Vascular permeability during antiangiogenesis treatment: MR imaging assay results as biomarker for subsequent tumor growth in rats.

PURPOSE: To prospectively evaluate in rats the acute change in tumor vascular leakiness (K(PS)) assayed at magnetic resonance (MR) imaging after a single dose of the angiogenesis inhibitor bevacizumab as a predictive biomarker of tumor growth response after a prolonged treatment course. MATERIALS AND METHODS: Institutional animal care and use committee approval was obtained. Seventeen female rats with implanted human breast cancers underwent dynamic albumin-(Gd-DTPA)(30)-enhanced MR imaging followed by an initial dose of bevacizumab or saline (as a control). Treatment was continued every 3rd day, for a total of four doses at five possible dose levels: 0 mg bevacizumab (n = 4 [control rats]), 0.1 mg bevacizumab (n = 3), 0.25 mg bevacizumab (n = 2), 0.5 mg bevacizumab (n = 5), and 1.0 mg bevacizumab (n = 3). A second MR imaging examination was performed 24 hours after the initial dose to enable calculation of the acute change in MR imaging-assayed leakiness, or Delta K(PS). This acute change in K(PS) at MR imaging was correlated with tumor growth response for each cancer at the completion of the 11-day treatment course. For statistical analyses, an unpaired two-tailed t test, analysis of variance, and linear regression analyses were used. RESULTS: The MR imaging-assayed change in tumor microvascular leakiness, tested as a potential biomarker, correlated strongly with tumor growth rate (R(2) = 0.74, P < .001). K(PS) and tumor growth decreased significantly in all bevacizumab-treated cancers compared with these values in control group cancers (P < .05). CONCLUSION: The MR imaging-assayed acute change in vascular leakiness after a single dose of bevacizumab was an early, measurable predictive biomarker of tumor angiogenesis treatment response.

MR imaging of antigen-induced arthritis with a new, folate receptor-targeted contrast agent.

The purpose of this study was to investigate if the new folate receptor-targeted Gd-chelate P866 may enhance immune-mediated arthritis. A monoarthritis was induced in the right knee of 15 Sprague-Dawley rats. MR imaging of both knees was performed at 2 T before and up to 2 h and 24 h after injection (p.i.) of P866 (n = 3 dose finding study and n = 6, 0.02 mmol Gd/kg), the non-FR targeted P866 analog P1001 (n = 3 at 24 h after P866-administration, 0.02 mmol Gd/kg) or Gd-DOTA (n = 6, 0.1 mmol Gd/kg). Pulse sequences comprised T(1)-SPGR 80 degrees /50 ms/1.7 ms (flip angle/TR/TE) and inversion recovery 10 degrees /3000 ms/1500 ms/50-3050, 10 000 ms (flip angle/TR/TE/TI) sequences. DeltaSI-data and T(1)-relaxation times of arthritic knees and contralateral normal knees were determined. Folate receptor expression was confirmed with histopathology. All three contrast agents showed an initial perfusion effect with significantly higher DeltaSI-data of arthritic knees compared with normal knees (p < 0.05). In addition, P866, but not P1001 or Gd-DOTA, showed a prolonged enhancement of the synovitis. Compared with precontrast values, the T(1)-relaxation times of inflamed synovia were significantly decreased at 2 h p.i. of P866 (p < 0.05), but not P1001 or Gd-DOTA (p > 0.05). Histopathology confirmed the presence of folate receptors in the inflamed joints, but not normal joints. Thus, results suggest a specific accumulation of the folate receptor-targeted Gd-chelate P866 in this arthritis model.

Dendritic iodinated contrast agents with PEG-cores for CT imaging: synthesis and preliminary characterization.

The purpose of this study was to design, synthesize, and initially characterize a representative set of novel constructs for large-molecular radiographic/computed tomography (CT) contrast agents, intended for a primarily intravascular distribution. A new assembly of well-known and biocompatible components consists of paired, symmetrical dendritic polylysines initiated from both ends of a poly(ethylene glycol) (PEG) core, yielding an array of multiple free amino groups to which were conjugated highly soluble and stable triiodophthalamide ("triiodo") moieties. An array of six dendritic contrast agents was synthesized originally, using three different PEG cores (3, 6, 12 kDa) with t-Boc lysine-generated dendrimer "amplifiers" (from three to five generations) containing 16 to 64 amino groups for conjugation with reactive triiodo moieties. A clinically used, nonionic, small molecular CT contrast agent, iobitridol, was derivatized via a hydroxyl protection/deprotection strategy, introducing a new carboxyl group available for conjugation to the lysine amino groups of dendrimers. Final products were purified by size exclusion chromatography and characterized by NMR, UV, HPLC, and elemental analysis. Preliminary evaluations were conducted for physicochemical characterization and in vivo CT contrast enhancement in a rat model. All six iodinated PEG-core dendrimer conjugates were synthesized in good yields, with a high degree of size monodispersity, large apparent molecular weight, favored physicochemical properties. A representative compound, PEG12000-carbamate-Gen4-IOB conjugate, 27% (w%) rich in iodine, demonstrated a desirable strong and persistent intravascular enhancement with a monoexponential blood half-life of approximately 35 min assayed by dynamic CT imaging and also showed high water solubility (>550 mg/mL at 25 degrees C), large apparent molecular size (comparable to a 143-kDa protein), high hydrophilicity (butanol-water partition coefficient 0.015), and stability to autoclaving conditions. This study showed the synthetic feasibility, desired basic characteristics, and potential utility for CT contrast enhancement achieved with a new type of iodinated, large-molecular PEG-core dendritic construct. Further development of this class of macromolecular contrast agents will be required to define the optimal formulation, pharmacology, safety profile, and the full range of diagnostic applications including tumor microvascular quantitative characterization by CT imaging.

