Advanced Drug Delivery Reviews 79–80 (2014) 107–118

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Advanced Drug Delivery Reviews

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Nanoparticle targeting of anti-cancer drugs that alter intracellularsignaling or influence the tumor microenvironment☆

Mathumai Kanapathipillai a, Amy Brock b, Donald E. Ingber a,c,d,⁎a Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, MA, USAb Department of Biomedical Engineering, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX USAc Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA, USAd School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

☆ This review is part of the Advanced Drug Delivery Revieof Tumor Microenvironments".⁎ Corresponding author at: Wyss Institute for Biolog

Harvard University, Boston, MA, USA.E-mail address: don.ingber@wyss.harvard.edu (D.E. In

http://dx.doi.org/10.1016/j.addr.2014.05.0050169-409X/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Available online 9 May 2014

Keywords:NanoparticleTumorNanotherapeuticsDeliveryMicroenvironmentDrug

Nanoparticle-based therapeutics are poised to become a leading delivery strategy for cancer treatment becausetheypotentially offer higher selectivity, reduced toxicity, longer clearance times, and increased efficacy comparedto conventional systemic therapeutic approaches. This article reviews existing nanoparticle technologies andmethods that are used to target drugs to treat cancer by altering signal transduction ormodulating the tumormi-croenvironment.Wealso consider the implications of recent advances in the nanotherapeuticsfield for the futureof cancer therapy.

© 2014 Elsevier B.V. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072. Targeting signaling networks in cancer cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

2.1. Surface-receptor mediated pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092.1.1. Transmembrane delivery vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

2.2. Targeting intracellular signaling molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102.2.1. Focused delivery of siRNAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

3. Targeting the tumor microenvironment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.1. Vasculature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

3.1.1. Angiogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113.1.2. Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

3.2. Immune response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1123.3. Extracellular matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1123.4. Multi-drug resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

4. Challenges for the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

ws theme issue on "Engineering

ically Inspired Engineering at

gber).

1. Introduction

Current cancer chemotherapies often fail to improve patient mor-tality and morbidity due to severe adverse effects on normal tissues.Targeted nanocarrier systems potentially offer a solution to thisproblem because they can be designed to deliver cargo preferentiallyto the tumor cells, sparing healthy tissue from dose-limiting sideeffects. Because their size and shape can be tailored as needed,nanotherapeutics also enhance bioavailability and plasma solubility,

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decrease systemic toxicity, increase patient compliance and improvepharmacokinetics of biologics and small molecules that otherwisehave short half-lives in vivo.

The field of nanotherapeutics has been made possible by thedevelopment of manufacturing methods that enable synthesis, self-assembly or fabrication of objects with defined size, shape and chemis-try on the nanometer scale and that are also biocompatible. These areeither composed of multiple molecules or single molecules that areengineered to contain multiple functional cassettes. Examples ofbiocompatible nanocarriers include those composed of liposomes,polymers, micelles, engineered multi-functional antibodies, and nano-particles that can be composed of metals (e.g., gold, silver), polymer,quantum dots, dendrimers, fullerenes, ferritin, proteins, DNA, other bio-logical molecules or combinations of these materials (Fig. 1) [1–4].Nanomaterials also can be precisely designed to achieve desiredphysical and chemical properties necessary to target delivery of drugsto the dynamic tumor microenvironment with higher therapeuticefficacy and lower toxicity. For example, surface to volume ratio, size,geometry, surface charge, shape and stimuli-responsive properties areexamples of design features that can be controlled when formulatingnanotherapeutics. Once the nanoparticles are created, they also can befunctionalized with additional chemical moieties, such as antibodiesor ligands for cell surface receptors, to target to selective sites, preventclearance from blood, and provide other desired functional properties.

To achieve effective targeting to cancerous tissues, systemically de-livered nanoparticles must first extravasate from the bloodstream,pass through the tumor extracellular matrix (ECM), bind to cells, andthen cross the surface membrane to enter the target cells and reach ap-propriate intracellular sites (Fig. 2) [5–7]. Two targeting strategies, oneactive and the other passive, have been utilized to enhance nanoparticle

Fig. 1.Multi-valent, multi-functional and stimuli-responsive nanocarrier delivery systems for tupolymers, micelles, engineered antibodies and nanoparticles decorated with stimuli-responsivedrugs or imaging agents (stars and suns).

delivery to tumors. In passive targeting, one capitalizes on the leaky na-ture of tumormicrovessels, which results in enhanced permeability andretention (EPR) responses that facilitate greater accumulation of nano-particles compared to individual soluble molecules or drugs in theperivascular tumormicroenvironment. The EPR effect varies dependingon the size and surface properties of the nanocarriers, and hence, nano-particles must be designed to achieve maximum targeting and thera-peutic efficacy. Nanocarriers in the size range of 20–200 nm can easilyextravasate through the walls of poorly formed microvessels in the an-giogenic tumor niche, and poor lymphatic drainage further enhancestheir accumulation. Several nanoparticles that utilize this EPR-basedpassive targeting strategy are currently in human clinical trials [8,9].Examples include the doxorubicin-liposome carriers Myocet and Doxil[10,11], which have increased half-lives in the blood due to the size ofthe nanocarrier and in the case of Doxil, chemical coating of the lipo-some with poly-ethyleneglycol (PEG). Passive targeting polymericmicelles, nanoparticles, and polymer-drug conjugates are also in clinicaltrials for breast, lung, pancreatic and ovarian cancers [9,11].

The creation of targeting antibodies in late 1970s led to the develop-ment of the first active or targeted nanoparticle delivery strategies [12,13]. The concept was simple: by coating nanoparticles with antibodies,they could be selectively directed to sites expressing the target antigen.This active targeted delivery approach was later extended by coatingnanoparticles with targeting ligands, lectin-carbohydrates, or antigenmolecules that recognize specific sites or endogenous antibodies to fa-cilitate intracellular drug delivery [5,14]; these targeting ligands includepeptides, antibodies, aptamers, small molecules and proteins amongothers [5,14,15]. The density of these ligands on the surface of the nano-particles also can be fine-tuned to optimize binding and targeting usingseveral physical and chemical immobilization techniques. Examples

mor targeting. Examples of nanocarrier delivery vehicles include (left to right) liposomes,cleavable stealth coatings (blue rectangles), targeting moieties (arrows), and anti-cancer

Fig. 2. A schematic depicting the mechanism by which nanoparticles are transported to the tumor and its surrounding microenvironment. Nanoparticles that escape reticuloendothelialsystem (RES) during circulation, reach tumor blood vessels and subsequently extravasate into the tumor interstitium. After overcoming transport barriers and diffusion limitations, nano-particles reach the targeted tumor cells, where they deliver their cargo or imaging agents.

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include technologies that enable precise control of size, shape, composi-tion and surface modification of nanoparticles [16,17] and a lipid inser-tion method that is used for targeted functionalization of erythrocyte-cloaked nanoparticles [18]. There are only a few active targeted cancernanotherapeutics in clinical trials. The two that are farthest along aredoxorubicin-containing immunoliposomes that are targeted to cancersusing a humanmonoclonal antibody, and transferrin-targeted oxaliplatinliposomes; however,most of the published results on these nanotechnol-ogies refer to preclinical studies [11,19,20].

The most common anti-cancer nanotherapeutics in developmenttarget receptors on the surface membranes of tumor cells to enhancelocal drug concentrations, facilitate drug entry into the cell, and selec-tively perturb specific receptor-mediated signaling pathways [5]. How-ever, as our understanding of cancer biology has advanced, there hasbeen increased recognition of the importance of intracellular signalingmolecules and particular genes for cancer development, as well asnew appreciation for the key role that the tumor microenvironment(e.g., capillary blood vessels, stroma, ECM composition and mechanics,immune cells, etc.) contributes to cancer control. Thus, nanocarriersare also being employed to selectively concentrate drugs at tumorsites based on the tumormicroenvironment, as well as to target specificintracellular signaling molecules, and genes. Nanoparticles with multi-valency,multi-functionality, and triggered or stimuli-responsive releaseproperties (Fig. 1) are all currently being explored for tumor targeting[6,21–23]. Clearly, there are still many challenges that need to be over-come before we can design fully effective, targeted, nanoscale, drugdelivery systems that will overcome the complex interactions betweenthe tumor cell's intracellular information processing network and theever-changing tumor microenvironment that govern cancer formationand expansion. Thus, in this review, we focus on various nanoparticle-based drug delivery approaches that are being developed to either tar-get intracellular signaling pathways or the tumor microenvironment,as shown in the schematic in Fig. 3. We also explore the implicationsof recent developments in this field for the future of targeted cancertherapy.

2. Targeting signaling networks in cancer cells

Cancers are heterogeneous in nature, and their growth and progres-sion depend on reciprocal interactions between tumor cells and theirsurrounding microenvironment [24–26]. Information processing net-works that govern cancer behavior include both chemical and geneticsignaling pathways inside individual tumor cells, as well as inter-cellular signaling networks that involve soluble cues transferred backand forth between tumor cells and surrounding vascular endothelial

cells, cancer-associated fibroblasts, and cells of the immune system[24,27,28]. In this section, we examine nanoparticle-based deliverystrategies that target drugs to these diverse information handling net-works that process soluble cues in the tumor.

2.1. Surface-receptor mediated pathways

Detailedmolecular characterization of tumor cell signaling networkshas identified changes in growth signaling receptors that characterizespecific tumor types. Active targeting of nanoparticles to these signalingcomponents could potentially increase therapeutic effectiveness and re-duce collateral damage caused by chemotherapeutic drugs on normalhealthy tissues. Molecular recognition of tumor cells may exploit li-gand–receptor interactions or antigen–antibody binding to efficientlytarget the nanoparticle drug delivery vehicle to the tumor. Humanizedantibodies are attractive for targeting cell surface receptors due totheir high specificity and low immune reactivity [29]. Active targetingvia antibody interactions can distinguish cancerous cells from normaltissue and also can target specific subpopulations of cancer cells [30].

Folate is one of the most extensively utilized ligands for targetedcancer nanotherapeutics due to its high affinity binding to the folate re-ceptor (Kd ~10−9) and because it is frequently overexpressed in diversetumor types including uterine sarcomas, ovarian carcinomas, osteosar-comas, and non-Hodgkin's lymphomas [30]. Folate recently was usedto target delivery of tamoxifen with albumin and alginate-based nano-particles [31] and enhanced in vivo targeting of camptothecin to pancre-atic xenografts was accomplished through the use of folate-coatedmesoporous silica nanoparticles loaded with this drug [32]. Significantreduction in tumor volume and enhanced renal clearance were ob-served comparedwith uncoated particles in the camptothecin nanopar-ticle studies.

