Delivery of molecular and cellular medicine to solid tumors

Antigen shedding may improve efficiencies for delivery of antibody-based anticancer agents in solid tumors

Recombinant immunotoxins (RIT) are targeted anticancer agents that are composed of a targeting antibody fragment and a protein toxin fragment. SS1P is a RIT that targets mesothelin on the surface of cancer cells and is being evaluated in patients with mesothelioma. Mesothelin, like many other target antigens, is shed from the cell surface. However, whether antigen shedding positively or negatively affects the delivery of RIT remains unknown. In this study, we used experimental data with SS1P to develop a mathematical model that describes the relationship between tumor volume changes and the dose level of the administered RIT, while accounting for the potential effects of antigen shedding.

Delivery of molecular and nanoscale medicine to tumors: transport barriers and strategies

Tumors are similar to organs, with unique physiology giving rise to an unusual set of transport barriers to drug delivery. Cancer therapy is limited by nonuniform drug delivery via blood vessels, inhomogeneous drug transport into tumor interstitium from the vascular compartment, and hindered transport through tumor interstitium to the target cells. Four major abnormal physical and physiological properties contribute to these transport barriers. Accumulated solid stress compresses blood vessels to diminish the drug supply to many tumor regions. Immature vasculature with high viscous and geometric resistances and reduced pressure gradients leads to sluggish and heterogeneous blood flow in tumors to further limit drug supply. Nonfunctional lymphatics coupled with highly permeable blood vessels result in elevated hydrostatic pressure in tumors to abrogate convective drug transport from blood vessels into and throughout most of the tumor tissue. Finally, a dense structure of interstitial matrix and cells serves as a tortuous, viscous, and steric barrier to diffusion of therapeutic agents. In this review, we discuss the origins and implications of these barriers. We then highlight strategies for overcoming these barriers by modulating either drug properties or the tumor microenvironment itself to enhance the delivery and effectiveness of drugs in tumors.

Antitumor effect of vascular endothelial growth factor inhibitor sunitinib in preclinical models of hepatocellular carcinoma

OBJECTIVE

Tumor recurrence and metastasis is the most common cause of mortality in hepatocellular carcinoma (HCC) patients. Despite positive results with vascular endothelial growth factor (VEGF) inhibitors in preclinical studies using HCC xenograft models, the clinical outcome in HCC patients has been disappointing. So far, only the multitargeted tyrosine kinase inhibitor sorafenib has been shown to significantly improve survival in HCC patients, suggesting that this class of agents could be effective against HCC. Recently, another VEGF inhibitor, sunitinib, showed survival benefits in HCC hepatitis B-positive patients, but failed to improve survival in HCC hepatitis C-positive patients. Obviously, concomitant liver disease, liver function in general, and the local liver environment have a huge impact on treatment outcomes. In this study, we aimed to examine the antiproliferative effect of sunitinib in different HCC cell lines in vitro, and then in xenograft and orthotopic models of HCC in order to assess the effect of the local liver vasculature on drug efficacy.

METHODS

Human cancer cell lines Huh7.5, Hep3B, and SK-Hep-1 were used for in-vitro studies. In in-vivo studies, each mouse carried Huh7.5 cells in both the subcutaneous and the intrahepatic compartment; therefore, drug exposure and treatment regimen were identical in both tumors.

RESULTS

Sunitinib has the potential to moderately inhibit proliferation in the Huh7.5 cell line, induce p53 in the p53-wild-type cell line SK-hep-1, and to increase the S-phase and the sub-G1 component of the cell cycle in the Hep3B cell line. Diverse responses to sunitinib in HCC cell lines emphasize the heterogeneity of HCC tumors and may further explain the discrepancy between preclinical and clinical results. The in-vivo results show that sunitinib treatment was far less effective against intrahepatic tumors compared with xenografts. Histological data indicate that large solid intrahepatic tumors are severely affected by sunitinib as shown by large areas of necrosis and diminished number of viable tumor cells.

CONCLUSION

The real problem when treating intrahepatic tumors with sunitanib and/or other VEGF inhibitors seems to arise from unopposed local growth of the small tumors and perhaps the development of distant micrometastases. Even though both xenograft and orthotopic models have limitations, these models add value to our understanding of tumor biology and help to better design treatment paradigms for patients with HCC. In comparison with xenograft models, the orthotopic HCC model allows for a more realistic assessment of drug efficacy in patients, in particular by enhancing our knowledge of the role that organ vasculature plays in the development of local metastasis and tumor resistance to antiangiogenic treatments.

PREPARATION OF GELATIN NANOPARTICLES WITH EGFR SELECTION ABILITY VIA BIOTINYLATED-EGF CONJUGATION FOR LUNG CANCER TARGETING

Lung cancer is the most malignant cancer today, and specific drug delivery has been developed for superior outcome. In this study, gelatin nanoparticles (GPs) were firstly employed as native carriers. Second, NeutrAvidinFITC was then grafted on the particle surface (GP-Av); finally much more amount of biotinylated EGF were able to be conjugated with NeutrAvidinFITC forming ligand- binding nanoparticles (GP-Av-bEGF) to enhance the targeting efficiency. These nanoparticles were applied as EGFR-seeking agents to detect lung cancer cells.

Results of particle characterization show that the modification process had no influence on size (230 nm). Round and smooth nanoparticles were observed by AFM. The surface property of nanoparticles was characterized by surface plasmon resonance (SPR) and flowcytometry analysis as well as by examining the interaction of the modified EGF on particle surface with the ability to recognize EGFR.

