DDDR-08. PIM1 INHIBITION: A NOVEL THERAPEUTIC APPROACH FOR IDH-MUTANT GLIOMAS

Abstract BACKGROUND PIM1, a constitutively active serine/threonine kinase has emerged as a relevant target in cancer treatment. Previously, we discovered that IDH-mutant glioma exhibited high kinase activity of PIM1, suggesting an increased sensitivity to PIM1 inhibition. Here we sought to investigate PIM1 inhibition as a therapeutic approach for IDH-mutant gliomas. METHODS Patient-derived IDH-mutant and wildtype glioma cell lines were used to evaluate the impact of PIM1inhibition on cell viability, proliferation, and colony formation. mRNA and protein expression of PIM1 were determined by qRT-PCR, Western-blot, and immunohistochemistry. m6A dot-blot assay was conducted to detect m6A RNA levels in glioma cells. m6A modification status and its location in PIM1 transcript were evaluated by m6A RNA immunoprecipitation array. RNA-binding protein immunoprecipitation was performed using anti-YTHDF1 antibody to identify PIM1 RNA-YTHDF1 protein interactions. RESULTS An upregulation of PIM1 protein is demonstrated in IDH-mutant patient tumor tissues and cells. A pan-PIM inhibitor, AZD1208 significantly suppressed cell viability, cell proliferation, and colony formation in IDH-mutant cells but had a lesser effect in IDH-wildtype cells. Interestingly, a lower mRNA expression of PIM1 is observed, while the protein level is significantly elevated in IDH-mutant cells compared to wildtype cells, suggesting post-transcriptional and translational regulation of PIM1 associated with IDH mutation. Mechanistically, 2-hydroxyglutarate, unique to IDH-mutant gliomas, competitively inhibits α-KG-dependent RNA demethylase FTO. We demonstrated suppressed FTO activity and an increased m6A RNA level in IDH-mutant glioma cells. An enrichment of m6A modification at motif “GG (m6A) CU” located in the 3’UTR is found in the PIM1 transcript. Furthermore, we demonstrated that the m6A modification site is recognized by the m6A reader YTHDF1 to promote protein translation, leading to an elevated PIM1 protein expression. CONCLUSION m6A RNA modification contributes to an enhanced PIM1 activity and thereby a selective sensitivity to PIM1 inhibition in IDH-mutant gliomas.