Nanotechnology has given scientists new tools for the development of advanced materials for the detection and diagnosis of disease. Iron oxide nanoparticles (SPIONs) in particular have been extensively investigated as novel magnetic resonance imaging (MRI) contrast agents due to a combination of favorable superparamagnetic properties, biodegradability, and surface properties of easy modification for improved in vivo kinetics and multifunctionality. This review discusses the basics of MR imaging, the origin of SPION’s unique magnetic properties, recent developments in MRI acquisition methods for detection of SPIONs, synthesis and post-synthesis processes that improve SPION’s imaging characteristics, and an outlook on the translational potential of SPIONs.

Gadolinium‐based chelates are a mainstay of contrast agents for magnetic resonance imaging (MRI) in the clinic. However, their toxicity elicits severe side effects and the Food and Drug Administration has issued many warnings about their potential retention in patients’ bodies, which causes safety concerns. Iron oxide nanoparticles (IONPs) are a potentially attractive alternative, because of their nontoxic and biodegradable nature. Studies in developing IONPs as T1 contrast agents have generated promising results, but the complex, interrelated parameters influencing contrast enhancement make the development difficult, and IONPs suitable for T1 contrast enhancement have yet to make their way to clinical use. Here, the fundamental principles of MRI contrast agents are discussed, and the current status of MRI contrast agents is reviewed with a focus on the advantages and limitations of current T1 contrast agents and the potential of IONPs to serve as safe and improved alternative to gadolinium‐based chelates. The past advances and current challenges in developing IONPs as a T1 contrast agent from a materials science perspective are presented, and how each of the key material properties and environment variables affects the performance of IONPs is assessed. Finally, some potential approaches to develop high‐performance and clinically relevant T1 contrast agents are discussed.

Multifunctional superparamagnetic nanoparticles have been developed for a wide range of applications in nanomedicine, such as serving as tumor targeted drug carriers and molecular imaging agents. To function in vivo, the development of these novel materials must overcome several challenging requirements including biocompatibility, stability in physiological solutions, non-toxicity and the ability to traverse biological barriers. Here we report a PEG-mediated synthesis process to produce well-dispersed, ultrafine, and highly stable iron oxide nanoparticles for in vivo applications. Utilizing a biocompatible PEG coating bearing amine functional groups, the produced nanoparticles serve as an effective platform with the ability to incorporate a variety of targeting, therapeutic or imaging ligands. In this study, we demonstrated tumor-specific accumulation of these nanoparticles through both magnetic resonance and optical imaging after conjugation with chlorotoxin, a peptide with high affinity toward tumors of the neuroectodermal origin, and Cy5.5, a near-infrared fluorescent dye. Furthermore, we performed preliminary biodistribution and toxicity assessments of these nanoparticles in wild-type mice through histological analysis of clearance organs and hematology assay, and the results demonstrated the relative biocompatibility of these nanoparticles.

Aims-This study examines the capabilities of an actively targeting superparamagnetic nanoparticle to specifically deliver therapeutic and magnetic resonance imaging contrast agents to cancer cells. Materials & methods-Ironoxide nanoparticles were synthesized and conjugated to both a chemotherapeutic agent, methotrexate, and a targeting ligand, chlorotoxin, through a poly(ethylene glycol) linker. Cytotoxicity of this nanoparticle conjugate was evaluated by Alamar Blue cell viability assays, while tumor cell specificity was examined in vitro and in vivo by magnetic resonance imaging.Results & discussion-Characterization of these multifunctional nanoparticles confirms the successful attachment of both drug and targeting ligands. The targeting nanoparticle demonstrated preferential accumulation and increased cytotoxicity in tumor cells. Furthermore, prolonged retention of these nanoparticles was observed within tumors in vivo.Conclusion-The improved specificity, extended particle retention, and increased cytotoxicity toward tumor cells demonstrated by this multifunctional nanoparticle system suggest that it possesses potential for applications in cancer diagnosis and treatment.Keywords iron oxide; nanoparticle; chlorotoxin; methotrexate; tumor; drug delivery; magnetic resonance imaging The development of tumor specific multifunctional nanoparticles is currently an area of intense research with the potential to revolutionize the diagnosis and treatment of cancer. These particle systems, also referred to as nanovectors, have been envisioned as novel contrast agents for non-invasive molecular imaging and targeted carriers for drug delivery [1,2]. As a major class of these materials, superparamagnetic iron oxide nanoparticles have been examined extensively for applications in cancer diagnosis and therapeutics due to their biocompatibility and magnetic properties [3,4]. Early forms of these nanoparticles, which exploit the body's natural clearance pathways (e.g. reticuloendothelial system (RES)-mediated passive targeting), * Author for correspondence: Department of Materials Science & Engineering, 302L Roberts Hall, University of Washington, Seattle, WA 98195-2120, Tel: (206) 616 9356, Fax: (206) 543 3100, mzhang@u.washington.edu. NIH Public AccessAuthor Manuscript Nanomedicine (Lond) In addition, the magnetic properties of these iron oxide nanoparticles have also been examined as a means of remotely directing therapeutic agents specifically to a disease site [7]. Nanoparticles possess a high surface area-to-volume ratio allowing them to be loaded with large amounts of a therapeutic or cytotoxic drug. As with other drug delivery systems, specific accumulation in malignant tissues results in reduced dosages necessary for a therapeutic effect and less deleterious side-effects associated with non-specific uptake of cytotoxic drugs by healthy tissue. Additional advantages of drug carrier systems over traditional systemic chemotherapy include the ability to improve the solubility of hydrophobic drugs, stabilizatio...

