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Biomedical subjects

Brian D Ross

Publications and source records attributed to Brian D Ross.

At least 37 records · Page 2Linked to original sources
PubMed2005

Development of a syngeneic rat brain tumor model expressing EGFRvIII and its use for molecular targeting studies with monoclonal antibody L8A4.

PURPOSE: The goals of the present study were 2-fold: (a) to develop and characterize a rat brain tumor model that could be used for studies of molecular targeting of EGFRvIII and (b) to study the tumor localizing properties of radiolabeled monoclonal antibody (mAb) L8A4, specifically directed against EGFRvIII, following systemic, i.t., and convection enhanced delivery to brain tumor-bearing rats. EXPERIMENTAL DESIGN AND RESULTS: F98 wild-type (F98WT) rat glioma cells were transfected with a gene encoding human EGFRvIII, and following selection and cloning, a cell line, designated F98(npEGFRvIII), was identified, which expressed a nonconstitutively phosphorylated form of the receptor. As determined by a radioligand binding assay, there were 1.2 x 10(5) EGFRvIII sites per cell compared with an undetectable number on F98WT cells. The tumorigenicity of the F98(npEGFRvIII) glioma was studied following i.c. implantation of 10(3), 10(4), or 10(5) cells into CD-Fischer rats. Mean survival times were 23, 17, and 13 days, respectively, which were equivalent to those obtained with F98EGFR and F98WT cells. As determined by magnetic resonance imaging, the mean doubling times for the F98WT and F98(npEGFRvIII) gliomas were similar (59.8 +/- 4.8 versus 52 +/- 3.3 hours). Following i.v. administration to glioma-bearing rats, mAb L8A4 specifically targeted the F98(npEGFRvIII) glioma, and at 24 hours, 7.7% of the injected dose per gram (ID/g) localized in the tumor. This increased 5-fold to 39.5% ID/g following i.t. injection and 7-fold to 59.8% ID/g at 24 hours following convection enhanced delivery. CONCLUSIONS: Based on these data, we have concluded that the F98(npEGFRvIII) glioma should be a valuable animal model for therapy studies focusing on molecular targeting of EGFRvIII by receptor specific mAbs.

Animals↗
PubMed2005

Continuous arterial spin labeling using a train of adiabatic inversion pulses.

PURPOSE: To develop a simple and robust magnetic resonance imaging (MRI) pulse sequence for the quantitative measurement of blood flow in the brain and cerebral tumors that has practical implementation advantages over currently used continuous arterial spin labeling (CASL) schemes. MATERIALS AND METHODS: Presented here is a single-coil protocol that uses a train of hyperbolic secant inversion pulses to produce continuous arterial spin inversion for perfusion weighting of fast spin echo images. Flow maps of normal rat brains and those containing a 9L gliosarcoma orthotopic tumor model conditions were acquired with and without carbogen. RESULTS: The perfusion-weighted images have reduced magnetization transfer signal degradation as compared to the traditional single-coil CASL while avoiding the use of a more complex two-coil CASL technique. Blood flow measurements in tumor and normal brain tissue were consistent with those previously reported by other CASL techniques. Contralateral and normal brain showed increased blood flow with carbogen breathing, while tumor tissue lacked the same CO(2) reactivity. CONCLUSION: This variation of the CASL technique is a quantitative, robust, and practical single-coil method for measuring blood flow. This CASL method does not require specialized radiofrequency coils or amplifiers that are not routinely used for anatomic imaging of the brain, therefore allowing these flow measurements to be easily incorporated into traditional rodent neuroimaging protocols.

Anesthetics, Inhalation↗
PubMed2005

Sodium magnetic resonance imaging of chemotherapeutic response in a rat glioma.

