Optical imaging of metabolism in HER2 overexpressing breast cancer cells

Abstract

The optical redox ratio (fluorescence intensity of NADH divided by that of FAD), was acquired for a panel of breast cancer cell lines to investigate how overexpression of human epidermal growth factor receptor 2 (HER2) affects tumor cell metabolism, and how tumor metabolism may be altered in response to clinically used HER2-targeted therapies. Confocal fluorescence microscopy was used to acquire NADH and FAD auto-fluorescent images. The optical redox ratio was highest in cells overexpressing HER2 and lowest in triple negative breast cancer (TNBC) cells, which lack HER2, progesterone receptor, and estrogen receptor (ER). The redox ratio in ER-positive/HER2-negative cells was higher than what was seen in TNBC cells, but lower than that in HER2 overexpressing cells. Importantly, inhibition of HER2 using trastuzumab significantly reduced the redox ratio in HER2 overexpressing cells. Furthermore, the combinatorial inhibition of HER2 and ER decreased the redox ratio in ER+/HER2+ breast cancer cells to a greater extent than inhibition of either receptor alone. Interestingly, trastuzumab had little impact upon the redox ratio in a cell line selected for acquired resistance to trastuzumab. Taken together, these data indicate that the optical redox ratio measures changes in tumor metabolism that reflect the oncogenic effects of HER2 activity within the cell, as well as the response of the cell to therapeutic inhibition of HER2. Therefore, optical redox imaging holds the promise of measuring response and resistance to receptor-targeted breast cancer therapies in real time, which could potentially impact clinical decisions and improve patient outcome.

Optical metabolic imaging quantifies heterogeneous cell populations

“…Previous studies have shown that OMI endpoints are sensitive to metabolism differences between cancer subtypes [9,13,14]. Additionally, the OMI endpoints provide dynamic readouts of cellular metabolism and detect pre-malignant transformations within tissues [15,16], classify subtypes of breast cancer cells [9,13], and detect response to anti-cancer drugs [14].…”

High-throughput measurements of the optical redox ratio using a commercial microplate reader

“…The redox ratio is sensitive to both ER and HER2 overexpression as well as drug response. [11][12][13] NADH and FAD are endogenous fluorophores, and thus enable metabolic measurements without requiring stains or dyes. Therefore, autofluorescence measurements are advantageous for high-throughput drug development.…”

“…For FAD fluorescence, the cells were excited at 430 to 470 nm and the emission signal was collected at 515 to 555 nm. 12 The instrument was operated under epi-mode with an integration time of 50 μs, a flash frequency of 400 Hz, and a gain of 80. Measurements of each plate were taken twice within ten minutes to rule out the occurrence of photobleaching, and data were collected on three separate days.…”

Functional Optical Imaging of Primary Human Tumor Organoids: Development of a Personalized Drug Screen

“…We have used OMI to study metabolic differences between nontransformed and malignant cells and tissues, the relationship between oncogenic signaling pathways and cellular metabolism, and drug-induced effects on metabolism (18,20,35,37,39). Importantly, our studies demonstrated that OMI is a sensitive and early reporter of drug efficacy in organoids (Fig.…”

“…Fluorescence lifetime studies of cancers have revealed metabolic differences between transformed and premalignant tissues (35,37). OMI can also detect changes in metabolism due to treatment with anticancer drugs (20,35).…”