Fusion of the HSV-1 tegument protein vp22 to cytosine deaminase confers enhanced bystander effect and increased therapeutic benefit

A major limitation in cancer gene therapy, specifically gene-dependent enzyme prodrug therapy (GDEPT), is inefficient gene delivery and expression. The suicide gene cytosine deaminase (CD) and its substrate, 5-fluorocytosine (5-FC), have been extensively explored due to the inherent 'bystander' effect achieved through diffusion of the toxic metabolite 5-fluorouracil (5-FU). In this study, we aimed to enhance this 'bystander' effect by fusing the Saccharomyces cerevisiae CD to the HSV-1 tegument protein vp22, a novel translocating protein. Two constructs were created: one with vp22 fused to CD (vp22CD) and a second wherein a truncated vp22, lacking the necessary residues for trafficking, fused to CD (delvp22CD). The generated 9L stable lines exhibited similar growth rates, enzyme expression, CD activity, and sensitivity to 5-FC and 5-FU. However, mixed population colony formation assays demonstrated greater bystander effect with the vp22CD fusion as compared to delvp22CD. This enhancement was maintained in vivo where 9L tumors expressing 20 or 50% vp22CD exhibited increased growth delay compared to the respective delvp22CD tumors. Moreover, adenoviral transduction of established wild-type 9L tumors showed increased growth delay with vp22CD (Ad-EF_vp22CD) as compared to equivalent CD (Ad-EF_CD) transduced tumors. Finally, confirming the increased efficacy, (19)F magnetic resonance spectroscopy (MRS) of vp22CD-expressing tumors demonstrated increased 5-FU levels as compared to tumors expressing the nontranslocating CD. These results together demonstrated that fusion of vp22 to CD resulted in CD translocation, which in turn amplified conversion of 5-FC to 5-FU in vivo and enhanced the therapeutic benefit of this GDEPT strategy.

Ultra-fast three dimensional imaging of hyperpolarized 13C in vivo

OBJECTIVE

PASADENA, a chemical method of enhancing nuclear spin polarization has demonstrated 13C polarizations of order unity for the nascent products of molecular addition by parahydrogen. The extreme brevity of signal enhancement obtained by hyperpolarization requires improved 13C MR in vivo imaging techniques for their optimum utility.

MATERIALS AND METHODS

13C imaging sequences, including 13C 3D FIESTA, were compiled for a GE LX 1.5 T clinical MR scanner. Two water soluble 13C imaging agents were hyperpolarized utilizing parahydrogen and an automated polarizer. 13C polarization was quantified in flow phantoms and in rats with jugular vein catheters.

RESULTS

Fast 3D FIESTA 13C MR imaging technique acquired sequential 3D images (3.66 s/acquisition) with superior SNR. Hyperpolarized 13C solutions and vascular phantoms achieved a maximum signal of 26,624+/-593. In vivo 13C MR images of the cardiopulmonary circulation showed maximum 13C signal of 2,402+/-158. 13C images acquired within 3.66 s showed signal enhancement over 10,000 compared to equilibrium polarization.

CONCLUSION

3D-FIESTA was effective for sub-second in vivo imaging of hyperpolarized 13C reagents produced in a custom-built parahydrogen polarizer. Application to 13C hyperpolarized by parahydrogen is demonstrated in vitro and in vivo.

Diffusion imaging for evaluation of tumor therapies in preclinical animal models

The increasing development of novel targeted therapies for treating solid tumors has necessitated the development of technology to determine their efficacy in preclinical animal models. One such technology that can non-invasively quantify early changes in tumor cellularity as a result of an efficacious therapy is diffusion MRI. In this overview we present some theories as to the origin of diffusion changes as a result of tumor therapy, a robust methodology for acquisition of apparent diffusion coefficient maps and some applications of determining therapeutic efficacy in a variety therapeutic regimens and animal models.

Membrane phospholipids and high-energy metabolites in childhood ataxia with CNS hypomyelination

BACKGROUND

Childhood ataxia with CNS hypomyelination (CACH) is a leukodystrophy with extreme rarefaction of white matter caused by mutations in one of the five subunits of the translation initiation factor 2B (eIF2B).

