Strategies in the design of nanoparticles for therapeutic applications

Factors controlling nanoparticle pharmacokinetics: an integrated analysis and perspective

Intravenously injected nanoparticulate drug carriers provide a wide range of unique opportunities for site-specific targeting of therapeutic agents to many areas within the vasculature and beyond. Pharmacokinetics and biodistribution of these carriers are controlled by a complex array of interrelated core and interfacial physicochemical and biological factors. Pertinent to realizing therapeutic goals, definitive maps that establish the interdependency of nanoparticle size, shape, and surface characteristics in relation to interfacial forces, biodistribution, controlled drug release, excretion, and adverse effects must be outlined. These concepts are critically evaluated and an integrated perspective is provided on the basis of the recent application of nanoscience approaches to nanocarrier design and engineering. The future of this exciting field is bright; some regulatory-approved products are already on the market and many are in late-phase clinical trials. With concomitant advances in extensive computational knowledge of the genomics and epigenomics of interindividual variations in drug responses, the boundaries toward development of personalized nanomedicines can be pushed further.

Perspectives and opportunities for nanomedicine in the management of atherosclerosis

The use of nanotechnology for medical purposes--nanomedicine--has grown exponentially over the past few decades. This is exemplified by the US Food and Drug Administration's approval of several nanotherapies for various conditions, as well as the funding of nanomedical programmes worldwide. Although originally the domain of anticancer therapy, recent advances have illustrated the considerable potential of nanomedicine in the diagnosis and treatment of atherosclerosis. This Review elaborates on nanoparticle-targeting concepts in atherosclerotic disease, provides an overview of the use of nanomedicine in atherosclerosis, and discusses potential future applications and clinical benefits.

In vivo targeted delivery of nanoparticles for theranosis

Therapy and diagnosis are two major categories in the clinical treatment of disease. Recently, the word "theranosis" has been created, combining the words to describe the implementation of these two distinct pursuits simultaneously. For successful theranosis, the efficient delivery of imaging agents and drugs is critical to provide sufficient imaging signal or drug concentration in the targeted disease site. To achieve this purpose, biomedical researchers have developed various nanoparticles composed of organic or inorganic materials. However, the targeted delivery of these nanoparticles in animal models and patients remains a difficult hurdle for many researchers, even if they show useful properties in cell culture condition. In this Account, we review our strategies for developing theranostic nanoparticles to accomplish in vivo targeted delivery of imaging agents and drugs. By applying these rational strategies, we achieved fine multimodal imaging and successful therapy. Our first strategy involves physicochemical optimization of nanoparticles for long circulation and an enhanced permeation and retention (EPR) effect. We accomplished this result by testing various materials in mouse models and optimizing the physical properties of the materials with imaging techniques. Through these experiments, we developed a glycol chitosan nanoparticle (CNP), which is suitable for angiogenic diseases, such as cancers, even without an additional targeting moiety. The in vivo mechanism of this particle was examined through rationally designed experiments. In addition, we evaluated and compared the biodistribution and target-site accumulation of bare and drug-loaded nanoparticles. We then focus on the targeting moieties that bind to cell surface receptors. Small peptides were selected as targeting moieties because of their stability, low cost, size, and activity per unit mass. Through phage display screening, the interleukin-4 receptor binding peptide was discovered, and we combined it with our nanoparticles. This product accumulated efficiently in atherosclerotic regions or tumors during both imaging and therapy. We also developed hyaluronic acid nanoparticles that can bind efficiently to the CD44 antigen receptors abundant in many tumor cells. Their delivery mechanism is based on both physicochemical optimization for the EPR effect and receptor-mediated endocytosis by their hyaluronic acid backbone. Finally, we introduce the stimuli-responsive system related to the chemical and biological changes in the target disease site. Considering the relatively low pH in tumors and ischemic sites, we applied pH-sensitive micelle to optical imaging, magnetic resonance imaging, anticancer drug delivery, and photodynamic therapy. In addition, we successfully evaluated the in vivo imaging of enzyme activity at the target site with an enzyme-specific peptide sequence and CNPs. On the basis of these strategies, we were able to develop self-assembled nanoparticles for in vivo targeted delivery, and successful results were obtained with them in animal models for both imaging and therapy. We anticipate that these rational strategies, as well as our nanoparticles, will be applied in both the diagnosis and therapy of many human diseases. These theranostic nanoparticles are expected to greatly contribute to optimized therapy for individual patients as personalized medicine, in the near future.

Self-assembled targeted nanoparticles: evolution of technologies and bench to bedside translation

