Vascular permeability enhancement in solid tumor: various factors, mechanisms involved and its implications

A non-steroidal anti-inflammatory drug (ketoprofen) does not delay beta-TCP bone graft healing

Beta-tricalcium phosphate (beta-TCP) is a suitable biomaterial in oral and maxillofacial surgery since it can induce a rapid proliferation of woven bone. Granules, prepared by the polyurethane foam method, were implanted in critical size defects performed in the femoral condyles of New Zealand rabbits. Animals were studied after 8 and 28 days. Ketoprofen (a non-steroidal anti-inflammatory drug (NSAID)) was given for 8 and 28 days to evaluate its effects on the healing of the graft. Before euthanasia, the rabbits received an intravenous injection of fluorescent microbeads. Bones were analyzed by microcomputed tomography. beta-TCP granules induced metaplastic bone trabeculae as early as 8 days post-surgery. At 28 days, the amount of bone was increased and the biomaterial volume decreased due to simultaneous macrophagic resorption. The amount of macrophages labeled with microbeads was less in the grafted area than in the vicinal intact marrow spaces. Ketoprofen had no effect on the amount of bone formed and on the number of labeled macrophages. The influence of small doses of NSAID, given in a short duration period, did not present deleterious effects on bone graft healing.

Gadolinium chloride augments tumor-specific imaging of targeted quantum dots in vivo

Nonspecific sequestration of nanoparticles by the reticulo-endothelial system (RES) results in the degradation of image quality of nanoparticle-based imaging. We demonstrate that gadolinium chloride (GdCl3) pretreatment inactivates RES macrophages, thereby increasing circulatory time and amplifying the tumor-specific signal of conjugated nanoparticles in vivo. The experimental results were validated using compartmental modeling, and the rate parameters for the observed kinetics pattern were estimated. This pretreatment strategy could have broad applicability across biomedical applications utilizing theranostic nanoparticles that are sequestered by the RES.

Bio and nanotechnological strategies for tumor-targeted gene therapy

Gene therapy is a new medical approach for the treatment of tumors. For safe and efficient gene therapy, therapeutic genes need to be delivered efficiently into the target tumor cells. Development of gene delivery systems to specifically recognize and target tumor cells and to distinguish them from normal cells, especially in the same tissue or organ, is one of the most important issues regarding the present gene delivery methodologies. The enhanced permeability and retention (EPR) effect using the characteristics of angiogenic tumor blood vessels, as well as gene delivery systems recognizing hyperactivated receptors or intracellular signals, is broadly applied to tumor-targeted gene therapy. In addition, bacterial vectors can be a useful means for targeting hypoxic or anoxic regions of a tumor.

Gold nanoparticles: opportunities and challenges in nanomedicine

IMPORTANCE OF THE FIELD

Site-specific drug delivery is an important area of research that is anticipated to increase the efficacy of the drug and reduce potential side effects. Owing to this, substantial work has been done developing non-invasive and targeted tumor treatment with nanoscale metallic particles.

AREAS COVERED IN THIS REVIEW

This review focuses on the work done in the last few years developing gold nanoparticles as cancer therapeutics and diagnostic agents. However, there are challenges in using gold nanoparticles as drug delivery systems, such as biodistribution, pharmacokinetics and possible toxicity. Approaches to limit these issues are proposed.

WHAT THE READER WILL GAIN

Different approaches from several different disciplines are discussed. Potential clinical applications of these engineered nanoparticles are also presented.

TAKE HOME MESSAGE

As a result of their unique size-dependent physicochemical and optical properties, adaptability, subcellular size and biocompatibility, these nanosized carriers offer a suitable means of transporting small molecules as well as biomacromolecules to diseased cells/tissues.

Inhibition of ABCB1 (MDR1) expression by an siRNA nanoparticulate delivery system to overcome drug resistance in osteosarcoma

Background

The use of neo-adjuvant chemotherapy in treating osteosarcoma has improved patients' average 5 year survival rate from 20% to 70% in the past 30 years. However, for patients who progress after chemotherapy, its effectiveness diminishes due to the emergence of multi-drug resistance (MDR) after prolonged therapy.

Methodology/Principal Findings

In order to overcome both the dose-limiting side effects of conventional chemotherapeutic agents and the therapeutic failure resulting from MDR, we designed and evaluated a novel drug delivery system for MDR1 siRNA delivery. Novel biocompatible, lipid-modified dextran-based polymeric nanoparticles were used as the platform for MDR1 siRNA delivery; and the efficacy of combination therapy with this system was evaluated. In this study, multi-drug resistant osteosarcoma cell lines (KHOS_R2 and U-2OS_R2) were treated with the MDR1 siRNA nanocarriers and MDR1 protein (P-gp) expression, drug retention, and immunofluoresence were analyzed. Combination therapy of the MDR1 siRNA loaded nanocarriers with increasing concentrations of doxorubicin was also analyzed. We observed that MDR1 siRNA loaded dextran nanoparticles efficiently suppresses P-gp expression in the drug resistant osteosarcoma cell lines. The results also demonstrated that this approach may be capable of reversing drug resistance by increasing the amount of drug accumulation in MDR cell lines.

