Dawen Zhao

Tumor oximetry: demonstration of an enhanced dynamic mapping procedure using fluorine-19 echo planar magnetic resonance imaging in the Dunning prostate R3327-AT1 rat tumor

PURPOSE We have developed an enhanced approach to measuring regional oxygen tension (pO(2)) dynamics in tumors. The technique is demonstrated in a group of 8 Dunning prostate rat tumors (R3327-AT1) with respect to respiratory challenge. METHODS AND MATERIALS Hexafluorobenzene was injected directly into the tumors of anesthetized rats. (19)F nuclear magnetic resonance echo planar imaging relaxometry was performed to obtain maps of regional tumor oxygenation under baseline conditions and when the inhaled gas was changed to oxygen or carbogen. RESULTS Sequential pO(2) maps required 8 min, with a typical precision of 1-3 torr at 30-100 individual regions across a tumor. When rats breathed 33% oxygen, distinct heterogeneity was observed for baseline oxygenation in each tumor with pO(2) values ranging from hypoxic to greater than 100 torr. Larger tumors showed significantly lower baseline pO(2). Respiratory challenge with oxygen or carbogen produced significant increases in tumor oxygenation with a close correlation between the response to each gas at individual locations. Regions of both small and large tumors responded to respiratory challenge, but the rate was generally much faster in initially well-oxygenated regions. CONCLUSIONS Regional pO(2) was assessed quantitatively and the response of multiple individual tumor regions observed simultaneously with respect to interventions.

Measuring Changes in Tumor Oxygenation

Publisher Summary This chapter discusses the measurement of changes in tumor oxygenation. The oxygen pressure determinations could be of great clinical value and they are also vital to many laboratory investigations of new drugs and studies of tumor development. Blood oxygen level dependent (BOLD) contrast proton nuclear magnetic resonance (NMR) facilitates rapid interrogation of vascular oxygenation, and is particularly appropriate for examining dynamic responses to interventions. Both spectroscopic and imaging approaches have been applied to tissue oxygen pressure measurements depending on the available signal to noise. It appears that uptake and distribution efficiency vary with tumor type, but in general, maximum signal is detected from the tumor periphery corresponding with regions of greater perfusion. The various aspects of fluorocarbon relaxometry using echo planar imaging for dynamic oxygen mapping (FREDOM) are elaborated. The results suggested FREDOM as a valuable tool for assessing the dynamic time course of interventions to provide clear insight into the mode of action of therapeutic approaches and aid in the high-throughput screening of new drugs, such as vascular targeting and antiangiogenic agents.

Vascular imaging of solid tumors in rats with a radioactive arsenic-labeled antibody that binds exposed phosphatidylserine.

Purpose: We recently reported that anionic phospholipids, principally phosphatidylserine, become exposed on the external surface of vascular endothelial cells in tumors, probably in response to oxidative stresses present in the tumor microenvironment. In the present study, we tested the hypothesis that a chimeric monoclonal antibody that binds phosphatidylserine could be labeled with radioactive arsenic isotopes and used for molecular imaging of solid tumors in rats. Experimental Design: Bavituximab was labeled with 74As (β+, T1/2 17.8 days) or 77As (β−, T1/2 1.6 days) using a novel procedure. The radionuclides of arsenic were selected because their long half-lives are consistent with the long biological half lives of antibodies in vivo and because their chemistry permits stable attachment to antibodies. The radiolabeled antibodies were tested for the ability to image subcutaneous Dunning prostate R3227-AT1 tumors in rats. Results: Clear images of the tumors were obtained using planar γ-scintigraphy and positron emission tomography. Biodistribution studies confirmed the specific localization of bavituximab to the tumors. The tumor-to-liver ratio 72 h after injection was 22 for bavituximab compared with 1.5 for an isotype-matched control chimeric antibody of irrelevant specificity. Immunohistochemical studies showed that the bavituximab was labeling the tumor vascular endothelium. Conclusions: These results show that radioarsenic-labeled bavituximab has potential as a new tool for imaging the vasculature of solid tumors.

Comparison of 1H blood oxygen level-dependent (BOLD) and 19F MRI to investigate tumor oxygenation.

