MR molecular imaging of the Her-2/neu receptor in breast cancer cells using targeted iron oxide nanoparticles

Off-resonance saturation MRI of superparamagnetic nanoprobes: theoretical models and experimental validations

Off-resonance saturation (ORS) is a new magnetic resonance imaging (MRI) method that has shown greatly improved contrast sensitivity for the detection of cancer-specific biomarkers by superparamagnetic nanoprobes in vivo. However, quantitative understanding of the ORS contrast mechanism and its dependence on the structural parameters of superparamagnetic nanoprobes are still lacking. Here we propose a quantitative model of ORS contrast and its experimental validation by superparamagnetic polymeric micelles (SPPM) with precisely controlled structural properties. Size selected, monodisperse Fe₃O₄ nanoparticles (6.1 ± 0.2 nm) were used to form a series of SPPM nanoprobes with specifically controlled corona thickness using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxypoly(ethylene glycol) (DSPE-PEG) with different PEG molecular weights. Transmission electron microscopy and dynamic light scattering showed that SPPM were uniform in size. The average hydrodynamic diameters of SPPM with PEG lengths of 0.55, 1, 2, and 5 kD were 16.6 ± 2.8, 18.4 ± 2.9, 24.1 ± 3.4, and 28.9 ± 3.4 nm, respectively. MRI experiments at 7 T determined that r₂ values of SPPM with 0.55, 1, 2, and 5 kD PEG as corona were 201 ± 3, 136 ± 8, 107 ± 5, and 108 ± 8 FemM⁻¹s⁻¹, respectively. ORS intensity from Z-spectra of SPPM showed a significant correlation with the inverse of T₂ relaxation rates (1/T₂, s⁻¹) of the SPPM nanoprobes regardless of the PEG corona thickness. These data provide the fundamental understanding of the structure-property relationships between the SPPM nanostructures and ORS sensitivity, which offers useful mechanistic insights for the future improvement of SPPM nanoprobes in cancer molecular imaging applications.

Composite polymeric magnetic nanoparticles for co-delivery of hydrophobic and hydrophilic anticancer drugs and MRI imaging for cancer therapy

Exercising complementary roles of polymer-coated magnetic nanoparticles for precise drug delivery and image contrast agents has attracted significant attention in biomedical applications. The objective of this study was to prepare and characterize magnetic nanoparticles embedded in polylactide-co-glycolide matrixes (PLGA-MNPs) as a dual drug delivery and imaging system capable of encapsulating both hydrophilic and hydrophobic drugs. PLGA-MNPs were capable of encapsulating both hydrophobic and hydrophilic drugs in a 2:1 ratio. Biocompatibility, cellular uptake, cytotoxicity, membrane potential, and apoptosis were carried out in two different cancer cell lines (MCF-7 and PANC-1). The molecular basis of induction of apoptosis was validated by Western blotting analysis. For targeted delivery of drugs, targeting ligand such as Herceptin was used, and such a conjugated system demonstrated enhanced cellular uptake and an augmented synergistic effect in an in vitro system when compared with native drugs. Magnetic resonance imaging was carried out both in vitro and in vivo to assess the efficacy of PLGA-MNPs as contrast agents. PLGA-MNPs showed a better contrast effect than commercial contrast agents due to higher T(2) relaxivity with a blood circulation half-life ∼ 47 min in the rat model. Thus, our results demonstrated the dual usable purpose of formulated PLGA-MNPs toward either, in therapeutics by delivering different hydrophobic or hydrophilic drugs individually or in combination and imaging for cancer therapeutics in the near future.

Principles and basic concepts of molecular imaging

Advanced knowledge in molecular biology and new technological developments in imaging modalities and contrast agents calls for molecular imaging (MI) to play a major role in the near future in many human diseases (Weissleder and Mahmood Radiology 219:316-333, 2001). Imaging systems are providing higher signal-to-noise ratio and higher spatial and/or temporal resolution. New specific contrast agents offer the opportunity to drive new challenges for obtaining functional and biological information on tissue characteristics and tissue processes. All this information could be relevant for diagnosis, prognosis and treatment follow-up and to drive local therapies, enhancing local drug/gene delivery. The recent explosion of all these developments is a radical change of perspective in our imaging community because they could have a tremendous impact on our clinical practice and on teaching programs and they call for a more prominent multidisciplinary approach in this field of research.

Targeted signal-amplifying enzymes enhance MRI of EGFR expression in an orthotopic model of human glioma

Epidermal growth factor receptor (EGFR) imaging in brain tumors is essential to visualize overexpression of EGFRvIII variants as a signature of highly aggressive gliomas and to identify patients that would benefit from anti-EGFR therapy. Seeking imaging improvements, we tested a novel pretargeting approach that relies on initial administration of enzyme-linked anti-EGFR monoclonal antibodies (mAb; EMD72000) followed by administration of a low-molecular-weight paramagnetic molecule (diTyr-GdDTPA) retained at the site of EGFR mAb accumulation. We hypothesized that diTyr-GdDTPA would become enzyme activated and retained on cells due to binding to tissue proteins. In support of this hypothesis, mAb-enzyme conjugates reacted with both membrane-isolated wild-type (wt) EGFR and EGFRvIII, but they bound primarily to EGFRvIII-expressing cells and not to EGFRwt-expressing cells. In vivo analysis of magnetic resonance (MR) tumor signal revealed differences in MR signal decay following diTyr-GdDTPA substrate administration. These differences were significant in that they suggested differences in substrate elimination from the tissue which relied on the specificity of the initial mAb binding: a biexponential signal decay was observed in tumors only upon preinjection with EGFR-targeted conjugates. Endpoint MRI in this setting revealed detailed images of tumors which correlated with immunohistochemical detection of EGFR expression. Together, our findings suggest an improved method to identify EGFRvIII-expressing gliomas in vivo that are best suited for treatment with therapeutic EGFR antibodies.

