Intravital imaging of tumor bioenergetics in metastatic and non-metastatic breast cancer

Abstract

Early detection of metastatic cancer can reduce patient mortality and decrease cost of cancer treatment. However, current methods of prognosis or genetic screening are expensive and might not be applicable to all tumors. Although previous studies indicated that cancer cells are glycolytic, the link between metabolism and metastatic progression is not fully understood. To better understand the tumor bioenergetics, we investigated in vivo the vascular oxygenation, glucose intake, and optical redox ratio between a metastatic breast cancer cell line (4T1), a non-metastatic isogenic cell line (168FARN), and a non-metastatic derivative of 4T1 (TWIST gene knockout). The vascular oxygenation was measured by injecting 10,000 cells into mouse dorsal window chambers and acquiring and processing trans-illumination images of the tumor from 520 nm-620 nm light wavelength in 10 nm intervals. Glucose intake was measured by continuous fluorescent imaging of the glucose analog, 2-NBDG, for 90 minutes. Optical redox ratio was measured by intrinsic fluorescence imaging of electron carrying intermediates, NADH and FAD, where an increase in the ratio (FAD/FAD+NADH) meant increased oxidative phosphorylation. Our data show that the optical redox ratio and vascular oxygenation are higher and glucose intake is lower in metastatic tumors compared to non-metastatic tumors, suggesting that metastatic tumors display decreased glycolysis and increased oxidative phosphorylation. We observed a similar trend in vitro, where the redox ratio increased as the cell metastatic potential increased, indicating that metastatic cells can efficiently produce energy. These findings indicate that optical redox ratio can be a potential prognosis tool for detecting malignant tumors.