This study investigates the comparative changes in the sodium MRI signal and proton diffusion following treatment using a 9L rat glioma model to develop markers of earliest response to cancer therapy. Sodium MRI and proton diffusion mapping were performed on untreated (n = 5) and chemotherapy 1,3-bis(2-chloroethyl)-1-nitrosourea-treated rats (n = 5). Animals were scanned serially at 2- to 3-day intervals for up to 30 days following therapy. The time course of Na concentration in a tumor showed a dramatic increase in the treated brain tumor compared to the untreated tumor, which correlates in time with an increase in tumor water diffusion. The largest posttreatment increase in sodium signal occurred 7-9 days following treatment and correlated to the period of the greatest chemotherapy-induced cellular necrosis based on diffusion and histopathology. Both Na MRI and proton ADC mapping revealed early changes in tumor sodium content and cellularity. This study demonstrates the possibility of Na MRI to function as a biomarker for monitoring early tumor treatment and validates the use of monitoring changes in diffusion MRI values for assessing tumor cellularity.

Animals↗
PubMed2005

Intratumoral injection of BCNU in ethanol (DTI-015) results in enhanced delivery to tumor--a pharmacokinetic study.

Solvent facilitated perfusion (SFP) has been proposed as a technique to increase the delivery of chemotherapeutic agents to tumors. SFP entails direct injection of the agent into the tumor in a water-miscible organic solvent, and because the solvent moves easily through both aqueous solutions and cellular membranes it drives the penetration of the solubilized anticancer agent throughout the tumor. To test this hypothesis, we compared the pharmacokinetics (PK) of 14C-labeled 1,3-bis-chlorethyl-1-nitrosourea (BCNU) in intra-cerebral 9L rat gliomas after intravenous (IV) infusion in 90% saline--10% ethanol or direct intratumoral (IT) injection of 14C-BCNU in 100% ethanol (DTI-015). Treatment with DTI-015 yielded a peak radioactive count (Cmax) for the 14C label that was 100-1000 fold higher in the tumor than in all other tissues in addition to a concentration in the tumor that was 100-fold higher than that achieved following IV infusion of 14C-BCNU. Pathologic and auto-radiographic analysis of tissue sections following IT injection of 14C-BCNU in ethanol into either tumor or normal rat brain revealed both an enhanced local volume of distribution and an increased concentration of BCNU delivered to tumor compared to non-tumor bearing brain. To investigate the mechanism behind the SFP of BCNU to the tumor both dynamic contrast and perfusion MRI were performed on 9L tumors before and after treatment and demonstrated a decrease in tumor perfusion following IT injection of DTI-015. Finally, initial PK of patient blood samples following administration of DTI-015 into relapsed high-grade glioma indicated a 20-fold decrease in systemic exposure to BCNU compared to IV infusion of BCNU providing further evidence for the enhanced therapeutic ratio observed for DTI-015.

Animals↗
PubMed2005

Magnetic resonance criteria for future trials of cardiac resynchronization therapy.

Current patient selection criteria for Cardiac Resynchronization Therapy (CRT), an efficacious treatment for heart failure, include no measure of disconjugate cardiac contractility other than prolonged QRS on electrocardiogram. Using cardiac magnetic resonance imaging, we examined the roles of cardiac asymmetry, asynchrony, and circumferential strain in DCC with the principal aim of generating a robust numerical index for use in future trials of CRT. Standard cardiac magnetic resonance imaging was done on a GE 1.5 Tesla Signa LX MRI clinical scanner (GE Healthcare, Milwaukee, WI, USA) and analyzed by MASS Analysis (MEDIS, Leiden, The Netherlands). The methods were evaluated in eleven patients with advanced heart failure due to ischemic and non-ischemic cardiomyopathy, who did not qualify under current criteria for CRT, five CRT candidates pre-op and eleven normal subjects. Using t-test and standardized differences (SD = sd/diff, Power (N) = number of patients to reach p < .05) we determined efficacy. Indices of asymmetry and asynchrony (Ism and Isn, respectively) could be measured with accuracy and provided excellent statistical power when used as surrogate markers to delineate heart failure and CRT patients from control subjects. Asymmetry and asynchrony in heart contraction are both critical components of dilated cardiomyopathy that can be improved by CRT. Magnetic resonance asynchrony is efficacious in screening patients and should now be compared with recently published echocardiography data to improve outcome for this costly but valuable therapy.

Adult↗
PubMed2005

Gd-enhanced cardiovascular MR imaging to identify left ventricular pseudoaneurysm.

