Injectable Thermogelling Nanostructured Ink as Simultaneous Optical and Magnetic Resonance Imaging Contrast Agent for Image-Guided Surgery.

The development of efficient and biocompatible contrast agents is particularly urgent for modern clinical surgery. Nanostructured materials raised great interest as contrast agents for different imaging techniques, for which essential features are high contrasts, and in the case of precise clinical surgery, minimization of the signal spatial dispersion when embedded in biological tissues. This study deals with the development of a multimodal contrast agent based on an injectable hydrogel nanocomposite containing a lanthanide-activated layered double hydroxide coupled to a biocompatible dye (indocyanine green), emitting in the first biological window. This novel nanostructured thermogelling hydrogel behaves as an efficient tissue marker for optical and magnetic resonance imaging because the particular formulation strongly limits its spatial diffusion in biological tissue by exploiting a simple injection. The synergistic combination of these properties permits to employ the hydrogel ink simultaneously for both optical and magnetic resonance imaging, easy monitoring of the biological target, and, at the same time, increasing the spatial resolution during a clinical surgery. The biocompatibility and excellent performance as contrast agents are very promising for possible use in image-guided surgery, which is currently one of the most challenging topics in clinical research.

Negative Pressure From an Internal Spiral Tissue Expander Generates New Subcutaneous Adipose Tissue in an In Vivo Animal Model.

BACKGROUND: Tissue expanders are widely utilized in plastic surgery. Traditional expanders usually are "inflatable balloons," which are planned to grow additional skin and/or to create space to be filled, for example, with an implant. In very recent years, reports suggest that negative pressure created by an external device (ie, Brava) induces both skin expansion and adipogenesis. OBJECTIVES: The authors evaluated and assessed the adipogenetic potential of a novel internal tissue expander in an in vivo animal model. METHODS: New Zealand female rabbits were enrolled in the study. A prototype spiral inner tissue expander was employed. It consisted of a-dynamic conic expander (DCE) with a valve at the end: when empty, it is flat (Archimedean spiral), whereas when filled with a fluid, it takes a conic shape. Inside the conic spiral, a negative pressure is therefore created. DCE is implanted flat under the latissimus dorsi muscle in experimental animals (rabbit) and then filled to reach the conical shape. Animals were investigated with magnetic resonance imaging, histology, and transmission electronic microscopy at 3, 6, and 12 months. RESULTS: Magnetic resonance imaging revealed a marked increase in newly formed adipose tissue, reaching its highest amount at 12 months after the DCE implantation. Histology confirmed the existence of new adipocytes, whereas transmission electronic microscopy ultrastructure confirmed that most of these new cells were mature adipocytes. CONCLUSIONS: Tensile stress, associated with negative-pressure expanders, generated newly white subcutaneous adipose tissue.

Multifunctional Nanovectors Based on Polyamidoamine Polymers for Theranostic Application.

We present multifunctional, biocompatible and biodegradable magnetic nanovectors based on different polyamidoamine (PAA) polymers tailored with different diagnostic and therapeutic properties. Using maghemite nanoparticles with average size 15.5 ± 2.8 nm prepared by thermal decomposition, superparamagnetic nanovectors were obtained by coating the nanoparticles with synthetic polymers of PAA. These have a segmented copolymer structure, and bear PAA segments containing different amount of carboxyl groups per repeating units together with PEG segments. These copolymers are thought to combine the binding properties of the carboxylated PAA segments to inorganic nanoparticles, with the stealth properties of the PEG ones. The magnetic, hyperthermal and relaxometric properties of the synthesized samples were investigated. Magnetic measurements revealed that the samples are superparamagnetic at room temperature and the overall magnetic behavior is not affected by the functionalization process. Calorimetric measurements demonstrated a good heating efficiency at alternating magnetic field parameters below the human tolerability threshold (SAR of ca. 70 W/g at 260 Hz and 10.8 kA/m). 1H-NMR relaxivities were relevant compared to the values of the commercial contrast agents over the whole investigated frequency range.

Magneto-plasmonic Au-Fe alloy nanoparticles designed for multimodal SERS-MRI-CT imaging.