Nanoparticles (NPs) have become an important tool in many industries including healthcare. The use of NPs for drug delivery and imaging has introduced exciting opportunities for the improvement of disease diagnosis and treatment. Over the past two decades, several first-generation therapeutic NP products have entered the market. Despite the lack of controlled release and molecular targeting properties in these products, they improved the therapeutic benefit of clinically validated drugs by enhancing drug tolerability and/or efficacy. NP-based imaging agents have also improved the sensitivity and specificity of different diagnostic modalities. The introduction of controlled-release properties and targeting ligands toward the development of next-generation NPs should enable the development of safer and more effective therapeutic NPs and facilitate their application in theranostic nanomedicine. Targeted and controlled-release NPs can drastically alter the pharmacological characteristics of their payload, including their pharmacokinetic and, in some cases, their pharmacodynamic properties. As a result, these NPs can improve drug properties beyond what can be achieved through classic medicinal chemistry. Despite their enormous potential, the translation of targeted NPs into clinical development has faced considerable challenges. One significant problem has been the difficulty in developing targeted NPs with optimal biophysicochemical properties while using robust processes that facilitate scale-up and manufacturing. Recently, efforts have focused on developing NPs through self-assembly or high-throughput processes to facilitate the development and screening of NPs with these distinct properties and the subsequent scale-up of their manufacture. We have also undertaken parallel efforts to integrate additional functionality within therapeutic and imaging NPs, including the ability to carry more than one payload, to respond to environmental triggers, and to provide real-time feedback. In addition, novel targeting approaches are being developed to enhance the tissue-, cell-, or subcellular-specific delivery of NPs for a myriad of important diseases. These include the selection of internalizing ligands for enhanced receptor-mediated NP uptake and the development of extracellular targeting ligands for vascular tissue accumulation of NPs. In this Account, we primarily review the evolution of marketed NP technologies. We also recount our efforts in the design and optimization of NPs for medical applications, which formed the foundation for the clinical translation of the first-in-man targeted and controlled-release NPs (BIND-014) for cancer therapy.

Glucan particles for macrophage targeted delivery of nanoparticles

Glucan particles (GPs) are hollow, porous 2–4 μm microspheres derived from the cell walls of Baker's yeast (Saccharomyces cerevisiae). The 1,3-β-glucan outer shell provides for receptor-mediated uptake by phagocytic cells expressing β-glucan receptors. GPs have been used for macrophage-targeted delivery of soluble payloads (DNA, siRNA, protein, and small molecules) encapsulated inside the hollow GPs via core polyplex and layer-by-layer (LbL) synthetic strategies. In this communication, we report the incorporation of nanoparticles as cores inside GPs (GP-NP) or electrostatically bound to the surface of chemically derivatized GPs (NP-GP). GP nanoparticle formulations benefit from the drug encapsulation properties of NPs and the macrophage-targeting properties of GPs. GP nanoparticle formulations were synthesized using fluorescent anionic polystyrene nanoparticles allowing visualization and quantitation of NP binding and encapsulation. Mesoporous silica nanoparticles (MSNs) containing the chemotherapeutic doxorubicin (Dox) were bound to cationic GPs. Dox-MSN-GPs efficiently delivered Dox into GP phagocytic cells resulting in enhanced Dox-mediated growth arrest.

Bone targeting for the treatment of osteoporosis

Osteoporosis represents a major public health burden especially considering the aging populations worldwide. Drug targeting will be important to better meet these challenges and direct the full therapeutic potential of therapeutics to their intended site of action. This review has been organized in modules, such that scientists working in the field can easily gain specific insight in the field of bone targeting for the drug class they are interested in. We review currently approved and emerging treatment options for osteoporosis and discuss these in light of the benefit these would gain from advanced targeting. In addition, established targeting strategies are reviewed and novel opportunities as well as promising areas are presented along with pharmaceutical strategies how to render novel composites consisting of a drug and a targeting moiety responsive to bone-specific or disease-specific environmental stimuli. Successful implementation of these principles into drug development programs for osteoporosis will substantially contribute to the clinical success of anti-catabolic and anabolic drugs of the future.

The journey of a drug-carrier in the body: an anatomo-physiological perspective

Recent advances in chemistry and material sciences have witnessed the emergence of an increasing number of novel and complex nanosized carriers for the delivery of drugs and imaging agents. Nevertheless, this raise in complexity does not necessarily offer more efficient systems. The lack of performance experienced by several colloidal drug carriers during the preclinical and clinical development processes can be explained by inadequate pharmacokinetic/biodistribution profiles and/or unacceptable toxicities. A comprehensive understanding of the body characteristics is necessary to predict and prevent these problems from the early stages of nanomaterial conception. In this manuscript, we review and discuss the anatomical and physiological elements which must be taken into account when designing new carriers for delivery or imaging purposes. This article gives a general overview of the main organs involved in the elimination of nanosized materials and briefly summarizes the knowledge acquired over more than 30 years of research and development in the field of drug targeting.

Silica nanorattle-doxorubicin-anchored mesenchymal stem cells for tumor-tropic therapy

Low targeting efficiency is one of the biggest limitations for nanoparticulate drug delivery system-based cancer therapy. In this study, an efficient approach for tumor-targeted drug delivery was developed with mesenchymal stem cells as the targeting vehicle and a silica nanorattle as the drug carrier. A silica nanorattle-doxorubicin drug delivery system was efficiently anchored to mesenchymal stem cells (MSCs) by specific antibody-antigen recognitions at the cytomembrane interface without any cell preconditioning. Up to 1500 nanoparticles were uploaded to each MSC cell with high cell viability and tumor-tropic ability. The intracellular retention time of the silica nanorattle was no less than 48 h, which is sufficient for cell-directed tumor-tropic delivery. In vivo experiments proved that the burdened MSCs can track down the U251 glioma tumor cells more efficiently and deliver doxorubicin with wider distribution and longer retention lifetime in tumor tissues compared with free DOX and silica nanorattle-encapsulated DOX. The increased and prolonged DOX intratumoral distribution further contributed to significantly enhanced tumor-cell apoptosis. This strategy has potential to be developed as a robust and generalizable method for targeted tumor therapy with high efficiency and low systematic toxicity.

