Transport of molecules, particles, and cells in solid tumors

Mechanical control of spheroid growth: distinct morphogenetic regimes

We develop a model of transport and growth in epithelio-mesenchymal interactions. Analysis of the growth of an avascular solid spheroid inside a passive mesenchyme or gel shows that sustained volumetric growth requires four generic mechanisms: (1) growth factor, (2) protease, (3) control of cellularity, and (4) swelling. The model reveals a bifurcation delineating two distinct morphogenetic regimes: (A) steady growth, (B) growth arrested by capsule formation in the mesenchyme. In both morphogenetic regimes, growth velocity is constant unless and until a complete capsule forms. Comprehensive exploration of the large parameter space reveals that the bifurcation is determined by just two ratios representing the relative strengths of growth and proteolytic activity. Growth velocity is determined only by the ratio governing growth, independent of proteolytic activity. There is a continuum of interior versus surface growth, with fastest growth at the surface. The model provides a theoretical basis for explaining observations of growth arrest despite proteolysis of surrounding tissue, and gives a quantitative framework for the design and interpretation of experiments involving spheroids, and tissues which are locally equivalent to spheroids.

Tumor accumulation of NIR fluorescent PEG-PLA nanoparticles: impact of particle size and human xenograft tumor model

Cancer therapies are often terminated due to serious side effects of the drugs. The cause is the nonspecific distribution of chemotherapeutic agents to both cancerous and normal cells. Therefore, drug carriers which deliver their toxic cargo specific to cancer cells are needed. Size is one key parameter for the nanoparticle accumulation in tumor tissues. In the present study the influence of the size of biodegradable nanoparticles was investigated in detail, combining in vivo and ex vivo analysis with comprehensive particle size characterizations. Polyethylene glycol-polyesters poly(lactide) block polymers were synthesized and used for the production of three defined, stable, and nontoxic near-infrared (NIR) dye-loaded nanoparticle batches. Size analysis based on asymmetrical field flow field fractionation coupled with multiangle laser light scattering and photon correlation spectroscopy (PCS) revealed narrow size distribution and permitted accurate size evaluations. Furthermore, this study demonstrates the constraints of particle size data only obtained by PCS. By the multispectral analysis of the Maestro in vivo imaging system the in vivo fate of the nanoparticles next to their accumulation in special red fluorescent DsRed2 expressing HT29 xenografts could be followed. This simultaneous imaging in addition to confocal microscopy studies revealed information about the accumulation characteristics of nanoparticles inside the tumor tissues. This knowledge was further combined with extended size-dependent fluorescence imaging studies at two different xenograft tumor types, the HT29 (colorectal carcinoma) and the A2780 (ovarian carcinoma) cell lines. The combination of two different size measurement methods allowed the characterization of the dependence of nanoparticle accumulation in the tumor on even rather small differences in the nanoparticle size. While two nanoparticle batches (111 and 141 nm in diameter) accumulated efficiently in the human xenograft tumor tissue, the slightly bigger nanoparticles (diameter 166 nm) were rapidly eliminated by the liver.

SPATIAL AND MECHANOEMISSION CHAOS OF MECHANICALLY DEFORMED TUMOR CELLS

The development and spreading of tumor process is accompanied by changes in nonlinear (chaotic) dynamics of mechanochemical interaction process in the group of cells. Taking into consideration spatial irregularity and heterogeneity of internal structures of tumor cells, we suggested that treatment by mechanically deformed (MD) syngeneic tumor cells (STC) would be accompanied by changed influence on malignant growth. The objective of this work was to compare spatial, mechanoemission (ME) chaos of MD STC of carcinoma Lewis and melanoma B16 and their malignant growth. MD STC preparation included the aseptic removal of the animal tumor, lyophilization and next mechanical deformation in the microvibratory mill. The suspension of non-deformed or MD STC was injected intraperitoneally. Morphological, morphometric and mechanoemission studies used for estimate of spatial chaos and heterogeneity structure in tumor cells and blood. For Lewis carcinoma the reduction of spatial and ME chaos of cells is accompanied by regression in tumor growth and metastasis. For melanoma B16 the decrease of spatial chaos and the increase of ME chaos in cells is accompanied by initiation of tumor growth and metastasis. These results illustrated equivalent tendencies in chaos changing in spatial and ME chaos for carcinoma Lewis, while opposite tendencies were observed for melanoma B16. Blood ME of mice with melanoma B16 have greater ME chaos in comparison with animals with Lewis carcinoma. This confirmed that the concept of deterministic chaos is hierarchical for the host during cancer process. Results of comparative analysis between spatial, mechanoemission chaos of MD STC and malignant growth could be useful for gain a better understanding relationship of nonlinear biomechanical processes to tumor cells.

SPATIAL AND MECHANOEMISSION CHAOS OF MECHANICALLY DEFORMED TUMOR CELLS

The development and spend of the tumor process is accompanied by changes in non-linear (chaotic) dynamics of mechanochemical interaction process in the group of cells. Taking into consideration spatial irregularity and heterogeneity of internal structures of tumor cells, we suggested that treatment by mechanically deformed (MD) syngeneic tumor cells (STC) would be accompanied by changed influence on malignant growth. The objective of this work was to compare spatial, mechanoemission (ME) chaos of MD STC of carcinoma Lewis and melanoma B16 and their malignant growth. MD STC preparation included the aseptic removal of the animal tumor, lyophilization and next mechanical deformation in the microvibratory mill. The suspension of non-deformed or MD STC was injected intraperitoneally. Morphological, morphometric and mechanoemission studies were used for the estimate of spatial chaos and heterogeneity structure in tumor cells and blood. For Lewis carcinoma, the reduction of spatial and ME chaos of cells is accompanied by regression in tumor growth and metastasis. For melanoma B16, the decrease of spatial chaos and the increase of ME chaos in cells are accompanied by the initiation of tumor growth and metastasis. These results illustrated equivalent tendencies in chaos changing in spatial and ME chaos for carcinoma Lewis, while opposite tendencies were observed for melanoma B16. Blood ME of mice with melanoma B16 have greater ME chaos in comparison with animals with Lewis carcinoma. This confirmed that the concept of deterministic chaos is hierarchical for the host during cancer process. Results of comparative analysis between spatial, mechanoemission chaos of MD STC and malignant growth could be useful to gain a better understanding relationship of non-linear biomechanical processes to tumor cells.

Predicting IGF-1R therapy response in bone sarcomas: immuno-SPECT imaging with radiolabeled R1507

PURPOSE

To investigate whether indium-111-labeled R1507 ((111)In-R1507) immuno-SPECT (single-photon emission computed tomography), a novel noninvasive, in vivo screening method to visualize membranous insulin-like growth factor 1 receptor (IGF-1R) expression and accessibility, can be used to predict IGF-1R treatment (R1507) response in bone sarcomas.

