Cornell researchers have developed an imaging method that can follow changes in living cells' metabolism more than 10 times faster than a commonly used technique while exposing cells to less light. The advance could help scientists study how cancer cells respond to experimental treatments, but it is a laboratory research tool, not a clinical test or therapy.
The method, described in a Cornell Chronicle account of the research and a study published Sept. 4 in Science Advances, measures a fluorescent signal from NADH, a molecule involved in the cell's energy production. The researchers used the signal to estimate the fraction of NADH moving freely rather than bound to proteins, an indicator of metabolic state.
The work was led in part by Lu Ling, a former Cornell postdoctoral researcher, and doctoral student Jack Crowley. Biomedical engineering professors Claudia Fischbach and Warren Zipfel collaborated on the project. Ling said the group wanted to follow cancer metabolism over minutes and hours, when changes can be missed or disrupted by existing imaging approaches.
A faster way to read the cell's signal
The standard method, fluorescence lifetime imaging microscopy, measures the time between exciting a molecule with light and detecting its fluorescence. That timing can reveal information about whether NADH is bound to other molecules. But collecting enough measurements over multiple time points can expose living cells to stressful amounts of light, Zipfel said in the Cornell account.
The Cornell approach, called two-photon fluorescence polarization ratiometric microscopy, scans polarized light across the sample and separates the resulting fluorescence into two detectors. The ratio reveals how rapidly the fluorescent molecules rotate. Slower rotation and a more polarized signal suggest more NADH is bound to proteins; freely moving molecules produce a less polarized signal.
The researchers reported that the method is more than an order of magnitude faster than fluorescence lifetime imaging and uses less light. They also said its equipment is simpler, although interpreting the measurements required new calibration, analysis methods and control experiments. It is a different way to estimate metabolic conditions, not a direct measurement of every chemical reaction in a cell.
In the study, the measurements tracked expected metabolic shifts after pharmaceutical and environmental changes. The team also compared the readout with cell shape and movement in two- and three-dimensional collagen environments, showing how the method could be used in tissue-like laboratory models.
Research potential and limits
Two-photon imaging can be used with three-dimensional tissue systems, including organoids and model organisms. Crowley said such settings allow cells to behave more like they do in the body than cells studied on a flat surface, making a faster, lower-light readout useful for experiments on dynamic responses.
The researchers see potential for screening treatments and examining cancer metabolism over time. The published findings establish the method's performance in experimental systems; they do not show that it can diagnose cancer, predict a patient's response to treatment or improve clinical outcomes.
The Cornell Center on the Physics of Cancer Metabolism supported the work. The researchers also used Cornell's Center for Materials Research and Biotechnology Resource Center, which receives support from the National Institutes of Health and New York State Stem Cell Science.
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