Abstract 5313: Phosphoproteomic analysis with reverse phase protein array identifies N-myc downstream regulated gene 1 (NDRG1) as a biomarker of phosphatidylinositol-3-kinase (PI3K)α inhibitor activity in a PTEN-deficient glioma cell line

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Aberrant activation of phosphoinositide 3-kinase (PI3K) signaling is commonly reported in cancer, and leads to deregulation of several intracellular processes, including cell survival, growth, proliferation and migration. PI3K activates AKT, serum/glucocorticoid regulated kinase (SGK), phosphoinositide -dependent kinase 1 (PDK1), mammalian target of rapamycin (mTOR), and several other molecules involved in cell progression and survival. Reports have also indicated that the deletion of the gene encoding the tumor suppressor phosphatase and tensin homologue (PTEN) is one of the key factors controlling activation of the PI3K pathway. Glioblastoma (GBM), the most common malignant brain tumor in adults, represents a compelling disease for kinase inhibitor therapy. Although many therapies to target the Ras-PI3K-mTOR axis in GBM have been attempted, their efficacies have not been pronounced, presumably because of the complexity of PI3K mediated signaling. To elucidate the role of PTEN in PI3K signaling, the phosphorylation status of two glioma cell lines, LN229 (wild type PTEN) and U-87 MG (PTEN deficient) was investigated with phosphoproteomic reverse phase protein array (RPPA). When basal phosphorylation was compared between both cell lines, the phosphorylation of N-myc downstream regulated gene 1 (NDRG1) (Thr346), a physiological substrate of SGK1, was increased in U-87 MG cells compared with levels in LN229 cells. These data suggest that PTEN deletion affects the phosphorylation status of NDRG1 in U-87 MG cells. Following treatment with PIK-90, a PI3Kα inhibitor, phosphorylation of Akt (Ser473) and its direct substrate PRAS40 (Thr246) were decreased in both cell lines, however, NDRG1 (Thr346) phosphorylation was strongly inhibited only in U-87 MG cells. These results suggest that the differential effects of PIK-90 on LN229 and U-87 MG cells is PTEN dependent, and that detecting NDRG1 (Thr346) phosphorylation could be a biomarker for PI3Kα inhibitor treatment in PTEN deleted cancer cells. Ongoing studies are focusing on elucidating the mechanism of action of PIK-90 in glioma cell lines. Citation Format: Takeomi Inoue, Naoko Iwata, Eiji Nishiwaki, Yasuyuki Kirii. Phosphoproteomic analysis with reverse phase protein array identifies N-myc downstream regulated gene 1 (NDRG1) as a biomarker of phosphatidylinositol-3-kinase (PI3K)α inhibitor activity in a PTEN-deficient glioma cell line. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5313. doi:10.1158/1538-7445.AM2014-5313