The binding ability of GPs with or without EGF modification is different. SPR assay showed that EGF-conjugated particles (GP-Av-bEGF) have stronger and faster bonding signal than the unmodified one (GP-Av). Free EGF competition results from SPR and A549 cell (lung adenocarcinoma cells) culture also confirmed the EGF receptormediated endocytosis mechanism for nanoparticles with EGF-modified binding. The in vitro targeting ability was confirmed by the uptake rate of different cells via flow cytometry assay. GP-Av-bEGF resulted in higher entrance efficiency on A549 than on normal lung cells (HFL1) and U2-OS (osteosarcoma cells) due to A549 possessing more amounts of EGFR. The targeting ability of GP-Av-bEGF nanoparticles with specific EGFR tracing ability was proved, which holds promise for further anticancer drug applications.

Triple stimulus-responsive polypeptide nanoparticles that enhance intratumoral spatial distribution

To address the limited tumor penetration of nanoparticle drug delivery vehicles, we report the first pH-responsive polypeptide micelle that dissociates at the low extracellular pH of solid tumors. This histidine-rich elastin-like polypeptide block copolymer self-assembles at 37 °C into spherical micelles that are stabilized by Zn(2+) and are disrupted as the pH drops from 7.4 to 6.4. These pH-sensitive micelles demonstrate better in vivo penetration and distribution in tumors than a pH-insensitive control.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Nanoscale drug delivery systems for enhanced drug penetration into solid tumors: current progress and opportunities

Poor penetration of anticancer drags into solid tumors significantly limits their efficacy. This phenomenon has long been observed for small-molecule chemotherapeutics, and it can be even more pronounced for nanoscale therapies. Nanoparticles have enormous potential for the treatment of cancer due to their wide applicability as drug delivery and imaging vehicles and their size-dependent accumulation into solid tumors by the enhanced permeability and retention (EPR) effect. Further, synthetic nanoparticles can be engineered to overcome barriers to drag delivery. Despite their promise for the treatment of cancer, relatively little work has been done to study and improve their ability to diffuse into solid tumors following passive accumulation in the tumor vasculature. In this review, we present the complex issues governing efficient penetration of nanoscale therapies into solid tumors. The current methods available to researchers to study nanoparticle penetration into malignant tumors are described, and the most recent works studying the penetration of nanoscale materials into solid tumors are summarized. We conclude with an overview of the important nanoparticle design parameters governing their tumor penetration, as well as by highlighting critical directions in this field.

Selective targeting of melanoma by PEG-masked protein-based multifunctional nanoparticles

Background

Nanoparticle-based systems are promising for the development of imaging and therapeutic agents. The main advantage of nanoparticles over traditional systems lies in the possibility of loading multiple functionalities onto a single molecule, which are useful for therapeutic and/or diagnostic purposes. These functionalities include targeting moieties which are able to recognize receptors overexpressed by specific cells and tissues. However, targeted delivery of nanoparticles requires an accurate system design. We present here a rationally designed, genetically engineered, and chemically modified protein-based nanoplatform for cell/tissue-specific targeting.

Methods

Our nanoparticle constructs were based on the heavy chain of the human protein ferritin (HFt), a highly symmetrical assembly of 24 subunits enclosing a hollow cavity. HFt-based nanoparticles were produced using both genetic engineering and chemical functionalization methods to impart several functionalities, ie, the α-melanocyte-stimulating hormone peptide as a melanoma-targeting moiety, stabilizing and HFt-masking polyethylene glycol molecules, rhodamine fluorophores, and magnetic resonance imaging agents. The constructs produced were extensively characterized by a number of physicochemical techniques, and assayed for selective melanoma-targeting in vitro and in vivo.

Results

Our HFt-based nanoparticle constructs functionalized with the α-melanocyte-stimulating hormone peptide moiety and polyethylene glycol molecules were specifically taken up by melanoma cells but not by other cancer cell types in vitro. Moreover, experiments in melanoma-bearing mice indicate that these constructs have an excellent tumor-targeting profile and a long circulation time in vivo.

Conclusion

By masking human HFt with polyethylene glycol and targeting it with an α-melanocyte-stimulating hormone peptide, we developed an HFt-based melanoma-targeting nanoplatform for application in melanoma diagnosis and treatment. These results could be of general interest, because the same strategy can be exploited to develop ad hoc nanoplatforms for specific delivery towards any cell/tissue type for which a suitable targeting moiety is available.

In vitro application of paclitaxel loaded magnetoliposomes for combined chemotherapy and hyperthermia

Paclitaxel loaded thermosensitive magnetoliposomes containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-glycerol (PG) were prepared by thin film hydration method. Encapsulation efficiencies of paclitaxel and citric acid coated Fe(3)O(4) nanoparticles were 83±3% and 74.6±5%, respectively. Based on the release study, DPPC/PG in 9:1 (w/w) liposomes (PCPG) formulation was found to be thermosensitive and showed 46 fold higher drug release at 43 °C than at 37 °C. Drug release was done under an alternating magnetic field of intensity 10 kA/m and a fixed frequency of 423 kHz. In-vitro cytotoxicity and hyperthermia studies were carried out using a human cervical cancer cell line (HeLa). IC(50) value of the magnetoliposomes formulation was 100 nM. When the magnetoliposomes with 100 nM drug was used to treat HeLa cells in combination with hyperthermia under AC magnetic field, 89% cells were killed and were found to be more effective than either hyperthermia or chemotherapy alone. So, PCPG liposomes which co-encapsulate both Fe(3)O(4) nanoparticles and paclitaxel may be useful for combined chemotherapy and hyperthermia.

