Influence of formulation variables on the biodistribution of multifunctional block copolymer micelles

Radiation nanomedicines for cancer treatment: a scientific journey and view of the landscape

BACKGROUND

Radiation nanomedicines are nanoparticles labeled with radionuclides that emit α- or β-particles or Auger electrons for cancer treatment. We describe here our 15 years scientific journey studying locally-administered radiation nanomedicines for cancer treatment. We further present a view of the radiation nanomedicine landscape by reviewing research reported by other groups.

MAIN BODY

Gold nanoparticles were studied initially for radiosensitization of breast cancer to X-radiation therapy. These nanoparticles were labeled with 111In to assess their biodistribution after intratumoural vs. intravenous injection. Intravenous injection was limited by high liver and spleen uptake and low tumour uptake, while intratumoural injection provided high tumour uptake but low normal tissue uptake. Further, [111In]In-labeled gold nanoparticles modified with trastuzumab and injected iintratumourally exhibited strong tumour growth inhibition in mice with subcutaneous HER2-positive human breast cancer xenografts. In subsequent studies, strong tumour growth inhibition in mice was achieved without normal tissue toxicity in mice with human breast cancer xenografts injected intratumourally with gold nanoparticles labeled with β-particle emitting 177Lu and modified with panitumumab or trastuzumab to specifically bind EGFR or HER2, respectively. A nanoparticle depot (nanodepot) was designed to incorporate and deliver radiolabeled gold nanoparticles to tumours using brachytherapy needle insertion techniques. Treatment of mice with s.c. 4T1 murine mammary carcinoma tumours with a nanodepot incorporating [90Y]Y-labeled gold nanoparticles inserted into one tumour arrested tumour growth and caused an abscopal growth-inhibitory effect on a distant second tumour. Convection-enhanced delivery of [177Lu]Lu-AuNPs to orthotopic human glioblastoma multiforme (GBM) tumours in mice arrested tumour growth without normal tissue toxicity. Other groups have explored radiation nanomedicines for cancer treatment in preclinical animal tumour xenograft models using gold nanoparticles, liposomes, block copolymer micelles, dendrimers, carbon nanotubes, cellulose nanocrystals or iron oxide nanoparticles. These nanoparticles were labeled with radionuclides emitting Auger electrons (111In, 99mTc, 125I, 103Pd, 193mPt, 195mPt), β-particles (177Lu, 186Re, 188Re, 90Y, 198Au, 131I) or α-particles (225Ac, 213Bi, 212Pb, 211At, 223Ra). These studies employed intravenous or intratumoural injection or convection enhanced delivery. Local administration of these radiation nanomedicines was most effective and minimized normal tissue toxicity.

CONCLUSIONS

Radiation nanomedicines have shown great promise for treating cancer in preclinical studies. Local intratumoural administration avoids sequestration by the liver and spleen and is most effective for treating tumours, while minimizing normal tissue toxicity.

Nanoparticles labeled with gamma-emitting radioisotopes: an attractive approach for in vivo tracking using SPECT imaging

Providing accurate molecular imaging of the body and biological process is critical for diagnosing disease and personalizing treatment with the minimum side effects. Recently, diagnostic radiopharmaceuticals have gained more attention in precise molecular imaging due to their high sensitivity and appropriate tissue penetration depth. The fate of these radiopharmaceuticals throughout the body can be traced using nuclear imaging systems, including single-photon emission computed tomography (SPECT) and positron emission tomography (PET) modalities. In this regard, nanoparticles are attractive platforms for delivering radionuclides into targets because they can directly interfere with the cell membranes and subcellular organelles. Moreover, applying radiolabeled nanomaterials can decrease their toxicity concerns because radiopharmaceuticals are usually administrated at low doses. Therefore, incorporating gamma-emitting radionuclides into nanomaterials can provide imaging probes with valuable additional properties compared to the other carriers. Herein, we aim to review (1) the gamma-emitting radionuclides used for labeling different nanomaterials, (2) the approaches and conditions adopted for their radiolabeling, and (3) their application. This study can help researchers to compare different radiolabeling methods in terms of stability and efficiency and choose the best way for each nanosystem.