Towards detecting the HER-2 receptor and metabolic changes induced by HER-2-targeted therapies using medical imaging

HER-2/neu (a receptor for human epidermal growth factor) is involved in cell survival, proliferation, angiogenesis and invasiveness. It is overexpressed in about 25% of breast cancers. Overexpression of HER-2 is associated with response to the anti-HER-2 antibody trastuzumab (herceptin). However, HER-2 expression can be heterogeneous within the primary tumour and can also exhibit discordant expression between a primary tumour and its metastases, bringing into question the practice of HER-2 screening to determine whether a patient is a candidate for trastuzumab using material obtained only from the primary tumour. Medical imaging modalities using HER-2-targeted tracers (or contrast agents) facilitate a global approach to the determination of HER-2 expression across all detectable tumour lesions, and could provide a more reliable indication of the patient's likely response to trastuzumab treatment. Here, I review the development and pre-clinical (and occasional clinical) assessment of HER-2-targeted tracers. I discuss studies in which established imaging tracers, such as (11)C-choline, have been used to determine response to trastuzumab in a range of medical imaging modalities, including positron emission tomography (PET), single photon emission tomography (SPECT), MRI and optical imaging.

In vivo angiogenesis imaging of solid tumors by alpha(v)beta(3)-targeted, dual-modality micellar nanoprobes

The objective of this study was to develop and evaluate an alpha(v)beta(3)-specific nanoprobe consisting of fluorescent superparamagnetic polymeric micelles (FSPPM) for in vivo imaging of tumor angiogenesis. Spherical micelles were produced using poly(ethylene glycol)-b-poly(d,l-lactide) co-polymers conjugated with tetramethylrhodamine, a fluorescent dye, and loaded with superparamagnetic iron oxide nanoparticles. The resulting micelle diameter was 50-70 nm by dynamic light scattering and transmission electron microscopy measurements. Micelles were encoded with an alpha(v)beta(3)-specific peptide, cyclic RGDfK, and optimized for maximum fluorescence and targeting in alpha(v)beta(3)-overexpressing cells in vitro. In mice, cRGD-FSPPM-treated animals showed alpha(v)beta(3)-specific FSPPM accumulation in human lung cancer subcutaneous tumor xenografts. Together with the histological validation, the three-dimensional gradient echo magnetic resonance imaging (MRI) data provide high spatial resolution mapping and quantification of angiogenic vasculature in an animal tumor model using targeted, ultrasensitive MRI nanoprobes.

Detection of Cancer Metastases with a Dual-labeled Near-Infrared/Positron Emission Tomography Imaging Agent

By dual labeling a targeting moiety with both nuclear and optical probes, the ability for noninvasive imaging and intraoperative guidance may be possible. Herein, the ability to detect metastasis in an immunocompetent animal model of human epidermal growth factor receptor 2 (HER-2)-positive cancer metastases using positron emission tomography (PET) and near-infrared (NIR) fluorescence imaging is demonstrated.

METHODS

((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) was synthesized, characterized, and administered to female Balb/c mice subcutaneously inoculated with highly metastatic 4T1.2neu/R breast cancer cells. ((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) (150 µg, 150 µCi, m = 2, n = 2) was administered through the tail vein at weeks 2 and 6 after implantation, and PET/computed tomography and NIR fluorescence imaging were performed 24 hours later. Results were compared with the detection capabilities of F-18 fluorodeoxyglucose ((18)FDG-PET).

RESULTS

Primary tumors were visualized with (18)FDG and ((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m), but resulting metastases were identified only with the dual-labeled imaging agent. (64)Cu-PET imaging detected lung metastases, whereas ex vivo NIR fluorescence showed uptake in regions of lung, skin, skeletal muscle, and lymph nodes, which corresponded with the presence of cancer cells as confirmed by histologic hematoxylin and eosin stains. In addition to detecting the agent in lymph nodes, the high signal-to-noise ratio from NIR fluorescence imaging enabled visualization of channels between the primary tumor and the axillary lymph nodes, suggesting a lymphatic route for trafficking cancer cells. Because antibody clearance occurs through the liver, we could not distinguish between nonspecific uptake and liver metastases.

CONCLUSION

((64)Cu-DOTA)(n)-trastuzumab-(IRDye800)(m) may be an effective diagnostic imaging agent for staging HER-2-positive breast cancer patients and intraoperative resection.

Efficient and rapid labeling of transplanted cell populations with superparamagnetic iron oxide nanoparticles using cell surface chemical biotinylation for in vivo monitoring by MRI

Determination of the dynamics of specific cell populations in vivo is essential for the development of cell-based therapies. For cell tracking by magnetic resonance imaging (MRI), cells need to internalize, or be surface labeled with a MRI contrast agent, such as superparamagnetic iron oxide nanoparticles (SPIOs): SPIOs give rise to signal loss by gradient-echo and T(2)-weighted MRI techniques. In this study, cancer cells were chemically tagged with biotin and then magnetically labeled with anti-biotin SPIOs. No significant detrimental effects on cell viability or death were observed following cell biotinylation. SPIO-labeled cells exhibited signal loss compared to non-SPIO-labeled cells by MRI in vitro. Consistent with the in vitro MRI data, signal attenuation was observed in vivo from SPIO-labeled cells injected into the muscle of the hind legs, or implanted subcutaneously into the flanks of mice, correlating with iron detection by histochemical and X-ray fluorescence (XRF) methods. To further validate this approach, human mesenchymal stem cells (hMSCs) were also employed. Chemical biotinylation and SPIO labeling of hMSCs were confirmed by fluorescence microscopy and flow cytometry. The procedure did not affect proliferation and multipotentiality, or lead to increased cell death. The SPIO-labeled hMSCs were shown to exhibit MRI signal reduction in vitro and was detectable in an in vivo model. In this study, we demonstrate a rapid, robust, and generic methodology that may be a useful and practical adjuvant to existing methods of cell labeling for in vivo monitoring by MRI. Further, we have shown the first application of XRF to provide iron maps to validate MRI data in SPIO-labeled cell tracking studies.