Diagnostic approaches based on multimodal imaging are needed for accurate selection of the therapeutic regimens in several diseases, although the dose of administered contrast drugs must be reduced to minimize side effects. Therefore, large efforts are deployed in the development of multimodal contrast agents (MCAs) that permit the complementary visualization of the same diseased area with different sensitivity and different spatial resolution by applying multiple diagnostic techniques. Ideally, MCAs should also allow imaging of diseased tissues with high spatial resolution during surgical interventions. Here a new system based on multifunctional Au-Fe alloy nanoparticles designed to satisfy the main requirements of an ideal MCA is reported and their biocompatibility and imaging capability are described. The MCAs show easy and versatile surface conjugation with thiolated molecules, magnetic resonance imaging (MRI) and computed X-ray tomography (CT) signals for anatomical and physiological information (i.e., diagnostic and prognostic imaging), large Raman signals amplified by surface enhanced Raman scattering (SERS) for high sensitivity and high resolution intrasurgical imaging, biocompatibility, exploitability for in vivo use and capability of selective accumulation in tumors by enhanced permeability and retention effect. Taken together, these results show that Au-Fe nanoalloys are excellent candidates as multimodal MRI-CT-SERS imaging agents.

Chronic overcirculation-induced pulmonary arterial hypertension in aorto-caval shunt.

Pulmonary arterial hypertension is a common complication of congenital heart defects with left-to-right shunts. Current preclinical models do not reproduce clinical characteristics of shunt-related pulmonary hypertension. Aorto-caval shunt was firstly described as a model of right ventricle volume overload. The pathophysiology and the possible determination of pulmonary arterial hypertension of different periods of shunt exposure are still undefined. A method to create standardized, reproducible aorto-caval shunt was developed in growing rats (260±40 g). Three groups of animals were considered: shunt exposure for 10 weeks, shunt exposure for 20 weeks and control (sham laparotomy). Echocardiography and magnetic resonance revealed increased right ventricular end diastolic area in shunt at 10 weeks compared to control. Hemodynamic analysis demonstrated increased right ventricular afterload and increased effective pulmonary arterial elastance (Ea) in shunt at 20 weeks compared to control (1.29±0.20 vs. 0.14±0.06 mmHg/µl, p=0.004). At the same time point, the maximal slope of end-systolic pressure-volume relationship (Ees) decreased (0.5±0.2 mmHg/ml vs. 1.2±0.3, p<0.001). Consequently, right ventricular-arterial coupling was markedly deteriorated with a ≈50% decrease in the ratio of end-systolic to pulmonary artery elastance (Ees/Ea). Finally, left ventricular preload diminished (≈30% decrease in left ventricular end-diastolic volume). Histology demonstrated medial hypertrophy and small artery luminal narrowing. Chronic exposure to aorto-caval shunt is a reliable model to produce right ventricular volume overload and secondary pulmonary arterial hypertension. This model could be an alternative with low mortality and high reproducibility for investigators on the underlying mechanisms of shunt-related pulmonary hypertension.

Age-Related In Vivo Structural Changes in the Male Mouse Olfactory Bulb and Their Correlation with Olfactory-Driven Behavior.

Olfactory areas in mammalian brains are linked to centers that modulate behavior. During aging, sensitivity to odors decreases and structural changes are described in olfactory areas. We explored, in two groups of male mice (young and elderly, 6 and 19 months old, respectively), the link between the changes in olfactory bulb structure, detected with magnetic resonance imaging, and behavioral changes in a battery of tests on motor, olfactory, cognitive performance, and emotional reactivity. The behavioral pattern of elderly mice appears less anxious, being less scared by new situations. Additionally, the olfactory bulb of young and elderly mice differed in two variables derived from magnetic resonance imaging (fractional anisotropy and T2 maps). A random forest approach allowed to select the variables most predictive of the differences between young and elderly mice, and correlations were found between three behavioral variables indicative of anxious behavior and the two magnetic resonance variables mentioned above. These data suggest that in the living mouse, it is possible to describe co-occurring age-related behavioral and structural changes in the olfactory bulb. These data serve as a basis for studies on normal and pathological aging in the mouse, but also open new opportunities for in vivo human aging studies.

Early versus late GD-DTPA MRI enhancement in experimental glioblastomas.

