Rachel Schafer

Multi-modality imaging of a murine mammary window chamber for breast cancer research

Window chamber models have been developed and utilized as a means to study the complex microenvironment in which cancers develop, proliferate, and metastasize in small animals. Here we utilize rapid prototyping printer technology to construct a new plastic orthotopic mammary window chamber that is compatible with magnetic resonance imaging, nuclear imaging, and optical imaging. Optical imaging allows for high-resolution cellular and molecular level analysis of tissues; magnetic resonance imaging provides quantitative measures of tumor size, perfusion, diffusion, fat/water content relaxation parameters; and a nuclear imaging technique, called the Beta Imager, supports functional and metabolic imaging. Our demonstration of the multiple imaging capabilities of this model suggests that it can be used as a powerful platform for studying basic cancer biology and developing new cancer therapies.

Dynamic oxygenation measurements using a phosphorescent coating within a mammary window chamber mouse model

Phosphorescent lifetime imaging was employed to measure the spatial and temporal distribution of oxygen partial pressure in tissue under the coverslip of a mammary window chamber breast cancer mouse model. A thin platinum-porphyrin coating, whose phosphorescent lifetime varies monotonically with oxygen partial pressure, was applied to the coverslip surface. Dynamic temporal responses to induced modulations in oxygenation levels were measured using this approach.

Measuring oxygen tension modulation, induced by a new pre-radiotherapy therapeutic, in a mammary window chamber mouse model

Tumor regions under hypoxic or low oxygen conditions respond less effectively to many treatment strategies, including radiation therapy. A novel investigational therapeutic, NVX-108 (NuvOx Pharma), has been developed to increase delivery of oxygen through the use of a nano-emulsion of dodecofluoropentane. By raising pO2 levels prior to delivering radiation, treatment efficacy may be improved. To aid in evaluating the novel drug, oxygen tension was quantitatively measured, spatially and temporally, to record the effect of administrating NVX-108 in an orthotopic mammary window chamber mouse model of breast cancer. The oxygen tension was measured through the use of an oxygen-sensitive coating, comprised of phosphorescent platinum porphyrin dye embedded in a polystyrene matrix. The coating, applied to the surface of the coverslip of the window chamber through spin coating, is placed in contact with the mammary fat pad to record the oxygenation status of the surface tissue layer. Prior to implantation of the window chamber, a tumor is grown in the SCID mouse model by injection of MCF-7 cells into the mammary fat pad. Two-dimensional spatial distributions of the pO2 levels were obtained through conversion of measured maps of phosphorescent lifetime. The resulting information on the spatial and temporal variation of the induced oxygen modulation could provide valuable insight into the optimal timing between administration of NVX-108 and radiation treatment to provide the most effective treatment outcome.

In-vivo measurements of oxy- and deoxyhemoglobin levels in breast cancer xenografts in a mammary window chamber model

Cancer cells are characterized by adaptive features that allow them to evade apoptosis and proliferate in an unchecked manner in the host tissue. Therapeutic strategies often involve targeting those adaptive molecular pathways leading to downstream effects such as changes in perfusion, metabolic rate, and/or oxygen utilization in the malignant tissue. Such surrogate biomarkers can be used to monitor therapeutic response, optimize treatment protocols, or assist in development of new therapeutic approaches. In this study, we present an optical methodology to make in vivo measurements of oxygen saturation as a surrogate biomarker in breast cancer xenografts within a mouse mammary window chamber (MWC) model. By using multi-spectral measurements of the reflectance off the tissue under the coverslip of the window chamber, we are able to obtain high resolution maps of the variation of oxygenation levels of the tissue, which allow continuous tracking of the level of tissue oxygenation during tumor growth and following treatment. The MWC, which was designed and fabricated in-house, is compatible with multiple imaging modalities such as MRI and high resolution intravital microscopy, providing the capability for cross validation of oxygenation measurements on multiple imaging platforms.