How stereological analysis of vascular morphology can quantify the blood volume fraction as a marker for tumor vasculature: comparison with magnetic resonance imaging

To assess angiogenesis noninvasively in a C6 rat brain tumor model, the rapid-steady-state-T(1) (RSST(1)) magnetic resonance imaging (MRI) method was used for microvascular blood volume fraction (BVf) quantification with a novel contrast agent gadolinium per (3,6 anhydro) α-cyclodextrin (Gd-ACX). In brain tissue contralateral to the tumor, equal BVfs were obtained with Gd-ACX and the clinically approved gadoterate meglumine (Gd-DOTA). Contrary to Gd-DOTA, which leaks out of the tumor vasculature, Gd-ACX was shown to remain vascular in the tumor tissue allowing quantification of the tumor BVf. We sought to confirm the obtained tumor BVf using an independent method: instead of using a 'standard' two-dimensional histologic method, we study here how vascular morphometry combined with a stereological technique can be used for three-dimensional assessment of the vascular volume fraction (V(V)). The V(V) is calculated from the vascular diameter and length density. First, the technique is evaluated on simulated data and the healthy rat brain vasculature and is then applied to the same C6 tumor vasculature previously quantified by RSST(1)-MRI with Gd-ACX. The mean perfused V(V) and the BVf obtained by MRI in tumor regions are practically equal and the technique confirms the spatial heterogeneity revealed by MRI.

The tumor microenvironment is a dominant force in multidrug resistance

The emergence of clinical drug resistance is still one of the most challenging factors in cancer treatment effectiveness. Until more recently, the assumption has been that random genetic lesions are sufficient to explain the progression of malignancy and escape from chemotherapy. Here we propose an additional perspective, one in which the tumor cells despite the malignant genome could find a microenvironment either within the tumor or as a dormant cell to remain polar and blend into an organized context. Targeting this dynamic interplay could be considered a new avenue to prevent therapeutic resistance, and may even provide a promising effective cancer treatment.

Radiolabeled antibodies for cancer imaging and therapy

Radiolabeled antibodies were studied first for tumor detection by single-photon imaging, but FDG PET stopped these developments. In the meantime, radiolabeled antibodies were shown to be effective in the treatment of lymphoma. Radiolabeling techniques are well established and radiolabeled antibodies are a clinical and commercial reality that deserves further studies to advance their application in earlier phase of the diseases and to test combination and adjuvant therapies including radiolabeled antibodies in hematological diseases. In solid tumors, more resistant to radiations and less accessible to large molecules such as antibodies, clinical efficacy remains limited. However, radiolabeled antibodies used in minimal or small-size metastatic disease have shown promising clinical efficacy. In the adjuvant setting, ongoing clinical trials show impressive increase in survival in otherwise unmanageable tumors. New technologies are being developed over the years: recombinant antibodies and pretargeting approaches have shown potential in increasing the therapeutic index of radiolabeled antibodies. In several cases, clinical trials have confirmed preclinical studies. Finally, new radionuclides, such as lutetium-177, with better physical properties will further improve the safety of radioimmunotherapy. Alpha particle and Auger electron emitters offer the theoretical possibility to kill isolated tumor cells and microscopic clusters of tumor cells, opening the perspective of killing the last tumor cell, which is the ultimate challenge in cancer therapy. Preliminary preclinical and preliminary clinical results confirm the feasibility of this approach.

Synergy in cancer treatment between liposomal chemotherapeutics and thermal ablation

Minimally invasive image-guided tumor ablation using short duration heating via needle-like applicators using energies such as radiofrequency or microwave has seen increasing clinical use to treat focal liver, renal, breast, bone, and lung tumors. Potential benefits of this thermal therapy include reduced morbidity and mortality compared to standard surgical resection and ability to treat non-surgical patients. However, improvements to this technique are required as achieving complete ablation in many cases can be challenging particularly at margins of tumors>3 cm in diameter and adjacent to blood vessels. Thus, one very promising strategy has been to combine thermal tumor ablation with adjuvant nanoparticle-based chemotherapy agents to improve efficiency. Here, we will primarily review principles of thermal ablation to provide a framework for understanding the mechanisms of combination therapy, and review the studies on combination therapy, including presenting preliminary data on the role of such variables as nanoparticle size and thermal dose on improving combination therapy outcome. We will discuss how thermal ablation can also be used to improve overall intratumoral drug accumulation and nanoparticle content release. Finally, in this article we will further describe the appealing off-shoot approach of utilizing thermal ablation techniques not as the primary treatment, but rather, as a means to improve efficiency of intratumoral nanoparticle drug delivery.

Single-chain antibody-based immunotoxins targeting Her2/neu: design optimization and impact of affinity on antitumor efficacy and off-target toxicity

Recombinant immunotoxins, consisting of single-chain variable fragments (scFv) genetically fused to polypeptide toxins, represent potentially effective candidates for cancer therapeutics. We evaluated the affinity of various anti-Her2/neu scFv fused to recombinant gelonin (rGel) and its effect on antitumor efficacy and off-target toxicity. A series of rGel-based immunotoxins were created from the human anti-Her2/neu scFv C6.5 and various affinity mutants (designated ML3-9, MH3-B1, and B1D3) with affinities ranging from 10(-8) to 10(-11) mol/L. Against Her2/neu-overexpressing tumor cells, immunotoxins with increasing affinity displayed improved internalization and enhanced autophagic cytotoxicity. Targeting indices were highest for the highest affinity B1D3/rGel construct. However, the addition of free Her2/neu extracellular domain (ECD) significantly reduced the cytotoxicity of B1D3/rGel because of immune complex formation. In contrast, ECD addition had little impact on the lower affinity constructs in vitro. In vivo studies against established BT474 M1 xenografts showed growth suppression by all immunotoxins. Surprisingly, therapy with the B1D3-rGel induced significant liver toxicity because of immune complex formation with shed Her2/neu antigen in circulation. The MH3-B1/rGel construct with intermediate affinity showed effective tumor growth inhibition without inducing hepatotoxicity or complex formation. These findings show that while high-affinity constructs can be potent antitumor agents, they may also be associated with mistargeting through the facile formation of complexes with soluble antigen leading to significant off-target toxicity. Constructs composed of intermediate-affinity antibodies are also potent agents that are more resistant to immune complex formation. Therefore, affinity is an exceptionally important consideration when evaluating the design and efficacy of targeted therapeutics.