Improved tumor targeting of polymer-based nanovesicles using polymer-lipid blends

Block copolymer-based vesicles have recently garnered a great deal of interest as nanoplatforms for drug delivery and molecular imaging applications due to their unique structural properties. These nanovesicles have been shown to direct their cargo to disease sites either through enhanced permeability and retention or even more efficiently via active targeting. Here, we show that the efficacy of nanovesicle targeting can be significantly improved when prepared from polymer-lipid blends compared with block copolymer alone. Polymer-lipid hybrid nanovesicles were produced from the aqueous coassembly of the diblock copolymer, poly(ethylene oxide)-block-polybutadiene (PEO-PBD), and the phospholipid, hydrogenated soy phosphatidylcholine (HSPC). The PEG-based vesicles, 117 nm in diameter, were functionalized with either folic acid or anti-HER2/neu affibodies as targeting ligands to confer specificity for cancer cells. Our results revealed that nanovesicles prepared from polymer-lipid blends led to significant improvement in cell binding compared to nanovesicles prepared from block copolymer alone in both in vitro cell studies and murine tumor models. Therefore, it is envisioned that nanovesicles composed of polymer-lipid blends may constitute a preferred embodiment for targeted drug delivery and molecular imaging applications.

Modulating pharmacokinetics, tumor uptake and biodistribution by engineered nanoparticles

Background

Inorganic nanoparticles provide promising tools for biomedical applications including detection, diagnosis and therapy. While surface properties such as charge are expected to play an important role in their in vivo behavior, very little is known how the surface chemistry of nanoparticles influences their pharmacokinetics, tumor uptake, and biodistribution.

Method/Principal Findings

Using a family of structurally homologous nanoparticles we have investigated how pharmacological properties including tumor uptake and biodistribution are influenced by surface charge using neutral (TEGOH), zwitterionic (Tzwit), negative (TCOOH) and positive (TTMA) nanoparticles. Nanoparticles were injected into mice (normal and athymic) either in the tail vein or into the peritoneum.

Conclusion

Neutral and zwitterionic nanoparticles demonstrated longer circulation time via both IP and IV administration, whereas negatively and positively charged nanoparticles possessed relatively short half-lives. These pharmacological characteristics were reflected on the tumor uptake and biodistribution of the respective nanoparticles, with enhanced tumor uptake by neutral and zwitterionic nanoparticles via passive targeting.

Redox-responsive nanoparticles from the single disulfide bond-bridged block copolymer as drug carriers for overcoming multidrug resistance in cancer cells

Multidrug resistance (MDR) is a major impediment to the success of cancer chemotherapy. The intracellular accumulation of drug and the intracellular release of drug molecules from the carrier could be the most important barriers for nanoscale carriers in overcoming MDR. We demonstrated that the redox-responsive micellar nanodrug carrier assembled from the single disulfide bond-bridged block polymer of poly(ε-caprolactone) and poly(ethyl ethylene phosphate) (PCL-SS-PEEP) achieved more drug accumulation and retention in MDR cancer cells. Such drug carrier rapidly released the incorporated doxorubicin (DOX) in response to the intracellular reductive environment. It therefore significantly enhanced the cytotoxicity of DOX to MDR cancer cells. It was demonstrated that nanoparticular drug carrier with either poly(ethylene glycol) or poly(ethyl ethylene phosphate) (PEEP) shell increased the influx but decreased the efflux of DOX by the multidrug resistant MCF-7/ADR breast cancer cells, in comparison with the direct incubation of MCF-7/ADR cells with DOX, which led to high cellular retention of DOX. Nevertheless, nanoparticles bearing PEEP shell exhibited higher affinity to the cancer cells. The shell detachment of the PCL-SS-PEEP nanoparticles caused by the reduction of intracellular glutathione significantly accelerated the drug release in MCF-7/ADR cells, demonstrated by the flow cytometric analyses, which was beneficial to the entry of DOX into the nuclei of MCF-7/ADR cells. It therefore enhanced the efficiency in overcoming MDR of cancer cells, which renders the redox-responsive nanoparticles promising in cancer therapy.

The effect of hydrophilic chain length and iRGD on drug delivery from poly(ε-caprolactone)-poly(N-vinylpyrrolidone) nanoparticles

Poly(ε-caprolactone)-b-Poly(N-vinylpyrrolidone) (PCL-b-PVP) copolymers with different PVP block length were synthesized by xanthate-mediated reverse addition fragment transfer polymerization (RAFT) and the xanthate chain transfer agent on chain end was readily translated to hydroxy or aldehyde for conjugating various functional moieties, such as fluorescent dye, biotin hydrazine and tumor homing peptide iRGD. Thus, PCL-PVP nanoparticles were prepared by these functionalized PCL-b-PVP copolymers. Furthermore, paclitaxel-loaded PCL-PVP nanoparticles with satisfactory drug loading content (15%) and encapsulation efficiency (>90%) were obtained and used in vitro and in vivo antitumor examination. It was demonstrated that the length of PVP block had a significant influence on cytotoxicity, anti-BSA adsorption, circulation time, stealth behavior, biodistribution and antitumor activity for the nanoparticles. iRGD on PCL-PVP nanoparticle surface facilitated the nanoparticles to accumulate in tumor site and enhanced their penetration in tumor tissues, both of which improved the efficacy of paclitaxel-loaded nanoparticles in impeding tumor growth and prolonging the life time of H22 tumor-bearing mice.