Imaging of tumor angiogenesis: current approaches and future prospects.

Tumor angiogenesis imaging should provide non-invasive assays of tumor vascular characteristics to supplement the now conventional diagnostic imaging goals of depicting tumor location, size, and morphology. This article will review the current status of angiogenesis imaging approaches, considering ultrasound, CT, MR, SPECT, PET and optical techniques with attention to their respective capabilities and limitations. As a group, these imaging methods have some potential to depict and quantify tumor microvascular features, including those considered to be functionally associated with tumor angiogenesis. Additionally, new molecule-specific imaging techniques may serve to depict those biochemical pathways and regulatory events that control blood vessel growth and proliferation. Non-invasive monitoring of anti-angiogenic therapies has great appeal and should find wide application for defining tumor microvascular and metabolic changes, because treatment-related changes in tumor morphology tend to occur rather late and are non-specific. Future developments are likely to include "fusion" or "hybrid" imaging methods. Superimposed data from MR imaging with spectroscopy, PET with CT, and PET with MR should be able to integrate advantages of different modalities yielding comprehensive information about tumor structure, function and microenvironment.

Optical imaging of experimental arthritis using allogeneic leukocytes labeled with a near-infrared fluorescent probe.

PURPOSE: The purpose of this study was to assess the feasibility of inflammation detection in an antigen-induced arthritis model using fluorescent leukocytes and optical imaging. METHODS: Antigen-mediated monoarthritis was induced in the right knee of 12 Sprague-Dawley rats. Six rats remained untreated and six rats were treated with cortisone. All rats received ex vivo fluorescent-labeled rat leukocytes. Optical images of both knees were acquired before and at 5 min, 1 h, 4 h, and 24 h after cell injection. Images were evaluated qualitatively and quantitatively by calculating signal intensity ratios between the right arthritic (A) and contralateral normal (N) knee. A/N ratios were tested for significant differences between baseline values and values after cell injection using a paired t test as well as between the untreated and cortisone-treated group using an unpaired t test. Synovial specimens were processed and evaluated for labeled cells with fluorescence microscopy. RESULTS: At 4 h and 24 h p.i., the A/N ratios of untreated arthritic knees showed a significant signal increase compared with baseline values (p<0.05) and a significant difference compared with A/N ratios of cortisone-treated animals (p<0.05). Fluorescent microscopy confirmed the presence of labeled cells in the arthritic synovium. CONCLUSION: Inflammation in antigen-induced arthritis can be detected with ex vivo labeled allogenic leukocytes and optical imaging.

MRI of arthritis: comparison of ultrasmall superparamagnetic iron oxide vs. Gd-DTPA.

PURPOSE: To compare the ability of the ultrasmall superparamagnetic iron oxide (USPIO) SHU555C vs. gadopentetate dimeglumine (Gd-DTPA) to detect antigen-induced monoarthritis with MRI. MATERIALS AND METHODS: Twelve seven-week-old female rats with an antigen-induced monoarthritis of the right knee were randomly assigned to two groups. Animals in group I (N = 6) underwent MRI using T1-weighted gradient-echo sequences before injection and at 2, 9, 17, 25, 33, 40, 47, 55, and 63 minutes postinjection (p.i.) of Gd-DTPA on day 1, and before injection and at 3, 23, 43, and 123 minutes p.i. of SHU555C on day 2. Animals in group II (N = 6) were imaged before injection and at 3, 23, 43, and 123 minutes p.i. using identical sequences. Signal-to-noise ratios (SNRs) and relative enhancement (DeltaSI%) of arthritic and normal synovium were determined from region-of-interest (ROI) measurements in consensus reading by two experienced radiologists. Data were tested for significant differences between the two agents and between the arthritic and normal knees using a mixed-effect model and F-tests (P < 0.05). Joints were processed for histopathology as the gold standard. RESULTS: USPIO and Gd-DTPA showed significant enhancement differences (P < 0.001). USPIO provided a progressive and persistent enhancement of arthritic joints while Gd-DTPA provided an early and rapidly declining enhancement. Maximal enhancement in synovitis was 400% at 40-120 minutes p.i. of USPIO vs. 300% at two minutes p.i. of Gd-DTPA. USPIO provided a significant higher difference in enhancement between the arthritic and normal synovium than Gd-DTPA (P < 0.001). Histopathology confirmed marked inflammatory synovial changes in all arthritis-induced right knee joints and normal synovium in all left knee joints. CONCLUSION: Both USPIO and Gd-DTPA detect arthritis by positive T1-enhancement. Compared to standard Gd-DTPA, the USPIO SHU555C provides a comparable maximal T1-enhancement (at two minutes p.i for Gd-DTPA and between 43 and 123 minutes p.i. for SHU555C), but in addition it provides a prolonged T1-enhancement of synovitis and a higher difference between the relative enhancement of arthritic and normal synovium.