Transferrin is an iron-binding plasma glycoprotein that facilitatesiron uptake by cells through binding to its membrane receptor, TfR[33], and this receptor is overexpressed by as much as 10-fold inmany tumor cell types [34]. Ligand binding of TfR initiates endocytosis,which has been exploited for targeted delivery of transferrin-coatednanoparticles. In vivo examples of this approach include the targetingof transferrin-conjugated paclitaxel-loaded nanoparticles to prostate[34], and delivery of transferrin-coated PLGA-nanoparticles to gliomas[35] in animal studies.

Epidermal growth factor receptor (EGFR) is over-expressed in manycancers and can serve as a target for nanotherapeutics through bindingof one of its two natural ligands: epidermal growth factor (EGF) ortransforming growth factor-alpha (TGF-α). EGF-conjugation of stearoylgemcitabine nanoparticles (GemC18-NPs) has been shown to result in a

Fig. 3. Schematic of potential strategies for selectively targeting nanoparticles to various key structures and features of the tumormicroenvironment, including the vasculature (1), hypoxicregions (2), and intracellular signaling networks (3, a) and surface receptors (3, b) on tumor cells, extracellular matrix (4) and the immune response (5). Insert at left shows a multi-functional nanoparticle decorated with targeting moieties and loaded with drugs.

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2-fold improvement in its targeting to tumor cells that over-expressEGFR [36]. Human epidermal growth factor receptor 2 (HER2) is over-expressed in breast, ovarian, gastric and uterine cancers and it is the tar-get of the monoclonal antibody trastuzumab (marketed as Herceptin).Human serum albumin nanoparticles that were surface-coated withtrastuzumab and loadedwith the cytostatic drug doxorubicin displayedenhanced cell uptake and biological activity [37]. Such targetedapproaches may be key to reducing clinical issues of cardiotoxicitythat can be a major source of morbidity in patients receiving doxorubi-cin. The challenge of doxorubicin resistance also may be overcome, orat least reduced, using nanoparticles that are not recognized byP-glycoprotein, which is one of the main protein pumps that mediatesthe multidrug resistance response.

2.1.1. Transmembrane delivery vehiclesSeveral transmembrane nanoparticle-based delivery strategies have

been reported to permit the delivery of small molecules, proteins, smallinterfering ribonucleic acids (siRNAs) and imaging agents to intracellu-lar compartments of tumor cells. Smallmolecule-mediatednanoparticledelivery of small molecules is commonly accomplished by utilizingmechanismsof endosomal escape and cytosolic release of nanoparticles.Delivery of doxorubicin bymesoporous silica nanoparticles coated withpolyethylenimine (PEI) [38] and gold nanoparticles coated with doxo-rubicin conjugated to an acid cleavable PEG linker [39] have both beenshown to effectively deliver smallmolecules into cytosol. More recently,it was shown to be possible to target chemotherapeutic drugs to mito-chondria using poly(lactic-co glycolic acid) (PLGA)–PEG nanoparticlesblended with triphenylphosphonium, a lipophilic cation known tocross mitochondrial membranes [40,41].

For intracellular protein delivery, silica nanoparticles that targetphospho-Akt (protein kinase B) to inhibit its kinase activity have beendeveloped [42]. The nanoparticles enter cells through the endosomalpathway and subsequent escape into the cytosol, causing protein deliv-ery and eventually, cell death. Intracellular protein delivery also hasbeen accomplished by targeting the ribosome inhibiting proteins (RIP)

that suppress translation [43]. Several “cell penetrating peptides,” suchas the TAT (transactivated-transcription) sequence, have been utilizedto mediate transfer of peptides and proteins across cell membranes anddirectly into the cytosol [44]. These have been used to create nanocarriersthat can enter the cytoplasm as well. Examples include TAT-conjugatedPLGA nanoparticles to deliver K237 peptides that target the kinase insertdomain receptor for brain drug delivery [45], and intracellular delivery ofquantum dot-mediated protein delivery and imaging [46].

The physical properties of nanoparticles also have been leveraged toenhance cellular internalization. For example, the specificity of targetingligand-coated nanoparticles can be augmented by engineering theirshape to exhibit distinct 3D geometries. PEG-hydrogel rods with ahigh aspect ratio of 150 × 450 nm exhibit higher cellular uptake com-pared with cylindrical particles with 200 × 200 nm dimensions [47].Uptake and internalization of trastuzumab-coated nanoparticles bybreast cancer cells alsowere found to be higher for rod-shaped particles,followed by disks, and then spheres [48]. Interestingly, rod-shaped par-ticles were also found to provide improved specificity of endothelialtargeting in lung and brain compared with other geometries [49].Thus, the ability to shape nanocarriers provides an alternativeway to af-fect drug delivery, independently of the drug being delivered or theirsurface coating.

2.2. Targeting intracellular signaling molecules

Intracellular signalingmolecules control cell proliferation, differenti-ation, and survival, aswell asmyriadmetabolic functions in cells. Duringcancer progression, the signaling networks undergo severe alterationand deregulation. Therapeutic targeting of specific molecules withinthese complex tumor signaling networks remains a challenge due topoor drug penetration into intracellular compartments. Nanocarriersoffer a new way to overcome this challenge because they can be tunedto deliver the cargo by receptor-mediated internalization as well asorganelle- or intracellular molecule-specific targeting. Below, we out-line some recent developments in this area.

111M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

2.2.1. Focused delivery of siRNAsThe recent development of siRNAs, which direct sequence-specific

degradation of target mRNA transcripts, has led to the development ofan entirely new class of therapeutics for cancer. As the siRNA moleculeitself is strongly negatively charged, delivery to cells is typically accom-plished by complexing it with a cationic carrier or lipid-based nanopar-ticle. In the first-in-human trials studies, siRNA was targeted to the M2subunit of ribonucleotide reductase via cyclodextrin–PEG nanoparticlescoated with human transferrin [50]. TfR receptor is expressed at highlevels on malignant cells as described above, and thus this enhancedaccumulation of the nanoparticles at tumor sites in patients with refrac-tory melanoma.

A new class of nanoparticle materials, termed “lipidoids,” has beendeveloped to facilitate siRNA delivery. Lipidoids are derived from anamine-containing backbone from which aliphatic chains extend; theamines appear to interact electrostatically with the nucleic acid phos-phate backbone and facilitate endosomal escape as the compartmentbecomes acidified. The efficacy of lipidoid nanoparticle-siRNA formula-tions has been demonstrated in the silencing of tight junction proteinclaudin-3 in animals models of ovarian cancer [51] as well as Parp1 inBrca1-deficient ovarian tumors [52] and glycolytic enzyme pyruvate ki-nase in several xenograftmodels [53]. Injection of lipidoid nanoparticlescarrying siHoxA1 through the nipple and directly into the mammaryduct prevented the progression of mammary tumors in the C3(1)SV40TAg transgenic mice [54].

Although siRNA delivery by nanoparticles is able to delivery micro-grams of drug per kilogram of animal body weight, there remainsroom for additional improvement. For example, better understandingof the endocytotic pathways of particular siRNA–nanoparticle formula-tions may improve their efficiency of delivery. After lipid nanoparticlesenter the cell, a significant amount of siRNA remains trapped in endocy-totic vesicles and does not reach its intracellular target. In parallel, vesiclerecycling continues to rapidly clear the siRNA–nanoparticles from the cellbefore the payload is delivered. One recent study identified Niemann–Pick type C1 (NPC1) as a critical regulator of the major recycling path-ways of lipid nanoparticle-formulated siRNAs. In cells lacking NPC1,there was enhanced retention of nanoparticles inside the endosomeand lysosomes of the recycling pathway, and the level of gene silencingachievedwith RNA interferencewas 10 to 15 times greater than that pro-duced in normal cells [55]. Strategies to target specific molecular compo-nents of endosome production, trafficking and recycling may beincorporated into the design of the next generation of nanocarriers forsiRNA delivery. Another challenge is that immune stimulation throughα/β interferons, RNA-dependent kinase effects, and Toll-like immunitycould limit the safety profiles of siRNAs. However, if this immune activat-ing activity of the siRNAs can be controlled or even exploited for useagainst the tumor, this side effect could potentially improve treatment ef-ficacy. The current status of nanoparticle-based RNAi therapies in clinicaltrials for oncology applications is shown in Table 1.

3. Targeting the tumor microenvironment

Over the past few decades, it has become recognized that tumorgrowth and progression are not solely the result of cumulative gene

Table 1Nanocarrier-mediated siRNA delivery systems in clinical trials.

Drug Disease Target Nanopa

FANG Ovarian tumors FURIN LiposomCALAA-01 Solid tumors RRM CyclodeALN-VSP02 Solid tumors with liver involvement VEGF, KSP SNALPAtu027 Advanced or metastatic solid tumors PKN3 LiposomsiG12D LODER Pancreatic ductal adenocarcinoma KRASG12D PolymeTKM 080301 Solid tumors PLK1 SNALPsiRNA–EphA2–DOPC Solid tumors EphA2 Liposom

mutations, but are also significantly influenced by the surroundingtumor microenvironment. In addition to cancer cells, the dynamictumor microenvironment consists of ECM, stromal cells, endothelialcells, and immune cells that are recruited from surrounding tissues aswell as from the bone marrow [25,56]. Interestingly, the chemistry,structure and mechanical properties of the tumor microenvironmentall influence the cellular information processing networks that drivephenotypic changes leading to tumor malignancy [24,56–59]. Hence, itis important to consider both cellular and non-cellular components oftumor microenvironment for cancer therapy as their complex interac-tions play a critical role in cancer progression. In this section we discussnanoparticle-based delivery systems that have been reported to targetvarious components of the tumor microenvironment.

3.1. Vasculature

In contrast to normal tissues, the vasculature of tumors is marked bya heterogeneous distribution of vessel sizes and shapes, generally largervessel diameters, higher vascular density, and enhanced permeability.This inherently leaky vasculature promotes preferential accumulationof nanoparticles in the tumor interstitial space, and when coupledwith impaired lymphatic drainage of macromolecules, this results inthe EPR effect characterized by increased accumulation of nanoparticlesthat is observed in many solid tumors [60], as described above. The EPReffect has been successfully exploited for passive targeting of drugs tosolid tumors in animals that are encapsulated in a variety of highmolec-ular weight carrier systems, including polymeric drug conjugates, lipo-somes, polymeric NPs and micelles [61–64]. However, below we focuson strategies for active targeting of nanotherapeutics to the tumorvasculature.

