Table 1.
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 |