Naimin Shao

Comparison of generation 3 polyamidoamine dendrimer and generation 4 polypropylenimine dendrimer on drug loading, complex structure, release behavior, and cytotoxicity

Background Polyamidoamine (PAMAM) and polypropylenimine (PPI) dendrimers are the commercially available and most widely used dendrimers in pharmaceutical sciences and biomedical engineering. In the present study, the loading and release behaviors of generation 3 PAMAM and generation 4 PPI dendrimers with the same amount of surface amine groups (32 per dendrimer) were compared using phenylbutazone as a model drug. Methods The dendrimer-phenylbutazone complexes were characterized by 1H nuclear magnetic resonance and nuclear Overhauser effect techniques, and the cytotoxicity of each dendrimer was evaluated. Results Aqueous solubility results suggest that the generation 3 PAMAM dendrimer has a much higher loading ability towards phenylbutazone in comparison with the generation 4 PPI dendrimer at high phenylbutazone-dendrimer feeding ratios. Drug release was much slower from the generation 3 PAMAM matrix than from the generation 4 PPI dendrimer. In addition, the generation 3 PAMAM dendrimer is at least 50-fold less toxic than generation 4 PPI dendrimer on MCF-7 and A549 cell lines. Conclusion Although the nuclear Overhauser effect nuclear magnetic resonance results reveal that the generation 4 PPI dendrimer with a more hydrophobic interior encapsulates more phenylbutazone, the PPI dendrimer-phenylbutazone inclusion is not stable in aqueous solution, which poses a great challenge during drug development.

Synergistic effect of amino acids modified on dendrimer surface in gene delivery

Design of an efficient gene vector based on dendrimer remains a great challenge due to the presence of multiple barriers in gene delivery. Single-functionalization on dendrimer cannot overcome all the barriers. In this study, we synthesized a list of single-, dual- and triple-functionalized dendrimers with arginine, phenylalanine and histidine for gene delivery using a one-pot approach. The three amino acids play different roles in gene delivery: arginine is essential in formation of stable complexes, phenylalanine improves cellular uptake efficacy, and histidine increases pH-buffering capacity and minimizes cytotoxicity of the cationic dendrimer. A combination of these amino acids on dendrimer generates a synergistic effect in gene delivery. The dual- and triple-functionalized dendrimers show minimal cytotoxicity on the transfected NIH 3T3 cells. Using this combination strategy, we can obtain triple-functionalized dendrimers with comparable transfection efficacy to several commercial transfection reagents. Such a combination strategy should be applicable to the design of efficient and biocompatible gene vectors for gene delivery.

Host–Guest Chemistry of Dendrimer–Cyclodextrin Conjugates: Selective Encapsulations of Guests within Dendrimer or Cyclodextrin Cavities Revealed by NOE NMR Techniques

In this study, G5 PAMAM dendrimer and α-, β-, γ-cyclodextrin (CD) conjugates were synthesized. Host-guest behaviors of the conjugates toward five guest molecules including sodium methotrexate (MTX), amantadine hydrochloride (ADH), sulfamethoxazole (SMZ), sodium deoxycholate (SDC), and sodium dodecyl sulfate (SDS) were analyzed by NOE NMR techniques. Among the five guest molecules, ADH only binds with β-CD in G5-β-CD, SDC shows higher priority to localize within the cavity of γ-CD in G5-γ-CD, while MTX exhibits selective encapsulation within the cavities of G5 dendrimer in G5-α-CD. SDS has high binding affinity with α-CD in G5-α-CD but forms a precipitate in the complex solution. SMZ shows simultaneous encapsulation within CDs (α-, β-, and γ-CD) or G5 in the presence of the three conjugates. The host behavior of G5-CD conjugates depends on CD cavity size, guest size, and hydrophobicity. The results obtained in this study are helpful in the optimization of dendrimer-CD conjugate-based drug delivery systems.

