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.

Topography, cell response, and nerve regeneration

In the body, cells encounter a complex milieu of signals, including topographical cues, in the form of the physical features of their surrounding environment. Imposed topography can affect cells on surfaces by promoting adhesion, spreading, alignment, morphological changes, and changes in gene expression. Neural response to topography is complex, and it depends on the dimensions and shapes of physical features. Looking toward repair of nerve injuries, strategies are being explored to engineer guidance conduits with precise surface topographies. How neurons and other cell types sense and interpret topography remains to be fully elucidated. Studies reviewed here include those of topography on cellular organization and function as well as potential cellular mechanisms of response.

Sustained VEGF delivery via PLGA nanoparticles promotes vascular growth

Technologies to increase tissue vascularity are critically important to the fields of tissue engineering and cardiovascular medicine. Currently, limited technologies exist to encourage angiogenesis and arteriogenesis in a controlled manner. In the present study, we describe an injectable controlled release system consisting of VEGF encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). The majority of VEGF was released gradually over 2-4 days from the NPs as determined by an ELISA release kinetics experiment. An in vitro aortic ring bioassay was used to verify the bioactivity of VEGF-NPs compared with empty NPs and no treatment. A mouse femoral artery ischemia model was then used to measure revascularization in VEGF-NP-treated limbs compared with limbs treated with naked VEGF and saline. 129/Sv mice were anesthetized with isoflurane, and a region of the common femoral artery and vein was ligated and excised. Mice were then injected with VEGF-NPs, naked VEGF, or saline. After 4 days, three-dimensional microcomputed tomography angiography was used to quantify vessel growth and morphology. Mice that received VEGF-NP treatment showed a significant increase in total vessel volume and vessel connectivity compared with 5 microg VEGF, 2.5 microg VEGF, and saline treatment (all P < 0.001). When the yield of the fabrication process was taken into account, VEGF-NPs were over an order of magnitude more potent than naked VEGF in increasing blood vessel volume. Differences between the VEGF-NP group and all other groups were even greater when only small-sized vessels under 300 mum diameter were analyzed. In conclusion, sustained VEGF delivery via PLGA NPs shows promise for encouraging blood vessel growth in tissue engineering and cardiovascular medicine applications.

Implanted neural electrodes cause chronic, local inflammation that is correlated with local neurodegeneration

Prosthetic devices that are controlled by intracortical electrodes recording one's 'thoughts' are a reality today, and no longer merely in the realm of science fiction. However, widespread clinical use of implanted electrodes is hampered by a lack of reliability in chronic recordings, independent of the type of electrodes used. One major hypothesis has been that astroglial scar electrically impedes the electrodes. However, there is a temporal discrepancy between stabilization of scar's electrical properties and recording failure with recording failure lagging by 1 month. In this study, we test a possible explanation for this discrepancy: the hypothesis that chronic inflammation, due to the persistent presence of the electrode, causes a local neurodegenerative state in the immediate vicinity of the electrode. Through modulation of chronic inflammation via stab wound, electrode geometry and age-matched control, we found that after 16 weeks, animals with an increased level of chronic inflammation were associated with increased neuronal and dendritic, but not axonal, loss. We observed increased neuronal and dendritic loss 16 weeks after implantation compared to 8 weeks after implantation, suggesting that the local neurodegenerative state is progressive. After 16 weeks, we observed axonal pathology in the form of hyperphosphorylation of the protein tau in the immediate vicinity of the microelectrodes (as observed in Alzheimer's disease and other tauopathies). The results of this study suggest that a local, late onset neurodegenerative disease-like state surrounds the chronic electrodes and is a potential cause for chronic recording failure. These results also inform strategies to enhance our capability to attain reliable long-term recordings from implantable electrodes in the CNS.

