KDM1 blockers reduce proliferation of oncogene-driven and therapy-resistant breast cancer cells. Therapy-resistant (A) MCF-7-HER2, (B) MCF-7-PELP1 and (C) MCF-7-TamR model cells were treated with or without NCL-1 (10 μM) alone or in combination with tamoxifen (Tam) or letrozole (Let), and cell proliferation was determined. (D) MCF-7-TamR cells were treated with or without KDM1 inhibitor (pargyline, 3 mM) alone or in combination with tamoxifen (Tam) or letrozole (Let), and cell proliferation was determined using the Cell Titer Glo assay. All experimental data points used are generated from three biological replicates. Statistical significance determined by Student's t test. ***P < 0.001, **P < 0.01, *P < 0.05. KDM1, lysine-specific histone demethylase 1; NCL-1, N-((1S)-3-(3-(trans-2-aminocyclopropyl)phenoxy)-1-(benzylcarbamoyl)propyl)benzamide; PELP1, proline glutamic acid and leucine-rich protein 1.