Abstract
Purpose
To develop a tool to measure the pH at the surfaces of individual cells.
Procedures
The SNARF pH-sensitive dye was conjugated to a pHLIP® peptide (pH-Low Insertion Peptide) that binds cellular membranes in tumor spheroids. A beam splitter allows simultaneous recording of two images (580 and 640 nm) by a CCD camera. The ratio of the two images is converted into a pH map resolving single spheroid cells. An average pH for each cell is calculated and a pH histogram is derived.
Results
Surface pH depends on cellular glycolytic activity, which was varied by adding glucose or deoxy-glucose. Glucose was found to decrease the surface pH relative to the pH of the bulk solution. The surface pH of metastatic cancer cells was lower than that of non-metastatic cells indicating a higher glycolytic activity.
Conclusions
Our method allows cell surface pH measurement and its correlation with cellular glycolytic activity.
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Acknowledgments
We would like to thank our colleagues Anna Moshnikova and Michael Anderson for useful discussions and suggestions.
Funding
Financial support was received from NIH RO1 GM073857 grant to DME, OAA, and YKR.
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Conflict of Interest
D.M.E., O.A.A., and Y.K.R. are founders of pHLIP, Inc. They have shares in the company, but the company did not fund any part of the work reported in the paper, which was done in their academic laboratories.
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Wei, D., Engelman, D.M., Reshetnyak, Y.K. et al. Mapping pH at Cancer Cell Surfaces. Mol Imaging Biol 21, 1020–1025 (2019). https://doi.org/10.1007/s11307-019-01335-4
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DOI: https://doi.org/10.1007/s11307-019-01335-4