Interaction of γ-Polyglutamic Acid/Polyethyleneimine/Plasmid DNA Ternary Complexes with Serum Components Plays a Crucial Role in Transfection in Mice.

Typical examples of non-viral vectors are binary complexes of plasmid DNA with cationic polymers such as polyethyleneimine (PEI). However, problems such as cytotoxicity and hemagglutination, owing to their positively charged surfaces, hinder their in vivo use. Coating binary complexes with anionic polymers, such as γ-polyglutamic acid (γ-PGA), can prevent cytotoxicity and hemagglutination. However, the role of interactions between these complexes and serum components in in vivo gene transfer remains unclear. In this study, we analyzed the contribution of serum components to in vivo gene transfer using PEI/plasmid DNA binary complexes and γ-PGA/PEI/plasmid DNA ternary complexes. In binary complexes, heat-labile components in the serum greatly contribute to the hepatic and splenic gene expression of the luciferase gene. In contrast, serum albumin and salts affected the hepatic and splenic gene expression in the ternary complexes. Changes in physicochemical characteristics, such as increased particle size and decreased absolute values of ζ-potential, might be involved in the enhanced gene expression. These findings would contribute to a better understanding of in vivo non-viral gene transfer using polymers, such as PEI and γ-PGA.

Immune complexome analysis of serum samples from non-small-cell lung cancer patients identifies predictive biomarkers for nivolumab therapy.

BACKGROUND: Immune checkpoint inhibitors (ICIs) have achieved important outcomes in cancer treatment. However, current clinical biomarker tests are not suitable for some patients because they require tumor tissues and have poor predictive value for treatment responses. Therefore, the identification of biomarkers that enable screening tests in all patients is necessary. METHODS: We performed an immune complexome analysis of non-small cell lung cancer patients treated with nivolumab to comprehensively identify and compare antigens incorporated into immune complexes (IC-antigens) in serum samples from the responders (n = 15) and non-responders (n = 20). Additionally, combinations of IC-antigens characteristic to the responder group were evaluated by logistic regression analysis and receiver operating characteristics curves to examine their predictiveness for ICI treatment responses. RESULTS: The combination of predictive biomarkers detected before treatment was profilin-1, purine nucleoside phosphorylase, alpha-enolase, and nucleoside diphosphate kinase A [p = 0.0043, odds ratio = 2.26, 95% confidence interval (CI) = 1.19-4.28, area under the curve = 0.76]. The combination of predictive biomarkers detected after treatment was peptidyl-prolyl cis-trans isomerase A, ubiquitin-like modifier-activating enzyme 1, complement component C8 beta chain, and apolipoprotein L1 (p = 0.0039, odds ratio = 2.56, 95% CI = 1.25-5.23, area under the curve = 0.77). CONCLUSION: Combinations of serum IC-antigens may predict the therapeutic effect of nivolumab in non-small cell lung cancer patients.

Delivery of pDNA to the Lung by Lipopolyplexes Using N-Lauroylsarcosine and Effect on the Pulmonary Fibrosis.

In a previous study, we constructed a lung-targeting lipopolyplex containing polyethyleneimine (PEI), 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA), and N-lauroylsarcosine (LS). The lipopolyplex exhibited an extremely high gene expression in the lung after intravenous administration. Here, we optimized the lipopolyplex and used it to deliver a TGF-ß1 shRNA to treat refractory pulmonary fibrosis. We constructed several lipopolyplexes with pDNA, various cationic polymers, cationic lipids, and LS to select the most effective formulation. Then, the pDNA encoding shRNA against mouse TGF-ß1 was encapsulated in the lipopolyplex and injected into mice with bleomycin-induced pulmonary fibrosis. After optimizing the lipopolyplex, dendrigraft poly-L-lysine (DGL) and DOTMA were selected as the appropriate cationic polymer and lipid, respectively. The lipopolyplex was constructed with a pDNA, DGL, DOTMA, and LS charge ratio of 1:2:2:4 showed the highest gene expression. After intravenous administration of the lipopolyplex, the highest gene expression was observed in the lung. In the in vitro experiment, the lipopolyplex delivered pDNA into the cells via endocytosis. As a result, the lipopolyplex containing pDNA encoding TGF-ß1 shRNA significantly decreased hydroxyproline in the pulmonary fibrosis model mice. We have successfully inhibited pulmonary fibrosis using a novel lung-targeting lipopolyplex.

