Suppression of the FOXM1 transcriptional programme via novel small molecule inhibition.

The transcription factor FOXM1 binds to sequence-specific motifs on DNA (C/TAAACA) through its DNA-binding domain (DBD) and activates proliferation- and differentiation-associated genes. Aberrant overexpression of FOXM1 is a key feature in oncogenesis and progression of many human cancers. Here--from a high-throughput screen applied to a library of 54,211 small molecules--we identify novel small molecule inhibitors of FOXM1 that block DNA binding. One of the identified compounds, FDI-6 (NCGC00099374), is characterized in depth and is shown to bind directly to FOXM1 protein, to displace FOXM1 from genomic targets in MCF-7 breast cancer cells, and induce concomitant transcriptional downregulation. Global transcript profiling of MCF-7 cells by RNA-seq shows that FDI-6 specifically downregulates FOXM1-activated genes with FOXM1 occupancy confirmed by ChIP-PCR. This small molecule-mediated effect is selective for FOXM1-controlled genes with no effect on genes regulated by homologous forkhead family factors.