Systematic evaluation of membrane-camouflaged nanoparticles in neutralizing Clostridium perfringens ε-toxin

Clostridium perfringens ε-toxin (ETX) is the main toxin leading to enterotoxemia of sheep and goats and is classified as a potential biological weapon. In addition, no effective treatment drug is currently available in clinical practice for this toxin. We developed membrane-camouflaged nanoparticles (MNPs) with different membrane origins to neutralize ETX and protect the host from fatal ETX intoxication. We evaluated the safety and therapeutic efficacy of these MNPs in vitro and in vivo. Compared with membranes from karyocytes, such as Madin-Darby canine kidney (MDCK) cells and mouse neuroblastoma N2a cells (N2a cells), membrane from erythrocytes, which do not induce any immune response, are superior in safety. The protective ability of MNPs was evaluated by intravenous injection and lung delivery. We demonstrate that nebulized inhalation is as safe as intravenous injection and that both modalities can effectively protect mice against ETX. In particular, pulmonary delivery of nanoparticles more effectively treated the challenge of inhaled toxins than intravenously injected nanoparticles. Moreover, MNPs can alter the biological distribution of ETX among different organs in the body, and ETX was captured, neutralized and slowly delivered to the liver and spleen, where nanoparticles with ETX could be phagocytized and metabolized. This demonstrates how MNPs treat toxin infections in vivo. Finally, we injected the MNPs into mice in advance to find out whether MNPs can provide preventive protection, and the results showed that the long-cycle MNPs could provide at least a 3-day protection in mice. These findings demonstrate that MNPs provide safe and effective protection against ETX intoxication, provide new insights into membrane choices and delivery routes of nanoparticles, and new evidence of the ability of nanoparticles to provide preventive protection against infections.

The in vivo fate of polymeric micelles

This review aims to provide a systemic analysis of the in vivo, as well as subcellular, fate of polymeric micelles (PMs), starting from the entry of PMs into the body. Few PMs are able to cross the biological barriers intact and reach the circulation. In the blood, PMs demonstrate fairly good stability mainly owing to formation of protein corona despite controversial results reported by different groups. Although the exterior hydrophilic shells render PMs "long-circulating", the biodistribution of PMs into the mononuclear phagocyte systems (MPS) is dominant as compared with non-MPS organs and tissues. Evidence emerges to support that the copolymer poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) is first broken down into pieces of PEG and PLA and then remnants to be eliminated from the body finally. At the cellular level, PMs tend to be internalized via endocytosis due to their particulate nature and disassembled and degraded within the cell. Recent findings on the effect of particle size, surface characteristics and shape are also reviewed. It is envisaged that unraveling the in vivo and subcellular fate sheds light on the performing mechanisms and gears up the clinical translation of PMs.

Recent developments in selenium-containing polymeric micelles: prospective stimuli, drug-release behaviors, and intrinsic anticancer activity

Selenium is capable of forming a dynamic covalent bond with itself and other elements and can undergo metathesis and regeneration reactions under optimum conditions. Its dynamic nature endows selenium-containing polymers with striking sensitivity towards some environmental alterations. In the past decade, several selenium-containing polymers were synthesized and used for the preparation of oxidation-, reduction-, and radiation-responsive nanocarriers. Recently, thioredoxin reductase, sonication, and osmotic pressure triggered the cleavage of Se-Se bonds and swelling or disassembly of nanostructures. Moreover, some selenium-containing nanocarriers form oxidation products such as seleninic acids and acrylates with inherent anticancer activities. Thus, selenium-containing polymers hold promise for the fabrication of ultrasensitive and multifunctional nanocarriers of radiotherapeutic, chemotherapeutic, and immunotherapeutic significance. Herein, we discuss the most recent developments in selenium-containing polymeric micelles in light of their architecture, multiple stimuli-responsive properties, emerging immunomodulatory activities, and future perspectives in the delivery and controlled release of anticancer agents.