Induction of mucosal immunity by pulmonary administration of a cell-targeting nanoparticle.

We previously found that a nanoparticle constructed with an antigen, benzalkonium chloride (BK) and γ-polyglutamic acid (γ-PGA) showed high Th1 and Th2-type immune induction after subcutaneous administration. For prophylaxis of respiratory infections, however, mucosal immunity should be induced. In this study, we investigated the effect of pulmonary administration of a nanoparticle comprising ovalbumin (OVA) as a model antigen, BK, and γ-PGA on induction of mucosal immunity in the lungs and serum. The complex was strongly taken up by RAW264.7 and DC2.4cells. After pulmonary administration, lung retention was longer for the OVA/BK/γ-PGA complex than for OVA alone. OVA-specific serum immunoglobulin (Ig)G was highly induced by the complex. High IgG and IgA levels were also induced in the bronchoalveolar lavage fluid, and in vivo toxicities were not observed. In conclusion, we effectively and safely induced mucosal immunity by pulmonary administration of an OVA/BK/γ-PGA complex.

Evaluation of transgene expression characteristics and DNA vaccination against melanoma metastasis of an intravenously injected ternary complex with biodegradable dendrigraft poly-L-lysine in mice.

We developed a biocompatible splenic vector for a DNA vaccine against melanoma. The splenic vector is a ternary complex composed of plasmid DNA (pDNA), biodegradable dendrigraft poly-L-lysine (DGL), and γ-polyglutamic acid (γ-PGA), the selective uptake of which by the spleen has already been demonstrated. The ternary complex containing pDNA encoding luciferase (pCMV-Luc) exhibited stronger luciferase activity for RAW264.7 mouse macrophage-like cells than naked pCMV-Luc. Although the ternary complex exhibited strong luciferase activity in the spleen after its tail vein injection, luciferase activity in the liver and spleen was significantly decreased by a pretreatment with clodronate liposomes, which depleted macrophages in the liver and spleen. These results indicate that the ternary complex is mainly transfected in macrophages and is a suitable formulation for DNA vaccination. We applied the ternary complex to a pUb-M melanoma DNA vaccine. The ternary complex containing pUb-M suppressed the growth of melanoma and lung metastasis by B16-F10 mouse melanoma cells. We also examined the acute and liver toxicities of the pUb-M ternary complex at an excess pDNA dose in mice. All mice survived the injection of the excess amount of the ternary complex. Liver toxicity was negligible in mice injected with the excess amount of the ternary complex. In conclusion, we herein confirmed that the ternary complex was mainly transfected into macrophages in the spleen after its tail vein injection. We also showed the prevention of melanoma metastasis by the DNA vaccine and the safety of the ternary complex.

Anionic Complex with Efficient Expression and Good Safety Profile for mRNA Delivery.

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.

Development of a DNA Vaccine for Melanoma Metastasis by Inhalation Based on an Analysis of Transgene Expression Characteristics of Naked pDNA and a Ternary Complex in Mouse Lung Tissues.

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.

[Development of Vaccines with Self-assembled Carriers That Deliver Drugs to Target Organs].

I have developed novel ternary complexes of various vaccines with cationic materials and anionic polymers. Plasmid DNA (pDNA) encoding firefly luciferase was used as a model drug to form adequate ternary complexes. Cationic binary complexes were constructed using pDNA and polyethylenimine, and these binary complexes were coated with various anionic polymers to form ternary complexes. These ternary complexes significantly improved cytotoxicity and aggregation with erythrocytes in comparison to the binary complexes. On the other hand, most of those ternary complexes showed little in vitro transgene efficiency because of their anionic surface charge. γ-Polyglutamic acid (γ-PGA)-ternary complexes, however, demonstrated high in vitro transgene efficiency. After the intravenous administration of γ-PGA-ternary complexes to mice, extremely high gene expression was detected in the marginal zone of the spleen, which is rich in antigen-presenting cells. This spleen-specific phenomenon of γ-PGA-ternary complexes appeared to be suited to DNA vaccines against cancer. I therefore examined the preventive effect of γ-PGA-ternary complexes containing pUb-M, a pDNA encoding melanoma surface antigen, against melanoma-bearing mice. Vaccinations of γ-PGA-ternary complexes into mice significantly suppressed the tumor growth of B16-F10 melanoma cells subcutaneously injected into the mice. In the same manner, vaccinations of γ-PGA-ternary complexes containing ovalbumin (OVA) completely suppressed the growth of E.G7-OVA cells expressing OVA. These results strongly suggest that γ-PGA-ternary complexes are useful in the manufacture of specific tumor vaccines.

