Abstract 350: NVP-BKM120: A selective pan-PI3 kinase inhibitor induces G2/M arrest in glioma cell lines via FOXO3a and GADD45a loop

Abstract

Abstract Genetic alterations that activate the phosphatidylinositol-3-kinase (PI3K)/PTEN/Akt pathway occur commonly in cancers, either via mutations in the p110α catalytic subunit of PI3K or loss of PTEN. 70-80% of malignant gliomas showed an abnormal activation of the PI3K/Akt signaling cascade -mostly by loss of PTEN (a negative regulator of the PI3K pathway)- that results in increased proliferation, survival, neovascularization, glycolysis and invasion. Therefore, kinases within this signaling pathway offer promising therapeutic targets for the identification of more effective treatments for gliomas. Herein, we describe the biological evaluation of a pan-PI3K inhibitor NVP-BKM120 (Novartis Pharma AG) in a panel of 10 well-characterized glioblastoma cell lines (e.g., U87, U251, LN229, LN18, and D54). NVP-BKM120 treatment for 72 hrs resulted in a dose-dependent growth inhibition with IC50 values in the low μM range. Consistent with its mechanism of action, NVP-BKM120 effectively blocks the PI3K/Akt signaling cascade reducing the phosphorylation levels of downstream effectors like Akt, p70S6K1, and pS6. Although no obvious relationship was established between sensitivity to NVP-BKM120 treatment and the PTEN and/or EGFR status of the tumor cell line, we observed a differential sensitivity pattern with respect to p53 status. Thus, wild type p53 glioma cells were more sensitive to NVP-BKM120 treatment than p53 mutant or null glioma cells. The signaling pathway from PI3K to Akt controls cell survival and proliferation by inhibiting the activity of members of the FOXO family of transcription factors. The mammalian FOXO family of transcription factors, consisting of FOXO1, FOXO3a, and FOXO4, functions downstream of the PI3K signaling pathway and is a direct substrate of the protein kinase Akt. We showed that NVP-BKM120 controls G2-M transition by controlling FOXO3a. Inhibition of the PI3K/Akt signaling by NVP-BKM120 reversed the effect of EGF on FOXO3a inactivation and resulted in a nuclear FOXO3a accumulation, and decreased the fraction of FOXO3a phosphorylation. The growth arrest and DNA damage response gene Gadd45a appeared to be a direct target of FOXO3a that mediates part of FOXO3a's effects on G2-M arrest. These findings suggest a role for FOXO3a in inducing a block in the G2-M phase in response to PI3K inhibition by NVP-BKM120 via a Gadd45a-dependent mechanism. Parallel to the assessment of the compound in in-vitro settings, in vivo efficacy studies were performed using an i.c. U87 tumor model. Oral treatment with NVP-BKM120 was well tolerated and increased the median survival from 26 days (control cohort) to 38 and 48 days (treated cohorts). Ex-vivo analyses of tumor tissues at the end of the in vivo study showed significant inhibition of p-AKT and p-S6 in the treated animals. Further studies are warranted to determine the potential clinical use of NVP-BKM120 in the treatment of gliomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 350.