Diffusion MRI in early cancer therapeutic response assessment.

Imaging biomarkers for the predictive assessment of treatment response in patients with cancer earlier than standard tumor volumetric metrics would provide new opportunities to individualize therapy. Diffusion-weighted MRI (DW-MRI), highly sensitive to microenvironmental alterations at the cellular level, has been evaluated extensively as a technique for the generation of quantitative and early imaging biomarkers of therapeutic response and clinical outcome. First demonstrated in a rodent tumor model, subsequent studies have shown that DW-MRI can be applied to many different solid tumors for the detection of changes in cellularity as measured indirectly by an increase in the apparent diffusion coefficient (ADC) of water molecules within the lesion. The introduction of quantitative DW-MRI into the treatment management of patients with cancer may aid physicians to individualize therapy, thereby minimizing unnecessary systemic toxicity associated with ineffective therapies, saving valuable time, reducing patient care costs and ultimately improving clinical outcome. This review covers the theoretical basis behind the application of DW-MRI to monitor therapeutic response in cancer, the analytical techniques used and the results obtained from various clinical studies that have demonstrated the efficacy of DW-MRI for the prediction of cancer treatment response. Copyright © 2016 John Wiley & Sons, Ltd.

Parametric Response Mapping of Bronchiolitis Obliterans Syndrome Progression After Lung Transplantation.

Bronchiolitis obliterans syndrome (BOS) remains a major complication after lung transplantation. Air trapping and mosaic attenuation are typical radiological features of BOS; however, quantitative evaluation remains troublesome. We evaluated parametric response mapping (PRM, voxel-to-voxel comparison of inspiratory and expiratory computed tomography [CT] scans) in lung transplant recipients diagnosed with BOS (n = 20) and time-matched stable lung transplant recipients (n = 20). Serial PRM measurements were performed prediagnosis, at time of BOS diagnosis, and postdiagnosis (Tpre , T0 , and Tpost , respectively), or at a postoperatively matched time in stable patients. PRM results were correlated with pulmonary function and confirmed by microCT analysis of end-stage explanted lung tissue. Using PRM, we observed an increase in functional small airway disease (fSAD), from Tpre to T0 (p = 0.006) and a concurrent decrease in healthy parenchyma (p = 0.02) in the BOS group. This change in PRM continued to Tpost , which was significantly different compared to the stable patients (p = 0.0002). At BOS diagnosis, the increase in fSAD was strongly associated with a decrease in forced expiratory volume in 1 s (p = 0.011). Micro-CT confirmed the presence of airway obliteration in a sample of a BOS patient identified with 67% fSAD by PRM. We demonstrated the use of PRM as an adequate output to monitor BOS progression in lung transplant recipients.

Potassium transport by the isolated perfused kidney.

Rat kidneys perfused outside of the body with an artificial medium are able to increase their fractional excretion of potassium in response to a rising concentration of potassium in the medium but never show net secretion of potassium. By contrast, isolated perfused kidneys from chronically potassium-loaded rats regularly secrete potassium in excess of the amount filtered. Ouabain completely blocks the secretion of potassium by these isolated kidneys, suggesting that Na-K-ATPase mediates potassium secretion by potassium-adapted rats. Neither sodium deprivation, pretreatment with deoxycorticosterone, nor pretreatment with methylprednisolone prepared the kidney to secrete potassium, despite stimulation of Na-K-ATPase activity in cortex or outer medulla. Potassium loading was the only maneuver tested that increased the activity of Na-Katpase in the inner medulla (white papilla) and also produced potassium secretion by the isolated kidney. Surgical ablation of the papilla abolished the net secretion of potassium normally seen in perfused kidneys of potassium-adapted rats, thus underlining the importance of the papilla in the process of potassium adaptation.

Human cerebral osmolytes during chronic hyponatremia. A proton magnetic resonance spectroscopy study.

The pathogenesis of morbidity associated with hyponatremia is postulated to be determined by the state of intracellular cerebral osmolytes. Previously inaccessible, these metabolites can now be quantitated by proton magnetic resonance spectroscopy. An in vivo quantitative assay of osmolytes was performed in 12 chronic hyponatremic patients (mean serum sodium 120 meq/liter) and 10 normal controls. Short echo time proton magnetic resonance spectroscopy of occipital gray and parietal white matter locations revealed dramatic reduction in the concentrations of several metabolites. In gray matter, myo-inositol was most profoundly reduced at 49% of control value. Choline containing compounds were reduced 36%, creatine/phosphocreatine 19%, and N-acetylaspartate 11% from controls. Similar changes were found in white matter. Recovery of osmolyte concentrations was demonstrated in four patients studied 8-14 wk later. These results are consistent with a reversible osmolyte reduction under hypoosmolar stress in the intact human brain and offer novel suggestions for treatment and monitoring of this common clinical event.

