Xiaoxuan Liu

An Amphiphilic Dendrimer for Effective Delivery of Small Interfering RNA and Gene Silencing In Vitro and In Vivo

An amphiphilic dendrimer bearing a hydrophobic alkyl chain and hydrophilic poly(amidoamine) dendrons is able to combine the advantageous features of lipid and dendrimer vectors to deliver a heat shock protein 27 siRNA and produce potent gene silencing and anticancer activity in vitro and in vivo in a prostate cancer model. This dendrimer can be used alternatively for treating various diseases.

Anticancer drug nanomicelles formed by self-assembling amphiphilic dendrimer to combat cancer drug resistance

Significance Nanotechnology-based drug delivery is expected to bring new hope for cancer treatment by enhancing anticancer drug efficacy, overcoming drug resistance, and reducing drug toxicity. In this respect, we developed an innovative drug delivery system based on a self-assembling amphiphilic dendrimer, which can generate supramolecular nanomicelles with large void space in their core to encapsulate anticancer drugs with high loading capacity. The resulting drug-encapsulated nanomicelles can effectively enhance drug potency and combat drug resistance by promoting cellular uptake and decreasing efflux of the anticancer drug. Moreover, this drug delivery system can significantly reduce the systemic toxicity of the free drug. The present study illustrates a successful example of how advances in dendrimer nanotechnology can be advantageously implemented to foster therapeutic perspectives. Drug resistance and toxicity constitute challenging hurdles for cancer therapy. The application of nanotechnology for anticancer drug delivery is expected to address these issues and bring new hope for cancer treatment. In this context, we established an original nanomicellar drug delivery system based on an amphiphilic dendrimer (AmDM), which could generate supramolecular micelles to effectively encapsulate the anticancer drug doxorubicin (DOX) with high drug-loading capacity (>40%), thanks to the unique dendritic structure creating large void space for drug accommodation. The resulting AmDM/DOX nanomicelles were able to enhance drug potency and combat doxorubicin resistance in breast cancer models by significantly enhancing cellular uptake while considerably decreasing efflux of the drug. In addition, the AmDM/DOX nanoparticles abolished significantly the toxicity related to the free drug. Collectively, our studies demonstrate that the drug delivery system based on nanomicelles formed with the self-assembling amphiphilic dendrimer constitutes a promising and effective drug carrier in cancer therapy.

Genome-Wide Profiling Identified a Set of miRNAs that Are Differentially Expressed in Glioblastoma Stem Cells and Normal Neural Stem Cells

A major challenge in cancer research field is to define molecular features that distinguish cancer stem cells from normal stem cells. In this study, we compared microRNA (miRNA) expression profiles in human glioblastoma stem cells and normal neural stem cells using combined microarray and deep sequencing analyses. These studies allowed us to identify a set of 10 miRNAs that are considerably up-regulated or down-regulated in glioblastoma stem cells. Among them, 5 miRNAs were further confirmed to have altered expression in three independent lines of glioblastoma stem cells by real-time RT-PCR analysis. Moreover, two of the miRNAs with increased expression in glioblastoma stem cells also exhibited elevated expression in glioblastoma patient tissues examined, while two miRNAs with decreased expression in glioblastoma stem cells displayed reduced expression in tumor tissues. Furthermore, we identified two oncogenes, NRAS and PIM3, as downstream targets of miR-124, one of the down-regulated miRNAs; and a tumor suppressor, CSMD1, as a downstream target of miR-10a and miR-10b, two of the up-regulated miRNAs. In summary, this study led to the identification of a set of miRNAs that are differentially expressed in glioblastoma stem cells and normal neural stem cells. Characterizing the role of these miRNAs in glioblastoma stem cells may lead to the development of miRNA-based therapies that specifically target tumor stem cells, but spare normal stem cells.