Methotrexate-Coated Complexes of Plasmid DNA and Polyethylenimine for Gene Delivery.

Folate receptors are overexpressed on the surface cancer cells. We successfully constructed a new gene delivery vector of methotrexate (MTX)-coated plasmid DNA-polyethylenimine (pDNA-PEI) complexes (PEI complexes) by electrostatic binding. The stable anionic nanoparticle was optimized at MTX charge ratios of 120 or more. pDNA-PEI-MTX complexes (MTX complexes) demonstrated gene expression efficiency as high as cationic pDNA-PEI complexes in the mouse melanoma cell line, B16-F10. The MTX complexes were taken up by the cell-specific uptake mechanisms via the folate receptor. MTX-coated complexes are useful as endocytosis ligands. The MTX120 complexes exhibited no blood aggregation. The transgene efficiency of MTX120 complexes in the liver and spleen after their intravenous administration was higher than that of PEI complexes. Therefore, MTX complexes are expected as a new gene vector in the future.

Splenic Delivery System of pDNA through Complexes Electrostatically Constructed with Protamine and Chondroitin Sulfate.

We developed and optimized a novel gene delivery vector constructed electrostatically with an anionic biological component and a cationic biological component. Cationic binary complexes of plasmid DNA (pDNA) with novo-protamine sulfate as a medical product (PRT complexes) demonstrated high gene expression with minimal cytotoxicity, likely related with its total cationic charge. Subsequently, anionic compounds were added to the PRT complexes to form ternary complexes with neutral or anionic charges. Among the anionic compounds examined, chondroitin sulfate sodium (CS) as a medical product encapsulated the PRT complexes to produce stable ternary complexes (CS complexes) at charge ratios of ≥4 with pDNA. CS complexes exhibited high gene expression without cytotoxicity in mouse melanoma cell line, B16-F10 cells, in vitro. An inhibition study with endocytosis inhibitors suggested that PRT complexes were mainly taken up by caveolae-mediated endocytosis, and CS complexes were mainly taken up by clathrin-mediated endocytosis in B16-F10 cells. We found that CS complexes including pDNA encoding Oplophorus gracilirostris luciferase induced selective gene expression in the spleen after intravenous administration into ddY male mice. Thus, we successfully constructed useful gene vectors with biological components as medical products.

Gene delivery system of pDNA using the blood glycoprotein fetuin.

Fetuin is a biocompatible plasma protein and strongly enhances phagocytosis of bacteria, DNA and apoptotic cells by peripheral blood cells such as monocytes, macrophages and dendritic cells. We developed a novel gene delivery system: ternary complexes constructed with pDNA, polyethylenimine (PEI) and fetuin. Without covalent binding, fetuin was able to coat pDNA-PEI complexes, and stable anionic nanoparticles formed at a weight ratio greater than 30. Optimised pDNA-PEI-fetuin complexes significantly decreased the cytotoxicity of pDNA-PEI complexes in the melanoma cell line B16F10. Furthermore, the pDNA-PEI-fetuin complexes had higher transgene efficiency compared to that of commercial lipofectin previously reported in B16F10 cells despite an anionic surface. The pDNA-PEI-fetuin complexes did not agglutinate with erythrocytes. The pDNA-PEI-fetuin complexes had high gene expression in the spleen after intravenous administration in mice. Thus, the pDNA-PEI-fetuin complexes were a useful in vivo gene delivery system with tropism for the spleen.

Activation of TNF-α-AID axis and co-inhibitory signals in coordination with Th1-type immunity in a mouse model recapitulating hepatitis B.