Nanoparticle preconditioning for enhanced thermal therapies in cancer

Nanoparticles show tremendous promise in the safe and effective delivery of molecular adjuvants to enhance local cancer therapy. One important form of local cancer treatment that suffers from local recurrence and distant metastases is thermal therapy. In this article, we review a new concept involving the use of nanoparticle-delivered adjuvants to 'precondition' or alter the vascular and immunological biology of the tumor to enhance its susceptibility to thermal therapy. To this end, a number of opportunities to combine nanoparticles with vascular and immunologically active agents are reviewed. One specific example of preconditioning involves a gold nanoparticle tagged with a vascular targeting agent (i.e., TNF-α). This nanoparticle embodiment demonstrates preconditioning through a dramatic reduction in tumor blood flow and induction of vascular damage, which recruits a strong and sustained inflammatory infiltrate in the tumor. The ability of this nanoparticle preconditioning to enhance subsequent heat or cold thermal therapy in a variety of tumor models is reviewed. Finally, the potential for future clinical imaging to judge the extent of preconditioning and thus the optimal timing and extent of combinatorial thermal therapy is discussed.

Nanocarriers for nitric oxide delivery

Nitric oxide (NO) is a promising pharmaceutical agent that has vasodilative, antibacterial, and tumoricidal effects. To study the complex and wide-ranging roles of NO and to facilitate its therapeutic use, a great number of synthetic compounds (e.g., nitrosothiols, nitrosohydroxyamines, N-diazeniumdiolates, and nitrosyl metal complexes) have been developed to chemically stabilize and release NO in a controlled manner. Although NO is currently being exploited in many biomedical applications, its use is limited by several factors, including a short half-life, instability during storage, and potential toxicity. Additionally, efficient methods of both localized and systemic in vivo delivery and dose control are needed. One strategy for addressing these limitations and thus increasing the utility of NO donors is based on nanotechnology.

Kinetic targeting of pegylated liposomal doxorubicin: a new approach to reduce toxicity during chemotherapy (CARL-trial)

BACKGROUND

The therapeutic success of chemotherapeutic agents is often limited by severe adverse effects. To reduce toxicity of these drugs, nanoscale particle-based drug delivery systems (DDS) are used. DDS accumulate to some extent in tumor tissues, but only a very small portion of a given dose reaches this target. Accumulation of DDS in tumor tissues is supposed to be much faster than in certain other tissues in which side effects occur ("Kinetic Targeting"). Once saturation in tumor tissue is achieved, most of the administered DDS still circulate in the plasma. The extracorporeal elimination of these circulating nanoparticles would probably reduce toxicity.

METHODS

For the CARL-trial (Controlled Application and Removal of Liposomal chemotherapeutics), pegylated liposomal doxorubicin (PLD) was used as chemotherapeutic agent and double filtration plasmapheresis (DFPP) was performed for extracorporeal elimination of liposomes. PLD was given as 40 mg/m2 every 3 weeks in combination with vinorelbine 2 × 25 mg/m2 (neoadjuvant treatment of breast cancer, 12 patients), or as 40 mg/m2 every 4 weeks (recurrent ovarian cancer, 3 patients). Primary endpoints were the efficiency and safety profile of DFPP, and secondary endpoints were side effects and tumor response.

RESULTS

DFPP eliminated ~62% of circulating PLD, corresponding to ~45% of the total dose (n = 57 cycles). AUC of doxorubicin was reduced by 50%. No leakage of doxorubicin was detected during elimination, and no relevant DFPP-related side effects occurred. Reduction in tumor size > 30% occurred in 10/12 (neoadjuvant) and in 1/3 patients (recurrent). Only five grade 2 events and one grade 3 event (mucositis, neutropenia or leucopenia) and a single palmar-plantar erythrodysesthesia grade 2 were reported.

CONCLUSION

Extracorporeal elimination of PLD by DFPP is safe and efficient. CARL can diminish the main dose-limiting side effects of PLD, and probably many different DDS alike.

TRIAL REGISTRATION

DRKS00000163.

Quantum dots and carbon nanotubes in oncology: a review on emerging theranostic applications in nanomedicine

Cancer is one of the main causes of death in the world, and according to the WHO it is projected to continue rising. Current diagnostic modalities for the detection of cancer include the use of x-rays, magnetic resonance imaging and positron emission tomography, among others. The treatment of cancer often involves the use (or combination) of chemotherapeutic drugs, radiotherapy and interventional surgery (for solid and operable tumors). The application of nanotechnology in biology and medicine is advancing rapidly. Recent evidence suggests that quantum dots (QDs) can be used to image cancer cells as they display superior fluorescent properties compared with conventional chromophores and contrast agents. In addition, carbon nanotubes (CNTs) have emerged as viable candidates for novel chemotherapeutic drug delivery-platforms. The unique photothermal properties of CNTs also allow them to be used in conjunction with near infrared radiation and lasers to thermally ablate cancer cells. Furthermore, mounting evidence indicates that it is possible to conjugate QDs to CNTs, making it possible to exploit their novel attributes in the realm of cancer theranostics (diagnostics and therapy). Here we review the current literature pertaining to the applications of QDs and CNTs in oncology, and also discuss the relevance and implications of nanomedicine in a clinical setting.

Suitable carriers for encapsulation and distribution of endostar: comparison of endostar-loaded particulate carriers

Background

Particulate carriers are necessary to control the release of endostar and prolong its circulation in vivo. The purpose of this study was to identify a suitable carrier for the capsulation and delivery of endostar.

Methods

We prepared a series of poly (DL-lactide-co-glycolide) (PLGA) and poly (ethylene glycol) (PEG)-modified PLGA (PEG-PLGA) particulate carriers, and then characterized them according to their ability to prolong the circulation of endostar, their physicochemical properties, endostar-loading content, and in vitro and in vivo particulate carrier release profiles.

