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 cells 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 17{beta}-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.\n\nStatement of SignificanceCombining non-linear optical microscopy (NLOM) and deuterium labeling provides insight into lipid metabolism in live cancer cells during cancer development and progression. The dynamic metabolic data is modelled with Michaelis-Menten-kinetics to independently quantify the lipid synthesis and utilization in cancer cells. Changes in lipid levels are found to originate from de novo lipid synthesis using glucose as a source, lipid consumption from {beta}-oxidation and lipid consumption from cell proliferation, processes that can separately analyzed with the Michaelis-Menten model. In this work, we isolate fatty acid synthesis/consumption rates and elucidated effects of altered lipid metabolism in T47D breast cancer cells in response to estradiol stimulation and etomoxir treatment, dynamic processes that cannot be easily observed without the application of appropriate models.