Hepatitis B virus (HBV) infection evokes host immune responses that primarily determine the outcome of HBV infection and the clinical features of HBV-associated liver disease. The precise mechanisms by which host factors restrict HBV replication, however, are poorly understood due to the lack of useful animal models that recapitulate immune responses to HBV. Here, we performed comprehensive immunologic gene expression profiling of the liver of a mouse model recapitulating anti-HBV immune response using a high sensitivity direct digital counting system. Anti-HBV cellular immunity with liver inflammation was elicited in mice hydrodynamically injected with a CpG-depleted plasmid encoding hepatitis B surface antigen (HBsAg) gene after preimmunization with HBsAg vaccine. Comprehensive expression analyses revealed the upregulation of Th1-associated genes including tumor necrosis factor (Tnf) and negative regulators of T cell function in the inflamed liver. Interestingly, activation-induced cytidine deaminase (Aicda, termed AID in humans), which reportedly suppresses HBV infection in vitro, was upregulated in hepatocytes in the course of anti-HBV immunity. Hepatocytic expression of Aicda in a Tnf-dependent manner was confirmed by the administration of Tnf antagonist into Aicda-tdTomato mice with anti-HBV immunity. Our findings suggest that activation of Tnf-Aicda axis and co-inhibitory signals to T cells in coordination with Th1-type immunity has critical roles in the immune response against HBV infection.

Biocompatible complex coated with glycosaminoglycan for gene delivery.

The purpose of this study was to develop a ternary complex of plasmid DNA (pDNA) electrostatically assembled with dendrigraft poly-l-lysine (DGL) and biodegradable glycosaminoglycan for effective and secure gene delivery. High gene expression of pDNA/DGL complex was confirmed with slight cytotoxicity and erythrocyte agglutination. Anionic ternary complexes of 55.4-223.8 nm were formed by the addition of a glycosaminoglycan such as chondroitin sulfate A (CS-A), chondroitin sulfate B (CS-B), chondroitin sulfate C (CS-C) or hyaluronic acid (HA). Using the cell line B16-F10, most of the ternary complexes showed only weak gene expression and little cytotoxicity, although the pDNA/DGL/CS-A complexes maintained a certain level of gene expression. In particular, the pDNA/DGL/CS-A8 complexes showed significantly higher gene expression than pDNA/DGL complexes in the presence of fetal bovine serum. Gene expression from the pDNA/DGL/CS-A8 complex was inhibited by a high concentration of CS-A and endocytosis inhibitors. After intravenous administration of the pDNA/DGL/CS-A8 complex and the pDNA/DGL complex into ddY mice, high gene expression was observed in the reticuloendothelial systems, the pDNA/DGL/CS-A complex is expected to be useful for gene therapy.

Application of biodegradable dendrigraft poly-l-lysine to a small interfering RNA delivery system.

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.

Splenic gene delivery system using self-assembling nano-complex with phosphatidylserine analog.

The recognition of phosphatidylserine on the erythrocyte membrane mediates erythrophagocytosis by resident spleen macrophages. The application of phosphatidylserine to a gene vector may be a novel approach for splenic drug delivery. Therefore, we chose 1,2-dioleoyl-sn-glycero-3-phospho-L-serin (DOPS) as an analogue of phosphatidylserine for splenic gene delivery of plasmid DNA (pDNA). In the present study, we successfully prepared a stable pDNA ternary complex using DOPS and polyethyleneimine (PEI) and evaluated its efficacy and safety. The pDNA/PEI complex had a positive charge and showed high transgene efficacy, although it caused cytotoxicity and agglutination. The addition of DOPS changed the ζ-potential of the pDNA/PEI complex to negative. It is known that anionic complexes are not taken up well by cells. Surprisingly, however, the pDNA/PEI/DOPS complex showed relatively high transgene efficacy in vitro. Fluorescence microscope observation revealed that the pDNA/PEI/DOPS complex internalized the cells while maintaining the complex formation. The injection of the pDNA/PEI complex killed most mice within 24 h at high doses, although all mice in the pDNA/PEI/DOPS complex group survived. The ternary complex with DOPS showed markedly better safety compared with the pDNA/PEI complex. The pDNA/PEI/DOPS complex showed high gene expression selectively in the spleen after intravenous injection into mice. Thus the ternary complex with DOPS can be used to deliver pDNA to the spleen, in which immune cells are abundant. It appears to have an excellent safety level, although further study to determine the mechanism of action is necessary.