EXPERIMENTAL DESIGN

BALB/c nude mice were subcutaneously implanted with IGF-1R-expressing human bone sarcoma xenografts (OS-1, EW-5, and EW-8) which showed high, modest, or no response, respectively, to R1507, a monoclonal antibody targeting the extracellular domain of IGF-1R. An IGF-1R-negative tumor (OS-33), unresponsive to IGF-1R inhibitors, was examined as well. Mice were injected with (111)In-R1507. Biodistribution and immuno-SPECT/computed tomography imaging studies were carried out 1, 3, and 7 days p.i. in mice with OS-1 and EW-5 xenografts and 3 days p.i. in mice with EW-8 and OS-33 xenografts.

RESULTS

Biodistribution studies showed specific accumulation of (111)In-R1507 in OS-1 and EW-5 xenografts (27.5 ± 6.5%ID/g and 14.0 ± 2.8%ID/g, 3 days p.i., respectively). Most importantly, (111)In-R1507 uptake in IGF-1R positive, but unresponsive, EW-8 xenografts (6.5 ± 1.5%ID/g, 3 days p.i.) was similar to that of the IGF-1R-negative OS-33 tumor (5.5 ± 0.6%ID/g, 3 days p.i.). Uptake in normal tissues was low and nonspecific. Corresponding immuno-SPECT images clearly discriminated between high, modest, and nonresponding tumors by showing a homogeneous (OS-1), heterogeneous (EW-5), or nonspecific (EW-8 and OS-33) tumor uptake of (111)In-R1507.

CONCLUSIONS

(111)In-R1507 immuno-SPECT is an excellent method to visualize membranous IGF-1R expression and target accessibility in vivo in human bone sarcoma xenografts and may serve as an independent marker to predict IGF-1R therapy (R1507) response in bone sarcoma patients.

Multistage nanovectors: from concept to novel imaging contrast agents and therapeutics

Over the last few decades a great variety of nanotechnology based platforms have been synthesized and fabricated to improve the delivery of active compounds to a disease site. Nanoparticles currently used in the clinic, and the majority of nanotherapeutics/nanodiagnostics under investigation, accommodate single- or multiple- functionalities on the same entity. Because many heterogeneous biological barriers can prevent therapeutic and imaging agents from reaching their intended targets in sufficient concentrations, there is an emerging requirement to develop a multimodular nanoassembly, in which different components with individual specific functions act in a synergistic manner. The multistage nanovectors (MSVs) were introduced in 2008 as the first system of this type. It comprises several nanocomponents or "stages", each of which is designed to negotiate one or more biological barriers. Stage 1 mesoporous silicon particles (S1MPs) were rationally designed and fabricated in a nonspherical geometry to enable superior blood margination and to increase cell surface adhesion. The main task of S1MPs is to efficiently transport nanoparticles that are loaded into their porous structure and to protect them during transport from the administration site to the disease lesion. Semiconductor fabrication techniques including photolithography and electrochemical etching allow for the exquisite control and precise reproducibility of S1MP physical characteristics such as geometry and porosity. Furthermore, S1MPs can be chemically modified with negatively/positively charged groups, PEG and other polymers, fluorescent probes, contrast agents, and biologically active targeting moieties including antibodies, peptides, aptamers, and phage. The payload nanoparticles, termed stage 2 nanoparticles (S2NPs), can be any currently available nanoparticles such as liposomes, micelles, inorganic/metallic nanoparticles, dendrimers, and carbon structures, within the approximate size range of 5-100 nm in diameter. Depending upon the physicochemical features of the S1MP (geometry, porosity, and surface modifications), a variety of S2NPs or nanoparticle "cocktails" can be loaded and efficiently delivered to the disease site. As demonstrated in the studies reviewed here, once the S2NPs are loaded into the S1MPs, a variety of novel properties emerge, which enable the design of new and improved imaging contrast agents and therapeutics. For example, the loading of the MRI Gd-based contrast agents onto hemispherical and discoidal S1MPs significantly increased the longitudal relaxivity (r1) to values of up to 50 times larger than those of clinically available gadolinium-based agents (~4 mM(-1) s(-1)/Gd(3+) ion). Furthermore, administration of a single dose of MSVs loaded with neutral nanoliposomes containing small interfering RNA (siRNA) targeted against the EphA2 oncoprotein enabled sustained EphA2 gene silencing for at least 21 days. As a result, the tumor burden was reduced in an orthotopic mouse model of ovarian cancer. We envision that the versatility of the MSV platform and its emerging properties will enable the creation of personalized solutions with broad clinical implications within and beyond the realm of cancer theranostics.

A systems approach for tumor pharmacokinetics

Recent advances in genome inspired target discovery, small molecule screens, development of biological and nanotechnology have led to the introduction of a myriad of new differently sized agents into the clinic. The differences in small and large molecule delivery are becoming increasingly important in combination therapies as well as the use of drugs that modify the physiology of tumors such as anti-angiogenic treatment. The complexity of targeting has led to the development of mathematical models to facilitate understanding, but unfortunately, these studies are often only applicable to a particular molecule, making pharmacokinetic comparisons difficult. Here we develop and describe a framework for categorizing primary pharmacokinetics of drugs in tumors. For modeling purposes, we define drugs not by their mechanism of action but rather their rate-limiting step of delivery. Our simulations account for variations in perfusion, vascularization, interstitial transport, and non-linear local binding and metabolism. Based on a comparison of the fundamental rates determining uptake, drugs were classified into four categories depending on whether uptake is limited by blood flow, extravasation, interstitial diffusion, or local binding and metabolism. Simulations comparing small molecule versus macromolecular drugs show a sharp difference in distribution, which has implications for multi-drug therapies. The tissue-level distribution differs widely in tumors for small molecules versus macromolecular biologic drugs, and this should be considered in the design of agents and treatments. An example using antibodies in mouse xenografts illustrates the different in vivo behavior. This type of transport analysis can be used to aid in model development, experimental data analysis, and imaging and therapeutic agent design.

Virotherapy induces massive infiltration of neutrophils in a subset of tumors defined by a strong endogenous interferon response activity

Oncolytic virotherapy has shown substantial promises as an alternative therapeutic modality for solid tumors in both preclinical studies and clinical trials. The main therapeutic activity of virotherapy derives from the direct lytic effect associated with virus replication and the induction of host immune responses to the infected tumor cells. Here we show that some human and murine tumor cell lines are highly resistant to the lytic effect of a type II herpes simplex virus-derived oncolytic virus, FusOn-H2, which was constructed by deleting the N-terminal region of the ICP10 gene. However, these tumor cells still respond exceptionally well to FusOn-H2 virotherapy in vivo. Histological examination of the treated tumors revealed that, in contrast to tumors supporting FusOn-H2 replication, implants of these highly resistant lines showed massive infiltration of neutrophils after virotherapy. Further analysis showed that there is a correlation between an intrinsically strong interferon response activity and the recruitment of neutrophils in these tumors. These results suggest that an innate immune response mainly represented by neutrophils may be part of the virotherapy-mediated antitumor mechanism in these tumors.