Hypoxic encephalopathy after near-drowning studied by quantitative 1H-magnetic resonance spectroscopy.

Early prediction of outcome after global hypoxia of the brain requires accurate determination of the nature and extent of neurological injury and is cardinal for patient management. Cerebral metabolites of gray and white matter were determined sequentially after near-drowning using quantitative 1H nuclear magnetic resonance spectroscopy (MRS) in 16 children. Significant metabolite abnormalities were demonstrated in all patients compared with their age-matched normal controls. Severity of brain damage was quantified from metabolite concentrations and ratios. Loss of N-acetylaspartate, a putative neuronal marker, from gray matter preceded that observed in white matter and was more severe. Total creatine decreased, while lactate and glutamine/glutamate concentrations increased. Changes progressed with time after injury. A spectroscopic prognosis index distinguished between good outcome (n = 5) and poor outcome (n = 11) with one false negative (bad outcome after borderline MRS result) and no false positive results (100% specificity). The distinction was made with 90% sensitivity early (after 48 h) and became 100% later (by days 3 and 4). This compared with 50-75% specificity and 70-100% sensitivity based upon single clinical criteria. MRS performed sequentially in occipital gray matter provides useful objective information which can significantly enhance the ability to establish prognosis after near-drowning.

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.

Dietary fat modulation of murine mammary tumor metabolism studied by in vivo 31P-nuclear magnetic resonance spectroscopy.

The effect of dietary fat concentration and saturation on high energy phosphate metabolites and phospholipid turnover in transplanted line 168 murine mammary tumors was studied using surface coil 31P-nuclear magnetic resonance spectroscopy. Female BALB/c mice were fed one of five diets each containing at least the minimum of essential fatty acids (EFA). Four diets contained additional safflower or palm oil for a total fat concentration of 5 or 20% by weight. The growth rate of tumors from mice fed the high safflower oil diet was significantly greater than the growth rate of tumors for mice fed all other diets including the one which contained the minimal EFA. 31P-nuclear magnetic resonance-observable phosphate metabolite ratios. ATP/Pi, ATP/phosphomonoester (ATP/PME), and PME/Pi, and tumor pH of line 168 tumors decreased with increasing tumor volume, indicating a shift from active to inactive tumor metabolism. The rates of those decreases with progressive tumor growth differed significantly among tumors of mice fed the different diets. Decreases in ATP/Pi, ATP/PME, and pH were the most rapid in the tumors of mice fed the high safflower oil diet and significantly faster than tumors of mice fed the diet containing minimum EFA. In addition, the decrease in the PME/Pi ratio of tumors was significantly greater in mice fed the high fat (high palm oil and high safflower oil) diets than mice fed the diet containing the minimum of EFA. The rate of decline of ATP/Pi and ATP/PME with progressive tumor growth was directly correlated with levels of linoleic acid as well as total unsaturated fat. High levels of a polyunsaturated fat had a significant effect on mammary tumor metabolism particularly during early stages of tumor growth. Differences in high energy phosphate metabolite dynamics relative to dietary fat were present in tumors of equal volume. Thus, dietary fat influences on mammary tumorigenesis may be related to high energy phosphate metabolites.

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.

A 15N-NMR study of isolated brain in portacaval-shunted rats after acute hyperammonemia.

Acute hyperammonemia was induced by 15NH4+ infusion in portacaval-shunted (PCS) and control rats to investigate its effects on cerebral metabolism of glutamine, glutamate and gamma-aminobutyrate. Cerebral 15N-metabolites were observed by 15N-NMR spectroscopy in the ex vivo brain, removed in toto at the end of infusion. Key 15N-metabolites in the brain and liver were quantitated and their specific activities measured by NMR and biochemical assays in perchloric acid extracts of the freeze-clamped organs. In the ex vivo brain, [gamma-15N]glutamine, present at tissue concentrations of 3-5 mumol/g with 15N enrichment of 36-48%, was observable within 6-13 min of data acquisition. [alpha-15N]glutamine/glutamate, each present at 0.5-1 mumol/g (approx. 10% enrichment), were observed in 27 min. The results demonstrate the feasibility of observing these cerebral metabolites by 15N-NMR within a physiological time scale. In a rat pretreated with glutamine synthetase inhibitor, L-methionine DL-sulfoximine, cerebral [15N]gamma-aminobutyrate was observed after 910 min. In PCS rats, decreased 15NH4+ removal in the liver was accompanied by formation of approx. 2-fold higher concentration of cerebral [gamma-15N]glutamine relative to that in weight-matched controls. The result suggests that increased diffusion of blood-borne 15NH3 into the brain led to increased [gamma-15N]glutamine synthesis in astrocytes as well as ammonia-mediated inhibition of glutaminase.

