The role of apolipoprotein E in the elimination of liposomes from blood by hepatocytes in the mouse

Lipid Nanoparticle Delivery of siRNA to Osteocytes Leads to Effective Silencing of SOST and Inhibition of Sclerostin In Vivo

Sclerostin is a protein secreted by osteocytes that is encoded by the SOST gene; it decreases bone formation by reducing osteoblast differentiation through inhibition of the Wnt signaling pathway. Silencing the SOST gene using RNA interference (RNAi) could therefore be an effective way to treat osteoporosis. Here, we investigate the utility of lipid nanoparticle (LNP) formulations of siRNA to silence the SOST gene in vitro and in vivo. It is shown that primary mouse embryonic fibroblasts (MEF) provide a useful model system in which the SOST gene can be induced by incubation in osteogenic media, allowing development of optimized SOST siRNA for silencing the SOST gene. Incubation of MEF cells with LNP containing optimized SOST siRNA produced significant, prolonged knockdown of the induced SOST gene in vitro, which was associated with an increase in osteogenic markers. Intravenous (i.v.) administration of LNP containing SOST siRNA to mice showed significant accumulation of LNP in osteocytes in compact bone, depletion of SOST mRNA and subsequent reduction of circulating sclerostin protein, establishing the potential utility for LNP siRNA systems to promote bone formation.

Structure, activity and uptake mechanism of siRNA-lipid nanoparticles with an asymmetric ionizable lipid

Lipid nanoparticles (LNPs) represent the most advanced platform for the systemic delivery of siRNA. We have previously reported the discovery of novel ionizable lipids with asymmetric lipid tails, enabling potent gene-silencing activity in hepatocytes in vivo; however, the structure and delivery mechanism had not been elucidated. Here, we report the structure, activity and uptake mechanism of LNPs with an asymmetric ionizable lipid. Zeta potential and hemolytic activity of LNPs showed that LNPs were neutral at the pH of the blood compartment but become increasingly charged and fusogenic in the acidic endosomal compartment. (31)P NMR experiments indicated that the siRNA was less mobile inside particles, presumably because of an electrostatic interaction with an ionizable lipid. The role of Apolipoprotein E (apoE) was studied using recombinant human apoE both in vitro and in vivo. A comparative study in wild-type and apoE-deficient mice revealed that apoE significantly influenced the in vivo biodistribution of LNPs and enhanced the cellular uptake. Pretreatment of mice with siRNA targeting low-density lipoprotein receptor (LDLR) impaired gene-silencing of the following siRNA treatment, demonstrating that in vivo activity of LNPs is dependent on LDLR. Our studies on the detailed mechanism should lead to the creation of more sophisticated LNP-based RNAi therapeutics.

Relationship Between the Physicochemical Properties of Lipid Nanoparticles and the Quality of siRNA Delivery to Liver Cells

While a variety of short interfering RNA (siRNA) delivery compounds have been developed, a deep understanding of the key parameters that determine the quality of siRNA delivery are not known with certainty. Therefore, an understanding of the factors required for the efficient, selective, and safe delivery of siRNA is a great challenge for successful siRNA delivery. Herein, we report on the development of two pH-sensitive cationic lipids and their use in examining the impact of the acid dissociation constant (pKa) value, lipase sensitivity and the size of lipid nanoparticles on the biodistribution, and efficiency and cell specificity of gene silencing in the liver. An increase in the pKa value resulted in a significant change in the intrahepatic localization of siRNA and gene-silencing efficiency in hepatocytes and liver sinusoidal endothelial cells (LSECs). The sensitivity of the pH-sensitive cationic lipid to lipases was a major factor in achieving hepatocyte-specific gene silencing. Increasing the particle size can improve the LSEC specificity of gene silencing. As a consequence, we succeeded in developing both a highly efficient, hepatocyte-specific formulation, and the most efficacious LSEC-targeted formulation reported to date. These findings will facilitate the development of more sophisticated siRNA delivery systems.