Results

All the particulate carriers had spherical core shell structures. The PEG-PLGA material and nanosize range appeared to enable the carriers to encapsulate more endostar, release endostar faster in vitro, and accumulate more endostar in vivo. The drug loading capacity of PEG-PLGA and PLGA nanoparticles was 8.03% ± 3.41% and 3.27% ± 5.26%, respectively, and for PEG-PLGA and PLGA microspheres was 15.32% ± 5.61% and 9.21% ± 4.73%. The cumulative amount of endostar released from the carriers in phosphate-buffered saline over 21 days was 23.79%, 20.45%, 15.13%, and 10.41%, respectively. Moreover, the terminal elimination half-life of endostar in the rabbit was 26.91 ± 7.93 hours and 9.32 ± 5.53 hours in the PEG-PLGA group and the PLGA nanoparticle group. Peak endostar concentration was reached at day 7 in the group treated with subcutaneous injection of PEG-PLGA microspheres and at day 14 in the group receiving subcutaneous injection of PLGA microspheres. Endostar was detectable in vivo in both groups after injection of the particulate carriers.

Conclusion

PEG-PLGA nanoparticles might be better than other nanoparticulate carriers for encapsulation and distribution of endostar.

Beauty is skin deep: a surface monolayer perspective on nanoparticle interactions with cells and bio-macromolecules

Surface recognition of biosystems is a critical component in the development of novel biosensors and delivery vehicles, and for the therapeutic regulation of biological processes. Monolayer-protected nanoparticles present a highly versatile scaffold for selective interaction with bio-macromolecules and cells. Through the engineering of the monolayer surface, nanoparticles can be tailored for surface recognition of biomolecules and cells. This review highlights recent progress in nanoparticle-bio-macromolecule/cellular interactions, emphasizing the effect of the surface monolayer structure on the interactions with proteins, DNA, and cell surfaces. The extension of these tailored interactions to hybrid nanomaterials, biosensing platforms, and delivery vehicles is also discussed.

Polymer nanoneedle-mediated intracellular drug delivery

Delivery of drugs into the cellular cytoplasm of target cells represents a major hurdle in treating various diseases. This challenge can be addressed by encapsulation of drugs onto or within nanoparticles, which can then be targeted to diseased cells. Here, needle-shaped particles are shown to exhibit substantially higher cytoplasmic delivery of drugs such as siRNA compared to their spherical counterparts. Furthermore, these needles are designed to lose their sharp tips over time and can render themselves ineffective over time, thereby offering control over their duration of activity and toxicity. Such polymer nanoneedles open new avenues for delivering drug molecules directly into the cytoplasm with low toxicity.

More effective nanomedicines through particle design

Nanomedicine is an emerging field that applies concepts in nanotechnology to develop novel diagnostics and therapies. Physical and chemical properties of particles, including size, shape, modulus, surface charge and surface chemistry, play an important role in determining particle-cell interactions, cellular trafficking mechanisms, biodistribution, and pharmacokinetics. This discussion focuses on both nanoparticles and microparticles since microparticles can also provide many insights for the development of drug carriers and possess advantages over nanoparticles in certain applications. This review covers recent major advancement in the nanomedicine field and also highlights studies using the PRINT technology.

Delivery of nanoparticle: complexed drugs across the vascular endothelial barrier via caveolae

The endothelial cell monolayer lining the vessel wall forms a size-selective, semi-permeable barrier between the blood and tissue that must be crossed by blood borne therapeutic agents to reach diseased extravascular tissue. Nanoparticles engineered to carry drugs present an opportunity to enhance the specificity and efficacy of drug delivery. Therefore, an understanding of how these engineered nanoparticles are transported across the vessel wall will help us to more fully exploit this powerful therapeutic technology. Vascular endothelial cells are rich in caveolae, cell surface invaginations 50-100 nm in diameter that mediate endocytosis of lipids, proteins, and viruses. Caveolar invaginations pinch off to form intracellular vesicles that can transport cargo across the cell and release the cargo into the extravascular space via exocytosis. Here, we will review the current concepts and state of development for delivering engineered nanoparticles across the endothelium via the caveolae-mediated pathway.

Beyond platinum: synthesis, characterization, and in vitro toxicity of Cu(II)-releasing polymer nanoparticles for potential use as a drug delivery vector

The field of drug delivery focuses primarily on delivering small organic molecules or DNA/RNA as therapeutics and has largely ignored the potential for delivering catalytically active transition metal ions and complexes. The delivery of a variety of transition metals has potential for inducing apoptosis in targeted cells. The chief aims of this work were the development of a suitable delivery vector for a prototypical transition metal, Cu2+, and demonstration of the ability to impact cancer cell viability via exposure to such a Cu-loaded vector. Carboxylate-functionalized nanoparticles were synthesized by free radical polymerization and were subsequently loaded with Cu2+ via binding to particle-bound carboxylate functional groups. Cu loading and release were characterized via ICP MS, EDX, XPS, and elemental analysis. Results demonstrated that Cu could be loaded in high weight percent (up to 16 wt.%) and that Cu was released from the particles in a pH-dependent manner. Metal release was a function of both pH and the presence of competing ligands. The toxicity of the particles was measured in HeLa cells where reductions in cell viability greater than 95% were observed at high Cu loading. The combined pH sensitivity and significant toxicity make this copper delivery vector an excellent candidate for the targeted killing of disease cells when combined with an effective cellular targeting strategy.

