Christopher A. Flask

Magnetic Resonance Imaging of Multifunctional Pluronic Stabilized Iron-Oxide Nanoparticles in Tumor-Bearing Mice

We are investigating the magnetic resonance imaging characteristics of magnetic nanoparticles (MNPs) that consist of an iron-oxide magnetic core coated with oleic acid (OA), then stabilized with a pluronic or tetronic block copolymer. Since pluronics and tetronics vary structurally, and also in the ratio of hydrophobic (poly[propylene oxide]) and hydrophilic (poly[ethylene oxide]) segments in the polymer chain and in molecular weight, it was hypothesized that their anchoring to the OA coating around the magnetic core could significantly influence the physical properties of MNPs, their interactions with biological environment following intravenous administration, and ability to localize to tumors. The amount of block copolymer associated with MNPs was seen to depend upon their molecular structures and influence the characteristics of MNPs. Pluronic F127-modified MNPs demonstrated sustained and enhanced contrast in the whole tumor, whereas that of Feridex IV was transient and confined to the tumor periphery. In conclusion, our pluronic F127-coated MNPs, which can also be loaded with anticancer agents for drug delivery, can be developed as an effective cancer theranostic agent, i.e. an agent with combined drug delivery and imaging properties.

CEST-FISP: A novel technique for rapid chemical exchange saturation transfer MRI at 7 T

Chemical exchange saturation transfer (CEST) and magnetization transfer techniques provide unique and potentially quantitative contrast mechanisms in multiple MRI applications. However, the in vivo implementation of these techniques has been limited by the relatively slow MRI acquisition techniques, especially on high‐field MRI scanners. A new, rapid CEST‐fast imaging with steady‐state free precession technique was developed to provide sensitive CEST contrast in ∼20 sec. In this study at 7 T with in vitro bovine glycogen samples and initial in vivo results in a rat liver, the CEST‐fast imaging with steady‐state free precession technique was shown to provide equivalent CEST sensitivity in comparison to a conventional CEST‐spin echo acquisition with a 50‐fold reduction in acquisition time. The sensitivity of the CEST‐fast imaging with steady‐state free precession technique was also shown to be dependent on k‐space encoding with centric k‐space encoding providing a 30–40% increase in CEST sensitivity relative to linear encoding for 256 or more k‐space lines. Overall, the CEST‐fast imaging with steady‐state free precession acquisition technique provides a rapid and sensitive imaging platform with the potential to provide quantitative CEST and magnetization transfer imaging data. Magn Reson Med, 2011.

A Novel PET Marker for In Vivo Quantification of Myelination

C-11-labeled N-methyl-4,4-diaminostilbene ([(11)C]MeDAS) was synthesized and evaluated as a novel radiotracer for in vivo microPET imaging of myelination. [(11)C]MeDAS exhibits optimal lipophilicity for brain uptake with a logP(oct) value of 2.25. Both in vitro and ex vivo staining exhibited MeDAS accumulation in myelinated regions such as corpus callosum and striatum. The corpus callosum region visualized by MeDAS is much larger in the hypermyelinated Plp-Akt-DD mouse brain than in the wild-type mouse brain, a pattern that was also consistently observed in Black-Gold or MBP antibody staining. Ex vivo autoradiography demonstrated that [(11)C]MeDAS readily entered the mouse brain and selectively labeled myelinated regions with high specificity. Biodistribution studies showed abundant initial brain uptake of [(11)C]MeDAS with 2.56% injected dose/whole brain at 5 min post injection and prolonged retention in the brain with 1.37% injected dose/whole brain at 60 min post injection. An in vivo pharmacokinetic profile of [(11)C]MeDAS was quantitatively analyzed through a microPET study in an Plp-Akt-DD hypermyelinated mouse model. MicroPET studies showed that [(11)C]MeDAS exhibited a pharmacokinetic profile that readily correlates the radioactivity concentration to the level of myelination in the brain. These studies suggest that MeDAS is a sensitive myelin probe that provides a direct means to detect myelin changes in the brain. Thus, it can be used as a myelin-imaging marker to monitor myelin pathology in vivo.