Growth kinetics and treatment response of the intracerebral rat 9L brain tumor model: a quantitative in vivo study using magnetic resonance imaging.

We report the use of magnetic resonance imaging (MRI) for in situ tumor growth rate studies of experimental intracranial 9L tumors. T2-weighted spin-echo coronal magnetic resonance images of rat brains with 9L tumors were obtained every 2 days beginning at 8-11 days postimplantation using a 7 tesla MRI system. Tumors were clearly delineated in the images as a hyperintense region with a relatively well-demarcated border and minimal peritumoral edema. Tumor volumes from individual slices were summed together to yield the total tumor volume. The accuracy of this methodology for volumetric determination was verified by MRI phantom studies. Tumor growth rates determined from sequential MRI measurements of tumor volumes were quantitated in terms of volumetric doubling time. Tumor doubling times were found to range from 50 to 81 h, with an average of 66 +/- 8 h (n = 10). Intracranial 9L tumors were found to grow exponentially over the entire life span of the animal, allowing treated animals to serve as their own controls since the volumetric doubling time could be determined from three to four MRI scans before treatment administration. The intracerebral tumor growth delay following a single injection of 1, 3-bis(2-chloroethyl)-1-nitrosourea (13.3 mg/kg i.p.) allowed for noninvasive determination of in vivo log cell kill. A 2.0 +/- 0.2 (n = 3) log cell kill from 1,3-bis(2-chloroethyl)-1-nitrosourea treatment was found from post-treatment MRI volume measurements. These results demonstrate that MRI provides a powerful and sensitive method for assessing the growth and treatment response of intracranial 9L tumors in the rat.

Assessment of ganciclovir toxicity to experimental intracranial gliomas following recombinant adenoviral-mediated transfer of the herpes simplex virus thymidine kinase gene by magnetic resonance imaging and proton magnetic resonance spectroscopy.

Magnetic resonance imaging and in vivo localized H magnetic resonance spectroscopy were used to evaluate a gene therapy approach for treating experimental brain tumors. This approach involved the use of an adenoviral vector to transfer the herpes simplex virus thymidine kinase (HSVtk) gene into intracerebral 9L gliosarcomas in rats followed by systemic administration of the antiherpetic agent ganciclovir. Magnetic resonance imaging quantitation of changes in intracranial 9L tumor doubling times revealed a significant variation in therapeutic response. Localized H magnetic resonance spectra of 9L tumors treated with Ad.RSVtk/ganciclovir revealed a dramatic increase in the resonance intensity at 0.9-1.3 ppm, corresponding to mobile lipids and/or lactate. Changes in intracranial tumor doubling times correlated with changes in H tumor magnetic resonance spectra, suggesting that specific changes in tumor metabolite levels may be predictive of the effectiveness of this gene therapy approach.

Monitoring early response of experimental brain tumors to therapy using diffusion magnetic resonance imaging.

Quantitative magnetic resonance imaging was performed to evaluate water diffusion and relaxation times, T1 and T2, as potential therapeutic response indicators for brain tumors using the intracranial 9L brain tumor model. Measurements were localized to a column that intersected tumor and contralateral brain and were repeated at 2-day intervals before and following a single injection of 1,3-bis(2-chloroethyl)-1-nitrosourea (13.3 mg/kg). Tumor growth was measured using T2-weighted magnetic resonance imaging to determine the volumetric tumor doubling time (Td) before (Td = 64 +/- 13 h, mean +/- SD, n = 16) and after (Td = 75 +/- 9 h, n = 4) treatment during exponential regrowth. Apparent diffusion coefficient of untreated tumors was independent of tumor volume or growth time, whereas relaxation times increased during early tumor growth. Diffusion displayed the strongest treatment effect and increased before tumor regression by 55% 6-8 days following treatment. Changes in relaxation times were also significant with increases of 16% for T1 and 27% for T2. Diffusion and relaxation times returned to pretreatment levels by 12 days after treatment. Histological examination supports the model that the observed increase in diffusion reflects an increase of extracellular space following treatment. Furthermore, the subsequent apparent diffusion coefficient decrease is a result of viable tumor cells that repopulate this space at a rate dependent on the surviving tumor cell fraction and recurrent tumor doubling time. Serial tumor volume measurements allowed determination of log cell kill of 1.0 +/- 0.3 (n = 4). These results suggest that diffusion measurements are sensitive to therapy-induced changes in cellular structure and may provide an early noninvasive indicator of treatment efficacy.