Microbubble-mediated ultrasonic techniques for improved chemotherapeutic delivery in cancer

BACKGROUND

Ultrasound (US) exposed microbubble (MB) contrast agents have the capability to transiently enhance cell membrane permeability. Using this technique in cancer treatment to increase the efficiency of chemotherapy through passive, localized delivery has been an emerging area of research.

PURPOSE

Investigation of the influence of US parameters on MB-mediated drug delivery in cancer.

METHODS

The 2LMP breast cancer cells were used for in vitro experiments and 2LMP tumor-bearing mice were used during in vivo experiments. Changes in membrane permeability were investigated after the influence of MB-mediated US therapy parameters (i.e. frequency, mechanical index, pulse repetition period, US duration, and MB dosing and characteristics) on cancer cells. Calcein, a non-permeable fluorescent molecule, and Taxol, chemotherapeutic, were used to evaluate membrane permeability. Tumor response was also assessed histologically.

RESULTS

Combination chemotherapy and MB-mediated US therapy with optimized parameters increased cancer cell death by 50% over chemotherapy alone.

DISCUSSION

Increased cellular uptake of chemotherapeutic was dependent upon US system parameters.

CONCLUSION

Optimized MB-mediated US therapy has the potential to improve cancer patient response to therapy via increased localized drug uptake, which may lead to a lowering of chemotherapeutic drug dosages and systemic toxicity.

Increased vascular delivery and efficacy of chemotherapy after inhibition of platelet-derived growth factor-B

Inhibition of platelet-derived growth factor-B (PDGF-B) has multiple effects on tumors, including loss of pericytes, regression of some vessels, normalization of other vessels, and reduction of interstitial pressure. PDGF-B inhibition also increases the efficacy of cancer therapeutics, but the role on tumor vessel efficiency and drug delivery is unclear. We sought to determine whether inhibition of PDGF-B signaling can increase delivery and efficacy of cyclophosphamide in Lewis lung carcinomas or RIP-Tag2 tumors. PDGF-B blockade in Lewis lung carcinoma tumors by the DNA aptamer AX102 for 14 days increased the number of perfused tumor vessels marked by lectin in the bloodstream by 50%. AX102 also increased the width of sleeves of viable tumor cells around blood vessels by 66%, increased tumor cell proliferation by 90%, and increased intratumoral delivery of Hoechst 33342 by 78%. A low dose of cyclophosphamide (20 mg/kg) reduced tumor cell proliferation by 31% when combined with AX102 but not when given alone. Synergy of cyclophosphamide and AX102 on tumor cell proliferation also was found in RIP-Tag2 tumors. Similarly, the PDGF receptor signaling inhibitor imatinib increased delivery of cyclophosphamide and reduced tumor burden in RIP-Tag2 mice, without evidence of tumor cell sensitization to chemotherapy. Together, these findings indicate that inhibition of PDGF-B signaling promotes the delivery and efficacy of chemotherapeutic agents by increasing the efficiency of tumor blood vessels.

Nanoparticle-based biocompatible and targeted drug delivery: characterization and in vitro studies

Paclitaxel nanoparticles (PAX NPs) prepared with the size of 110 ± 10 nm and ζ potential of -40 ± 3 mV were encapsulated in synthetic/biomacromolecule shell chitosan, dextran-sulfate using a layer-by-layer self-assembly technique. Zeta potential measurements, analysis of X-ray photoelectron spectroscopy, and scanning electron microscopy confirmed the successful adsorption of each layer. Surface modifications of these core-shell NPs were performed by covalently conjugating with poly(ethylene glycol) (H(2)N-PEG-carboxymethyl, M(w) 3400) and fluorescence labeled wheat germ agglutinin (F-WGA) to build a biocompatible and targeted drug delivery system. 32% of PAX was released from four bilayers of biomacromolecule assembled NPs within 8 h as compared with >85% of the drug released from the bare NPs. Moreover, high cell viability with PEG conjugation and high binding capacity of WGA-modified NPs with Caco-2 cells were observed. This biocompatible and targeted NP-based drug delivery system, therefore, may be considered as a potential candidate for the treatment of colonic cancer and other diseases.

Intratumoral drug delivery with nanoparticulate carriers

Stiff extracellular matrix, elevated interstitial fluid pressure, and the affinity for the tumor cells in the peripheral region of a solid tumor mass have long been recognized as significant barriers to diffusion of small-molecular-weight drugs and antibodies. However, their impacts on nanoparticle-based drug delivery have begun to receive due attention only recently. This article reviews biological features of many solid tumors that influence transport of drugs and nanoparticles and properties of nanoparticles relevant to their intratumoral transport, studied in various tumor models. We also discuss several experimental approaches employed to date for enhancement of intratumoral nanoparticle penetration. The impact of nanoparticle distribution on the effectiveness of chemotherapy remains to be investigated and should be considered in the design of new nanoparticulate drug carriers.

Extravasation of polymeric nanomedicines across tumor vasculature

Tumor microvasculature is fraught with numerous physiological barriers which hinder the efficacy of anticancer agents. These barriers include chaotic blood supply, poor tumor vasculature permeability, limited transport across the interstitium due to high interstitial pressure and absence of lymphatic network. Abnormal microvasculature also leads to hypoxia and acidosis which limits effectiveness of chemotherapy. These barriers restrict drug or drug carrier extravasation which hampers tumor regression. Targeting key features of the tumor microenvironment such as tumor microvessels, interstitial hypertension and tumor pH is a promising approach to improving the efficacy of anticancer drugs. This review highlights the current knowledge on the distinct tumor microenvironment generated barriers which limit extravasation of drugs and focuses on modalities for overcoming these barriers using multi-functional polymeric carriers. Special attention is given to utilizing polymeric nanomedicines to facilitate extravasation of anticancer drugs for future cancer therapy.