Delivery of siRNAs to Dendritic Cells Using DEC205-Targeted Lipid Nanoparticles to Inhibit Immune Responses

Due to their ability to knock down the expression of any gene, siRNAs have been heralded as ideal candidates for treating a wide variety of diseases, including those involving "undruggable" targets. However, the therapeutic potential of siRNAs remains severely limited by a lack of effective delivery vehicles. Recently, lipid nanoparticles (LNPs) containing ionizable cationic lipids have been developed for hepatic siRNA delivery. However, their suitability for delivery to other cell types has not been determined. We have modified LNPs for preferential targeting to dendritic cells (DCs), central regulators of immune responses. To achieve directed delivery, we coated LNPs with a single-chain antibody (scFv; DEC-LNPs), specific to murine DEC205, which is highly expressed on distinct DC subsets. Here we show that injection of siRNAs encapsulated in DEC-LNPs are preferentially delivered to DEC205(+) DCs. Gene knockdown following uptake of DEC-LNPs containing siRNAs specific for the costimulatory molecules CD40, CD80, and CD86 dramatically decreases gene expression levels. We demonstrate the functionality of this knockdown with a mixed lymphocyte response (MLR). Overall, we report that injection of LNPs modified to restrict their uptake to a distinct cell population can confer profound gene knockdown, sufficient to inhibit powerful immune responses like the MLR.

Expression kinetics of nucleoside-modified mRNA delivered in lipid nanoparticles to mice by various routes

In recent years, in vitro transcribed messenger RNA (mRNA) has emerged as a potential therapeutic platform. To fulfill its promise, effective delivery of mRNA to specific cell types and tissues needs to be achieved. Lipid nanoparticles (LNPs) are efficient carriers for short-interfering RNAs and have entered clinical trials. However, little is known about the potential of LNPs to deliver mRNA. Here, we generated mRNA-LNPs by incorporating HPLC purified, 1-methylpseudouridine-containing mRNA comprising codon-optimized firefly luciferase into stable LNPs. Mice were injected with 0.005-0.250mg/kg doses of mRNA-LNPs by 6 different routes and high levels of protein translation could be measured using in vivo imaging. Subcutaneous, intramuscular and intradermal injection of the LNP-encapsulated mRNA translated locally at the site of injection for up to 10days. For several days, high levels of protein production could be achieved in the lung from the intratracheal administration of mRNA. Intravenous and intraperitoneal and to a lesser extent intramuscular and intratracheal deliveries led to trafficking of mRNA-LNPs systemically resulting in active translation of the mRNA in the liver for 1-4 days. Our results demonstrate that LNPs are appropriate carriers for mRNA in vivo and have the potential to become valuable tools for delivering mRNA encoding therapeutic proteins.

Lipid nanoparticles for short interfering RNA delivery

The discovery of RNA interference (RNAi) in mammalian cells has created a new class of therapeutics based on the reversible silencing of specific disease-causing genes. This therapeutic potential depends on the ability to deliver inducers of RNAi, such as short-interfering RNA (siRNA) and micro-RNA (miRNA), to cells of target tissues. This chapter reviews various challenges and delivery strategies for siRNA, with a particular focus on the development of lipid nanoparticle (LNP) delivery technologies. Currently, LNP delivery systems are the most advanced technology for systemic delivery of siRNA, with numerous formulations under various stages of clinical trials. We also discuss methods to improve gene silencing potency of LNP-siRNA, as well as application of LNP technologies beyond siRNA to the encapsulation of other nucleic acids such as mRNA and clustered regularly interspaced short palindromic repeats (CRISPR).

Multifunctional enveloped nanodevices (MENDs)

It is anticipated that nucleic acid medicines will be in widespread use in the future, since they have the potential to cure diseases based on molecular mechanisms at the level of gene expression. However, intelligent delivery systems are required to achieve nucleic acid therapy, since they can perform their function only when they reach the intracellular site of action. We have been developing a multifunctional envelope-type nanodevice abbreviated as MEND, which consists of functional nucleic acids as a core and lipid envelope, and can control not only biodistribution but also the intracellular trafficking of nucleic acids. In this chapter, we review the development and evolution of the MEND by providing several successful examples, including the R8-MEND, the KALA-MEND, the MITO-Porter, the YSK-MEND, and the PALM.