Molecular magnetic resonance imaging approaches used to aid in the understanding of the tissue regeneration marker Met in vivo: implications for tissue engineering

The levels of Met, a tyrosine kinase receptor for the hepatocyte growth factor or scatter factor, are elevated during tissue regeneration, and can be used to assess tissue regeneration associated with engineered tissue grafts. This study involved the development and assessment of a novel magnetic resonance imaging (MRI) molecular probe for the in vivo detection of Met in an experimental rodent (rat) model of disease (C6 glioma). The implication of using these probes in tissue engineering is discussed. The molecular targeting agent we used in our study incorporated a magnetite-based dextran-coated nanoparticle backbone covalently bound to an anti-Met antibody. We used molecular MRI with an anti-Met probe to detect in vivo Met levels as a molecular marker for gliomas. Tumor regions were compared to normal tissue, and found to significantly (p < 0.05) decrease MR signal intensity and T(2) relaxation in tumors. Nonimmune nonspecific normal rat IgG coupled to the dextran-coated nanoparticles was used as a control. Met levels in tumor tissues were confirmed in Western blots. Based on our results, in vivo evaluation of tissue regeneration using molecular MRI is possible in tissue engineering applications.

The role of porphyrin chemistry in tumor imaging and photodynamic therapy

In recent years several review articles and books have been published on the use of porphyrin-based compounds in photodynamic therapy (PDT). This critical review is focused on (i) the basic concept of PDT, (ii) advantages of long-wavelength absorbing photosensitizers (PS), (iii) a brief discussion on recent advances in developing PDT agents, and (iv) the various synthetic strategies designed at the Roswell Park Cancer Institute, Buffalo, for developing highly effective long-wavelength PDT agents and their utility in constructing the conjugates with tumor-imaging and therapeutic potential (Theranostics). The clinical status of certain selected PDT agents is also summarized (205 references).

lacZ as a genetic reporter for real-time MRI

Molecular imaging based on MRI is currently hampered by the lack of genetic reporters for in vivo imaging. We determined that the commercially available substrate S-Gal can be used to detect genetically engineered beta-galactosidase expressing cells by MRI. The effect and specificity of the reaction between beta-galactosidase and S-Gal on MRI contrast were determined both in vitro and in vivo. beta-galactosidase activity in the presence of S-Gal resulted in enhanced T(2) and T*(2) MR-contrast, which was amplified with increasing magnetic field strengths (4.7-17.6 T) in phantom studies. Using both lacZ(+) transgenic animals and lacZ(+) tissue transplants, we were able to detect labeled cells in live animals in real time. Similar to phantom studies, detection of the labeled cells/tissues in vivo was enhanced at high magnetic fields. These results demonstrate that the genetic reporter, lacZ, can be used as an in vivo marker gene using high-field-strength MRI.

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

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

Quantitative MR imaging of targeted SPIO particles on the cell surface and comparison to flow cytometry

PURPOSE

To detect anti-CEACAM5 targeted superparamagnetic iron oxide (SPIO) particles in vitro on the cell surface by quantitative magnetic resonance (MR) imaging and to compare with flow cytometry.

MATERIALS AND METHODS

The monoclonal mouse antibody T84.1 and an appropriate IgG isotype antibody were conjugated to dextran-coated SPIO particles. HT29 cells expressing carcinoembryonic antigen (CEACAM5) were treated with antibody-conjugated SPIO particles. Purified cell samples were examined on a 3.0-T MR scanner using a multi-echo spin-echo sequence for MR relaxometry. Aliquots of the cell samples were further treated with a fluorescein isothiocyanate (FITC) anti-dextran antibody and an Alexa Fluor 488 anti-mouse antibody for the corresponding flow cytometry.

RESULTS

MR relaxometry revealed a dose-dependent binding of T84.1-conjugated SPIO particles with a positive correlation between R(2) relaxation rate of cell samples and SPIO particle concentration during incubation (r=0.993, P<.01). Positive correlations were also observed between R(2) relaxation rate and flow cytometry (geometric mean) with both fluorescent antibodies (r=0.972 and r=0.953, both P<.01), respectively.

CONCLUSION

The study revealed the feasibility of quantitative MR imaging of targeted SPIO particles on the cell surface comparable to flow cytometry.

HER2 targeting as a two-sided strategy for breast cancer diagnosis and treatment: Outlook and recent implications in nanomedical approaches

At present, mammary carcinoma is the second most common type of malignant tumor in adult women after lung cancer, as more than one million women are diagnosed with breast cancer every year. Despite advances in diagnosis and treatment, which have resulted in a decrease in mortality in recent decades, breast cancer remains a major public health problem. One of the most significant unresolved clinical and scientific problems is the occurrence of resistance to clinical treatments and their toxicity (and how to predict, prevent and overcome them). However, the heterogeneity of human breast cancer in terms of genetic features, molecular profiles and clinical behavior represents a constraint obstructing the discovery of a solution to the disease. It is currently considered that the chances of success of therapy may increase if the tumor cells are selectively removed before they can evolve to their mature stages up to metastases production. Therefore, novel and more sensitive diagnostic tools are being developed, with the aim of improving the early and noninvasive detection of rising malignancies and the accuracy of tumor tissue localization. Meanwhile, there is an emerging use of targeted therapies in oncology, depending on the expression of specific proteins or genes present in tumor cells. Among the molecular targets considered for the treatment of breast cancer cells so far, we chose to focus on examples involving overexpression and/or gene amplification of "Human Epidermal growth factor Receptor 2" (HER2) protein. In current studies, various types of nanoparticles conjugated with the anti-HER2 monoclonal antibody, the so-called "trastuzumab", are investigated extensively due to promising results in biological and preclinical applications aimed at improving the treatment of breast cancer. In this paper, we present a critical review of the preparation and use of different kinds of trastuzumab-functionalized nanoparticles, with an emphasis on the therapeutic and diagnostic (theranostic) potential of this generation of hybrid nanoparticles, exploiting the multifaceted mechanisms of action of trastuzumab against malignant cells.