Nanotechnology-based detection and targeted therapy in cancer: nano-bio paradigms and applications

The application of nanotechnology to biomedicine, particularly in cancer diagnosis and treatment, promises to have a profound impact on healthcare. The exploitation of the unique properties of nano-sized particles for cancer therapeutics is most popularly known as nanomedicine. The goals of this review are to discuss the current state of nanomedicine in the field of cancer detection and the subsequent application of nanotechnology to treatment. Current cancer detection methods rely on the patient contacting their provider when they feel ill, or relying on non-specific screening methods, which unfortunately often result in cancers being detected only after it is too late for effective treatment. Cancer treatment paradigms mainly rely on whole body treatment with chemotherapy agents, exposing the patient to medications that non-specifically kill rapidly dividing cells, leading to debilitating side effects. In addition, the use of toxic organic solvents/excipients can hamper the further effectiveness of the anticancer drug. Nanomedicine has the potential to increase the specificity of treatment of cancer cells while leaving healthy cells intact through the use of novel nanoparticles. This review discusses the use of nanoparticles such as quantum dots, nanoshells, nanocrystals, nanocells, and dendrimers for the detection and treatment of cancer. Future directions and perspectives of this cutting-edge technology are also discussed.

Targeted magnetic hyperthermia

Many nanotechnologies, which enable unique approaches to treat cancer, have been developed based upon non-toxic organic and inorganic materials to improve current cancer treatments. The use of inorganic materials to form magnetic nanoparticles for hyperthermia therapy is of great interest for localized treatment of cancers without effecting adjacent healthy tissue. Extensive clinical trials have begun using magnetic hyperthermia in animal models. The purpose of this article is to address different factors that affect targeting, heating and biodistribution to safely control the therapeutic efficacy of targeted magnetic hyperthermia. This method involves accumulation of magnetic nanoparticles at a tumor site and then manipulating the magnetic properties of the nanoparticles to heat the targeted tissues.

T cells enhance gold nanoparticle delivery to tumors in vivo

Gold nanoparticle-mediated photothermal therapy (PTT) has shown great potential for the treatment of cancer in mouse studies and is now being evaluated in clinical trials. For this therapy, gold nanoparticles (AuNPs) are injected intravenously and are allowed to accumulate within the tumor via the enhanced permeability and retention (EPR) effect. The tumor is then irradiated with a near infrared laser, whose energy is absorbed by the AuNPs and translated into heat. While reliance on the EPR effect for tumor targeting has proven adequate for vascularized tumors in small animal models, the efficiency and specificity of tumor delivery in vivo, particularly in tumors with poor blood supply, has proven challenging. In this study, we examine whether human T cells can be used as cellular delivery vehicles for AuNP transport into tumors. We first demonstrate that T cells can be efficiently loaded with 45 nm gold colloid nanoparticles without affecting viability or function (e.g. migration and cytokine production). Using a human tumor xenograft mouse model, we next demonstrate that AuNP-loaded T cells retain their capacity to migrate to tumor sites in vivo. In addition, the efficiency of AuNP delivery to tumors in vivo is increased by more than four-fold compared to injection of free PEGylated AuNPs and the use of the T cell delivery system also dramatically alters the overall nanoparticle biodistribution. Thus, the use of T cell chaperones for AuNP delivery could enhance the efficacy of nanoparticle-based therapies and imaging applications by increasing AuNP tumor accumulation.

The synthesis and bio-applications of magnetic and fluorescent bifunctional composite nanoparticles

Magnetic-fluorescent composite nanoparticles as a new kind of nanoparticle have attracted much attention in recent years. The composite nanoparticles combine the fluorescent properties, magnetic properties and the physical properties of nano-size, so they can offer a range of potential applications, such as bioseparation and bio-imaging, tumor cell localization, and even cancer treatment. This Minireview will introduce the main synthesis strategies for the fabrication of magnetic-fluorescent composite nanoparticles, the current and potential bio-application of magnetic-fluorescent nanocomposites, including protein and DNA separation and detection, bio-imaging and sorting in vitro and in vivo, drug delivery and the cancer treatment.

Tumor delivery of macromolecular drugs based on the EPR effect

Enhanced permeability and retention (EPR) effect is the physiology-based principal mechanism of tumor accumulation of large molecules and small particles. This specific issue of Advanced Drug Delivery Reviews is summing up multiple data on the EPR effect-based drug design and clinical outcome. In this commentary, the role of the EPR effect in the intratumoral delivery of protein and peptide drugs, macromolecular drugs and drug-loaded long-circulating pharmaceutical nanocarriers is briefly discussed together with some additional opportunities for drug delivery arising from the initial EPR effect-mediated accumulation of drug-containing macromolecular systems in tumors.

Multi-stage delivery nano-particle systems for therapeutic applications

BACKGROUND

The daunting task for drug molecules to reach pathological lesions has fueled rapid advances in Nanomedicine. The progressive evolution of nanovectors has led to the development of multi-stage delivery systems aimed at overcoming the numerous obstacles encountered by nanovectors on their journey to the target site.

SCOPE OF REVIEW

This review summarizes major findings with respect to silicon-based drug delivery vectors for cancer therapeutics and imaging. Based on rational design, well-established silicon technologies have been adapted for the fabrication of nanovectors with specific shapes, sizes, and porosities. These vectors are part of a multi-stage delivery system that contains multiple nano-components, each designed to achieve a specific task with the common goal of site-directed delivery of therapeutics.

MAJOR CONCLUSIONS

Quasi-hemispherical and discoidal silicon microparticles are superior to spherical particles with respect to margination in the blood, with particles of different shapes and sizes having unique distributions in vivo. Cellular adhesion and internalization of silicon microparticles is influenced by microparticle shape and surface charge, with the latter dictating binding of serum opsonins. Based on in vitro cell studies, the internalization of porous silicon microparticles by endothelial cells and macrophages is compatible with cellular morphology, intracellular trafficking, mitosis, cell cycle progression, cytokine release, and cell viability. In vivo studies support superior therapeutic efficacy of liposomal encapsulated siRNA when delivered in multi-stage systems compared to free nanoparticles. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

In vivo imaging of human malignant mesothelioma grown orthotopically in the peritoneal cavity of nude mice

Malignant mesothelioma (MM) causes significant morbidity and mortality in patients. With increasing efforts devoted to developing therapeutics targeting mesothelioma, a xenograft mouse model with in vivo tumor imaging is especially desired for evaluating anti-tumor therapies. In the present study, we fluorescently labeled the NCI-H226 human mesothelioma cell line by a lentiviral vector harboring a luciferase-GFP (Luc/GFP) fusion gene driven by the RNA polymerase II promoter. After single-cell cloning by flow cytometry, a clone (named LMB-H226-GL) that stably expresses high levels of Luc/GFP was obtained. The in vivo tumorigenicity of Luc/GFP-labeled LMB-H226-GL was determined by using intraperitoneal injections of the cells in nude mice. LMB-H226-GL was found to be able to consistently form solid tumors in the peritoneum of mice. Tumor growth and aggressive progression could be quantitated via in vivo bioluminescence imaging. The model exhibited the pathological hallmarks consistent with the clinical progression of MM in terms of tumor growth and spread inside the peritoneal cavity. To evaluate the in vivo efficacy of drugs targeting mesothelioma, we treated mice with SS1P, a recombinant immunotoxin currently evaluated in Phase II clinical trials for treatment of mesothelioma. All the tumor-bearing mice had a significant response to SS1P treatment. Our results showed that this is a well-suited model for mesothelioma, and may be useful for evaluating other novel agents for mesothelioma treatment in vivo.