Autoimmune therapies targeting costimulation and emerging trends in multivalent therapeutics

Proteins participating in immunological signaling have emerged as important targets for controlling the immune response. A multitude of receptor-ligand pairs that regulate signaling pathways of the immune response have been identified. In the complex milieu of immune signaling, therapeutic agents targeting mediators of cellular signaling often either activate an inflammatory immune response or induce tolerance. This review is primarily focused on therapeutics that inhibit the inflammatory immune response by targeting membrane-bound proteins regulating costimulation or mediating immune-cell adhesion. Many of these signals participate in larger, organized structures such as the immunological synapse. Receptor clustering and arrangement into organized structures is also reviewed and emerging trends implicating a potential role for multivalent therapeutics is posited.

Multifunctional surface modification of gold-stabilized nanoparticles by bioorthogonal reactions

Nanocarriers that combine multiple properties in an all-in-one system hold great promise for drug delivery. The absence of technology to assemble highly functionalized devices has, however, hindered progress in nanomedicine. To address this deficiency, we have chemically synthesized poly(ethylene oxide)-β-poly(ε-caprolactone) (PEO-b-PCL) block polymers modified at the apolar PCL terminus with thioctic acid and at the polar PEO terminus with an acylhydrazide, amine, or azide moiety. The resulting block polymers were employed to prepare nanoparticles that have a gold core, an apolar polyester layer for drug loading, a polar PEO corona to provide biocompatibility, and three different types of surface reactive groups for surface functionalization. The acylhydrazide, amine, or azide moieties of the resulting nanoparticles could be reacted with high efficiencies with modules having a ketone, isocyanate, or active ester and alkyne function, respectively. To demonstrate proof of principle of the potential of multisurface functionalization, we prepared nanoparticles that have various combinations of an oligo-arginine peptide to facilitate cellular uptake, a histidine-rich peptide to escape from lysosomes, and an Alexa Fluor 488 tag for imaging purposes. It has been shown that uptake and subcellular localization of the nanoparticles can be controlled by multisurface modification. It is to be expected that the modular synthetic methodology provides unique opportunities to establish optimal configurations of nanocarriers for disease-specific drug delivery.

Single-step production of a recyclable nanobiocatalyst for organophosphate pesticides biodegradation using functionalized bacterial magnetosomes

Enzymes are versatile catalysts in laboratories and on an industrial scale; improving their immobilization would be beneficial to broadening their applicability and ensuring their (re)use. Lipid-coated nano-magnets produced by magnetotactic bacteria are suitable for a universally applicable single-step method of enzyme immobilization. By genetically functionalizing the membrane surrounding these magnetite particles with a phosphohydrolase, we engineered an easy-to-purify, robust and recyclable biocatalyst to degrade ethyl-paraoxon, a commonly used pesticide. For this, we genetically fused the opd gene from Flavobacterium sp. ATCC 27551 encoding a paraoxonase to mamC, an abundant protein of the magnetosome membrane in Magnetospirillum magneticum AMB-1. The MamC protein acts as an anchor for the paraoxonase to the magnetosome surface, thus producing magnetic nanoparticles displaying phosphohydrolase activity. Magnetosomes functionalized with Opd were easily recovered from genetically modified AMB-1 cells: after cellular disruption with a French press, the magnetic nanoparticles are purified using a commercially available magnetic separation system. The catalytic properties of the immobilized Opd were measured on ethyl-paraoxon hydrolysis: they are comparable with the purified enzyme, with K(m) (and k(cat)) values of 58 µM (and 178 s(-1)) and 43 µM (and 314 s(-1)) for the immobilized and purified enzyme respectively. The Opd, a metalloenzyme requiring a zinc cofactor, is thus properly matured in AMB-1. The recycling of the functionalized magnetosomes was investigated and their catalytic activity proved to be stable over repeated use for pesticide degradation. In this study, we demonstrate the easy production of functionalized magnetic nanoparticles with suitably genetically modified magnetotactic bacteria that are efficient as a reusable nanobiocatalyst for pesticides bioremediation in contaminated effluents.

Toward therapeutic delivery with layer-by-layer engineered particles

Layer-by-layer (LbL)-engineered particles have recently emerged as a promising class of materials for applications in biomedicine, with studies progressing from in vitro to in vivo. The versatility of LbL assembly coupled with particle templating has led to engineered particles with specific properties (e.g., stimuli-responsive, high cargo encapsulation efficiency, targeting), thus offering new opportunities in targeted and triggered therapeutic release. This Perspective highlights an important development by Poon et al. on tumor targeting in vivo using LbL-engineered nanoparticles containing a pH-responsive poly(ethylene glycol) (PEG) surface layer. Further, we summarize recent progress in the application of LbL particles in the fields of drug, gene, and vaccine delivery and cancer imaging. Finally, we explore future directions in this field, focusing on the biological processing of LbL-assembled particles.

Effect of gold nanoparticle morphology on adsorbed protein structure and function

Many biomedical applications of gold nanoparticles (NPs) rely on proteins that are covalently attached or adsorbed on the NP surface. The biological functionality of the protein-NP conjugate depends on the protein's ability to interact with target molecules, which is affected by NP characteristics such as size, curvature, aspect ratio, morphology, crystal structure, and surface chemistry. In the present study, the effect of gold nanoparticle morphology on the structure and function of adsorbed enzymes, lysozyme (Lyz) and α-chymotrypsin (ChT), has been investigated. Gold nanospheres (AuNS) were synthesized with diameters 10.6 ± 1 nm, and gold nanorods (AuNR) were synthesized with dimensions of (10.3 ± 2) × (36.4 ± 9) nm. Under saturating conditions, proteins adsorb with a higher surface density on AuNR when compared to AuNS. In the case of Lyz, adsorption on AuNS and AuNR resulted in a 10% and 15% loss of secondary structure, respectively, leading to conjugate aggregation and greatly reduced enzymatic activity. ChT retained most of its secondary structure and activity on AuNS and AuNR at low surface coverages; however, as protein loading approached monolayer conditions on AuNR, a 40% loss in secondary structure and 86% loss of activity was observed. Subsequent adsorption of ChT in multilayers on the AuNR surface allowed the conjugates to recover activity and remain stable. It is clear that AuNP morphology does affect adsorbed protein structure; a better understanding of these differences will be essential to engineer fully functional nanobioconjugates.