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.

Enzyme/prodrug therapy for head and neck cancer using a catalytically superior cytosine deaminase.

The use of cytosine deaminase (CD) in conjunction with 5-fluorocytosine (5-FC) has been studied for cancer gene therapy as a means of achieving tumor-specific generation of the toxic metabolite 5-fluorouracil (5-FU). Since 5-FC is frequently used as an antifungal agent, and because it has little or no efficacy as an antibacterial agent, we hypothesized that yeast CD (YCD) might be more efficient at utilizing 5-FC as a substrate and hence be a better choice for a CD/5-FC gene therapy strategy than the typically utilized bacterial CD (BCD). To that end Saccharomyces cerevisiae CD was cloned from yeast genomic DNA and expressed in vitro. Functional analysis of BCD and YCD expressed in COS-1 cells indicated that BCD and YCD both utilized cytosine with equal efficacy; however, 5-FC was an extremely poor substrate for BCD, with an apparent catalytic efficiency 280-fold lower than that observed for YCD. Retroviral infection of tumor cell lines in vitro indicated that the IC50 of 5-FC was 30-fold lower in YCD-infected cultures as compared with cultures infected with BCD retrovirus. In addition, when SCCVII murine squamous cell carcinoma cells were infected in vitro at low rates of infection (< or =10%) there was no significant cytotoxicity toward BCD-expressing cells while there was potent cytotoxicity to both YCD-expressing cells and "bystander cells" even at this low level of expression. Finally, stable BCD- or YCD-expressing SCCVII clones were developed and used in an orthotopic immune-competent model of head and neck cancer. Subsequent treatment with 5-FC followed by monitoring of tumor growth by noninvasive magnetic resonance imaging (MRI) and survival of animals indicated a growth delay during the course of 5-FC treatment for BCD-expressing tumors, which quickly regrew at the end of treatment. In contrast, YCD-expressing tumors exhibited not only a growth delay, which was of longer duration, but also in some cases frank tumor regression and complete cures occurred.

Induction of cytotoxic oxidative stress by D-alanine in brain tumor cells expressing Rhodotorula gracilis D-amino acid oxidase: a cancer gene therapy strategy.

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) generated in the stereoselective deamination of D-amino acids catalyzed by D-amino acid oxidase (DAAO). H2O2 readily crosses cellular membranes and damages DNA, proteins, and lipids. The scarcity of DAAO substrates in mammalian organisms and its co-localization with catalase in the peroxisomal matrix suggested that the cytotoxicity of ROS could be harnessed by administration of D-amino acids to tumor cells ectopically expressing DAAO in the cytoplasm. To evaluate this hypothesis, the cDNA encoding the highly active DAAO from the red yeast Rhodotorula gracilis was mutated to remove the carboxy-terminal peroxisomal targeting sequence. A clonal line of 9L glioma cells stably transfected with this construct (9Ldaao17) was found to synthesize active R. gracilis DAAO. Exposure of 9Ldaao17 cells to D-alanine resulted in cytotoxicity at concentrations that were nontoxic to parental 9L cells. Depletion of cellular glutathione further sensitized 9Ldaao17 cells to D-alanine (D-Ala). This result, combined with stimulation of pentose phosphate pathway activity and the production of extracellular H2O2 by 9Ldaao17 cells incubated with D-alanine implicates oxidative stress as the mediator of cytotoxicity. These results demonstrate that expression of R. gracilis DAAO in tumor cells confers chemosensitivity to D-alanine that could be exploited as a novel cancer gene therapy paradigm.

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.

Applications of magnetic resonance in model systems: cancer therapeutics.

The lack of information regarding the metabolism and pathophysiology of individual tumors limits, in part, both the development of new anti-cancer therapies and the optimal implementation of currently available treatments. Magnetic resonance [MR, including magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and electron paramagnetic resonance (EPR)] provides a powerful tool to assess many aspects of tumor metabolism and pathophysiology. Moreover, since this information can be obtained nondestructively, pre-clinical results from cellular or animal models are often easily translated into the clinic. This review presents selected examples of how MR has been used to identify metabolic changes associated with apoptosis, detect therapeutic response prior to a change in tumor volume, optimize the combination of metabolic inhibitors with chemotherapy and/or radiation, characterize and exploit the influence of tumor pH on the effectiveness of chemotherapy, characterize tumor reoxygenation and the effects of modifiers of tumor oxygenation in individual tumors, image transgene expression and assess the efficacy of gene therapy. These examples provide an overview of several of the areas in which cellular and animal model studies using MR have contributed to our understanding of the effects of treatment on tumor metabolism and pathophysiology and the importance of tumor metabolism and pathophysiology as determinants of therapeutic response.