Toxicity of MRI and CT contrast agents

Anatomical and physiological imaging using CT and MRI are playing a critical role in patients' diagnosis, disease characterization and treatment planning. CT- and MRI-based protocols increasingly require an injection of iodinated CT and gadolinium (Gd)-based MRI contrast media. Although routinely used in clinical practice, iodinated and to a less extent Gd-based contrast media possess side effects: life-threatening contrast-induced nephropathy (CIN) is associated with CT and nephrogenic systemic fibrosis (NSF) with MRI contrast agents. CIN is defined as an acute decline in renal functions (serum creatinine increase > 0.5 mg/dl) after administration of iodinated contrast media. Patients with moderate-to-severe chronic kidney disease are considered the highest risk group for development of CIN. CIN is more common with ionic high-osmolar contrast CT media. NSF is a rare condition characterized by the formation of connective tissue in the skin and systemically in the lung, liver, heart and kidney. Patients with end stage kidney disease, acute kidney injury and stage 4-5 chronic kidney disease are at a high risk for NSF. The nonionic linear Gd-chelates are associated with the highest risk of NSF. This review summarizes the incidence, symptoms, safety profile of various CT and MRI contrast agents based on their physiochemical properties.

Targeting the tumor microenvironment with anti-neu/anti-CD40 conjugated nanoparticles for the induction of antitumor immune responses

Clinical and preclinical data indicate that immunotherapeutic interventions could induce immune responses capable of controlling or retard the tumor growth. However, immunotherapies need to be further optimized. We hypothesized that a more effective strategy for tumor eradication is to directly target the tumor microenvironment in order to generate a proinflammatory response and induce a localized antitumor immune response capable of eliminating the tumor cells. Nanoparticles have been proven to be an effective delivery system. In these studies we evaluated conjugated anti-RNEU and anti-CD40 antibodies onto PLA-(poly dl-lactic acid)-biodegradable nanoparticles (PLA-NP) for the induction of antitumor immune responses. The anti-neu/anti-CD40-NP were functional in vitro recognizing RNEU(+) tumors and activating dendritic cells. The delivery of anti-neu/anti-CD40-NP but not anti-neu-NP or anti-CD40-NP induced an antitumor response resulting in complete tumor elimination and generation of protective memory responses. The anti-neu/anti-CD40-NP specifically activated an antitumor response against RNEU(+) tumors but not against RNEU(-) tumors. The antitumor immune responses correlate with the induction of a Th1-proinflammatory response, reduction in the number of Tregs within the tumor and activation of a specific cytotoxic response. These results indicate that anti-neu/anti-CD40-NP with immunomodulatory properties are safe and can be used effectively as cancer vaccines strategy for the specific induction of antitumor immune responses.

Cell-penetrating peptides and peptide nucleic acid-coupled MRI contrast agents: evaluation of cellular delivery and target binding

Molecular imaging of cells and cellular processes can be achieved by tagging intracellular targets such as receptors, enzymes, or mRNA. Seeking to visualize the presence of specific mRNAs by magnetic resonance (MR) imaging, we coupled peptide nucleic acids (PNA) with gadolinium-based MR contrast agents using cell-penetrating peptides for intracellular delivery. Antisense to mRNA of DsRed2 protein was used as proof of principle. The conjugates were produced by continuous solid-phase synthesis followed by chelation with gadolinium. Their cellular uptake was confirmed by fluorescence microscopy and spectroscopy as well as by MR imaging of labeled cells. The cell-penetrating peptide D-Tat(57-49) was selected over two other derivatives of HIV-1 Tat peptide, based on its superior intracellular delivery of the gadolinium-based contrast agents. Further improved delivery of conjugates was achieved upon coupling peptide nucleic acids (antisense to mRNA of DsRed2 protein and nonsense with no natural counterpart). Significant enhancement in MR contrast was obtained in cells labeled with concentrations as low as 2.5 μM of these agents. Specific binding of the targeting PNA containing conjugate to its complementary oligonucleotide sequence was proven by in vitro cell-free assay. In contrast, a lack of specific enrichment was observed in transgenic cells containing the target due to nonspecific vesicular entrapment of contrast agents. Preliminary biodistribution studies showed conjugate-related fluorescence in several organs, especially the liver and bladder, indicating high mobility of the agent in spite of its high molecular weight. No conjugate related toxicity was observed. These results are encouraging, as they warrant further molecular optimization and consecutive specificity studies in vivo of this new generation of contrast agents.

Polymeric nanomedicine for cancer MR imaging and drug delivery

Multifunctional nanomedicine is emerging as a highly integrated platform that allows for molecular diagnosis, targeted drug delivery, and simultaneous monitoring and treatment of cancer. Advances in polymer and materials science are critical for the successful development of these multi-component nanocomposites in one particulate system with such a small size confinement (<200 nm). Currently, several nanoscopic therapeutic and diagnostic systems have been translated into clinical practice. In this feature article, we will provide an up-to-date review on the development and biomedical applications of nanocomposite materials for cancer diagnosis and therapy. An overview of each functional component, i.e. polymer carriers, MR imaging agents, and therapeutic drugs, will be presented. Integration of different functional components will be illustrated in several highlighted examples to demonstrate the synergy of the multifunctional nanomedicine design.