Resistance to temozolomide (TMZ) based chemotherapy in glioblastoma multiforme (GBM) has been attributed to the upregulation of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). Inhibition of MGMT using O6-benzylguanine (BG) has shown promise in these patients, but its clinical use is hindered by poor pharmacokinetics that leads to unacceptable toxicity. To improve BG biodistribution and efficacy, we developed superparamagnetic iron oxide nanoparticles (NP) for targeted convection-enhanced delivery (CED) of BG to GBM. The nanoparticles (NPCP-BG-CTX) consist of a magnetic core coated with a redox-responsive, cross-linked, biocompatible chitosan-PEG copolymer surface coating (NPCP). NPCP was modified through covalent attachment of BG and tumor targeting peptide chlorotoxin (CTX). Controlled, localized BG release was achieved under reductive intracellular conditions and NPCP-BG-CTX demonstrated proper trafficking of BG in human GBM cells in vitro. NPCP-BG-CTX treated cells showed a significant reduction in MGMT activity and the potentiation of TMZ toxicity. In vivo, CED of NPCP-BG-CTX produced an excellent volume of distribution (Vd) within the brain of mice bearing orthotopic human primary GBM xenografts. Significantly, concurrent treatment with NPCP-BG-CTX and TMZ showed a 3-fold increase in median overall survival in comparison to NPCP-CTX/TMZ treated and untreated animals. Furthermore, NPCP-BG-CTX mitigated the myelosuppression observed with free BG in wild-type mice when administered concurrently with TMZ. The combination of favorable physicochemical properties, tumor cell specific BG delivery, controlled BG release, and improved in vivo efficacy demonstrates the great potential of these NPs as a treatment option that could lead to improved clinical outcomes.

Glioblastoma (GBM) is a deadly and debilitating brain tumor with an abysmal prognosis. The standard therapy for GBM is surgery followed by radiation and chemotherapy with temozolomide (TMZ). Treatment of GBMs remains a challenge, largely due to the fast degradation of TMZ, inability to deliver an effective dose of TMZ to tumors, and lack of target specificity which may cause systemic toxicity. Here, we present a simple method to synthesize a nanoparticle-based carrier that can protect TMZ from rapid degradation in physiological solutions and can specifically deliver them to GBM cells through the mediation of a tumor targeting peptide chlorotoxin (CTX). Our nanoparticle, namely NP-TMZ-CTX, had a hydrodynamic size of less than 100 nm, exhibited sustained stability in cell culture media for up to two weeks, and could accommodate stable drug loading. TMZ bound to nanoparticles showed much higher stability at physiological pH, with a half-life 7-fold greater than free TMZ. NP-TMZ-CTX was able to target GBM cells and achieved 2–6-fold higher uptake and 50–90% reduction of IC50 at 72 h post-treatment as compared to non-targeted NP-TMZ. NP-TMZ-CTX showed great promise in its ability to deliver a high therapeutic dose of TMZ to GBM cells, and could serve as a template for targeted delivery of other therapeutics.

Breast cancer remains one of the most prevalent and lethal malignancies in women. The inability to diagnose small volume metastases early has limited effective treatment of stage 4 breast cancer. Here we report the rational development and use of a multifunctional superparamagnetic iron oxide nanoparticle (SPION) for targeting metastatic breast cancer in a transgenic mouse model and imaging with magnetic resonance (MR). SPIONs coated with a copolymer of chitosan and polyethylene glycol (PEG) were labeled with a fluorescent dye for optical detection and conjugated with a monoclonal antibody against the neu receptor (NP-neu). SPIONs labeled with mouse IgG were used as a non-targeting control (NP-IgG). These SPIONs had desirable physiochemical properties for in vivo applications such as near neutral zeta potential and hydrodynamic size around 40 nm, and were highly stable in serum containing medium. Only NP-neu showed high uptake in neu expressing mouse mammary carcinoma (MMC) cells which was reversed by competing free neu antibody, indicating their specificity to the neu antigen. In vivo, NP-neu was able to tag primary breast tumors and significantly, only NP-neu bound to spontaneous liver, lung, and bone marrow metastases in a transgenic mouse model of metastatic breast cancer, highlighting the necessity of targeting for delivery to metastatic disease. The SPIONs provided significant contrast enhancement in MR images of primary breast tumors; thus, they have the potential for MRI detection of micrometastases, and provide an excellent platform for further development of an efficient metastatic breast cancer therapy.

Certain genetic mutations lead to the development of cancer through unchecked cell growth and division. Cancer is typically treated through surgical resection, radiotherapy, and small-molecule chemotherapy. A relatively recent approach to cancer therapy involves the use of a natural process wherein small RNA molecules regulate gene expression in a pathway known as RNA interference (RNAi). RNA oligos pair with a network of proteins to form an RNA-induced silencing complex which inhibits the translation of messenger RNA into proteins, thereby controlling the expression of gene products. Synthetically produced RNA oligos may be designed to target and silence specific oncogenes to provide cancer therapy.