DNA Methylation‐Based Epigenetic Repression of SLC22A4 Promotes Resistance to Cytarabine in Acute Myeloid Leukemia

Reduced expression of the uptake transporter, OCTN1 (SLC22A4), has been reported as a strong predictor of poor event‐free and overall survival in multiple cohorts of patients with acute myeloid leukemia (AML) receiving the cytidine nucleoside analog, cytarabine (Ara‐C). To further understand the mechanistic basis of interindividual variability in the functional expression of OCTN1 in AML, we hypothesized a mechanistic connection to DNA methylation‐based epigenetic repression of SLC22A4. We found increased basal SLC22A4 methylation was associated with decreased Ara‐C uptake in AML cell lines. Pre‐treatment with hypomethylating agents, 5‐azacytidine, or decitabine, restored SLC22A4 mRNA expression, increased cellular uptake of Ara‐C, and was associated with increased cellular sensitivity to Ara‐C compared with vehicle‐treated cells. Additionally, lower SLC22A4 methylation status was associated with distinct clinical advantages in both adult and pediatric patients with AML. These findings suggest a regulatory mechanism is involved in the interindividual variability in response to Ara‐C, and provides a basis for the integration of hypomethylating agents into Ara‐C‐based treatment regimens.