Abstract B23: Intravital optical imaging of tumor vascular oxygenation and metabolism in murine breast cancer xenografts of varying metastatic potential
Authors: Rajaram Narasimhan , Rasul Raisa 
Published: August 2018

Abstract
About 90% of breast cancer patients die due to metastatic spread and not due to the primary tumor. Therefore, several patients receive neoadjuvant chemotherapy to eliminate the risk associated with developing metastases even if they may be at a lower risk of developing metastases. Current clinical guidelines laid out by the American Society for Clinical Oncology (ASCO) recommend consideration of the Oncotype DX score to determine risk of recurrence so that only patients classified as high-risk receive chemotherapy. In addition to this genetic test, there is a need to develop more cost-effective prognostic indicators that can reduce the number of patients receiving life-altering chemotherapy for early-stage breast cancers with very low recurrence risk. Recent studies have shown that primary, circulating, and metastasized cancer cells adopt different metabolic profiles to fuel their survival and growth. Furthermore, highly invasive primary cancer cells may favor mitochondrial oxidative metabolism to efficiently generate ATP and promote a migratory phenotype. Optical imaging of the endogenous fluorescent molecules nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) provides a nondestructive and label-free method for determining cell metabolism. The optical redox ratio (FAD/FAD+NADH) is sensitive to the balance between glycolysis and oxidative phosphorylation (OXPHOS). We previously demonstrated that a short duration of hypoxia-reoxygenation stress (1 hour of hypoxia followed by 1 hour of reoxygenation) led to metastatic potential-dependent changes in optical redox ratio in a panel of isogenic murine breast cancer cell lines (4T1, 4T07, 168FARN, 67NR). Specifically, highly metastatic 4T1 cells were found to switch to mitochondrial oxidative metabolism whereas nonmetastatic 168FARN cells were highly glycolytic and did not exhibit any changes post-stress. We further determined that deletion of TWIST, a key promoter of metastasis, in the 4T1 cell line caused these cells to respond in the same way as 168FARN to hypoxic stress. The objective of this study was to investigate these metabolic profiles in vivo and determine the relationship between tumor oxygenation and metabolism in tumor xenografts grown from the aforementioned cell lines. Tumors were grown in dorsal skinfold window chambers by injecting approx. 10-20,000 cancer cells. Imaging and quantification of vascular oxygenation was accomplished by acquiring transillumination images at wavelengths corresponding to absorption by hemoglobin (520-620 nm). Glucose uptake was imaged 60 minutes after intravenous injection of a fluorescent glucose analog called 2-NBDG. Our data show higher vascular oxygenation and lower glucose uptake in primary tumors with higher metastatic potential compared with nonmetastatic tumors, suggesting that tumors with high metastatic potential display decreased glycolysis and increased oxidative phosphorylation. Our preliminary results indicate that optical imaging of tumor bioenergetics could shed light on the metastatic tendencies of primary breast tumors.
Citation Format: Narasimhan Rajaram, Raisa Rasul. Intravital optical imaging of tumor vascular oxygenation and metabolism in murine breast cancer xenografts of varying metastatic potential [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B23.