Heterogeneity of tumor cell DNA content

Anaplasia and Heterogeneity of Gfap Expression in Gliomas

GFAP (glial fibrillary acidic protein) distribution was investigated in selected areas of glioblastomas and astrocytomas. The proliferating cell population of glioblastomas was GFAP negative and contained many mitoses which were also negative. The old, deeply located areas were composed of cells with visible cytoplasm, intensely GFAP-positive; mitoses in these areas were both GFAP-positive and negative. GFAP-positive reactive astrocytes, once trapped in the tumor, were no longer distinguishable from positive tumor cells. They sometimes contained mitoses. In astrocytoma, anaplasia was due to the development of a GFAP-negative population with negative mitoses. The problem of dedifferentiation and differentiation of malignant gliomas in discussed taking into account the possiblity that malignancy may be due to increasing mutation rates of tumors. The problem of redifferentiation of already dedifferentiated cells is also discussed.

The mitotic machinery as a source of genetic instability in cancer

Development and growth of all organisms involves the faithful reproduction of cells and requires that the genome be accurately replicated and equally partitioned between two cellular progeny. In human cells, faithful segregation of the genome is accomplished by an elaborate macromolecular machine, the mitotic spindle. It is not difficult to envision how defects in components of this complex machine molecules that control its organization and function and regulators that temporally couple spindle operation to other cell cycle events could lead to chromosome missegregation. Recent evidence indicates that the persistent missegregation of chromosomes result in gains and losses of chromosomes and may be an important cause of aneuploidy. This form of chromosome instability may contribute to tumor development and progression by facilitating loss of heterozygocity (LOH) and the phenotypic expression of mutated tumor suppressor genes, and by favoring polysomy of chromosomes that harbor oncogenes. In this review, we will discuss mitotic defects that cause chromosome missegregation, examine components and regulatory mechanisms of the mitotic machine implicated in cancer, and explore mechanisms by which chromosome missegregation could lead to cancer.

Chromosome number and carmustine sensitivity in human gliomas

BACKGROUND

Although some patients with malignant gliomas respond to treatment with chemotherapeutic agents like BCNU, tumor recurrence inevitably occurs, heralding the development of chemoresistance. Treating and/or preventing chemoresistance requires distinguishing newly developed resistance from the presence of intrinsically resistant cells in the primary tumor population. This study relates the chromosomal complements of freshly resected astrocytomas to the cells' chemosensitivity and ultimately to the patients' response to treatment.

METHODS

The authors dissociated 31 freshly resected human gliomas (5 astrocytomas, 10 anaplastic astrocytomas, 16 glioblastomas multiforme) into single cells, and performed cytogenetic analysis and BCNU sensitivity testing using the colony-forming assay (CFA) on first division cells from these tumors.

RESULTS

The major cytogenetic abnormalities involved the loss of a sex chromosome in all three classes of gliomas and the gain of chromosome 7 in anaplastic astrocytoma and glioblastoma multiforme; clonal marker chromosomes were observed in only anaplastic astrocytoma and glioblastoma multiforme with no common rearrangement observed among the tumors. The five astrocytomas were near-diploid (2n+/-, 35-57 chromosomes/cell), and all were resistant to BCNU. Seven of ten anaplastic astrocytomas were composed primarily of 2n+/- cells and were BCNU resistant. Three other anaplastic astrocytomas had a 39% or greater representation of 4n+/- cells (88-101 chromosomes/cell), and these tumors were sensitive to BCNU. Ten of 16 glioblastomas multiforme were composed predominantly of 2n+/- cells and were resistant to carmustine. Six other glioblastomas multiforme had at least 41% 3n+/- (58-87 chromosomes/metaphase) and 4n+/- cell populations and were sensitive to carmustine. Thus, gliomas demonstrating BCNU sensitivity were more than 60% hyperdiploid (60 or more chromosomes/metaphase) with 1 to 8 clonal marker chromosomes and multiple clonal populations involving complex karyotypic deviations. In contrast, all 22 resistant tumors were composed primarily of near-diploid cells. Only 4 of 22 tumors had a clonal marker, and the chromosome ploidy changes were less extensive.

CONCLUSIONS

In freshly resected untreated human gliomas, BCNU is most effective against hyperdiploid cells that have extensive ploidy changes and chromosome rearrangement, whereas resistance to carmustine is characteristic of near-diploid populations with few ploidy changes and rearranged chromosomes. This observation was consistent for all three classes of gliomas.