METHODS

Seven children with this disease and nine age-matched control subjects were studied with proton-decoupled phosphorus magnetic resonance (MR) spectroscopy.

RESULTS

In patients with CACH, cerebral concentrations of high-energy phosphate metabolites were abnormal. Of the metabolites involved in biosynthesis and catabolism of membrane phospholipids, glycerophosphorylethanolamine was reduced (0.24 +/- 0.18 mmol/kg brain vs 0.44 +/- 0.14; p < 0.02), and phosphorylethanolamine was increased (2.32 +/- 0.53 vs 1.53 +/- 0.22; p < 0.01), whereas the choline-containing phosphorylated metabolites were unchanged. Nucleoside triphosphate (NTP) was reduced (2.44 +/- 0.34 mmol/kg brain tissue vs 3.09 +/- 0.58; p < 0.01), phosphocreatine was elevated (4.11 +/- 0.63 vs 3.27 +/- 0.33; p < 0.01), and inorganic phosphate was reduced (0.77 +/- 0.32 vs 1.06 +/- 0.26; p < 0.05). Intracellular pH was elevated in patients (7.03 +/- 0.04 vs 6.99 +/- 0.02; p < 0.02).

CONCLUSIONS

The authors found an altered energy state of the residual cell population investigated. Together with previously identified replacement of white matter by CSF, the present findings raise the possibility that the genetic defect in eIF2B may result in impairment of myelin membrane synthesis or myelin membrane transport in the in vivo CACH brain. Ethanolamine metabolites constitute the plasmalogens, and the present findings may include a defect in plasmalogen metabolism.

13C enrichment of extracellular neurotransmitter glutamate in rat brain--combined mass spectrometry and NMR studies of neurotransmitter turnover and uptake into glia in vivo

13C-enrichment analysis of glutamate in the extracellular fluid (GLU(ECF): 2-3 microM) by gas-chromatography/mass-spectrometry (GCMS) was combined with in vivo NMR observation of whole-brain GLU (approximately10 mM) to study neurotransmitter uptake. Brain GLU C5 was 13C-enriched by intravenous [2,5-13C]glucose infusion. GLU(ECF) was collected by microdialysis from the cortico-striatal region of awake rats. The 13C-enrichment of basal dialysate GLU C5 during 0.75-1.25 hr of infusion was 0.263 +/- 0.01, very close to the enrichment of whole-brain GLU C5. The result strongly suggests that dialysate GLU consists predominantly of neurotransmitter GLU. For selective 13C-enrichment of neurotransmitter GLU, the whole-brain 13C-enrichment was followed by [12C]glucose infusion to chase 13C from the small glial GLU pool. This leaves [5-13C]GLU mainly in the large neuronal metabolic pool and the vesicular neurotransmitter pool. The uptake of synaptic [5-13C]GLU(ECF) into glia and metabolism to glutamine (GLN) were monitored in vivo by NMR observation of [5-13C,15N]GLN formed during 15NH4Ac infusion. The rate of GLN synthesis, derived from neurotransmitter GLU(ECF) (which provided 80-90% of the substrate) was 6.4 +/- 0.44 micromol/g/hr. Hence, the observed rate represents a reasonable estimate for the rate of glial uptake of GLU(ECF), a process that is crucial for protecting the brain from GLU excitotoxicity.

Magnetic resonance imaging in cancer research

Non-invasive assessment of antineoplastic response and correlation of the location, magnitude and duration of transgene expression in vivo would be particularly useful for evaluating cancer gene therapy protocols. This review presents selected examples of how magnetic resonance (MR) has been used to assess therapeutic efficacy by non-invasive quantitation of cell kill, to detect a therapeutic response prior to a change in tumour volume and to detect spatial heterogeneity of the tumour response and quantitate transgene expression. In addition, applications of the use of bioluminescence imaging (BLI) for the evaluation of treatment efficacy and in vivo transgene expression are also presented. These examples provide an overview of areas in which imaging of animal tumour models can contribute towards improving the evaluation of experimental therapeutic agents.