Interdependency of influential parameters in therapeutic nanomedicine

Introduction:Current challenges to successful clinical translation of therapeutic nanomedicine have discouraged many stakeholders, including patients. Significant effort has been devoted to uncovering the reasons behind the less-than-expected success, beyond failures or ineffectiveness, of therapeutic nanomedicine products (e.g. cancer nanomedicine). Until we understand and address the factors that limit the safety and efficacy of NPs, both individually and in combination, successful clinical development will lag.Areas covered:This review highlights the critical roles of interdependent factors affecting the safety and therapeutic efficacy of therapeutic NPs for drug delivery applications.Expert opinion:Deep analysis of the current nanomedical literature reveals ahistory of unanticipated complexity by awide range of stakeholders including researchers. In the manufacture of nanomedicines themselves, there have been persistent difficulties with reproducibility and batch-to-batch variation. The unanticipated complexity and interdependency of nano-bio parameters has delayed our recognition of important factors affecting the safety and therapeutic efficacy of nanomedicine products. These missteps have had many factors including our lack of understanding of the interdependency of various factors affecting the biological identity and fate of NPs and biased interpretation of data. All these issues could raise significant concern regarding the reproducibility- or even the validity- of past publications that in turn formed the basis of many clinical trials of therapeutic nanomedicines. Therefore, the individual and combined effects of previously overlooked factors on the safety and therapeutic efficacy of NPs need to be fully considered in nanomedicine reports and product development.

The Use of Alternative Strategies for Enhanced Nanoparticle Delivery to Solid Tumors

Nanomaterial (NM) delivery to solid tumors has been the focus of intense research for over a decade. Classically, scientists have tried to improve NM delivery by employing passive or active targeting strategies, making use of the so-called enhanced permeability and retention (EPR) effect. This phenomenon is made possible due to the leaky tumor vasculature through which NMs can leave the bloodstream, traverse through the gaps in the endothelial lining of the vessels, and enter the tumor. Recent studies have shown that despite many efforts to employ the EPR effect, this process remains very poor. Furthermore, the role of the EPR effect has been called into question, where it has been suggested that NMs enter the tumor via active mechanisms and not through the endothelial gaps. In this review, we provide a short overview of the EPR and mechanisms to enhance it, after which we focus on alternative delivery strategies that do not solely rely on EPR in itself but can offer interesting pharmacological, physical, and biological solutions for enhanced delivery. We discuss the strengths and shortcomings of these different strategies and suggest combinatorial approaches as the ideal path forward.

Poly(2-oxazoline) nanoparticle delivery enhances the therapeutic potential of vismodegib for medulloblastoma by improving CNS pharmacokinetics and reducing systemic toxicity

We report a nanoparticle formulation of the SHH-pathway inhibitor vismodegib that improves efficacy for medulloblastoma, while reducing toxicity. Limited blood-brain barrier (BBB) penetration and dose-limiting extitle/citraneural toxicities complicate systemic therapies for brain tumors. Vismodegib is FDA-approved for SHH-driven basal cell carcinoma, but implementation for medulloblastoma has been limited by inadequate efficacy and excessive bone toxicity. To address these issues through optimized drug delivery, we formulated vismodegib in polyoxazoline block copolymer micelles (POx-vismo). We then evaluated POx-vismo in transgenic mice that develop SHH-driven medulloblastomas with native vasculature and tumor microenvironment. POx-vismo improved CNS pharmacokinetics and reduced bone toxicity. Mechanistically, the nanoparticle carrier did not enter the CNS, and acted within the vascular compartment to improve drug delivery. Unlike conventional vismodegib, POx-vismo extended survival in medulloblastoma-bearing mice. Our results show the broad potential for non-targeted nanoparticle formulation to improve systemic brain tumor therapy, and specifically to improve vismodegib therapy for SHH-driven cancers.

