Abstract 797: Interaction of multitargeted tyrosine kinase inhibitors with human nucleoside transporters
Authors: Damaraju Vijaya L. , Kuzma Michelle , Mowles Delores , Cass Carol E. , Sawyer Michael B. 
Published: May 2015

Abstract
Several oral multitargeted kinase (MTK) inhibitors are approved for use in the clinic among which, axitinib, pazopanib and sunitinib are used to treat many solid tumors. Several clinical trials of combinations of MTK inhibitors with gemcitabine, a nucleoside analog, have been attempted in pancreas, renal, lung, ovarian and other malignancies with little benefit to patients. We propose that inhibition of human nucleoside transporters (hNTs) by MTK inhibitors results in lowered intracellular nucleoside drug accumulation leading to poor outcomes of combination clinical trials of MTKs with gemcitabine.
Interactions of MTK inhibitors with hNTs was studied by assessing inhibition of [3H]uridine uptake in yeast producing recombinant hNTs individually. Inhibition of uridine uptake and gemcitabine accumulation was examined in the pancreatic adenocarcinoma cell line AsPC-1, lung adenocarcinoma cell line A549 and renal cell carcinoma cell line Caki-1. We also examined sequential vs. simultaneous combination cytotoxicity with gemcitabine and MTKs in Caki-1 cells.
In yeast, pazopanib, sunitinib and axitinib inhibited hENT1 at 4 ± 0.3, 31 ± 5 and 46 ± 4 µM, respectively, concentrations of test compound that inhibited [3H]uridine uptake by 50 % relative to that of untreated cells (IC50 values). Inhibition of hENT2, hCNT1, hCNT2 and hCNT3 by all three MTKs was seen with IC50 values greater than or equal to 100 µM. In A549, AsPC-1 and Caki-1 cells, which possess major hENT1 and minor hENT2 activities, [3H]uridine uptake and [3H]gemcitabine accumulation were inhibited by all three MTK inhibitors. In Caki-1 cells pretreatment or co-treatment of cells with MTK inhibitors and [3H]uridine or gemcitabine resulted in reduced cellular accumulation of [3H]nucleosides thus indicating that scheduling of MTK inhibitors with nucleoside drugs is important. In combination cytotoxicity experiments of sequential vs. simultaneous addition of drugs in Caki-1 cells, cytotoxicity was greatest when gemcitabine was added prior to MTK inhibitors.
Pazopanib &gt; axitinib ≥ sunitinib inhibited hNTs, especially hENT1, resulting in reduced intracellular gemcitabine accumulation. In the clinical setting, concentrations of MTK inhibitors in plasma and tumor tissues are sufficient to inhibit hENT1 activity thus blocking nucleoside chemotherapy drug uptake in cancer cells leading to reduced efficacy in combination schedules. A prior knowledge of such interactions is important when combining MTK inhibitors with nucleoside chemotherapy drugs such as gemcitabine.
Citation Format: Vijaya L. Damaraju, Michelle Kuzma, Delores Mowles, Carol E. Cass, Michael B. Sawyer. Interaction of multitargeted tyrosine kinase inhibitors with human nucleoside transporters. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 797. doi:10.1158/1538-7445.AM2014-797