Structure-Activity Relationship of N -Phenylthieno[2,3- b ]pyridine-2-carboxamide Derivatives Designed as Forkhead Box M1 Inhibitors: The Effect of Electron-Withdrawing and Donating Substituents on the Phenyl Ring.

We report synthesis, characterization, biological evaluation, and molecular-docking studies of 18 thieno[2,3- b ]pyridines with a phenylacetamide moiety at position 2, which is disubstituted with F, Cl, Br, or I at position 4, and with electron-withdrawing and electron-donating groups (-CN, -NO 2 , -CF 3 , and -CH 3 ) at position 2, to study how the electronic properties of the substituents affected the FOXM1-inhibitory activity. Among compounds 1 - 18 , only those bearing a -CN (regardless of the halogen) decreased FOXM1 expression in a triple-negative breast cancer cell line (MDA-MB-231), as shown by Western blotting. However, only compounds 6 and 16 decreased the relative expression of FOXM1 to a level lower than 50%, and hence, we determined their anti-proliferative activity (IC 50 ) in MDA-MB-231 cells using the MTT assay, which was comparable to that observed with FDI-6 , in contrast to compound 1 , which was inactive according to both Western blot and MTT assays. We employed molecular docking to calculate the binding interactions of compounds 1 - 18 in the FOXM1 DNA-binding site. The results suggest a key role for residues Val296 and Leu289 in this binding. Furthermore, we used molecular electrostatic potential maps showing the effects of different substituents on the overall electron density.