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

Area of Science:

• Biomedical Imaging
• Molecular Imaging
• Cell Biology

Background:

• 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) is a PET radiotracer used to measure cell proliferation.
• PET imaging provides aggregate uptake data, leaving single-cell distribution of (18)F-FLT unknown.
• Understanding single-cell uptake is crucial for accurate proliferation assessment.

Purpose of the Study:

• To investigate the single-cell distribution of (18)F-FLT in live cells.
• To determine if (18)F-FLT uptake varies between individual arrested and proliferating cells.
• To correlate (18)F-FLT uptake with established proliferation markers at the single-cell level.

Main Methods:

• Utilized a novel in vitro radioluminescence microscopy technique for single-cell imaging.
• Quantified (18)F-FLT uptake in MDA-MB-231 cells under varying serum conditions.
• Compared (18)F-FLT uptake with 5-ethynyl-2'-deoxyuridine (EdU) incorporation, a marker of DNA synthesis.

Main Results:

• Serum deprivation reduced cell cycling (1% EdU positive), while 20% serum increased it (71% EdU positive).
• (18)F-FLT uptake was heterogeneous and low under serum deprivation.
• A subpopulation of (18)F-FLT-avid cells (61%) emerged under 20% serum, with 5-fold higher uptake than other cells.
• This dichotomous distribution differs from tracers like (18)F-FDG.

Conclusions:

• Increased (18)F-FLT uptake in proliferating cells is attributed to a larger fraction of (18)F-avid cells, not increased uptake per cell.
• This is consistent with thymidine kinase 1 expression, which is higher in dividing cells.
• Changes in (18)F-FLT PET signal reflect changes in the number of actively dividing cells.