TWIST1, an epithelial-mesenchymal transition (EMT) transcription factor, is 
critical for oncogene-driven non-small cell lung cancer (NSCLC) tumorigenesis. 
Given the potential of TWIST1 as a therapeutic target, a chemical-bioinformatic 
approach using connectivity mapping (CMAP) analysis was used to identify TWIST1 
inhibitors. Characterization of the top ranked candidates from the unbiased 
screen revealed that harmine, a harmala alkaloid, inhibited multiple TWIST1 
functions, including single-cell dissemination, suppression of normal branching 
in 3D epithelial culture, and proliferation of oncogene driver-defined NSCLC 
cells. Harmine treatment phenocopied genetic loss of TWIST1 by inducing 
oncogene-induced senescence or apoptosis. Mechanistic investigation revealed 
that harmine targeted the TWIST1 pathway through its promotion of TWIST1 protein 
degradation. As dimerization is critical for TWIST1 function and stability, the 
effect of harmine on specific TWIST1 dimers was examined. TWIST1 and its dimer 
partners, the E2A proteins, which were found to be required for TWIST1-mediated 
functions, regulated the stability of the other heterodimeric partner 
posttranslationally. Harmine preferentially promoted degradation of the 
TWIST1-E2A heterodimer compared with the TWIST-TWIST1 homodimer, and targeting 
the TWIST1-E2A heterodimer was required for harmine cytotoxicity. Finally, 
harmine had activity in both transgenic and patient-derived xenograft mouse 
models of KRAS-mutant NSCLC. These studies identified harmine as a 
first-in-class TWIST1 inhibitor with marked anti-tumor activity in 
oncogene-driven NSCLC including EGFR mutant, KRAS mutant and MET altered 
NSCLC.Implications: TWIST1 is required for oncogene-driven NSCLC tumorigenesis 
and EMT; thus, harmine and its analogues/derivatives represent a novel 
therapeutic strategy to treat oncogene-driven NSCLC as well as other solid tumor 
malignancies. Mol Cancer Res; 15(12); 1764-76. ©2017 AACR.