Single-Cell Characterization of 18F-FLT Uptake with Radioluminescence Microscopy

The radiotracer 3'-deoxy-3'-¹⁸F-fluorothymidine (¹⁸F-FLT) is commonly used to measure cell proliferation in vivo. As a marker of cell proliferation, ¹⁸F-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 ¹⁸F-FLT is unknown. We used a novel in vitro radioluminescence microscopy technique to measure the differential distribution of ¹⁸F-FLT radiotracer with single-cell precision. Methods: Using radioluminescence microscopy, we imaged the absolute uptake of ¹⁸F-FLT in live MDA-MB-231 cells grown under different serum conditions. We then compared ¹⁸F-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 ¹⁸F-FLT reflected this dynamic. At 0% serum, uptake of ¹⁸F-FLT was heterogeneous but relatively low. At 20% serum, a subpopulation of ¹⁸F-FLT–avid cells, representing 61% of the total population, emerged. Uptake of ¹⁸F-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 ¹⁸F-FDG. Conclusion: These results suggest that increased ¹⁸F-FLT uptake by proliferating cells is due to a greater fraction of ¹⁸F-FLT–avid cells rather than a change in ¹⁸F-FLT uptake by individual cells. This finding is consistent with the fact that ¹⁸F-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 ¹⁸F-FLT uptake reflect changes in the number of actively dividing cells, provided other parameters remain the same.

from #MedicinebyAlexandrosSfakianakis via xlomafota13 on Inoreader http://ift.tt/297E3YY
via IFTTT