Differential distribution of blood-derived proteins in xenografted human adenocarcinoma tissues by in vivo cryotechnique and cryobiopsy

Tumor behavior depends on the complex tumor interstitium and microenvironment, which influence transport of fluid and soluble molecules from blood vessels. The purpose of this study was to reveal how complex tumor tissues affect the immunodistribution of serum proteins and time-dependent translocation of bovine serum albumin (BSA) from blood vessels, using relatively differentiated human adenocarcinoma produced by the xenografted A549 cell line. Histological architecture and immunodistribution of the serum proteins in adenocarcinomatous tissues were clearly detected by the in vivo cryotechnique and cryobiopsy. Both albumin and IgG1 were detected in blood vessels, connective tissues around the tumor mass, and the interstitium among tumor cell nests. IgM was mainly detected in blood vessels and connective tissues around the tumor mass but was not detected in the interstitium among the tumor cell nests. At 10 or 30 min after BSA injection, BSA was observed only in blood vessels, but 1 h after the injection, it was also detected in the interstitium and surrounding connective tissues of the tumor mass. The present findings showed topographic variation of molecular permeation in the adenocarcinomatous tumor mass. The interstitial tissues with augmented permeability of serum proteins would increase accessibility of tumor cells to blood-derived molecules.

Methylselenocysteine: a promising antiangiogenic agent for overcoming drug delivery barriers in solid malignancies for therapeutic synergy with anticancer drugs

INTRODUCTION

Despite progress, chemotherapeutic response in solid malignancies has remained limited. Although initial results of the use of antiangiogenic agents in combination chemotherapy indicated an enhanced therapeutic response, recent data indicate that the surviving cancer is not only able to surmount therapy, but also actually able to adapt a more aggressive metastatic phenotype. Thus, selecting an antiangiogenic agent that is less likely to lead to tumor resurgence is a key to future therapeutic success of antiangiogenic agents in a combinatorial setting.

AREAS COVERED

Against the broad spectrum of antiangiogenic agents used at present in the clinic, the putative benefits of the use of organoselenium compounds, such as methylselenocysteine (MSC), are discussed in this review.

EXPERT OPINION

MSC, being part of the mammalian physiology, is a well-tolerated, versatile and economical antiangiogenic agent. It downregulates multiple key upstream tumor survival markers, and enhances tumor drug delivery, at a given systemic dose of an anticancer agent, while protecting normal tissue from cytotoxic adverse effects. Further clinical trials, especially in poorly differentiated cancers, are warranted.

Improving drug potency and efficacy by nanocarrier-mediated subcellular targeting

Nanocarrier-mediated drug targeting is an emerging strategy for cancer therapy and is being used, for example, with chemotherapeutic agents for ovarian cancer. Nanocarriers are selectively accumulated in tumors as a result of their enhanced permeability and retention of macromolecules, thereby enhancing the antitumor activity of the nanocarrier-associated drugs. We investigated the real-time subcellular fate of polymeric micelles incorporating (1,2-diaminocyclohexane) platinum(II) (DACHPt/m), the parent complex of oxaliplatin, in tumor tissues by fluorescence-based assessment of their kinetic stability. These observations revealed that DACHPt/m was extravasated from blood vessels to the tumor tissue and dissociated inside each cell. Furthermore, DACHPt/m selectively dissociated within late endosomes, enhancing drug delivery to the nearby nucleus relative to free oxaliplatin, likely by circumvention of the cytoplasmic detoxification systems such as metallothionein and methionine synthase. Thus, these drug-loaded micelles exhibited higher antitumor activity than did oxaliplatin alone, even against oxaliplatin-resistant tumors. These findings suggest that nanocarriers targeting subcellular compartments may have considerable benefits in clinical applications.

Overcoming in vivo barriers to targeted nanodelivery

Nanoparticles have been investigated as promising nanocarriers for delivery of imaging and therapeutic agents for several decades, but have met with limited success. Although enormous progress in the fields of nanotechnology and nanoscience has been achieved, basic discoveries have not yet translated into effective targeted therapies. Nanoparticles can potentially improve the pharmacokinetics and pharmacodynamics of drugs; however, the complexity of in vivo systems imposes multiple barriers that severely inhibit efficiency and have to be overcome to fully exploit the theoretical potential of nanoparticles. Here, we address two major challenges to effective systemic nanodelivery. Both limited penetration across the vascular endothelium and uptake by the reticuloendothelial system (RES) substantially impede effectiveness of nanoparticle delivery into tissues. Although the design of nanoparticles with extended circulation half-life is essential, it is not sufficient for effective penetration of nanoparticles across the formidable barrier formed by the vascular endothelium. Current nanodelivery systems rely on passive transvascular exchange and tissue accumulation. They require high dosages to create large concentration gradients that drive nanoparticles passively across the blood-tissue interface. However, passive accumulation has resulted in only a fractional dosage of nanoparticles penetrating into target tissue. This inevitably diminishes therapeutic efficacy and aggravates potential side effects. Although there are multiple ways to augment passive delivery, active delivery of targeted nanoparticles across the vascular endothelium could significantly increase the therapeutic index and decrease side effects of nanoparticle-based drug delivery systems. Use of active transendothelial transport pathways, such as caveolae, may provide an effective solution to both target and deliver nanoparticles.