Quaternary complexes modified from pDNA and poly-l-lysine complexes to enhance pH-buffering effect and suppress cytotoxicity.

We developed a modified complex of pDNA and poly-l-lysine (PLL) by the addition of poly-l-histidine (PLH) and γ-polyglutamic acid (γ-PGA) to enhance its pH-buffering effect and suppress cytotoxicity. The binary and ternary complexes of pDNA with PLL or/and PLH showed particle sizes of approximately 52-76 nm with cationic surface charge. The ternary complexes showed much higher gene expression than the binary complexes with PLL. The mixed solution of PLL and PLH showed higher buffering capacity than PLL solution. The high gene expression of ternary complexes was reduced by bafilomycin A1 . These results indicated the addition of PLH to PLL complexes promoted endosomal escape by enhancing the pH-buffering effect. The binary and ternary complexes showed cytotoxicity and blood agglutination because of their cationic surface charge. We therefore developed quaternary complexes by the addition of anionic γ-PGA, which was reported to decrease the toxicity of cationic complexes. In fact, quaternary complexes showed no cytotoxicity and blood agglutination. Also, quaternary complexes showed higher gene expression than ternary complexes regardless of their anionic surface charge. Quaternary complexes showed selectively high gene expression in the spleen after their intravenous administration. Thus, we successfully developed the quaternary complexes with high gene expression and no toxicity.

Immunogenicity and anti-fecundity effect of nanoparticle coated glutathione S-transferase (SjGST) DNA vaccine against murine Schistosoma japonicum infection.

There is still urgent need for a vaccine against schistosomiasis, especially in Schistosoma japonicum endemic areas where even a vaccine that will interrupt zoonotic transmission will be potentially effective as an intervention tool. We had developed a novel nanoparticle gene delivery system, which has proven efficacious in gene transfection to target immune cells with complementary adjuvant effect and high protective efficacy in several diseases. Here, we applied this nanoparticle system in combination with S. japonicum glutathione S-transferase (SjGST) DNA vaccine to show the immunogenicity and anti-fecundity effect of the nanoparticle coated vaccine formulation against murine schistosomiasis. The nanoparticle-coated DNA vaccine formulation induced desired immune responses. In comparison with the nanoparticle coated empty vector, it produced significantly increased antigen-specific humoral response, T-helper 1 polarized cytokine environment, higher proportion of IFN-γ producing CD4(+) T-cells and the concomitant decrease in IL-4 producing CD4(+) T-cells. Although there was no effect on worm burden, we recorded a marked reduction in tissue egg burden. There was up to 71.3% decrease in tissue egg burden and 55% reduction in the fecundity of female adult worms. Our data showed that SjGST DNA vaccine, delivered using the nanoparticle gene delivery system, produced anti-fecundity effect on female adult schistosomes as previously described by using conventional subunit vaccine with adjuvant, proving this DNA vaccine formulation as a promising candidate for anti-pathology and transmission blocking application.

Secure and effective gene delivery system of plasmid DNA coated by polynucleotide.

Polynucleotides are anionic macromolecules which are expected to transfer into the targeted cells through specific uptake mechanisms. So, we developed polynucleotides coating complexes of plasmid DNA (pDNA) and polyethylenimine (PEI) for a secure and efficient gene delivery system and evaluated their usefulness. Polyadenylic acid (polyA), polyuridylic acid (polyU), polycytidylic acid (polyC), and polyguanylic acid (polyG) were examined as the coating materials. pDNA/PEI/polyA, pDNA/PEI/polyU, and pDNA/PEI/polyC complexes formed nanoparticles with a negative surface charge although pDNA/PEI/polyG was aggregated. The pDNA/PEI/polyC complex showed high transgene efficiency in B16-F10 cells although there was little efficiency in pDNA/PEI/polyA and pDNA/PEI/polyU complexes. An inhibition study strongly indicated the specific uptake mechanism of pDNA/PEI/polyC complex. Polynucleotide coating complexes had lower cytotoxicity than pDNA/PEI complex. The pDNA/PEI/polyC complex showed high gene expression selectively in the spleen after intravenous injection into mice. The pDNA/PEI/polyC complex showed no agglutination with erythrocytes and no acute toxicity although these were observed in pDNA/PEI complex. Thus, we developed polynucleotide coating complexes as novel vectors for clinical gene therapy, and the pDNA/PEI/polyC complex as a useful candidate for a gene delivery system.