Conclusions/Significance

Lipid-modified dextran-based polymeric nanoparticles are a promising platform for siRNA delivery. Nanocarriers loaded with MDR1 siRNA are a potential treatment strategy for reversing MDR in osteosarcoma.

Coadministration of a tumor-penetrating peptide enhances the efficacy of cancer drugs

Poor penetration of anticancer drugs into tumors can be an important factor limiting their efficacy. We studied mouse tumor models to show that a previously characterized tumor-penetrating peptide, iRGD, increased vascular and tissue permeability in a tumor-specific and neuropilin-1-dependent manner, allowing coadministered drugs to penetrate into extravascular tumor tissue. Importantly, this effect did not require the drugs to be chemically conjugated to the peptide. Systemic injection with iRGD improved the therapeutic index of drugs of various compositions, including a small molecule (doxorubicin), nanoparticles (nab-paclitaxel and doxorubicin liposomes), and a monoclonal antibody (trastuzumab). Thus, coadministration of iRGD may be a valuable way to enhance the efficacy of anticancer drugs while reducing their side effects, a primary goal of cancer therapy research.

Targeting gold nanocages to cancer cells for photothermal destruction and drug delivery

IMPORTANCE OF THE FIELD

Plasmonic nanoparticles provide a new route to treat cancer owing to their ability to convert light into heat effectively for photothermal destruction. Combined with the targeting mechanisms possible with nanoscale materials, this technique has the potential to enable highly targeted therapies to minimize undesirable side effects.

AREAS COVERED IN THIS REVIEW

This review discusses the use of gold nanocages, a new class of plasmonic nanoparticles, for photothermal applications. Gold nanocages are hollow, porous structures with compact sizes and precisely controlled plasmonic properties and surface chemistry. Also, a recent study of gold nanocages as drug-release carriers by externally controlling the opening and closing of the pores with a smart polymer whose conformation changes at a specific temperature is discussed. Release of the contents can be initiated remotely through near-infrared irradiation. Together, these topics cover the years from 2002 to 2009.

WHAT THE READER WILL GAIN

The reader will be exposed to different aspects of gold nanocages, including synthesis, surface modification, in vitro studies, initial in vivo data and perspectives on future studies.

TAKE HOME MESSAGE

Gold nanocages are a promising platform for cancer therapy in terms of both photothermal destruction and drug delivery.

Nanoparticles for photoacoustic imaging

Nanoparticles have been designed and applied as contrast enhancers in various optical imaging techniques, such as optical coherence tomography, fluorescence imaging, and optical reflectance microscopy. As an emerging hybrid imaging modality, photoacoustic imaging (PAI) has also benefited from the application of these nanoparticle-based contrast agents. We review this rapidly growing field and describe the applications of nanoparticles in PAI. Particular focus is given to nanoparticles whose absorption mechanism is based on surface plasmon resonance, including gold nanoshells, nanorods, and nanocages. Dye-embedded nanoparticles are also reviewed. Specifically, the design and application of each nanoparticle-based contrast agent in relation to the field of PAI are detailed.

X-ray fluorescence computed tomography (XFCT) imaging of gold nanoparticle-loaded objects using 110 kVp x-rays

A conventional x-ray fluorescence computed tomography (XFCT) technique requires monochromatic synchrotron x-rays to simultaneously determine the spatial distribution and concentration of various elements such as metals in a sample. However, the synchrotron-based XFCT technique appears to be unsuitable for in vivo imaging under a typical laboratory setting. In this study we demonstrated, for the first time to our knowledge, the possibility of performing XFCT imaging of a small animal-sized object containing gold nanoparticles (GNPs) at relatively low concentrations using polychromatic diagnostic energy range x-rays. Specifically, we created a phantom made of polymethyl methacrylate plastic containing two cylindrical columns filled with saline solution at 1 and 2 wt% GNPs, respectively, mimicking tumors/organs within a small animal. XFCT scanning of the phantom was then performed using microfocus 110 kVp x-ray beam and cadmium telluride (CdTe) x-ray detector under a pencil beam geometry after proper filtering of the x-ray beam and collimation of the detector. The reconstructed images clearly identified the locations of the two GNP-filled columns with different contrast levels directly proportional to gold concentration levels. On the other hand, the current pencil-beam implementation of XFCT is not yet practical for routine in vivo imaging tasks with GNPs, especially in terms of scanning time. Nevertheless, with the use of multiple detectors and a limited number of projections, it may still be used to image some objects smaller than the current phantom size. The current investigation suggests several modification strategies of the current XFCT setup, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-top XFCT system for GNP-based preclinical molecular imaging applications.

