A novel in vivo tumor oxygen profiling assay: Combining functional and molecular imaging with multivariate mathematical modeling

Purpose: The objective of this study is to develop and test a novel high spatio-temporal in vivo assay to quantify tumor oxygenation and hypoxia. The assay implements a biophysical model of oxygen transport to fuse parameters acquired from in vivo functional and molecular imaging modalities. ^ Introduction: Tumor hypoxia plays an important role in carcinogenesis. It triggers pathological angiogenesis to supply more oxygen to the tumor cells and promotes cancer cell metastasis. Preclinical and clinical evidence show that anti-angiogenic treatment is capable of normalizing the tumor vasculature both structurally and functionally. The resulting normalized vasculature provides a more efficient and uniform microcirculation that enhances oxygen and drug delivery to the tumor cells and improves second-line treatments such as traditional radiation or chemotherapy. Early studies using the overall or average tumor hypoxia as a prognostic biomarker of anti-angiogenic therapy efficacy was ambivalent; however, recent studies have discovered that the etiology of hypoxia and its heterogeneity could be used as reliable prognostic biomarkers. The capability to longitudinally map tumor hypoxia with high spatial and temporal resolution has the potential to enhance fundamental cancer research and ultimately cancer patient care. ^ Method: A novel methodology to identify and characterize tumor hypoxia by fusing the physiological hemodynamic parametric maps obtained from functional and molecular imaging modalities and technique using a modified Krogh model of oxygen transport (MPO2) was developed. First, simulations studies were performed to validate this technique. Microscopy data of tumor and brain tissue (control) provided both the vasculature and rheology data. A Green\u27s function algorithm was used to solve the ordinary differential equation and calculate the oxygen profile at a microscopic scale (15 μm) (GPO2), which was used as a reference. From this data, simulated physiological maps (perfusion, fractional plasma volume, fractional interstitial volume) and hemoglobin status (oxygen saturation, hemoglobin concentration) was used as input to MPO2 and used to calculate pO2 levels as a function of scanner spatial resolution and noise. Second, MPO2 was compared to pO2 measurements in xenograft breast tumors using OxyLite oxygen sensor as a Gold Standard, where DCE-CT and PCT-S images were acquired to obtain hemodynamic images. Finally, the vascular physiology measurements obtained from an anti-angiogenic therapeutic study in pancreatic tumors was applied to MPO2 and compared to therapeutic response. ^ Results: The simulation results using Green\u27s function pO2 as standard showed that the MPO2 model performance was dependent on the spatial resolution (voxel size) of the images. Sensitivity and error analysis of this model were also investigated in this study. These oxygen transport simulations results suggest the oxygen saturation and hemoglobin concentration were two key factors in tissue oxygenation, and concomitant with blood perfusion and tumor metabolic rate. Comparisons of the pO2 profile obtained from MPO2 and OxyLite probe in MCF7 tumor model demonstrated a significant correlation and approached a slope of one (after accounting for a few outliers). Simulation studies implementing the physiological data obtained from the anti-angiogenic therapeutic study in pancreatic tumors using the MPO2 model agreed with the experimental findings that blood perfusion is a valuable prognostic biomarker in therapeutic efficacy. This model also predicted the oxygenation improvement difference from two vascular renormalization modes (topological normalization and geometrical normalization). ^ Conclusion: The results from the simulation and in vivo studies demonstrated the feasibility of this novel hypoxia assay. Simulation results of the pancreatic tumors provide an example of the impact the MPO2 model in conjunction with imaging can provide when evaluating the therapeutic significance of various normalization modes in anti-angiogenic therapy, and suggests potential approaches to further improve anti-angiogenic therapy efficacy

Using Computed Tomography Perfusion to Evaluate the Blood-Brain-Barrier and Blood-Tumor-Barrier Response following Focused Ultrasound Sonication with Microbubble Administration

