Correlation between genetic alterations and growth of human malignant glioma xenografted in nude mice.

In order to develop preclinical models of malignant astrocytomas and oligodendrogliomas, a series of 54 resected gliomas (37 from oligodendroglial lineage and 17 from astrocytic lineage) were xenografted subcutaneously into nude mice. Molecular alterations commonly observed in gliomas subtypes, including LOH 1p and 1q, LOH 19q, LOH 10p and 10q, LOH 9p, TP53 and PTEN mutations, EGFR amplification, CDKN2A homozygous deletion and telomerase reactivation were systematically screened in the original and xenografted tumours. In all, 23 gliomas grew in nude mice. The most anaplastic tumours were selected as shown by pathological and molecular studies of the original tumour as well as shorter survival in patients whose tumours were successfully grafted. Comparison between the two growth profiles showed that 10q LOH and EGFR amplification gave a tumorigenic advantage. With a few exceptions, the genetic pattern was remarkably stable before and after growth in nude mice. These results suggest that subcutaneous xenografts are useful and reproducible models to analyse the molecular profile of malignant astrocytoma and oligodendroglioma. This represents the first step to improve our understanding of the correlations between molecular alterations and response to standard or experimental therapies.

Telomerase reactivation in malignant gliomas and loss of heterozygosity on 10p15.1.

An inhibitor of telomerase activity maps to chromosome 10p15.1. A series of 51 high-grade gliomas was analyzed for loss of heterozygosity (LOH) on chromosome 10 and for telomerase activity. In univariate analysis, LOH10p (59%) and LOH10q (61%) were associated with telomerase activity (55%; p < 0.0001 and p = 0.0006). In multivariate analysis, only LOH10p remained statistically related to telomerase activity, suggesting that the telomerase repressor gene located on 10p15.1 is inactivated in high-grade gliomas.

Molecular heterogeneity of oligodendrogliomas suggests alternative pathways in tumor progression.

OBJECTIVE: To identify different genetic molecular profiles in oligodendrogliomas and to evaluate their prognostic significance. METHODS: The main genetic alterations reported in glial tumors were investigated in 26 oligodendrogliomas (10 World Health Organization grade II and 16 World Health Organization grade III). Correlation between identified molecular changes and pathologic grade or clinical course was subsequently analyzed using univariate and multivariate statistical analyses. RESULTS: Loss of heterozygosity (LOH) on chromosome 1p, 19q, and 10; P16/CDKN2A homozygous deletion; EGFR (epidermal growth factor receptor) amplification; and TP53 and PTEN mutations were observed in 14 (54%), 15 (58%), 9 (35%), 7 (27%), 5 (19%), 1 (4%), and 0 cases. LOH 1p and 19q were tightly associated (p < 0.0001). A mutual exclusion was found between LOH 1p/19q and EGFR amplification (p = 0.01), P16/CDKN2A deletions (p = 0.001), or LOH on 10q (p = 0.03), suggesting the existence of distinct genetic subsets in oligodendrogliomas. On univariate analysis, age <50 years (p = 0.002) and LOH 1p (p = 0.01) were associated with a longer progression-free survival (PFS) whereas LOH 10q (p = 0.03) and EGFR amplification (p = 0.007) were associated with a worse PFS. In multivariate analyses, age <50 years (p = 0.001) and LOH 1p (p = 0.006) remained independent predictive factors for PFS. CONCLUSION: These results provide evidence for two alternative molecular pathways of progression in oligodendrogliomas. The first one is associated with loss of 1p and 19q and the second one with P16/CDKN2A deletion, 10q loss, and EGFR amplification. The findings confirm the value of loss of 1p as predictor of longer progression-free survival; in addition, the study demonstrates the unfavorable impact of 10q loss and EGFR amplification on the prognosis.

Glioblastomas with an oligodendroglial component: a pathological and molecular study.

Glioblastoma (GBM) is considered by the WHO classification to represent the most malignant grade of the astrocytic tumors. However, a subset of GBM includes recognizable areas with oligodendroglial features, suggesting that some GBM may also have an oligodendroglial origin. The aim of this study was to analyze the molecular profile of GBM associated with an oligodendroglial component (GBMO). We analyzed a series of 25 GBMO. Loss of heterozygosity (LOH) on 1p and 19q, known as common markers of oligodendroglial tumors, were observed in 40% and 60% of cases, respectively; 72% of the tumors displayed one or both of these markers. All but 4 tumors (84%) showed alterations known to be preferentially involved in the progression of astrocytic tumors to GBM, such as EGFR amplification (44%), P16 deletion (48%), LOH on 10q (64%), PTEN (20%), and TP53 (24%) mutations. Therefore, GBMO displayed all the genetic aberrations found in "standard" GBM with a comparable incidence, but differed from GBM by having a higher rate of LOH on 1p and 19q. These results suggest that GBMO might represent a subgroup of tumors of oligodendroglial origin that is distinct from the "standard" GBM in terms of tumorigenesis pathway.

OLIG2 as a specific marker of oligodendroglial tumour cells.

OLIG2 is a recently identified transcription factor involved in the specification of cells in the oligodendroglial lineage. We investigated the expression of OLIG2 by in-situ hybridisation in 21 brain tumours: nine grade II and III oligodendrogliomas, three grade II oligoastrocytomas, and nine non-oligodendroglial tumours (four grade IV astrocytomas, two meningiomas, a dysembryoplastic neuroepithelial tumour, and two metastases). OLIG2-positive cells corresponding to neoplastic oligodendrocytes were present in all oligodendrogliomas and oligoastrocytomas. By contrast, OLIG2 expression was not detected in the non-oligodendroglial tumours. Thus, oligodendroglioma probably arise from oligodendrocyte precursor cells. OLIG2 should prove a useful marker for the diagnosis of oligodendroglial tumours.

P18 tumor suppressor gene and progression of oligodendrogliomas to anaplasia.

P18INK4C is a good candidate to be the tumor suppressor gene involved in oligodendrogliomas on 1p32. Loss of heterozygosity on 1p, mutation(s), homozygous deletion(s), and expression of p18 in 30 oligodendroglial tumors were investigated. Loss of heterozygosity on 1p was found in 15 tumors. A p18 mutation was found at an recurrence of an anaplastic oligodendroglioma, but not in the primary, low-grade tumor. No homozygous deletions were found and p18 was expressed in all cases. These results show that p18 alteration is involved in tumor progression in a subset of oligodendrogliomas.

Frequent loss of 1p32 region but no mutation of the p18 tumor suppressor gene in meningiomas.

After chromosome 22 and NF2 inactivation, the loss of chromosome 1p is one of the most frequent abnormalities encountered in meningiomas. However the putative tumor suppressor gene located on 1p inactivated in meningiomas has still to be identified. We screened 68 meningiomas for LOH on chromosome 22 and 1. We found 34 LOH on the NF2 region on chromosome 22 (50%) and 19 LOH on 1p (28%), 16 being associated with loss of chromosome 22. Partial deletions delimited a candidate region located between D1S234 and D1S2797. The p18INK4C tumor suppressor gene, a member of the genes family coding for inhibitors of cyclin-dependent kinases, is located in this region. To determine whether p18 is involved in development of meningiomas, we performed a mutation analysis of the p18 gene and a search for homozygous deletion in the 19 meningiomas with 1p loss. Sequencing analysis of the p18 gene revealed one polymorphism, but no somatic mutations and no homozygous deletions were found. These results confirm that the loss of chromosome 1p32 is a frequent feature in meningiomas, however the p18 tumor suppressor gene which is located in this region, does not seem to be involved.