The potential of 5-fluorocytosine/cytosine deaminase enzyme prodrug gene therapy in an intrahepatic colon cancer model

Colorectal cancer can metastasize to the liver, but remain liver confined for years. A critical step in developing treatments for intrahepatic cancer involves assessment in an orthotopic intrahepatic model. The purpose of this study was to develop a noninvasive intrahepatic tumor model to study the efficacy of 5-flucytosine/yeast cytosine deaminase (5FC/yCD)-based gene therapy for liver tumors. Luciferase expressing human colorectal carcinoma (HT-29luc) cells were generated by retroviral infection and implanted in the left liver lobe of nude mice. The bioluminescence was measured every week for a period of 1 month, then animals were killed and tumors were measured by calipers. After we found a correlation between photon counts and tumor size, animals were implanted with tumors composed of either 0%, 10%, or 100% yCD/HT-29luc cells, and treated with 5FC. Tumor bioluminescence was measured during treatment and tumor histology examined at the time of death. We found that 5FC caused significant regression of yCD expressing tumors. Furthermore, visible tumors at the time of death, which emitted little bioluminescence, contained little or no viable tumor. We then developed an adenoviral vector for yCD. Intraperitoneal administration of adenovirus containing yCD led to the production of yCD enzyme within intrahepatic tumors. These results suggest that (1) intrahepatic cancer responds to 5FC when cells express yCD; (2) the luciferin-luciferase system permits non-invasive real time imaging of viable intrahepatic cancer; and (3) this system can be used to carry out gene therapy experiments using yCD adenovirus.

Tricarboxylic acid cycle of glia in the in vivo human brain

In the brain, acetate is exclusively oxidized by glia. To determine the contribution of glial metabolism to the tricarboxylic acid cycle (TCA), 1-(13)C-acetate was infused in six studies in three normal adult subjects and -one epileptic receiving valproic acid for seizure control. Ten grams of 99% 1-(13)C labeled acetate were infused intravenously as a 3.3% w/v solution over 60 min, during which in vivo 13C MR spectra of the brain were acquired. As expected, 13C label rapidly enriched cerebral bicarbonate, glutamate and glutamine C5. The mean rate of acetate oxidation calculated from steady-state 13C enrichment of bicarbonate in fasted normal subjects was 0.13 +/- 0.03 micromol/g/min (n=4), approximately 20% of the total cerebral TCA cycle rate.

The first in vivo observation of (13)C-(15)N coupling in mammalian brain

[5-(13)C,(15)N]Glutamine, with (1)J((13)C-(15)N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by (13)C MRS at 4.7 T. The brain [5-(13)C]glutamine peak consisted of the doublet from [5-(13)C,(15)N]glutamine and the center [5-(13)C,(14)N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-(13)C,(15)N]glutamine was monitored in vivo with a time resolution of 20-35 min. This [5-(13)C,(15)N]glutamine was formed by glial uptake of released neurotransmitter [5-(13)C]glutamate and its reaction with (15)NH(3) catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively (13)C-enriched by intravenous [2,5-(13)C]glucose infusion to (13)C-label whole-brain glutamate C5, followed by [(12)C]glucose infusion to chase (13)C from the small and rapidly turning-over glial glutamate pool, leaving (13)C mainly in the neurotransmitter [5-(13)C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-(13)C,(15)N]glutamine arises from a coupling between (13)C of neuronal origin and (15)N of glial origin. Measurement of the rate of brain [5-(13)C,(15)N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity.

