Optical imaging of tumor hypoxia dynamics

Abstract

Abstract. The influence of the tumor microenvironment and hypoxia plays a significant role in determining cancer progression, treatment response, and treatment resistance. That the tumor microenvironment is highly heterogeneous with significant intratumor and intertumor variability presents a significant challenge in developing effective cancer therapies. Critical to understanding the role of the tumor microenvironment is the ability to dynamically quantify oxygen levels in the vasculature and tissue in order to elucidate the roles of oxygen supply and consumption, spatially and temporally. To this end, we describe the use of hyperspectral imaging to characterize hemoglobin absorption to quantify hemoglobin content and oxygen saturation, as well as dual emissive fluorescent/phosphorescent boron nanoparticles, which serve as ratiometric indicators of tissue oxygen tension. Applying these techniques to a window-chamber tumor model illustrates the role of fluctuations in hemoglobin saturation in driving changes in tissue oxygenation, the two being significantly correlated (r = 0.77). Finally, a green-fluorescence-protein reporter for hypoxia inducible factor-1 (HIF-1) provides an endpoint for hypoxic stress in the tumor, which is used to demonstrate a significant association between tumor hypoxia dynamics and HIF-1 activity in an in vivo demonstration of the technique. Tumor hypoxia plays an important role in cancer progression, metastasis, and the effectiveness of therapies.1-3 It is a highly dynamic process and the temporal dynamics can play a significant role in treatment resistance and tumor aggressiveness. 2,4-10A recent trend in therapeutic strategies is to target tumor angiogenesis in order to modify the microenvironment and make tumors more sensitive to conventional therapies.11 The ability to measure pO 2 and image tumor hypoxia on the microscopic level is essential to further understanding microenvironmental factors and modifying therapies, depending on treatment response. Characterizing the local microenvironment, particularly hypoxia, longitudinally, on a microscopic scale would be ideal. This is a challenging problem, however, and one for which no established imaging technique exists. Many methods have been developed that range from histological staining with reducible nitroimidazole reagents, protein markers, and green fluorescence protein (GFP) or luciferase reporter genes, to electrochemical probe methods, and optical, nuclear medicine, and magnetic resonance techniques 12 although some methods are only suitable for the laboratory, others have been translated into the clinic, and all have their advantages and drawbacks. 13,14 The key point is that there is no easily implemented technique for imaging vascular oxygenation (hemoglobin oxygenation) in combination with tissue oxygen tension on the microcirculatory level. We present an approach based on hyperspectral imaging of hemoglobin absorption and dual emissive boron nanoparticles (BNPs). The combination of these techniques enables quantification of...

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Imaging molecular dynamics in vivo – from cell biology to animal models

“…Instead of measuring enzymatic activity, Blum et al have designed a fluorescent probe that labels and inhibits cysteine cathepsins of the papain family in mouse tumors (Blum et al, 2007). Kuchimaru and colleagues have taken an alternative approach by using Halotag chemistry to conjugate an infrared fluorophore to the oxygendependent degradation and protein-transduction domains (ODD-PTD) of hypoxia-inducible factor  (HIF1A) to generate a probe that is actively taken up by cells in hypoxic environments (Kuchimaru et al, 2010;Palmer et al, 2010). These functional dyes can provide valuable information about the local tumor environment and are easy to combine with any genetic model.…”