Previous studies have suggested that non-APL AML cells, compared to APL cells, generally accumulate lower intracellular amounts of ATO and have demonstrated that low intracellular accumulation of ATO can be attributed to low expression of the arsenic transporter Aquaporin-9 (AQP9), thus making these cells less sensitive to ATO treatment [19]. This evidence concerns the gene AQP9 and acute promyelocytic leukemia.