3.1.1. AngiogenesisOne of the major angiogenic factors elaborated by tumors – vascular

endothelial growth factor (VEGF) – both stimulates new capillary in-growth and increases the permeability of blood vessels [65]. Targetingthe VEGF receptor on endothelial cells is therefore an effective methodto prevent cancer growth by blocking tumor angiogenesis. Targetingthe VEGF receptor-2 (VEGFR-2) has been investigated as a way to en-hance delivery of various nanoparticle systems to tumor vessels, includ-ing boronated dendrimers and radioisotype-labeled polymerizedliposomes [66]. VEGF targeting also was accomplished in an animalmodel of hepatic carcinoma using dextran magnetic nanoparticles(DMNs) conjugated to radiolabeled 131I-anti-VEGF monoclonal anti-bodies [67].

One of the first angiogenic inhibitors TNP-470 demonstrated broadspectrum activity in early trials, including efficacy in metastatic diseasein human patients, but then stalled in part due to neurotoxicities. Areformulation of this angiogenesis inhibitor composed of polymericPEG–PLGA nanoparticles surrounding a TNP-470 core, called Lodamin,was shown to prevent the compound from crossing the blood–brainbarrier, eliminating its neurotoxicity, while retaining its potency andbroad-spectrum activity [68–70]. The new Lodamin formulation alsogreatly improved oral availability as the polymeric PEG and PLA protectthe inner active compound from degradation by the acidic stomach

rticle Company Stage Status

e Gradalis, Inc. Phase II Activextrin/PEG, transferrin Calando Pharm Phase I Ongoing

Alnylam Pharm. Phase I/II Completede Silence Therapeutics Phase I Completedr matrix Silenseed Ltd. Phase I Ongoing

Tekmira Pharma Phase I Recruitinge M.D. Anderson Cancer Center Phase I Recruiting

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environment. Lodamin is also under investigation as a therapeutic forophthalmologic diseases of the vasculature including diabetic retinopa-thy and age-related macular degeneration.

Vascular cell adhesionmolecule-1 (VCAM-1) is an immunoglobulin-like transmembrane glycoprotein receptorwhichmediates immune celladhesion that is expressed at high levels on the surfaces of endothelialcells in tumor blood vessels. Liposome nanoparticles coated with anti-VCAM-1 antibodies selectively target the human tumor vasculaturein vivo in xenograft studies [71]. Thus, VCAM-1-targeted nanocarrierscould provide a way to both enhance delivery of drugs to growingtumor vessels and alter endothelial function.

Knowledge of themechanism bywhich nanoparticles enter vascularendothelial cells also has given rise to modifications that further en-hance targeting. Caveolae-mediated endocytosis is the most prominenttransendothelial delivery pathway and has attracted interest because ithas the capability to bypass lysosomes. Surface modifications thatenhance caveolae targeting, such as coating gold nanoparticles withan antibody to the caveolae-enriched protein aminopeptidase P, havebeen shown to be effective in concentrating the nanomedicine in lungtumor microvasculature [72].

3.1.2. HypoxiaHypoxia is a hallmark of cancer, which results from rapid tumor cell

growth that overcomes the rate of vascular ingrowth. Hypoxic regionsin tumors experience high interstitial pressure build updue to compres-sion of blood vessels, poor lymphatic drainage and deterioration ofstructural features of tissues that support diffusion. Hypoxia is also com-monly associated with poor circulation, tumor progression, malignancyand multi-drug resistance and hence, the delivery of drugs to hypoxicmicroenvironments remains a significant clinical challenge in cancertherapy [73–75].

Several nanotherapeutic strategies have been used to developtheranostics (combined therapeutics and diagnostics) for hypoxic envi-ronmentswithin tumors. For example, a layer-by-layer assembled poly-electrolyte nanoparticle has been shown to selective target to hypoxicregions of tumors [76]. Targeting is based on the low pH in the hypoxicmicroenvironment, which triggers shedding of the outer layer of thenanoparticle, revealing a charged nanoparticle surface that is subse-quently taken up by cells. Hypoxia-activated, near-infrared (NIR)light-triggered chitosan nanoparticles also have been developed todeliver drugs to cancer cells [77]. This smart nanosystem consists of ahypoxic sensor, a photoactivatable trigger, and a caged drug; as it ishighly specific to the hypoxic tumor microenvironment, its selectivityis greatly increased. Polystyrene nanoparticles doped with an oxygen-sensitive NIR-emissive palladium meso-tetraphenylporphyrin that se-lectively activate and emit optical signalswhen they experience hypoxicconditions also have been developed [78]. In vitro, the nanoparticleswere easily phagocytosed bymurine alveolarmacrophages and exhibit-ed sensitivity to low oxygen concentrations resulting from induction ofhypoxia inducible factor-1α (HIF-1α). Experiments performed in vivowith tumor-bearing mice confirmed that these nanoparticles can beused as imagingprobes for tumor hypoxia; however, the sameapproachpotentially could be leveraged to develop therapeutics.

3.2. Immune response

Renewed recognition of the critical role of the immune system incancer has driven the development of immunotherapies that targetexisting tumors and enhance long-term immune surveillance. Nanopar-ticle carriers improve specificity of immune-cell targeting, permitsimultaneous delivery of antigens and immune agents, and enhancesustained release.

Human interleukin 12 (IL-12) induces a potent anti-tumor immuneresponse, but systemic administration of IL-12 in early clinical trialsresulted in serious dose-dependent toxicities, including death. In xeno-graft models, intratumoral injection of IL-12 loaded liposomes resulted

in an enhanced memory T cell response [79]. Importantly, the drugdid not enter the peripheral blood circulation, suggesting that thiscould help to improve its safety profile [79].

Biodegradable nanoparticles are emerging as tools for targetingtumor antigens to dendritic cells, which is a critical step in eliciting cyto-toxic T cell activation for antitumor vaccine efficacy [80]. Several studieshave demonstrated the successful use of mannose-grafted nanocarriersand an increase in the uptake of these carriers by dendritic cells. For ex-ample, PLGA nanoparticles coated with mannan, a natural polymannoseisolated from the cell wall of Saccharomyces cerevisae, have been shownto have a stronger binding affinity and produce increased CD4+ andCD8+ T cell responses compared to unmodified nanoparticle surfaces[81]. Other particulate vaccines have been successfully developed to spe-cifically target the mannose receptor, such as mannose–PEG3–NH2-dec-orated PLGAmannose [82], mannosylated-gelatin nanoparticles [83] andliposomes containing mannosyl lipid derivatives [84]. Targeting antigensto C-type lectin receptors also has been shown to result in enhanced hu-moral and cellular responses which are sufficient to induce immunityagainst melanomas tumors in vivo [85]. Moreover, similar targeting canbe accomplished using anti-lectin antibodies instead of lectin ligands[86].

Another attractive property of nanoparticle carriers is that they offerthe potential to deliver both antigen and adjuvant simultaneously to thesame cell, thus improving the sustained immune response. Several Toll-like receptor (TLR) ligands have been tested as adjuvants of cancer vac-cines in clinical trials for various cancers, includingmelanoma, lympho-ma, glioblastoma, breast, prostate, ovarian and lung. As some TLRligands have severe systemic side effects, nanoparticle delivery to thedesired site of action can greatly improve their safety profile and permituse of lower doses. In addition, nanocarriers can improve intracellularuptake, thus expanding the range of targeting options to intracellularreceptor family members such as TLR3, 7, 8 and 9 [87].

Another approach uses programmable macroporous 3D PLGA scaf-folds containing nanoparticles to induce endogenous dendritic cells torecognize tumor antigens placed within the scaffold, and to mount asystemic anti-cancer response in vivo [88]. The scaffolds contain tumorantigens from biopsy samples along with PLGA microspheres thatrelease the chemokine GM-CSF to recruit the dendritic cells, andpolyethylenimine (PEI)–CpG cationic nanoparticles containing the im-mune adjuvant CpG to stimulate dendritic cell maturation. When im-planted in a mice tumor melanoma model, this nanoparticle-enabledvaccine resulted in survival of 90% of tumor-bearing animals [88] andintracranial regression of glioma has been demonstrated in rats [89].These programmable scaffolds comprising micro and nanoparticlesshow potential in future cancer immune therapy, and human Phase Iclinical trials were recently initiated with this technology.

Onenew approach to stimulating the host immune response is usinglight-activated nanoparticles: biodegradable polymer and zinc phthalo-cyanine (ZnPc) photosensitizer nanoparticles target the mitochondriaof cancer cells and subsequent light activation elicits the production oftumor antigen, triggering dendritic cell activation [90]. These ex vivostudies suggest that secreted compounds from mitochondria-targetedand light-activated cancer cells also might be useful as cancer vaccines.

3.3. Extracellular matrix

Tumors have a dense ECM consisting of highly interconnected cross-linked collagen fibers and associated large glycoproteins and proteogly-cans. Changes in the structure and mechanical properties of the ECMcan alter cellular mechanical signaling pathways and thereby influencesubsequent tumor progression and metastasis [57,91,92]. For example,during tumor progression, overexpression of the ECM-modifying en-zyme lysyl oxidase (LOX) results increased collagen cross-linking,thereby increasing ECM rigidity and tissue tension [93,94]. Moreover,experimental inhibition of LOXenzymeactivity suppresses tumor growthand prevents cancer progression, and this is mediated by decreasing

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collagen cross-linking and restoring more normal-like tissue compliance[91,95]. Importantly, when blocking LOX antibodies were delivered onbiodegradable PLGA-based polymer nanoparticles (~200 nm diameter)created using self-assembly, they produced more effective tumor inhibi-tion in animals using lower doses, and they had a higher therapeuticindex (Fig. 4) [96]. Compared to systemic injection of free LOX antibody,this LOX antibody-coated nanotherapeutic exhibited significanttumor inhibition with only ~1/30th dose normally used for systemicadministration.

Proteoglycans are also a major contributor to ECMmechanics and inparticular, studies have focused on the roles of hyaluronic acid (HA) andthe proteoglycan versican in tumor ECM mechanics. Interactionbetween versican with HA and its cell surface receptor, CD44, servesto modulate the ECMmechanical environment, thereby altering cancercell proliferation and migration [97,98]. Several studies have utilizedHA-conjugated nanocarriers to target CD44 over-expressing cancercells and to deliver anti-cancer drug to the tumor site. For example,intelligent core-corona HA–PEG–PCL nanoparticles have been usedto deliver doxorubicin in Ehrlich ascites tumor-bearing mice, and

Self-assem

aqueous soPLGA-b-PEG-COOH

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Fig. 4. A) Schematic of the process by which lysyl oxidase-antibody (LOX-ab) coated PLGA nangation. B) Size characterization of the LOX-ab nanoparticles using transmission electron micro~200 nm indiameter and that they are spherical in form. C) The therapeutic potential of these nain a mammary tumor xenograft model; this resulted in significant inhibition of tumor growthremoval of the tumors (right) (adapted with permission from Kanapathipillai et al. [96]).

