Simultaneous evaluation of vascular morphology, blood volume and transvascular permeability using SPION-based, dual-contrast MRI: imaging optimization and feasibility test

Using imaging modalities to predict nanoparticle distribution and treatment efficacy in solid tumors: The growing role of ultrasound

Nanomedicine in oncology has not had the success in clinical impact that was anticipated in the early stages of the field's development. Ideally, nanomedicines selectively accumulate in tumor tissue and reduce systemic side effects compared to traditional chemotherapeutics. However, this has been more successful in preclinical animal models than in humans. The causes of this failure to translate may be related to the intra- and inter-patient heterogeneity of the tumor microenvironment. Predicting whether a patient will respond positively to treatment prior to its initiation, through evaluation of characteristics like nanoparticle extravasation and retention potential in the tumor, may be a way to improve nanomedicine success rate. While there are many potential strategies to accomplish this, prediction and patient stratification via noninvasive medical imaging may be the most efficient and specific strategy. There have been some preclinical and clinical advances in this area using MRI, CT, PET, and other modalities. An alternative approach that has not been studied as extensively is biomedical ultrasound, including techniques such as multiparametric contrast-enhanced ultrasound (mpCEUS), doppler, elastography, and super-resolution processing. Ultrasound is safe, inexpensive, noninvasive, and capable of imaging the entire tumor with high temporal and spatial resolution. In this work, we summarize the in vivo imaging tools that have been used to predict nanoparticle distribution and treatment efficacy in oncology. We emphasize ultrasound imaging and the recent developments in the field concerning CEUS. The successful implementation of an imaging strategy for prediction of nanoparticle accumulation in tumors could lead to increased clinical translation of nanomedicines, and subsequently, improved patient outcomes. This article is categorized under: Diagnostic Tools In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery Emerging Technologies.

Visualizing stem cells in vivo using magnetic resonance imaging

Stem cell (SC) therapies displayed encouraging efficacy and clinical outcome in various disorders. Despite this huge hype, clinical translation of SC therapy has been disheartening due to contradictory results from clinical trials. The ability to monitor migration and engraftment of cells in vivo represents an ideal strategy in cell therapy. Therefore, suitable imaging approach to track MSCs would allow understanding of migratory and homing efficiency, optimal route of delivery and engraftment of cells at targeted location. Hence, longitudinal tracking of SCs is crucial for the optimization of treatment parameters, leading to improved clinical outcome and translation. Magnetic resonance imaging (MRI) represents a suitable imaging modality to observe cells non-invasively and repeatedly. Tracking is achieved when cells are incubated prior to implantation with appropriate contrast agents (CA) or tracers which can then be detected in an MRI scan. This review explores and emphasizes the importance of monitoring the distribution and fate of SCs post-implantation using current contrast agents, such as positive CAs including paramagnetic metals (gadolinium), negative contrast agents such as superparamagnetic iron oxides and ¹⁹ F containing tracers, specifically for the in vivo tracking of MSCs using MRI. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Spatiotemporal heterogeneity of tumor vasculature during tumor growth and antiangiogenic treatment: MRI assessment using permeability and blood volume parameters

Tumor heterogeneity is an important concept when assessing intratumoral variety in vascular phenotypes and responses to antiangiogenic treatment. This study explored spatiotemporal heterogeneity of vascular alterations in C6 glioma mice during tumor growth and antiangiogenic treatment on serial MR examinations (days 0, 4, and 7 from initiation of vehicle or multireceptor tyrosine kinase inhibitor administration). Transvascular permeability (TP) was quantified on dynamic‐contrast‐enhanced MRI (DCE‐MRI) using extravascular extracellular agent (Gd‐DOTA); blood volume (BV) was estimated using intravascular T₂ agent (SPION). With regard to region‐dependent variability in vascular phenotypes, the control group demonstrated higher TP in the tumor center than in the periphery, and greater BV in the tumor periphery than in the center. This distribution pattern became more apparent with tumor growth. Antiangiogenic treatment effect was regionally heterogeneous: in the tumor center, treatment significantly suppressed the increase in TP and decrease in BV (ie, typical temporal change in the control group); in the tumor periphery, treatment‐induced vascular alterations were insignificant and BV remained high. On histopathological examination, the control group showed greater CD31, VEGFR2, Ki67, and NG2 expression in the tumor periphery than in the center. After treatment, CD31 and Ki67 expression was significantly suppressed only in the tumor center, whereas VEGFR2 and α‐caspase 3 expression was decreased and NG2 expression was increased in the entire tumor. These results demonstrate that MRI can reliably depict spatial heterogeneity in tumor vascular phenotypes and antiangiogenic treatment effects. Preserved angiogenic activity (high BV on MRI and high CD31) and proliferation (high Ki67) in the tumor periphery after treatment may provide insights into the mechanism of tumor resistance to antiangiogenic treatment.