Drug delivery strategies for therapeutic angiogenesis and antiangiogenesis

INTRODUCTION

Angiogenesis is essential to human biology and of great clinical significance. Excessive or reduced angiogenesis can result in, or exacerbate, several disease states, including tumor formation, exudative age-related macular degeneration (AMD) and ischemia. Innovative drug delivery systems can increase the effectiveness of therapies used to treat angiogenesis-related diseases.

AREAS COVERED

This paper reviews the basic biology of angiogenesis, including current knowledge about its disruption in diseases, with the focus on cancer and AMD. Anti- and proangiogenic drugs available for clinical use or in development are also discussed, as well as experimental drug delivery systems that can potentially improve these therapies to enhance or reduce angiogenesis in a more controlled manner.

EXPERT OPINION

Laboratory and clinical results have shown pro- or antiangiogenic drug delivery strategies to be effective in drastically slowing disease progression. Further research in this area will increase the efficacy, specificity and duration of these therapies. Future directions with composite drug delivery systems may make possible targeting of multiple factors for synergistic effects.

Multistage nanoparticle delivery system for deep penetration into tumor tissue

Current Food and Drug Administration-approved cancer nanotherapeutics, which passively accumulate around leaky regions of the tumor vasculature because of an enhanced permeation and retention (EPR) effect, have provided only modest survival benefits. This suboptimal outcome is likely due to physiological barriers that hinder delivery of the nanotherapeutics throughout the tumor. Many of these nanotherapeutics are ≈ 100 nm in diameter and exhibit enhanced accumulation around the leaky regions of the tumor vasculature, but their large size hinders penetration into the dense collagen matrix. Therefore, we propose a multistage system in which 100-nm nanoparticles "shrink" to 10-nm nanoparticles after they extravasate from leaky regions of the tumor vasculature and are exposed to the tumor microenvironment. The shrunken nanoparticles can more readily diffuse throughout the tumor's interstitial space. This size change is triggered by proteases that are highly expressed in the tumor microenvironment such as MMP-2, which degrade the cores of 100-nm gelatin nanoparticles, releasing smaller 10-nm nanoparticles from their surface. We used quantum dots (QD) as a model system for the 10-nm particles because their fluorescence can be used to demonstrate the validity of our approach. In vitro MMP-2 activation of the multistage nanoparticles revealed that the size change was efficient and effective in the enhancement of diffusive transport. In vivo circulation half-life and intratumoral diffusion measurements indicate that our multistage nanoparticles exhibited both the long circulation half-life necessary for the EPR effect and the deep tumor penetration required for delivery into the tumor's dense collagen matrix.

Inorganic nanoparticles in cancer therapy

Nanotechnology is an evolving field with enormous potential for biomedical applications. The growing interest to use inorganic nanoparticles in medicine is due to the unique size- and shape-dependent optoelectronic properties. Herein, we will focus on gold, silver and platinum nanoparticles, discussing recent developments for therapeutic applications with regard to cancer in terms of nanoparticles being used as a delivery vehicle as well as therapeutic agents. We will also discuss some of the key challenges to be addressed in future studies.

The development and characterization of a human mesothelioma in vitro 3D model to investigate immunotoxin therapy

Background

Tumor microenvironments present significant barriers to penetration by antibodies and immunoconjugates. Tumor microenvironments, however, are difficult to study in vitro. Cells cultured as monolayers exhibit less resistance to therapy than those grown in vivo and an alternative research model more representative of the in vivo tumor is more desirable. SS1P is an immunotoxin composed of the Fv portion of a mesothelin-specific antibody fused to a bacterial toxin that is presently undergoing clinical trials in mesothelioma.

Methodology/Principal Findings

Here, we examined how the tumor microenvironment affects the penetration and killing activity of SS1P in a new three-dimensional (3D) spheroid model cultured in vitro using the human mesothelioma cell line (NCI-H226) and two primary cell lines isolated from the ascites of malignant mesothelioma patients. Mesothelioma cells grown as monolayers or as spheroids expressed comparable levels of mesothelin; however, spheroids were at least 100 times less affected by SS1P. To understand this disparity in cytotoxicity, we made fluorescence-labeled SS1P molecules and used confocal microscopy to examine the time course of SS1P penetration within spheroids. The penetration was limited after 4 hours. Interestingly, we found a significant increase in the number of tight junctions in the core area of spheroids by electron microscopy. Expression of E-Cadherin, a protein involved in the assembly and sealing of tight junctions and highly expressed in malignant mesothelioma, was found significantly increased in spheroids as compared to monolayers. Moreover, we found that siRNA silencing and antibody inhibition targeting E-Cadherin could enhance SS1P immunotoxin therapy in vitro.

Conclusion/Significance

This work is one of the first to investigate immunotoxins in 3D tumor spheroids in vitro. This initial description of an in vitro tumor model may offer a simple and more representative model of in vivo tumors and will allow for further investigations of the microenvironmental effects on drug penetration and tumor cell killing. We believe that the methods developed here may apply to the studies of other tumor-targeting antibodies and immunoconjugates in vitro.

A new era for cancer treatment: gold-nanoparticle-mediated thermal therapies

Nanotechnology-based cancer treatment approaches potentially provide localized, targeted therapies that aim to enhance efficacy, reduce side effects, and improve patient quality of life. Gold-nanoparticle-mediated hyperthermia shows particular promise in animal studies, and early clinical testing is currently underway. In this article, the rapidly evolving field of gold nanoparticle thermal therapy is reviewed, highlighting recent literature and describing current challenges to clinical translation of the technology.

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.

Cell penetrating elastin-like polypeptides for therapeutic peptide delivery

Current treatment of solid tumors is limited by side effects that result from the non-specific delivery of drugs to the tumor site. Alternative targeted therapeutic approaches for localized tumors would significantly reduce systemic toxicity. Peptide therapeutics are a promising new strategy for targeted cancer therapy because of the ease of peptide design and the specificity of peptides for their intracellular molecular targets. However, the utility of peptides is limited by their poor pharmacokinetic parameters and poor tissue and cellular membrane permeability in vivo. This review article summarizes the development of elastin-like polypeptide (ELP) as a potential carrier for thermally targeted delivery of therapeutic peptides (TP), and the use of cell penetrating peptides (CPP) to enhance the intracellular delivery of the ELP-fused TPs. CPP-fused ELPs have been used to deliver a peptide inhibitor of c-Myc function and a peptide mimetic of p21 in several cancer models in vitro, and both polypeptides are currently yielding promising results in in vivo models of breast and brain cancer.