Thyroid hormone-responsive pituitary hyperplasia independent of somatostatin receptor 2

Mice homozygous for the targeted disruption of the glycoprotein hormone alpha-subunit (alphaGsu) display hypertrophy and hyperplasia of the anterior pituitary thyrotropes. Thyrotrope hyperplasia results in tumors in aged alphaGsu(-/-) mice. These adenomatous pituitaries can grow independently as intrascapular transplants in hypothyroid mice, suggesting that they have progressed beyond simple hyperplasia. We used magnetic resonance imaging to follow the growth and regression of thyrotrope adenomatous hyperplasia in response to thyroid hormone treatment and discovered that the tumors retain thyroid hormone responsiveness. Somatostatin (SMST) and its diverse receptors have been implicated in cell proliferation and tumorigenesis. To test the involvement of SMST receptor 2 (SMSTR2) in pituitary tumor progression and thyroid hormone responsiveness in alphaGsu(-/-) mutants, we generated Smstr2(-/-), alphaGsu(-/-) mice. Smstr2(-/-), alphaGsu(-/-) mice develop hyperplasia of thyrotropes, similar to alphaGsu(-/-) mutants, demonstrating that SMSTR2 is dispensable for the development of pituitary adenomatous hyperplasia. Thyrotrope hyperplasia in Smstr2(-/-), alphaGsu(-/-) mice regresses in response to T4 treatment, suggesting that SMSTR2 is not required in the T4 feedback loop regulating TSH secretion.

Accumulation of methylsulfonylmethane in the human brain: identification by multinuclear magnetic resonance spectroscopy

Methylsulfonylmethane (MSM) is a widely available 'alternative' medicine. In vivo magnetic resonance spectroscopy (MRS) was used to detect and quantify MSM in the brains of four patients with memory loss and in three normal volunteers all of who had ingested MSM at the recommended doses of 1-3 g daily. MSM was detected in all subjects at concentrations of 0.42-3.40 mmole/kg brain and was equally distributed between gray and white matter. MSM was undetectable in drug-naïve normal subjects (N=25), patients screened for 'toxic exposure' (N=50) or patients examined with 1H MRS for the diagnosis of probable Alzheimer Disease (N=520) between 1991 and 2001. No adverse clinical or neurochemical effects were observed. Appearance of MSM in significant concentrations in the human brain indicates ready transfer across the intact blood-brain barrier, of a compound with no known medical benefits.

Short-echo time proton MR spectroscopy in the presence of gadolinium

PURPOSE

The purpose of this work was to quantify the impact of contrast agents on short-TE single-voxel 1H MR spectroscopy (MRS) diagnosis of recurrent brain tumors.

METHOD

Short-TE 1H MRS was performed in 49 patients with biopsy-proven brain tumors and 14 control subjects. Eight patients (nine paired exams) were examined before and after administration of Gd-DTPA (interval approximately 5-7 min).

RESULTS

Tumor spectra showed increased choline/creatine ratio (Cho/Cr; p < 0.009) and Cho concentrations (p < 0.02). Receiver operator characteristic for Cho/Cr = 0.93 differentiated 100% of tumors from control in the absence or presence of contrast agent. Repeated 1H MRS varied <3%. Cho T2 was significantly longer than Cr T2 (p < 0.02).

CONCLUSION

Proton MRS with TE of 30 ms may safely be used in combined contrast-enhanced MRI/MRS protocols. Further study is required with long-TE MRS because of the prolonged T2 of Cho.

Magnetic resonance imaging of ethyl-nitrosourea-induced rat gliomas: a model for experimental therapeutics of low-grade gliomas

Human low-grade gliomas represent a population of brain tumors that remain a therapeutic challenge. Preclinical evaluation of agents, to test their preventive or therapeutic efficacy in these tumors, requires the use of animal models. Spontaneous gliomas develop in models of chemically induced carcinogenesis, such as in the transplacental N-ethyl-N-nitrosourea (ENU) rat model. However, without the ability to detect initial tumor formation, multiplicity or to measure growth rates, it is difficult to test compounds for their interventional or preventional capabilities. In this study Fisher-334 rats, treated transplacentally with ENU, underwent magnetic resonance imaging (MRI) examination in order to evaluate this approach for detection of tumor formation and growth. ENU-induced intracranial cerebral tumors were first observable in T2-weighted images beginning at 4 months of age and grew with a mean doubling time of 0.487 +/- 0.112 months. These tumors were found histologically to be predominately mixed gliomas. Two therapeutic interventions were evaluated using MRI, vitamin A (all-trans retinol palmitate, RP), as a chemopreventative agent and the anti-angiogenic drug SU-5416. RP was found to significantly delay the time to first tumor observation by one month (P = 0.05). No differences in rates of tumor formation or growth rates were observed between control and RP-treated groups. MRI studies of rats treated with SU-5416 resulted in reduction in tumor growth rates compared to matched controls. These results show that MRI can be used to provide novel information relating to the therapeutic efficacy of agents against the ENU-induced tumor model.