Nanomaterials for cancer therapy and imaging

A variety of organic and inorganic nanomaterials with dimensions below several hundred nanometers are recently emerging as promising tools for cancer therapeutic and diagnostic applications due to their unique characteristics of passive tumor targeting. A wide range of nanomedicine platforms such as polymeric micelles, liposomes, dendrimers, and polymeric nanoparticles have been extensively explored for targeted delivery of anti-cancer agents, because they can accumulate in the solid tumor site via leaky tumor vascular structures, thereby selectively delivering therapeutic payloads into the desired tumor tissue. In recent years, nanoscale delivery vehicles for small interfering RNA (siRNA) have been also developed as effective therapeutic approaches to treat cancer. Furthermore, rationally designed multi-functional surface modification of these nanomaterials with cancer targeting moieties, protective polymers, and imaging agents can lead to fabrication versatile theragnostic nanosystems that allow simultaneous cancer therapy and diagnosis. This review highlights the current state and future prospects of diverse biomedical nanomaterials for cancer therapy and imaging.

Magnetotactic bacteria penetration into multicellular tumor spheroids for targeted therapy

Preliminary experiments showed that MC-1 magnetotactic bacteria (MTB) could be used for the delivery of therapeutic agents to tumoral lesions. Each bacterium can provide a significant thrust propulsion force generated by two flagella bundles exceeding 4pN. Furthermore, a chain of single-domain magnetosomes embedded in the cell allows computer directional control and tracking using a magnetic resonance imaging (MRI) system. Although these embedded functionalities suggest that MTB when under the influence of an external computer could be considered as biological microrobots with the potential of targeting tumors, little is known about their level of penetration in tumoral tissues. In this paper, in vitro experiments were performed to assess the capability of these bacteria to penetrate tumor tissue for the delivery of therapeutic agents. Multicellular tumor spheroids were used since they reproduce many properties of solid tumors. The results show the ability of these MTB when submitted to a directional magnetic field to penetrate inside a 3D multicellular tumor spheroid through openings present in the tissue.

Polymeric nanoparticles for photodynamic therapy

Photodynamic therapy is a relatively new clinical therapeutic modality that is based on three key components: photosensitizer, light, and molecular oxygen. Nanoparticles, especially targeted ones, have recently emerged as an efficient carrier of drugs or contrast agents, or multiple kinds of them, with many advantages over molecular drugs or contrast agents, especially for cancer detection and treatment. This paper describes the current status of PDT, including basic mechanisms, applications, and challenging issues in the optimization and adoption of PDT; as well as recent developments of nanoparticle-based PDT agents, their advantages, designs and examples of in vitro and in vivo applications, and demonstrations of their capability of enhancing PDT efficacy over existing molecular drug-based PDT.

Shape-specific polymeric nanomedicine: emerging opportunities and challenges

Size and shape are fundamental properties of micro/nanoparticles that are critically important for nanomedicine applications. Extensive studies have revealed the effect of particle size on spherical particles with respect to circulation, extravasation and distribution in vivo. In contrast, the importance of particle shape has only recently begun to emerge. For example, cylindrically-shaped filomicelles (diameter 22–60 nm, length 8–18 μm) have shown persistent blood circulation for up to one week after intravenous injection, much longer than their spherical counterparts. Disc-shaped nanoparticles have demonstrated higher in vivo targeting specificity to endothelial cells expressing intercellular adhesion molecule receptors in mice than spherical particles of similar size. In this Minireview, we will discuss the recent advances in the fabrication of shape-specific nanoparticles and their unique biological and pharmacological properties. Computational models are presented to provide mechanistic understanding of the shape effects on cell targeting under flow conditions. Shape-specific nanoparticles have the potential to significantly improve the performance of nanomedicine in diagnostic imaging and targeted drug delivery applications.

Evaluation of tumor microenvironment in an animal model using a nanoparticle contrast agent in computed tomography imaging

RATIONALE AND OBJECTIVES

Non-invasive longitudinal imaging of tumor vasculature could provide new insights into the development of solid tumors, facilitating efficient delivery of therapeutics. In this study, we report three-dimensional imaging and characterization of tumor vascular architecture using a nanoparticle contrast agent and high-resolution computed tomography (CT) imaging.

MATERIALS AND METHODS

Five Balb/c mice implanted with 4T1/Luc syngeneic breast tumors cells were used for the study. The nanoparticle contrast agent was systemically administered and longitudinal CT imaging was performed pre-contrast and at serial time points post-contrast, for up to 7 days for studying the characteristics of tumor-associated blood vessels. Gene expression of tumor angiogenic biomarkers was measured using quantitative real-time polymerase chain reaction.

RESULTS

Early-phase imaging demonstrated the presence of co-opted and newly developed tumor vessels. The co-opted vessels demonstrated wall-permeability and "leakiness" characteristics evident by an increase in extravascular nanoparticle-based signal enhancement visible well beyond the margins of tumor. Diameters of tumor-associated vessels were larger than the contralateral normal vessels. Delayed-phase imaging also demonstrated significant accumulation of nanoparticle contrast agent both within and in areas surrounding the tumor. A heterogeneous pattern of signal enhancement was observed both within and among individual tumors. Gene-expression profiling demonstrated significant variability in several angiogenic biomarkers both within and among individual tumors.

CONCLUSIONS

The nanoparticle contrast agent and high-resolution CT imaging facilitated visualization of co-opted and newly developed tumors vessels as well as imaging of nanoparticle accumulation within tumors. The use of this agent could provide novel insights into tumor vascular biology and could have implications on the monitoring of tumor status.