HA-decorated PLGA nanoparticles enhance doxorubicin uptake by cul-tured human breast adenocarcinoma cells [99,100]. Efficient CD44targeting also has been accomplished using HA-modified magneticnanocrystals for MRI imaging of breast cancer cells [101]. Importantly,HA is also a viable target for cancer delivery (independently of CD44)because it is often over-expressed during tumor progression. Hyaluron-idase liposomes disrupt the HAmatrix when injected intravenously in ahuman osteosarcoma solid tumor model [102] and silica nanoparticlescoated with hyaluronidase enzyme have been used to deliver adjuvantdrugs to treat skin cancer [103].

Apart from activation of chemical signaling, the tumor stroma phys-ically limits the penetration of nanotherapeutics and molecular drugsinto the tumor. For this reason, co-delivery of proteases, such as collage-nase, gelatinase and hyaluronidase, significantly aids in breakdown ofthe dense ECM barrier and thereby, increases transport of nanoparticlesinto the tumor and enhances targeted delivery [1,104,105]. Other en-zymes (e.g., transglutaminase) and proteins (e.g., the proteoglycanslumican, decorin and biglycan) also may play a role in modifying tumorECM properties and influencing cancer development [106–111]. For

bly in

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Size (nm)

oparticles are formed by solvent displacement, aqueous self-assembly and surface conju-scopy (TEM) (left) and dynamic light scattering (DLS) (right) confirming that their size isnoparticleswas demonstrated by injecting the LOX-ab coated nanoparticles intravenouslywhen analyzed over time (left) or by visual inspection at the end of the experiment after

114 M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

example, macromolecular drugs (e.g., FITC-dextran, FITC-albumin) pene-trate more deeply into tumor tissue after degradation of collagen anddecorin in the ECM [112]. Thus, nanoparticle-based strategies to modu-late these ECM enzymes and protein functions, will likely improve cancertargeting specificity, drug diffusion and accumulation, as well as drug re-tention at the tumor site.

The ECM is a dynamic structure as it is maintained through ongoingcoupling between synthetic and degradative mechanisms; however,ECM remodeling becomes deregulated during tumor progression [57]and this is mediated by elevated expression and activity of various pro-teolytic enzymes, including matrix metalloproteinases (MMPs) andurokinase-based plasminogen activator systems [113,114]. Interesting-ly, several nanoparticle-based theranostics have been designed to bothmonitor MMP expression and inhibit their activity in the tumor micro-environment. For example, liposomes modified with the GPLPLR pep-tide sequence to target MT1-MMP showed higher binding efficiencyand higher therapeutic efficiency in tumors than uncoated liposomes[115]. Nanoparticle-based prodrug strategies also have been developedby taking advantage of MMP-sensitive activation mechanisms whichare selectively triggered in the tumor microenvironment. An albumin-binding doxorubicin prodrug that is sensitive to MMP2 has beenshown to be effective in malignant melanoma [116]. Gold nanoparticlesconjugated to MMP-sensitive peptides also have been used in tumorimaging and drug delivery [117,118]. Recently, MMP-2-sensitivedenuding of gold nanoparticles in human breast adenocarcinoma cellshas been shown to improve their uptake and hence, enhance targeteddelivery to tumor cells [119]. Tumor-triggered release of doxorubicinfrom MMP-sensitive gold nanoparticles also has been demonstrated ina SSC-7 subcutaneous tumor model [120].

The serine protease inhibitor, urokinase (uPA), plays a major role intumor cell invasion and metastasis and uPA-targeting nanoparticleshave been developed for tumor targeting and imaging. Magnetic nano-particles coated with uPA receptor (uPAR)-targeting peptides havehigher rates of uptake in uPAR positive cancer cells compared with un-coated particles [121], and uPA-targeting iron oxide nanoparticles havebeen used for in vivo imaging of breast cancer [122]. These nanoparticleswere coated with a recombinant peptide of the amino terminal frag-ment of uPA, which targets the uPAR that is overly expressed in thebreast cancer tissue microenvironment.

Nanoparticles or small molecule drug carriers also have been de-veloped to target tumor support structures. The cyclic decapeptide,CGLIIQKNEC, which is known to bind fibronectin–fibrin complexesin the tumor ECM, has been conjugated to gadolinium-containingdendrimers for targeting breast tumor xenografts [123]. The tumorstromaalso contains an abnormalmeshwork of clotted plasma proteins,such as fibrin. The plasma clot-binding peptide, CREKA, which was se-lected using phage display [124] has been used for targeted deliveryto the fibrin mesh in tumor stroma [125]. Nanoparticles and liposomeswere conjugated to the CREKA peptide and shown to both target to thetumor stroma and also to induce self-triggered clotting.

3.4. Multi-drug resistance

Nanoparticles also have the potential to overcomemulti-drug resis-tance (MDR) that can severely restrict the effectiveness of conventionalchemotherapeutic drugs in the tumor microenvironment [126]. Due tonon-specific and ligand receptor-mediated targeted uptake, nano-particles are able to bypass efflux by ABC transporter proteins andaccumulate intracellularly; this is in contrast to free drugs whichcan be highly susceptible to ABC transporter P-glycoprotein (P-gp)capture and efflux [127,128]. For instance, P-gp efflux and multi-drug resistance could be overcome in cultured P388 leukemia cellsusing doxorubicin-loaded poly(alkyl-cyanoacrylate) nanoparticles[129,130]. In murine cancer models, these nanoparticles circulatedlonger and displayed increased accumulation in tumor tissue whencoated with PEG-modified drug.

Another strategy to overcome MDR is to exploit the cell-surface re-ceptor binding strategies of nanoparticles. Studies using transferrin-conjugated nanoparticles or liposomes-containing paclitaxel andoxaliplatin, aswell as pH-stimuli-responsive polymericmicelles contain-ing doxorubicin, have all shown less development of drug-resistance intumor mouse models compared to free drug [20,34,131]. Other recentstudies on MDR-modifying nanoparticles with increased therapeutic ef-ficacy include doxorubicin-loaded lipid nanoparticles in human breastand ovarian cancer cells [132], anti-P-glycoprotein-conjugated PEG–PLGA, and poloxamer-modified PLGA nanoparticles for the targeted de-livery drugs to cervical carcinoma cells over-expressing P-gp [133].

4. Challenges for the future

While there have many great advances in the area of nanocarrier-based drug delivery over the past few decades, many challenges remainfor the design of effective nanotherapeutics for clinical cancer therapy.Nanomaterials that target specifically to the cancer cell or the tumormicroenvironment, but do not exhibit long-term toxicity and can beeffectively cleared from the circulation and removed from the body,without compromising circulation time or bioavailability must be de-veloped [134]. A deeper understanding of the complexities involved incancer cell physiology and the tumor microenvironment, as well asdrug and particle pharmacokinetics are key for the development ofsuccessful new cancer therapeutics. It will be crucial to develop smartnanomaterials that improve stability, extend circulation time, enhancetargeting and improve retention at the tumor site, while minimizingshort- and long-term systemic toxicities. Emerging nanoparticletechnologies for the delivery of siRNA, anti-metastatic agents, andmulti-resistant drugs [8,135,136] show promise, and demonstratethe ability to overcome many of the roadblocks that have limitedthe effectiveness of conventional drug delivery approaches. More re-cent identification of CD47 as a “marker of self”which helps to evadephagocytosis uptake of nanoparticles by macrophages, and is alsooverexpressed in several solid tumors [137,138], raises the possibil-ity of further increasing the effectiveness of nanocarrier drug deliv-ery systems. In fact, nanobead circulation times and therapeuticefficacy were shown to be significantly enhanced in lung carcinoma-bearing mice when the nanoparticles were decorated with CD47 oranti-CD47 antibodies [138].

Another emerging technology in nanotherapeutics is the develop-ment of DNA-based nanostructures that form through programmableself-assembly [139,140]. The ability to create virtually any 3D shapeusing this approach provides a potentially powerful new way totailor nanoparticle design to optimize its function. For example, self-programmable DNA nanorobots that are capable of selectively deliver-ing anti-cancer payloads (ligands for apoptosis-inducing receptors)only when they bind to specific types of cancer cells (Fig. 5) were re-cently developed [141]. Exploration of the value of this approach fortreatment of human cancer will require demonstration of biocompati-bility and stability of these materials when injected in vivo. However,the range of design control and the programmability of these nanoscalerobots are huge, and hence, this area will be interesting to watch overthe next decade.

Further, in vitro tumor engineering and tumor organ on a chip tech-nologies could serve in optimal design and screening of nanoparticlesprior to preclinical studies. For example, the potential of using tumorspheroids for drug screening and delivery to pathological tissues has re-cently been reported [142]. Spheroids resemble the 3D architecture oftumor tissues, mimicking cell–cell interactions and diffusional limita-tions ofmass andfluid transport, and therefore represent amore suitableplatform for testing drugs and nanotherapeutics than conventional pla-nar culture substrates [142,143]. A microfluidic tumor culture device or“tumor-on-a-chip”model, also has beendeveloped to study nanoparticletransport in tissues [144]. Tumor-like spheroids were incorporatedinto the microfluidic channels and accumulation of nanoparticles was

Fig. 5.A) Schematic depicting self-programmableDNAnanorobots loadedwith antibody payload, in locked position (left) and the ligand lockingmechanism(middle) and open position ofnanorobot after ligand–receptor interaction exposing thepayload. B) Eight different nanorobotswere loadedwithfluorescently labeled anti-HLA-A/B/C antibody fragments and their bind-ing specificity was tested in 6 different cancer cell types expressing various combinations of apoptosis-inducing receptors. The histograms show count of cells versus fluorescence due toanti-HLA-A/BC labeling (reproduced with permission from Ref. [141]).

115M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

measured in real-time at physiological blood flow rates. In a further ad-vancement of this organ-on-a-chip approach, the in vivo microenviron-ment of a breathing human lung alveolar-capillary interface wasrecreated in a microfluidic chip [145], and this platform was shown tobe effective at detecting both physiological nanoparticle absorption andrelevant toxicities in vitro [146]. Hence, these organ-on-chip devicesmight be used in the future as a replacement for animal studies forrapid testing nanotherapeutic efficacy as well as toxicity. In this manner,emerging tumor engineering technologies may synergize with new ad-vances in nanobiotechnology to accelerate the development of more ef-fective nanocarriers while reducing both the time and cost ofinvestigations required to meet these goals.

