title: Genome-wide effects of MELK-inhibitor in triple-negative breast cancer cells indicate context-dependent response with p53 as a key determinant.
abstract: Triple-negative breast cancer (TNBC) is an aggressive, highly recurrent breast cancer subtype, affecting approximately one-fifth of all breast cancer patients. Subpopulations of treatment-resistant cancer stem cells within the tumors are considered to contribute to disease recurrence. A potential druggable target for such cells is the maternal embryonic leucine-zipper kinase (MELK). MELK expression is upregulated in mammary stem cells and in undifferentiated cancers, where it correlates with poor prognosis and potentially mediates treatment resistance. Several MELK inhibitors have been developed, of which one, OTSSP167, is currently in clinical trials. In order to better understand how MELK and its inhibition influence TNBC, we verified its anti-proliferative and apoptotic effects in claudin-low TNBC cell lines MDA-MB-231 and SUM-159 using MTS assays and/or trypan blue viability assays together with analysis of PARP cleavage. Then, using microarrays, we explored which genes were affected by OTSSP167. We demonstrate that different sets of genes are regulated in MDA-MB-231 and SUM-159, but in both cell lines genes involved in cell cycle, mitosis and protein metabolism and folding were regulated. We identified p53 (TP53) as a potential upstream regulator of the regulated genes. Using western blot we found that OTSSP167 downregulates mutant p53 in all tested TNBC cell lines (MDA-MB-231, SUM-159, and BT-549), but upregulates wild-type p53 in the luminal A subtype MCF-7 cell line. We propose that OTSSP167 might have context-dependent or off-target effects, but that one consistent mechanism of action could involve the destabilization of mutant p53.
authors.affiliation: Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Texas, United States of America.
authors.forename: Marisa
authors.initials: M
authors.lastname: Simon
authors.affiliation: Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Texas, United States of America.
authors.forename: Fahmi
authors.initials: F
authors.lastname: Mesmar
authors.affiliation: Institute for Research in Biomedicine, Department of Biosciences, University of Aveiro, Aveiro, Portugal.
authors.forename: Luisa
authors.initials: L
authors.lastname: Helguero
authors.affiliation: Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, Texas, United States of America.|Division of Proteomics, SciLifeLab, School of Biotechnology, KTH - Royal Institute of Technology, Solna, Sweden.|Department of Biosciences and Nutrition, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Cecilia
authors.identifier: http://orcid.org/0000-0002-0602-2062
authors.initials: C
authors.lastname: Williams
mesh_terms: D017209:Apoptosis; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004252:DNA Mutational Analysis; D016208:Databases, Factual; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D042361:Mammary Glands, Human / Q000166:cytology; D008938:Mitosis; D050505:Mutant Proteins / Q000187:drug effects*; D009287:Naphthyridines / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects*; D015854:Up-Regulation
chemical_list: C585656:1-(6-(3,5-dichloro-4-hydroxyphenyl)-4-((4-((dimethylamino)methyl)cyclohexyl)amino)-1,5-naphthyridin-3-yl)ethanone; D050505:Mutant Proteins; D009287:Naphthyridines; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C484610:MELK protein, human; D017346:Protein Serine-Threonine Kinases