Expression order of alpha-v and beta-3 integrin subunits in the N-methyl-N-nitrosourea-induced rat mammary tumor model

We investigated the developmental time course of molecular expression of alpha(v)beta(3) subunits in a carcinogen-induced rat mammary tumor model for human ductal carcinoma in situ (DCIS). Tumors during various stages of growth (from <0.1 to >2.0 cm) were analyzed immunohistochemically for the expression of the alpha(v)beta(3) integrin and its subunits. In general, the expression profiles of these integrin subunits were directly proportional to the size of the tumor. The pattern of immunostaining revealed that anti-alpha(v)beta(3) monoclonal antibody binds to specific sites of tumor sections, forming isolated stained patches. This isolated patch pattern was found in more developed larger tumors. This could be due to the fact that the integrin molecule might be involved in migration and nesting of tumor cells into specific regions to form DCIS or intraductal carcinoma. Results also showed that the alpha(v) subunit expresses earlier than the beta(3) subunit. These data provide insight into tumor cell biology and developmental characteristics that will guide the future construction and use of targeted contrast and therapeutic agents capable of tracking, imaging, or treating a tumor at the earliest stage of formation.

Nanomedicine: perspective and promises with ligand-directed molecular imaging

Molecular imaging and targeted drug delivery play an important role toward personalized medicine, which is the future of patient management. Of late, nanoparticle-based molecular imaging has emerged as an interdisciplinary area, which shows promises to understand the components, processes, dynamics and therapies of a disease at a molecular level. The unprecedented potential of nanoplatforms for early detection, diagnosis and personalized treatment of diseases, have found application in every biomedical imaging modality. Biological and biophysical barriers are overcome by the integration of targeting ligands, imaging agents and therapeutics into the nanoplatform which allow for theranostic applications. In this article, we have discussed the opportunities and potential of targeted molecular imaging with various modalities putting a particular emphasis on perfluorocarbon nanoemulsion-based platform technology.

Magnetic resonance imaging enhanced by superparamagnetic iron oxide particles: usefulness for distinguishing between focused ultrasound-induced blood-brain barrier disruption and brain hemorrhage

PURPOSE

To investigate the usefulness of a fully flow-compensated heavy T2*-weighted imaging enhanced by superparamagnetic iron oxide (SPIO) particles for distinguishing between focused ultrasound-induced disruption of blood-brain barrier (BBB) and brain hemorrhage.

MATERIALS AND METHODS

Focused ultrasound (frequency: 1.5 MHz) was used to induce disruption of the BBB in 39 rats. Two T2*-weighted images were obtained before and after SPIO administration. Preenhanced T2*-weighted images were used to detect hemorrhage. Detection of BBB disruption was performed on SPIO-enhanced images. Thirty-four rats were sacrificed after magnetic resonance (MR) scanning for histological confirmation of brain lesions. The remaining five animals were followed up for 35 days. Prussian blue staining was performed on histological sections to detect SPIO particles in the brain.

RESULTS

After SPIO injection the areas of BBB disruption in rat brain were significantly enlarged. The area of mismatch between the T2*-weighted images indicated a safe region where BBB opening occurred without hemorrhagic complications. In the longitudinal study, removal of SPIO occurred at a faster rate in hemorrhagic areas, albeit being closer to that occurring in the liver. The presence of SPIO was confirmed by Prussian blue staining in brain parenchyma and capillary endothelial cells in areas of BBB disruption.

CONCLUSION

T2*-weighted images-either with and without SPIO enhancement-may differentiate focused ultrasound-induced BBB disruption from brain hemorrhage.

In vitro diagnostic prospects of nanoparticles

There is a constant need to improve the performance of current diagnostic assays as well as develop innovative testing strategies to meet new testing challenges. The use of nanoparticles promises to help promote in vitro diagnostics to the next level of performance. Quantum dots (QDs), gold nanoparticles (AuNPs), and superparamagnetic nanoparticles are the most promising nanostructures for in vitro diagnostic applications. These nanoparticles can be conjugated to recognition moieties such as antibodies or oligonucleotides for detection of target biomolecules. Nanoparticles have been utilized in immunoassays, immunohistochemistry, DNA diagnostics, bioseparation of specific cell populations, and cellular imaging. Nanoparticle-based diagnostics may open new frontiers for detection of tumours, infectious diseases, bio-terrorism agents, and neurological diseases, to name a few. More work is necessary to fully optimize use of nanoparticles for clinical diagnosis and to resolve some concerns regarding potential health and environmental risks related to their use. However, we envision further developments of nanoparticle-based diagnostics will yield unique assays with enhanced sensitivity and multiplexing capability for the modern clinical laboratory.

Multiparametric monitoring of tumor response to chemotherapy by noninvasive imaging

With the emerging concept of individualized cancer therapy, it becomes crucial to develop methods for the noninvasive assessment of treatment outcome. With this in mind, we designed a novel approach for the comprehensive evaluation of response to chemotherapy with the established agent doxorubicin in a preclinical breast cancer model. This approach delivers information not only about change in tumor size but also about target antigen expression. Our strategy relies on a tumor-specific contrast agent (MN-EPPT) targeting the underglycosylated MUC-1 (uMUC-1) tumor antigen, found on more than 90% of breast cancers and predictive of chemotherapeutic response. MN-EPPT consists of superparamagnetic iron oxide nanoparticles (MN) for magnetic resonance imaging, modified with Cy5.5 dye (for near-IR fluorescence optical imaging), and conjugated to peptides (EPPT), specifically recognizing uMUC-1. In vivo, treatment of mice bearing orthotopic human breast carcinomas with doxorubicin led to a reduction in tumor mass and resulted in down-regulation of uMUC-1. The tumor-specific accumulation of MN-EPPT allowed the assessment of change in tumor volume by noninvasive imaging. Furthermore, in mice injected with MN-EPPT, tumor delta-T2 was significantly reduced after treatment with doxorubicin, indicating a lower accumulation of MN-EPPT and reflecting the reduced expression of uMUC-1. With these studies, we have shown the utility of magnetic resonance imaging for the multiparametric characterization of breast tumor response to chemotherapy. This approach has the potential of significantly advancing our ability to better direct the development of molecularly targeted individualized therapy protocols because it permits the monitoring of therapy on a molecular scale.

