary disturbance. Immunomodulatory treatments are the main strategy for HAM/TSP, but several issues are associated with long-term treatment. We conducted a clinical trial with prosultiamine (which has apoptotic activity against HTLV-I-infected cells) as a novel therapy in HAM/TSP patients.

The present study investigated a pulmonary delivery system of plasmid DNA (pDNA) and its application to melanoma DNA vaccines. pCMV-Luc, pEGFP-C1, and pZsGreen were used as a model pDNA to evaluate transfection efficacy after inhalation in mice. Naked pDNA and a ternary complex, consisting of pDNA, dendrigraft poly-l-lysine (DGL), and γ-polyglutamic acid (γ-PGA), both showed strong gene expression in the lungs after inhalation. The transgene expression was detected in alveolar macrophage-rich sites by observation using multi-color deep imaging. On the basis of these results, we used pUb-M, which expresses melanoma-related antigens (ubiquitinated murine melanoma gp100 and tyrosinase-related protein 2 (TRP2) peptide epitopes), as DNA vaccine for melanoma. The inhalation of naked pUb-M and its ternary complex significantly inhibited the metastasis of B16-F10 cells, a melanoma cell line, in mice. The levels of the inflammatory cytokines, such as TNF-α, IFN-γ, and IL-6, which enhance Th1 responses, were higher with the pUb-M ternary complex than with naked pUb-M and pEGFP-C1 ternary complex as control. In conclusion, we clarified that the inhalation of naked pDNA as well as its ternary complex are a useful technique for cancer vaccination.