The role of carrier size in the pharmacodynamics of antisense and siRNA oligonucleotides

Effective therapeutic utilization of antisense and siRNA oligonucleotides represents a major challenge to drug delivery science. Although many strategies and technologies have been applied to oligonucleotide delivery, a key issue remains the role of molecular or carrier size. In this brief review, we address some of the size-related parameters that regulate the biodistribution of oligonucleotides. We also reprise several recent studies that have examined the inter-relationship of size and shape in influencing delivery.

Targeted imaging and therapy of brain cancer using theranostic nanoparticles

The past decade has seen momentous development in brain cancer research in terms of novel imaging-assisted surgeries, molecularly targeted drug-based treatment regimens or adjuvant therapies and in our understanding of molecular footprints of initiation and progression of malignancy. However, mortality due to brain cancer has essentially remained unchanged in the last three decades. Thus, paradigm-changing diagnostic and therapeutic reagents are urgently needed. Nanotheranostic platforms are powerful tools for imaging and treatment of cancer. Multifunctionality of these nanovehicles offers a number of advantages over conventional agents. These include targeting to a diseased site thereby minimizing systemic toxicity, the ability to solubilize hydrophobic or labile drugs leading to improved pharmacokinetics and their potential to image, treat and predict therapeutic response. In this article, we will discuss the application of newer theranostic nanoparticles in targeted brain cancer imaging and treatment.

Resistance to antitumor chemotherapy due to bounded-noise-induced transitions

Tumor angiogenesis is a landmark of solid tumor development, but it is also directly relevant to chemotherapy. Indeed, the density and quality of neovessels may influence the effectiveness of therapies based on blood-born agents. In this paper, first we define a deterministic model of antiproliferative chemotherapy in which the drug efficacy is a unimodal function of vessel density, and then we show that under constant continuous infusion therapy the tumor-vessel system may be multistable. However, the actual drug concentration profiles are affected by bounded even if possibly large fluctuations. Through numerical simulations, we show that the tumor volume may undergo transitions to the higher equilibrium value induced by the bounded noise. In case of periodically delivered boli-based chemotherapy, we model the fluctuations due to time variability of both the drug clearance rate and the distribution volume, as well as those due to irregularities in drug delivery. We observed noise-induced transitions also in case of periodic delivering. By applying a time dense scheduling with constant average delivered drug (metronomic scheduling), we observed an easier suppression of the transitions. Finally, we propose to interpret the above phenomena as an unexpected non-genetic kind of resistance to chemotherapy.

Gold Nanocages: A Novel Class of Multifunctional Nanomaterials for Theranostic Applications

Gold nanocages represent a novel class of nanostructures, well-suited for biomedical applications. They can be readily prepared via the galvanic replacement reaction between silver nanocubes and chloroauric acid. Their optical resonance peaks can be easily and precisely tuned to the near-infrared region from 650-900 nm, the transparent window for blood and soft tissue. Furthermore, their surface can be conveniently conjugated with various ligands for targeting cancer. In this feature article, we highlight recent advances in the large-scale synthesis of gold nanocages and their applications in cancer diagnosis and treatment. Specifically, we have scaled up the production of gold nanocages for in vivo studies and evaluated their tumor targeting capabilities. We have also demonstrated their use as contrast agents for photoacoustic tumor imaging and the mapping of sentinel lymph node, as photothermal transducers for cancer treatment, and as smart carriers for controlled release with a near-infrared laser.

Hand-held spectroscopic device for in vivo and intraoperative tumor detection: contrast enhancement, detection sensitivity, and tissue penetration

Surgery is one of the most effective and widely used procedures in treating human cancers, but a major problem is that the surgeon often fails to remove the entire tumor, leaving behind tumor-positive margins, metastatic lymph nodes, and/or satellite tumor nodules. Here we report the use of a hand-held spectroscopic pen device (termed SpectroPen) and near-infrared contrast agents for intraoperative detection of malignant tumors, based on wavelength-resolved measurements of fluorescence and surface-enhanced Raman scattering (SERS) signals. The SpectroPen utilizes a near-infrared diode laser (emitting at 785 nm) coupled to a compact head unit for light excitation and collection. This pen-shaped device effectively removes silica Raman peaks from the fiber optics and attenuates the reflected excitation light, allowing sensitive analysis of both fluorescence and Raman signals. Its overall performance has been evaluated by using a fluorescent contrast agent (indocyanine green, or ICG) as well as a surface-enhanced Raman scattering (SERS) contrast agent (pegylated colloidal gold). Under in vitro conditions, the detection limits are approximately 2-5 × 10(-11) M for the indocyanine dye and 0.5-1 × 10(-13) M for the SERS contrast agent. Ex vivo tissue penetration data show attenuated but resolvable fluorescence and Raman signals when the contrast agents are buried 5-10 mm deep in fresh animal tissues. In vivo studies using mice bearing bioluminescent 4T1 breast tumors further demonstrate that the tumor borders can be precisely detected preoperatively and intraoperatively, and that the contrast signals are strongly correlated with tumor bioluminescence. After surgery, the SpectroPen device permits further evaluation of both positive and negative tumor margins around the surgical cavity, raising new possibilities for real-time tumor detection and image-guided surgery.

A reexamination of active and passive tumor targeting by using rod-shaped gold nanocrystals and covalently conjugated peptide ligands

The targeted delivery of nanoparticles to solid tumors is one of the most important and challenging problems in cancer nanomedicine, but the detailed delivery mechanisms and design principles are still not well understood. Here we report quantitative tumor uptake studies for a class of elongated gold nanocrystals (called nanorods) that are covalently conjugated to tumor-targeting peptides. A major advantage in using gold as a "tracer" is that the accumulated gold in tumors and other organs can be quantitatively determined by elemental mass spectrometry (gold is not a natural element found in animals). Thus, colloidal gold nanorods are stabilized with a layer of polyethylene glycols (PEGs) and are conjugated to three different ligands: (i) a single-chain variable fragment (ScFv) peptide that recognizes the epidermal growth factor receptor (EGFR); (ii) an amino terminal fragment (ATF) peptide that recognizes the urokinase plasminogen activator receptor (uPAR); and (iii) a cyclic RGD peptide that recognizes the a(v)β(3) integrin receptor. Quantitative pharmacokinetic and biodistribution data show that these targeting ligands only marginally improve the total gold accumulation in xenograft tumor models in comparison with nontargeted controls, but their use could greatly alter the intracellular and extracellular nanoparticle distributions. When the gold nanorods are administered via intravenous injection, we also find that active molecular targeting of the tumor microenvironments (e.g., fibroblasts, macrophages, and vasculatures) does not significantly influence the tumor nanoparticle uptake. These results suggest that for photothermal cancer therapy, the preferred route of gold nanorod administration is intratumoral injection instead of intravenous injection.

