Abnormal microvascular function and angiogenesis are key components of various diseases that can contribute to
the perpetuation of the disease. Several skin diseases and ophthalmic pathologies are characterized by
hypervascularity, and in cancer the microvasculature of tumors is structurally and functionally abnormal. Thus, the
microvasculature can be an important target for treatment of diseases characterized by abnormal microvasculature.
Motivated largely by cancer research, significant effort has been devoted to research on drugs that target the
microvasculature. Several vascular targeting drugs for cancer therapy are in clinical trials and approved for clinical
use, and several off-label uses of these drugs have been reported for non-cancer diseases. The ability to image and
measure parameters related to microvessel function preclinically in laboratory animals can be useful for
development and comparison of vascular targeting drugs. For example, blood supply time measurements give
information related to microvessel morphology and can be measured with first-pass fluorescence imaging.
Hemoglobin saturation measurements give an indication of microvessel oxygen transport and can be measured with
spectral imaging. While each measurement individually gives some information regarding microvessel function, the
measurements together may yield even more information since theoretically microvessel morphology can influence
microvessel oxygenation, especially in metabolically active tissue like tumors. However, these measurements have
not yet been combined. In this study, we report the combination of blood supply time imaging and hemoglobin
saturation imaging of microvessel networks in tumors using widefield fluorescence and spectral imaging,
respectively. The correlation between the measurements in a mouse mammary tumor is analyzed.
Abnormal microvascular physiology and function is common in many diseases. Numerous pathologies include hypervascularity, aberrant angiogenesis, or abnormal vascular remodeling among the characteristic features of the disease, and quantitative imaging and measurement of microvessel function can be important to increase understanding of these diseases. Several optical techniques are useful for direct imaging of microvascular function. Spectral imaging is one such technique that can be used to assess microvascular oxygen transport function with high spatial and temporal resolution in microvessel networks through measurements of hemoglobin saturation. We highlight novel observation made with our intravital microscopy spectral imaging system employed with mouse dorsal skin-fold window chambers for imaging hemoglobin saturation in microvessel networks. Specifically, we image acute oxygenation fluctuations in a tumor microvessel network, the development of arteriovenous malformations in a mouse model of hereditary hemorrhagic telangiectasia, and the formation of spontaneous and induced microvascular thromboses and occlusions.
Tumors are highly metabolically active and thus require ample oxygen and nutrients to proliferate. Neovasculature
generated by angiogenesis is required for tumors to grow beyond a size of about 1-2mm. Functional tumor vasculature
also provides an access point for development of distant metastases. Due to the importance of the microvasculature for
tumor growth, proliferation, and metastasis, the microvasculature has emerged as a therapeutic target for treatment of
solid tumors. We employed spectral imaging in a rodent window chamber model to observe and measure the oxygen
transport function of tumor microvasculature in a human renal cell carcinoma after treatment with a fast acting vascular
disrupting agent. Human Caki-1 cells were grown in a dorsal skin-fold window chamber in athymic nude mice.
Spectral imaging was used to measure hemoglobin saturation immediately before, immediately after and also at 2, 4, 6,
8, 24 and 48 hours after administration of the tubulin binding agent OXi4503. Up to 4 hours after treatment, tumor
microvasculature was disrupted from the tumor core towards the periphery as seen in deoxygenation as well as
structural changes of the vasculature. Reoxygenation and neovascularization commenced from the periphery towards
the core from 6 - 48 hours after treatment. The timing of the effects of vascular disrupting agents can influence
scheduling of repeat treatments and combinatorial treatments such as chemotherapy and radiation therapy. Spectral
imaging can potentially provide this information in certain laboratory models from endogenous signals with microvessel