Arginine-Terminated Generation 4 PAMAM Dendrimer as an Effective Nanovector for Functional siRNA Delivery in Vitro and in Vivo

Successful therapeutic implementation of RNA interference critically depends on systems able to safely and efficiently deliver small interfering RNA (siRNA). Dendrimers are emerging as appealing nanovectors for siRNA delivery by virtue of their unique well-defined dendritic nanostructure within which is confined an intriguing cooperativity and multivalency. We have previously demonstrated that structurally flexible triethanolamine (TEA) core poly(amidoamine) (PAMAM) dendrimers of high generations are effective nanovectors for siRNA delivery in vitro and in vivo. In the present study, we have developed arginine-terminated dendrimers with the aim of combining and harnessing the unique siRNA delivery properties of the TEA-core PAMAM dendrimer and the cell-penetrating advantages of the arginine-rich motif. A generation 4 dendrimer of this family (G4Arg) formed stable dendriplexes with siRNA, leading to improved cell uptake of siRNA by comparison with its nonarginine bearing dendrimer counterpart. Moreover, G4Arg was demonstrated to be an excellent nanocarrier for siRNA delivery, yielding potent gene silencing and anticancer effects in prostate cancer models both in vitro and in vivo with no discernible toxicity. Consequently, importing an arginine residue on the surface of a dendrimer is an appealing option to improve delivery efficiency, and at the same time, the dendrimer G4Arg constitutes a highly promising nanovector for efficacious siRNA delivery and holds great potential for further therapeutic applications.

Novel RNA oligonucleotide improves liver function and inhibits liver carcinogenesis in vivo

Hepatocellular carcinoma (HCC) occurs predominantly in patients with liver cirrhosis. Here we show an innovative RNA‐based targeted approach to enhance endogenous albumin production while reducing liver tumor burden. We designed short‐activating RNAs (saRNA) to enhance expression of C/EBPα (CCAAT/enhancer‐binding protein‐α), a transcriptional regulator and activator of albumin gene expression. Increased levels of both C/EBPα and albumin mRNA in addition to a 3‐fold increase in albumin secretion and 50% decrease in cell proliferation was observed in C/EBPα‐saRNA transfected HepG2 cells. Intravenous injection of C/EBPα‐saRNA in a cirrhotic rat model with multifocal liver tumors increased circulating serum albumin by over 30%, showing evidence of improved liver function. Tumor burden decreased by 80% (P = 0.003) with a 40% reduction in a marker of preneoplastic transformation. Since C/EBPα has known antiproliferative activities by way of retinoblastoma, p21, and cyclins, we used messenger RNA (mRNA) expression liver cancer‐specific microarray in C/EBPα‐saRNA‐transfected HepG2 cells to confirm down‐regulation of genes strongly enriched for negative regulation of apoptosis, angiogenesis, and metastasis. Up‐regulated genes were enriched for tumor suppressors and positive regulators of cell differentiation. A quantitative polymerase chain reaction (PCR) and western blot analysis of C/EBPα‐saRNA‐transfected cells suggested that in addition to the known antiproliferative targets of C/EBPα, we also observed suppression of interleukin (IL)6R, c‐Myc, and reduced STAT3 phosphorylation. Conclusion: A novel injectable saRNA‐oligonucleotide that enhances C/EBPα expression successfully reduces tumor burden and simultaneously improves liver function in a clinically relevant liver cirrhosis/HCC model. (Hepatology 2014;58:216–227)

Structurally Flexible Triethanolamine Core PAMAM Dendrimers Are Effective Nanovectors for DNA Transfection in Vitro and in Vivo to the Mouse Thymus

With the aim of developing dendrimer nanovectors with a precisely controlled architecture and flexible structure for DNA transfection, we designed PAMAM dendrimers bearing a triethanolamine (TEA) core, with branching units pointing away from the center to create void spaces, reduce steric congestion, and increase water accessibility for the benefit of DNA delivery. These dendrimers are shown to form stable nanoparticles with DNA, promote cell uptake mainly via macropinocytosis, and act as effective nanovectors for DNA transfection in vitro on epithelial and fibroblast cells and, most importantly, in vivo in the mouse thymus, an exceedingly challenging organ for immune gene therapy. Collectively, these results validate our rational design approach of structurally flexible dendrimers with a chemically defined structure as effective nanovectors for gene delivery, and demonstrate the potential of these dendrimers in intrathymus gene delivery for future applications in immune gene therapy.

Structurally flexible triethanolamine-core poly(amidoamine) dendrimers as effective nanovectors to deliver RNAi-based therapeutics.

RNAi-based nucleic acid molecules have attracted considerable attention as compelling therapeutics providing safe and competent delivery systems are available. Dendrimers are emerging as appealing nanocarriers for nucleic acid delivery thanks to their unique well-defined architecture and the resulting cooperativity and multivalency confined within a nanostructure. The present review offers a brief overview of the structurally flexible triethanolamine-core poly(amidoamine) (PAMAM) dendrimers developed in our group as nanovectors for the delivery of RNAi therapeutics. Their excellent activity for delivering different RNAi therapeutics in various disease models in vitro and in vivo will be highlighted here.