T1 and T2 relaxivity of intracellular and extracellular USPIO at 1.5T and 3T clinical MR scanning.

In this study we evaluated the effects of intracellular compartmentalization of the ultrasmall superparamagnetic iron oxide (USPIO) ferumoxtran-10 on its proton T1 and T2 relaxivities at 1.5 and 3T. Monocytes were labeled with ferumoxtran-10 by simple incubation. Decreasing quantities of ferumoxtran-10-labeled cells (2.5x10(7)-0.3x10(7) cells/ml) and decreasing concentrations of free ferumoxtran-10 (without cells) in Ficoll solution were evaluated with 1.5 and 3T clinical magnetic resonance (MR) scanners. Pulse sequences comprised axial spin echo (SE) sequences with multiple TRs and fixed TE and SE sequences with fixed TR and increasing TEs. Signal intensity measurements were used to calculate T1 and T2 relaxation times of all samples, assuming a monoexponential signal decay. The iron content in all samples was determined by inductively coupled plasma atomic emission spectrometry and used for calculating relaxivities. Measurements at 1.5T and 3T showed higher T1 and T2 relaxivity values of free extracellular ferumoxtran-10 as opposed to intracellularly compartmentalized ferumoxtran-10, under the evaluated conditions of homogeneously dispersed contrast agents/cells in Ficoll solution and a cell density of up to 2.5x10(7) cells/ml. At 3T, differences in T1-relaxivities between intra- and extracellular USPIO were smaller, while differences in USPIO T2-relaxivities were similar compared with 1.5T. In conclusion, cellular compartmentalization of ferumoxtran-10 changes proton relaxivity.

Ultrasmall supraparamagnetic iron oxide-enhanced magnetic resonance imaging of antigen-induced arthritis: a comparative study between SHU 555 C, ferumoxtran-10, and ferumoxytol.

OBJECTIVES: We sought to compare the ability of 3 ultrasmall superparamagnetic iron oxides (USPIOs) to detect and characterize antigen-induced arthritis with MR imaging. MATERIALS AND METHODS: A monoarthritis was induced in the right knee of 18 rats. The left knee served as a normal control. Knees underwent magnetic resonance (MR) imaging before, up to 2 hours, and 24 hours after injection (p.i.) of 200 mumol Fe/kg SHU 555 C (n= 6), ferumoxtran-10 (n = 6), or ferumoxytol (n = 6), using T2-2D-SE 100/20,40,60,80/90 (TR/TE/flipangle), T2*-3D-spoiled gradient recalled (SPGR) 100/15/38, and T1-3D-SPGR 50/1,7/60 sequences. RESULTS: Quantitative signal to noise ratio and DeltaSI data of arthritic knees on T1- and T2*-weighted MR images showed no significant differences between the 3 USPIOs (P > 0.05). At 2 hours p.i., SNR and DeltaSI data were significantly increased from baseline on T1-weighted images and significantly decreased on T2*-weighted images (P < 0.001). At 24 hours p.i., the T1-enhancement returned to baseline, whereas the T2*-enhancement remained significantly elevated (P < 0.001). Immunostains demonstrated an USPIO compartmentalization in macrophages in the arthritic synovium. CONCLUSIONS: Based on the relatively small number of animals in our study group, inflammation in antigen-induced arthritis can be equally detected and characterized with any of the three USPIOs evaluated.

Ultrasmall superparamagnetic iron-oxide-enhanced MR imaging of normal bone marrow in rodents: original research original research.

