Kinetic Analysis of Lipid Metabolism in Live Breast Cancer Cells via Nonlinear Optical Microscopy

Investigating the behavior of breast cancer cells via reaction kinetics may help unravel the mechanisms that underlie metabolic changes in tumors. However, obtaining human in vivo kinetic data is challenging due to difficulties associated with measuring these parameters. Non-destructive methods of measuring lipid content in live cells, provide a novel approach to quantitatively model lipid synthesis and consumption. In this study, two-photon excited fluorescence (TPEF) was used to determine metabolic rates via the cell9s optical redox ratio (ORR) as reported by fluorescence intensity ratios of metabolic coenzymes, nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD+). Concurrently, coherent Raman scattering (CRS) microscopy was used to probe de novo intracellular lipid content. Combining non-linear optical microscopy and Michaelis-Menten-kinetics based simulations, we isolated fatty acid synthesis/consumption rates and elucidated effects of altered lipid metabolism in T47D breast cancer cells. When treated with 17β-Estradiol (E2), cancer cells showed a 3-fold increase in beta-oxidation rate as well as a 50% increase in cell proliferation rate. Similarly, the rate of de novo lipid synthesis in cancer cells treated with E2 was increased by 60%. Furthermore, we treated T47D cells with etomoxir (ETO) and observed that cancer cells treated with ETO exhibited a ~70% reduction in beta-oxidation. These results show the ability to probe lipid alterations in live cells with minimum interruption, to characterize both glucose and lipid metabolism in breast cancer cells via quantitative kinetic models and parameters.