Complement activation in vitro and reactogenicity of low-molecular weight dextran-coated SPIONs in the pig CARPA model: Correlation with physicochemical features and clinical information

The unique magnetic properties of superparamagnetic iron oxide nanoparticles (SPIONs) have led to their increasing use in drug delivery and imaging applications. Some polymer-coated SPIONs, however, share with many other nanoparticles the potential of causing hypersensitivity reactions (HSRs) known as complement (C) activation-related pseudoallergy (CARPA). In order to explore the roles of iron core composition and particle surface coating in SPION-induced CARPA, we measured C activation by 6 different SPIONs in a human serum that is known to react to nanoparticles (NPs) with strong C activation. Remarkably, only the carboxymethyldextran-coated (ferucarbotran, Resosvist®) and dextran-coated (ferumoxtran-10, Sinerem®) SPIONs caused significant C activation, while the citric acid, phosphatidylcholine, starch and chitosan-coated SPIONs had no such effect. Focusing on Resovist and Sinerem, we found Sinerem to be a stronger activator of C than Resovist, although the individual variation in 15 different human sera was substantial. Further analysis of C activation by Sinerem indicated biphasic dose dependence and significant production of C split product Bb but not C4d, attesting to alternative pathway C activation only at low doses. Consistent with the strong C activation by Sinerem and previous reports of HSRs in man, injection of Sinerem in a pig led to dose-dependent CARPA, while Resovist was reaction-free. Using nanoparticle tracking analysis, it was further determined that Sinerem, more than Resovist, displayed multimodal size distribution and significant fraction of aggregates - factors which are known to promote C activation and CARPA. Taken together, our findings offer physicochemical insight into how key compositional factors and nanoparticle size distribution affect SPION-induced CARPA, a knowledge that could lead to the development of SPIONs with improved safety profiles.

A new class of cubic SPIONs as a dual-mode T1 and T2 contrast agent for MRI

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely used as a robust negative contrast agent on conventional MRI. In this study, we (a) synthesized a new class of cubic SPIONs as a dual-mode contrast agent in MRI and (b) showed the in-vivo feasibility of these nanaoparticles as a simultaneous positive and negative contrast agent. Relaxation properties and contrast enhancement analysis of the synthesized SPIONs with two different shapes (cubic vs. spherical) and three different sizes 7nm, 11nm, and 14nm were investigated to evaluate contrast enhancement in-vitro. In-vivo MRI experiments were performed on a 3T MR scanner, where a healthy anesthetized rat was imaged before, and from 20 to 80min after intravenous injection of 1mg/kg of contrast agent. Representative transmission electron microscopy (TEM) images of the synthesized nanoparticles reveal that the particles are well dispersed in a solvent and do not aggregate. The in-vitro relaxivity and contrast enhancement analysis show that, among all six SPIONs tested, 11-nm cubic SPIONs possess optimal molar relaxivities and contrast enhancement values, which can shorten the spin-lattice and spin-spin relaxation times, simultaneously. No noticeable toxicity is observed during in-vitro cytotoxicity analysis. In-vivo T₁-and T₂-weighted acquisitions at 60-min post-injection of 11-nm cubic SPIONs result in 64% and 48% contrast enhancement on the T₁-and T₂-weighted images, respectively. By controlling the shape and size of SPIONs, we have introduced a new class of cubic SPIONs as a synergistic (dual-mode) MRI contrast agent. 11-nm cubic SPIONs with smaller size and high positive and negative contrast enhancements were selected as a promising candidate for dual-mode contrast agent. Our proof-of-concept MRI experiments on rat demonstrate the in-vivo dual-mode contrast enhancement feasibility of these nanoparticles.

Prediction of Anti-cancer Nanotherapy Efficacy by Imaging

Anticancer nanotherapeutics have shown mixed results in clinical trials, raising the questions of whether imaging should be used to i) identify patients with a higher likelihood of nanoparticle accumulation, ii) assess nanotherapeutic efficacy before traditional measures show response, and iii) guide adjuvant treatments to enhance therapeutic nanoparticle (TNP) delivery. Here we review the use of a clinically approved MRI nanoparticle (ferumoxytol, FMX) to predict TNP delivery and efficacy. It is becoming increasingly apparent that nanoparticles used for imaging, despite clearly distinct physicochemical properties, often co-localize with TNP in tumors. This evidence offers the possibility of using FMX as a generic “companion diagnostic” nanoparticle for multiple TNP formulations, thus potentially allowing many of the complex regulatory and cost challenges of other approaches to be avoided.