The blood-brain-barrier (BBB) is the single most limiting factor in the delivery of neurotherapeutics into the brain. Focused ultrasound sonication combined with intravenous microbubble administration (FUSwMB) is a novel technique that can transiently disrupt the BBB, with minimal vascular or tissue damage, allowing for localized drug delivery over the targeted region. The goals of this thesis are to: 1) use computed tomography (CT) perfusion to measure the permeability surface area product (PS) following USwMB in normal rabbits with an intact BBB, and 2) to evaluate the blood-tumor-barrier (BTB) PS response following FUSwMB in a C6 rat glioma model

The Skeletal Muscle Microvasculature and Its Effects on Metabolism

Skeletal muscle is a major metabolic organ that plays a critical role in regulating glucose homeostasis and lipid utilization. Impaired muscle metabolic response is evident in diseases such as diabetes, obesity and cardiovascular diseases, and is also often associated with microvascular dysfunction. Here, we investigate the changes that can occur in the muscle microvasculature and the profound impact they can have on metabolism

MRI in Cancer: Improving Methodology for Measuring Vascular Properties and Assessing Radiation Treatment Effects in Brain

Tumors cannot survive, progress and metastasize without recruiting new blood vessels. Vascular properties, including perfusion and permeability, provide valuable information for characterizing cancers and assessing therapeutic outcomes. Dynamic contrast-enhanced (DCE) MRI is a non-invasive imaging technique that affords quantitative parameters describing the underlying vascular structure of tissue. To date, the clinical application of DCE-MRI has been hampered by the lack of standardized and validated quantitative modeling approaches for data analysis. From a therapeutic perspective, radiation therapy is a central component of the standard treatment for patients with cancer. Besides killing cancer cells, radiation also induces parenchymal and stromal changes in normal tissue, limiting radiation dose and complicating treatment response evaluation. Further, emerging evidence suggest that the radiation-modulated tumor microenvironment may also contribute to the enhanced tumor regrowth and resistance to therapy. Given these clinical problems, the objectives of this dissertation were to: i) improve the DCE MRI-based measurements of vascular properties; and ii) assess the radiation treatment effects on normal tissue (parenchyma) and the interaction between radiation-modulated parenchyma and tumor growth. For the first goal, Bayesian probability theory-based model selection was employed to evaluate four commonly employed DCE-MRI tracer kinetic models against both in silico DCE-MRI data and high-quality clinical data collected from patients with advanced-staged cervical cancer. Further, a constrained local arterial input function (cL-AIF) modeling approach was developed to improve the pharmacokinetic analysis of DCE-MRI data. For the second goal, a novel mouse model of radiation-mediated effects on normal brain was developed. The efficacy of anti-vascular endothelial growth factor (VEGF) antibody treatment of delayed, radiation-induced necrosis (RN) was evaluated. Also, the effects of radiation-modulated brain parenchyma on glioblastoma cell growth were studied. It was found that 1) complex DCE-MRI signal models are more sensitive to noise than simpler models with respect to parameter estimation accuracy and precision. Caution is thus advised when considering application of complex DCE-MRI kinetic models. It follows that data-driven model selection is an important prerequisite to DCE-MRI data analysis; 2) the proposed cL-AIF method, which estimates an unique local-AIF amplitude and arrival time for each voxel within the tissue of interest, provides better measurements vascular properties than the conventional approach employing a single, remotely measured AIF; 3) anti-VEGF antibody decreased MR-derived RN lesion volumes, while large areas of focal calcification formed and the expression of VEGF remained high post-treatment. More effective therapeutic strategies for RN are still needed; 4) the radiation-modulated brain parenchyma promotes aggressive, infiltrative glioma growth. The histologic features of such tumors are consistent with those commonly observed in recurrent high-grade tumors in patients. These findings afford new insights into the highly aggressive tumor regrowth patterns observed following radiotherapy

Intravital Multiphoton Microscopy Analysis of Spatial Relationships in Murine Skull Bone Marrow

