Molecular cytogenetic comparison between stem-like cell lines isolated from glioblastoma multiforme

Emerging evidence in the literature suggests the presence of a small subset of cells within tumors, called cancer stem cells (CSCs), that drive tumor formation and growth and are responsible for tumor recurrence. Long-lived stem cells are strongly exposed to genotoxic stresses and, therefore, are prone to the accumulation of different mutations, a key factor in carcinogenesis. Brain tumor stem cells have been identified and isolated from different types of brain tumors, including glioblastoma multiforme (GBM), one of the most common and malignant tumors of central nervous system. GBM is characterized by resistance to surgical resection, radiotherapy, and chemotherapy. In fact, conventional therapies may reduce the tumor mass by killing mainly cells with limited proliferative potential (the “bulk tumor”), but they do not kill CSCs that are able to re-generate new tumors. Therefore it would be interesting to study the mechanism that controls CSCs from the genetic point of view, in order to design new targeted therapeutic approaches restricted to stem cells. In this study we carried out a molecular cytogenetic analysis on two CSC lines isolated from a patient affected by GBM, named GBM2 and GBM7. In particular the karyotypes were evaluated using conventional cytogenetic analysis through QFQ-banding. Then the molecular karyotypes were investigated by array CGH using a Human Genome CGH microarray kit 44K (Agilent Technologies) to underline similarities and differences between the two lines. In particular we found in both lines polyploidy for chromosome 7 (more than four copies) and a complete loss of the region 9p21.1-21.3, which includes the CDKN2A and CDKN2B genes implicated in cell cycle regulatory pathways, including the p53 and retinoblastoma pathways. Therefore, we tested the efficacy of two antineoplastic drugs such as valproic acid (a histone deacetylase inhibitor) and paclitaxel (a microtubule depolymerization inhibitor) assessing, both on drug-treated and untreated cultures, different cytologic and cytogenetics parameters: chromosome number per metaphase, mitotic index, and nuclear morphology. All these data will be compared in order to address future studies on specific genes and to establish guidelines for expression studies and drug testing.