Tumor-targeted drug delivery and MRI contrast enhancement by chlorotoxin-conjugated iron oxide nanoparticles

AIMS

This study examines the capabilities of an actively targeting superparamagnetic nanoparticle to specifically deliver therapeutic and MRI contrast agents to cancer cells.

MATERIALS & METHODS

Iron oxide 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 MRI.

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.

A Novel Strategy for Surface Modification of Superparamagnetic Iron Oxide Nanoparticles for Lung Cancer Imaging

Superparamagnetic iron oxide (SPIO) nanoparticles are widely used in magnetic resonance imaging (MRI) as versatile ultra-sensitive nanoprobes for cellular and molecular imaging of cancer. In this study, we report a one-step procedure for the surface functionalization of SPIO nanoparticles with a lung cancer-targeting peptide. The hydrophobic surfactants on the as-synthesized SPIO are displaced by the peptide containing a poly(ethylene glycol)-tethered cysteine residue through ligand exchange. The resulting SPIO particles are biocompatible and demonstrate high T(2) relaxivity. The nanoprobes are specific in targeting α(v)β(6)-expressing lung cancer cells as demonstrated by MR imaging and Prussian blue staining. This facile surface chemistry and the functional design of the proposed SPIO system may provide a powerful nanoplatform for the molecular diagnosis of lung cancer.

Inorganic nanoparticles for predictive oncology of breast cancer

Nanoparticles (NPs) and nanosized objects are being incorporated rapidly into clinical medicine and particularly into the field of medical oncology, including breast cancer. A number of novel methods for breast cancer diagnosis and treatment, which are based on NPs and other nanodevices, are now available for translation into clinical practice. Computer tomography and MRI with iron-based magnetic NPs are promising methods for radiological detection of cancers. Semiconductor fluorescent NPs (quantum dots) are being developed for simultaneous detection and localization of multiple breast cancer biomarkers, enabling the personalization of therapeutic regimens for each patient. Additionally, inorganic NPs can be conjugated with tumor-specific ligands and used for tumor-selective delivery of chemotherapeutic or hormonal agents. NPs bearing tumor-targeted antibodies and oligonucleotides for anticancer gene therapy are a novel and rapidly developing therapeutic approach in oncology. Nab-paclitaxel and liposomal anthracyclines are US FDA-approved NP-based drug-delivery systems that have demonstrated at least equivalent efficacy and decreased toxicity compared with conventional chemotherapeutic agents used in the treatment of breast cancer. This review focuses on recent applications of NPs into predictive oncology of breast cancer with an emphasis placed on the role of inorganic nanosized objects in the diagnosis and treatment of this malignancy.

Imaging of siRNA delivery and silencing

The fast developing field of RNA interference (RNAi) requires monitoring of small interfering RNA (siRNA) delivery to targeted organs and evaluating the efficiency of target gene silencing. The molecular imaging approach fits perfectly to fulfill these needs and provides information in a fast, reproducible, and noninvasive manner. This review serves as a first attempt to summarize existing information on various imaging modalities and their application for siRNA imaging. It is noteworthy that new publications in this field appear almost on a weekly basis and the authors have made a sincere attempt to reflect the development of this area in their review.

Molecular and functional imaging of breast cancer

Despite several major advances in breast cancer diagnosis and treatment, the American Cancer Society has estimated that in the US alone 43300 women and 400 men will die from breast cancer in 2007. Breast cancer typically is a multi-focal, multi-faceted disease, with the major cause of mortality being complications due to metastasis. Whereas a decade ago genetic alterations were the primary focus in cancer research, it is now apparent that the physiological tumor microenvironment, interactions between cancer cells and stromal cells such as endothelial cells, fibroblasts and macrophages, the extracellular matrix, and a multitude of secreted factors and cytokines influence progression, aggressiveness, and response of the disease to treatment. Prevention, early diagnosis, and treatment are the three broad challenges for MR molecular and functional imaging in reducing mortality from this disease. Multi-parametric molecular and functional MRI provides unprecedented opportunities for identifying novel targets for imaging and therapy at the bench, as well as for accurate diagnosis and monitoring response to therapy at the bedside. Here we provide an overview of the current status of molecular and functional MRI of breast cancer, outlining some key developments, as well as identifying some of the important challenges facing this field in the future.

Targeted magnetic iron oxide nanoparticles for tumor imaging and therapy

Magnetic iron oxide (IO) nanoparticles with a long blood retention time, biodegradability and low toxicity have emerged as one of the primary nanomaterials for biomedical applications in vitro and in vivo. IO nanoparticles have a large surface area and can be engineered to provide a large number of functional groups for cross-linking to tumor-targeting ligands such as monoclonal antibodies, peptides, or small molecules for diagnostic imaging or delivery of therapeutic agents. IO nanoparticles possess unique paramagnetic properties, which generate significant susceptibility effects resulting in strong T2 and T*2 contrast, as well as T1 effects at very low concentrations for magnetic resonance imaging (MRI), which is widely used for clinical oncology imaging. We review recent advances in the development of targeted IO nanoparticles for tumor imaging and therapy.

