The abnormal vasculature of malignant brain tumors is a critical determinant of their perfusion, oxygenation, and response to therapy. Therefore, the assessment of early structural and functional changes in the microvasculature of pre-clinical brain tumor models can provide invaluable information for directing the dosing/scheduling of new therapies and providing early measurable signs of relapse and recurrence in patients. However, this requires an in vivo imaging technique capable of assessing changes in microvascular (~10?m) morphology and perfusion over the entire life-cycle of a tumor. Laser speckle contrast imaging (LSCI) is an optical imaging technique that meets these requirements and does not require the administration of exogenous fluorescent dyes or contrast agents. Therefore, we are proposing to build a state-of-the-art wireless, head-mounted LSCI system for assessing in vivo changes in microvascular architecture and perfusion combined with a fluorescence module for imaging hypoxia-induced green fluorescent protein (GFP) expression in a transgenic brain tumor model (i.e. 9L-HRE-GFP). We expect this head-mounted image to enable quantification of the physiological consequences of abnormal brain tumor microvasculature, such as decreased/intermittent tumor blood flow and elevated hypoxia. Since certain therapeutics (e.g. anti-VEGF agents, dexamethasone etc.) have been shown to 'normalize'the structure/function of tumor vessels and enhance drug delivery, we will test the ability of our head-mounted imager to detect these changes. As a test case, we propose to characterize the 'normalizing'effects of the clinically used corticosteroid, dexamethasone, on 9L-HRE-GFP brain tumors. We expect LSCI to reveal a shift in the microvasculature towards a more 'normal'architecture accompanied by improved perfusion, and fluorescence imaging to reveal alleviation of hypoxia (i.e. a reduction in inducible GFP expression) following 'vascular normalization'due to dexamethasone. Finally, we expect the innovative combination of multi-modal (i.e. LSCI and fluorescence) imaging and inducible cell lines (e.g. 9L-HRE-GFP) developed in this proposal to be applicable to other diseases involving the pathological vasculature. Collectively, the results of the proposed studies will promote a fundamental understanding of brain tumor biology and establish a novel platform for the pre-clinical testing of new therapies against human brain tumors.
The proposed research is relevant to public health because in vivo imaging of the brain tumor microenvironment at the microvascular scale is ultimately expected to increase our understanding of the angiogenesis pathway in human gliomas, and facilitate the development of new therapeutic approaches for their treatment. The proposed research is relevant to the NIH's mission because the assessment of early neurovascular changes in pre-clinical brain tumor models can provide invaluable insight for directing dosing/scheduling of new therapies and providing early measurable signs of relapse and recurrence in patients with malignant glioma.