A pseudoaneurysm occurs when incomplete rupture of the heart seals within organizing thrombus, hematoma, and pericardium and maintains communication with the left ventricle. A pseudoaneurysm may cause arterial emboli and drain off a considerable portion of ventricular stroke volume. Cardiovascular magnetic resonance imaging proves to be an adequate technique to not only identify pseudoaneurysms but also quantify function measurements of the left ventricle and allow for projections of post-surgical function. When complemented with myocardial delayed enhancement, it is the best technique for identifying the viability of myocardial tissue, an important aspect in surgical planning.

Aged↗
PubMed2005

Suppression of glial glutamine release to the extracellular fluid studied in vivo by NMR and microdialysis in hyperammonemic rat brain.

Release of glial glutamine (GLN) to the extracellular fluid (ECF), mainly mediated by the bidirectional system N transporter SN1, was studied in vivo in hyperammonemic rat brain, using (15)N-nuclear magnetic resonance (NMR) to monitor intracellular [5-(15)N]GLN and microdialysis/gradient (1)H-(15)N heteronuclear single-quantum correlation NMR to analyse extracellular [5-(15)N]GLN. GLN(ECF) was elevated to 2.4 +/- 0.2 mm after 4.5 h of intravenous ammonium acetate infusion. The [GLN(i)]/[GLN(ECF)] ratio (i = intracellular) was 9.6 +/- 0.9, compared with 17-20 in normal brain. GLN(ECF) then decreased substantially at t = 4.9 +/- 0.1 h. Comparison of the time-courses of intra- and extra-cellular [5-(15)N]GLN strongly suggested that the observed decrease reflects partial suppression of glial GLN release to ECF. Suppression also followed elevation of GLN(ECF) to 1.9 mM, resulting in a [GLN](i)/[GLN(ECF)] ratio of 8.4, upon perfusion of alpha-(methylamino)isobutyrate which inhibits neuronal uptake of GLN(ECF) mediated by sodium-coupled amino acid transporter (SAT). The results provide first evidence for bidirectional operation of SN1 in vivo, and clarify the effect of transmembrane GLN gradient on glial GLN release at physiological Na(+) gradient. Implications of the results for SN1 as an additional regulatory site in the glutamine/glutamate cycle and utility of this approach for examining the role of GLN in an experimental model of fulminant hepatic failure are discussed.

Animals↗
PubMed2005

Efficacy of proton magnetic resonance spectroscopy in neurological diagnosis and neurotherapeutic decision making.

Anatomic and functional neuroimaging with magnetic resonance imaging (MRI) includes the technology more widely known as magnetic resonance spectroscopy (MRS). Now a routine automated "add-on" to all clinical magnetic resonance scanners, MRS, which assays regional neurochemical health and disease, is therefore the most accessible diagnostic tool for clinical management of neurometabolic disorders. Furthermore, the noninvasive nature of this technique makes it an ideal tool for therapeutic monitoring of disease and neurotherapeutic decision making. Among the more than 100 brain disorders that fall within this broad category, MRS contributes decisively to clinical decision making in a smaller but growing number. In this review, we will cover how MRS provides therapeutic impact in brain tumors, metabolic disorders such as adrenoleukodystrophy and Canavan's disease, Alzheimer's disease, hypoxia, secondary to trauma or ischemia, human immunodeficiency virus dementia and lesions, as well as systemic disease such as hepatic and renal failure. Together, these eight indications for MRS apply to a majority of all cases seen. This review, which examines the role of MRS in enhancing routine neurological practice and treatment concludes: 1) there is added value from MRS where MRI is positive; 2) there is unique decision-making information in MRS when MRI is negative; and 3) MRS usefully informs decision making in neurotherapeutics. Additional efficacy studies could extend the range of this capability.

AIDS Dementia Complex↗
PubMed2004

Therapeutic efficacy of DTI-015 using diffusion magnetic resonance imaging as an early surrogate marker.