Functionalization of alkyne-terminated thermally hydrocarbonized porous silicon nanoparticles with targeting peptides and antifouling polymers: effect on the human plasma protein adsorption

Porous silicon (PSi) nanomaterials combine a high drug loading capacity and tunable surface chemistry with various surface modifications to meet the requirements for biomedical applications. In this work, alkyne-terminated thermally hydrocarbonized porous silicon (THCPSi) nanoparticles were fabricated and postmodified using five bioactive molecules (targeting peptides and antifouling polymers) via a single-step click chemistry to modulate the bioactivity of the THCPSi nanoparticles, such as enhancing the cellular uptake and reducing the plasma protein association. The size of the nanoparticles after modification was increased from 176 to 180-220 nm. Dextran 40 kDa modified THCPSi nanoparticles showed the highest stability in aqueous buffer. Both peptide- and polymer-functionalized THCPSi nanoparticles showed an extensive cellular uptake which was dependent on the functionalized moieties presented on the surface of the nanoparticles. The plasma protein adsorption study showed that the surface modification with different peptides or polymers induced different protein association profiles. Dextran 40 kDa functionalized THCPSi nanoparticles presented the least protein association. Overall, these results demonstrate that the "click" conjugation of the biomolecules onto the alkyne-terminated THCPSi nanoparticles is a versatile and simple approach to modulate the surface chemistry, which has high potential for biomedical applications.

A neutral lipid envelope-type nanoparticle composed of a pH-activated and vitamin E-scaffold lipid-like material as a platform for a gene carrier targeting renal cell carcinoma

A renal cell carcinoma (RCC) is one of the refractory tumors, since it readily acquires resistance against chemotherapy. Thus, alternative therapeutic approaches such as obstructing the neovasculature are needed. We previously reported on the development of a plasmid DNA (pDNA)-encapsulating liposomal nanoparticle (LNP) as a hepatic gene delivery system that is applicable to systemic administration. The key molecular component is a SS-cleavable and pH-activated lipid-like material (ssPalm) that mounts dual sensing motifs (ternary amines and disulfide bonding) that are responsive to the intracellular environment. The main purpose of the present study was to expand its application to a tumor-targeting gene delivery system in mice bearing tumors established from a RCC (OS-RC-2). When the modification of the surface of the particle is optimized for the polyethyleneglycol (PEG), stability in the blood circulation is improved, and consequently tumor-selective gene expression can be achieved. Furthermore, gene expression in the tumor was increased slightly when the hydrophobic scaffold of the ssPalm was replaced from the conventionally used myristic acid (ssPalmM) to α-tocopherol succinate (ssPalmE). Moreover, tumor growth was significantly suppressed when the completely CpG-free pDNA encoding the solute form of VEGFR (fms-like tyrosine kinase-1: sFlt-1) was used, especially when it was delivered by the LNP formed with ssPalmE (LNP(ssPalmE)). Thus, the PEG-modified LNP(ssPalmE) is a promising gene carrier for the cancer gene therapy of RCC.

Development of lipid nanoparticle formulations of siRNA for hepatocyte gene silencing following subcutaneous administration

Recently developed lipid nanoparticle (LNP) formulations of siRNA have proven to be effective agents for hepatocyte gene silencing following intravenous administration with at least three LNP-siRNA formulations in clinical trials. The aim of this work was to develop LNP-siRNA systems for hepatocyte gene silencing that can be administered subcutaneously (s.c.). Three parameters were investigated, namely LNP size, residence time of the polyethylene glycol (PEG)-lipid coating and the influence of hepatocyte-specific targeting ligands. LNP sizes were varied over the range of 30 to 115 nm in diameter and PEG-lipid that dissociates rapidly (PEG-DMG) and slowly (PEG-DSG) were employed. In mice, results show that large (~80 nm) LNP exhibited limited accumulation in the liver and poor Factor VII (FVII) gene silencing at 1mg siRNA/kg body weight. Conversely, small (~30 nm) LNP systems showed maximal liver accumulation yet still had minimal activity. Interestingly, intermediate size (~45 nm) LNP containing PEG-DSG exhibited nearly equivalent liver accumulation as the smaller systems following s.c. administration but reduced FVII levels by 80% at 1mg siRNA/kg body weight. Smaller systems (~35 nm diameter) containing either PEG-DMG or PEG-DSG were less active; however addition of 0.5 mol.% of a GalNAc-PEG lipid to these smaller systems improved activity to levels similar to that observed for the ~45 nm diameter systems. In summary, this work shows that appropriately designed LNP-siRNA systems can result in effective hepatocyte gene silencing following s.c administration.

