Abstract LB239: CryoVizTM and photoacoustic imaging for assessment of tumor vasculature in mouse models of pancreatic tumors
Authors: Gargesha Madhusudhana , Goel Shreya , Scott Bryan , Pagel Mark D. , Roy Debashish 
Published: July 2021

Abstract
Introduction: Assessing the tumor vasculature in models of pancreatic tumors can improve the characterization of these models, which can then support the eventual assessments of anti-cancer treatments. In this study, we sought to relate hypoxia, vascular perfusion, and vascular patency using synergistic imaging methods. In vivo Multispectral Optoacoustic Tomography (MSOT; also known as photoacoustic imaging) can measure %sO2 a relative measurement of oxy- vs. deoxy-hemoglobin in tumors. In vivo Dynamic Contrast Enhanced (DCE) MSOT can measure vascular perfusion. CryoVizTM imaging, a serial-sectioning-and-block-face-imaging technique, provides high-resolution 3D microscopic color anatomy and sensitive fluorescence making it ideal for assessing vascular perfusion by imaging ICG uptake and vascular patency by imaging Dylight488 lectin uptake. Methods: We performed MSOT and CryoVizTM imaging with subcutaneous tumor mouse models of SU.86.86 and MIA PaCa-2 pancreatic cancer. We performed MSOT with 21% O2 and 100% O2 carrier gas, which measures %sO2 (% oxyhemoglobin/total hemoglobin) as a biomarker of hypoxia. We performed DCE MSOT with 50 nmol indocyanine green (ICG), which measures Kapp (uptake rate from blood to tumor tissue) - a biomarker of vascular perfusion. To assess microvessel patency, we injected Dylight488 lectin via retro-orbital injection into the mice 3 min before euthanasia to enable CryoVizTM visualization of functional blood vessels. Subsequently, mice were euthanized, embedded in optimal cutting temperature (OCT) gel and flash-frozen in liquid nitrogen, and then imaged on the CryoVizTM. We acquired brightfield color anatomy, Dylight488 lectin (visible) fluorescence (ex: 460-490 nm, em&gt;510nm) and ICG (NIR) fluorescence images (ex: 747/11 nm, em: &gt;790nm) with an in-plane resolution of 10.232µm and a section thickness of 40 µm. Results: The in vivo MSOT analysis indicated that the MIA PaCa-2 model was more hypoxic than the SU.86.86 model, based on lower %sO2 measurements with both carrier gases. The in vivo DCE MSOT analysis indicated that the MIA PaCa-2 model had greater vascular perfusion than SU.86.86, based on a higher Kapp value. CryoVizTM images showed higher levels of lectin and ICG fluorescence in MIA PaCa-2 as compared to SU.86.86, indicating greater vascular patency and perfusion in the former. A strong lectin signal was observed in the injection site (retro-orbital sinuses), and in the renal medulla. ICG was also found to be retained in the axillary lymph node in both MIA PaCa-2 and SU.86.86, and in the kidney/adrenal glands of the MIA PaCa-2 mouse. Conclusion: Together, these results confirmed that the MIA PACa-2 model had higher hypoxia, vascular perfusion, and vascular patency, demonstrating the relationship between hypoxia and angiogenesis. This study reveals the power of 3D CryoVizTM imaging as a gold standard validation tool in cancer imaging.
Citation Format: Madhusudhana Gargesha, Shreya Goel, Bryan Scott, Mark D. Pagel, Debashish Roy. CryoVizTM and photoacoustic imaging for assessment of tumor vasculature in mouse models of pancreatic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB239.