Alternative 1-(13)C glucose infusion protocols for clinical (13)C MRS examinations of the brain

Clinical utility of (13)C MRS is limited by cost and long examination times. Three 1-(13)C glucose infusion protocols-a high-dose i.v., low-dose i.v., and oral administration of 1-(13)C glucose-were compared on a GE 1.5T MR scanner. Resolution and sensitivity were sufficient to identify (13)C glucose (1alpha and 1beta), glutamate (C1-C4), glutamine (C1-C4), aspartate (C2 and C3), lactate, alanine, and bicarbonate in brain spectra. The three protocols were efficacious, as measured by cerebral enrichment of 1-(13)C glucose (62%, 42%, and 38%) and its principal metabolite, 4-(13)C glutamate (13%, 11%, and 16%), respectively. Intravenous infusion of 1-(13)C glucose 0.23 g/kg body weight (low dose) provides equivalent information at one third the cost of previous regimes. Magn Reson Med 46:39-48, 2001.

[1-13C]glucose MRS in chronic hepatic encephalopathy in man

[1-13C]-labeled glucose was infused intravenously in a single dose of 0.2 g/kg body weight over 15 min in six patients with chronic hepatic encephalopathy, and three controls. Serial 13C MR spectra of the brain were acquired. Patients exhibited the following characteristics relative to normal controls: 1) Cerebral glutamine concentration was increased (12.6 +/- 3.8 vs. 6.5 +/- 1.9 mmol/kg, P < 0.006) and glutamate was reduced (8.2 +/- 1.0 vs. 9.9 +/- 0.6 mmol/kg, P < 0.02). 2) 13C incorporation into glutamate C4 and C2 positions was reduced in patients (80 min after start of infusion C4: 0.43 +/- 0.09 vs. 0.84 +/- 0.15 mmol/kg, P < 0.001; C2: 0.20 +/- 0.03 vs. 0.45 +/- 0.07 mmol/kg, P < 0.0001). 3) 13C incorporation into bicarbonate was delayed (90 +/- 21 vs. 40 +/- 10 min, P < 0.003), and the time interval between detection of glutamate C4 and C2 labeling was longer in patients (22 +/- 8 vs. 12 +/- 3 min, P < 0.03). 4) Glutamate C2 turnover time was reduced in chronic hepatic encephalopathy (17.1 +/- 6.8 vs. 49.6 +/- 8.7 min, P < 0.0002). 5) 13C accumulation into glutamine C2 relative to its substrate glutamate C2 increased progressively with the severity of clinical symptoms (r = 0.96, P < 0.01). These data indicate disturbed neurotransmitter glutamate/glutamine cycling and reduced glucose oxidation in chronic hepatic encephalopathy. [1-13C] glucose MRS provides novel insights into disease progression and the pathophysiology of chronic hepatic encephalopathy.

Direct determination of the N-acetyl-L-aspartate synthesis rate in the human brain by (13)C MRS and [1-(13)C]glucose infusion

A non-invasive (13)C magnetic resonance spectroscopy (MRS) technique is described for the determination of the N-acetyl-L-aspartate (NAA) synthesis rate, V(NAA), in the human brain in vivo. In controls, the mean V(NAA) was 9.2 +/- 3.9 nmol/min/g. In Canavan disease, where [NAA] is increased (p < 0.001) and [aspartate] is deceased (p < 0.001), V(NAA) was significantly reduced to 3.6 +/- 0.1 nmol/min/g (p < 0.001). These rates are in close agreement with the activity of the biosynthetic enzyme measured in vitro in animals, and with the rate of urinary excretion of NAA in human subjects with Canavan disease. The present result is consistent with the regulation of NAA synthesis by the activity of a single enzyme, L-aspartate-N-acetyltransferase, in vivo, and with its control in Canavan disease by limited substrate supply and/or product inhibition. The (13)C MRS technique provides the means for further determination of abnormal rates of neuronal NAA synthesis among neurological disorders in which low cerebral [NAA] has been identified.

