Effect of hypoxia on human equilibrative nucleoside transporters hENT1 and hENT2 in breast cancer

Elevated proliferation rates in cancer can be visualized with positron emission tomography (PET) using 3‘‐deoxy‐3‘‐ l ‐[ 18 F]fluorothymidine ([ 18 F]FLT). This study investigates whether [ 18 F]FLT transport proteins are regulated through hypoxia. Expression and function of human equilibrative nucleoside transporter (hENT)‐1, hENT2, and thymidine kinase 1 (TK1) were studied under normoxic and hypoxic conditions, and assessed with [ 18 F] FLT‐PET in estrogen receptor positive (ER+)‐MCF7, triple‐negative MDA‐MB231 breast cancer (BC) cells, and MCF10A cells (human mammary epithelial cells). Functional involvement of hENT2 [ 18 F]FLT transport was demonstrated in all cell lines. In vitro [ 18 F]FLT uptake was higher in MDA‐MB231 than in MCF7:242 ± 9 vs. 147 ± 18% radioactivity/mg protein after 60 min under normoxia. Hypoxia showed no significant change in radiotracer uptake. Protein analysis revealed increased hENT1 ( P < 0.0963) in MDA‐MB231. Hypoxia did not change expression of either hENT1, hENT2, or TK1. In vitro inhibition experiments suggested involvement of hENT1, hENT2, and human concentrative nucleoside transporters during [ 18 F]FLT uptake into all cell lines. In vivo PET imaging revealed comparable tumor uptake in MCF7 and MDA‐MB231 tumors over 60 min, reaching standardized uptake values of 0.96 ± 0.05 vs. 0.89 ± 0.08 ( n = 3). Higher hENT1 expression in MDA‐MB231 seems to drive nucleoside transport, whereas TK1 expression in MCF7 seems responsible for comparable [ 18 F]FLT retention in ER + tumors. Our study demonstrates that hypoxia does not significantly affect nucleoside transport as tested with [ 18 F]FLT in BC.—Krys, D., Hamann, I., Wuest, M., Wuest, F. Effect of hypoxia on human equilibrative nucleoside transporters hENT1 and hENT2 in breast cancer. FASEB J. 33, 13837‐13851 (2019). www.fasebj.org