Nanoparticle ligand presentation for targeting solid tumors

Among the many scientific advances to come from the study of nanoscience, the development of ligand-targeted nanoparticles to eliminate solid tumors is predicted to have a major impact on human health. There are many reports describing novel designs and testing of targeted nanoparticles to treat cancer. While the principles of the technology are well demonstrated in controlled lab experiments, there are still many hurdles to overcome for the science to mature into truly efficacious targeted nanoparticles that join the arsenal of agents currently used to treat cancer in humans. One of these hurdles is overcoming unwanted biodistribution to the liver while maximizing delivery to the tumor. This almost certainly requires advances in both nanoparticle stealth technology and targeting. Currently, it continues to be a challenge to control the loading of ligands onto polyethylene glycol (PEG) to achieve maximal targeting. Nanoparticle cellular uptake and subcellular targeting of genes and siRNA also remain a challenge. This review examines the types of ligands that have been most often used to target nanoparticles to solid tumors. As the science matures over the coming decade, careful control over ligand presentation on nanoparticles of precise size, shape, and charge will likely play a major role in achieving success.

Anionic nanoparticles based on Span 80 as low-cost, simple and efficient non-viral gene-transfection systems

The existing strategies in the design of non-viral vectors for gene therapy are primarily conceived for cationic systems. However, the safety concerns associated with the use of positively charged systems for nucleic acid delivery and several reports regarding the efficacy of negatively charged systems highlights the need for improved gene-delivery vectors. With these premises in mind, we investigated the development of new negatively charged nanoparticles based on Sorbitan esters (Span(®)) – extremely cheap excipients broadly used in the pharmaceutical industry – on the basis of a simple, one-step and easily scalable procedure. For their specific use in gene therapy, we have incorporated oleylamine (OA) or poly-L-arginine (PA) into these nanosystems. Thus, we used Sorbitan monooleate (Span(®) 80) to design Span(®) 80-oleylamine and Span(®) 80-poly-L-arginine nanosystems (SP-OA and SP-PA, respectively). These systems can associate with the model plasmid pEGFP-C3 and show mean particle sizes of 304 nm and 247 nm and surface charges of -13 mV and -17 mV, respectively. The nanoparticles developed were evaluated in terms of in vitro cell viability and transfection ability. Both systems exhibited an appropriate cell-toxicity profile and are able to transfect the plasmid effectively. Specifically, the nanosystems including OA among their components provided higher transfection levels than the SP-PA nanoparticles. In conclusion, anionic nanoparticles based on Span(®) 80 can be considered low-cost, simple and efficient non-viral anionic gene-transfection systems.

Application of apolipoprotein E-modified liposomal nanoparticles as a carrier for delivering DNA and nucleic acid in the brain

An innovative drug delivery technology is urgently needed to satisfy unmet medical needs in treating various brain disorders. As a fundamental carrier for plasmid DNA or nucleic acids, we developed a liposomal nanoparticle (multifunctional envelope-type nano device [MEND]) containing a proton-ionizable amino lipid (YSK-MEND). Here we report on the impact of apolipoprotein E (ApoE) modification on the function of YSK-MEND in terms of targeting brain cells. The cellular uptake and function of YSK-MEND encapsulating short interference RNA or plasmid DNA were significantly improved as a result of ApoE modification in mouse neuron-derived cell lines (Neuro-2a and CAD). Intracerebroventricular administration of ApoE-modified YSK-MEND (ApoE/YSK-MEND) encapsulating plasmid DNA also resulted in higher transgene expression in comparison with YSK-MEND that was not modified with ApoE. Moreover, observation of fluorescence-labeled ApoE/YSK-MEND and expression of mCherry (fluorescence protein) derived from plasmid DNA indicated that this carrier might be useful for delivering and conferring transgene expression in neural stem cells and/or neural progenitor cells. Thus, this system may be a useful tool for the treatment of neurodegenerative disease.