However, to develop truly effective cancer nanotherapeutics, wehave to focus beyond the design of the nanoparticle itself and instead,learn more about the process of cancer formation and progression aswell as how we might more selectively interfere with, or prevent,these critical processes. For example, as it is becoming increasinglyclear that cancer is not merely a disease of uncontrolled cell growth,and instead that it is a disease of normal tissue development [26],then we might think to explore ways to harness knowledge about de-velopment control to create new cancer therapeutics. In this context,it is interesting that developmental biology studies have shown thatwhen ECM isolated from embryonic tissue is combined with adult epi-thelial cancers, it is capable of normalizing the cancer by suppressinggrowth and stimulating tissue-specific differentiation [147,148]. Thus,development of biomimetic nanomaterials that mimic the inductivecues found within embryonic ECM could lead to the development ofnovel nanotherapeutics that might normalize the cancer tissue micro-environment rather than simply kill all growing cancer cells [26]. Inter-estingly, molecules within embryonic ECM that are responsible for this

type of cancer-normalizing activity (e.g., biglycan) are beginning to beidentified [111]. Given the key role of ECM mechanics in cancer devel-opment, it also might be possible to design nanotherapeutics that pre-vent tumor growth or normalize the cancer phenotype by selectivelymodulating themechanical or structural properties of the tumormicro-environment [26]. This could be facilitated by development of smartnanotechnologies that have programmable mechanical properties, orthat can be triggered to alter their physical properties bymicroenviron-mental cues, as is possible, for example, with self assemblingDNA nano-structures [149].

In conclusion, it is clear that simultaneously advancements in geno-mic, proteomic and nanotechnology fields have enabled many types ofnew nanotherapeutics to be developed that offer the potential to trans-form cancer therapy. The newest wave of nanomaterials are multi-functional, programmable, and even self-assembling; they also offerways to provide longer circulation times, higher selectivity, and moreeffective targeting to tumor sites. The recent clinical approval of theliposomal-doxorubicin nanoparticles, Doxil and Abraxane [1,11], hasvalidated the value of nanotechnology for cancer treatment. However,the future is even brighter, and the continuing exciting advances in de-velopment nanoparticle-based therapeutics will hopefully attract manynew investigators in various disciplines into this exciting interdisciplin-ary field.

Acknowledgments

We thank K. Johnson for help with the graphics. This work was sup-ported by the Wyss Institute for Biologically Inspired Engineering atHarvard University, and grants from the Department of Defense(W81XWH-08-1-0659 and W81XWH-10-1-0565).

116 M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

References

[1] T. Lammers, F. Kiessling, W.E. Hennink, G. Storm, Drug targeting to tumors: princi-ples, pitfalls and (pre-) clinical progress, J. Control. Release 161 (2012) 175–187.

[2] Y. Ding, S. Li, G. Nie, Nanotechnological strategies for therapeutic targeting oftumor vasculature, Nanomedicine (London) 8 (2013) 1209–1222.

[3] S. Nie, Y. Xing, G.J. Kim, J.W. Simons, Nanotechnology applications in cancer, Annu.Rev. Biomed. Eng. 9 (2007) 257–288.

[4] F. Alexis, E.M. Pridgen, R. Langer, O.C. Farokhzad, Nanoparticle technologies forcancer therapy, Handb. Exp. Pharmacol. (2010) 55–86.

[5] T.M. Allen, Ligand-targeted therapeutics in anticancer therapy, Nat. Rev. Cancer 2(2002) 750–763.

[6] A. Ozcelikkale, S. Ghosh, B. Han, Multifaceted transport characteristics ofnanomedicine: needs for characterization in dynamic environment, Mol. Pharm.10 (2013) 2111–2126.

[7] L.Y. Rizzo, B. Theek, G. Storm, F. Kiessling, T. Lammers, Recent progress innanomedicine: therapeutic, diagnostic and theranostic applications, Curr. Opin.Biotechnol. 24 (2013) 1159–1166.

[8] Y. Matsumura, K. Kataoka, Preclinical and clinical studies of anticancer agent-incorporating polymer micelles, Cancer Sci. 100 (2009) 572–579.

[9] W.J. Gradishar, S. Tjulandin, N. Davidson, H. Shaw, N. Desai, P. Bhar, M. Hawkins, J.O'Shaughnessy, Phase III trial of nanoparticle albumin-bound paclitaxel comparedwith polyethylated castor oil-based paclitaxel in women with breast cancer, J. Clin.Oncol. 23 (2005) 7794–7803.

[10] R.D. Hofheinz, S.U. Gnad-Vogt, U. Beyer, A. Hochhaus, Liposomal encapsulated anti-cancer drugs, Anticancer Drugs 16 (2005) 691–707.

[11] F. Danhier, O. Feron, V. Preat, To exploit the tumor microenvironment: passive andactive tumor targeting of nanocarriers for anti-cancer drug delivery, J. Control. Re-lease 148 (2010) 135–146.

[12] P. Decuzzi, S. Lee, B. Bhushan,M. Ferrari, A theoretical model for the margination ofparticles within blood vessels, Ann. Biomed. Eng. 33 (2005) 179–190.

[13] M. Tiwari, Nano cancer therapy strategies, J. Cancer Res. Ther. 8 (2012) 19–22.[14] T.M. Allen, P. Sapra, E. Moase, J. Moreira, D. Iden, Adventures in targeting, J. Lipo-

some Res. 12 (2002) 5–12.[15] F. Alexis, J.W. Rhee, J.P. Richie, A.F. Radovic-Moreno, R. Langer, O.C. Farokhzad, New

frontiers in nanotechnology for cancer treatment, Urol. Oncol. 26 (2008) 74–85.[16] J.L. Perry, K.P. Herlihy, M.E. Napier, J.M. Desimone, PRINT: a novel platform toward

shape and size specific nanoparticle theranostics, Acc. Chem. Res. 44 (2011)990–998.

[17] P. Kolhar, A.C. Anselmo, V. Gupta, K. Pant, B. Prabhakarpandian, E. Ruoslahti, S.Mitragotri, Using shape effects to target antibody-coated nanoparticles to lungand brain endothelium, Proc. Natl. Acad. Sci. U. S. A. 110 (2013) 10753–10758.

[18] R.H. Fang, C.M. Hu, K.N. Chen, B.T. Luk, C.W. Carpenter, W. Gao, S. Li, D.E. Zhang, W.Lu, L. Zhang, Lipid-insertion enables targeting functionalization of erythrocytemembrane-cloaked nanoparticles, Nanoscale 5 (2013) 8884–8888.

[19] Y. Matsumura, M. Gotoh, K. Muro, Y. Yamada, K. Shirao, Y. Shimada, M. Okuwa, S.Matsumoto, Y. Miyata, H. Ohkura, K. Chin, S. Baba, T. Yamao, A. Kannami, Y.Takamatsu, K. Ito, K. Takahashi, Phase I and pharmacokinetic study of MCC-465,a doxorubicin (DXR) encapsulated in PEG immunoliposome, in patients with met-astatic stomach cancer, Ann. Oncol. 15 (2004) 517–525.

[20] R. Suzuki, T. Takizawa, Y. Kuwata, M. Mutoh, N. Ishiguro, N. Utoguchi, A. Shinohara,M. Eriguchi, H. Yanagie, K. Maruyama, Effective anti-tumor activity of oxaliplatinencapsulated in transferrin-PEG-liposome, Int. J. Pharm. 346 (2008) 143–150.

[21] Y.C. Chen, C.L. Lo, G.H. Hsiue, Multifunctional nanomicellar systems for deliveringanticancer drugs, J. Biomed. Mater. Res. A 102 (2013) 2024–2038.

[22] A.A. Alexander-Bryant, W.S. Vanden Berg-Foels, X. Wen, Bioengineering strategiesfor designing targeted cancer therapies, Adv. Cancer Res. 118 (2013) 1–59.

[23] R. Cheng, F. Meng, C. Deng, H.A. Klok, Z. Zhong, Dual and multi-stimuli responsivepolymeric nanoparticles for programmed site-specific drug delivery, Biomaterials34 (2013) 3647–3657.

[24] D.E. Ingber, Tensegrity II. How structural networks influence cellular informationprocessing networks, J. Cell Sci. 116 (2003) 1397–1408.

[25] H. Fang, Y.A. Declerck, Targeting the tumor microenvironment: from understand-ing pathways to effective clinical trials, Cancer Res. 73 (2013) 4965–4977.

[26] D.E. Ingber, Can cancer be reversed by engineering the tumor microenvironment?Semin. Cancer Biol. 18 (2008) 356–364.

[27] M. Allinen, R. Beroukhim, L. Cai, C. Brennan, J. Lahti-Domenici, H. Huang, D. Porter,M. Hu, L. Chin, A. Richardson, S. Schnitt,W.R. Sellers, K. Polyak,Molecular character-ization of the tumor microenvironment in breast cancer, Cancer Cell 6 (2004)17–32.

[28] M.M. Mueller, N.E. Fusenig, Friends or foes — bipolar effects of the tumour stromain cancer, Nat. Rev. Cancer 4 (2004) 839–849.

[29] M.A. Phillips, M.L. Gran, N.A. Peppas, Targeted nanodelivery of drugs and diagnos-tics, Nano Today 5 (2010) 143–159.

[30] F.X. Gu, R. Karnik, A.Z. Wang, F. Alexis, E. Levy-Nissenbaum, S. Hong, R.S.Langer, O.C. Farokhzad, Targeted nanoparticles for cancer therapy, NanoToday 2 (2007) 14–21.

[31] A. Martinez, R. Olmo, I. Iglesias, J.M. Teijon, M.D. Blanco, Folate-targeted nanoparticlesbased on albumin and albumin/alginate mixtures as controlled release systems of ta-moxifen: synthesis and in vitro characterization, Pharm. Res. 31 (2013) 182–193.

[32] J. Lu, Z. Li, J.I. Zink, F. Tamanoi, In vivo tumor suppression efficacy of mesoporoussilica nanoparticles-based drug-delivery system: enhanced efficacy by folate mod-ification, Nanomedicine 8 (2012) 212–220.

[33] P. Ponka, C.N. Lok, The transferrin receptor: role in health and disease, Int. J.Biochem. Cell Biol. 31 (1999) 1111–1137.

[34] S.K. Sahoo, W. Ma, V. Labhasetwar, Efficacy of transferrin-conjugated paclitaxel-loaded nanoparticles in a murine model of prostate cancer, Int. J. Cancer 112(2004) 335–340.

[35] J. Chang, A. Paillard, C. Passirani, M. Morille, J.P. Benoit, D. Betbeder, E. Garcion,Transferrin adsorption onto PLGA nanoparticles governs their interaction with bi-ological systems from blood circulation to brain cancer cells, Pharm. Res. 29 (2012)1495–1505.