Surfactant-assisted controlled release of hydrophobic drugs using anionic surfactant templated mesoporous silica nanoparticles

A series of mesoporous silica nanoparticles (MSNs) were synthesized using the co-structure directing method. A non-cytotoxic anionic surfactant, undec-1-en-11-yltetra(ethylene glycol) phosphate monoester surfactant (PMES), was used as a structure directing agent (SDA) together with aminopropyltrimethoxysilane that functioned as a co-structure directing agent (CSDA). The morphology and mesoporous structure of these materials were tuned by changing the molar ratio of CSDA and SDA. These mesoporous nanomaterials containing PMES inside the pores showed excellent biocompatibility in vitro. The cellular internalization and endosome escape of PMES-MSNs in cervical cancer cells (HeLa) was demonstrated by flow cytometry and confocal microscopy, respectively. The PMES-MSNs were used as drug delivery carriers for resveratrol, a low water solubility drug, by taking advantage of the hydrophobic environment created by the PMES micelle inside the pores. This surfactant-assisted delivery strategy was tested under physiological conditions showing an increase of the drug loading compared to the material without surfactant and steady release of resveratrol. Finally, the therapeutic properties of resveratrol-loaded PMES-MSNs were evaluated in vitro using HeLa and Chinese hamster ovarian cells. We envision that this surfactant-assisted drug delivery method using MSNs as nanovehicles would lead to a new generation of carrier materials for intracellular delivery of a variety of hydrophobic therapeutic agents.

Acid-degradable cationic dextran particles for the delivery of siRNA therapeutics

We report a new acid-sensitive, biocompatible, and biodegradable microparticulate delivery system, spermine modified acetalated-dextran (Spermine-Ac-DEX), which can be used to efficiently encapsulate siRNA. These particles demonstrated efficient gene knockdown in HeLa-luc cells with minimal toxicity. This knockdown was comparable to that obtained using Lipofectamine, a commercially available transfection reagent generally limited to in vitro use due to its high toxicity.

Functionalized Gold Nanoparticles and Their Biomedical Applications

Metal nanoparticles are being extensively used in various biomedical applications due to their small size to volume ratio and extensive thermal stability. Gold nanoparticles (GNPs) are an obvious choice due to their amenability of synthesis and functionalization, less toxicity and ease of detection. The present review focuses on various methods of functionalization of GNPs and their applications in biomedical research. Functionalization facilitates targeted delivery of these nanoparticles to various cell types, bioimaging, gene delivery, drug delivery and other therapeutic and diagnostic applications. This review is an amalgamation of recent advances in the field of functionalization of gold nanoparticles and their potential applications in the field of medicine and biology.

Stimuli-responsive liposome-nanoparticle assemblies

INTRODUCTION

Nanoscale assemblies are needed that achieve multiple therapeutic objectives, including cellular targeting, imaging, diagnostics and drug delivery. These must exhibit high stability, bioavailability and biocompatibility, while maintaining or enhancing the inherent activity of the therapeutic cargo. Liposome-nanoparticle assemblies (LNAs) combine the demonstrated potential of liposome-based therapies, with functional nanoparticles. Specifically, LNAs can be used to concentrate and shield the nanoparticles and, in turn, stimuli-responsive nanoparticles that respond to external fields can be used to control liposomal release. The ability to design LNAs via nanoparticle encapsulation, decoration or bilayer-embedment offers a range of configurations with different structures and functions.

AREAS COVERED

This paper reviews the current state of research and understanding of the design, characterization and performance of LNAs. A brief overview is provided on liposomes and nanoparticles for therapeutic applications, followed by a discussion of the opportunities and challenges associated with combining the two in a single assembly to achieve controlled release via light or radiofrequency stimuli.

EXPERT OPINION

LNAs offer a unique opportunity to combine the therapeutic properties of liposomes and nanoparticles. Liposomes act to concentrate small nanoparticles and shield nanoparticles from the immune system, while the nanoparticle can be used to initiate and control drug release when exposed to external stimuli. These properties provide a platform to achieve nanoparticle-controlled liposomal release. LNA design and application are still in infancy. Research concentrating on the relationships among LNA structure, function and performance is essential for the future clinical use of LNAs.

Nanoparticle PEGylation for imaging and therapy

Nanoparticles are an essential component in the emerging field of nanomedical imaging and therapy. When deployed in vivo, these materials are typically protected from the immune system by polyethylene glycol (PEG). A wide variety of strategies to coat and characterize nanoparticles with PEG has established important trends on PEG size, shape, density, loading level, molecular weight, charge and purification. Strategies to incorporate targeting ligands are also prevalent. This article presents a background to investigators new to stealth nanoparticles, and suggests some key considerations needed prior to designing a nanoparticle PEGylation protocol and characterizing the performance features of the product.