To investigate diffusion weighted magnetic resonance imaging as a quantitative surrogate marker for evaluating the therapy-induced cellular changes in an orthotopic experimental glioma model, tumors were treated with direct intratumoral administration of DTI-015, a solution of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in 100% EtOH. Intracerebral 9L tumors were induced in Fischer 344 rats, and three treatment groups were established: DTI-015, EtOH, and sham. Two groups of rats received intratumoral injection of either 67 mg/mL BCNU in EtOH or EtOH alone at 50% of the tumor volume up to a maximum of 30 mul under stereotactic guidance. Diffusion magnetic resonance images were acquired before treatment and after treatment at 1, 24, 48, and 72 hours and then 3 times per week thereafter. Tumor cell viability was examined using multislice diffusion weighted magnetic resonance imaging with diffusion weighted transverse magnetic resonance images and histogram plots of each tumor quantified over time. Control animals (EtOH- or sham-treated animals) showed mean apparent diffusion coefficients (ADCs) that remained essentially unchanged over the experimental time course. In contrast, rats treated with DTI-015 showed a significant increase in ADC relative to the pretreatment within 24 hours, which further increased over time, followed by a significant therapeutic response as evidenced by subsequent tumor volume shrinkage, development of a cystic region, and enhanced animal survival. Finally, not only were ADC measurements predictive of differences between treatment groups, but they also yielded spatial and temporal data regarding the efficacy of treatment within individual treated animals that could be used to guide subsequent therapy.

Animals↗
PubMed2004

The use of 19F spectroscopy and diffusion-weighted MRI to evaluate differences in gene-dependent enzyme prodrug therapies.

To evaluate noninvasive measures of gene expression and tumor response in a gene-dependent enzyme prodrug therapy (GDEPT), a bifunctional fusion gene between Saccharomyces cerevisiae cytosine deaminase (CD) and Haemophilus influenzae uracil phosphoribosyltransferase (UPRT) was constructed. CD deaminates 5-fluorocytosine (5FC) to 5-fluorouracil (5FU), and UPRT subsequently converts 5FU to fluorouridine monophosphate, and both of these reactions can be monitored noninvasively in vitro and in vivo using 19F magnetic resonance spectroscopy (MRS). Following transient transfection the CD-UPRT fusion protein exhibited both UPRT and CD enzymatic activities as documented by 19F MRS. In addition, an increase in CD activity and thermal stability was witnessed for the fusion protein compared to native CD. Stable expression of CD-UPRT in 9L glioma cells increased both 5FC and 5FU sensitivity in vitro compared to CD-expressing and wild-type 9L cells. Noninvasive 19F MRS of both CD and UPRT gene function in vivo demonstrated that in animals bearing CD-expressing tumors there was limited conversion of 5FC to 5FU with no measurable accumulation of cytotoxic fluorinated nucleotides (F-nucs). In contrast, CD-UPRT-expressing tumors had increased CD gene activity with a threefold higher intratumoral accumulation of 5FU and significant generation of F-nucs. Finally, CD-UPRT yielded increased efficacy in an orthotopic animal model of high-grade glioma. More importantly, early changes in cellular water mobility, which are felt to reflect cellular death, as measured by diffusion-weighted MRI, were predictive of both durable response and increased animal survival. These results demonstrate the increased efficacy of the CD-UPRT GDEPT compared to CD alone both biochemically and in a preclinical model and validate both 19F MRS and diffusion-weighted MRI as tools to assess gene function and therapeutic efficacy.

Animals↗
PubMed2004

Quantitative determination of extracellular glutamine concentration in rat brain, and its elevation in vivo by system A transport inhibitor, alpha-(methylamino)isobutyrate.

The basal concentration of glutamine in the extracellular fluid, [GLN(ECF)], was determined to be 385 +/- 16 microm in the cortico-striatal region of awake rats. This in vivo concentration was determined by measuring glutamine concentrations in dialysates collected at several flow rates (0.2-4 microL/min), and extrapolating to the concentration at zero flow-rate. Dialysate glutamine concentrations in the somatosensory cortex, hippocampus and thalamus showed no statistically significant difference. In these brain regions, [GLN(ECF)] was elevated 1.5- to 1.8-fold upon perfusion of 50-250 mmalpha-(methylamino)isobutyrate (MeAIB), a competitive inhibitor of glutamine uptake by system A amino acid transporter. The results show, for the first time, that MeAIB causes elevation of brain GLN(ECF)in vivo. The MeAIB-induced elevation of [GLN(ECF)] provides additional support for the current view that system A GLN transporter (Gln T/SAT 1) is the major pathway for the uptake of GLN(ECF) by neurons, while GLN release from glia is mainly mediated by a system N transporter (SN1) which is not inhibitable by MeAIB. The steady-state GLN(ECF) concentration and the effectiveness of MeAIB in inhibiting neuronal GLN uptake in vivo, reported in this study, will be useful, when combined with the known in vitro kinetic properties of the GLN transporters, for study of GLN transport in the intact brain.

