Luteolin inhibits Musashi1 binding to RNA and disrupts cancer phenotypes in glioblastoma cells

RNA binding proteins have emerged as critical oncogenic factors and potential targets in cancer therapy. In this study, we evaluated Musashi1 (Msi1) targeting as a strategy to treat glioblastoma (GBM); the most aggressive brain tumor type. Msi1 expression levels are often high in GBMs and other tumor types and correlate with poor clinical outcome. Moreover, Msi1 has been implicated in chemo- and radio-resistance. Msi1 modulates a range of cancer relevant processes and pathways and regulates the expression of stem cell markers and oncogenic factors via mRNA translation/stability. To identify Msi1 inhibitors capable of blocking its RNA binding function, we performed a similar to 25,000 compound fluorescence polarization screen. NMR and LSPR were used to confirm direct interaction between Msi1 and luteolin, the leading compound. Luteolin displayed strong interaction with Msi1 RNA binding domain 1 (RBD1). As a likely consequence of this interaction, we observed via western and luciferase assays that luteolin treatment diminished Msi1 positive impact on the expression of pro-oncogenic target genes. We tested the effect of luteolin treatment on GBM cells and showed that it reduced proliferation, cell viability, colony formation, migration and invasion of U251 and U343 GBM cells. Luteolin also decreased the proliferation of patient-derived glioma initiating cells (GICs) and tumor-organoids but did not affect normal astrocytes. Finally, we demonstrated the value of combined treatments with luteolin and olaparib (PARP inhibitor) or ionizing radiation (IR). Our results show that luteolin functions as an inhibitor of Msi1 and demonstrates its potential use in GBM therapy.