Receptor-targeted nanocarriers for therapeutic delivery to cancer

Efficient and site-specific delivery of therapeutic drugs is a critical challenge in clinical treatment of cancer. Nano-sized carriers such as liposomes, micelles, and polymeric nanoparticles have been investigated for improving bioavailability and pharmacokinetic properties of therapeutics via various mechanisms, for example, the enhanced permeability and retention (EPR) effect. Further improvement can potentially be achieved by conjugation of targeting ligands onto nanocarriers to achieve selective delivery to the tumour cell or the tumour vasculature. Indeed, receptor-targeted nanocarrier delivery has been shown to improve therapeutic responses both in vitro and in vivo. A variety of ligands have been investigated including folate, transferrin, antibodies, peptides and aptamers. Multiple functionalities can be incorporated into the design of nanoparticles, e.g., to enable imaging and triggered intracellular drug release. In this review, we mainly focus on recent advances on the development of targeted nanocarriers and will introduce novel concepts such as multi-targeting and multi-functional nanoparticles.

Nanoparticle-mediated thermal therapy: evolving strategies for prostate cancer therapy

PURPOSE

Recent advances in nanotechnology have resulted in the manufacture of a plethora of nanoparticles of different sizes, shapes, core physicochemical properties and surface modifications that are being investigated for potential medical applications, particularly for the treatment of cancer. This review focuses on the therapeutic use of customised gold nanoparticles, magnetic nanoparticles and carbon nanotubes that efficiently generate heat upon electromagnetic (light and magnetic fields) stimulation after direct injection into tumours or preferential accumulation in tumours following systemic administration. This review will also focus on the evolving strategies to improve the therapeutic index of prostate cancer treatment using nanoparticle-mediated hyperthermia.

CONCLUSIONS

Nanoparticle-mediated thermal therapy is a new and minimally invasive tool in the armamentarium for the treatment of cancers. Unique challenges posed by this form of hyperthermia include the non-target biodistribution of nanoparticles in the reticuloendothelial system when administered systemically, the inability to visualise or quantify the global concentration and spatial distribution of these particles within tumours, the lack of standardised thermal modelling and dosimetry algorithms, and the concerns regarding their biocompatibility. Nevertheless, novel particle compositions, geometries, activation strategies, targeting techniques, payload delivery strategies, and radiation dose enhancement concepts are unique attributes of this form of hyperthermia that warrant further exploration. Capitalising on these opportunities and overcoming these challenges offers the possibility of seamless and logical translation of this nanoparticle-mediated hyperthermia paradigm from the bench to the bedside.

Mechanistic modelling of dynamic MRI data predicts that tumour heterogeneity decreases therapeutic response

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) contains crucial information about tumour heterogeneity and the transport limitations that reduce drug efficacy. Mathematical modelling of drug delivery and cellular responsiveness based on underutilised DCE-MRI data has the unique potential to predict therapeutic responsiveness for individual patients.

METHODS

To interpret DCE-MRI data, we created a modelling framework that operates over multiple time and length scales and incorporates intracellular metabolism, nutrient and drug diffusion, trans-vascular permeability, and angiogenesis. The computational methodology was used to analyse DCE-MR images collected from eight breast cancer patients at Baystate Medical Center in Springfield, MA.

RESULTS

Computer simulations showed that trans-vascular transport was correlated with tumour aggressiveness because increased vessel growth and permeability provided more nutrients for cell proliferation. Model simulations also indicate that vessel density minimally affects tissue growth and drug response, and nutrient availability promotes growth. Finally, the simulations indicate that increased transport heterogeneity is coupled with increased tumour growth and poor drug response.

CONCLUSION

Mathematical modelling based on DCE-MRI has the potential to aid treatment decisions and improve overall cancer care. This model is the critical first step in the creation of a comprehensive and predictive computational method.

A system and mathematical framework to model shear flow effects in biomedical DW-imaging and spectroscopy

The pulsed-field gradient (PFG) MR experiment enables one to measure particle displacements, velocities, and even higher moments of complex fluid motions. In diffusion-weighted MRI (DWI) in living tissue, where the PFG MRI experiment is used to measure diffusion, Brownian motion is assumed to dominate the displacements causing the observed signal loss. However, motions of water molecules caused by various active biological processes occurring at different length and time scales may also cause additional dephasing of magnetization and signal loss. To help understand their relative effects on the DWI signal attenuation, we used an integrated experimental and theoretical framework: a Rheo-NMR, which served as an experimental model system to precisely prescribe a microscopic velocity distribution; and a mathematical model that relates the DW signal intensity in the Rheo-NMR to experimental parameters that characterize the impressed velocity field. A technical innovation reported here is our use of 'natural' (in this case, polar) coordinates both to simplify the description the fluid motion within the Couette cell of the Rheo-NMR, as well as to acquire and reconstruct magnitude and phase MR images obtained within it. We use this integrated model system to demonstrate how shear flows appears as pseudo-diffusion in magnitude DW MR signals obtained using PFG spin-echo (PGSE) NMR and MRI sequences. Our results lead us to reinterpret the possible causes of signal loss in DWI in vivo, in particular to revise and generalize the previous notion of intra-voxel incoherent motion (IVIM) in order to describe activity driven flows that appear as pseudo-diffusion over multiple length and time scales in living tissues.

Understanding specific and nonspecific toxicities: a requirement for the development of dendrimer-based pharmaceuticals

Dendrimer conjugates for pharmaceutical development are capable of enhancing the local delivery of cytotoxic drugs. The ability to conjugate different targeting ligands to the dendrimer allows for the cytotoxic drug to be focused at the intended target cell while minimizing collateral damage in normal cells. Dendrimers offer several advantages over other polymer conjugates by creating a better defined, more monodisperse therapeutic scaffold. Toxicity from the dendrimer, targeted and nonspecific, is not only dependent upon the number of targeting and therapeutic ligands conjugated, but can be influenced by the repeating building blocks that grow the dendrimer, the dendrimer generation, as well as the surface termination.

In vivo assembly of nanoparticle components to improve targeted cancer imaging

Many small molecular anticancer agents are often ineffective at detecting or treating cancer due to their poor pharmacokinetics. Using nanoparticles as carriers can improve this because their large size reduces clearance and improves retention within tumors, but it also slows their rate of transfer from circulation into the tumor interstitium. Here, we demonstrate an alternative strategy whereby a molecular contrast agent and engineered nanoparticle undergo in vivo molecular assembly within tumors, combining the rapid influx of the smaller and high retention of the larger component. This strategy provided rapid tumor accumulation of a fluorescent contrast agent, 16- and 8-fold faster than fluorescently labeled macromolecule or nanoparticle controls achieved. Diagnostic sensitivity was 3.0 times that of a passively targeting nanoparticle, and this improvement was achieved 3 h after injection. The advantage of the in vivo assembly approach for targeting is rapid accumulation of small molecular agents in tumors, shorter circulation time requirements, possible systemic clearance while maintaining imaging sensitivity in the tumor, and nanoparticle anchors in tumors can be utilized to alter the pharmacokinetics of contrast agents, therapeutics, and other nanoparticles. This study demonstrates molecular assembly of nanoparticles within tumors, and provides a new basis for the future design of nanomaterials for medical applications.

Solid-tumor radionuclide therapy dosimetry: new paradigms in view of tumor microenvironment and angiogenesis

PURPOSE

The objective of this study is to evaluate requirements for radionuclide-based solid tumor therapy by assessing the radial dose distribution of beta-particle-emitting and alpha-particle-emitting molecules localized either solely within endothelial cells of tumor vasculature or diffusing from the vasculature throughout the adjacent viable tumor cells.