[36] M.A. Sandoval, B.R. Sloat, P.D. Lansakara, A. Kumar, B.L. Rodriguez, K. Kiguchi, J.Digiovanni, Z. Cui, EGFR-targeted stearoyl gemcitabine nanoparticles show en-hanced anti-tumor activity, J. Control. Release 157 (2012) 287–296.

[37] M.G. Anhorn, S. Wagner, J. Kreuter, K. Langer, H. von Briesen, Specific targeting ofHER2 overexpressing breast cancer cells with doxorubicin-loaded trastuzumab-modified human serum albumin nanoparticles, Bioconjug. Chem. 19 (2008)2321–2331.

[38] H. Meng, M. Liong, T. Xia, Z. Li, Z. Ji, J.I. Zink, A.E. Nel, Engineered design of mesopo-rous silica nanoparticles to deliver doxorubicin and P-glycoprotein siRNA to over-come drug resistance in a cancer cell line, ACS Nano 4 (2010) 4539–4550.

[39] F. Wang, Y.C. Wang, S. Dou, M.H. Xiong, T.M. Sun, J. Wang, Doxorubicin-tetheredresponsive gold nanoparticles facilitate intracellular drug delivery for overcomingmultidrug resistance in cancer cells, ACS Nano 5 (2011) 3679–3692.

[40] S. Marrache, S. Dhar, Engineering of blended nanoparticle platform for delivery ofmitochondria-acting therapeutics, Proc. Natl. Acad. Sci. U. S. A. 109 (2012)16288–16293.

[41] R.A. Smith, C.M. Porteous, A.M. Gane, M.P. Murphy, Delivery of bioactive moleculesto mitochondria in vivo, Proc. Natl. Acad. Sci. U. S. A. 100 (2003) 5407–5412.

[42] S.S. Bale, S.J. Kwon, D.A. Shah, A. Banerjee, J.S. Dordick, R.S. Kane, Nanoparticle-mediated cytoplasmic delivery of proteins to target cellular machinery, ACSNano 4 (2010) 1493–1500.

[43] P.S. Lai, C.L. Pai, C.L. Peng, M.J. Shieh, K. Berg, P.J. Lou, Enhanced cytotoxicity ofsaporin by polyamidoamine dendrimer conjugation and photochemical internali-zation, J. Biomed. Mater. Res. A 87 (2008) 147–155.

[44] F. Heitz, M.C. Morris, G. Divita, Twenty years of cell-penetrating peptides: frommo-lecular mechanisms to therapeutics, Br. J. Pharmacol. 157 (2009) 195–206.

[45] D.H. Yu, Q. Lu, J. Xie, C. Fang, H.Z. Chen, Peptide-conjugated biodegradable nano-particles as a carrier to target paclitaxel to tumor neovasculature, Biomaterials 31(2010) 2278–2292.

[46] B.Y. Kim, W. Jiang, J. Oreopoulos, C.M. Yip, J.T. Rutka, W.C. Chan, Biodegradablequantum dot nanocomposites enable live cell labeling and imaging of cytoplasmictargets, Nano Lett. 8 (2008) 3887–3892.

[47] S.E. Gratton, P.A. Ropp, P.D. Pohlhaus, J.C. Luft, V.J. Madden, M.E. Napier, J.M.DeSimone, The effect of particle design on cellular internalization pathways,Proc. Natl. Acad. Sci. U. S. A. 105 (2008) 11613–11618.

[48] S. Barua, J.W. Yoo, P. Kolhar, A. Wakankar, Y.R. Gokarn, S. Mitragotri, Particle shapeenhances specificity of antibody-displaying nanoparticles, Proc. Natl. Acad. Sci. U. S.A. 110 (2013) 3270–3275.

[49] R. Agarwal, V. Singh, P. Jurney, L. Shi, S.V. Sreenivasan, K. Roy, Mammalian cellspreferentially internalize hydrogel nanodiscs over nanorods and use shape-specific uptakemechanisms, Proc. Natl. Acad. Sci. U. S. A. 110 (2013) 17247–17252.

[50] M.E. Davis, J.E. Zuckerman, C.H. Choi, D. Seligson, A. Tolcher, C.A. Alabi, Y. Yen, J.D.Heidel, A. Ribas, Evidence of RNAi in humans from systemically administeredsiRNA via targeted nanoparticles, Nature 464 (2010) 1067–1070.

[51] Y.H. Huang, Y. Bao, W. Peng, M. Goldberg, K. Love, D.A. Bumcrot, G. Cole, R. Langer,D.G. Anderson, J.A. Sawicki, Claudin-3 gene silencing with siRNA suppresses ovariantumor growth and metastasis, Proc. Natl. Acad. Sci. U. S. A. 106 (2009) 3426–3430.

[52] M.S. Goldberg, D. Xing, Y. Ren, S. Orsulic, S.N. Bhatia, P.A. Sharp, Nanoparticle-mediated delivery of siRNA targeting Parp1 extends survival of mice bearing tu-mors derived from Brca1-deficient ovarian cancer cells, Proc. Natl. Acad. Sci. U. S.A. 108 (2011) 745–750.

[53] M.S. Goldberg, P.A. Sharp, Pyruvate kinase M2-specific siRNA induces apoptosisand tumor regression, J. Exp. Med. 209 (2012) 217–224.

[54] A. Brock, S. Krause, H. Li, M. Kowalski, M.S. Goldberg, J.J. Collins, D.E. Ingber, Silenc-ing HoxA1 by intraductal injection of siRNA lipidoid nanoparticles prevents mam-mary tumor progression in mice, Sci. Transl. Med. 6 (2014) 217ra212.

[55] G. Sahay, W. Querbes, C. Alabi, A. Eltoukhy, S. Sarkar, C. Zurenko, E. Karagiannis, K.Love, D. Chen, R. Zoncu, Y. Buganim, A. Schroeder, R. Langer, D.G. Anderson, Effi-ciency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling,Nat. Biotechnol. 31 (2013) 653–658.

[56] N.E. Sounni, A. Noel, Targeting the tumor microenvironment for cancer therapy,Clin. Chem. 59 (2013) 85–93.

[57] D.E. Ingber, J.A. Madri, J.D. Jamieson, Role of basal lamina in neoplastic disorganiza-tion of tissue architecture, Proc. Natl. Acad. Sci. U. S. A. 78 (1981) 3901–3905.

[58] P. Lu, V.M. Weaver, Z. Werb, The extracellular matrix: a dynamic niche in cancerprogression, J. Cell Biol. 196 (2012) 395–406.

[59] J. Zhang, J. Liu, Tumor stroma as targets for cancer therapy, Pharmacol. Ther. 137(2013) 200–215.

[60] H. Maeda, The enhanced permeability and retention (EPR) effect in tumor vascula-ture: the key role of tumor-selective macromolecular drug targeting, Adv. Enzym.Regul. 41 (2001) 189–207.

[61] V.P. Torchilin, Recent advances with liposomes as pharmaceutical carriers, Nat.Rev. Drug Discov. 4 (2005) 145–160.

[62] V.P. Torchilin, Targeted pharmaceutical nanocarriers for cancer therapy and imag-ing, AAPS J. 9 (2007) E128–E147.

[63] J.K. Vasir, V. Labhasetwar, Targeted drug delivery in cancer therapy, Technol.Cancer Res. Treat. 4 (2005) 363–374.

[64] S. Parveen, S.K. Sahoo, Polymeric nanoparticles for cancer therapy, J. Drug Target.16 (2008) 108–123.

117M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

[65] L. Claesson-Welsh, Blood vessels as targets in tumor therapy, Ups. J. Med. Sci. 117(2012) 178–186.

[66] M.V. Backer, T.I. Gaynutdinov, V. Patel, A.K. Bandyopadhyaya, B.T. Thirumamagal,W. Tjarks, R.F. Barth, K. Claffey, J.M. Backer, Vascular endothelial growth factor se-lectively targets boronated dendrimers to tumor vasculature, Mol. Cancer Ther. 4(2005) 1423–1429.

[67] J. Chen, H.Wu, D. Han, C. Xie, Using anti-VEGFMcAb andmagnetic nanoparticles asdouble-targeting vector for the radioimmunotherapy of liver cancer, Cancer Lett.231 (2006) 169–175.

[68] R. Satchi-Fainaro, M. Puder, J.W. Davies, H.T. Tran, D.A. Sampson, A.K. Greene, G.Corfas, J. Folkman, Targeting angiogenesis with a conjugate of HPMA copolymerand TNP-470, Nat. Med. 10 (2004) 255–261.

[69] R. Satchi-Fainaro, R. Mamluk, L. Wang, S.M. Short, J.A. Nagy, D. Feng, A.M. Dvorak,H.F. Dvorak, M. Puder, D. Mukhopadhyay, J. Folkman, Inhibition of vessel perme-ability by TNP-470 and its polymer conjugate, caplostatin, Cancer Cell 7 (2005)251–261.

[70] O. Benny, O. Fainaru, A. Adini, F. Cassiola, L. Bazinet, I. Adini, E. Pravda, Y. Nahmias,S. Koirala, G. Corfas, R.J. D'Amato, J. Folkman, An orally delivered small-moleculeformulation with antiangiogenic and anticancer activity, Nat. Biotechnol. 26(2008) 799–807.

[71] S. Gosk, T. Moos, C. Gottstein, G. Bendas, VCAM-1 directed immunoliposomes se-lectively target tumor vasculature in vivo, Biochim. Biophys. Acta 1778 (2008)854–863.

[72] P. Oh, P. Borgstrom, H. Witkiewicz, Y. Li, B.J. Borgstrom, A. Chrastina, K. Iwata, K.R.Zinn, R. Baldwin, J.E. Testa, J.E. Schnitzer, Live dynamic imaging of caveolaepumping targeted antibody rapidly and specifically across endothelium in thelung, Nat. Biotechnol. 25 (2007) 327–337.

[73] D. Hanahan, R.A. Weinberg, Hallmarks of cancer: the next generation, Cell 144(2011) 646–674.

[74] M. Hockel, P. Vaupel, Tumor hypoxia: definitions and current clinical, biologic, andmolecular aspects, J. Natl. Cancer Inst. 93 (2001) 266–276.

[75] A.K. Iyer, A. Singh, S. Ganta, M.M. Amiji, Role of integrated cancer nanomedicine inovercoming drug resistance, Adv. Drug Deliv. Rev. 65 (2013) 1784–1802.

[76] Z. Poon, D. Chang, X. Zhao, P.T. Hammond, Layer-by-layer nanoparticles with a pH-sheddable layer for in vivo targeting of tumor hypoxia, ACS Nano 5 (2011)4284–4292.