Recent advances in characterization of nonviral vectors for delivery of nucleic acids: impact on their biological performance

INTRODUCTION

Nucleic acid delivery is a complex process that requires transport across numerous extracellular and intracellular barriers, whose impact is often neglected during optimization studies. As such, the development of nonviral vectors for efficient delivery would benefit from an understanding of how these barriers relate to the physicochemical properties of lipoplexes and polyplexes.

AREAS COVERED

This review focuses on the evaluation of parameters associated with barriers to delivery such as blood and immune cells compatibility which, as a collective, may serve as a useful prescreening tool for the advancement of nonviral vectors in vivo. An outline of the most relevant rationally developed polyplexes and lipoplexes for clinical application is also given.

EXPERT OPINION

The evaluation of scientifically recognized parameters enabled the identification of systemic delivered nonviral vectors' behavior while in blood as one of the key determinants of vectors function and activity both in vitro and in vivo. This multiparametric approach complements the use of in vitro efficacy results alone for prescreening and improves in vitro-in vivo translation by minimizing false negatives. Further, it can aid in the identification of meaningful structure-function-activity relationships, improve the in vitro screening process of nonviral vectors before in vivo use and facilitate the future development of potent and safe nonviral vectors.

Barriers to drug delivery in solid tumors

Over the last decade, significant progress has been made in the field of drug delivery. The advent of engineered nanoparticles has allowed us to circumvent the initial limitations to drug delivery such as pharmacokinetics and solubility. However, in spite of significant advances to tumor targeting, an effective treatment strategy for malignant tumors still remains elusive. Tumors possess distinct physiological features which allow them to resist traditional treatment approaches. This combined with the complexity of the biological system presents significant hurdles to the site-specific delivery of therapeutic drugs. One of the key features of engineered nanoparticles is that these can be tailored to execute specific functions. With this review, we hope to provide the reader with a clear understanding and knowledge of biological barriers and the methods to exploit these characteristics to design multifunctional nanocarriers, effect useful dosing regimens and subsequently improve therapeutic outcomes in the clinic.

Enhancing siRNA delivery by employing lipid nanoparticles

For several decades extensive research has been conducted into the development of fusogenic lipid nanoparticles (LNPs) capable of introducing large, charged molecules into the cytoplasm of target cells. The majority of this work has focused on cationic LNPs encapsulating nucleic acids ranging from small oligonucleotides to large plasmid constructs thousands of bases long. However, since the introduction of siRNA payloads this quest for a non-viral, intracellular delivery systems has advanced significantly. Of particular importance was the demonstration that LNPs containing ionizable, dialkylamino lipids, enable potent hepatic gene silencing across species including humans. This review focuses on the evolution of this delivery system, summarizes the promising data now emerging from clinical trials and considers future directions for the platform.

In vivo therapeutic potential of Dicer-hunting siRNAs targeting infectious hepatitis C virus

The development of RNA interference (RNAi)-based therapy faces two major obstacles: selecting small interfering RNA (siRNA) sequences with strong activity, and identifying a carrier that allows efficient delivery to target organs. Additionally, conservative region at nucleotide level must be targeted for RNAi in applying to virus because hepatitis C virus (HCV) could escape from therapeutic pressure with genome mutations. In vitro preparation of Dicer-generated siRNAs targeting a conserved, highly ordered HCV 5′ untranslated region are capable of inducing strong RNAi activity. By dissecting the 5′-end of an RNAi-mediated cleavage site in the HCV genome, we identified potent siRNA sequences, which we designate as Dicer-hunting siRNAs (dh-siRNAs). Furthermore, formulation of the dh-siRNAs in an optimized multifunctional envelope-type nano device inhibited ongoing infectious HCV replication in human hepatocytes in vivo. Our efforts using both identification of optimal siRNA sequences and delivery to human hepatocytes suggest therapeutic potential of siRNA for a virus.