Modeling of plasmonic heating from individual gold nanoshells for near-infrared laser-induced thermal therapy

Gold nanoparticles can be engineered to target cancerous cells and at the same time designed to absorb specific wavelengths of light. Consequently, with the presence of optically tunable gold nanoparticles such as gold nanoshells, light can be effectively converted to heat via photothermal effect well enough to raise the temperature of medium surrounding gold nanoshells for thermal ablation or hyperthermia treatments of cancers. In this study, the authors proposed a new computational method to estimate thermal response of gold nanoshells embedded in a tissue-like medium when illuminated by a near-infrared (NIR) laser. Specifically, the light transport theory with diffusion approximation was initially applied to model the temperature rise within a medium without gold nanoshells as a result of the dissipation of the NIR laser power throughout the medium. After then, the heat generated by individual gold nanoshells due to photothermal effect was calculated and combined with the results for the medium without gold nanoshells to estimate the global elevation of temperature within the gold nanoshell-laden medium. The current computational model was tested for its validity using two different phantom examples, one of which was similar to a previously reported phantom experiment. The test demonstrated the capability of the current model in terms of producing qualitatively reasonable results, while it also revealed a number of potential differences in the assumptions for the current model and previous experiment. After an adjustment in the model parameters to properly take into account such differences, the computational results and the experimental data matched reasonably well within the average percentage difference of 10%.

An integrated approach for the rational design of nanovectors for biomedical imaging and therapy

The use of nanoparticles for the early detection, cure, and imaging of diseases has been proved already to have a colossal potential in different biomedical fields, such as oncology and cardiology. A broad spectrum of nanoparticles are currently under development, exhibiting differences in (i) size, ranging from few tens of nanometers to few microns; (ii) shape, from the classical spherical beads to discoidal, hemispherical, cylindrical, and conical; (iii) surface functionalization, with a wide range of electrostatic charges and biomolecule conjugations. Clearly, the library of nanoparticles generated by combining all possible sizes, shapes, and surface physicochemical properties is enormous. With such a complex scenario, an integrated approach is here proposed and described for the rational design of nanoparticle systems (nanovectors) for the intravascular delivery of therapeutic and imaging contrast agents. The proposed integrated approach combines multiscale/multiphysics mathematical models with in vitro assays and in vivo intravital microscopy (IVM) experiments and aims at identifying the optimal combination of size, shape, and surface properties that maximize the nanovectors localization within the diseased microvasculature.

Photothermal therapy in a murine colon cancer model using near-infrared absorbing gold nanorods

The photothermal ablation of solid tumors using exogenous, near-infrared (NIR)-absorbing nanoparticles has been previously investigated using various preclinical models and is currently being evaluated in the clinic. Here, we evaluate the circulation kinetics, preliminary toxicity, and efficacy of photothermal ablation of solid tumors using gold nanorods systemically delivered and passively accumulated in a murine subcutaneous colon cancer model. Tumored animals were infused with nanorods followed by the percutaneous illumination of the tumor with an 808-nm laser. Control groups consisted of laser-only, nanorod-only, and untreated tumored animals. The survival of the treated and control groups were monitored for 60 days post-treatment. The survival of the photothermally treated group was statistically longer than the control groups, with approximately 44% tumor free through the evaluation period. Histopathology of the major organs of animals infused with nanorods did not indicate any significant toxicity at 60 days post-treatment. Particle biodistribution was evaluated by elemental analysis of the major organs of untumored mice at 1, 7, and 30 days after infusion with nanorods. Elemental analysis indicates nanorod clearance from the blood and retention by the reticuloendothelial system. This study indicates that gold nanorods are promising agents for photothermal ablation of solid tumors.

Gold nanorods: from synthesis and properties to biological and biomedical applications

Noble metal nanoparticles are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle's dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle's radiative properties, such as absorption and scattering. Moreover, by confining the photon's wavelength to the nanoparticle's small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.