Amino Acid Transport System A↗
PubMed2004

Bioluminescence detection of cells having stabilized p53 in response to a genotoxic event.

Inactivation of p53 is one of the most frequent molecular events in neoplastic transformation. Approximately 60% of all human tumors have mutations in both p53 alleles. Wild-type p53 activity is regulated in large part by the proteosome-dependent degradation of p53, resulting in a short p53 half-life in unstressed and untransformed cells. Activation of p53 by a variety of stimuli, including DNA damage induced by genotoxic drugs or radiation, is accomplished by stabilization of wild-type p53. The stabilized and active p53 can result in either cell-cycle arrest or apoptosis. Surprisingly, the majority of tumor-associated, inactivating p53 mutations also result in p53 accumulation. Thus, constitutive elevation of p53 levels in cells is a reliable measure of p53 inactivation, whereas transiently increased p53 levels reflect a recent genotoxic stress. In order to facilitate noninvasive imaging of p53 accumulation, we here describe the construction of a p53-luciferase fusion protein. Induction of DNA damage in cells expressing the fusion protein resulted in a time-dependent accumulation of the fusion that was noninvasively detected using bioluminescence imaging and validated by Western blot analysis. The p53-Luc protein retains p53 function because its expression in HCT116 cells lacking functional p53 resulted in activation of p21 expression as well as induction of apoptosis in response to a DNA damaging event. Employed in a transgenic animal model, the proposed p53-reporter fusion protein will be useful for studying p53 activation in response to exposure to DNA-damaging carcinogenic agents. It could also be used to study p53 stabilization as a result of inactivating p53 mutations. Such studies will further our understanding of p53's role as the "guardian of the genome" and its function in tumorigenesis.

Apoptosis↗
PubMed2003

Sp1 and Sp3 are oxidative stress-inducible, antideath transcription factors in cortical neurons.

Neuronal cell death in response to oxidative stress may reflect the failure of endogenous adaptive mechanisms. However, the transcriptional activators induced by oxidative stress in neurons that trigger adaptive genetic responses have yet to be fully elucidated. We report that basal DNA binding of the zinc finger transcription factors Sp1 and Sp3 is unexpectedly low in cortical neurons in vitro and is significantly induced by glutathione depletion-induced or hydrogen peroxide-induced oxidative stress in these cells. The increases in Sp1/Sp3 DNA binding reflect, in part, increased levels of Sp1 and Sp3 protein in the nuclei of cortical neurons. Similar induction of Sp1 and Sp3 protein is also observed in neurons in vivo in a chemical or a genetic model of Huntington's disease, two rodent models in which neuronal loss has been attributed to oxidative stress. Sustained high-level expression of full-length Sp1 or full-length Sp3, but not the Sp1 zinc finger DNA-binding domain alone, prevents death in response to oxidative stress, DNA damage, or both. Taken together, these results establish Sp1 and Sp3 as oxidative stress-induced transcription factors in cortical neurons that positively regulate neuronal survival.

Animals↗
PubMed2003

Evaluation of (E)-2'-deoxy-2'-(fluoromethylene)cytidine on the 9L rat brain tumor model using MRI.

(E)-2'-deoxy-2'-(fluoromethylene)cytidine (FMdC), was evaluated as a potential treatment for malignant gliomas using the rat 9L brain tumor model. FMdC was shown to be an effective inhibitor of cell proliferation in cultured 9L cells with an EC(50) of 40 ng/ml. In vitro studies also revealed that this compound significantly inhibited incorporation of [(3)H]thymidine in 9L cells. In vivo therapeutic efficacy of FMdC was evaluated in rats harboring intracerebral 9L tumors which were treated daily with 15 mg/kg, i.p. Treatment response was quantified from changes in tumor growth rates as assessed from sequential magnetic resonance imaging (MRI) tumor volume measurements. In vivo tumor cell kill in individual animals was calculated by fitting tumor volume data with an iterative computer routine. It was estimated that therapeutically responsive rats treated with FMdC daily produced a >/= 0.1 log kill per therapeutic dose which resulted in a significant reduction in tumor growth rate. In addition, localized (1)H-MRS of intracerebral 9L tumors revealed changes in metabolite levels which correlated with therapeutic response. These results provide evidence supporting the use of FMdC in clinical trials for the treatment of malignant gliomas and reveals that MR can play an important role in the pre-clinical evaluation of novel compounds using orthotopic tumor models.