In vivo dual substrate bioluminescent imaging.

Our understanding of how and when breast cancer cells transit from established primary tumors to metastatic sites has increased at an exceptional rate since the advent of in vivo bioluminescent imaging technologies 1-3. Indeed, the ability to locate and quantify tumor growth longitudinally in a single cohort of animals to completion of the study as opposed to sacrificing individual groups of animals at specific assay times has revolutionized how researchers investigate breast cancer metastasis. Unfortunately, current methodologies preclude the real-time assessment of critical changes that transpire in cell signaling systems as breast cancer cells (i) evolve within primary tumors, (ii) disseminate throughout the body, and (iii) reinitiate proliferative programs at sites of a metastatic lesion. However, recent advancements in bioluminescent imaging now make it possible to simultaneously quantify specific spatiotemporal changes in gene expression as a function of tumor development and metastatic progression via the use of dual substrate luminescence reactions. To do so, researchers take advantage for two light-producing luciferase enzymes isolated from the firefly (Photinus pyralis) and sea pansy (Renilla reniformis), both of which react to mutually exclusive substrates that previously facilitated their wide-spread use in in vitro cell-based reporter gene assays 4. Here we demonstrate the in vivo utility of these two enzymes such that one luminescence reaction specifically marks the size and location of a developing tumor, while the second luminescent reaction serves as a means to visualize the activation status of specific signaling systems during distinct stages of tumor and metastasis development. Thus, the objectives of this study are two-fold. First, we will describe the steps necessary to construct dual bioluminescent reporter cell lines, as well as those needed to facilitate their use in visualizing the spatiotemporal regulation of gene expression during specific steps of the metastatic cascade. Using the 4T1 model of breast cancer metastasis, we show that the in vivo activity of a synthetic Smad Binding Element (SBE) promoter was decreased dramatically in pulmonary metastasis as compared to that measured in the primary tumor 4-6. Recently, breast cancer metastasis was shown to be regulated by changes within the primary tumor microenvironment and reactive stroma, including those occurring in fibroblasts and infiltrating immune cells 7-9. Thus, our second objective will be to demonstrate the utility of dual bioluminescent techniques in monitoring the growth and localization of two unique cell populations harbored within a single animal during breast cancer growth and metastasis.

Prolylcarboxypeptidase deficiency is associated with increased blood pressure, glomerular lesions, and cardiac dysfunction independent of altered circulating and cardiac angiotensin II

Prolylcarboxypeptidase (PRCP) is a carboxypeptidase that cleaves angiotensin II (AngII) forming Ang(1–7). The impact of genetic PRCP deficiency on AngII metabolism, blood pressure (BP), kidney histology, and cardiac phenotype was investigated in two lines of PRCP-deficient mice: KST302 derived in C57BL/6 background and GST090 derived in FVB/N background. The GST090 line had increased mean arterial pressure (MAP) (113.7xa0±xa02.07 vs. WT 105.0xa0±xa01.23xa0mmHg; pxa0<xa00.01) and left ventricular hypertrophy (LVH) (ratio of diastolic left ventricular posterior wall dimension to left ventricular diameter 0.239xa0±xa00.0163 vs. WT 0.193xa0±xa00.0049; pxa0<xa00.05). Mice in the KST302 line also had mild hypertension and LVH. Cardiac defects, increased glomerular size, and glomerular mesangial expansion were also observed. After infusion of AngII to mice in the KST302 line, both MAP and LVH increased, but the constitutive differences between the gene trap mice and controls were no longer observed. Plasma and cardiac AngII and Ang(1–7) were not significantly different between PRCP-deficient mice and controls. Thus, PRCP deficiency is associated with elevated blood pressure and cardiac alterations including LVH and cardiac defects independently of systemic or cardiac AngII and Ang(1–7). An ex vivo assay showed that recombinant PRCP, unlike recombinant ACE2, did not degrade AngII to form Ang(1–7) in plasma at pH 7.4. PRCP was localized in α-intercalated cells of the kidney collecting tubule. The low pH prevailing at this site and the acidic pH preference of PRCP suggest a role of this enzyme in regulating AngII degradation in the collecting tubule where this peptide increases sodium reabsorption and therfore BP. However, there are other potential mechanisms for increased BP in this model that need to be considered as well. PRCP converts AngII to Ang(1–7) but only at an acidic pH. Global PRCP deficiency causes heart and kidney alterations and a moderate rise in BP. PRCP is abundant in the kidney collecting tubules, where the prevailing pH is low. In collecting tubules, PRCP deficiency could result in impaired AngII degradation. Increased AngII at this nephron site stimulates Na reabsorption and increases BP.Key messageProlylcarboxypeptidase (PRCP) converts AngII to Ang (1–7) but only at an acidic pH.Global PRCP deficiency causes heart and kidney alterations and a moderate rise in BP.PRCP is abundant in the kidney collecting tubules, where the prevailing pH is low.In collecting tubules, PRCP deficiency could result in impaired AngII degradation.Increased AngII at this nephron site stimulates Na reabsorption and increases BP.