Quantifying spectral changes experienced by plasmonic nanoparticles in a cellular environment to inform biomedical nanoparticle design

Metal nanoparticles (NPs) scatter and absorb light in precise, designable ways, making them agile candidates for a variety of biomedical applications. When NPs are introduced to a physiological environment and interact with cells, their physicochemical properties can change as proteins adsorb on their surface and they agglomerate within intracellular endosomal vesicles. Since the plasmonic properties of metal NPs are dependent on their geometry and local environment, these physicochemical changes may alter the NPs' plasmonic properties, on which applications such as plasmonic photothermal therapy and photonic gene circuits are based. Here we systematically study and quantify how metal NPs' optical spectra change upon introduction to a cellular environment in which NPs agglomerate within endosomal vesicles. Using darkfield hyperspectral imaging, we measure changes in the peak wavelength, broadening, and distribution of 100-nm spherical gold NPs' optical spectra following introduction to human breast adenocarcinoma Sk-Br-3 cells as a function of NP exposure dose and time. On a cellular level, spectra shift up to 78.6 ± 23.5 nm after 24 h of NP exposure. Importantly, spectra broaden with time, achieving a spectral width of 105.9 ± 11.7 nm at 95% of the spectrum's maximum intensity after 24 h. On an individual intracellular NP cluster (NPC) level, spectra also show significant shifting, broadening, and heterogeneity after 24 h. Cellular transmission electron microscopy (TEM) and electromagnetic simulations of NPCs support the trends in spectral changes we measured. These quantitative data can help guide the design of metal NPs introduced to cellular environments in plasmonic NP-mediated biomedical technologies.

Advances in Lipid Nanoparticles for siRNA Delivery

Technological advances in both siRNA (small interfering RNA) and whole genome sequencing have demonstrated great potential in translating genetic information into siRNA-based drugs to halt the synthesis of most disease-causing proteins. Despite its powerful promises as a drug, siRNA requires a sophisticated delivery vehicle because of its rapid degradation in the circulation, inefficient accumulation in target tissues and inability to cross cell membranes to access the cytoplasm where it functions. Lipid nanoparticle (LNP) containing ionizable amino lipids is the leading delivery technology for siRNA, with five products in clinical trials and more in the pipeline. Here, we focus on the technological advances behind these potent systems for siRNA-mediated gene silencing.

Lactosylated gramicidin-based lipid nanoparticles (Lac-GLN) for targeted delivery of anti-miR-155 to hepatocellular carcinoma

Lactosylated gramicidin-containing lipid nanoparticles (Lac-GLN) were developed for delivery of anti-microRNA-155 (anti-miR-155) to hepatocellular carcinoma (HCC) cells. MiR-155 is an oncomiR frequently elevated in HCC. The Lac-GLN formulation contained N-lactobionyl-dioleoyl phosphatidylethanolamine (Lac-DOPE), a ligand for the asialoglycoprotein receptor (ASGR), and an antibiotic peptide gramicidin A. The nanoparticles exhibited a mean particle diameter of 73 nm, zeta potential of +3.5mV, anti-miR encapsulation efficiency of 88%, and excellent colloidal stability at 4°C. Lac-GLN effectively delivered anti-miR-155 to HCC cells with a 16.1- and 4.1-fold up-regulation of miR-155 targets C/EBPβ and FOXP3 genes, respectively, and exhibited significant greater efficiency over Lipofectamine 2000. In mice, intravenous injection of Lac-GLN containing Cy3-anti-miR-155 led to preferential accumulation of the anti-miR-155 in hepatocytes. Intravenous administration of 1.5 mg/kg anti-miR-155 loaded Lac-GLN resulted in up-regulation of C/EBPβ and FOXP3 by 6.9- and 2.2-fold, respectively. These results suggest potential application of Lac-GLN as a liver-specific delivery vehicle for anti-miR therapy.

