Breanne Landry

Impact of Lipid Substitution on Assembly and Delivery of siRNA by Cationic Polymers

Characterization of a polymer library engineered to enhance their ability to protect and deliver their nucleotide cargo to the cells is reported. The ζ-potential continuously increased with higher polymer:siRNA weight ratio, and the ζ-potential of lipid-modified polymers:siRNA complexes were higher than PEI2 at all ratios. At polymer:siRNA ratio of 1:1, all lipid-substituted polymers showed complete protection against degradation. Lipid-modified polymers significantly increased the cellular uptake of siRNA complexes and down-regulation of GAPDH and P-gp (max. 66% and 67%, respectively). The results indicate that hydrophobic modification of low molecular PEI could render this otherwise ineffective polymer to a safe effective delivery system for intracellular siRNA delivery and protein silencing.

Induction of apoptosis by survivin silencing through siRNA delivery in a human breast cancer cell line.

Post-transcriptional silencing of antiapoptotic genes is a promising strategy for cancer therapy, but delivering short interfering RNA (siRNA) molecules against such targets is challenging due to inability of anionic siRNA to cross cellular membranes. Lipid substitution on small molecular weight, nontoxic polyethylenimine (PEI) has been investigated as a promising approach for effective siRNA delivery. In this study, we report on the ability of low molecular weight, lipid-substituted PEI to deliver siRNA against the antiapoptotic protein survivin. Toxicity of a library of lipid-substituted PEIs, as well as their siRNA delivery and survivin silencing efficiency, was evaluated in MDA-MB-231 human breast cancer cells. A significant increase in cellular delivery of siRNA was observed as a result of lipid substitution. Most significant downregulation of survivin was established by caprylic acid-substituted polymers, which resulted in significant levels of apoptosis induction and resultant loss of cell viability. Survivin downregulation prior to anticancer drug treatment decreased the IC(50) of several drugs by 50- to 120-fold. Our experiments indicated an effective downregulation of survivin, a cell protective protein upregulated in tumor cells, by delivering siRNA with hydrophobically modified PEI. This study introduces a promising delivery system for safe and effective siRNA delivery that will be suitable for further investigation in preclinical animal models.

Lipid substitution on low molecular weight (0.6-2.0 kDa) polyethylenimine leads to a higher zeta potential of plasmid DNA and enhances transgene expression.

Cationic polymers are desirable gene carriers because of their better safety profiles than viral delivery systems. Low molecular weight (MW) polymers are particularly attractive, since they display little cytotoxicity, but they are also ineffective for gene delivery. To create effective carriers from low MW polymers palmitic acid (PA) was substituted on 0.6-2.0 kDa polyethylenimines (PEIs) and their efficiency for plasmid DNA (pDNA) delivery was evaluated. The extent of lipid substitution was dependent on the lipid/PEI feed ratio and the polymer MW. While the hydrodynamic size of the polymer/pDNA complexes (polyplexes) increased or decreased depending on the extent of lipid substitution, the ζ potential of the assembled complexes was consistently higher as a result of lipid substitution. Lipid substitution generally increased the in vitro toxicity of the PEIs, but it was significantly lower than that of the 25 kDa branched PEI. The in vitro transfection efficiency of the lipid-substituted polymers was higher than that of native PEIs, which were not at all effective. The delivery efficiency was proportional to the extent of lipid substitution as well as the polymer MW. This correlated with the increased uptake of lipid-substituted polyplexes, based on confocal microscopic investigations with FITC-labeled pDNA. The addition of chloroquine further increased the transfection efficiency of lipid-substituted PEIs, indicating that endosomal release was a limiting factor affecting the efficiency of these carriers. This study indicates that lipid substitution on low MW PEIs makes their assembly more effective, resulting in better delivery of pDNA into mammalian cells.

Effective down-regulation of breast cancer resistance protein (BCRP) by siRNA delivery using lipid-substituted aliphatic polymers.