PURPOSE: To compare early versus late enhancement in two glioblastoma models characterized by different infiltrative/edematous patterns. MATERIALS AND METHODS: Three weeks after inoculation into nude mice of U87MG and U251 cells, T1-weighted images were acquired early (10.5 min), intermediate (21 min) and late (30.5 min) after a bolus injection of Gd-DTPA at 300 µ mol/kg dosage. EARLY(TH) and LATE(TH) were the corresponding volumes with an enhancement higher than a threshold TH, defined by the mean (µ) and standard deviation (σ) on a contralateral healthy area. ADD(TH) was the enhancing volume found in LATE(TH) but not in EARLY(TH). T2 imaging of both tumors was performed, and T2 mapping of U251. RESULTS: In all tumors, LATE(TH) was significantly higher than EARLY(TH) for TH ranging from µ+σ to µ+5σ. The ADD(TH) /EARLY(TH) ratio was not significantly different when U251 and U87MG tumors were compared. In the U87MG tumors, some enhancement was observed outside the regularly demarcated T2-hyperintense area. In the U251 tumors, irregularly T2 demarcated, a large portion of ADD(µ+3σ) had normal T2 values. At histology, U251 showed a higher infiltrative pattern than U87MG. CONCLUSION: In these models, the increase over time in the enhancing volume did not depend on the different infiltrative/edematous patterns and was not closely related with edema.

A smaller olfactory bulb in a mouse model of Down syndrome.

Persons with trisomy 21 (Down syndrome) present different phenotypes, including early neurodegeneration, which is prominent in the brain olfactory areas, and olfactory deficit. The use of in vivo techniques in animal models allows to characterize and follow up these slowly developing phenomena. We explored by means of magnetic resonance imaging the olfactory bulb of the Ts65Dn mouse, an established model of Down syndrome, searching for possible syndrome­related changes. In vivo imaging provided a first glimpse of the trisomic olfactory bulb as compared to euploid one. The olfactory bulb volume was smaller in trisomic mice, suggesting that changes in olfactory bulb may be apparent already in the young adult (2­ to 8­month­old) mice, which are amenable to follow­up in vivo. These findings lead the way to future work aimed at characterizing the Down syndrome­related development of morphological alterations in the olfactory bulb and relating them to changes in olfactory performance, which were detected in this mouse model.

Slow versus fast rewarming after hypothermic circulatory arrest: effects on neuroinflammation and cerebral oedema.

OBJECTIVES: Among the factors that could determine neurological outcome after hypothermic circulatory arrest (HCA) rewarming is rarely considered. The optimal rewarming rate is still unknown. The goal of this study was to investigate the effects of 2 different protocols for rewarming after HCA on neurological outcome in an experimental animal model. METHODS: Forty-four Sprague Dawley rats were cooled to 19 ± 1°C body core temperature by cardiopulmonary bypass (CPB). HCA was maintained for 60 min. Animals were randomized to receive slow (90 min) or fast (45 min) assisted rewarming with CPB to a target temperature of 35°C. After a total of 90 min of reperfusion in both groups, brain samples were collected and analysed immunohistochemically and with immunofluorescence. In 10 rats, magnetic resonance imaging was performed after 2 and after 24 h to investigate cerebral perfusion and cerebral oedema. RESULTS: Interleukin 6, chemokine (C-C motif) ligand 5, intercellular adhesion molecule 1 and tumour necrosis factor α in the hippocampus are significantly less expressed in the slow rewarming group, and microglia cells are significantly less activated in the slow rewarming group. Magnetic resonance imaging analysis demonstrated better cerebral perfusion and less water content in brains that underwent slow rewarming at 2 and 24 h. CONCLUSIONS: Slow rewarming after HCA might be superior to fast rewarming in neurological outcome. The present experimental study demonstrated reduction in the inflammatory response, reduction of inflammatory cell activation in the brain, enhancement of cerebral blood flow and reduction of cerebral oedema when slow rewarming was applied.

Washout of small molecular contrast agent in carcinoma-derived experimental tumors.

The use of contrast-enhanced magnetic resonance imaging (MRI) for the assessment of breast carcinomas reveals satisfactory sensitivity, but due to low specificity, it does not obviate the need for subsequent tissue sampling. Its capability to differentiate benign from malignant lesion is under continuous investigation. Dynamic contrast-enhanced MRI (DCE-MRI) could improve specificity of MRI through the analysis of the kinetic of contrast enhancement. In particular, the study of the washout pattern is considered a promising tool to improve in vivo diagnosis and even to evaluate the response under chemotherapy. To provide a comprehensive characterization of this parameter in malignant tumor models, in vivo mapping of the washout of small molecular contrast agent (Gd-DTPA, molecular weight 0.57 kDa) was carried out in three transplanted/spontaneous mammary tumors, which differed in their histopathological and microvascular features. It resulted that in all models around 40% of tumor volume lacks efficient washout; washout areas are frequently, but not always, restricted to the tumor periphery and that non-washout areas are not restricted to necrotic regions. Difference in the distribution of lymphatic vessels characterized spontaneous vs. transplanted tumors but did not produce a corresponding different washout pattern, confirming that Gd-DTPA drainage does not mainly depend on lymphatic architecture. Finally, the efficiency of washout is correlated with parameters obtainable during the earlier phases of the enhancement curve and in malignant tumors it could be indirectly estimated from them.