Small molecule ligands for enhanced intracellular delivery of lipid nanoparticle formulations of siRNA

Gene silencing activity of lipid nanoparticle (LNP) formulations of siRNA requires LNP surface factors promoting cellular uptake. This study aimed to identify small molecules that enhance cellular uptake of LNP siRNA systems, then use them as LNP-associated ligands to improve gene silencing potency. Screening the Canadian Chemical Biology Network molecules for effects on LNP uptake into HeLa cells found that cardiac glycosides like ouabain and strophanthidin caused the highest uptake. Cardiac glycosides stimulate endocytosis on binding to plasma membrane Na(+)/K(+) ATPase found in all mammalian cells, offering the potential to stimulate LNP uptake into various cell types. A PEG-lipid containing strophanthidin at the end of PEG (STR-PEG-lipid) was synthesized and incorporated into LNP. Compared to non-liganded systems, STR-PEG-lipid enhanced LNP uptake in various cell types. Furthermore, this enhanced uptake improved marker gene silencing in vitro. Addition of STR-PEG-lipid to LNP siRNA may have general utility for enhancing gene silencing potency.

FROM THE CLINICAL EDITOR

In this study, the authors identified small molecules that enhance cellular uptake of lipid nanoparticle siRNA systems, then used them as LNP-associated ligands to improve gene silencing potency.

Treating metastatic cancer with nanotechnology

Metastasis accounts for the vast majority of cancer deaths. The unique challenges for treating metastases include their small size, high multiplicity and dispersion to diverse organ environments. Nanoparticles have many potential benefits for diagnosing and treating metastatic cancer, including the ability to transport complex molecular cargoes to the major sites of metastasis, such as the lungs, liver and lymph nodes, as well as targeting to specific cell populations within these organs. This Review highlights the research, opportunities and challenges for integrating engineering sciences with cancer biology and medicine to develop nanotechnology-based tools for treating metastatic disease.

An in vitro assay based on surface plasmon resonance to predict the in vivo circulation kinetics of liposomes

The adsorption of blood proteins onto liposomes and other colloidal particles is an important process influencing the circulation time. Proteins adsorbed to the surface of liposomes can mediate recognition of the liposomes by macrophages of the reticuloendothelial system (RES) facilitating their clearance from the circulation. Coating liposomes with poly(ethylene glycol) (PEG) decreases the blood clearance considerably, most likely due to reduced protein adsorption and/or liposome aggregation. By using the relation between clearance and protein binding, the present study introduces an in vitro assay measuring interactions of liposomes with proteins to predict their blood clearance in vivo. Such assay is valuable since it limits time and costs, and importantly reduces the number of animals required for pharmacokinetic investigations of new formulations. In the current study, Surface Plasmon Resonance (SPR) and fluorescence Single Particle Tracking (fSPT) were used to study liposome-protein interactions and blood induced liposome aggregation in vitro. By means of SPR the interactions between proteins and liposomes coated with PEG of different molecular weights and at different densities (PEG(2000) in 2.5%, 5% and 7%; PEG(5000) in 0.5%, 1.5% and 2.5%), were measured for several plasma proteins: human serum albumin (HSA), apolipoprotein E (ApoE), α2-macroglobulin (α2-M), β2-glycoprotein (β2-G) and fibronectin (Fn). Liposomes coated with PEG interacted less with all proteins, an effect which increased with the PEG surface density. In parallel, fSPT analysis showed that the exposure of liposomes to full blood did not change the liposome size, indicating that aggregation is not a strong attributive factor in the clearance of these liposomes. In addition, the SPR measurements of the interactions between liposomes and proteins were correlated with the blood clearance of the liposomes. For each protein, the degree of protein-liposome interaction as determined by SPR showed a moderate to strong positive correlation with the clearance of the liposome type.

Interactions of nanoparticles with plasma proteins: implication on clearance and toxicity of drug delivery systems

INTRODUCTION

Intravenously injected nanoparticles, like any other foreign pathogen that enters the body, encounter multiple lines of defense intended to neutralize and eliminate the invading substance. Adsorption of plasma proteins on the nanoparticle surface is the first barrier of defense, which could lead to physical changes in the formulation, such as aggregation and charge neutralization, biochemical activation of defense cascades, and trigger elimination by multiple types of phagocytic cell.

