Potential Indexing of the Invasiveness of Breast Cancer Cells by Mitochondrial Redox Ratios

Abstract

The invasive/metastatic potential of cancer cells is an important factor in tumor progression. The redox ratios obtained from ratios of the endogenous fluorescent signals of NADH and FAD, can effectively respond to the alteration of cancer cells in its mitochondrial energy metabolism. It has been shown previously that the redox ratios may predict the metastatic potential of cancer mouse xenografts. In this report, we aimed to investigate the metabolic state represented by the redox ratios of cancer cells in vitro. Fluorescence microscopic imaging technology was used to observe the changes of the endogenous fluorescence signals of NADH and FAD in the energy metabolism pathways. We measured the redox ratios (FAD/NADH) of breast cancer cell lines MDA-MB-231, MDA-MB-468, MCF-7, and SKBR3. We found that the more invasive cancer cells have higher FAD/NADH ratios, largely consistent with previous studies on breast cancer xenografts. Furthermore, by comparing the fluorescence signals of the breast cancer cells under different nutritional environments including starvation and addition of glutamine, pyruvate and lactate, we found that the redox ratios still effectively distinguished the highly invasive MDA-MB-231 cells from less invasive MCF-7 cells. These preliminary data suggest that the redox ratio may potentially provide a new index to stratefy breast cancer with different degrees of aggressiveness, which could have significance for the diagnosis and treatment of breast cancer.

Keywords: Breast cancer; FAD; Invasive potential; NADH; Redox ratio.

Fig. 16.1

The addition of rotenone to MCF-7 cells (number of FOVs = 6 from two dishes at one experimental session) results in an increase in NADH fluorescence, a decrease in FAD fluorescence, and a decrease in FAD/NADH ratio. Left Y-axis is for NADH and FAD, and the right Y-axis for FAD/NADH ratio. Bar height represents the mean and error bar represents the standard error (SE). Ctrl represents the control group. There was 10 mM glucose in the imaging solution as the basic supply of nutrient for each of the three groups. For the DMSO group, 8 μl DMSO was added into 1 ml imaging solution. DMSO&Rote represents the group in which 8 μl DMSO with rotenone was added into 1 ml imaging solution. The final concentration of rotenone was 10 μM

Fig. 16.2

Normalized FAD, NADH, and FAD/NADH values of MDA-MB-231, MDA-MB-468, MCF-7, and SKBr3 breast cancer cell lines (three experiments at different days, duplicated dishes each time, with total number of FOVs = 24). There was 10 mM glucose in the imaging solutions of all groups. Bar height represents the mean and the error bar represents the SE

Fig. 16.3

Comparison of FAD/NADH ratios of MDA-MB-231 and MCF-7 when the microenvironments were changed (three experiments at different days, duplicated dishes each time, with total number of FOVs = 24). Starvation indicates there was no nutrition in the media. Glc+Gln, Glc+Lac, and Glc+Pyr represent 10 mM glucose + 20 mM glutamine, 10 mM glucose + 20 mM lactate, and 10 mM glucose + 20 mM pyruvate in the media, respectively