Thin-film enhanced nerve guidance channels for peripheral nerve repair

It has been demonstrated that nerve guidance channels containing stacked thin-films of aligned poly(acrylonitrile-co-methylacrylate) fibers support peripheral nerve regeneration across critical sized nerve gaps, without the aid of exogenous cells or proteins. Here, we explore the ability of tubular channels minimally supplemented with aligned nanofiber-based thin-films to promote endogenous nerve repair. We describe a technique for fabricating guidance channels in which individual thin-films are fixed into place within the lumen of a polysulfone tube. Because each thin-film is <10 microm thick, this technique allows fine control over the positioning of aligned scaffolding substrate. We evaluated nerve regeneration through a 1-film guidance channel--containing a single continuous thin-film of aligned fibers--in comparison to a 3-film channel that provided two additional thin-film tracks. Thirty rats were implanted with one of the two channel types, and regeneration across a 14 mm tibial nerve gap was evaluated after 6 weeks and 13 weeks, using a range of morphological and functional measures. Both the 1-film and the 3-film channels supported regeneration across the nerve gap resulting in functional muscular reinnervation. Each channel type characteristically influenced the morphology of the regeneration cable. Interestingly, the 1-film channels supported enhanced regeneration compared to the 3-film channels in terms of regenerated axon profile counts and measures of nerve conduction velocity. These results suggest that minimal levels of appropriately positioned topographical cues significantly enhance guidance channel function by modulating endogenous repair mechanisms, resulting in effective bridging of critically sized peripheral nerve gaps.

Imaging nanoprobe for prediction of outcome of nanoparticle chemotherapy by using mammography

PURPOSE

To prospectively predict the effectiveness of a clinically used nanochemotherapeutic agent by detecting and measuring the intratumoral uptake of an x-ray contrast agent nanoprobe by using digital mammography.

MATERIALS AND METHODS

All animal procedures were approved by the institutional animal care and use committee. A long-circulating 100-nm-scale injectable liposomal probe encapsulating 155 mg/mL iodine was developed. Preliminary studies were performed to identify the agent dose that would result in adequate tumor enhancement without enhancement of the normal vasculature in rats. This dose was used to image a rat breast tumor (n = 14) intermittently for 3 days by using a digital mammography system; subsequently, the animals were treated with liposomal doxorubicin. The predictive capability of the probe was characterized by creating good- and bad-prognosis subgroups, on the basis of tumor enhancement found during imaging, and analyzing the tumor growth after treatment of the animals in these two subgroups.

RESULTS

A dose of 455 mg of iodine per kilogram of body weight was found to produce an undetectable signal from the blood while achieving enough intratumoral accumulation of the probe to produce adequate signal for detection. The good- and bad-prognosis subgroups demonstrated differential tumor growth rates (P < .003). An inverse linear relationship between the contrast enhancement rate constant during imaging and the tumor growth rate constant during treatment was found (slope = -0.576, R(2) = 0.838).

CONCLUSION

In this animal model, quantitative measurement of vascular permeability enabled prediction of therapeutic responsiveness of tumors to liposomal doxorubicin.

Nanoparticle-mediated local delivery of Methylprednisolone after spinal cord injury

Systemic administration of a high-dose of Methylprednisolone (MP) can reduce neurological deficits after acute spinal cord injury (SCI). However, the use of high-dose MP in treating acute SCI is controversial due to significant dose related side effects and relatively modest improvements in neurological function. Here, using a rat model of SCI, we compare the efficacy of controlled, nanoparticle-enabled local delivery of MP to the injured spinal cord with systemic delivery of MP, and a single local injection of MP without nanoparticles. Based on histological and behavioral data, we report that local, sustained delivery of MP via nanoparticles is significantly more effective than systemic delivery. Relative to systemic delivery, MP-nanoparticle therapy significantly reduced lesion volume and improved behavioral outcomes. Nanoparticle-enabled delivery of MP presents an effective method for introducing MP locally after SCI and significantly enhances therapeutic effectiveness compared to bare MP administered either systemically or locally.

