Mutant IDH1 inhibits PI3K/Akt signaling in human glioma.

BACKGROUND: Recently, isocitrate dehydrogenase 1 (IDH1) was identified as a major participant in glioma pathogenesis. At present, the enzymatic activity of the protein has been the main topic in investigating its physiological function, but its signaling pathway allocation was unsuccessful. Interestingly, proteins regulated by phosphoinositide 3-kinase (PI3K)/Akt signaling, are among the top downregulated genes in gliomas associated with high percentage of IDH1 and IDH2 mutations. The aim of this study was to investigate a hypothetical relation between IDH1 and PI3K signaling. METHODS: The presence of mutant IDH1 and markers for active PI3K/Akt signaling, present as phosphorylated Akt and podoplanin (PDPN), were investigated in a discovery cohort of 354 patients with glioma. In vitro experiments were used to confirm functional links. RESULTS: This study shows an inverse correlation between mutant IDH1 and markers for active PI3K/Akt signaling. In support of a functional link between these molecules, in vitro expression of mutant IDH1 inhibited Akt phosphorylation in a 2-hydroxyglutarate-dependent manner. CONCLUSIONS: This study provides patient tumor and in vitro evidence suggesting that mutant IDH1 inhibits PI3K/Akt signaling.

Additive effect on survival of Raf kinase inhibitor protein and signal transducer and activator of transcription 3 in high-grade glioma.

BACKGROUND: Animal studies have shown cooperative contribution of the Ras/Raf/MAPK and PI3K/Akt/mTOR signaling pathways in glioblastoma formation. However, this joint action has not yet been confirmed in human studies. METHODS: The expression of Raf kinase inhibitory protein (RKIP) was examined in 159 patients with high-grade and low-grade gliomas and correlated with previously obtained data on the activation of signal transducer and activator of transcription 3 (STAT3), a downstream effector of the PI3K/Akt/mTOR signaling pathway. RESULTS: RKIP expression was associated with a longer overall survival in high-grade glioma cases without showing a direct or inverse correlation with tyrosine-705 phosphorylation of STAT3 (pSTAT3). Notably, RKIP-positive and pSTAT3 negative cases demarcate a patients group with exceptionally long survival, exceeding the prognostic impact of each single marker. CONCLUSIONS: The results of this study indicated that 1) RKIP expression correlates with tumor grade and is a marker for good prognosis in high-grade gliomas; 2) RKIP expression and lack of pSTAT3 have a cumulative prognostic impact; and 3) RKIP and pSTAT3 are likely to operate independently to influence survival. These findings represented the first human evidence of an additive effect of 2 distinct signaling pathways in high-grade glioma, suggesting that simultaneous inhibition of multiple pathways should be considered as a treatment strategy for these patients.

STAT3 tyrosine phosphorylation influences survival in glioblastoma.

Signal transducer and activator of transcription protein 3 (STAT3) is a regulator of central nervous system (CNS) development and a promising therapeutic target in human cancers. Activation of STAT3 promotes oncogenesis in a variety of tissues, but knowledge of its role in glioblastoma is still limited. Recent results indicate that STAT3 acts as a tumor suppressor or an oncogene depending upon the genetic background of the tumor. Here we immunohistochemically assessed Y705-phosphorylated STAT3 (pY705-STAT3) in formalin-fixed, paraffin-embedded specimens of 111 patients with supratentorial glioblastomas and 25 patients with supratentorial grade III gliomas. We found that glioblastoma patients with high or very high numbers of pY705-STAT3-positive tumor cells had significantly shorter overall survival than those with no or low numbers (P = 0.001, Cox regression). Interestingly the proportion of grade III glioma cases with high or very high numbers of pY705-STAT3-positive tumor cells was similar to that in glioblastoma. Our findings provide evidence that activation of STAT3 by Y705 phosphorylation is linked with clinically more aggressive behavior in glioblastomas, but is most likely not associated with tumor progression of grade III gliomas. In sum, our results suggest that STAT3 inhibition should be considered as a therapeutic approach in malignant gliomas.

Expression of mutated isocitrate dehydrogenase-1 in gliomas is associated with p53 and EGFR expression.

Gliomas are the most common primary brain tumours. Several independent studies have shown that isocitrate dehydrogenase 1 (IDH1) mutation in diffuse gliomas is associated with a more favourable patient outcome. The aim of this study was to evaluate the prognostic relevance of an antibody specifically detecting the R132H point mutation of IDH1 in tissue sections in a large series of human gliomas. Surgical specimens of 220 consecutive patients with infiltrative low and high-grade gliomas were included in this retrospective study. In multivariate analysis, IDH expression did not reach significance (p = 0.122) in regard to prognosis, in contrast to WHO grade and age at time of surgery (p < 0.001, Cox regression). A significant correlation of p53 expression to mutated IDH1 and histological grading and an inverse correlation to truncated EGFR expression were observed (p < 0.001, Mann-Whitney test). In sum, our results indicate that IDHR132H mutation correlates significantly with p53 and inversely with EGFR mutations. Further studies should investigate whether these correlations reflect involvement of these three molecules in a common signalling pathway.