Easy formulation of liposomal doxorubicin modified with a bombesin peptide analogue for selective targeting of GRP receptors overexpressed by cancer cells.

The article concerns the obtainment of liposomal doxorubicin (Dox) in which liposomes are externally modified with a targeting peptide able to drive the formulation in a selective way on membrane receptors overexpressed in tumors. We developed a kit composed by three different vials: (A) a vial containing a sterile, translucent, red dispersion of the liposomal doxorubicin drug (Doxil®), (B) a vial filled with a lyophilized powder of a modified phospholipid with a reactive function (DSPE-Peg-maleimide), and (C) a vial containing a 1-9 bombesin peptide analogue (Cys-BN-AA1) chemically modified to react in stoichiometric ratio respect to DSPE-Peg-maleimide. The chosen peptide is a stable analogue antagonist of the wild-type 1-9 bombesin peptide; it is very stable in serum; maintains high specificity, with nanomolar affinity, towards gastrin release peptide receptors (GRPRs indicated also as BB2); and is overexpressed in some cancer cells. Results on animal studies clearly indicate that in mice treated with the kit product (i.e., pegylated liposomal Dox modified with the bombesin analogue, Doxil-BN-AA1), tumor growth is reduced, with an improved efficacy respect to mice treated with non-modified pegylated liposomal Dox or with saline solution.

Polymer-coated superparamagnetic iron oxide nanoparticles as T2 contrast agent for MRI and their uptake in liver.

AIM: To study the efficiency of multifunctional polymer-based superparamagnetic iron oxide nanoparticles (bioferrofluids) as a T2 magnetic resonance contrast agent and their uptake and toxicity in liver. MATERIALS & METHODS: Mice were intravenously injected with bioferrofluids and Endorem®. The magnetic resonance efficiency, uptake and in vivo toxicity were investigated by means of magnetic resonance imaging (MRI) and histological techniques. RESULTS: Bioferrofluids are a good T2 contrast agent with a higher r2/r1 ratio than Endorem. Bioferrofluids have a shorter blood circulation time and persist in liver for longer time period compared with Endorem. Both bioferrofluids and Endorem do not generate any noticeable histological lesions in liver over a period of 60 days post-injection. CONCLUSION: Our bioferrofluids are powerful diagnostic tool without any observed toxicity over a period of 60 days post-injection.

Drug targeting of airway surface liquid: a pharmacological MRI approach.

Pharmacological MRI at 4.7 T was used to investigate the secretory response to Sylvestris pine oil stimuli in the rat airways, with the aim of developing an in vivo model in a small laboratory animal. The availability of such a model would greatly facilitate the drug discovery process using compounds active on airway surface liquid (ASL) production, and would make it possible to obtain information on chemoreceptoral mechanisms and to test the effects of environmental substances on the airways. T1- and T2-weighted images were acquired in the trachea and larynx before and at various times after exposure to pine oil. Several post-processing procedures were tested in order to improve the visibility of the secretory response and to measure the enhancement of the signal intensity of ASL. A semiautomatic application software was written to localize and to measure the volume involved in the secretory response to a compound administration. A significant effect of the pine oil administration on the secretory response was founded in trachea (p<0.01) and in the salivary glands (p<0.01). 3D reconstructions of MRI data and virtual endoscopy permitted a quick visualization of tracheal morphology and localization of the greatest response to stimulus. The study demonstrated that, despite technical problems due to the air/tissue interface and to the small dimensions of the experimental animals, the secretory response can be evaluated and the pharmacological MRI (phMRI) of the rat airways is feasible. The potential and the limitations of phMRI investigation in drug targeting of ASL are discussed.

Magnetosomes Extracted from Magnetospirillum gryphiswaldense as Theranostic Agents in an Experimental Model of Glioblastoma.