Animals↗
PubMed2003

In vivo characterization of fatty acids in human adipose tissue using natural abundance 1H decoupled 13C MRS at 1.5 T: clinical applications to dietary therapy.

Natural abundance proton-decoupled (13)C magnetic resonance spectroscopy was used to establish the in vivo lipid composition of normal adipose tissue and the corresponding effects of altered lipid diets. Experiments were performed on a standard 1.5 T clinical MR scanner using a double-tuned (1)H-(13)C coil. Peaks from double-bonded and methylene carbons were analyzed. Normal lipid composition was established in 20 control subjects. For comparison, five subjects on altered lipid diets were studied. Four subjects were on a fish oil supplement diet or predominantly seafood diet (polyunsaturated fatty acids), and one subject was on a Lorenzo's oil diet (monounsaturated fatty acids). Well-resolved (13)C spectra were obtained from the calf adipose tissue with a total acquisition time of 10 min. Model oil solutions were used to identify specific (13)C resonances. Subjects on lipid diets showed significantly elevated levels of monounsaturated and polyunsaturated fatty acids for Lorenzo's and fish oil diets, respectively. We conclude that (13)C MR spectroscopy can readily detect changes in lipid composition due to medium- and long-term therapeutic lipid diets. Since the examination is rapid, robust and noninvasive, opportunities arise for large clinical trials of preventive or therapeutic diets to be performed with (13)C MRS on a clinical MR scanner.

Adipose Tissue↗
PubMed2003

Reduced glutamate neurotransmission in patients with Alzheimer's disease -- an in vivo (13)C magnetic resonance spectroscopy study.

Cognitive impairment in Alzheimer's disease (AD) is not fully explained. PET indicates reduced cerebral metabolic rate for glucose. Since glutamate neurotransmission (GNT) consumes more than 80% of the ATP generated from metabolism, a pilot study was carried out to determine the neuronal tricarboxylic acid cycle (TCA) based on the hypothesis that reduced GNT could contribute to cognitive impairment in AD. Three AD patients with cognitive impairment (mini-mental state exam: 24 vs 30, P<0.05) and significant reduction in both N-acetyl aspartate (NAA)/Creatine (Cr) ( P<0.009) and NAA/myo-inositol (mI) ratio ( P<0.01), and three age-matched controls each received 0.014-0.016 g/kg/min 99%1-13C glucose IV. Quantitative (1)H and proton-decoupled (13)C MR brain spectra were acquired from combined posterior-parietal white matter and posterior-cingulate gray matter every 5 min for 140 min.(13)C magnetic resonance spectroscopy (MRS) measures of glucose oxidation and neuronal TCA rate, including prolonged time to (13)C enrichment of glutamate (Glu2) ( P<0.004) and bicarbonate (HCO(3)) ( P<0.03) as well as reduced relative enrichment of Glu(2)/Glu(4) between 60 and 100 min ( P<0.04), were significantly different in AD patients vs. controls. (13)C measures of GNT, glutamine (Gln)(2)/Glu(2) ( P<0.02) and rates of glutamate enrichment (Glu(2)/glucose: 0.34 vs 0.86, P=ns and Glu(4)/glucose 0.26 vs 0.83, P=ns), were also reduced.(13)C MRS measures of neuronal TCA cycle, glucose oxidation and GNT were significantly correlated with measures of neuronal integrity: NAA/Cr, [NAA] and mI/NAA as determined by (1)H MRS ( R(2)=0.73-0.95; P<0.05-0.01), suggesting that impairment of GNT may be a contributing factor in the cognitive impairment characteristic of AD.

Adult↗