Breast Cancer Resistance Protein (BCRP, ABCG2) is an efflux protein whose aberrant activity has been linked to multidrug resistance in cancer. Although siRNA delivery to down-regulate BCRP expression is promising to sensitize tumor cells against drugs, therapeutic use of siRNA requires effective carriers that can deliver siRNA intracellularly with minimal toxicity on target cells. This study explored the feasibility of special class of cationic polymers, namely lipid-substituted low molecular weight (2kDa) polyethyleneimine (PEI), as a carrier for siRNA-mediated BCRP down-regulation. Structure-function studies methodically evaluated the effect of a range of lipophilic substitutions for siRNA delivery and BCRP down-regulation. Our results showed a significant increase in siRNA delivery as a function of lipid substitution for a range of lipids ranging from C8 to C18. The BCRP silencing was correlated to siRNA delivery efficiency of the polymers, and effectively lasted for ∼5days after a single treatment of siRNA. BCRP down-regulation sensitized the drug-resistant cells to cytotoxic effect of mitoxantrone by a ∼14-fold decrease in the IC(50) value, whose effect was evident even after 14days. This study demonstrated the possibility of functional siRNA delivery by lipid-modified low molecular weight PEI and highlighted the importance of the extent and nature of lipid substitution in effective siRNA delivery.

Effective non-viral delivery of siRNA to acute myeloid leukemia cells with lipid-substituted polyethylenimines.

Use of small interfering RNA (siRNA) is a promising approach for AML treatment as the siRNA molecule can be designed to specifically target proteins that contribute to aberrant cell proliferation in this disease. However, a clinical-relevant means of delivering siRNA molecules must be developed, as the cellular delivery of siRNA is problematic. Here, we report amphiphilic carriers combining a cationic polymer (2 kDa polyethyleneimine, PEI2) with lipophilic moieties to facilitate intracellular delivery of siRNA to AML cell lines. Complete binding of siRNA by the designed carriers was achieved at a polymer:siRNA ratio of ∼0.5 and led to siRNA/polymer complexes of ∼100 nm size. While the native PEI2 did not display cytotoxicity on AML cell lines THP-1, KG-1 and HL-60, lipid-modification on PEI2 slightly increased the cytotoxicity, which was consistent with increased interaction of polymers with cell membranes. Cellular delivery of siRNA was dependent on the nature of lipid substituent and the extent of lipid substitution, and varied among the three AML cell lines used. Linoleic acid-substituted polymers performed best among the prepared polymers and gave a siRNA delivery equivalent to better performing commercial reagents. Using THP-1 cells and a reporter (GFP) and an endogenous (CXCR4) target, effective silencing of the chosen targets was achieved with 25 to 50 nM of siRNA concentrations, and without adversely affecting subsequent cell growth. We conclude that lipid-substituted PEI2 can serve as an effective delivery of siRNA to leukemic cells and could be employed in molecular therapy of leukemia.

Does nanocrystalline silver have a transferable effect

This study examined the mechanism of nanocrystalline silver antiinflammatory activity, and tested nanocrystalline silver for systemic antiinflammatory effects. Secondary ion mass spectroscopy of skin treated directly with nanocrystalline silver for 24 hours showed that at skin surfaces there were significant deposits at weights corresponding to Ag, AgO, AgCl, AgNO3, Ag2O, and silver clusters Ag2‐6, but silver penetration was minimal. To test for translocation of the effect, a porcine contact dermatitis model in which wounds were induced on one side of the back and then treated with nanocrystalline silver on the opposite side of the back was used. Visual and histological data showed improvement relative to animals treated with saline only. Significantly increased induction of apoptosis in the inflammatory cells present in the dermis was observed with remote nanocrystalline silver treatments. In addition, immunohistochemical analysis showed decreased levels of proinflammatory cytokines tumor necrosis factor‐α and interleukin‐8, and increased levels of antiinflammatory cytokine interleukin‐4, epidermal growth factor, keratinocyte growth factor, and keratinocyte growth factor‐2. Thus, the antiinflammatory effects of nanocrystalline silver appear to be induced by interactions with cells in the top layers of the skin, which then release biological signals resulting in widespread antiinflammatory activity.

Progress in RNAi-mediated Molecular Therapy of Acute and Chronic Myeloid Leukemia

Leukemias arise from genetic alterations in normal hematopoietic stem or progenitor cells, leading to impaired regulation of proliferation, differentiation, apoptosis, and survival of the transformed cells. With the advent of RNA interference (RNAi) and the short interfering RNA (siRNA) as its pharmacological mediator, it is becoming possible to modulate specific targets at will. This article summarizes current attempts to utilize RNAi reagents for therapy of leukemias, focusing on acute and chronic myeloid leukemia. We first present unique aspects of RNAi-mediated therapy, followed by a brief background on the delivery technology of RNAi reagents. The need for leukemia-specific delivery of siRNA is discussed by describing approaches that targeted agents to leukemic cells. Pharmacokinetics and biodistribution of RNAi agents are then presented, highlighting the critical issues pertinent to emerging siRNA therapy. Efforts to deliver specific RNAi therapies are then summarized in the context of expected clinical outcomes, focusing on limiting leukemic cell survival, sensitizing malignant cells to chemotherapy, mobilization of leukemic cells, and eradication of leukemic stem cells. We conclude with a perspective on the future of RNAi therapy, emphasizing the technological requirements and mechanistic challenges for clinical entry.