Mitochondrial targeting dendrimer allows efficient and safe gene delivery

Cationic dendrimers are promising tools in the introduction of nucleic acids into mammalian cells, however, present dendrimer-based gene vectors have modest transfection efficacy and significant toxicity. Here, we synthesized triphenylphosphonium (TPP) conjugated dendrimers and used them as polymeric gene vectors. TPP-conjugated dendrimers can effectively target mitochondria and showed efficient transfection efficacy on HeLa and COS-7 cells with low cytotoxicity on the transfected cells. These materials achieved much higher efficacy than the commercial transfection reagent SuperFect and comparable efficacy with Lipofectamine 2000. This study provides a new insight into the design of efficient and biocompatible gene vectors using dendrimers as scaffolds.

Inclusion complexes of isoflavones with two commercially available dendrimers: Solubility, stability, structures, release behaviors, cytotoxicity, and anti-oxidant activities

We prepared and characterized the inclusion complexes of daidzein with poly(amidoamine) (PAMAM) and poly(propylene imine) (PPI) dendrimers. Aqueous solubility of daidzein was significantly enhanced by both PAMAM and PPI (186- and 650-fold at 0.36mM, respectively). Daidzein in G3 PAMAM solution is more stable than that in G4 PPI. NMR studies reveal the encapsulation of daidzein within the interior cavities of PPI through hydrophobic interactions. Daidzein exhibits a slower release behavior from PPI than that from PAMAM. PPI/daidzein complex is much more toxic than PAMAM/daidzein complex on several cell lines. PAMAM/daidzein complexes showed similar protective effect on oxidative stress-induced cytotoxicity as compared to free daidzein. These results suggest that the inclusion of daidzein with dendrimer can effectively improve the solubility, prolong the delivery, and maintain the anti-oxidant activity of daidzein. This research provides new insights into dendrimer-based drug delivery systems and will be helpful for the design of novel dendrimer/drug formulations.

Surface-engineered dendrimers with a diaminododecane core achieve efficient gene transfection and low cytotoxicity.

Cationic dendrimers are widely used as gene vectors; however, these materials are usually associated with unsatisfied transfection efficiency and biocompatibility. In this study, we used an aliphatic hydrocarbon-cored polyamidoamine (PAMAM) dendrimer as an alternative to traditional cationic PAMAM dendrimers in the design of efficient gene vectors. Diaminododecane-cored generation 4 (C12G4) PAMAM dendrimer showed dramatically higher efficacy in luciferase and EGFP gene transfection than diaminoethane-cored generation 4 (C2G4) and diaminohexane-cored generation 4 (C6G4) PAMAM dendrimers. The viability of cells incubated with C12G4 at transfection concentrations is above 90%. The significantly improved gene transfection efficacy of C12G4 is attributed to the hydrophobic core of C12G4 which increases the cellular uptake of dendrimer/DNA polyplexes. Further modification of C12G4 with functional ligands such as arginine, 2,4-diamino-1,3,5-triazine, and fluorine compounds significantly increase its transfection efficiency on several cell lines. These results suggest that diaminododecane-cored dendrimers can be developed as a versatile scaffold in the design of efficient gene vectors.

Triazine-modified dendrimer for efficient TRAIL gene therapy in osteosarcoma.

Osteosarcoma is a high-grade malignant bone tumor that usually develops in the teenagers. Despite improvement in therapy, the five-year survival rate is poor for patients not responding to treatment or with metastases. Tumor necrosis factor (TNF) related apoptosis inducing ligand (TRAIL) gene therapy is a new strategy in the treatment of cancers, however, the lack of efficient and low toxic vectors remains the major obstacle in TRAIL gene therapy. In this study, a triazine-modified dendrimer G5-DAT66 was synthesized and used as a vector for TRAIL gene therapy in vitro and in vivo. The material shows much higher transfection efficacy on osteosarcoma MG-63 cell line than commercial transfection reagents such as Lipofectamine 2000 and SuperFect. It effectively induces apoptosis in MG-63 cells and three-dimensional MG-63 cell cultures when delivering a TRAIL plasmid. In vivo studies further prove that G5-DAT66 efficiently transfects TRAIL plasmid in tumors and inhibits tumor growth in osteosarcoma-bearing mice. These results suggest that triazine-modified dendrimer has promising potential for TRAIL gene therapy in osteosarcoma.