Functional virus-based polymer-protein nanoparticles by atom transfer radical polymerization

Viruses and virus-like particles (VLPs) are useful tools in biomedical research. Their defined structural attributes make them attractive platforms for engineered interactions over large molecular surface areas. In this report, we describe the use of VLPs as multivalent macroinitiators for atom transfer radical polymerization. The introduction of chemically reactive monomers during polymerization provides a robust platform for post-synthetic modification via the copper-catalyzed azide-alkyne cycloaddition reaction. These results provide the basis to construct nanoparticle delivery vehicles and imaging agents using protein-polymer conjugates.

Controlling drug nanoparticle formation by rapid precipitation

Nanoparticles are a drug delivery platform that can enhance the efficacy of active pharmaceutical ingredients, including poorly-water soluble compounds, ionic drugs, proteins, peptides, siRNA and DNA therapeutics. To realize the potential of these nano-sized carriers, manufacturing processes must be capable of providing reproducible, scalable and stable formulations. Antisolvent precipitation to form drug nanoparticles has been demonstrated as one such robust and scalable process. This review discusses the nucleation and growth of organic nanoparticles at high supersaturation. We present process considerations for controlling supersaturations as well as physical and chemical routes for modifying API solubility to optimize supersaturation and control particle size. We conclude with a discussion of post-precipitation factors which influence nanoparticle stability and efficacy in vivo and techniques for stabilization.

Tailoring nanocarriers for intracellular protein delivery

Proteins play a crucial role in life, taking part in all vital processes in the body. In the past decade, there was increasing interest in delivering active forms of proteins to specific cells and organs. Intracellular protein delivery holds enormous promise for biological and medical applications, including cancer therapy, vaccination, regenerative medicine, treatment for loss-of-function genetic diseases and imaging. This tutorial review surveys recent developments in intracellular protein delivery using various nanocarriers. Methods such as lipid-mediated colloidal systems, polymeric nanocarriers, inorganic systems and protein-mediated carriers are reviewed. Advantages and limitations of current strategies, as well as future opportunities and challenges are also discussed.

Controlling in vivo stability and biodistribution in electrostatically assembled nanoparticles for systemic delivery

This paper demonstrates the generation of systemically deliverable layer-by-layer (LbL) nanoparticles for cancer applications. LbL-based nanoparticles designed to navigate the body and deliver therapeutics in a programmable fashion are promising new and alternative systems for drug delivery, but there have been very few demonstrations of their systemic delivery in vivo due to a lack of knowledge in building LbL nanofilms that mimic traditional nanoparticle design to optimize delivery. The key to the successful application of these nanocarriers in vivo requires a systematic analysis of the influence of film architecture and adsorbed polyelectrolyte outer layer on their pharmacokinetics, which has thus far not been examined for this new approach to nanoparticle delivery. Herein, we have taken the first steps in stabilizing and controlling the systemic distribution of multilayer nanoparticles. Our findings highlight the unique character of LbL systems; the electrostatically assembled nanoparticles gain increased stability in vivo with larger numbers of deposited layers, and the final layer adsorbed generates a critical surface cascade, which dictates the surface chemistry and biological properties of the nanoparticle. This outer polyelectrolyte layer dramatically affects not only the degree of nonspecific particle uptake, but also the nanoparticle biodistribution. For hyaluronic acid (HA) outer layers, a long blood elimination half-life (∼9 h) and low accumulation (∼10-15% recovered fluorescence/g) in the liver were observed, illustrating that these systems can be designed to be highly appropriate for clinical translation.

Folate-decorated nanogels for targeted therapy of ovarian cancer

Nanogels are comprised of swollen polymer networks and nearly 95% water and can entrap diverse chemical and biological agents for cancer therapy with very high loading capacities. Here we use diblock copolymer poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMA) to form nanogels with the desired degree of cross-linking. The nanogels are further conjugated to folic acid (FA) and loaded with different types of drugs (cisplatin, doxorubicin). For the first time we demonstrate a tumor-specific delivery and superior anti-tumor effect in vivo of an anti-cancer drug using these polyelectrolyte nanogels decorated with folate-targeting groups. This reinforces the use of nanogels for the therapy of ovarian and other cancers, where folate receptor (FR) is overexpressed.

Silica and titanium dioxide nanoparticles cause pregnancy complications in mice

The increasing use of nanomaterials has raised concerns about their potential risks to human health. Recent studies have shown that nanoparticles can cross the placenta barrier in pregnant mice and cause neurotoxicity in their offspring, but a more detailed understanding of the effects of nanoparticles on pregnant animals remains elusive. Here, we show that silica and titanium dioxide nanoparticles with diameters of 70 nm and 35 nm, respectively, can cause pregnancy complications when injected intravenously into pregnant mice. The silica and titanium dioxide nanoparticles were found in the placenta, fetal liver and fetal brain. Mice treated with these nanoparticles had smaller uteri and smaller fetuses than untreated controls. Fullerene molecules and larger (300 and 1,000 nm) silica particles did not induce these complications. These detrimental effects are linked to structural and functional abnormalities in the placenta on the maternal side, and are abolished when the surfaces of the silica nanoparticles are modified with carboxyl and amine groups.

Size-controlled long-circulating PICsome as a ruler to measure critical cut-off disposition size into normal and tumor tissues

Selective disposition of nanocarriers into target tissue is an essential issue in drug delivery. Critical size of nanocarriers (∼150 nm) discriminating the permeability into normal and tumor tissues was determined by the use of size-tunable, polyion complex hollow vesicles (PICsome) as a ruler.