METHODS

Tumor blood vessels were modeled as a group of microcylindrical layers comprising endothelial cells (one-cell thick, 10 microm diameter), viable tumor cells (25-cell thick, 250 microm radius), and necrotic tumor region (> 250 microm from any blood vessel). Sources of radioactivity were assumed to distribute uniformly in either endothelial cells or in concentric cylindrical 10 microm shells within the viable tumor-cell region. The EGSnrc Monte Carlo simulation code system was used for beta particle dosimetry and a dose-point kernel method for alpha particle dosimetry. The radioactive decays required to deposit cytocidal doses (> or = 100 Gy) in the vascular endothelial cells (endothelial cell mean dose) or, alternatively, at the tumor edge [tumor-edge mean dose (TEMD)] of adjacent viable tumor cells were then determined for six beta (32P, 33P, 67Cu, 90Y 131I, and 1188Re) and two alpha (211At and 213Bi) particle emitters.

RESULTS

Contrary to previous modeling in targeted radionuclide therapy dosimetry of solid tumors, the present work restricts the region of tumor viability to 250 microm around tumor blood vessels for consistency with biological observations. For delivering > or = 100 Gy at the viable tumor edge (TEMD) rather than throughout a solid tumor, energetic beta emitters 90Y, 32P, and 188Re can be effective even when the radionuclide is confined to the blood vessel (i.e., no diffusion into the tumor). Furthermore, the increase in tumor-edge dose consequent to beta emitter diffusion is dependent on the energy of the emitted beta particles, being much greater for lower-energy emitters 131I, 67Cu, and 33P relative to higher-energy emitters 90Y, 32P, and 188Re. Compared to alpha particle emitters, a approximately 150-400 times higher number of beta-particle-emitting radioactive atoms is required to deposit the same dose in tumor neovasculature. However, for the alpha particle emitters 211At and 213Bi to be effective in irradiating viable tumor-cell regions in addition to the vasculature the carrier molecules must diffuse substantially from the vasculature into the viable tumor.

CONCLUSION

The presented data enable comparison of radionuclides used for antiangiogenic therapy on the basis of their radioactive decay properties, tumor neovasculature geometry, and tumor-cell viability. For alpha particle emitters or low-energy beta particle emitters, the targeting carrier molecule should be chosen to permit the radiopharmaceutical to diffuse from the endothelial wall of the blood vessel, while for long-range energetic beta particle emitters that target neovasculature, a radiopharmaceutical that binds to newly formed endothelial cells and does not diffuse is preferable. The work is a first approximation to modeling of tumor neovasculature that ignores factors such as pharmacokinetics and targeting capability of carrier molecules. The calculations quantify the interplay between irradiation of neovasculature, the surrounding viable tumor cells, and the physical properties of commonly used radionuclides and can be used to assist estimation of radioactivity to be administered for neovasculature-targeted tumor therapy.

Radiotherapy in combination with vascular-targeted therapies

BACKGROUND

Given the critical role of tumor vasculature in tumor development, considerable efforts have been spent on developing therapeutic strategies targeting the tumor vascular network. A variety of agents have been developed, with two general approaches being pursued. Antiangiogenic agents (AAs) aim to interfere with the process of angiogenesis, preventing new tumor blood vessel formation. Vascular-disrupting agents (VDAs) target existing tumor vessels causing tumor ischemia and necrosis. Despite their great therapeutic potential, it has become clear that their greatest clinical utility may lie in combination with conventional anticancer therapies. Radiotherapy is a widely used treatment modality for cancer with its distinct therapeutic challenges. Thus, combining the two approaches seems reasonable.

CONCLUSIONS

Strong biological rationale exist for combining vascular-targeted therapies with radiation. AAs and VDAs were shown to alter the tumor microenvironment in such a way as to enhance responses to radiation. The results of preclinical and early clinical studies have confirmed the therapeutic potential of this new treatment strategy in the clinical setting. However, concerns about increased normal tissue toxicity, have been raised.

Tuning payload delivery in tumour cylindroids using gold nanoparticles

Nanoparticles have great potential as controllable drug delivery vehicles because of their size and modular functionality. Timing and location are important parameters when optimizing nanoparticles for delivery of chemotherapeutics. Here, we show that gold nanoparticles carrying either fluorescein or doxorubicin molecules move and localize differently in an in vitro three-dimensional model of tumour tissue, depending on whether the nanoparticles are positively or negatively charged. Fluorescence microscopy and mathematical modelling show that uptake, not diffusion, is the dominant mechanism in particle delivery. Our results indicate that positive particles may be more effective for drug delivery because they are taken up to a greater extent by proliferating cells. Negative particles, which diffuse more quickly, may perform better when delivering drugs deep into tissues. An understanding of how surface charge can control tissue penetration and drug release may overcome some of the current limitations in drug delivery.

Tumor delivery and in vivo processing of disulfide-linked and thioether-linked antibody-maytansinoid conjugates

Antibody-drug conjugates (ADCs) are designed to eradicate cancer cells that express the target antigen on their cell surface. A key component of an ADC is the linker that covalently connects the cytotoxic agent to the antibody. Several antibody-maytansinoid conjugates prepared with disulfide-based linkers such as those targeting the CanAg antigen have been shown to display more activity in preclinical mouse xenograft models than corresponding conjugates prepared with uncleavable thioether-based linkers. To investigate how the linker influences delivery and activation of antibody-maytansinoid conjugates, we isolated and characterized the [(3)H]maytansinoids from CanAg-positive tumor tissues following a single intravenous administration of 300 microg/kg (based on maytansinoid dose) of anti-CanAg antibody (huC242)-(3)H-maytansinoid conjugates prepared with cleavable disulfide linkers and an uncleavable thioether linker. We identified three target-dependent tumor metabolites of the disulfide-linked huC242-SPDB-DM4, namely, lysine-N(epsilon)-SPDB-DM4, DM4, and S-methyl-DM4. We found similar metabolites for the less hindered disulfide-linked huC242-SPP-DM1 conjugate with the exception that no S-methyl-DM1 was detected. The sole metabolite of the uncleavable thioether-linked huC242-SMCC-DM1 was lysine-N(epsilon)-SMCC-DM1. The AUC for the metabolites of huC242-SMCC-DM1 at the tumor over 7 d was about 2-fold greater than the corresponding AUC for the metabolites of the disulfide-linked conjugates. The lipophilic metabolites of the disulfide-linked conjugates were found to be nearly 1000 times more cytotoxic than the more hydrophilic lysine-N(epsilon)-linker-maytansinoids in cell-based viability assays when added extracellularly. The cell killing properties associated with the lipophilic metabolites of the disulfide-linked conjugates (DM4 and S-methyl-DM4, and DM1) provide an explanation for the superior in vivo efficacy that is often observed with antibody-maytansinoid conjugates prepared with disulfide-based linkers in xenograft mouse models.