Screening of efficient siRNA carriers in a library of surface-engineered dendrimers

Polymers are widely used as non-viral carriers for siRNA delivery, but concern has also arisen in their limited efficacy and inherent toxicity. Whilst many of previous efforts have been documented towards improving the performance of polymers via chemical modifications, the structure-activity relationships (SAR) of these ligand-modified polymers are not well understood. To address this issue, we systemically prepared a library of surface-engineered dendrimers (>300) as the screening pool to discover efficient siRNA carriers. The modified ligands include alkyls and fluoroalkyls, amino acids, benzene derivatives and heterocyclic compounds. Gene silencing results showed that the lead material shows excellent efficacy even in hard-to-transfect cells such as mesenchymal stem cells. The SAR studies revealed that ligands containing appropriate hydrophobicity, or ligands with both hydrophobic and functional atoms/groups are essential for polymers to achive efficient knockdown efficacy. A second-generation library designed based on the above principles further confirms the proposed design criteria. The results enable the future rational design of potent siRNA carriers.

Polymers modified with double-tailed fluorous compounds for efficient DNA and siRNA delivery.

Cationic polymers are widely used as gene carriers, however, these polymers are usually associated with low transfection efficacy and non-negligible toxicity. Fluorination on polymers significantly improves their performances in gene delivery, but a high density of fluorous chains must be conjugated on a single polymer. Here we present a new strategy to construct fluorinated polymers with minimal fluorous chains for efficient DNA and siRNA delivery. A double-tailed fluorous compound 2-chloro-4,6-bis[(perfluorohexyl)propyloxy]-1,3,5-triazine (CBT) was conjugated on dendrimers of different generations and low molecular weight polyethylenimine via a facile synthesis. The yielding products with average numbers of 1-2 conjugated CBT moieties showed much improved EGFP and luciferase transfection efficacy compared to unmodified polymers. In addition, these polymers show high siRNA delivery efficacy on different cell lines. Among the synthesized polymers, generation 1 (G1) dendrimer modified with an average number of 1.9 CBT moieties (G1-CBT1.9) shows the highest efficacy when delivering both DNA and siRNA and its efficacy approaches that of Lipofectamine 2000. G1-CBT1.9 also shows efficient gene silencing in vivo. All of the CBT-modified polymers exhibit minimal toxicity on the cells at their optimal transfection conditions. This study provides a new strategy to design efficient fluorous polymers for DNA and siRNA delivery.

Clustering Small Dendrimers into Nanoaggregates for Efficient DNA and siRNA Delivery with Minimal Toxicity

Cationic dendrimers are widely used as nonviral gene vectors, however, current gene materials based on dendrimers are either little effective or too toxic on the transfected cells. Here, a facile strategy is presented to prepare high efficient dendrimers with low transfection toxicity. Small dendrimers with 2 nm are clustered into nanoaggregates (≈100 nm) via phenylboronic acid modification and the self-assembled materials enable efficient DNA and siRNA delivery on several cell lines. The clustered nanostructures can disassemble into small dendrimers in acidic conditions thus exerting significantly less toxicity on the transfected cells. Further structure-function relationship studies reveal that both the phenyl group and boronic acid group play essential roles in the self-assembly and gene delivery processes. The transfection efficacy of phenylboronic acid-modified dendrimers can be down-regulated by blocking the boronic acid groups on dendrimers with diols or degrading the groups with hydrogen peroxide. This study provides a facile strategy in the development of efficient and biocompatible gene vectors based on low molecular weight polymers and clearly demonstrates the structure-function relationship of phenylboronic acid-modified polymers in gene delivery.