Rational identification of a novel peptide for targeting nanocarriers to 9L glioma

Traditional therapies for high grade gliomas are limited in part by collateral damage to normal tissues. Selective delivery of therapies to tumors is, therefore, needed. Here, we report that liposomal nanocarriers coated with a novel oligopeptide enhance uptake by 9L gliosarcoma. A targeting nine amino acid peptide sequence (RSI) was identified by differential panning of random peptide phage display libraries on 9L cells and rat blood cells and plasma. Peptides were coupled to the surface of liposomal nanocarriers which were subsequently loaded with doxorubicin. The ability of RSI coated liposomes to facilitate drug uptake and cytotoxicity was compared with conventional liposomal nanocarriers and controls. In addition, plasma clearance profiles of the RSI peptide coupled liposomal nanocarriers were evaluated in adult immuno-competent rats. RSI peptide-coupled liposomal nanocarriers enhanced drug uptake by 9L cells by 500% compared with conventional liposomal nanocarriers, and significantly increased cytotoxicity. The plasma half-lives confirmed that the presence of the RSI peptide on the liposomal nanocarriers did not compromise circulation time in the blood in comparison with Stealth liposomal nanocarriers. These data suggest that phage-identified oligopeptides could lead to the development of new tumor selective nanocarriers.

Biomaterials for the central nervous system

Biomaterials are widely used to help treat neurological disorders and/or improve functional recovery in the central nervous system (CNS). This article reviews the application of biomaterials in (i) shunting systems for hydrocephalus, (ii) cortical neural prosthetics, (iii) drug delivery in the CNS, (iv) hydrogel scaffolds for CNS repair, and (v) neural stem cell encapsulation for neurotrauma. The biological and material requirements for the biomaterials in these applications are discussed. The difficulties that the biomaterials might face in each application and the possible solutions are also reviewed in this article.

Multifunctional nanocarriers for mammographic quantification of tumor dosing and prognosis of breast cancer therapy

Nanoscale therapeutic interventions are increasingly important elements in the portfolio of cancer therapeutics. The efficacy of nanotherapeutics is dictated, in part, by the access they have to tumors via the leaky tumor vasculature. Yet, the extent of tumor vessel leakiness in individual tumors varies widely resulting in a correspondingly wide tumor dosing and resulting range of responses to therapy. Here we report the design of a multifunctional nanocarrier that simultaneously encapsulates a chemotherapeutic and a contrast agent which enables a personalized nanotherapeutic approach for breast cancer therapy by permitting tracking of the nanocarrier distribution by mammography, a widely used imaging modality. Following systemic administration in a rat breast tumor model, imaging demonstrated a wide range of intratumoral deposition of the nanocarriers, indicating variable tumor vessel leakiness. Notably, specific tumors that exhibited high uptake of the nanocarrier as visualized by imaging were precisely the animals that responded best to the treatment as quantified by low tumor growth and prolonged survival.

MRI mediated, non-invasive tracking of intratumoral distribution of nanocarriers in rat glioma

Nanocarrier mediated therapy of gliomas has shown promise. The success of systemic nanocarrier-based chemotherapy is critically dependent on the so-called leaky vasculature to permit drug extravasation across the blood-brain barrier. Yet, the extent of vascular permeability in individual tumors varies widely, resulting in a correspondingly wide range of responses to the therapy. However, there exist no tools currently for rationally determining whether tumor blood vessels are amenable to nanocarrier mediated therapy in an individualized, patient specific manner today. To address this need for brain tumor therapy, we have developed a multifunctional 100 nm scale liposomal agent encapsulating a gadolinium-based contrast agent for contrast-enhanced magnetic resonance imaging with prolonged blood circulation. Using a 9.4 T MRI system, we were able to track the intratumoral distribution of the gadolinium-loaded nanocarrier in a rat glioma model for a period of three days due to improved magnetic properties of the contrast agent being packaged in a nanocarrier. Such a nanocarrier provides a tool for non-invasively assessing the suitability of tumors for nanocarrier mediated therapy and then optimizing the treatment protocol for each individual tumor. Additionally, the ability to image the tumor in high resolution can potentially constitute a surgical planning tool for tumor resection.