Nucleic acid aptamers for clinical diagnosis: cell detection and molecular imaging

Nucleic acid aptamers have recently attracted significant attention in the field of clinical diagnosis because they have numerous merits, such as high affinity, high specificity, small size, little immunogenicity, stable structures, and ease of synthesis. This review focuses on discussing the potential applications of aptamers in cell detection and molecular imaging. For the ex vivo cell detection, this review discusses the status of five strategies: endogenous nucleic acid analysis, flow cytometry analysis, nanoparticle-based cell sensing, microfluidic cell separation, and histological examination. This review also discusses in vivo molecular and cell imaging by introducing aptamer-based molecular imaging, cell imaging, and integrated imaging and therapy. On the basis of the status of these promising studies, this review summarizes several challenging issues and unmet needs that may require more effort or attention in the future.

Delivering nanomedicine to solid tumors

Recent advances in nanotechnology have offered new hope for cancer detection, prevention, and treatment. While the enhanced permeability and retention effect has served as a key rationale for using nanoparticles to treat solid tumors, it does not enable uniform delivery of these particles to all regions of tumors in sufficient quantities. This heterogeneous distribution of therapeutics is a result of physiological barriers presented by the abnormal tumor vasculature and interstitial matrix. These barriers are likely to be responsible for the modest survival benefit offered by many FDA-approved nanotherapeutics and must be overcome for the promise of nanomedicine in patients to be realized. Here, we review these barriers to the delivery of cancer therapeutics and summarize strategies that have been developed to overcome these barriers. Finally, we discuss design considerations for optimizing the delivery of nanoparticles to tumors.

The brain microenvironment and cancer metastasis

The process of metastasis consists of a series of sequential, selective steps that few cells can complete. The outcome of cancer metastasis depends on multiple interactions between metastatic cells and homeostatic mechanisms that are unique to one or another organ microenvironment. The specific organ microenvironment determines the extent of cancer cell proliferation, angiogenesis, invasion and survival. Many lung cancer, breast cancer, and melanoma patients develop fatal brain metastases that do not respond to therapy. The blood-brain barrier is intact in and around brain metastases that are smaller than 0.25 mm in diameter. Although the blood-brain barrier is leaky in larger metastases, the lesions are resistant to many chemotherapeutic drugs. Activated astrocytes surround and infiltrate brain metastases. The physiological role of astrocytes is to protect against neurotoxicity. Our current data demonstrate that activated astrocytes also protect tumor cells against chemotherapeutic drugs.

Increasing tumoral 5-fluorouracil concentrations during a 5-day continuous infusion: a microdialysis study

Purpose

Response to anticancer therapy is believed to be directly related to the concentration of the anticancer drug in the tumor itself. Assessment of intra-tumor drug pharmacokinetics can be helpful to gain more insight into mechanisms involved in the (in)sensitivity of tumors to anticancer therapy. We explored the pharmacokinetics of 5-fluorouracil in both plasma and tumor tissue during a 5-day continuous infusion of 5-fluorouracil in patients with cancer. Sampling for measurement of 5-fluorouracil in tumor tissue was performed using microdialysis.

Experimental design

In seven patients with an accessible (sub)cutaneous tumor treated with a continuous 5-fluorouracil infusion, plasma and microdialysate samples from tumor and normal adipose tissue were collected over a period of 5 days.

Results

For six patients, drug concentrations in both tumor tissue and plasma were available. Concentration–time curves of unbound 5-fluorouracil were lower in tumor tissue compared to the curves in plasma, but exposure ratios of tumor tissue versus plasma increased during the 5-day infusion period. The presence of circadian rhythmicity of 5-fluorouracil pharmacokinetics in the tumor itself was demonstrated as 5-fluorouracil concentrations in tumor extracellular fluid were higher during the night than during daytime.

Conclusion

Microdialysis was successfully employed in patients with cancer during a continuous 5-day 5-fluorouracil infusion. Plasma and tumor pharmacokinetics of 5-fluorouracil differed substantially with increasing 5-fluorouracil concentrations in tumor over time, possibly resulting from a lowered interstitial fluid pressure by 5-fluorouracil itself. This microdialysis 5-fluorouracil model might be useful to monitor the effect of drug delivery modulating strategies in future studies.

Stimulus-responsive macromolecules and nanoparticles for cancer drug delivery

Nanoparticles and macromolecular carriers have been widely used to increase the efficacy of chemotherapeutics, largely through passive accumulation provided by the enhanced permeability and retention effect. Stimulus-responsive peptide and polymer vehicles can further enhance the efficacy of antitumor therapeutics compared with the administration of free drug by three mechanisms: increasing the overall accumulation within solid tumors; providing a homogeneous spatial distribution in tumor tissues; and increasing the intracellular localization of anticancer therapeutics. This article highlights recent developments in 'smart' - stimulus-responsive - peptide, polymer and lipid drug carriers designed to enhance the localization and efficacy of therapeutic payloads as compared with free drug.

Biomedical Nanomagnetics: A Spin Through Possibilities in Imaging, Diagnostics, and Therapy

Biomedical nanomagnetics is a multidisciplinary area of research in science, engineering and medicine with broad applications in imaging, diagnostics and therapy. Recent developments offer exciting possibilities in personalized medicine provided a truly integrated approach, combining chemistry, materials science, physics, engineering, biology and medicine, is implemented. Emphasizing this perspective, here we address important issues for the rapid development of the field, i.e., magnetic behavior at the nanoscale with emphasis on the relaxation dynamics, synthesis and surface functionalization of nanoparticles and core-shell structures, biocompatibility and toxicity studies, biological constraints and opportunities, and in vivo and in vitro applications. Specifically, we discuss targeted drug delivery and triggered release, novel contrast agents for magnetic resonance imaging, cancer therapy using magnetic fluid hyperthermia, in vitro diagnostics and the emerging magnetic particle imaging technique, that is quantitative and sensitive enough to compete with established imaging methods. In addition, the physics of self-assembly, which is fundamental to both biology and the future development of nanoscience, is illustrated with magnetic nanoparticles. It is shown that various competing energies associated with self-assembly converge on the nanometer length scale and different assemblies can be tailored by varying particle size and size distribution. Throughout this paper, while we discuss our recent research in the broad context of the multidisciplinary literature, we hope to bridge the gap between related work in physics/chemistry/engineering and biology/medicine and, at the same time, present the essential concepts in the individual disciplines. This approach is essential as biomedical nanomagnetics moves into the next phase of innovative translational research with emphasis on development of quantitative in vivo imaging, targeted and triggered drug release, and image guided therapy including validation of delivery and therapy response.