Nanotechnology applications in surgical oncology

Surgery is currently the most effective and widely used procedure in treating human cancers, and the single most important predictor of patient survival is a complete surgical resection. Major opportunities exist to develop new and innovative technologies that could help the surgeon to delineate tumor margins, to identify residual tumor cells and micrometastases, and to determine if the tumor has been completely removed. Here we discuss recent advances in nanotechnology and optical instrumentation, and how these advances can be integrated for applications in surgical oncology. A fundamental rationale is that nanometer-sized particles such as quantum dots and colloidal gold have functional and structural properties that are not available from either discrete molecules or bulk materials. When conjugated with targeting ligands such as monoclonal antibodies, peptides, or small molecules, these nanoparticles can be used to target malignant tumor cells and tumor microenvironments with high specificity and affinity. In the "mesoscopic" size range of 10-100 nm, nanoparticles also have large surface areas for conjugating to multiple diagnostic and therapeutic agents, opening new possibilities in integrated cancer imaging and therapy.

Oscillatory dynamics in a model of vascular tumour growth--implications for chemotherapy

BACKGROUND

Investigations of solid tumours suggest that vessel occlusion may occur when increased pressure from the tumour mass is exerted on the vessel walls. Since immature vessels are frequently found in tumours and may be particularly sensitive, such occlusion may impair tumour blood flow and have a negative impact on therapeutic outcome. In order to study the effects that occlusion may have on tumour growth patterns and therapeutic response, in this paper we develop and investigate a continuum model of vascular tumour growth.

RESULTS

By analysing a spatially uniform submodel, we identify regions of parameter space in which the combination of tumour cell proliferation and vessel occlusion give rise to sustained temporal oscillations in the tumour cell population and in the vessel density. Alternatively, if the vessels are assumed to be less prone to collapse, stable steady state solutions are observed. When spatial effects are considered, the pattern of tumour invasion depends on the dynamics of the spatially uniform submodel. If the submodel predicts a stable steady state, then steady travelling waves are observed in the full model, and the system evolves to the same stable steady state behind the invading front. When the submodel yields oscillatory behaviour, the full model produces periodic travelling waves. The stability of the waves (which can be predicted by approximating the system as one of lambda-omega type) dictates whether the waves develop into regular or irregular spatio-temporal oscillations. Simulations of chemotherapy reveal that treatment outcome depends crucially on the underlying tumour growth dynamics. In particular, if the dynamics are oscillatory, then therapeutic efficacy is difficult to assess since the fluctuations in the size of the tumour cell population are enhanced, compared to untreated controls.

CONCLUSIONS

We have developed a mathematical model of vascular tumour growth formulated as a system of partial differential equations (PDEs). Employing a combination of numerical and analytical techniques, we demonstrate how the spatio-temporal dynamics of the untreated tumour may influence its response to chemotherapy.

REVIEWERS

This manuscript was reviewed by Professor Zvia Agur and Professor Marek Kimmel.

Gold nanocages as photothermal transducers for cancer treatment

Gold nanocages represent a new class of nanomaterials with compact size and tunable optical properties for biomedical applications. They exhibit strong light absorption in the near-infrared region in which light can penetrate deeply into soft tissue. After PEGylation, the Au nanocages can be passively delivered to tumors in animals. Analysis of tissue distribution for the PEGylated Au nanocages showed that the tumor uptake was 5.7 %ID/g at 96 h post injection. The Au nanocages were found not only on the surface, but also in the core of the tumor. By exposing tumors to a near-infrared diode laser (0.7 W/cm2, CW, λ=808 nm) for 10 min, the photothermal effect of the Au nanocages could selectively destroy tumor tissue with minimum damage to the surrounding healthy tissue. Data from functional [18F]fluorodexoyglucose positron emission tomography revealed a decrease in tumor metabolic activity upon the photothermal treatment. Histological examination identified extensive damage to the nuclei of tumor cells and tumor interstitium.

Transmural flow modulates cell and fluid transport functions of lymphatic endothelium

RATIONALE

Lymphatic transport of peripheral interstitial fluid and dendritic cells (DCs) is important for both adaptive immunity and maintenance of tolerance to self-antigens. Lymphatic drainage can change rapidly and dramatically on tissue injury or inflammation, and therefore increased fluid flow may serve as an important early cue for inflammation; however, the effects of transmural flow on lymphatic function are unknown.

OBJECTIVE

Here we tested the hypothesis that lymph drainage regulates the fluid and cell transport functions of lymphatic endothelium.

METHODS AND RESULTS

Using in vitro and in vivo models, we demonstrated that lymphatic endothelium is sensitive to low levels of transmural flow. Basal-to-luminal flow (0.1 and 1 mum/sec) increased lymphatic permeability, dextran transport, and aquaporin-2 expression, as well as DC transmigration into lymphatics. The latter was associated with increased lymphatic expression of the DC homing chemokine CCL21 and the adhesion molecules intercellular adhesion molecule-1 and E-selectin. In addition, transmural flow induced delocalization and downregulation of vascular endothelial cadherin and PECAM-1 (platelet/endothelial cell adhesion molecule-1). Flow-enhanced DC transmigration could be reversed by blocking CCR7, intercellular adhesion molecule-1, or E-selectin. In an experimental model of lymphedema, where lymphatic drainage is greatly reduced or absent, lymphatic endothelial expression of CCL21 was nearly absent.

CONCLUSIONS

These findings introduce transmural flow as an important regulator of lymphatic endothelial function and suggest that flow might serve as an early inflammatory signal for lymphatics, causing them to regulate transport functions to facilitate the delivery of soluble antigens and DCs to lymph nodes.

Targeting of drugs and nanoparticles to tumors

The various types of cells that comprise the tumor mass all carry molecular markers that are not expressed or are expressed at much lower levels in normal cells. These differentially expressed molecules can be used as docking sites to concentrate drug conjugates and nanoparticles at tumors. Specific markers in tumor vessels are particularly well suited for targeting because molecules at the surface of blood vessels are readily accessible to circulating compounds. The increased concentration of a drug in the site of disease made possible by targeted delivery can be used to increase efficacy, reduce side effects, or achieve some of both. We review the recent advances in this delivery approach with a focus on the use of molecular markers of tumor vasculature as the primary target and nanoparticles as the delivery vehicle.

Design and fabrication of magnetic nanoparticles for targeted drug delivery and imaging

Magnetic nanoparticles (MNPs) represent a class of non-invasive imaging agents that have been developed for magnetic resonance (MR) imaging. These MNPs have traditionally been used for disease imaging via passive targeting, but recent advances have opened the door to cellular-specific targeting, drug delivery, and multi-modal imaging by these nanoparticles. As more elaborate MNPs are envisioned, adherence to proper design criteria (e.g. size, coating, molecular functionalization) becomes even more essential. This review summarizes the design parameters that affect MNP performance in vivo, including the physicochemical properties and nanoparticle surface modifications, such as MNP coating and targeting ligand functionalizations that can enhance MNP management of biological barriers. A careful review of the chemistries used to modify the surfaces of MNPs is also given, with attention paid to optimizing the activity of bound ligands while maintaining favorable physicochemical properties.