Magnetic fluid hyperthermia (MFH) with chemically synthesized nanoparticles is currently used in clinical trials as it destroys tumor cells with an extremely localized deposition of thermal energy. In this paper, we investigated an MFH protocol based on magnetic nanoparticles naturally produced by magnetotactic bacteria: magnetosomes. The efficacy of such protocol is tested in a xenograft model of glioblastoma. Mice receive a single intratumoral injection of magnetosomes, and they are exposed three times in a week to an alternating magnetic field with concurrent temperature measurements. MRI is used to visualize the nanoparticles and to monitor tumor size before and after the treatment. Statistically significant inhibition of the tumor growth is detected in subjects exposed to the alternating magnetic field compared to control groups. Moreover, thanks to magnetosomes high transversal relaxivity, their effective delivery to the tumor tissue is monitored by MRI. It is apparent that the efficacy of this protocol is limited by inhomogeneous delivery of magnetosomes to tumor tissue. These results suggest that naturally synthesized magnetosomes could be effectively considered as theranostic agent candidates for hyperthermia based on iron oxide nanoparticles.

A SERRS/MRI multimodal contrast agent based on naked Au nanoparticles functionalized with a Gd(iii) loaded PEG polymer for tumor imaging and localized hyperthermia.

Multimodal contrast agents offer new interesting diagnostic possibilities, summing the benefits of multiple imaging techniques. Magnetic resonance and optical imaging are complementary techniques. The first allows total body screening, even though it suffers from low spatial resolution and needs high loadings, whereas the second shows lower penetration, but bright signals, and a higher spatial resolution and needs lower loadings. We present a plasmonic nanosystem as a MRI (magnetic resonance imaging) and SERRS (surface enhanced resonance Raman scattering) multimodal contrast agent. Naked gold nanoparticles, obtained by laser ablation synthesis in solution, are organized as a highly efficient SERRS substrate with a naphthalocyanine reporter and functionalized with a MRI contrast agent with a newly synthesized 3DOTA-PEG polymer, with a high GdIII loading. As a proof of concept, in vivo and ex vivo MRI and SERRS experiments are also performed. The plasmonic property of the nanosystem is then exploited to show its usefulness for localized hyperthermia.

Nanoaggregates of iron poly-oxo-clusters obtained by laser ablation in aqueous solution of phosphonates.

Laser ablation in liquid (LAL) emerged as a versatile technique for the synthesis of nanoparticles with various structures and compositions, although the control over products remains challenging in most cases. For instance, it is still difficult to drive the size of metal oxide crystalline domains down to the level of few atom clusters with LAL. Here we demonstrate that laser ablation of a bulk iron target in aqueous solution of phosphonates gives phosphonate-grafted iron oxo-clusters polymerized into nanoaggregates with Fe:ligand ratio of 2:1, instead of the usual nanocrystalline iron oxides. We attribute this result to the strong ability of phosphonate groups to bind iron oxide clusters and prevent their further growth into crystalline iron oxide. These laser generated poly-oxo-clusters are biocompatible and trackable by magnetic resonance imaging, providing interesting features for use in biological environments, such as nano-vehicles for iron administration. Besides, this method is promising for the generation of atom-scale metal-oxide clusters, which are ubiquitary in chemistry and of interest in biochemistry, catalysis, molecular magnetism and materials science.

Liposomes derivatized with multimeric copies of KCCYSL peptide as targeting agents for HER-2-overexpressing tumor cells.

Mixed liposomes, obtained by coaggregation of 1,2-dioleoyl-sn-glycero-3-phosphocholine and of the synthetic monomer containing a gadolinium complex ([C18]2DTPA[Gd]) have been prepared. Liposomes externally decorated with KCCYSL (P6.1 peptide) sequence in its monomeric, dimeric, and tetrameric forms are studied as target-selective delivery systems toward cancer cells overexpressing human epidermal growth factor receptor-2 (HER-2) receptors. Derivatization of liposomal surface with targeting peptides is achieved using the postmodification method: the alkyne-peptide derivative Pra-KCCYSL reacts, through click chemistry procedures, with a synthetic surfactant modified with 1, 2, or 4 azido moieties previously inserted in liposome formulation. Preliminary in vitro data on MDA-MB-231 and BT-474 cells indicated that liposomes functionalized with P6.1 peptide in its tetrameric form had better binding to and uptake into BT-474 cells compared to liposomes decorated with monomeric or dimeric versions of the P6.1 peptide. BT-474 cells treated with liposomes functionalized with the tetrameric form of P6.1 showed high degree of liposome uptake, which was comparable with the uptake of anti-HER-2 antibodies such as Herceptin. Moreover, magnetic MRI experiments have demonstrated the potential of liposomes to act as MRI contrast agents.