AREAS COVERED

In this review, recent knowledge on the mechanisms that govern the interactions of nanoparticles (micelles, liposomes, polymeric and inorganic nanoparticles) with plasma proteins is discussed. In particular, the role of the nanoparticle surface properties and protective polymer coating in these interactions is described. The mechanisms of protein adsorption on different nanoparticles are analyzed and the implications on the clearance, toxicity and efficacy of drug delivery are discussed. The review provides readers with the biological insight into the plasma/blood interactions of nanoparticles.

EXPERT OPINION

The immune recognition of nanoparticles can seriously affect the drug delivery efficacy and toxicity. There is at present not enough knowledge on the mechanisms that dictate the nanoparticle immune recognition and stability in the biological milieu. Understanding the mechanisms of recognition will become an important part of nanoparticle design.

Targeted delivery of RNAi therapeutics with endogenous and exogenous ligand-based mechanisms

Lipid nanoparticles (LNPs) have proven to be highly efficient carriers of short-interfering RNAs (siRNAs) to hepatocytes in vivo; however, the precise mechanism by which this efficient delivery occurs has yet to be elucidated. We found that apolipoprotein E (apoE), which plays a major role in the clearance and hepatocellular uptake of physiological lipoproteins, also acts as an endogenous targeting ligand for ionizable LNPs (iLNPs), but not cationic LNPs (cLNPs). The role of apoE was investigated using both in vitro studies employing recombinant apoE and in vivo studies in wild-type and apoE(-/-) mice. Receptor dependence was explored in vitro and in vivo using low-density lipoprotein receptor (LDLR(-/-))-deficient mice. As an alternative to endogenous apoE-based targeting, we developed a targeting approach using an exogenous ligand containing a multivalent N-acetylgalactosamine (GalNAc)-cluster, which binds with high affinity to the asialoglycoprotein receptor (ASGPR) expressed on hepatocytes. Both apoE-based endogenous and GalNAc-based exogenous targeting appear to be highly effective strategies for the delivery of iLNPs to liver.

Differential proteomics analysis of the surface heterogeneity of dextran iron oxide nanoparticles and the implications for their in vivo clearance

In order to understand the role of plasma proteins in the rapid liver clearance of dextran-coated superparamagnetic iron oxide (SPIO) in vivo, we analyzed the full repertoire of SPIO-binding blood proteins using novel two-dimensional differential mass spectrometry approach. The identified proteins showed specificity for surface domains of the nanoparticles: mannan-binding lectins bound to the dextran coating, histidine-rich glycoprotein and kininogen bound to the iron oxide part, and the complement lectin and contact clotting factors were secondary binders. Nanoparticle clearance studies in knockout mice suggested that these proteins, as well as several previously identified opsonins, do not play a significant role in the SPIO clearance. However, both the dextran coat and the iron oxide core remained accessible to specific probes after incubation of SPIO in plasma, suggesting that the nanoparticle surface could be available for recognition by macrophages, regardless of protein coating. These data provide guidance to rational design of bioinert, long-circulating nanoparticles.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Time-dependent changes in opsonin amount associated on nanoparticles alter their hepatic uptake characteristics

The relationship between the time-dependent change in serum proteins adsorbed on nanoparticles and their disposition to the liver was investigated by employing lecithin-coated polystyrene nanosphere with a size of 50 nm (LNS-50) as a model nanoparticle in rats. The total amount of proteins adsorbed on LNS-50 increased and the qualitative profile of serum proteins adsorbed on LNS-50 changed during the incubation with serum up to 360 min. The liver perfusion study indicated that the hepatic uptake of LNS-50 incubated with serum for 360 min was significantly larger than those of LNS-50 incubated for shorter period. It was suggested that the increase in the hepatic uptake of LNS-50 with the increase in incubation time would be ascribed mainly to the increase in the opsonin-mediated uptake by Kupffer cells. Semi-quantification of major opsonins, complement C3 (C3) and immunoglobulin G (IgG), and in vitro uptake study in primary cultured Kupffer cells demonstrated that the increase in C3 and IgG amounts adsorbed on LNS-50 was directly reflected in the increased disposition of LNS-50 to Kupffer cells. These results indicate that the amounts of opsonins associated on nanoparticles would change over time and this process would be substantially reflected in the alteration of their hepatic disposition characteristics.