Radiolabelling of nanomaterials for medical imaging and therapy

Nanomaterials offer unique physical, chemical and biological properties of interest for medical imaging and therapy. Over the last two decades, there has been an increasing effort to translate nanomaterial-based medicinal products (so-called nanomedicines) into clinical practice and, although multiple nanoparticle-based formulations are clinically available, there is still a disparity between the number of pre-clinical products and those that reach clinical approval. To facilitate the efficient clinical translation of nanomedicinal-drugs, it is important to study their whole-body biodistribution and pharmacokinetics from the early stages of their development. Integrating this knowledge with that of their therapeutic profile and/or toxicity should provide a powerful combination to efficiently inform nanomedicine trials and allow early selection of the most promising candidates. In this context, radiolabelling nanomaterials allows whole-body and non-invasive in vivo tracking by the sensitive clinical imaging techniques positron emission tomography (PET), and single photon emission computed tomography (SPECT). Furthermore, certain radionuclides with specific nuclear emissions can elicit therapeutic effects by themselves, leading to radionuclide-based therapy. To ensure robust information during the development of nanomaterials for PET/SPECT imaging and/or radionuclide therapy, selection of the most appropriate radiolabelling method and knowledge of its limitations are critical. Different radiolabelling strategies are available depending on the type of material, the radionuclide and/or the final application. In this review we describe the different radiolabelling strategies currently available, with a critical vision over their advantages and disadvantages. The final aim is to review the most relevant and up-to-date knowledge available in this field, and support the efficient clinical translation of future nanomedicinal products for in vivo imaging and/or therapy.

A framework for designing delivery systems

The delivery of medical agents to a specific diseased tissue or cell is critical for diagnosing and treating patients. Nanomaterials are promising vehicles to transport agents that include drugs, contrast agents, immunotherapies and gene editors. They can be engineered to have different physical and chemical properties that influence their interactions with their biological environments and delivery destinations. In this Review Article, we discuss nanoparticle delivery systems and how the biology of disease should inform their design. We propose developing a framework for building optimal delivery systems that uses nanoparticle-biological interaction data and computational analyses to guide future nanomaterial designs and delivery strategies.

Quercetin Loaded Nanoparticles in Targeting Cancer: Recent Development

The spread of metastatic cancer cell is the main cause of death worldwide. Cellular and molecular basis of the action of phytochemicals in the modulation of metastatic cancer highlights the importance of fruits and vegetables. Quercetin is a natural bioflavonoid present in fruits, vegetables, seeds, berries, and tea. The cancer-preventive activity of quercetin is well documented due to its anti-inflammatory, anti-proliferative and anti-angiogenic activities. However, poor water solubility and delivery, chemical instability, short half-life, and low-bioavailability of quercetin limit its clinical application in cancer chemoprevention. A better understanding of the molecular mechanism of controlled and regulated drug delivery is essential for the development of novel and effective therapies. To overcome the limitations of accessibility by quercetin, it can be delivered as nanoconjugated quercetin. Nanoconjugated quercetin has attracted much attention due to its controlled drug release, long retention in tumor, enhanced anticancer potential, and promising clinical application. The pharmacological effect of quercetin conjugated nanoparticles typically depends on drug carriers used such as liposomes, silver nanoparticles, silica nanoparticles, PLGA (Poly lactic-co-glycolic acid), PLA (poly(D,L-lactic acid)) nanoparticles, polymeric micelles, chitosan nanoparticles, etc. In this review, we described various delivery systems of nanoconjugated quercetin like liposomes, silver nanoparticles, PLGA (Poly lactic-co-glycolic acid), and polymeric micelles including DOX conjugated micelles, metal conjugated micelles, nucleic acid conjugated micelles, and antibody-conjugated micelles on in vitro and in vivo tumor models; as well as validated their potential as promising onco-therapeutic agents in light of recent updates.

Structure-Dependent Biodistribution of Liposomal Spherical Nucleic Acids

Spherical nucleic acids (SNAs) are a class of nanomaterials with a structure defined by a radial distribution of densely packed, short DNA or RNA sequences around a nanoparticle core. This structure allows SNAs to rapidly enter mammalian cells, protects the displayed oligonucleotides from nuclease degradation, and enables co-delivery of other drug cargoes. Here, we investigate the biodistribution of liposomal spherical nucleic acid (LSNA) conjugates, SNA architectures formed from liposome templates and DNA modified with hydrophobic end groups (tails). We compared linear DNA with two types of LSNAs that differ only by the affinity of the modified DNA sequence for the liposome template. We use single-stranded DNA (ssDNA) terminated with either a low-affinity cholesterol tail (CHOL-LSNA) or a high-affinity diacylglycerol lipid tail (DPPE-LSNA). Both LSNA formulations, independent of DNA conjugation, reduce the inflammatory cytokine response to intravenously administered DNA. The difference in the affinity for the liposome template significantly affects DNA biodistribution. DNA from CHOL-LSNAs accumulates in greater amounts in the lungs than DNA from DPPE-LSNAs. In contrast, DNA from DPPE-LSNAs exhibits greater accumulation in the kidneys. Flow cytometry and fluorescence microscopy of tissue sections indicate that different cell populations-immune and nonimmune-sequester the DNA depending upon the chemical makeup of the LSNA. Taken together, these data suggest that the chemical structure of the LSNAs represents an opportunity to direct the biodistribution of nucleic acids to major tissues outside of the liver.