RATIONALE AND OBJECTIVES: The objective is to compare three different ultrasmall superparamagnetic iron oxides (USPIOs) for magnetic resonance (MR) imaging of normal bone marrow in rodents. MATERIALS AND METHODS: Femoral bone marrow in 18 Sprague-Dawley rats was examined by using MR imaging before and up to 2 and 24 hours postinjection (PI) of 200 mumol of Fe/kg of SHU555C (n = 6), ferumoxtran-10 (n = 6), or ferumoxytol (n = 6), using T1-weighted (50 ms/1.7 ms/60 degrees = repetition time [TR]/echo time [TE]/flip angle) and T2*-weighted (100 ms/15 ms/38 degrees = TR/TE/flip angle) three-dimensional spoiled gradient recalled echo sequences. USPIO-induced bone marrow was evaluated qualitatively and quantified as signal-to-noise ratio (SNR) and change in signal intensity (DeltaSI) values. A mixed-effect model was fitted to the SNR and DeltaSI values, and differences among USPIOs were tested for significance by using F tests. RESULTS: At 2 hours PI, all three USPIOs showed marked positive signal enhancement on T1-weighted images and a corresponding marked signal loss on T2*-weighted images. At 24 hours PI, the T1 effect of all three USPIOs disappeared, whereas T2*-weighted images showed persistent signal loss on SHU555C and ferumoxytol-enhanced MR images, but not ferumoxtran-10-enhanced MR images. Corresponding SNR and DeltaSI values on T2*-weighted MR images at 24 hours PI were significantly different from baseline for SHU555C and ferumoxytol, but not ferumoxtran-10. CONCLUSION: All three USPIO contrast agents, ferumoxtran-10, ferumoxytol, and SHU555C, can be applied for MR imaging of bone marrow. Ferumoxtran-10 apparently reveals a different kinetic behavior in bone marrow than ferumoxytol and SHU555C.

Initial computed tomography imaging experience using a new macromolecular iodinated contrast medium in experimental breast cancer.

OBJECTIVE: The objective of this study was to evaluate computed tomography (CT) enhancement characteristics for a new iodinated macromolecular contrast medium (MMCM), PEG12000-Gen4-triiodo, for angiographic effect and for assessment of abnormal vascular permeability in cancer. MATERIALS AND METHODS: Time persistence of angiographic effect was evaluated on rat CT images acquired over 30 minutes using the iodinated polyethyleneglycol- (PEG) based macromolecule. Dynamic CT imaging after PEG12000-Gen4-triiodo-enhancement in tumor-bearing rats was used to quantitatively estimate plasma volume and microvascular transendothelial permeability for both tumor and normal soft tissue. Using identical doses of iodine, 300 mg iodine/kg, blood curves for this MMCM and iohexol were compared. RESULTS: Serial whole-body CT angiograms using PEG12000-Gen4-triiodo showed diagnostic vascular detail through 20 minutes, and the blood enhancement curve was higher and more persistent than with small-molecular iohexol. Permeability estimates were significantly (P<0.02; paired t test) higher in tumors (48.2+/-18.1 microL/min-1 100 mL) than in muscle (2.5+/-5.7 microL/min-1 100 mL). CONCLUSIONS: Use of PEG-based MMCM for experimental CT allowed for a persistent angiographic enhancement and for quantitative estimation of tumor microvascular characteristics.

Comparison of iron oxide labeling properties of hematopoietic progenitor cells from umbilical cord blood and from peripheral blood for subsequent in vivo tracking in a xenotransplant mouse model XXX.

RATIONALE AND OBJECTIVES: To compare and optimize ferumoxides labeling of human hematopoietic progenitor cells from umbilical cord blood and from peripheral blood for subsequent in vivo tracking with a clinical 1.5 T MR scanner. MATERIALS AND METHODS: Human hematopoietic progenitor cells, derived from umbilical cord blood or peripheral blood, were labeled with Ferumoxides by simple incubation or lipofection. Cellular iron uptake was quantified with spectrometry. Then, 3 x 10(7)-labeled cells were injected into the tail vein of 12 female nude Balb/c mice. The mice underwent magnetic resonance imaging before and 24 hours after injection. Precontrast and postcontrast signal intensities of liver, spleen, and bone marrow were measured and tested for significant differences with the t-test. Immunostains served as a histopathologic standard of reference. RESULTS: After labeling by simple incubation, only umbilical cord blood cells, but not peripheral blood cells, showed a significant iron uptake and could be tracked in vivo with magnetic resonance imaging. Using lipofection, both cell types could be tracked in vivo. A significant decline in signal intensity was observed in liver, spleen, and bone marrow at 24 hours after injection of efficiently labeled ferumoxides cells (P < .05). Histopathology proved the distribution of iron oxide-labeled cells to these organs. CONCLUSION: Hematopoietic progenitor cells from umbilical cord blood can be labeled by simple incubation with an Food and Drug Administration-approved magnetic resonance contrast agent with sufficient efficiency to provide an in vivo cell tracking at 1.5 T. Progenitor cells from peripheral blood need to be labeled with adjunctive transfection techniques to be depicted in vivo at 1.5 T.