The role of aligned polymer fiber-based constructs in the bridging of long peripheral nerve gaps

Peripheral nerve regeneration across long nerve gaps is clinically challenging. Autografts, the standard of therapy, are limited by availability and other complications. Here, using rigorous anatomical and functional measures, we report that aligned polymer fiber-based constructs present topographical cues that facilitate the regeneration of peripheral nerves across long nerve gaps. Significantly, aligned but not randomly oriented fibers elicit regeneration, establishing that topographical cues can influence endogenous nerve repair mechanisms in the absence of exogenous growth promoting proteins. Axons regenerated across a 17 mm nerve gap, reinnervated muscles, and reformed neuromuscular junctions. Electrophysiological and behavioral analyses revealed that aligned but not randomly oriented constructs facilitated both sensory and motor nerve regeneration, significantly improved functional outcomes. Additionally, a quantitative comparison of DRG outgrowth in vitro and nerve regeneration in vivo on aligned and randomly oriented fiber films clearly demonstrated the significant role of sub-micron scale topographical cues in stimulating endogenous nerve repair mechanisms.

Differences between the effect of anisotropic and isotropic laminin and nerve growth factor presenting scaffolds on nerve regeneration across long peripheral nerve gaps

Anisotropic scaffolds of agarose hydrogels containing gradients of laminin-1 (LN-1) and nerve growth factor (NGF) molecules were used to promote sciatic nerve regeneration across a challenging 20mm nerve gap in rats. Step and continuous gradient anisotropic scaffolds were fabricated and characterized, and regeneration was compared to that in isotropic scaffolds with uniform concentrations of LN-1 and NGF and sciatic nerve grafts harvested from syngenic rats. Polysulfone tubular guidance channels were used to present the agarose-based scaffolds to the nerve stumps. Four months after implantation, regenerating axons were observed in animals implanted with anisotropic scaffolds with gradients of both LN-1 and NGF molecules and nerve grafts, but not in animals with isotropic scaffold implants. Also, the scaffolds with gradients of either LN-1 or NGF, with the other component being uniformly distributed in the scaffold, did not elicit axonal regeneration. The total number of myelinated axons was similar for the anisotropic scaffold and the nerve graft conditions, with the anisotropic scaffolds having a higher density of axons than the nerve grafts. Axonal diameter distribution was similar for the anisotropic scaffolds and the nerve grafts. The nerve grafts and anisotropic scaffolds resulted in better functional outcome compared to isotropic scaffolds as measured by the relative gastrocnemius muscle weight (RGMW). Additionally the state of neuromuscular junctions as assessed by pre- and post-synaptic staining revealed that both the anisotropic scaffolds performed as well as nerve grafts.

Extraction force and cortical tissue reaction of silicon microelectrode arrays implanted in the rat brain

Micromotion of implanted silicon multielectrode arrays (Si MEAs) is thought to influence the inflammatory response they elicit. The degree of strain that micromotion imparts on surrounding tissue is related to the extent of mechanical integration of the implanted electrodes with the brain. In this study, we quantified the force of extraction of implanted four shank Michigan electrodes in adult rat brains and investigated potential cellular and extracellular matrix contributors to tissue-electrode adhesion using immunohistochemical markers for microglia, astrocytes and extracellular matrix deposition in the immediate vicinity of the electrodes. Our results suggest that the peak extraction force of the implanted electrodes increases significantly from the day of implantation (day 0) to the day of extraction (day 7 and day 28 postimplantation) (1.68 +/- 0.54 g, 3.99 +/- 1.31 g, and 4.86 +/- 1.49 g, respectively; mean +/- SD; n = 4). For an additional group of four shank electrode implants with a closer intershank spacing we observed a significant increase in peak extraction force on day 28 postimplantation compared to day 0 and day 7 postimplantation (5.56 +/- 0.76 g, 0.37 +/- 0.12 g and 1.87 +/- 0.88 g, respectively; n = 4). Significantly, only glial fibrillary acidic protein (GFAP) expression was correlated with peak extraction force in both electrode designs of all the markers of astroglial scar studied. For studies that try to model micromotion-induced strain, our data implies that adhesion between tissue and electrode increases after implantation and sheds light on the nature of implanted electrode-elicited brain tissue reaction.