Fluorine‐19 [19F] MRI oximetry and 1H blood oxygen level–dependent (BOLD) MRI were used to investigate tumor oxygenation in rat breast 13762NF carcinomas, and correlations between the techniques were examined. A range of tissue oxygen partial pressure (pO2) values was found in the nine tumors while the anesthetized rats breathed air, with individual tumor pO2 ranging from a mean of 1 to 36 torr and hypoxic fraction (HF10) (<10 torr) ranging from 0% to 75%, indicating a large intra‐ and intertumor heterogeneity. Breathing oxygen produced significant increase in tumor pO2 (mean ΔpO2 = 50 torr) and decrease in HF10 (P < 0.01). 1H BOLD MRI observed using a spin echo‐planar imaging (EPI) sequence revealed a heterogeneous response and significant increase in mean tumor signal intensity (SI) (ΔSI = 7%, P < 0.01). R  2* measured by multigradient‐echo (MGRE) MRI decreased significantly in response to oxygen (mean ΔR  2* = −4 s−1; P < 0.05). A significant correlation was found between changes in mean tumor pO2 and mean EPI BOLD ΔSI accompanying oxygen breathing (r2 > 0.7, P < 0.001). Our results suggest that BOLD MRI provides information about tumor oxygenation and may be useful to predict pO2 changes accompanying interventions. Significantly, the magnitude of the BOLD response appears to be predictive for residual tumor HFs. Magn Reson Med, 2009.

A perspective on vascular disrupting agents that interact with tubulin: preclinical tumor imaging and biological assessment

The tumor microenvironment provides a rich source of potential targets for selective therapeutic intervention with properly designed anticancer agents. Significant physiological differences exist between the microvessels that nourish tumors and those that supply healthy tissue. Selective drug-mediated damage of these tortuous and chaotic microvessels starves a tumor of necessary nutrients and oxygen and eventually leads to massive tumor necrosis. Vascular targeting strategies in oncology are divided into two separate groups: angiogenesis inhibiting agents (AIAs) and vascular disrupting agents (VDAs). The mechanisms of action between these two classes of compounds are profoundly distinct. The AIAs inhibit the actual formation of new vessels, while the VDAs damage and/or destroy existing tumor vasculature. One subset of small-molecule VDAs functions by inhibiting the assembly of tubulin into microtubules, thus causing morphology changes to the endothelial cells lining the tumor vasculature, triggered by a cascade of cell signaling events. Ultimately this results in catastrophic damage to the vessels feeding the tumor. The rapid emergence and subsequent development of the VDA field over the past decade has led to the establishment of a synergistic combination of preclinical state-of-the-art tumor imaging and biological evaluation strategies that are often indicative of future clinical efficacy for a given VDA. This review focuses on an integration of the appropriate biochemical and biological tools necessary to assess (preclinically) new small-molecule, tubulin active VDAs for their potential to be clinically effective anticancer agents.

Correlations of noninvasive BOLD and TOLD MRI with pO2 and relevance to tumor radiation response

To examine the potential use of blood oxygenation level dependent (BOLD) and tissue oxygenation level dependent (TOLD) contrast MRI to assess tumor oxygenation and predict radiation response.

Interplay of tumor vascular oxygenation and tumor pO2 observed using near-infrared spectroscopy, an oxygen needle electrode, and 19F MR pO2 mapping

This study investigates the correlation of tumor blood oxygenation and tumor pO(2) with respect to carbogen inhalation. After having refined and validated the algorithms for calculating hemoglobin concentrations, we used near-infrared spectroscopy (NIRS) to measure changes of oxygenated hemoglobin concentration (delta[HbO(2)]) and used an oxygen needle electrode and (19)F MRI for pO(2) measurements in tumors. The measurements were taken from Dunning prostate R3327 tumors implanted in rats, while the anesthetized rats breathed air or carbogen. The NIRS results from tumor measurements showed significant changes in tumor vascular oxygenation in response to carbogen inhalation, while the pO(2) electrode results showed an apparent heterogeneity for tumor pO(2) response to carbogen inhalation, which was also confirmed by (19)F MR pO(2) mapping. Furthermore, we developed algorithms to estimate hemoglobin oxygen saturation, sO(2), during gas intervention based on the measured values of delta[HbO(2)] and pO(2). The algorithms have been validated through a tissue-simulating phantom and used to estimate the values of sO(2) in the animal tumor measurement based on the NIRS and global mean pO(2) values. This study demonstrates that the NIRS technology can provide an efficient, real-time, noninvasive approach to monitoring tumor physiology and is complementary to other techniques, while it also demonstrates the need for an NIR imaging technique to study spatial heterogeneity of tumor vasculature under therapeutic interventions.