1-(13)C glucose magnetic resonance spectroscopy of pediatric and adult brain disorders

With protocols designed for use in a clinical environment we investigated the feasibility and diagnostic potential of (13)C MRS after 1-(13)C labeled glucose infusion. (13)C MRS brain examinations were performed in 27 subjects (17 children and pediatric patients, six adult patients, and four adult controls), using a standard 1.5 T clinical MR scanner. 1-(13)C glucose, 99% enriched (20% w/v) was administered intravenously (690 or 210 mg/kg body weight) or orally (730 mg/kg). Cerebral (13)C-enrichment patterns and time courses were compared. 1-(13)C glucose appeared in brain spectra within 2.5-15 min, with ensuing enrichment of its metabolites. No complications were encountered. When data obtained in patients were compared with controls, striking abnormalities in hepatic encephalopathy and in premature brain were observed, consistent with reduced cerebral glucose metabolism. Abnormalities in the (13)C enrichment pattern were also observed in pediatric patients with leukodystrophies and mitochondrial disorders. In this preliminary survey, we conclude that (13)C MRS in combination with glucose infusion is safe and efficient and provides new insights into the pathophysiology of brain disorders.

Diffusion magnetic resonance imaging: an early surrogate marker of therapeutic efficacy in brain tumors

BACKGROUND

A surrogate marker for treatment response that can be observed earlier than comparison of sequential magnetic resonance imaging (MRI) scans, which depends on relatively slow changes in tumor volume, may improve survival of brain tumor patients by providing more time for secondary therapeutic interventions. Previous studies in animals with the use of diffusion MRI revealed rapid changes in tumor water diffusion values after successful therapeutic intervention.

METHODS

The present study examined the sensitivity of diffusion MRI measurements in orthotopic rat brain tumors derived from implanted rat 9L glioma cells. The effectiveness of therapy for individual brain cancer patients was evaluated by measuring changes in tumor volume on neuroimaging studies conducted 6--8 weeks after the conclusion of a treatment cycle.

RESULTS

Diffusion MRI could detect water diffusion changes in orthotopic 9L gliomas after doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU or carmustine) that resulted in as little as 0.2 log cell kill, a measure of tumor cell death. Mean apparent diffusion coefficients in tumors were found to be correlated with and highly sensitive to changes in tumor cellularity (r =.78; two-sided P =.041). The feasibility of serial diffusion MRI in the clinical management of primary brain tumor patients was also demonstrated. Increased diffusion values could be detected in human brain tumors shortly after treatment initiation. The magnitude of the diffusion changes corresponded with clinical outcome.

CONCLUSIONS

These results suggest that diffusion MRI will provide an early surrogate marker for quantification of treatment response in patients with brain tumors.

Yeast cytosine deaminase improves radiosensitization and bystander effect by 5-fluorocytosine of human colorectal cancer xenografts