Mouse Positron Emission Tomography Study of the Biodistribution of Gold Nanoparticles with Different Surface Coatings Using Embedded Copper-64

By taking advantage of the ability of ⁶⁴Cu to bind nonspecifically to gold surfaces, we have developed a methodology to embed this radionuclide inside gold nanoparticles (AuNPs). ⁶⁴Cu enables the in vivo imaging of AuNPs by positron emission tomography (PET). AuNPs have a multitude of uses within health technology and are useful tools for general nanoparticle research. ⁶⁴Cu-AuNPs were prepared by incubating AuNP seeds with ⁶⁴Cu²⁺, followed by the entrapment of the radionuclide by grafting on a second layer of gold. This resulted in radiolabeling efficiencies of 53 ± 6%. The radiolabel showed excellent stability when incubated with EDTA for 2 days (95% radioactivity retention) and showed no loss of ⁶⁴Cu when incubated with 50% mouse serum for 2 days. The methodology was chelator-free, removing traditional concerns over chelator instability and altered AuNP properties due to surface modification. Radiolabeled ⁶⁴Cu-AuNP cores were prepared in biomedically relevant sizes of 20-30 nm and used to investigate the in vivo stability of three different AuNP coatings by PET imaging in a murine xenograft tumor model. We found the longest plasma half-life (T_1/2 about 9 h) and tumor accumulation (3.9%ID/g) to result from a polyethylene glycol coating, while faster elimination from the bloodstream was observed with both a Tween 20-stabilized coating and a zwitterionic coating based on a mixture of sulfonic acids and quaternary amines. In the in vivo model, the ⁶⁴Cu was observed to closely follow the AuNPs for each coating, again attributed to the excellent stability of the radiolabel.

Mechanism of hard-nanomaterial clearance by the liver

The liver and spleen are major biological barriers to translating nanomedicines because they sequester the majority of administered nanomaterials and prevent delivery to diseased tissue. Here we examined the blood clearance mechanism of administered hard nanomaterials in relation to blood flow dynamics, organ microarchitecture and cellular phenotype. We found that nanomaterial velocity reduces 1,000-fold as they enter and traverse the liver, leading to 7.5 times more nanomaterial interaction with hepatic cells relative to peripheral cells. In the liver, Kupffer cells (84.8 ± 6.4%), hepatic B cells (81.5 ± 9.3%) and liver sinusoidal endothelial cells (64.6 ± 13.7%) interacted with administered PEGylated quantum dots, but splenic macrophages took up less material (25.4 ± 10.1%) due to differences in phenotype. The uptake patterns were similar for two other nanomaterial types and five different surface chemistries. Potential new strategies to overcome off-target nanomaterial accumulation may involve manipulating intra-organ flow dynamics and modulating the cellular phenotype to alter hepatic cell interactions.