Magnetic resonance methods and applications in pharmaceutical research

This review presents an overview of some recent magnetic resonance (MR) techniques for pharmaceutical research. MR is noninvasive, and does not expose subjects to ionizing radiation. Some methods that have been used in pharmaceutical research MR include magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) methods, among them, diffusion-weighted MRI, perfusion-weighted MRI, functional MRI, molecular imaging and contrast-enhance MRI. Some applications of MR in pharmaceutical research include MR in metabonomics, in vivo MRS, studies in cerebral ischemia and infarction, degenerative joint diseases, oncology, cardiovascular disorders, respiratory diseases and skin diseases. Some of these techniques, such as cardiac and joint imaging, or brain fMRI are standard, and are providing relevant data routinely. Skin MR and hyperpolarized gas lung MRI are still experimental. In conclusion, considering the importance of finding and characterizing biomarkers for improved drug evaluation, it can be expected that the use of MR techniques in pharmaceutical research is going to increase in the near future.

Non-invasive detection of transplanted pancreatic islets

Type 1 diabetes (insulin-dependent, IDDM) results in immune-mediated destruction of pancreatic beta cells, which leads to a deficiency in insulin secretion and as a result, to hyperglycaemia. Keeping blood glucose levels under tight control represents the most effective way either to prevent the onset or to reduce the progression of the chronic complications of IDDM. At present, pancreatic islet transplantation is emerging as the most promising clinical modality, which can stop diabetes progression without increasing the incidence of hypoglycaemic events. Although early results of clinical trials using the Edmonton Protocol and its variations are very encouraging, it is still unclear how long the islets will survive and how often the transplantation procedure will be successful. In order to monitor transplantation efficiency and graft survival, reliable non-invasive imaging methods are critically needed. If such methods are introduced clinically, essential information regarding the location, function and viability of transplanted islets can be obtained repeatedly and non-invasively. This review will focus on the latest advancements in the field of in vivo imaging of islet transplantation and describe various islet labelling and imaging techniques. In addition, we will critically look into limitations and obstacles currently present on the way to successful clinical implementation of this approach.

MRI in ocular drug delivery

Conventional pharmacokinetic methods for studying ocular drug delivery are invasive and cannot be conveniently applied to humans. The advancement of MRI technology has provided new opportunities in ocular drug-delivery research. MRI provides a means to non-invasively and continuously monitor ocular drug-delivery systems with a contrast agent or compound labeled with a contrast agent. It is a useful technique in pharmacokinetic studies, evaluation of drug-delivery methods, and drug-delivery device testing. Although the current status of the technology presents some major challenges to pharmaceutical research using MRI, it has a lot of potential. In the past decade, MRI has been used to examine ocular drug delivery via the subconjunctival route, intravitreal injection, intrascleral injection to the suprachoroidal space, episcleral and intravitreal implants, periocular injections, and ocular iontophoresis. In this review, the advantages and limitations of MRI in the study of ocular drug delivery are discussed. Different MR contrast agents and MRI techniques for ocular drug-delivery research are compared. Ocular drug-delivery studies using MRI are reviewed.

MagA is sufficient for producing magnetic nanoparticles in mammalian cells, making it an MRI reporter

Magnetic resonance imaging (MRI) is routinely used to obtain anatomical images that have greatly advanced biomedical research and clinical health care today, but the full potential of MRI in providing functional, physiological, and molecular information is only beginning to emerge. In this work, we sought to provide a gene expression marker for MRI based on bacterial magnetosomes, tiny magnets produced by naturally occurring magnetotactic bacteria. Specifically, magA, a gene in magnetotactic bacteria known to be involved with iron transport, is expressed in a commonly used human cell line, 293FT, resulting in the production of magnetic, iron-oxide nanoparticles by these cells and leading to increased transverse relaxivity. MRI shows that these particles can be formed in vivo utilizing endogenous iron and can be used to visualize cells positive for magA. These results demonstrate that magA alone is sufficient to produce magnetic nanoparticles and that it is an appropriate candidate for an MRI reporter gene.

Effect of trastuzumab-modified antisense oligonucleotide-loaded human serum albumin nanoparticles prepared by heat denaturation

Nanoparticles represent a promising tool for targeted drug delivery to tumour cells and are able to protect drugs against degradation. In our present study we developed targeted nanoparticles loaded with antisense oligonucleotides (ASOs) against Plk1 (polo-like kinase 1) prepared by heat denaturation instead of using glutaraldehyde. Glutaraldehyde can lead to an inactivation of ASOs through chemical crosslinking and is a toxic entity. We examined the ideal preparation conditions and characterised the resulting particles in terms of physico-chemical properties, ASO recovery after enzymatic degradation and stability. Stable monodisperse nanoparticles with an ASO recovery of more than 80% could be prepared at a temperature of 105 degrees C for 10 min. Furthermore we performed quantitative real-time PCR and Western blot to detect an ASO-mediated effect on Plk1 in BT-474 cells. We observed a significant reduction of Plk1 mRNA and protein expression. Thus, this is the first report of ASO-loaded HSA nanoparticles prepared by heat denaturation, where an impact on gene expression could be observed. The data provide the basis for the further development of carrier systems for ASOs to reduce off-target effects evoked by systemically administered ASOs and to achieve a better penetration into primary and metastatic target cells.

Magnetic nanoparticles in MR imaging and drug delivery

Magnetic nanoparticles (MNPs) possess unique magnetic properties and the ability to function at the cellular and molecular level of biological interactions making them an attractive platform as contrast agents for magnetic resonance imaging (MRI) and as carriers for drug delivery. Recent advances in nanotechnology have improved the ability to specifically tailor the features and properties of MNPs for these biomedical applications. To better address specific clinical needs, MNPs with higher magnetic moments, non-fouling surfaces, and increased functionalities are now being developed for applications in the detection, diagnosis, and treatment of malignant tumors, cardiovascular disease, and neurological disease. Through the incorporation of highly specific targeting agents and other functional ligands, such as fluorophores and permeation enhancers, the applicability and efficacy of these MNPs have greatly increased. This review provides a background on applications of MNPs as MR imaging contrast agents and as carriers for drug delivery and an overview of the recent developments in this area of research.