Specific labeling with potent radiolabels alters the uptake of cell-penetrating peptides

Radiolabeled peptides play an important role in radiopharmacy not only as tumor markers but also as transport vectors. Therefore, cell-penetrating peptides (CPP) may serve as very effective delivery tools, as well. Recently, CPP based on the human hormone calcitonin (hCT) have been developed. Especially, branched hCT-peptide sequences turned out to have highly efficient internalization capacities. Labeling these peptides with radionuclides would generate promising new tools for imaging and therapy applications in radiopharmacy. However, the influence of the metal complexation on the internalization capacity of CPP has not been elucidated yet in detail. In this study we quantified the uptake of Ga-DOTA modified hCT-carrier peptides in HeLa cells by using atomic absorption spectroscopy (AAS) and compared the results to the uptake of fluorescently-labeled peptides. Interestingly, we measured different uptake rates depending on the attached label. Unexpectedly, modification with a Ga-DOTA complex can have tremendous effects on the uptake efficiency. The results of these studies support the need of detailed analysis of each carrier peptide/cargo construct, especially in the field of metal complex modified CPP.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

Design and development of polymer conjugates as anti-angiogenic agents

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is one of the central key steps in tumor progression and metastasis. Consequently, it became an important target in cancer therapy, making novel angiogenesis inhibitors a new modality of anticancer agents. Although relative to conventional chemotherapy, anti-angiogenic agents display a safer toxicity profile, the vast majority of these agents are low-molecular-weight compounds exhibiting poor pharmacokinetic profile with short half-life in the bloodstream and high overall clearance rate. The "Polymer Therapeutics" field has significantly improved the therapeutic potential of low-molecular-weight drugs and proteins for cancer treatment. Drugs can be conjugated to polymeric carriers that can be either directly conjugated to targeting proteins or peptides or derivatized with adapters conjugated to a targeting moiety. This approach holds a significant promise for the development of new targeted anti-angiogenic therapies as well as for the optimization of existing anti-angiogenic drugs or polypeptides. Here we overview the innovative approach of targeting tumor angiogenesis using polymer therapeutics.

PEG conjugates in clinical development or use as anticancer agents: an overview

During the almost forty years of PEGylation, several antitumour agents, either proteins, peptides or low molecular weight drugs, have been considered for polymer conjugation but only few entered clinical phase studies. The results from the first clinical trials have shared and improved the knowledge on biodistribution, clearance, mechanism of action and stability of a polymer conjugate in vivo. This has helped to design conjugates with improved features. So far, most of the PEG conjugates comprise of a protein, which in the native form has serious shortcomings that limit the full exploitation of its therapeutic action. The main issues can be short in vivo half-life, instability towards degrading enzymes or immunogenicity. PEGylation proved to be effective in shielding sensitive sites at the protein surface, such as antigenic epitopes and enzymatic degradable sequences, as well as in prolonging the drug half-life by decreasing the kidney clearance. In this review PEG conjugates of proteins or low molecular weight drugs, in clinical development or use as anticancer agents, will be taken into consideration. In the case of PEG-protein derivatives the most represented are depleting enzymes, which act by degrading amino acids essential for cancer cells. Interestingly, PEGylated conjugates have been also considered as adjuvant therapy in many standard anticancer protocols, in this regard the case of PEG-G-CSF and PEG-interferons will be presented.

C-end rule peptides mediate neuropilin-1-dependent cell, vascular, and tissue penetration

Screening of phage libraries expressing random peptides for binding to prostate cancer cells primarily yielded peptides that had a C-terminal arginine (or rarely lysine) residue, usually in a consensus context R/KXXR/K. Phage expressing these sequences and synthetic nanoparticles coated with them bound to and were internalized into cells. The C-terminal arginine (or lysine) was essential to the activity; adding another amino acid, or even blocking the free carboxyl group of this arginine residue by amidation, eliminated the binding and internalizing activity. An internal R/KXXR/K can be exposed and switched on by a cleavage by a protease. The strict requirement for C-terminal exposure of the motif prompted us to term the phenomenon the C-end rule (CendR). Affinity chromatography showed that the CendR peptides bind to neuropilin-1 (NRP-1) on the target cells. NRP-1 is a cell-surface receptor that plays an essential role in angiogenesis, regulation of vascular permeability, and the development of the nervous system. VEGF-A165 and other ligands of NRP-1 possess a C-terminal CendR sequence that interacts with the b1 domain of NRP-1 and causes cellular internalization and vascular leakage. Our CendR peptides have similar effects, particularly when made multivalent through coupling to a particle. We also noted a unique and important activity of these peptides: penetration and transportation through tissues. The peptides were able to take payloads up to the nanoparticle size scale deep into extravascular tissue. Our observations have implications in drug delivery and penetration of tissue barriers and tumors.