The BM is a key organ of hematopoiesis and also has an important role in the immune system. The BM microenvironment is a complex, highly vascularized 3D structure composed of different cell types and extracellular matrix. Intense cellular traffic takes place from the peripheral blood to the BM and vice versa. However, the precise arrangement and microscopic dimensions of this environment have only been inferred so far from static imaging of sectioned tissue. We developed a new model to characterize and analyze the 3D microanatomy of murine skull BM in its physiological state using intravital MPM. This technology offers deep tissue penetration, low phototoxicity, superior image contrast and 3D resolution compared to other microscopy techniques. This makes MPM a powerful tool to investigate the BM, overcoming its anatomic inaccessibility. To quantify the dimensions of the BM compartment, we used high molecular weight FITC-dextran and Rhodamine 6G, which delineated the intra- and extravascular space, respectively. Measurements were generated using the 3D visualization and measurement software VoxBlast 3.1 after using a thresholding technique carried out by Adobe Photoshop 6.0. Results were expressed as the ratio of intravascular to extravascular space for different microvascular segments. Moreover, we performed adoptive transfer experiments with isolated naïve B-cells and TCM and studied their location within the BM compartment. The new approach presented here will be a useful tool for further in vivo investigations of cell behavior, trafficking and interactions in the BM

Hemodynamics

Hemodynamics is study of the mechanical and physiologic properties controlling blood pressure and flow through the body. The factors influencing hemodynamics are complex and extensive. In addition to systemic hemodynamic alterations, microvascular alterations are frequently observed in critically ill patients. The book "Hemodynamics: New Diagnostic and Therapeuric Approaches" is formed to present the up-to-date research under the scope of hemodynamics by scientists from different backgrounds

Magnetic Resonance imaging Assessment of Tumor Microvessels and Response to Antiangiogenesis Therapy

Magnetic resonance Imaging (MRI) is a diagnostic modality with high inherent contrast resolution and multiplanar imaging capability. Advances in MR technology and image processing have increased the utility and availability of this technique in the past two decades. MRI has become one of the leading modalities in current diagnostic imaging, combining soft tissue contrast with high anatomic and temporal resolution. MRI is now a widely employed diagnostic method for the clinical evaluation of tumors. One of the most recent applications of MRI is the investigation of angiogenesis using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). DCE-MRI represents the acquisition of serial MR images before, during, and after the administration of an intravenous contrast agent. The use of contrast enhancement in conjunction with magnetic resonance imaging provides a means to evaluate tissue function, as well as morphology. Tissue blood volume, blood flow, perfusion and capillary permeability represent indicators of the status of the vasculature that can be investigated with DCE-MRI. Use of such quantitation potentially allows tumors to be characterized in terms of pathophysiology and to be monitored over time, during the course of therapeutic interventions. The understanding of the angiogenesis process and the evaluation of new drugs that inhibit or stimulate angiogenesis are directly related to the development of an imaging assay of angiogenic activity. This method should provide functionally relevant and quantitative images, should be high in spatial resolution, should sample the entire tumor and could be repeated at frequent intervals. DCE-MRI has grown in importance with the development of antiangiogenic and neoadjuvant strategies for tumor therapy. Dedicated software makes it possible to interpret imaging pharmacokinetics and aid the assessment of physiological parameters such as capillary permeability and tissue perfusion. For instance, the permeability of functional tumor microvessels can be assessed noninvasively by dynamic MRI of contrast agent uptake in the tumor tissue (1-4). The analysis of contrast kinetics can be applied to differentiate between a malignant and a benign lesion and to determine whether a tumor is responding to treatment (5). It has been demonstrated that the permeability of blood vessels correlates with the ability of the tumor to metastasize, and with its response to treatment (6, 7). Thus, information concerning the status of vascular permeability might help assessing the metastatic potential of tumors and predict the sensitivity to chemotherapy or to antiangiogenic treatment