Imaging and cancer: a review

Multiple biomedical imaging techniques are used in all phases of cancer management. Imaging forms an essential part of cancer clinical protocols and is able to furnish morphological, structural, metabolic and functional information. Integration with other diagnostic tools such as in vitro tissue and fluids analysis assists in clinical decision-making. Hybrid imaging techniques are able to supply complementary information for improved staging and therapy planning. Image guided and targeted minimally invasive therapy has the promise to improve outcome and reduce collateral effects. Early detection of cancer through screening based on imaging is probably the major contributor to a reduction in mortality for certain cancers. Targeted imaging of receptors, gene therapy expression and cancer stem cells are research activities that will translate into clinical use in the next decade. Technological developments will increase imaging speed to match that of physiological processes. Targeted imaging and therapeutic agents will be developed in tandem through close collaboration between academia and biotechnology, information technology and pharmaceutical industries.

PAMAM dendrimer-based contrast agents for MR imaging of Her-2/neu receptors by a three-step pretargeting approach

Pretargeting of receptors is a useful approach in molecular imaging and therapy to reduce background noise or toxicity and enhance selectivity. In this study a three-step pretargeting approach that includes a biotinylated antibody, avidin/streptavidin, and a biotinylated imaging agent is described. A PAMAM dendrimer generation 4 (G4D)-based MRI T(1) agent biotin-G4D-DTPA-Gd (bG4D-Gd) and its sister compound with remaining free surface amine groups blocked by succinic anhydride to reduce positive charges (bG4D-Gd-SA) were synthesized. Limited selective enhancement in MRI was observed in a Her-2/neu mouse tumor xenograft by this three-step pretargeting approach that includes biotinylated trastuzumab, avidin and bG4D-Gd, or bG4D-Gd-SA. However, these dendrimer-based MRI agents with molecular weight around 29 kD reached and remained in the tumor through the enhanced permeability and retention effect. Prolonged and extensive accumulation of both bG4D-Gd and b-G4-Gd-SA in the kidneys was also observed.

Near infrared fluorescent optical imaging for nodal staging

Current techniques to assess lymph node metastases in cancer patients include lymphoscintigraphy after administration of a nonspecific radiocolloid in order to locate and resect lymph nodes for pathological examination of harbored cancer cells. Clinical trials involving intradermal or subcutaneous injection of antibody-based nuclear imaging agents have demonstrated the feasibility for target-specific, molecular imaging of cancer-positive lymph nodes. The basis for employing near-infrared (NIR) optical imaging for assessing disease is evidenced by recent work showing functional lymph imaging in mice, swine, and humans. We review antibody-based immunolymphoscintigraphy with an emphasis on the use of trastuzumab (or Herceptin) to target human epidermal growth factor receptor-2 (HER2) overexpressed in some breast cancers. Specifically, we review in vitro and preclinical imaging data from our laboratory that show how the dual-labeled agent ((111)In-DTPA)(n)-trastuzumab-(IRDye800)(m) utilizes the high photon count provided by an NIR fluorescent dye, IRDye 800CW, and the radioactive signal from a gamma emitter, Indium-111, for possible detection of HER2 metastasis in lymph nodes. We show that the accumulation and clearance of ((111)In-DTPA)(n)-trastuzumab-(IRDye800)(m) from the axillary nodes of mice occurs 48 h after intradermal injection into the dorsal aspect of the foot. The requirement for long clearance times from normal, cancer-negative nodes presents challenges for nuclear imaging agents with limited half-lives but does not hamper NIR optical imaging.

Quantitative measurements of C-reactive protein using silicon nanowire arrays

A silicon nanowire-based sensor for biological application showed highly desirable electrical responses to either pH changes or receptor-ligand interactions such as protein disease markers, viruses, and DNA hybridization. Furthermore, because the silicon nanowire can display results in real-time, it may possess superior characteristics for biosensing than those demonstrated in previously studied methods. However, despite its promising potential and advantages, certain process-related limitations of the device, due to its size and material characteristics, need to be addressed. In this article, we suggest possible solutions. We fabricated silicon nanowire using a top-down and low cost micromachining method, and evaluate the sensing of molecules after transfer and surface modifications. Our newly designed method can be used to attach highly ordered nanowires to various substrates, to form a nanowire array device, which needs to follow a series of repetitive steps in conventional fabrication technology based on a vapor-liquid-solid (VLS) method. For evaluation, we demonstrated that our newly fabricated silicon nanowire arrays could detect pH changes as well as streptavidin-biotin binding events. As well as the initial proof-of-principle studies, C-reactive protein binding was measured: electrical signals were changed in a linear fashion with the concentration (1 fM to 1 nM) in PBS containing 1.37 mM of salts. Finally, to address the effects of Debye length, silicon nanowires coupled with antigen proteins underwent electrical signal changes as the salt concentration changed.

In vivo imaging of molecular targets and their function in endocrinology

Imaging is one of the fastest growing fields of study. New technologies and multimodal approaches are increasing the application of imaging to determine molecular targets and functional processes in vivo. The identification of a specific target, transporter, or biological process using imaging has introduced major breakthroughs to the field of endocrinology primarily utilizing computed tomography, magnetic resonance imaging, ultrasonography, positron emission tomography, single-photon emission computed tomography, and optical imaging. This review provides a general background to the specific developments in imaging that pertains to in vivo function and target identification in endocrine-based diseases.