Aminoglycoside-derived amphiphilic nanoparticles for molecular delivery

The development of effective drug carriers can lead to improved outcomes in a variety of disease conditions. Aminoglycosides have been used as antibacterial therapeutics, and are attractive as monomers for the development of polymeric materials in various applications. Here, we describe the development of novel aminoglycoside-derived amphiphilic nanoparticles for drug delivery, with an eye towards ablation of cancer cells. The aminoglycoside paromomycin was first cross-linked with resorcinol diglycidyl ether leading to the formation of a poly (amino ether), PAE. PAE molecules were further derivatized with methoxy-terminated poly(ethylene glycol) or mPEG resulting in the formation of mPEG-PAE polymer, which self-assembled to form nanoparticles. Formation of the mPEG-PAE amphiphile was characterized using (1)H NMR, (13)C NMR, gel permeation chromatography (GPC) and FTIR spectroscopy. Self-assembly of the polymer into nanoparticles was characterized using dynamic light scattering, zeta potential analyses, atomic force microscopy (AFM) and the pyrene fluorescence assay. mPEG-PAE nanoparticles were able to carry significant amounts of doxorubicin (DOX), presumably by means of hydrophobic interactions between the drug and the core. Cell-based studies indicated that mPEG-PAE nanoparticles, loaded with doxorubicin, were able to induce significant loss in viabilities of PC3 human prostate cancer, MDA-MB-231 human breast cancer, and MB49 murine bladder cancer cells; empty nanoparticles resulted in negligible losses of cell viability under the conditions investigated. Taken together, our results indicate that the mPEG-PAE nanoparticle platform is attractive for drug delivery in different applications, including cancer.

Development of polymeric micelles for targeting intractable cancers

In relation to recent advances in nanobiotechnologies, cancer-targeted therapy using nano-scaled drug carriers (nanocarriers) has been attracting enormous attention with success in clinical studies. Polymeric micelles, core-shell-type nanoparticles formed through the self-assembly of block copolymers, are one of the most promising nanocarrier, because their critical features such as size, stability, and drug incorporation efficiency and release rate can be modulated by designing the constituent block copolymers. The utilities of polymeric micelles have been reported not only in experimental tumor models in mice but also in clinical studies. In this article, we aim to explain the rationale of designing polymeric micelles for targeting intractable cancers such as pancreatic cancer, glioblastoma, and metastases. Also, we review recent progress in clinical studies on polymeric micelles incorporating anticancer drugs. In addition, we introduce the next generation of polymeric micelles as the platform integrated with smart functionalities such as targetability, environmental sensitivity, and imaging properties. Thus, polymeric micelles can realize safe and effective cancer therapy, and offer tailor-made medicines for individual patients.

Polymeric Micelle Platform for Multimodal Tomographic Imaging to Detect Scirrhous Gastric Cancer

Scirrhous gastric cancer (SGC) is a recalcitrant tumor, which is among the most lethal cancers. A critical issue for the improvement of SGC prognosis is the lack of an effective imaging method for accurate detection and diagnosis. Because combined nuclear medicine imaging with magnetic resonance imaging (MRI) has the ability to detect cancer with high sensitivity, and quantitation and spatial resolution, it has potential to overcome the issues with SGC detection. Herein, we designed and synthesized a new block copolymer poly(ethylene glycol)-b-poly(γ-benzyl l-glutamate) linked with a chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-PEG-b-PBLG) to provide a platform for multimodal tomographic imaging. We then successfully prepared DOTA-functionalized polymeric micelles (DOTA/m) measuring 30 nm in diameter, which is an appropriate size to penetrate deeply into tumors with thick fibrosis, including SGC. ¹¹¹In-labeled DOTA/m highly accumulated in Colon-26 tumors (mouse colon cancer with hyperpermeability), but also in OCUM-2 M LN tumors (SGC with hypopermeability), clearly depicting both tumors by single photon emission computed tomography (SPECT). Gd-labeled DOTA/m clearly visualized OCUM-2 M LN tumors by MRI with high spatial resolution. Moreover, ¹¹¹In/Gd-labeled micelles, as well as the mixture of ¹¹¹In- and Gd-labeled DOTA/m demonstrated the capability of this system for selective multimodal SPECT/MR imaging of SCG. Our findings support ¹¹¹In/Gd-DOTA-labeled micelles as a clinical translationable modality for multimodal tomographic imaging capable of detecting SGC.