[77] Q. Lin, C. Bao, Y. Yang, Q. Liang, D. Zhang, S. Cheng, L. Zhu, Highly discriminatingphotorelease of anticancer drugs based on hypoxia activatable phototrigger conju-gated chitosan nanoparticles, Adv. Mater. 25 (2013) 1981–1986.

[78] J. Napp, T. Behnke, L. Fischer, C. Wurth, M. Wottawa, D.M. Katschinski, F. Alves, U.Resch-Genger, M. Schaferling, Targeted luminescent near-infrared polymer-nanoprobes for in vivo imaging of tumor hypoxia, Anal. Chem. 83 (2011)9039–9046.

[79] M.R. Simpson-Abelson, V.S. Purohit, W.M. Pang, V. Iyer, K. Odunsi, T.L. Demmy, S.J.Yokota, J.L. Loyall, R.J. Kelleher Jr., S. Balu-Iyer, R.B. Bankert, IL-12 deliveredintratumorally by multilamellar liposomes reactivates memory T cells in humantumor microenvironments, Clin. Immunol. 132 (2009) 71–82.

[80] M.D. Joshi, W.J. Unger, G. Storm, Y. van Kooyk, E. Mastrobattista, Targeting tumorantigens to dendritic cells using particulate carriers, J. Control. Release 161(2012) 25–37.

[81] S. Hamdy, A. Haddadi, A. Shayeganpour, J. Samuel, A. Lavasanifar, Activation ofantigen-specific T cell-responses by mannan-decorated PLGA nanoparticles,Pharm. Res. 28 (2011) 2288–2301.

[82] N. Brandhonneur, F. Chevanne, V. Vie, B. Frisch, R. Primault, M.F. Le Potier, P. LeCorre, Specific and non-specific phagocytosis of ligand-grafted PLGA microspheresby macrophages, Eur. J. Pharm. Sci. 36 (2009) 474–485.

[83] G.K. Saraogi, B. Sharma, B. Joshi, P. Gupta, U.D. Gupta, N.K. Jain, G.P. Agrawal,Mannosylated gelatin nanoparticles bearing isoniazid for effective managementof tuberculosis, J. Drug Target. 19 (2011) 219–227.

[84] S. Espuelas, C. Thumann, B. Heurtault, F. Schuber, B. Frisch, Influence of ligandvalency on the targeting of immature human dendritic cells bymannosylated lipo-somes, Bioconjug. Chem. 19 (2008) 2385–2393.

[85] L.Z. He, A. Crocker, J. Lee, J. Mendoza-Ramirez, X.T. Wang, L.A. Vitale, T. O'Neill, C.Petromilli, H.F. Zhang, J. Lopez, D. Rohrer, T. Keler, R. Clynes, Antigenic targetingof the human mannose receptor induces tumor immunity, J. Immunol. 178(2007) 6259–6267.

[86] N. Romani, M. Thurnher, J. Idoyaga, R.M. Steinman, V. Flacher, Targeting of antigensto skin dendritic cells: possibilities to enhance vaccine efficacy, Immunol. Cell Biol.88 (2010) 424–430.

[87] D.N. Nguyen, K.P. Mahon, G. Chikh, P. Kim, H. Chung, A.P. Vicari, K.T. Love, M.Goldberg, S. Chen, A.M. Krieg, J. Chen, R. Langer, D.G. Anderson, Lipid-derivednanoparticles for immunostimulatory RNA adjuvant delivery, Proc. Natl. Acad.Sci. U. S. A. 109 (2012) E797–E803.

[88] O.A. Ali, N. Huebsch, L. Cao, G. Dranoff, D.J. Mooney, Infection-mimicking materialsto program dendritic cells in situ, Nat. Mater. 8 (2009) 151–158.

[89] O.A. Ali, E. Doherty, W.J. Bell, T. Fradet, J. Hudak, M.T. Laliberte, D.J. Mooney, D.F.Emerich, Biomaterial-based vaccine induces regression of established intracranialglioma in rats, Pharm. Res. 28 (2011) 1074–1080.

[90] S. Marrache, S. Tundup, D.A. Harn, S. Dhar, Ex vivo programming of dendritic cellsby mitochondria-targeted nanoparticles to produce interferon-gamma for cancerimmunotherapy, ACS Nano 7 (2013) 7392–7402.

[91] K.R. Levental, H. Yu, L. Kass, J.N. Lakins, M. Egeblad, J.T. Erler, S.F. Fong, K. Csiszar, A.Giaccia, W. Weninger, M. Yamauchi, D.L. Gasser, V.M. Weaver, Matrix crosslinkingforces tumor progression by enhancing integrin signaling, Cell 139 (2009) 891–906.

[92] S. Huang, D.E. Ingber, Cell tension, matrix mechanics, and cancer development,Cancer Cell 8 (2005) 175–176.

[93] Q. Xiao, G. Ge, Lysyl oxidase, extracellular matrix remodeling and cancer metasta-sis, Cancer Microenviron. 5 (2012) 261–273.

[94] C. Rodriguez, A. Rodriguez-Sinovas, J. Martinez-Gonzalez, Lysyl oxidase as a poten-tial therapeutic target, Drug News Perspect. 21 (2008) 218–224.

[95] M.R. Ng, J.S. Brugge, A stiff blow from the stroma: collagen crosslinking drivestumor progression, Cancer Cell 16 (2009) 455–457.

[96] M. Kanapathipillai, A. Mammoto, T. Mammoto, J.H. Kang, E. Jiang, K. Ghosh, N.Korin, A. Gibbs, R. Mannix, D.E. Ingber, Inhibition of mammary tumor growthusing lysyl oxidase-targeting nanoparticles to modify extracellular matrix, NanoLett. 12 (2012) 3213–3217.

[97] V.M. Platt, F.C. Szoka Jr., Anticancer therapeutics: targeting macromolecules andnanocarriers to hyaluronan or CD44, a hyaluronan receptor, Mol. Pharm. 5(2008) 474–486.

[98] S. Misra, P. Heldin, V.C. Hascall, N.K. Karamanos, S.S. Skandalis, R.R. Markwald, S.Ghatak, Hyaluronan–CD44 interactions as potential targets for cancer therapy,FEBS J. 278 (2011) 1429–1443.

[99] A.K. Yadav, P. Mishra, A.K.Mishra, P. Mishra, S. Jain, G.P. Agrawal, Development andcharacterization of hyaluronic acid-anchored PLGA nanoparticulate carriers ofdoxorubicin, Nanomedicine 3 (2007) 246–257.

[100] W. Hyung, H. Ko, J. Park, E. Lim, S.B. Park, Y.J. Park, H.G. Yoon, J.S. Suh, S. Haam, Y.M.Huh, Novel hyaluronic acid (HA) coated drug carriers (HCDCs) for human breastcancer treatment, Biotechnol. Bioeng. 99 (2008) 442–454.

[101] T. Lee, E.K. Lim, J. Lee, B. Kang, J. Choi, H.S. Park, J.S. Suh, Y.M. Huh, S. Haam, EfficientCD44-targeted magnetic resonance imaging (MRI) of breast cancer cells usinghyaluronic acid (HA)-modified MnFe2O4 nanocrystals, Nanoscale Res. Lett. 8(2013) 149.

[102] L. Eikenes, M. Tari, I. Tufto, O.S. Bruland, C. de Lange Davies, Hyaluronidase inducesa transcapillary pressure gradient and improves the distribution and uptake of li-posomal doxorubicin (Caelyx) in human osteosarcoma xenografts, Br. J. Cancer93 (2005) 81–88.

[103] P. Scodeller, P.N. Catalano, N. Salguero, H. Duran, A. Wolosiuk, G.J. Soler-Illia,Hyaluronan degrading silica nanoparticles for skin cancer therapy, Nanoscale 5(2013) 9690–9698.

[104] T.T. Goodman, P.L. Olive, S.H. Pun, Increased nanoparticle penetration incollagenase-treated multicellular spheroids, Int. J. Nanomedicine 2 (2007)265–274.

[105] Q. Liu, R.T. Li, H.Q. Qian, M. Yang, Z.S. Zhu, W. Wu, X.P. Qian, L.X. Yu, X.Q. Jiang, B.R.Liu, Gelatinase-stimuli strategy enhances the tumor delivery and therapeutic effi-cacy of docetaxel-loaded poly(ethylene glycol)-poly(varepsilon-caprolactone)nanoparticles, Int. J. Nanomedicine 7 (2012) 281–295.

[106] M. Decitre, C. Gleyzal, M. Raccurt, S. Peyrol, E. Aubert-Foucher, K. Csiszar, P.Sommer, Lysyl oxidase-like protein localizes to sites of de novo fibrinogenesis infibrosis and in the early stromal reaction of ductal breast carcinomas, Lab. Invest.78 (1998) 143–151.

[107] B.S. Wiseman, Z. Werb, Stromal effects on mammary gland development andbreast cancer, Science 296 (2002) 1046–1049.

[108] G. Akiri, E. Sabo, H. Dafni, Z. Vadasz, Y. Kartvelishvily, N. Gan, O. Kessler, T. Cohen,M. Resnick, M. Neeman, G. Neufeld, Lysyl oxidase-related protein-1 promotestumor fibrosis and tumor progression in vivo, Cancer Res. 63 (2003) 1657–1666.

[109] S. Alowami, S. Troup, S. Al-Haddad, I. Kirkpatrick, P.H. Watson, Mammographicdensity is related to stroma and stromal proteoglycan expression, Breast CancerRes. 5 (2003) R129–R135.

[110] T.Y. Eshchenko, V.I. Rykova, A.E. Chernakov, S.V. Sidorov, E.V. Grigorieva, Expres-sion of different proteoglycans in human breast tumors, Biochemistry 72 (2007)1016–1020.

[111] A.G. Bischof, D. Yuksel, T. Mammoto, A. Mammoto, S. Krause, D.E. Ingber, Breastcancer normalization induced by embryonic mesenchyme ismediated by extracel-lular matrix biglycan, Integr. Biol. 5 (2013) 1045–1056.

[112] M. Magzoub, S. Jin, A.S. Verkman, Enhanced macromolecule diffusion deep in tu-mors after enzymatic digestion of extracellular matrix collagen and its associatedproteoglycan decorin, FASEB J. 22 (2008) 276–284.

[113] S. Ulisse, E. Baldini, S. Sorrenti,M.D'Armiento, The urokinase plasminogen activatorsystem: a target for anti-cancer therapy, Curr. Cancer Drug Targets 9 (2009) 32–71.

[114] K. Kessenbrock, V. Plaks, Z. Werb, Matrix metalloproteinases: regulators of thetumor microenvironment, Cell 141 (2010) 52–67.