EGFR-Targeted Magnetic Nanovectors Recognize, in Vivo, Head and Neck Squamous Cells Carcinoma-Derived Tumors.

Head and neck squamous cell carcinomas (HNSCC) are a diverse group of tumors with high morbidity and mortality that have remained mostly unchanged over the past decades. The epidermal growth factor receptor (EGFR) is often overexpressed and activated in these tumors and strongly contributes to their pathogenesis. Still, EGFR-targeted therapies such as monoclonal antibodies and kinase inhibitors have demonstrated only limited improvements in the clinical outcome of this disease. Here, we take advantage of the extraordinary affinity of EGF for its cognate receptor to specifically target magnetite-containing nanoparticles to HNSCC cells and mediate, in vitro, their cellular upload. On the basis of this, we show efficient accumulation, in vivo, of such nanoparticles in subcutaneous xenograft tumor tissues in sufficient amounts to be able to mediate visualization by magnetic resonance imaging. Overall, our EGF-coated nanosystem may warrant, in the near future, novel and very efficient theranostic approaches to HNSCC.

The hydrolipidic ratio in age-related maturation of adipose tissues.

The hydrolipidic ratio (HLR) expresses the amount of water and fat in a tissue. HLR can be studied non-invasively in the living organism and can be mapped in different areas of the body with high spatial and temporal resolution. In the present work we have evaluated the HLR in different adipose tissue depots in young or adult rats using tissue arrays of fat fragments by 1H-spectroscopy. In young animals, the highest percentage of water (33%) was found in the interscapular brown adipose tissue (iBAT). Mesenteric fat (mWAT) also appeared highly hydrated (24%). The deposits composed of epididymal, retroperitoneal and pelvic white adipose tissue (eWAT, rWAT and pWAT, respectively) contained an amount of water ranging from 14% to 17%. In adult animals, a reduction of the water content was found in all the depots. In e/r/pWAT, the age-related maturation was characterized by large changes in adipocyte diameter accompanied by a small change in HLR. In the iBAT, the maturation was accompanied by small change in adipocyte diameter and a greater diminution of HLR. mWAT showed an intermediate pattern between e/r/pWAT and iBAT. In all the studied depots, an age-related increase in leptin expression was found. This increase was relatively low in iBAT (40%) and high in the e/r/pWAT (204-273%). The work expand the knowledge about the physiological significance of the HLR by 1H-spectroscopy.

Early antiangiogenic activity of SU11248 evaluated in vivo by dynamic contrast-enhanced magnetic resonance imaging in an experimental model of colon carcinoma.

PURPOSE: To compare two dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) techniques in terms of their ability in assessing the early antiangiogenic effect of SU11248, a novel selective multitargeted tyrosine kinase inhibitor, that exhibits direct antitumor and antiangiogenic activity via inhibition of the receptor tyrosine kinases platelet-derived growth factor receptor, vascular endothelial growth factor receptor, KIT, and FLT3. EXPERIMENTAL DESIGN: A s.c. tumor model of HT29 human colon carcinoma in athymic mice was used. Two DCE-MRI techniques were used based, respectively, on macromolecular [Gd-diethylenetriaminepentaacetic acid (DTPA)-albumin] and low molecular weight (Gd-DTPA) contrast agents. The first technique provided a quantitative measurement of transendothelial permeability and fractional plasma volume, accepted surrogate markers of tumor angiogenesis. With the second technique, we quantified the initial area under the concentration-time curve, which gives information related to tumor perfusion and vascular permeability. Experiments were done before and 24 hours after a single dose administration of SU11248. RESULTS: The early antiangiogenic effect of SU11248 was detected by DCE-MRI with macromolecular contrast agent as a 42% decrease in vascular permeability measured in the tumor rim. The effect was also detected by DCE-MRI done with Gd-DTPA as a 31% decrease in the initial area under the concentration-time curve. Histologic slices showed a statistically significant difference in mean vessel density between the treated and control groups. CONCLUSIONS: The early antiangiogenic activity of SU11248 was detected in vivo by DCE-MRI techniques using either macromolecular or low molecular weight contrast agents. Because DCE-MRI techniques with low molecular weight contrast agents can be used in clinical studies, these results could be relevant for the design of clinical trials based on new paradigms.