Dexamethasone-coated neural probes elicit attenuated inflammatory response and neuronal loss compared to uncoated neural probes

Glial scar formation around implanted silicon neural probes compromises their ability to facilitate long-term recordings. One approach to modulate the tissue reaction around implanted probes in the brain is to develop probe coatings that locally release anti-inflammatory drugs. In this study, we developed a nitrocellulose-based coating for the local delivery of the anti-inflammatory drug dexamethasone (DEX). Silicon neural probes with and without nitrocellulose-DEX coatings were implanted into rat brains, and inflammatory response was evaluated 1 week and 4 weeks post implantation. DEX coatings significantly reduced the reactivity of microglia and macrophages 1 week post implantation as evidenced by ED1 immunostaining. CS56 staining demonstrated that DEX treatment significantly reduced chondroitin sulfate proteoglycan (CSPG) expression 1 week post implantation. Both at 1-week and at 4-week time points, GFAP staining for reactive astrocytes and neurofilament (NF) staining revealed that local DEX treatment significantly attenuated astroglial response and reduced neuronal loss in the vicinity of the probes. Weak ED1, neurocan, and NG2-positive signal was detected 4 weeks post implantation for both coated and uncoated probes, suggesting a stabilization of the inflammatory response over time in this implant model. In conclusion, this study demonstrates that the nitrocellulose-DEX coating can effectively attenuate the inflammatory response to the implanted neural probes, and reduce neuronal loss in the vicinity of the coated probes. Thus anti-inflammatory probe coatings may represent a promising approach to attenuate astroglial scar and reduce neural loss around implanted neural probes.

Polylysine-functionalised thermoresponsive chitosan hydrogel for neural tissue engineering

Foetal mouse cortical cells were cultured on 2D films and within 3D thermally responsive chitosan/glycerophosphate salt (GP) hydrogels. The biocompatibility of chitosan/GP 2D films was assessed in terms of cell number and neurites per cell. Osmolarity of the hydrogel was a critical factor in promoting cell survival with isotonic GP concentrations providing optimal conditions. To improve cell adhesion and neurite outgrowth, poly-D-lysine (PDL) was immobilised onto chitosan via azidoaniline photocoupling. Increase in PDL concentrations did not alter cell survival in 2D cultures but neurite outgrowth was significantly inhibited. Neurons exhibited a star-like morphology typical of 2D culture systems. The effects of PDL attachment on cell number, cell morphology and neurite outgrowth were more distinct in 3D culture conditions. Neurones exhibited larger cell bodies and sent out single neurites within the macroporous gel. Immobilised PDL improved cell survival up to an optimum concentration of 0.1%, however, further increases resulted in drops in cell number and neurite outgrowth. This was attributed to a higher cell interaction with PDL within a 3D hydrogel compared to the corresponding 2D surface. The results show that thermally responsive chitosan/GP hydrogels provide a suitable 3D scaffolding environment for neural tissue engineering.

Nanoscale laminin coating modulates cortical scarring response around implanted silicon microelectrode arrays

Neural electrodes could significantly enhance the quality of life for patients with sensory and/or motor deficits as well as improve our understanding of brain functions. However, long-term electrical connectivity between neural tissue and recording sites is compromised by the development of astroglial scar around the recording probes. In this study we investigate the effect of a nanoscale laminin (LN) coating on Si-based neural probes on chronic cortical tissue reaction in a rat model. Tissue reaction was evaluated after 1 day, 1 week, and 4 weeks post-implant for coated and uncoated probes using immunohistochemical techniques to evaluate activated microglia/macrophages (ED-1), astrocytes (GFAP) and neurons (NeuN). The coating did not have an observable effect on neuronal density or proximity to the electrode surface. However, the response of microglia/macrophages and astrocytes was altered by the coating. One day post-implant, we observed an approximately 60% increase in ED-1 expression near LN-coated probe sites compared with control uncoated probe sites. Four weeks post-implant, we observed an approximately 20% reduction in ED-1 expression along with an approximately 50% reduction in GFAP expression at coated relative to uncoated probe sites. These results suggest that LN has a stimulatory effect on early microglia activation, accelerating the phagocytic function of these cells. This hypothesis is further supported by the increased mRNA expression of several pro-inflammatory cytokines (TNF-alpha, IL-1 and IL-6) in cultured microglia on LN-bound Si substrates. LN immunostaining of coated probes immediately after insertion and retrieval demonstrates that the coating integrity is not compromised by the shear force during insertion. We speculate, based on these encouraging results, that LN coating of Si neural probes could potentially improve chronic neural recordings through dispersion of the astroglial scar.