Quantitative proton-decoupled 31P MRS and 1H MRS in the evaluation of Huntington's and Parkinson's diseases.

OBJECTIVE: To determine cerebral energy status in patients with Huntington's disease (HD) and Parkinson's disease (PD). METHODS: The study included 15 patients with DNA-proven, symptomatic HD and five patients with medically treated, idiopathic PD, all of whom were candidates for neurotransplant treatment, as well as 20 age-related normal subjects. Quantitative noninvasive, MRI-guided proton MRS was performed of single volumes in putamen of basal ganglia (BG), occipital gray matter, and posterior parietal white matter; in addition, quantitative phosphorus and proton-decoupled phosphorus MRS of superior biparietal white and gray matter was done. Outcome measures were quantitative metabolite ratios and millimolar concentrations of neuronal and glial markers, creatine (Cr) and adenosine triphosphate (ATP), and intracellular pH. RESULTS: In volume-corrected control BG (10.46 +/- 0.37 mM), [Cr] was 29% (p < 0.05) higher than in control gray matter (8.10 +/- 1.04 mM). In HD and PD, energy metabolism was not abnormal in the four cerebral locations measured by MRS. No increase in cerebral lactate or decrease in phosphocreatine and ATP was detected. Small, systematic abnormalities in N-acetylaspartate (NAA, decreased), Cr (decreased), choline-containing compounds (Cho, increased), and myoinositol (mI, increased) were demonstrable in all patient's individually and in summed spectra but were insufficient to make diagnosis possible in the individual patient. CONCLUSION: Previously described failure of global energy metabolism in HD was not confirmed. However, quantitative 1-hydrogen MRS and decoupled 31-phosphorus MRS are sensitive to +/-10% alterations in key cerebral metabolites, and may be of value in noninvasive monitoring of appropriate therapies.

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.

Enhancement of hyperthermia effect in vivo by amiloride and DIDS.

PURPOSE: Intracellular pH is regulated mainly by Na+/H+ antiport and Cl-/HCO3- exchange through the cell membrane. Amiloride (3,5-diamino-6-chloro-N-(diaminomethylene)pyrazine carboxamide) is a diuretic drug that blocks Na+/H+ antiport and DIDS (4,4-diisothiocyanatostilbene-2,2'-disulfonic acid) is an inhibitor of Cl-/HCO3- exchange. We investigated the potency of these drugs to lower pHi and increase the thermosensitivity of tumors in vivo. MATERIALS AND METHODS: The cytocidal effect of heat in combination with drug effect in vivo was studied using the in vivo-in vitro clonogenic assay method and the tumor growth delay method with SCK tumors, a mammary adenocarcinoma, on the hind limbs of A/J mice. The effects of amiloride and DIDS on tumor pHi and high energy phosphate levels were investigated using 31P-NMR. RESULTS: We observed that amiloride or DIDS alone increased the effect of hyperthermia at 42.5 degrees C or 43.5 degrees C to suppress tumor growth. The thermosensitization was greater when the two drugs were combined. For example, hyperthermia at 43.5 degrees C alone resulted in a tumor growth delay of about 4 days. When 10 mg/kg amiloride or 25 mg/kg DIDS was injected prior to heating, the growth delay increased to about 6 days. When both drugs were injected prior to heating, a total growth delay of 8 days was obtained. In vivo-in vitro excision assays for cell survival demonstrated that these drugs enhanced the heat-induced tumor cell death. An i.p. injection of 10 mg/kg amiloride plus 25 mg/kg DIDS did not lower the tumor pHi over a 120 min interval. Heating the tumors at 42.5 degrees C for 1 hr significantly lowered the pHi and when the tumor-bearing mice were injected i.p with amiloride and DIDS, and the tumors were heated 1 hr later, the drop in pHi was greater relative to that by heating alone. Heating alone significantly lowered the tumor energy levels as indicated by PCr/Pi and beta-ATP/Pi ratios and an i.p. injection of 25 mg/kg amiloride prior to heating further reduced the energy status in the tumors. CONCLUSION: Amiloride or its analogs and DIDS may be useful in increasing the therapeutic efficacy of hyperthermia treatments by enhancing the reduction in tumor pHi.