Targeting CXCR4/SDF-1 axis by lipopolymer complexes of siRNA in acute myeloid leukemia

In spite of high complete remission rates in Acute Myeloid Leukemia (AML), little progress has been made in the long-term survival of relapsing AML patients, urging for the development of novel therapies. The CXCR4/SDF-1 axis is a potential therapeutic target in AML to reduce the enhanced survival and proliferation of leukemic cells, with current drug development efforts focusing on antagonists and blocking antibodies. The RNAi technology mediated by siRNA is a promising alternative; however, further development of clinically relevant siRNA carriers is needed since siRNA on its own is an incompetent silencing agent. Here, we report on lipid-substituted polymeric carriers for siRNA delivery to AML cells, specifically targeting CXCR4. Our results demonstrate an effective suppression of CXCR4 protein with the polymeric siRNA delivery in AML THP-1 cells. The suppression of CXCR4 as well as its ligand, SDF-1 (CXCL12), decreased THP-1 cell numbers due to reduced cell proliferation. The reduced proliferation was also observed in the presence of human bone marrow stromal cells (hBMSC), suggesting that our approach would be effective in the protective bone marrow microenvironment. The combination of CXCR4 silencing and cytarabine treatment resulted in more effective cytotoxicity when the cells were co-incubated with hBMSC. We observed a decrease in the toxicity of the lipopolymer/siRNA complexes when THP-1 cells were treated in the presence of hBMSC but this effect did not negatively affect CXCR4 silencing. In addition, siRNA delivery to mononuclear cells derived from AML patients led to significant CXCR4 silencing in 2 out of 5 samples, providing a proof-of-concept for clinical translation. We conclude that decreasing CXCR4 expression via lipopolymer/siRNA complexes is a promising option for AML therapy and could provide an effective alternative to current CXCR4 inhibition strategies.

The kinetics of thermal instability in nanocrystalline silver and the effect of heat treatment on the antibacterial activity of nanocrystalline silver dressings.

The kinetics of nanocrystalline silver dressing heat treatment was investigated via isothermal heat treatments at 90 degrees C, 100 degrees C, and 110 degrees C lasting 2-50h. Bactericidal efficacy of the dressings was measured via log reductions, while bacteriostatic longevity was determined via plate-to-plate transfer corrected zones of inhibition. Morphological evolution of the dressing was studied by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, while changes in heat flow were measured by differential scanning calorimetry. Increasing temperature increased the rate at which dressing bactericidal activity and bacteriostatic longevity decreased. Once changes in dressing properties began, they occurred nonlinearly with time. The earliest biological, chemical, and physical indicators of altered dressing properties were loss of bacteriostatic longevity, silver-oxygen bonds, and fine features, respectively. An early change in heat flow appeared to be responsible for these indicators, while a later change corresponded to rapid grain growth occurring after a critical crystallite size (approximately 30 nm) was reached. The grain growth exponent was determined to be 2.8 for temperatures of 100-110 degrees C, with an activation energy of 177 kJ/mol, suggesting that normal grain growth occurred, with volume and/or grain boundary diffusion as the dominant forms of diffusion. The thermal instability of nanocrystalline silver should be accounted for during production, storage, and use of dressings. The properties required for nanosilver antimicrobial efficacy demonstrated in this study, as well as its thermal instability, should be taken into consideration for the development of nanosilver products in the future.

Current attempts to implement siRNA-based RNAi in leukemia models.

Leukemias arise from genetic alterations in normal hematopoietic stem or progenitor cells, leading to abnormal blood population with transformed cells. With the advent of RNAi and its pharmacological mediator siRNA, it has become possible to downregulate specific drivers causing leukemias. In this review, we present unique aspects of RNAi-mediated therapy and delivery technologies. Recent updates on molecular targets and delivery systems are discussed emanating from in vitro cell models and preclinical animal models. We conclude with a view on the future of RNAi in leukemia therapy, emphasizing possible measures to achieve higher efficacy and improved safety.