Table 1.
Summary of the factors important for cellular [18F]FLT uptake.
| Baseline [18F]FLT uptake in tumors and its change in response to therapy varies greatly as a result of an overall balance of some or all of the factors below: |
| - TK1 expression levels |
| - TK1 activity |
| - ATP levels, as a cofactor for TK1 activity |
| - TS levels and activity (de novo DNA pathway), competing with the salvage DNA synthesis |
| - TP expression and activity, influencing endogenous tumor thymidine levels |
| - Thymidine levels in tumor, reflecting the nucleotide turnover rates |
| - Expression of nucleoside transporters, which are essential for the transport of [18F]FLT (notably hENT1) |
| - Delivery of the tracer |
| - Blood-brain barrier hampers [18F]FLT uptake in brain tumors |
| - Thymidine levels in blood plasma, which are competing with [18F]FLT |
| - Animal body temperature |
| - Anesthetics used |
| - Oxygen breathing |
| - Tumor vascularity, and the changes thereof by antiangiogenic treatments |