The efficacy of cancer gene therapy using bacterial cytosine deaminase (bCD)/5-fluorocytosine (5-FC) enzyme/prodrug strategy is limited by the inefficiency of cytosine deaminase (CD)-catalyzed conversion of 5-FC into 5-fluorouracil (5-FU). We have shown previously that yeast CD (yCD) is more efficient at the conversion of 5-FC than bCD. In the current study, we hypothesized that the increased production of 5-FU by yCD would enhance the efficacy of the CD/5-FC treatment strategy by increasing the bystander effect as well as the efficacy of radiotherapy because of the radiosensitizing capacity of 5-FU. To test this hypothesis, we generated stable HT29 human colon cancer cell lines expressing either bCD (HT29/bCD) or yCD (HT29/yCD). The amount of 5-FU produced in HT29/yCD tumors after a single injection of 5-FC (1000 mg/kg, i.p.) was 15-fold higher than that produced in HT29/bCD tumors. In tumor-bearing nude mice, the average minimum relative tumor size (compared with pretreatment values) of HT29/bCD tumors treated with 5-FC and radiation (500 mg/kg i.p. and 3 Gy, 5 days a week for 2 weeks) was 0.55+/-0.1, compared with 0.01+/-0.01 in HT29/yCD tumors (P = 0.002). Moreover, an increased cytotoxic and radiosensitizing effect of 5-FC on bystander cells was observed in vitro and in vivo when yCD was expressed in HT29 cells instead of bCD. In mice bearing HT29 tumors containing 10% HT29/yCD cells, the combined treatment resulted in a minimum tumor size of 0.20+/-0.07 compared with 0.60+/-0.1 in 10% HT29/bCD cells (P < 0.001). These results demonstrate that the use of yCD in the CD/5-FC strategy has a high potential to improve the therapeutic outcome of combined gene therapy and radiotherapy in cancer patients.

Rapid and quantitative assessment of cancer treatment response using in vivo bioluminescence imaging

Current assessment of orthotopic tumor models in animals utilizes survival as the primary therapeutic end point. In vivo bioluminescence imaging (BLI) is a sensitive imaging modality that is rapid and accessible, and may comprise an ideal tool for evaluating antineoplastic therapies. Using human tumor cell lines constitutively expressing luciferase, the kinetics of tumor growth and response to therapy have been assessed in intraperitoneal, and subcutaneous, and intravascular cancer models. However, use of this approach for evaluating orthotopic tumor models has not been demonstrated. In this report, the ability of BLI to noninvasively quantitate the growth and therapeutic-induced cell kill of orthotopic rat brain tumors derived from 9L gliosarcoma cells genetically engineered to stably express firefly luciferase (9LLuc) was investigated. Intracerebral tumor burden was monitored over time by quantitation of photon emission and tumor volume using a cryogenically cooled CCD camera and magnetic resonance imaging (MRI), respectively. There was excellent correlation (r=0.91) between detected photons and tumor volume. A quantitative comparison of tumor cell kill determined from serial MRI volume measurements and BLI photon counts following 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) treatment revealed that both imaging modalities yielded statistically similar cell kill values (P=.951). These results provide direct validation of BLI imaging as a powerful and quantitative tool for the assessment of antineoplastic therapies in living animals.

Real or imaginary? Human metabolism through nuclear magnetism

This account of the beginnings and later applications of the use of nuclear magnetic resonance for noninvasive medical diagnosis was presented at a Symposium held in Oxford, UK, during September 13-15, 2000 to mark the centenary of the birth of Hans Krebs, on August 25, 1900.

Diffusion MRI detects early events in the response of a glioma model to the yeast cytosine deaminase gene therapy strategy

Detection of a therapeutic response early in the course of cancer treatment, before tumor growth delay or regression, is not currently possible in experimental models or clinical medicine. New interim measures of therapeutic response would be particularly useful in the development of cancer chemosensitization gene therapy by facilitating optimization of gene transfer protocols and prodrug dosing schedules. Diffusion MRI is a sensitive technique producing quantitative and noninvasive images of the apparent mobility of water within a tissue. We investigated the utility of diffusion MRI for detecting early changes associated with a refined cytosine deaminase (CD)/5-fluorocytosine (5FC) chemosensitization gene therapy paradigm in orthotopic 9L gliomas stably expressing the recently cloned S. cerevisiae CD gene. Mean tumor diffusion increased 31% within 8 days of initiating 5-FC treatment, preceding tumor growth arrest and regression. Complete regression of the intracranial tumor was observed in four of five treated animals, and recurrent tumor in the remaining animal exhibited water diffusion behavior similar to primary, untreated tumors. These results demonstrate the efficacy of the yCD/5FC strategy for glioma and suggest that increased tumor water diffusion is an indicator of active therapeutic intervention.