The Receptor Interacting Protein 1 Inhibits p53 Induction through NF-κB Activation and Confers a Worse Prognosis in Glioblastoma

Nuclear factor-kappaB (NF-kappaB) activation may play an important role in the pathogenesis of cancer and also in resistance to treatment. Inactivation of the p53 tumor suppressor is a key component of the multistep evolution of most cancers. Links between the NF-kappaB and p53 pathways are under intense investigation. In this study, we show that the receptor interacting protein 1 (RIP1), a central component of the NF-kappaB signaling network, negatively regulates p53 tumor suppressor signaling. Loss of RIP1 from cells results in augmented induction of p53 in response to DNA damage, whereas increased RIP1 level leads to a complete shutdown of DNA damage-induced p53 induction by enhancing levels of cellular mdm2. The key signal generated by RIP1 to up-regulate mdm2 and inhibit p53 is activation of NF-kappaB. The clinical implication of this finding is shown in glioblastoma, the most common primary malignant brain tumor in adults. We show that RIP1 is commonly overexpressed in glioblastoma, but not in grades II and III glioma, and increased expression of RIP1 confers a worse prognosis in glioblastoma. Importantly, RIP1 levels correlate strongly with mdm2 levels in glioblastoma. Our results show a key interaction between the NF-kappaB and p53 pathways that may have implications for the targeted treatment of glioblastoma.

Antivascular effects of combretastatin A4 phosphate in breast cancer xenograft assessed using dynamic bioluminescence imaging and confirmed by MRI

Bioluminescence imaging (BLI) has found significant use in evaluating long‐term cancer therapy in small animals. We have now tested the feasibility of using BLI to assess acute effects of the vascular disrupting agent combretastatin A4 phosphate (CA4P) on luciferase‐expressing MDA‐MB‐231 human breast tumor cells growing as xenografts in mice. Following administration of luciferin substrate, there is a rapid increase in light emission reaching a maximum after about 6 min, which gradually decreases over the following 20 min. The kinetics of light emission are highly reproducible;however, following i.p. administration of CA4P (120 mg/kg), the detected light emission was decreased between 50 and 90%, and time to maximum was significantly delayed. Twenty‐four hours later, there was some recovery of light emission following further administration of luciferin substrate. Comparison with dynamic contrast‐enhanced MRI based on the paramagnetic contrast agent Omniscan showed comparable changes in the tumors consistent with the previous literature. Histology also confirmed shutdown of tumor vascular perfusion. We believe this finding provides an important novel application for BLI that could have widespread application in screening novel therapeutics expected to cause acute vascular changes in tumors.—Zhao, D., Richer, E., Antich, P. P., Mason, R. P. Antivascular effects of combretastatin A4 phosphate in breast cancer xenograft assessed using dynamic bioluminescence imaging and confirmed by MRI. FASEB J. 22, 2445–2451 (2008)

Correlation of tumor oxygen dynamics with radiation response of the Dunning prostate R3327-HI tumor

Abstract Zhao, D., Constantinescu, A., Chang, C. H., Hahn, E. W. and Mason, R. P. Correlation of Tumor Oxygen Dynamics with Radiation Response of the Dunning Prostate R3327-HI Tumor. Radiat. Res. 159, 621–631 (2003). Our previous studies have shown that oxygen inhalation significantly reduces tumor hypoxia in the moderately well-differentiated HI subline of the Dunning prostate R3327 rat carcinoma. To test our hypothesis that modifying hypoxia could improve the radiosensitivity of these tumors, we performed experimental radiotherapy to compare the tumor response to ionizing radiation alone or in combination with oxygen inhalation. Tumor pO2 measurements were performed on size-selected tumors several hours before radiotherapy using 19F nuclear magnetic resonance echo planar imaging relaxometry (FREDOM) of the reporter molecule hexafluorobenzene. In common with our previous findings, the larger tumors (>3.5 cm3) exhibited greater hypoxia than the smaller tumors (<2 cm3; P < 0.001), and oxygen inhalation reduced the hypoxic fraction (<10 Torr): In the larger tumors, hypoxic fraction dropped significantly from a mean baseline value of 80% to 17% (P < 0.001). The effect of oxygen administered 30 min before and during irradiation on tumor response to a single 30-Gy dose of photons was evaluated by growth delay. For the smaller tumors, no difference in growth delay was found when treatment was given with or without oxygen breathing. By contrast, breathing oxygen before and during irradiation significantly enhanced the growth delay in the larger tumors (additional 51 days). The differential behavior may be attributed to the low baseline hypoxic fraction (<10 Torr) in small tumors (20%) as a target for oxygen inhalation. There was a strong correlation between the estimated initial pO2 value and the radiation-induced tumor growth delay (R > 0.8). Our histological studies showed a good match between the perfused vessels marked by Hoechst 33342 dye and the total vessels immunostained by anti-CD31 and indicated extensive perfusion in this tumor line. In summary, the present results suggest that the ability to detect modulation of tumor pO2, in particular, the residual hypoxic fraction, with respect to an intervention, could have prognostic value for predicting the efficacy of radiotherapy.