Sengupta D, Pratx G. Single-Cell Characterization of 18F-FLT Uptake with Radioluminescence Microscopy.
J Nucl Med 2016;
57:1136-40. [PMID:
27081170 DOI:
10.2967/jnumed.115.167734]
[Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 03/11/2016] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED
The radiotracer 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) is commonly used to measure cell proliferation in vivo. As a marker of cell proliferation, (18)F-FLT is expected to be differentially taken up by arrested and actively dividing cells, but PET measures only aggregate uptake by tumor cells and therefore the single-cell distribution of (18)F-FLT is unknown. We used a novel in vitro radioluminescence microscopy technique to measure the differential distribution of (18)F-FLT radiotracer with single-cell precision.
METHODS
Using radioluminescence microscopy, we imaged the absolute uptake of (18)F-FLT in live MDA-MB-231 cells grown under different serum conditions. We then compared (18)F-FLT uptake with a standard measure of cell proliferation, using fluorescence microscopy of 5-ethynyl-2'-deoxyuridine incorporation in fixed cells.
RESULTS
According to 5-ethynyl-2'-deoxyuridine staining, few cells (1%) actively cycled under serum deprivation whereas most of them (71%) did under 20% serum. The distribution of (18)F-FLT reflected this dynamic. At 0% serum, uptake of (18)F-FLT was heterogeneous but relatively low. At 20% serum, a subpopulation of (18)F-FLT-avid cells, representing 61% of the total population, emerged. Uptake of (18)F-FLT in this population was 5-fold higher than in the remainder of the cells. Such a dichotomous distribution is not typically observed with other radiotracers, such as (18)F-FDG.
CONCLUSION
These results suggest that increased (18)F-FLT uptake by proliferating cells is due to a greater fraction of (18)F-FLT-avid cells rather than a change in (18)F-FLT uptake by individual cells. This finding is consistent with the fact that (18)F-FLT uptake is mediated by thymidine kinase 1 expression, which is higher in actively dividing cells. Overall, these findings suggest that, within the same patient, changes in (18)F-FLT uptake reflect changes in the number of actively dividing cells, provided other parameters remain the same.
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