Numerical analysis of apparent decitabine uptake in HCT116 cells: Incorporation of a bidirectional first-order kinetic parameter for ENT1 transport and Michaelis-Menten parameters for subsequent phosphorylation

Abstract

Decitabine (DAC), a DNA methylation inhibitor, is transported into cancer cells mainly via equilibrative nucleoside transporter 1 (ENT1) and subsequently phosphorylated by deoxycytidine kinase (dCK). We previously reported that apparent DAC uptake into cells may be described using a simple compartment model with clearance for facilitated diffusion (PS) and subsequent phosphorylation (CLmet). In the present study, time course of apparent intracellular [3H]-DAC uptake was analyzed numerically, and PS and CLmet values were calculated using the compartment model in human colon cancer HCT116 cells. PS at 0.1 μM [3H]-DAC was markedly decreased in the presence of 100 μM irinotecan or etoposide, while CLmet was markedly decreased in the presence of 100 μM cytarabine or gemcitabine. CLmet at 0.1–10 μM [3H]-DAC varied in a concentration-dependent manner and was described by Michaelis-Menten parameters Km,met and Vmax,met. In conclusion, DAC uptake mainly via ENT1 may be described by a bidirectional first-order kinetic parameter, while phosphorylation by dCK may be described by Michaelis-Menten parameters.