Impact of siRNA Overhangs for Dendrimer-Mediated siRNA Delivery and Gene Silencing

Small interfering RNA (siRNA) have attracted considerable attention, as compelling therapeutics providing safe and competent delivery systems are available. Dendrimers are emerging as appealing siRNA delivery vectors thanks to their unique, well-defined architecture and the resulting cooperativity and multivalency confined within a nanostructure. We have recently disclosed the structurally flexible fifth-generation TEA-core PAMAM dendrimer (G5) as an effective nanocarrier for delivery of sticky siRNA bearing long complementary sequence overhangs (dA)n/(dT)n (n = 5 or 7). Here, using combined experimental/computational approaches, we successfully clarified (i) the underlying mechanisms of interaction between the dendrimer nanovector G5 and siRNA molecules bearing either complementary or noncomplementary sequence overhangs of different length and chemistry and (ii) the impact of siRNA overhangs contributing toward the improved delivery potency. Using siRNA with complementary overhangs offer the best action in term of gene silencing through the formation of concatemers, that is, supramolecular structures resulting from synergistic and cooperative binding via (dA)n/(dT)n bridges (n = 5 or 7). On the other hand, although siRNA bearing long, noncomplementary overhangs (dA)n/(dA)n or (dT)n/(dT)n (n = 5 or 7) are endowed with considerably higher gene silencing potency than normal siRNA with (dT)2/(dT)2, they remain less effective than their sticky siRNA counterparts. The observed gene silencing potency depends on length, nature, and flexibility of the overhangs, which behave as a sort of clamps that hold and interact with the dendrimer nanovectors, thus impacting siRNA delivery performance and, ultimately, gene silencing. Our findings can be instrumental in designing siRNA entities with enhanced capability to achieve effective RNA interference for therapeutic applications.

Targeted delivery of Dicer-substrate siRNAs using a dual targeting peptide decorated dendrimer delivery system

UNLABELLED Small interfering RNAs (siRNA) are emerging as novel therapeutic agents, providing competent delivery systems that are available. Dendrimers, a special family of synthetic macromolecules, represent an exciting delivery platform by virtue of their well-defined dendritic structure and unique multivalency and cooperativity confined within a nanoscale volume. Here, we report a Dicer-substrate siRNA (dsiRNA) which, when delivered using a structurally flexible triethanolamine-core poly(amidoamine) dendrimer of generation 5 as the nanocarrier, gives rise to a much greater RNAi response than that produced with conventional siRNA. Further decoration of the dsiRNA/dendrimer complexes with a dual targeting peptide simultaneously promoted cancer cell targeting through interacting with integrins and cell penetration via the interaction with neuropilin-1 receptors, which led to improved gene silencing and anticancer activity. Altogether, our results disclosed here open a new avenue for therapeutic implementation of RNAi using dendrimer nanovector based targeted delivery. FROM THE CLINICAL EDITOR This study demonstrates superior therapeutic properties of siRNA when combined with a dendrimer-based targeted nano-delivery system. Similar approaches may eventually gain clinical utility following additional studies determining safety and efficacy.

Combination of Dendrimer-Nanovector-Mediated Small Interfering RNA Delivery to Target Akt with the Clinical Anticancer Drug Paclitaxel for Effective and Potent Anticancer Activity in Treating Ovarian Cancer

The recently discovered small interfering RNA (siRNA) holds great promise in cancer therapy. However, efficient and safe delivery systems are required for the development of new therapeutic paradigms. Ovarian cancer has the highest mortality of all gynecologic tumors, and there is an urgent need for specific and effective therapies. The phosphatidylinositol 3-kinase/Akt pathway, which is strongly implicated in the biology of ovarian cancer, constitutes an attractive therapeutic target. In this study, we describe a triethanolamine-core poly(amidoamine) dendrimer which forms stable nanoparticles with the Akt siRNA, protects siRNA against RNase digestion, and is highly effective for initiating Akt target-gene silencing both in vitro and in vivo, while being minimally toxic. Most importantly, it could potentiate the antitumor effect of the anticancer drug paclitaxel. These results represent the proof-of-concept, demonstrating that dendrimer-mediated Akt siRNA delivery, in combination with a chemotherapeutic regimen, may constitute a promising nanomedicine approach in cancer therapy.