Targeted drug delivery for treatment and imaging of glioblastoma multiforme

Glioblastoma multiforme is a grade IV astrocytic tumor with a very high mortality rate. Although current treatment often includes surgical resection, this rarely removes all primary tumor cells, so is usually followed by radiation and/or chemotherapy. Remaining migratory tumor cells invade surrounding healthy tissue and contribute to secondary and tertiary tumor recurrence; therefore, despite significant research into glioma removal and treatment, prognosis remains poor. A variety of treatment modalities have been investigated to deliver drug to these cells, including systemic, diffusive and convection-enhanced delivery (CED). As systemic delivery is limited by molecules larger than approximately 500 Da being unable to cross the blood-brain barrier (BBB), therapeutic concentrations are difficult to attain; thus, localized delivery options relying on diffusion and CED have been used to circumvent the BBB. Although CED enables delivery to a greater volume of tissue than diffusive delivery alone, limitations still exist, requiring that these delivery strategies be improved. This review enumerates the strengths and weaknesses of these currently used strategies and details how predictive mathematical modeling can be used to aid investigators in optimizing these delivery modalities for clinical application.

Control of optical contrast using gold nanoshells for optical coherence tomography imaging of mouse xenograft tumor model in vivo

The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography (OCT). In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2 x 10(9) particles/ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor (EGFR) surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

The dosimetric feasibility of gold nanoparticle-aided radiation therapy (GNRT) via brachytherapy using low-energy gamma-/x-ray sources

The preferential accumulation of gold nanoparticles within tumors and the increased photoelectric absorption due to the high atomic number of gold cooperatively account for the possibility of significant tumor dose enhancement during gold nanoparticle-aided radiation therapy (GNRT). Among the many conceivable ways to implement GNRT clinically, a brachytherapy approach using low-energy gamma-/x-ray sources (i.e. E(avg) < 100 keV) appears to be highly feasible and promising, because it may easily fulfill some of the technical and clinical requirements for GNRT. Therefore, the current study investigated the dosimetric feasibility of implementing GNRT using the following sources: (125)I, 50 kVp and (169)Yb. Specifically, Monte Carlo (MC) calculations were performed to determine the macroscopic dose enhancement factors (MDEF), defined as the ratio of the average dose in the tumor region with and without the presence of gold nanoparticles during the irradiation of the tumor, and the photo/Auger electron spectra within a tumor loaded with gold nanoparticles. The current study suggests that a significant tumor dose enhancement (e.g. >40%) could be achievable using (125)I, 50 kVp and (169)Yb sources and gold nanoparticles. When calculated at 1.0 cm from the center of the source within a tumor loaded with 18 mg Au g(-1), macroscopic dose enhancement was 116, 92 and 108% for (125)I, 50 kVp and (169)Yb, respectively. For a tumor loaded with 7 mg Au g(-1), it was 68, 57 and 44% at 1 cm from the center of the source for (125)I, 50 kVp and (169)Yb, respectively. The estimated MDEF values for (169)Yb were remarkably larger than those for (192)Ir, on average by up to about 70 and 30%, for 18 mg Au and 7 mg Au cases, respectively. The current MC study also shows a remarkable change in the photoelectron fluence and spectrum (e.g. more than two orders of magnitude) and a significant production (e.g. comparable to the number of photoelectrons) of the Auger electrons within the tumor region due to the presence of gold nanoparticles during low-energy gamma-/x-ray irradiation. The radiation sources considered in this study are currently available and tumor gold concentration levels considered in this investigation are deemed achievable. Therefore, the current results strongly suggest that GNRT can be successfully implemented via brachytherapy with low energy gamma-/x-ray sources, especially with a high dose rate (169)Yb source.

Synthesis and use of pHEMA microbeads with human EA.hy 926 endothelial cells

Cancer has become a major problem in public health and the resulting bone metastases a worsening factor. Facing it, different strategies have been proposed and mechanisms involved in tumor angiogenesis are being studied. Enhanced permeability retention (EPR) effect is a key step in designing new anticancer drugs. We have prepared poly 2-hydroxyethyl methacrylate (pHEMA) microbeads to target human endothelial EA.hy 926 cells, a cell line derived from human umbilical vein endothelial cells. Microbeads were synthesized by emulsion precipitation method and carried positive or negative charges. EA.hy 926 cells were cultured in 24-well plates and microbeads were deposited on cells at various times. Scanning and transmission electron microscopy, flow cytometry, confocal microscopy, and three-dimensional (3D) reconstruction were used to characterize microbeads and their location outside and inside cells. Microbeads were uptaken by endothelial cells with a better internalization for negatively charged microbeads. 3D reconstruction of confocal optical sections clearly evidenced the uptake and internalization of microbeads by endothelial cells. pHEMA microbeads could represent potential drug carrier in tumor model of metastases.

Screening of nanoparticulate delivery systems for the photodetection of cancer in a simple and cost-effective model

AIMS

In urology, fluorescence-based imaging methods have been proven to significantly improve the detection of small, barely visible tumors and reduce the recurrence rate. Under ethical and economical pressure, new effective screening systems have to be developed to exploit and assess novel strategies for fluorescence photodetection in other areas. For this purpose, the chorioallantoic membrane (CAM) of the developing chick embryo is an attractive alternative model to the mammalian models.