Device localization and dynamic scan plane selection using a wireless magnetic resonance imaging detector array.

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.

Abstract 5297: Dual-modality imaging of hepatocellular carcinoma

Choline compounds are linked to malignancy since elevation of the intensity of choline peak reflects increased biosynthesis of membrane phospholipids and can be a marker for cellular proliferation. Positron Emission Tomography (PET) images an injected tracer dose (nM∼pM) of [11C]-choline while Proton MR Spectroscopy (1H MRS) can characterize endogenous choline-containing compounds usually in the mM range. There have been studies on brain and prostate cancers with both imaging modalities although correlation between the results from PET and MRS is inconsistent. The transient radiolabeled choline metabolism measured by PET is different from the relative steady total choline contents measured by MRS. However, it begs the question of whether the two imaging modalities are measuring the same metabolic pathways of choline in cancer. For primary Hepatocellular Carcinoma (HCC), there have been [11C]-choline PET studies, both pre-clinical and clinical, showing focal uptake. Likewise, there have been 1H-MRS studies of choline with animals and humans showing significantly high choline levels in HCC. So far, there is no comparison study reported to link the two measurements in HCC. This study was conducted with a woodchuck model of hepatitis viral infection-induced HCC, which is regarded as a naturally occurring animal model of human HCC with similar pathology and clinical behavior. The original objective of the study was to examine the effects of animals being fed and fasted on PET scans using [11C]-choline. MRI and MRS were added and performed immediately before PET imaging. Experiments were first performed with animals at the fed state using a 4T MR scanner with a human head coil. Dynamic PET images were then generated from a nearby clinical PET/CT scanner right after, spanning 50 minutes starting from [11C]-choline injection. Time-activity curves and tracer contrast uptake between focal uptake in HCC and that in the surrounding hepatic tissues were calculated in liver regions. The same animals were scanned again four days later following the exact same procedure, except that the animals were fasted over night. The results from PET imaging with [11C]-choline showed that the dietary state of fed or fast had little impact on radio-choline uptake in HCC while the results from 1H MRS of choline found similar choline/lipids ratios in HCC regardless of whether the animal was fed or fasted. These results are very promising for correlating the two measurements although further experiments are needed to confirm that the two imaging modalities are measuring related lipid metabolic pathways in HCC involving choline. This work is supported in part by NCI grants R01 CA095307 and U24 CA110943. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5297. doi:10.1158/1538-7445.AM2011-5297

Device localization and dynamic scan plane selection using a wireless MRI detector array

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.

Device localization and dynamic scan plane selection using a wireless magnetic resonance imaging detector array: Device Localization Using a Wireless MRI Array

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.