Long-circulating liposomal contrast agents for magnetic resonance imaging

Contrast-enhanced magnetic resonance imaging (CE-MRI) is a dynamic technique for imaging vasculature. However, the currently used gadolinium (Gd) chelates, such as Gd-DTPA, restrict the time window for image acquisition due to their rapid elimination from blood and their rapid diffusion into the extravascular space, which prevents their use in steady-state imaging, particularly for MR angiography (MRA). The goal of this study was to prepare long-circulating polyethylene glycol-bearing ((PEG)ylated) liposomes encapsulating Gd chelate, and characterize and demonstrate their utility for MRA. The liposomes were prepared by hydrating a mixture of lipids with gadodiamide (Omniscan). The liposomes were sized down to around 100 nm by extruder and exhaustively dialysed to remove the unencapsulated gadodiamide. The Gd liposomes exhibited a significant sustained (>4 hr) contrast enhancement of the vasculature with improved spatial details in a rat model with little leakage relative to Gd-DTPA controls as shown by MRI. We suggest that such long-circulating liposomal formulations allow for high spatial resolution imaging without the confounding effects of clearance and extravascular diffusion of the agent complicating the data and image analysis.

Anisotropic scaffolds facilitate enhanced neurite extension in vitro

Tissue engineering (TE) techniques to enhance nerve regeneration following nerve damage have had limited success in matching the performance of autografts across short nerve gaps (< 10 mm). For regeneration over longer nerve gaps, TE techniques have been less successful than autografts. Most engineered scaffolds do not present directional cues to the regenerating nerves. In our efforts to design a TE scaffold to replace the autograft, we hypothesize that anisotropic hydrogel scaffolds with gradients of a growth-promoting glycoprotein, laminin-1 (LN-1), may promote directional neurite extension and enhance regeneration. In this study we report the engineering of three-dimensional (3D) agarose scaffolds with photoimmobilized gradients of LN-1 of differing slopes. Dorsal root ganglia (DRG) from chicken embryos were cultured in the agarose scaffolds and their neurite extension rate was determined. DRG neurite extension rates were significantly higher in the anisotropic scaffolds, with a maximal growth rate in an anisotropic scaffold twice that of the maximal growth rate in isotropic scaffolds of LN-1. We suggest that these anisotropic scaffolds, presenting an optimal gradient of LN-1, may significantly impact nerve regeneration. Such anisotropic scaffolds may represent a new generation of tissue engineered materials with built-in directional cues for guided tissue or nerve regeneration.

A dual-ligand approach for enhancing targeting selectivity of therapeutic nanocarriers

Conjugation of ligands to nano-scale drug carriers targeting over-expressed cell surface receptors is a promising approach for delivery of therapeutic agents to tumor cells. However, most commonly utilized ligands are directed at receptors expressed not only on target cells but also on other cells in the body, leading to unintended uptake in these off-target cells. In this study, a novel, dual-ligand approach is reported, which targets tumor cells while sparing off-target cells by exploiting the fact that tumor cells typically over-express multiple types of surface receptors. This approach was tested in the human KB cell line, which over-expresses both folate receptor (FR) and the epidermal growth factor receptor (EGFR). Liposomal nanocarriers loaded with doxorubicin and bearing controlled numbers of both folic acid and a monoclonal antibody against the EGFR were designed. Cytotoxicity was used to determine targeting selectivity of the designed carriers in vitro by utilizing KB cells expressing both FR and EGFR and off-target control cells in which one or both receptors were blocked. The data demonstrates that nanocarriers can be designed to achieve toxicity only when all targeted receptors are available, providing an approach to improve selectivity over current single-ligand approaches.