MATERIALS & METHODS

Hypericin encapsulated into nanoparticles for the photodetection of ovarian metastases was evaluated in the CAM model with respect to vascular extravazation and tumor targeting and compared with free drug following intravenous administration.

RESULTS

To validate the CAM model as a valuable screening system for photodetection of cancer, we drew a comparison with results obtained on a conventional rodent model.

CONCLUSION

Rodent and CAM models led to the same conclusion regarding the benefits of nanoencapsulation to improve selective accumulation of drug in ovarian micrometastases.

Mediating tumor targeting efficiency of nanoparticles through design

Here we systematically examined the effect of nanoparticle size (10-100 nm) and surface chemistry (i.e., poly(ethylene glycol)) on passive targeting of tumors in vivo. We found that the physical and chemical properties of the nanoparticles influenced their pharmacokinetic behavior, which ultimately determined their tumor accumulation capacity. Interestingly, the permeation of nanoparticles within the tumor is highly dependent on the overall size of the nanoparticle, where larger nanoparticles appear to stay near the vasculature while smaller nanoparticles rapidly diffuse throughout the tumor matrix. Our results provide design parameters for engineering nanoparticles for optimized tumor targeting of contrast agents and therapeutics.

Albumin-bound formulation of paclitaxel (Abraxane ABI-007) in the treatment of breast cancer

Breast cancer is the most common type of malignancy diagnosed in women. In the metastatic setting this disease is still uncurable. Taxanes represent an important class of antitumor agents which have proven to be fundamental in the treatment of advanced and early-stage breast cancer, but the clinical advances of taxanes have been limited by their highly hydrophobic molecular status. To overcome this poor water solubility, lipid-based solvents have been used as a vehicle, and new systemic formulations have been developed, mostly for paclitaxel, which are Cremophor-free and increase the circulation time of the drug. ABI-007 is a novel, albumin-bound, 130-nm particle formulation of paclitaxel, free from any kind of solvent. It has been demonstrated to be superior to an equitoxic dose of standard paclitaxel with a significantly lower incidence of toxicities in a large, international, randomized phase III trial. The availability of new drugs, such as Abraxane, in association with other traditional and non-traditional drugs (new antineoplastic agents and targeted molecules), will give the oncologist many different effective treatment options for patients in this setting.

Nanotechnology for breast cancer therapy

Breast cancer is the field of medicine with the greatest presence of nanotechnological therapeutic agents in the clinic. A pegylated form of liposomally encapsulated doxorubicin is routinely used for treatment against metastatic cancer, and albumin nanoparticulate chaperones of paclitaxel were approved for locally recurrent and metastatic disease in 2005. These drugs have yielded substantial clinical benefit, and are steadily gathering greater beneficial impact. Clinical trials currently employing these drugs in combination with chemo and biological therapeutics exceed 150 worldwide. Despite these advancements, breast cancer morbidity and mortality is unacceptably high. Nanotechnology offers potential solutions to the historical challenge that has rendered breast cancer so difficult to contain and eradicate: the extreme biological diversity of the disease presentation in the patient population and in the evolutionary changes of any individual disease, the multiple pathways that drive disease progression, the onset of 'resistance' to established therapeutic cocktails, and the gravity of the side effects to treatment, which result from generally very poor distribution of the injected therapeutic agents in the body. A fundamental requirement for success in the development of new therapeutic strategies is that breast cancer specialists-in the clinic, the pharmaceutical and the basic biological laboratory-and nanotechnologists-engineers, physicists, chemists and mathematicians-optimize their ability to work in close collaboration. This further requires a mutual openness across cultural and language barriers, academic reward systems, and many other 'environmental' divides. This paper is respectfully submitted to the community to help foster the mutual interactions of the breast cancer world with micro- and nano-technology, and in particular to encourage the latter community to direct ever increasing attention to breast cancer, where an extraordinary beneficial impact may result. The paper initiates with an introductory overview of breast cancer, its current treatment modalities, and the current role of nanotechnology in the clinic. Our perspectives are then presented on what the greatest opportunities for nanotechnology are; this follows from an analysis of the role of biological barriers that adversely determine the biological distribution of intravascularly injected therapeutic agents. Different generations of nanotechnology tools for drug delivery are reviewed, and our current strategy for addressing the sequential bio-barriers is also presented, and is accompanied by an encouragement to the community to develop even more effective ones.

