KEYWORDS: Radiotherapy, Oxygen, Tumors, Photoacoustic spectroscopy, Photoacoustic imaging, Imaging spectroscopy, Tumor growth modeling, Signal generators, In vivo imaging, Chemical analysis
Presented here is an application of the new approach of chemical imaging, performing an in-vivo chemical analysis, to predict a given tumor’s response to radiation therapy. Cancer tumors’ oxygen distributions in PDX mice was imaged by photoacoustic imaging with tumor-targeted oxygen sensor nanoparticles. Following radiation therapy, we established a quantitatively significant correlation between the spatial distribution of the initial oxygen levels and the spatial distribution of the therapy’s efficacy: the higher the local oxygen, the higher the local radiation therapy efficacy. The presented cancer chemical imaging provides a non-invasive method to predict the efficacy of radiotherapy for a given tumor.
Choroidal neovascularization (CNV) is a hallmark of advanced age-related macular degeneration and is a leading cause of irreversible vision loss and blindness in the world. There is a lack of imaging modalities that can detect CNV early. Photoacoustic microscopy (PAM) combines acoustic and optical imaging to create high-resolution images that can delineate microvasculature non-invasively and permit for visualization of CNV. However, to distinguish CNV from native microvasculature, molecular contrast agents can be applied to increase the sensitivity of PAM imaging. In this study, functionalized indocyanine green (ICG) with RGD ligands (ICG-RGD) was synthesized and applied to in vivo imaging of CNV in the rabbit retina using a custom-built high-resolution PAM imaging system. RGD ligands selective binds to integrins present in neovascularization. The CNV model was created in three New Zealand White rabbits via subretinal injection of human vascular endothelial grow factor (VEGF-165). Three-dimensional in vivo PAM images of CNV were acquired before and after intravenous injection of 400 µL ICG-RGD at a concentration of 2.5 mg/mL over a period of 14 days. In addition, color fundus photography and fluorescence imaging were also acquired. This enables visualization of the newly developed CNV as well as monitoring the changes in CNV over time. With the administration of ICG-RGD, PAM signal amplitudes enhanced up to 15.7-fold at day 1 post-injection and persisted up to 5 days. The PAM results were also confirmed by fluorescence imaging. Biosafety studies show no systemic toxicity of the ICG-RGD. These studies demonstrate the potential of molecular PAM imaging for the characterization of microvasculature pathologies.
Recently, Eil et al. showed that tumors with necrotic cores had elevated K+ concentrations due to the release of K+ by necrosis, which acts to suppress T-cell function by high extracellular K+ concentration. These findings demonstrate the importance of developing a tool for imaging K+ distributions. Here, we demonstrate K+ nanosensor-enabled photoacoustic imaging for measuring K+ levels in vivo. The nanosensor is an in-house synthesized optical contrast agent that is sensitive to K+ levels within biological ranges. The use of this K+ nanosensor, combined with multi-spectral photoacoustic imaging, allowed measurement of K+ levels in vivo.
Ion selective optical nanosensors allow accurate ion measurements in biological systems, without the physical limitations and invasiveness of ion selective electrodes. Optically based nanosensors (Photonic Explorers for Bioanalysis with Biologically Localized Embedding, PEBBLEs), have been optimized for fluorescence microscopy imaging, and have been applied for imaging various biochemical analytes. In here, we report the first example of a potassium selective nanosensor optimized for photoacoustic (PA) imaging. Notably, PA imaging overcomes the severe light penetration depth problem faced by fluorescence imaging in vivo. The new potassium selective nanosensor shows excellent response in the biological range, from 0 to 200 mM, as confirmed by both UV-Vis Spectroscopy and PA Spectroscopy. Furthermore, the K+ PEBBLE showed a 2 orders of magnitude, or higher, selectivity to K+ , relative to any other biological cations, such as Li+, Na+, Ca2+, and Mg2+.
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