Difference in the intratumoral distributions of extracellular-fluid and intravascular MR contrast agents in glioblastoma growth

Contrast enhancement by an extracellular-fluid contrast agent (CA) (Gd-DOTA) depends primarily on the blood-brain-barrier permeability (bp), and transverse-relaxation change caused by intravascular T₂ CA (superparamagnetic iron oxide nanoparticles, SPIONs) is closely associated with the blood volume (BV). Pharmacokinetic (PK) vascular characterization based on single-CA-using dynamic contrast-enhanced MRI (DCE-MRI) has shown significant measurement variation according to the molecular size of the CA. Based on this recognition, this study used a dual injection of Gd-DOTA and SPIONs for tracing the changes of bp and BV in C6 glioma growth (Days 1 and 7 after the tumor volume reached 2 mL). bp was quantified according to the non-PK parameters of Gd-DOTA-using DCE-MRI (wash-in rate, maximum enhancement ratio and initial area under the enhancement curve (IAUC)). BV was estimated by SPION-induced ΔR₂ * and ΔR₂ . With validated measurement reliability of all the parameters (coefficients of variation ≤10%), dual-contrast MRI demonstrated a different region-oriented distribution between Gd-DOTA and SPIONs within a tumor as follows: (a) the BV increased stepwise from the tumor center to the periphery; (b) the tumor periphery maintained the augmented BV to support continuous tumor expansion from Day 1 to Day 7; (c) the internal tumor area underwent significant vascular shrinkage (i.e. decreased ΔR₂ and ΔR₂ ) as the tumor increased in size; (d) the tumor center showed greater bp-indicating parameters, i.e. wash-in rate, maximum enhancement ratio and IAUC, than the periphery on both Days 1 and 7 and (e) the tumor center showed a greater increase of bp than the tumor periphery in tumor growth, as suggested to support tumor viability when there is insufficient blood supply. In the MRI-histologic correlation, a prominent BV increase in the tumor periphery seen in MRI was verified with increased fluorescein isothiocyanate-dextran signals and up-regulated immunoreactivity of CD31-VEGFR. In conclusion, the spatiotemporal alterations of BV and bp in glioblastoma growth, i.e. augmented BV in the tumor periphery and increased bp in the center, can be sufficiently evaluated by MRI with dual injection of extracellular-fluid Gd chelates and intravascular SPION.

UTE-ΔR2 -ΔR2 * combined MR whole-brain angiogram using dual-contrast superparamagnetic iron oxide nanoparticles

The ability to visualize whole-brain vasculature is important for quantitative in vivo investigation of vascular malfunctions in cerebral small vessel diseases, including cancer, stroke and neurodegeneration. Transverse relaxation-based ΔR2 and ΔR2 * MR angiography (MRA) provides improved vessel-tissue contrast in animal deep brain with the aid of intravascular contrast agents; however, it is susceptible to orientation dependence, air-tissue interface artifacts and vessel size overestimation. Dual-mode MRA acquisition with superparamagnetic iron oxide nanoparticles (SPION) provides a unique opportunity to systematically compare and synergistically combine both longitudinal (R1 ) and transverse (ΔR2 and ΔR2 *) relaxation-based MRA. Through Monte Carlo (MC) simulation and MRA experiments in normal and tumor-bearing animals with intravascular SPION, we show that ultrashort TE (UTE) MRA acquires well-defined vascularization on the brain surface, minimizing air-tissue artifacts, and combined ΔR2 and ΔR2 * MRA simultaneously improves the sensitivity to intracortical penetrating vessels and reduces vessel size overestimation. Consequently, UTE-ΔR2 -ΔR2 * combined MRA complements the shortcomings of individual angiograms and provides a strategy to synergistically merge longitudinal and transverse relaxation effects to generate more robust in vivo whole-brain micro-MRA. Copyright © 2016 John Wiley & Sons, Ltd.

Iron Oxide as an MRI Contrast Agent for Cell Tracking

Iron oxide contrast agents have been combined with magnetic resonance imaging for cell tracking. In this review, we discuss coating properties and provide an overview of ex vivo and in vivo labeling of different cell types, including stem cells, red blood cells, and monocytes/macrophages. Furthermore, we provide examples of applications of cell tracking with iron contrast agents in stroke, multiple sclerosis, cancer, arteriovenous malformations, and aortic and cerebral aneurysms. Attempts at quantifying iron oxide concentrations and other vascular properties are examined. We advise on designing studies using iron contrast agents including methods for validation.