The N 6-methyladenosine (m6A) demethylase FTO is overexpressed in acute myeloid leukemia (AML) cells and promotes leukemogenesis. We previously developed tricyclic benzoic acid FB23 as a highly potent FTO inhibitor in vitro. However, it showed a moderate antiproliferative effect on AML cells. In this work, we performed a structure–activity relationship study of tricyclic benzoic acids as FTO inhibitors. The analog 13a exhibited excellent inhibitory effects on FTO similar to that of FB23 in vitro. In contrast to FB23, 13a exerted a strong antiproliferative effect on AML cells. Like FTO knock down, 13a upregulated ASB2 and RARA expression and increased the protein abundance while it downregulated MYC expression and decreased MYC protein abundance. These genes are key FTO targets in AML cells. Finally, 13a treatment improved the survival rate of MONOMAC6-transplanted NSG mice. Collectively, our data suggest that targeting FTO with tricyclic benzoic acid inhibitors may be a potential strategy for treating AML.

The fat mass and obesity-associated protein (FTO) is an RNA N 6-methyladenosine (m6A) demethylase highly expressed in diverse cancers including acute myeloid leukemia (AML). To improve antileukemia drug-like properties, we have designed 44/ZLD115, a flexible alkaline side-chain-substituted benzoic acid FTO inhibitor derived from FB23. A combination of structure–activity relationship analysis and lipophilic efficiency-guided optimization demonstrates that 44/ZLD115 exhibits better drug-likeness than the previously reported FTO inhibitors, FB23 and 13a/Dac85. Then, 44/ZLD115 shows significant antiproliferative activity in leukemic NB4 and MOLM13 cell lines. Moreover, 44/ZLD115 treatment noticeably increases m6A abundance on the AML cell RNA, upregulates RARA gene expression, and downregulates MYC gene expression in MOLM13 cells, which are consistent with FTO gene knockdown. Lastly, 44/ZLD115 exhibits antileukemic activity in xenograft mice without substantial side effects. This FTO inhibitor demonstrates promising properties that can be further developed for antileukemia applications.