Novel technologies for antiangiogenic drug delivery in the brain

Antiangiogenic therapies aimed at inhibiting the formation of tumor vasculature hold great promise for cancer therapy, with multiple compounds currently undergoing clinical trials. As with many forms of chemotherapy, antiangiogenic drugs face numerous hurdles in their translation to clinical use. Many such promising agents exhibit a short half-life, low solubility, poor bioavailability and multiple toxic side effects. Furthermore, when targeting malignant brain tumors the blood-brain barrier represents a formidable obstacle, preventing drugs from penetrating into the central nervous system (CNS). In this review, we discuss several preclinical antiangiogenic therapies and describe issues related to the unique conditions in the brain with regard to cancer treatment and neurotoxicity. We focus on the limitations of antiangiogenic drugs in the brain, along with numerous solutions that involve novel biomaterials and nanotechnological approaches. We also discuss an example in which modifying the properties of an antiangiogenic compound enhanced its clinical efficacy in treating tumors while simultaneously mitigating undesirable neurological side-effects.

Nitric oxide synthase gene therapy enhances the toxicity of cisplatin in cancer cells

BACKGROUND

Nitric oxide (NO.) derived from donor drugs has been shown to be an effective chemosensitizer in vitro. We investigated the combination of inducible nitric oxide synthase (iNOS) gene transfer, driven by a strong constitutive promoter (cytomegalovirus; CMV) with the DNA cross-linking agent cisplatin in mouse and human tumour cell lines.

METHODS

Proof of principal experiments were performed in the radiation-induced fibrosarcoma-1 (RIF-1) murine cell line. Cells were transfected with constitutively expressed CMV/iNOS plasmid DNA using a cationic lipid vector, before exposure to cisplatin. In vivo efficacy was determined in an intradermal RIF-1 tumour model, with intraperitoneal administration of cisplatin. Additionally, treatment potential was investigated in various human tumour cell lines including human prostate (DU145 and PC3) and human colon (HT29 and HCT116) cancer cell lines. Experimental endpoints were established using western blot, Greiss test, clonogenic assay and tumour growth delay.

RESULTS

Transfection of RIF-1 tumour cells in vitro with the CMV/iNOS significantly enhanced the cytotoxicity of cisplatin (0.2-1.0 microM). In vivo transfer of CMV/iNOS by direct injection into established RIF-1 tumours caused a significant (p = 0.0027) delay in tumour growth. CMV/iNOS gene transfer in vitro resulted in the strong expression of iNOS DNA in all cell lines, and significantly increased levels of NO. in all cell lines except HCT116.

CONCLUSIONS

Significant chemosensitization of cisplatin cytotoxicity was observed in the presence of NO. derived from the overexpression iNOS. We conclude that p53 status of the various cell lines was unlikely to be responsible for cisplatin-induced apoptosis.

Near-infrared narrow-band imaging of gold/silica nanoshells in tumors

Gold nanoshells (GNS) are a new class of nanoparticles that can be optically tuned to scatter or absorb light from the near-ultraviolet to near-infrared (NIR) region by varying the core (dielectric silica)/shell (gold) ratio. In addition to spectral tunability, GNS are inert and bioconjugatable, making them potential labels for in vivo imaging and therapy of tumors. We report the use of GNS as exogenous contrast agents for enhanced visualization of tumors using narrow-band imaging (NBI). NBI takes advantage of the strong NIR absorption of GNS to distinguish between blood and nanoshells in the tumor by imaging in narrow wavelength bands in the visible and NIR, respectively. Using tissue-simulating phantoms, we determined the optimum wavelengths to enhance contrast between blood and GNS. We then used the optimum wavelengths for ex vivo imaging of tumors extracted from human colon cancer xenograft bearing mice injected with GNS. Systemically delivered GNS accumulated passively in tumor xenografts by the enhanced permeability and retention (EPR) effect. Ex vivo NBI of tumor xenografts demonstrated heterogeneous distribution of GNS with a clear distinction from the tumor vasculature. The results of this study demonstrate the feasibility of using GNS as contrast agents to visualize tumors using NBI.

Nanofabricated upconversion nanoparticles for photodynamic therapy

We present a novel process for the production of three-layer Composite Nanoparticles (CNPs) in the size range 100-300 nm with an up-converting phosphor interior, a coating of porphyrin photosensitizer, and a biocompatible PEG outer layer to prevent clearance by the reticuloendothelial system. We show that these CNPs produce millimolar amounts of singlet oxygen at NIR intensities far less than other two-photon techniques.

Targeted delivery with peptidomimetic conjugated self-assembled nanoparticles

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed.