The challenges facing block copolymer micelles for cancer therapy: In vivo barriers and clinical translation

The application of block copolymer micelles (BCMs) in oncology has benefitted from advances in polymer chemistry, drug formulation and delivery as well as in vitro and in vivo biological models. While great strides have been made in each of these individual areas, there remains some disappointment overall, citing, in particular, the absence of more BCM formulations in clinical evaluation and practice. In this review, we aim to provide an overview of the challenges presented by in vivo systems to the effective design and development of BCMs. In particular, the barriers posed by systemic administration and tumor properties are examined. The impact of critical features, such as the size, stability and functionalization of BCMs is discussed, while key pre-clinical endpoints and models are critiqued. Given clinical considerations, we present this work as a means to stimulate a renewed focus on the unique chemical versatility bestowed by BCMs and a measured grasp of representative in vitro and in vivo models.

Nanomedicines for cancer therapy: state-of-the-art and limitations to pre-clinical studies that hinder future developments

The ability to efficiently deliver a drug or gene to a tumor site is dependent on a wide range of factors including circulation time, interactions with the mononuclear phagocyte system, extravasation from circulation at the tumor site, targeting strategy, release from the delivery vehicle, and uptake in cancer cells. Nanotechnology provides the possibility of creating delivery systems where the design constraints are decoupled, allowing new approaches for reducing the unwanted side effects of systemic delivery, increasing tumor accumulation, and improving efficacy. The physico-chemical properties of nanoparticle-based delivery platforms introduce additional complexity associated with pharmacokinetics, tumor accumulation, and biodistribution. To assess the impact of nanoparticle-based delivery systems, we first review the design strategies and pharmacokinetics of FDA-approved nanomedicines. Next we review nanomedicines under development, summarizing the range of nanoparticle platforms, strategies for targeting, and pharmacokinetics. We show how the lack of uniformity in preclinical trials prevents systematic comparison and hence limits advances in the field.

Multifunctional polymeric micelles for delivery of drugs and siRNA

Polymeric micelles, self-assembling nano-constructs of amphiphilic copolymers with a core-shell structure have been used as versatile carriers for delivery of drugs as well as nucleic acids. They have gained immense popularity owing to a host of favorable properties including their capacity to effectively solubilize a variety of poorly soluble pharmaceutical agents, biocompatibility, longevity, high stability in vitro and in vivo and the ability to accumulate in pathological areas with compromised vasculature. Moreover, additional functions can be imparted to these micelles by engineering their surface with various ligands and cell-penetrating moieties to allow for specific targeting and intracellular accumulation, respectively, to load them with contrast agents to confer imaging capabilities, and incorporating stimuli-sensitive groups that allow drug release in response to small changes in the environment. Recently, there has been an increasing trend toward designing polymeric micelles which integrate a number of the above functions into a single carrier to give rise to “smart,” multifunctional polymeric micelles. Such multifunctional micelles can be envisaged as key to improving the efficacy of current treatments which have seen a steady increase not only in hydrophobic small molecules, but also in biologics including therapeutic genes, antibodies and small interfering RNA (siRNA). The purpose of this review is to highlight recent advances in the development of multifunctional polymeric micelles specifically for delivery of drugs and siRNA. In spite of the tremendous potential of siRNA, its translation into clinics has been a significant challenge because of physiological barriers to its effective delivery and the lack of safe, effective and clinically suitable vehicles. To that end, we also discuss the potential and suitability of multifunctional polymeric micelles, including lipid-based micelles, as promising vehicles for both siRNA and drugs.

Tailoring polymeric micelles to optimize delivery to solid tumors

Block copolymer micelles have shown great potential in drug delivery systems, not only for overcoming the drawbacks of small agents such as water insolubility and wide distribution in normal tissues, but also for avoiding traditional nanoparticle formulation shortcomings, including in vivo instability and fast clearance from the blood. However, for translating micellar formulations to clinical practice, it is essential to overcome the many in vivo obstacles. Surmounting these barriers strongly depends on micellar physicochemical properties, which can be further optimized by the unique physiological aspects of solid tumors such as low pH, high temperature and the presence of abnormal vessels. Herein, based on the Flory parameter and scaling theory, the fundamental mechanisms and correlations in vitro/in vivo between self assembly, drug loading and release, stability, intracellular delivery and in vivo distribution, as well as micellar composition, size and microstructural tailoring are systematically revisited. The methods for enhancing micellar performance in solid tumors were consequently proposed through well-defined core-corona structure tailoring.