Radiolabeled γ-polyglutamic acid complex as a nano-platform for sentinel lymph node imaging.

We established a ternary anionic complex constructed with polyamidoamine dendrimer (4th generation; G4) modified with chelating agents (diethylenetriamine pentaacetic acid (DTPA) derivative), polyethyleneimine (PEI), and γ-polyglutamic acid (PGA) as a safe nano-platform for molecular imaging. We prepared indium-111-labeled DTPA-G4/PEI/γ-PGA, and evaluated the effectiveness as a nuclear imaging probe for sentinel lymph node (LN), the first LN that drains the primary tumor. (111)In-DTPA-G4/PEI with strong cationic charge agglutinated with erythrocytes and showed extremely high cytotoxicity. By contrast, the anionic (111)In-DTPA-G4/PEI/γ-PGA had little agglutination activity with erythrocytes and no cytotoxicity, indicating their high biocompatibility. (111)In-DTPA-G4/PEI/γ-PGA was highly taken up by macrophage cells (high populations in LNs) comparable to (111)In-DTPA-G4/PEI. The uptake mechanisms of (111)In-DTPA-G4/PEI/γ-PGA were suggested to be both phagocytosis and γ-PGA-specific pathway. Upon administration of each (111)In-labeled nano-platform into rat footpads intradermally, significantly higher radioactivity of (111)In-DTPA-G4/PEI/γ-PGA was observed in the first draining popliteal LN when compared with that of (111)In-DTPA-G4/PEI. Moreover, (111)In-DTPA-G4/PEI/γ-PGA clearly visualized the sentinel LN with single photon emission computed tomography (SPECT) compared with (111)In-DTPA-G4/PEI. Thus, (111)In-DTPA-G4/PEI/γ-PGA can be useful as a nano-platform for molecular imaging including sentinel LN imaging.

Novel siRNA delivery system using a ternary polymer complex with strong silencing effect and no cytotoxicity.

We developed a novel small interfering RNA (siRNA) delivery system using a ternary complex with polyethyleneimine (PEI) and γ-polyglutamic acid (γ-PGA), which showed silencing effect and no cytotoxicity. The binary complexes of siRNA with PEI were approximately 73-102 nm in particle size and 45-52 mV in ζ-potential. The silencing effect of siRNA/PEI complexes increased with an increase of PEI, and siRNA/PEI complexes with a charge ratio greater than 16 showed significant luciferase knockdown in a mouse colon carcinoma cell line regularly expressing luciferase (Colon26/Luc cells). However, strong cytotoxicity and blood agglutination were observed in the siRNA/Lipofectamine complex and siRNA/PEI16 complex. Recharging cationic complexes with an anionic compound was reported to be a promising method for overcoming these toxicities. We therefore prepared ternary complexes of siRNA with PEI (charge ratio 16) by the addition of γ-PGA to reduce cytotoxicity and deliver siRNA. As expected, the cytotoxicity of the ternary complexes decreased with an increase of γ-PGA content, which decreased the ζ-potential of the complexes. A strong silencing effect comparable to siRNA/Lipofectamine complex was discovered in ternary complexes including γ-PGA with an anionic surface charge. The high incorporation of ternary complexes into Colon26/Luc cells was confirmed with fluorescence microcopy. Having achieved knockdown of an exogenously transfected gene, the ability of the complex to mediate knockdown of an endogenous housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), was assessed in B16-F10 cells. The ternary complex (siRNA/PEI16/γ-PGA12 complex) exhibited a significant GAPDH knockdown effect. Thus, we developed a useful siRNA delivery system.