Inhibition of sodium-independent and sodium-dependent nucleobase transport activities by tyrosine kinase inhibitors.
OBJECTIVE
Effects of tyrosine kinase inhibitors (TKIs) on equilibrative nucleobase transport (ENBT) and sodium-dependent nucleobase transport (SNBT) activities were investigated in normal human renal proximal tubule epithelial cells (hRPTECs) and in pig kidney cell line (LLC-PK1).


METHODS
Uptake assays were performed by assessing accumulation of radiolabeled nucleobases over time into hRPTECs or LLC-PK1 cell lines which express ENBT and SNBT activities, respectively. Dose-response curves for inhibition of 1 µM [(3)H]adenine or 1 µM [(3)H]hypoxanthine were examined in hRPTECs and in LLC-PK1 cells with varying TKI concentrations (0-100 µM) to calculate the IC50 values (mean ± S.E) for inhibition.


RESULTS
Gefitinib inhibited ENBT activity with an IC50 value of 0.7 µM, thus indicating strong interactions of ENBT with gefitinib in hRPTECs. Erlotinib > sorafenib > imatinib > sunitinib inhibited ENBT with IC50 values of 15, 40, 60, 78 µM, respectively, whereas dasatinib, lapatinib, and vandetanib were not inhibitory at concentrations >100 µM. Similar studies in LLC-PK1 cells which exhibit SNBT activity showed that vandetanib was the most potent inhibitor followed by sorafenib > erlotinib > gefitinib > sunitinib > imatinib with IC50 values of 14, 25, 28, 40, 47, 94 µM, respectively, whereas dasatinib and lapatinib were not inhibitory at concentrations >100 µM.


CONCLUSIONS
These results suggest for the first time inhibition of both ENBT and SNBT transport activities by TKIs. These results suggest that it is important to consider potential effects on combination regimens using TKIs with nucleobase drugs such as 5-FU in cancer treatment.
Department of Oncology, University of Alberta, Edmonton, AB, Canada.
Vijaya L
VL
Damaraju
Department of Medical Oncology, Cross Cancer Institute, 11560 University Avenue NW, Edmonton, AB, T6G 1Z2, Canada.
Michelle
M
Kuzma
Department of Oncology, University of Alberta, Edmonton, AB, Canada.
Carol E
CE
Cass
Department of Oncology, University of Alberta, Edmonton, AB, Canada. michael.sawyer@albertahealthservices.ca.|Department of Medical Oncology, Cross Cancer Institute, 11560 University Avenue NW, Edmonton, AB, T6G 1Z2, Canada. michael.sawyer@albertahealthservices.ca.
Michael B
MB
Sawyer
D000225:Adenine / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects*; D002460:Cell Line; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors; D033702:Nucleobase Transport Proteins / Q000037:antagonists & inhibitors* / Q000145:classification; D047428:Protein Kinase Inhibitors / Q000145:classification / Q000493:pharmacokinetics / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D012964:Sodium / Q000502:physiology*; D034421:Sus scrofa; D013552:Swine
D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D033702:Nucleobase Transport Proteins; D047428:Protein Kinase Inhibitors; D012964:Sodium; D011505:Protein-Tyrosine Kinases; D000225:Adenine
5-Fluorouracil; Capecitabine; Nucleobase; Transport; Tyrosine kinase inhibitors