Exploring Cancer Stem Cells (CSCs) pathways to design novel therapies for glioblastoma treatment

Glioblastoma multiforme (GBM) is the most aggressive and common form of primary brain tumor in adults, with a median survival rate of 14 months (Taphoorn et al.;2005 ). GBM is characterized by rapid diffusely infiltrative growth and high level of cellular heterogeneity, which are fueled by dysregulation of multiple signaling pathaways. It is also characterized by multiple genetic alterations: the most frequent is the loss of heterozygosity (LOH) 10q; there are also epidermal growth factor receptor (EGFR) amplifications, TP53 and phosphatase and tensin homolog (PTEN) mutations. GBM is classified into primary glioblastoma developing rapidly de novo and secondary glioblastoma, usually developing from lower grade astrocytomas. Despite major therapeutic improvements made by combining neurosurgery, radiotherapy and chemotherapy, the prognosis and survival rate for patients with GBM remains poor (A.F.Carpentier and J.Y. Delattre. ;2005). There is a recognized need for new approaches based on increased understanding of the biological and molecular nature of these tumors. In recent years, it has been demonstrated that GBM possesses a hierarchical organization of heterogeneous cell populations which differ in their tumor-forming potential: there are both cells with a limited lifespan that are destined to abortive differentiation and will eventually stop dividing, and a small subset of self-renewing tumoral cells capable of initiating and maintaining tumor growth. These cells are called Glioblastoma Stem Cells (GBM-SCs) and share several features with neural stem cells (NSCs) including: the expression of neural markers such as Nestin and Sox2, the ability to migrate within the brain, the capacity to self-renew and to undergo multilineage differentiation and the responsiveness to similar signalling cues. Moreover, when compared to their non-stem progeny, GBM-SCs also show increased resistance to drugs and to the apoptosis-inducing mechanisms that are effective in conventional tumoral cell lines. The isolation of GBM-SCs has introduced a new and revolutionary paradigm in cancer therapy, since these cells are likely to include a population able to support tumor relapse and should therefore be considered a primary therapeutic target (Hirschmann-Jax, C. et al.;2004, Dean, Fojo, & Bates; 2005). Current therapeutic strategies do not take into account potential differences in drug sensitivity between the tumorigenic and the more abundant non-tumorigenic cells in the tumor. The opportunity to study GBM-SCs adds a radical change to the perspective by which the neoplastic phenomenon is observed and prompts for a detailed analysis of the molecular determinants of tumorigenicity. Indeed it has been suggested that tumor relapse after conventional chemotherapeutic treatment might be a consequence of an expansion sustained by Cancer Stem Cells (CSCs) that are spared by virtue of their relative quiescence and the expression of drug-effluxing membrane transporters. In this project, we proposed to identify therapeutic agents that efficiently kill GBM-SCs and might be useful to set up more effective treatments for GBM . To this aim, we analyzed the expression profiling of microRNAs (miRNAs) in samples in order to identify those with potential importance in tumor biology and we performed in vitro citotoxicity assays on our GBM-SC lines using a library of 80 kinase inhibitors, in order to identify and target pathways involved in tumor progression and maintenance. MiRNAs are emerging as important regulators of many biological processes, such as cellular differentiation and proliferation and have been implicated in the etiology of a variety of cancer. Libraries of synthetic compounds with known specificity have been screened in-vitro with the aim to study the sensitivity of tumor cells to the inhibition of a specific signal transduction pathway and the consequent development of targeted therapies.