Preclinical therapeutic efficacy of a novel blood-brain barrier-penetrant dual PI3K/mTOR inhibitor with preferential response in PI3K/PTEN mutant glioma.
A new tumor suppressor gene PTEN/MMAC1 was recently isolated at chromosome 10q23 and found to be inactivated by point mutation or homozygous deletion in glioma, prostate and breast cancer.
In this study we compared the intratumoral and circulating EPCs of glioma patients for a set of common glioma genotypical aberrations (amplification of EGFR; deletion of PTEN and aneusomy of chromosomes 7 and 10).
In contrast, ectopic expression of wild type PTEN, but not the PTEN(G129R) mutant, in PTEN-mutant gliomas markedly sensitizes these cells to irradiation and to CD95-ligand (CD95L)-induced apoptosis.
The present study suggests that PTEN mutations are late events in the malignant progression of glioma and the occurrence of PTEN mutations are significantly correlated to patients' short-term survival.
Six constitutional missense mutations of the p53 gene were identified (13.6%), but no mutations of the p16 and PTEN genes were found, suggesting that (1) germline p53 mutations contribute to a small portion of astrocytic tumors, (2) inherited mutations of the p16 and PTEN gene do not predispose to the development of gliomas, and (3) other genes are involved in glioma predisposition.
Moreover, the clinical PtdIns3K-mTOR inhibitor NVP-BEZ235 cooperates with the clinical lysosomotropic autophagy inhibitor chloroquine to induce apoptosis in PTEN-mutant glioma xenografts in vivo, offering a therapeutic approach translatable to patients.
However, knockdown of both PTEN and p53 mutation could significantly rescue the p53 depletion-mediated growth inhibition, suggesting that the R280T mutation in glioma may promote the proliferation through an underlying mechanism related to PTEN.
Then, we also analyzed the impact of TERT promoter mutations, PTEN deletion, EGFR amplification and MGMT promoter methylation in diagnosis, prognosis and response to therapy in glioma molecular subgroup.
The sequence analysis of PTEN/MMAC1 revealed nucleotide alterations in 1/8 (12.5%) low-grade gliomas in a tumor with LOH at l0q21-qtel and in 5/21 (24%) high-grade gliomas displaying LOH that always included 10q23-26.
The effects of LY294002, a biochemical inhibitor of PI3-kinase, on the response to radiation were examined in the PTEN mutant glioma cell line U251 MG. Low doses of LY294002 sensitized U251 MG to clinically relevant doses of radiation.
These findings indicate that PTEN gene mutation contributes not only to the neoplastic evolution in gliomas but also to the meningeal dissemination of glioma cells.
Univariate analysis showed that tumour grade, vascularization, PTEN mutation, LOH and combination of both PTEN mutation and LOH were significantly associated with glioma patients' survival.
We did whole exome sequencing for 11 GBM-PN cases and found that the percentage of TP53, PIK3CA, PIK3R1, or PTEN mutation in our GBM-PN cases (72.7%, 27.3%, 27.3%, and 27.3% respectively) was much higher than that in cases in TCGA GBM 2008, TCGA GBM 2013, and TCGA lower-grade glioma databases.
Although the phosphatidylinositol 3-kinase to Akt to mammalian target of rapamycin (PI3K-Akt-mTOR) pathway promotes survival signaling, inhibitors of PI3K and mTOR induce minimal cell death in PTEN (phosphatase and tensin homolog deleted from chromosome 10) mutant glioma.
The reported patient, in addition to glioma, had suffered from benign meningioma in the past but did not show any clinical signs of Cowden disease or other hereditary diseases typically associated with PTEN germline mutations.
Ethnicity-stratified subgroup analysis demonstrated that PTEN gene mutations were closely linked to poor prognosis in glioma among Americans (HR = 3.72, 95 % CI = 1.72∼5.73, P < 0.001), while similar correlations were not observed among populations in Sweden, Italy, and Malaysia (all P > 0.05).
In order to study the mechanisms by which migration of glioma cells can be inhibited by the upregulation of the PTEN gene, we studied two glioma cell lines (SNB19 and U251) and two glioma xenograft cell lines (4910 and 5310) alone and in co-culture with human umbilical cord blood-derived mesenchymal stem cells (hUCBSC).