Monomerization of Homodimeric Trefoil Factor 3 (TFF3) by an Aminonitrile Compound Inhibits TFF3-Dependent Cancer Cell Survival

Trefoil factor 3 (TFF3) is a secreted protein with an established oncogenic function and a highly significant association with clinical progression of various human malignancies. Herein, a novel small molecule that specifically targets TFF3 homodimeric functions was identified. Utilizing the concept of reversible covalent interaction, 2-amino-4-(4-(6-fluoro-5-methylpyridin-3-yl)phenyl)-5-oxo-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile (AMPC) was identified as a molecule that interacted with TFF3. AMPC monomerized the cellular and secreted TFF3 homodimer at the cysteine (Cys)57-Cys57 residue with subsequent more rapid degradation of the generated TFF3 monomers. Hence, AMPC treatment also resulted in cellular depletion of TFF3 with consequent decreased cell viability in various human carcinoma-derived TFF3 expressing cell lines, including estrogen receptor positive (ER+) mammary carcinoma (MC). AMPC treatment of TFF3 expressing ER+ MC cells significantly suppressed total cell number in a dose-dependent manner. Consistently, exposure of TFF3 expressing ER+ MC cells to AMPC decreased soft agar colony formation, foci formation, and growth in suspension culture and inhibited growth of preformed colonies in 3D Matrigel. AMPC increased apoptosis in TFF3 expressing ER+ MC cells associated with decreased activity of EGFR, p38, STAT3, AKT, and ERK, decreased protein levels of CCND1, CCNE1, BCL2, and BCL-XL, and increased protein levels of TP53, CDKN1A, CASP7, and CASP9. siRNA-mediated depletion of TFF3 expression in ER+ MC cells efficiently abrogated AMPC-stimulated loss of cell viability and CASPASE 3/7 activities. Furthermore, in mice bearing ER+ MC cell-generated xenografts, AMPC treatment significantly impeded xenograft growth. Hence, AMPC exemplifies a novel mechanism by which small molecule drugs may inhibit a dimeric oncogenic protein and provides a strategy to impede TFF3-dependent cancer progression.