Nanoshell-enabled photothermal cancer therapy: impending clinical impact

Much of the current excitement surrounding nanoscience is directly connected to the promise of new nanoscale applications in cancer diagnostics and therapy. Because of their strongly resonant light-absorbing and light-scattering properties that depend on shape, noble metal nanoparticles provide a new and powerful tool for innovative light-based approaches. Nanoshellsspherical, dielectric core, gold shell nanoparticleshave been central to the development of photothermal cancer therapy and diagnostics for the past several years. By manipulating nanoparticle shape, researchers can tune the optical resonance of nanoshells to any wavelength of interest. At wavelengths just beyond the visible spectrum in the near-infrared, blood and tissue are maximally transmissive. When nanoshell resonances are tuned to this region of the spectrum, they become useful contrast agents in the diagnostic imaging of tumors. When illuminated, they can serve as nanoscale heat sources, photothermally inducing cell death and tumor remission. As nanoshell-based diagnostics and therapeutics move from laboratory studies to clinical trials, this Account examines the highly promising achievements of this approach in the context of the challenges of this complex disease. More broadly, these materials present a concrete example of a highly promising application of nanochemistry to a biomedical problem. We describe the properties of nanoshells that are relevant to their preparation and use in cancer diagnostics and therapy. Specific surface chemistries are necessary for passive uptake of nanoshells into tumors and for targeting specific cell types by bioconjugate strategies. We also describe the photothermal temperature increases that can be achieved in surrogate structures known as tissue phantoms and the accuracy of models of this effect using heat transport analysis. Nanoshell-based photothermal therapy in several animal models of human tumors have produced highly promising results, and we include nanoparticle dosage information, thermal response, and tumor outcomes for these experiments. Using immunonanoshells, infrared diagnostic imaging contrast enhancement and photothermal therapy have been integrated into a single procedure. Finally, we examine a novel "Trojan horse" strategy for nanoparticle delivery that overcomes the challenge of accessing and treating the hypoxic regions of tumors, where blood flow is minimal or nonexistent. The ability to survive hypoxia selects aggressive cells which are likely to be the source of recurrence and metastasis. Treatment of these regions has been incredibly difficult. Ultimately, we look beyond the current research and assess the next challenges as nanoshell-based photothermal cancer therapy is implemented in clinical practice.

PEGylated nanostructured lipid carriers loaded with 10-hydroxycamptothecin: an efficient carrier with enhanced anti-tumour effects against lung cancer

Most drugs do not have the pharmacokinetic features required for optimal pulmonary delivery. In this study, we developed PEGylated nanostructured lipid carriers (PEG-NLCs) to improve the delivery of anti-tumour agents to lung tumours. PEG-40 NLCs modified with PEG-40 stearate (molecular weight 2000 Da), PEG-100 NLCs modified with PEG-100 stearate (molecular weight 5000 Da) and NLCs without PEG modification were prepared by melt-emulsification and homogenization, and were loaded with 10-hydroxycamptothecin (HCPT). They were investigated in terms of physiological characteristics, biodistribution, cellular uptake, and anti-tumour effect in-vivo. PEG-NLCs exhibited regular morphology, with a spherical shape. The particle size (measured by laser diffraction) was approximately 100 nm. Encapsulation in PEG-NLCs protected the active lactone form of HCPT compared with HCPT solution after incubation with plasma. In biodistribution studies, PEG-NLCs, especially PEG-40 NLCs, had longer circulation time and decreased uptake by the reticuloendothelial system (RES) compared with unmodified NLCs. PEG-NLCs accumulated in the lungs after i.v. injection in mice. PEG-NLCs showed enhanced cellular uptake by human lung adenocarcinoma epithelial A549 cells. In-vivo experiments indicated that PEG-NLCs loaded with HCPT have superior efficacy against A549 lung cancer compared with HCPT solution and NLCs. These results suggest that PEG-NLCs is a promising delivery system for HCPT in the treatment of lung cancer.

Photothermal therapy of Lewis lung carcinoma in mice using gold nanoshells on carboxylated polystyrene spheres

A new approach towards the design of gold nanoshells on carboxylated polystyrene spheres (GNCPSs) is reported here. Gold nanoshells were self-assembled on the surface of carboxylated polystyrene spheres by a seed growth method. Chitosan (CHI) was used as a functional agent of carboxylated polystyrene spheres for attaching gold seeds. The surface plasmon resonance (SPR) peak of GNCPSs can be tuned, greatly redshifted, over a broad spectral range including the near-infrared (NIR) wavelength region, which provides maximal penetration of light through tissue. Irradiation of GNCPSs at their peak extinction coefficient results in the conversion of light to heat energy that produces a local rise in temperature. Our study revealed that the Lewis lung carcinoma (LLC) in mice treated with GNCPSs exposed to a low dose of NIR light (808 nm, 4 W cm(-2)) induced irreversible tissue damage. The tumor volumes of the treatment group by GNCPSs were significantly lower than those of control groups, with an average inhibition rate over 55% (P<0.005). This study proves that GNCPSs are promising in plasmonic photothermal tumor therapy.