Novel peak assignments of in vivo (13)C MRS in human brain at 1.5 T

(13)C MRS studies at natural abundance and after intravenous 1-(13)C glucose infusion were performed on a 1.5-T clinical scanner in four subjects. Localization to the occipital cortex was achieved by a surface coil. In natural abundance spectra glucose C(3beta,5beta), myo-inositol, glutamate C(1,2,5), glutamine C(1,2,5), N-acetyl-aspartate C(1-4,C=O), creatine CH(2), CH(3), and C(C=N), taurine C(2,3), bicarbonate HCO(-)(3) were identified. After glucose infusion (13)C enrichment of glucose C(1alpha,1beta), glutamate C(1-4), glutamine C(1-4), aspartate C(2,3), N-acetyl-aspartate C(2,3), lactate C(3), alanine C(3), and HCO(-)(3) were observed. The observation of (13)C enrichment of resonances resonating at >150 ppm is an extension of previously published studies and will provide a more precise determination of metabolic rates and substrate decarboxylation in human brain.

Combined effect of tumor necrosis factor-related apoptosis-inducing ligand and ionizing radiation in breast cancer therapy

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent endogenous activator of the cell death pathway and functions by activating the cell surface death receptors 4 and 5 (DR4 and DR5). TRAIL is nontoxic in vivo and preferentially kills neoplastically transformed cells over normal cells by an undefined mechanism. Radiotherapy is a common treatment for breast cancer as well as many other cancers. Here we demonstrate that ionizing radiation can sensitize breast carcinoma cells to TRAIL-induced apoptosis. This synergistic effect is p53-dependent and may be the result of radiation-induced up-regulation of the TRAIL-receptor DR5. Importantly, TRAIL and ionizing radiation have a synergistic effect in the regression of established breast cancer xenografts. Changes in tumor cellularity and extracellular space were monitored in vivo by diffusion-weighted magnetic resonance imaging (diffusion MRI), a noninvasive technique to produce quantitative images of the apparent mobility of water within a tissue. Increased water mobility was observed in combined TRAIL- and radiation-treated tumors but not in tumors treated with TRAIL or radiation alone. Histological analysis confirmed the loss of cellularity and increased numbers of apoptotic cells in TRAIL- and radiation-treated tumors. Taken together, our results provide support for combining radiation with TRAIL to improve tumor eradication and suggest that efficacy of apoptosis-inducing cancer therapies may be monitored noninvasively, using diffusion MRI.

Experimental gliosarcoma induces chemokine receptor expression in rat brain

Macrophage/microglial infiltration is a characteristic feature of brain tumors. The functional role(s) of these cells is complex and could include both trophic and suppressive effects on tumors. Information has recently emerged about the molecular signals that regulate the accumulation and function of monocytes in pathological disorders. Recent data indicate that the chemokine, monocyte chemoattractant protein-1 (MCP-1), a potent monocyte activating and chemotactic factor, is a primary regulator of the macrophage response in brain tumors. We hypothesized that if MCP-1 regulates macrophage/microglial infiltration, then expression of the specific MCP-1 receptor, CCR2, will be induced in peritumoral tissue and/or within brain tumors. Identification of a specific receptor that is preferentially expressed in brain tumors could be important both in terms of tumor biology and as a potential therapeutic target. We used an established experimental gliosarcoma model, induced by intracranial transplantation of cultured 9L cells into adult rat brain, to test this hypothesis. RT-PCR analysis showed high levels of both MCP-1 and CCR2 mRNA and Western blot analysis demonstrated increased CCR2 protein in tumor extracts. Immunocytochemistry showed CCR2 immunoreactive microglia in peritumoral tissue and, unexpectedly, that intrinsic tumor cells, rather than monocytes, were the predominant source of CCR2. These results demonstrate that CCR2 expression is markedly upregulated in this brain tumor model.