Nuclear, optical, and magnetic resonance imaging in a mouse mammary window chamber model

An orthotopic mouse mammary window chamber (MWC) model has been developed for multimodal in-vivo functional and anatomical imaging of breast cancer xenografts. Capabilities to image numerous physiological aspects of the same tumor microenvironment over time has important applications such as in experiments studying the efficacies of therapeutic interventions, improvement of cancer detection and investigating basic cancer biology. The compatibility of this MWC model with optical, nuclear and magnetic resonance imaging (MRI) makes it possible to perform a multitude of studies ranging from cellular imaging to whole body imaging. Thus, the MWC represents a powerful tool for breast cancer research. Here, two imaging applications are highlighted, namely the nuclear imaging of glycolytic metabolism with 18FFDG and MRI of tissue perfusion. Nuclear imaging is performed with the use of a 3μm thin phosphor scintillator placed directly in contact with the tissue and visible light from the scintillation is directly detected in a low noise, light tight imaging system. Tissue perfusion is imaged either qualitatively with a dynamic contrast enhancement (DCE) MRI technique or quantitatively with an arterial spin labeling flow-sensitive alternating inversion recovery-rapid acquisition with relaxation enhancement (FAIR-RARE) technique.

Measurement of Tumor Environment Oxygen Levels within a Mammary Window Chamber Mouse Model

Phosphorescent lifetime imaging of a platinum-porphyrin based coating was implemented within a mammary window chamber mouse model, allowing for spatial and temporal measurements of the partial pressure of oxygen in a breast cancer tumor environment.

Multi-Modality Imaging in a Mammary Window Chamber Mouse Model

A mammary window chamber model, compatible with optical, MRI and nuclear techniques, has been developed that allows multiple imaging modalities to be employed in a single animal study and comparison of results between different modalities.

Multimodal Imaging of Breast Cancer Xenografts in a Mouse Mammary Window Chamber Model to Investigate Chemotherapy Response

Multispectral imaging was used to follow blood oxygenation changes in breast cancer xenografts in mice treated with chemotherapy. The correlation between tissue perfusion, glycolytic metabolism and blood oxygenation was also investigated with nuclear and MR imaging techniques.

Multimodality imaging in an orthotopic mammary window chamber model

Window chamber models have been utilized for many years to investigate cancer development and the tumor microenvironment. Orthotopic mammary window chamber model have been developed for detailed study of breast cancer. Orthotopic window chamber models, due to the native environment, support more realistic growth and tumor behavior than ectopic models. The work by other groups thus far utilizing mammary window chamber models has focused solely on optical imaging techniques, limited to probing the first millimeter or less of tissue. These techniques do not take full advantage of the unrestricted, three-dimensional tumor growth the model supports. We have developed a custom plastic structure compatible with multimodality imaging. We present in this work the implementation of our custom window chamber in a mouse model and the successful imaging of the window chamber cancer model with MRI, nuclear imaging, and optical techniques. MRI provides a full three-dimensional view of the tumor growth and allows for additional, potentially clinically translatable, approaches to be utilized in investigating the cancer microenvironment. Nuclear imaging is accomplished using the Beta Imager, which is a novel approach to nuclear imaging of window chambers. The Beta Imager detects photons after the interaction of a single positron with a scintillator, instead of the coincidence detection of annihilation gamma ray pairs. We utilized the radioisotope glucose analog, 2-deoxy-2- (18F)fluoro-D-glucose or FDG, with the Beta Imager to obtain information on the glycolytic metabolism of the tumor and surrounding region.

Multimodality pH imaging in a mouse dorsal skin fold window chamber model.

Upregulate levels of expression and activity of membrane H+ ion pumps in cancer cells drives the extracellular pH (pHe,) to values lower than normal. Furthermore, disregulated pH is indicative of the changes in glycolytic metabolism in tumor cells and has been shown to facilitate extracellular tissue remodeling during metastasis Therefore, measurement of pHe could be a useful cancer biomarker for diagnostic and therapy monitoring evaluation. Multimodality in-vivo imaging of pHe in tumorous tissue in a mouse dorsal skin fold window chamber (DSFWC) model is described. A custom-made plastic window chamber structure was developed that is compatible with both imaging optical and MR imaging modalities and provides a model system for continuous study of the same tissue microenvironment on multiple imaging platforms over a 3-week period. For optical imaging of pHe, SNARF-1 carboxylic acid is injected intravenously into a SCID mouse with an implanted tumor. A ratiometric measurement of the fluorescence signal captured on a confocal microscope reveals the pHe of the tissue visible within the window chamber. This imaging method was used in a preliminary study to evaluate sodium bicarbonate as a potential drug treatment to reverse tissue acidosis. For MR imaging of pHe the chemical exchange saturation transfer (CEST) was used as an alternative way of measuring pHe in a DSFWC model. ULTRAVIST®, a FDA approved x-ray/CT contrast agent has been shown to have a CEST effect that is pH dependent. A ratiometric analysis of water saturation at 5.6 and 4.2 ppm chemical shift provides a means to estimate the local pHe.