Peptidic tumor targeting agents: the road from phage display peptide selections to clinical applications

Cancer has become the number one cause of death amongst Americans, killing approximately 1,600 people per day. Novel methods for early detection and the development of effective treatments are an eminent priority in medicine. For this reason, isolation of tumor-specific ligands is a growing area of research. Tumor-specific binding agents can be used to probe the tumor cell surface phenotype and to customize treatment accordingly by conjugating the appropriate cell-targeting ligand to an anticancer drug. This refines the molecular diagnosis of the tumor and creates guided drugs that can target the tumor while sparing healthy tissues. Additionally, these targeting agents can be used as in vivo imaging agents that allow for earlier detection of tumors and micrometastasis. Phage display is a powerful technique for the isolation of peptides that bind to a particular target with high affinity and specificity. The biopanning of intact cancer cells or tumors in animals can be used as the bait to isolate peptides that bind to cancer-specific cell surface biomarkers. Over the past 10 years, unbiased biopanning of phage-displayed peptide libraries has generated a suite of cancer targeting peptidic ligands. This review discusses the recent advances in the isolation of cancer-targeting peptides by unbiased biopanning methods and highlights the use of the isolated peptides in clinical applications.

Spatiotemporal temperature distribution and cancer cell death in response to extracellular hyperthermia induced by gold nanorods

Plasmonic nanoparticles have shown promise in hyperthermic cancer therapy, both in vitro and in vivo. Previous reports have described hyperthermic ablation using targeted and nontargeted nanoparticles internalized by cancer cells, but most reports do not describe a theoretical analysis for determining optimal parameters. The focus of the current research was first to evaluate the spatiotemporal temperature distribution and cell death induced by extracellular hyperthermia in which gold nanorods (GNRs) were maintained in the dispersion outside human prostate cancer cells. The nanorod dispersion was irradiated with near-infrared (NIR) laser, and the spatiotemporal distribution of temperature was determined experimentally. This information was employed to develop and validate theoretical models of spatiotemporal temperature profiles for gold nanorod dispersions undergoing laser irradiation and the impact of the resulting heat generation on the viability of human prostate cancer cells. A cell injury/death model was then coupled to the heat transfer model to predict spatial and temporal variations in cell death and injury. The model predictions agreed well with experimental measurements of both temperature and cell death profiles. Finally, the model was extended to examine the impact of selective binding of gold nanorods to cancer cells compared to nonmalignant cells, coupled with a small change in cell injury activation energy. The impact of these relatively minor changes results in a dramatic change in the overall cell death rate. Taken together, extracellular hyperthermia using gold nanorods is a promising strategy, and tailoring the cellular binding efficacy of nanorods can result in varying therapeutic efficacies using this approach.

Drug delivery systems for intraperitoneal therapy

Disorders associated with the peritoneal cavity include peritoneal adhesions and intraperitoneal (IP) malignancies. To prevent peritoneal adhesions, physical barrier devices are used to prevent organs from contacting other structures in the abdomen and forming adhesions, or pharmacological agents that interfere with adhesion formation are administered intraperitoneally. IP malignancies are other disorders confined to the peritoneal cavity, which are treated by combination of surgical removal and chemotherapy of the residual tumor. IP drug delivery helps in the regional therapy of these disorders by providing relatively high concentration and longer half-life of a drug in the peritoneal cavity. Various studies suggest that IP delivery of anti-neoplastic agents is a promising approach for malignancies in the peritoneal cavity compared to the systemic administration. However, IP drug delivery faces several challenges, such as premature clearance of a small molecular weight drug from the peritoneal cavity, lack of target specificity, and poor drug penetration into the target tissues. Previous studies have proposed the use of micro/nanoparticles and/or hydrogel-based systems for prolonging the drug residence time in the peritoneal cavity. This commentary discusses the currently used IP drug delivery systems either clinically or experimentally and the remaining challenges in IP drug delivery for future development.

Erbb2 DNA vaccine combined with regulatory T cell deletion enhances antibody response and reveals latent low-avidity T cells: potential and limits of its therapeutic efficacy

Rat (r)Erbb2 transgenic BALB-neuT mice genetically predestined to develop multiple invasive carcinomas allow an assessment of the potential of a vaccine against the stages of cancer progression. Because of rErbb2 expression in the thymus and its overexpression in the mammary gland, CD8(+) T cell clones reacting at high avidity with dominant rErbb2 epitopes are deleted in these mice. In BALB-neuT mice with diffuse and invasive in situ lesions and almost palpable carcinomas, a temporary regulatory T cells depletion combined with anti-rErbb2 vaccine markedly enhanced the anti-rErbb2 Ab response and allowed the expansion of latent pools of low-avidity CD8(+) T cells bearing TCRs repertoire reacting with the rErbb2 dominant peptide. This combination of a higher Ab response and activation of a low-avidity cytotoxic response persistently blocked tumor progression at stages in which the vaccine alone was ineffective. However, when diffuse and invasive microscopic cancers become almost palpable, this combination was no longer able to secure a significant extension of mice survival.