[115] M. Kondo, T. Asai, Y. Katanasaka, Y. Sadzuka, H. Tsukada, K. Ogino, T. Taki, K. Baba,N. Oku, Anti-neovascular therapy by liposomal drug targeted to membrane type-1matrix metalloproteinase, Int. J. Cancer 108 (2004) 301–306.

[116] A.M. Mansour, J. Drevs, N. Esser, F.M. Hamada, O.A. Badary, C. Unger, I. Fichtner, F.Kratz, A new approach for the treatment of malignant melanoma: enhanced anti-tumor efficacy of an albumin-binding doxorubicin prodrug that is cleaved by ma-trix metalloproteinase 2, Cancer Res. 63 (2003) 4062–4066.

[117] G.B. Kim, K.H. Kim, Y.H. Park, S. Ko, Y.P. Kim, Colorimetric assay of matrix metallo-proteinase activity based on metal-induced self-assembly of carboxy gold nano-particles, Biosens. Bioelectron. 41 (2013) 833–839.

[118] I.C. Sun, D.K. Eun, H. Koo, C.Y. Ko, H.S. Kim, D.K. Yi, K. Choi, I.C. Kwon, K. Kim, C.H.Ahn, Tumor-targeting gold particles for dual computed tomography/optical cancerimaging, Angew. Chem. 50 (2011) 9348–9351.

[119] A.K.W. Suresh, Y. Weng, Z. Li, R. Zerda, D. Van Haute, J.C. Williams, J.M. Berlin, Ma-trix metalloproteinase-triggered denuding of engineered gold nanoparticles for se-lective cell uptake, J. Mater. Chem. B 1 (2013) 2341–2349.

[120] W.H. Chen, X.D. Xu, H.Z. Jia, Q. Lei, G.F. Luo, S.X. Cheng, R.X. Zhuo, X.Z. Zhang, Ther-apeutic nanomedicine based on dual-intelligent functionalized gold nanoparticlesfor cancer imaging and therapy in vivo, Biomaterials 34 (2013) 8798–8807.

[121] L. Hansen, E.K. Unmack Larsen, E.H. Nielsen, F. Iversen, Z. Liu, K. Thomsen, M.Pedersen, T. Skrydstrup, N.C. Nielsen, M. Ploug, J. Kjems, Targeting of peptide

118 M. Kanapathipillai et al. / Advanced Drug Delivery Reviews 79–80 (2014) 107–118

conjugated magnetic nanoparticles to urokinase plasminogen activator receptor(uPAR) expressing cells, Nanoscale 5 (2013) 8192–8201.

[122] L. Yang, X.H. Peng, Y.A. Wang, X.Wang, Z. Cao, C. Ni, P. Karna, X. Zhang, W.C. Wood,X. Gao, S. Nie, H. Mao, Receptor-targeted nanoparticles for in vivo imaging of breastcancer, Clin. Cancer Res. 15 (2009) 4722–4732.

[123] M. Tan, X. Wu, E.K. Jeong, Q. Chen, Z.R. Lu, Peptide-targeted Nanoglobular Gd-DOTA monoamide conjugates for magnetic resonance cancer molecular imaging,Biomacromolecules 11 (2010) 754–761.

[124] J.A. Hoffman, E. Giraudo, M. Singh, L. Zhang, M. Inoue, K. Porkka, D. Hanahan, E.Ruoslahti, Progressive vascular changes in a transgenic mouse model of squamouscell carcinoma, Cancer Cell 4 (2003) 383–391.

[125] D. Simberg, T. Duza, J.H. Park, M. Essler, J. Pilch, L. Zhang, A.M. Derfus, M. Yang, R.M.Hoffman, S. Bhatia, M.J. Sailor, E. Ruoslahti, Biomimetic amplification of nanoparti-cle homing to tumors, Proc. Natl. Acad. Sci. U. S. A. 104 (2007) 932–936.

[126] L. Milane, S. Ganesh, S. Shah, Z.F. Duan, M. Amiji, Multi-modal strategies for over-coming tumor drug resistance: hypoxia, the Warburg effect, stem cells, and multi-functional nanotechnology, J. Control. Release 155 (2011) 237–247.

[127] M.E. Davis, Z.G. Chen, D.M. Shin, Nanoparticle therapeutics: an emerging treatmentmodality for cancer, Nat. Rev. Drug Discov. 7 (2008) 771–782.

[128] F. Shen, S. Chu, A.K. Bence, B. Bailey, X. Xue, P.A. Erickson, M.H. Montrose, W.T.Beck, L.C. Erickson, Quantitation of doxorubicin uptake, efflux, and modulation ofmultidrug resistance (MDR) in MDR human cancer cells, J. Pharmacol. Exp. Ther.324 (2008) 95–102.

[129] X. Pepin, L. Attali, C. Domrault, S. Gallet, J.M. Metreau, Y. Reault, P.J. Cardot, M.Imalalen, C. Dubernet, E. Soma, P. Couvreur, On the use of ion-pair chromatogra-phy to elucidate doxorubicin release mechanism from polyalkylcyanoacrylatenanoparticles at the cellular level, J. Chromatogr. B Biomed. Sci. Appl. 702 (1997)181–191.

[130] C. Vauthier, C. Dubernet, C. Chauvierre, I. Brigger, P. Couvreur, Drug delivery to re-sistant tumors: the potential of poly(alkyl cyanoacrylate) nanoparticles, J. Control.Release 93 (2003) 151–160.

[131] E.S. Lee, K. Na, Y.H. Bae, Doxorubicin loaded pH-sensitive polymericmicelles for re-versal of resistant MCF-7 tumor, J. Control. Release 103 (2005) 405–418.

[132] J. Miao, Y.Z. Du, H. Yuan, X.G. Zhang, F.Q. Hu, Drug resistance reversal activity of an-ticancer drug loaded solid lipid nanoparticles in multi-drug resistant cancer cells,Colloids Surf. B: Biointerfaces 110 (2013) 74–80.

[133] P. Iangcharoen, W. Punfa, S. Yodkeeree, W. Kasinrerk, C. Ampasavate, S.Anuchapreeda, P. Limtrakul, Anti-P-glycoprotein conjugated nanoparticles fortargeting drug delivery in cancer treatment, Arch. Pharm. Res. 34 (2011) 1679–1689.

[134] S. Nazir, T. Hussain, A. Ayub, U. Rashid, A.J. Macrobert, Nanomaterials in combatingcancer: therapeutic applications and developments, Nanomedicine 10 (2013)19–34.

[135] A.K. Vaishnaw, J. Gollob, C. Gamba-Vitalo, R. Hutabarat, D. Sah, R. Meyers, T. deFougerolles, J. Maraganore, A status report on RNAi therapeutics, Silence 1 (2010) 14.

[136] X. Dong, R.J. Mumper, Nanomedicinal strategies to treat multidrug-resistant tu-mors: current progress, Nanomedicine (London) 5 (2010) 597–615.

[137] S.B. Willingham, J.P. Volkmer, A.J. Gentles, D. Sahoo, P. Dalerba, S.S. Mitra, J. Wang,H. Contreras-Trujillo, R. Martin, J.D. Cohen, P. Lovelace, F.A. Scheeren, M.P. Chao, K.Weiskopf, C. Tang, A.K. Volkmer, T.J. Naik, T.A. Storm, A.R. Mosley, B. Edris, S.M.Schmid, C.K. Sun, M.S. Chua, O. Murillo, P. Rajendran, A.C. Cha, R.K. Chin, D. Kim,M. Adorno, T. Raveh, D. Tseng, S. Jaiswal, P.O. Enger, G.K. Steinberg, G. Li, S.K. So,R. Majeti, G.R. Harsh, M. van de Rijn, N.N. Teng, J.B. Sunwoo, A.A. Alizadeh, M.F.Clarke, I.L. Weissman, The CD47-signal regulatory protein alpha (SIRPa) interactionis a therapeutic target for human solid tumors, Proc. Natl. Acad. Sci. U. S. A. 109(2012) 6662–6667.

[138] P.L. Rodriguez, T. Harada, D.A. Christian, D.A. Pantano, R.K. Tsai, D.E. Discher, Min-imal “Self” peptides that inhibit phagocytic clearance and enhance delivery ofnanoparticles, Science 339 (2013) 971–975.

[139] A.V. Pinheiro, D. Han,W.M. Shih, H. Yan, Challenges and opportunities for structur-al DNA nanotechnology, Nat. Nanotechnol. 6 (2011) 763–772.

[140] C.H. Lu, B. Willner, I. Willner, DNA nanotechnology: from sensing and DNAmachines to drug-delivery systems, ACS Nano 7 (2013) 8320–8332.

[141] S.M. Douglas, I. Bachelet, G.M. Church, A logic-gated nanorobot for targeted trans-port of molecular payloads, Science 335 (2012) 831–834.

[142] A. Oloumi, W. Lam, J.P. Banath, P.L. Olive, Identification of genes differentiallyexpressed in V79 cells grown as multicell spheroids, Int. J. Radiat. Biol. 78 (2002)483–492.

[143] S.H. Kim, H.J. Kuh, C.R. Dass, The reciprocal interaction: chemotherapy and tumormicroenvironment, Curr. Drug Discov. Technol. 8 (2011) 102–106.

[144] A. Albanese, A.K. Lam, E.A. Sykes, J.V. Rocheleau,W.C. Chan, Tumour-on-a-chip pro-vides an optical window into nanoparticle tissue transport, Nat. Commun. 4 (2013)2718.

[145] D. Huh, B.D. Matthews, A. Mammoto, M. Montoya-Zavala, H.Y. Hsin, D.E. Ingber,Reconstituting organ-level lung functions on a chip, Science 328 (2010)1662–1668.

[146] D. Huh, D.C. Leslie, B.D. Matthews, J.P. Fraser, S. Jurek, G.A. Hamilton, K.S.Thorneloe, M.A. McAlexander, D.E. Ingber, A human disease model of drugtoxicity-induced pulmonary edema in a lung-on-a-chip microdevice, Sci. Transl.Med. 4 (2012) 159ra147.

[147] J.J. DeCosse, C.L. Gossens, J.F. Kuzma, B.R. Unsworth, Breast cancer: induction of dif-ferentiation by embryonic tissue, Science 181 (1973) 1057–1058.

[148] D.E. Ingber, J.A. Madri, J.D. Jamieson, Basement membrane as a spatial organizer ofpolarized epithelia. Exogenous basementmembrane reorients pancreatic epithelialtumor cells in vitro, Am. J. Pathol. 122 (1986) 129–139.

[149] T. Liedl, B. Hogberg, J. Tytell, D.E. Ingber, W.M. Shih, Self-assembly of three-dimensional prestressed tensegrity structures from DNA, Nat. Nanotechnol. 5(2010) 520–524.