Cellules dendritiques et gliomes : un espoir en immunothérapie ?

Editorial: on the road to multi-modal and pluri-disciplinary treatment of glioblastomas

Despite major advances in the management of malignant gliomas of which glioblastomas represent the ultimate grade of malignancy, they remain incurable. Indeed, glioblastoma patients have a median survival expectancy of only 14 months on the current standard treatment of surgical resection to the extent which is feasible, followed by adjuvant radiotherapy plus temozolomide given concomitantly with and after radiotherapy (Lefranc et al., J Clin Oncol 23:2411-2422, 2005; Expert Rev Anticancer Ther 6:719-732, 2006; Stummer et al., Neurosurgery 62:564-576, 2008). Accordingly, the present editorial discusses (1) the high cell motility and resistance to apoptosis which characterise glioblastoma growth and malignancy with respect to the failure of conventional therapy, (2) ways to overcome apoptosis resistance and the real hope offered by temozolomide, (3) targeted chemotherapeutic approaches and the disappointing results obtained in monotherapy but their potential in combination therapy, (4) anti-migratory strategies that could supplement conventional therapy notably by inhibiting a new target; the alpha1 subunit of the sodium pump, (5) dendritic cell therapy, (6) cancer stem cell targeting and finally (7) topical therapies and new surgical approaches for more radical resection which could be used to complement multi-modal treatments within a multi-disciplinary approach.

Present and potential future adjuvant issues in high-grade astrocytic glioma treatment

Despite major advances in the management of malignant gliomas of which glioblastomas represent the ultimate grade of malignancy, they remain characterized by dismal prognoses. Glioblastoma patients have a median survival expectancy of only 14 months on the current standard treatment of surgical resection to the extent feasible, followed by adjuvant radiotherapy plus temozolomide, given concomitantly with and after radiotherapy. Malignant gliomas are associated with such dismal prognoses because glioma cells can actively migrate through the narrow extra-cellular spaces in the brain, often travelling relatively long distances, making them elusive targets for effective surgical management. Clinical and experimental data have demonstrated that invasive malignant glioma cells show a decrease in their proliferation rates and a relative resistance to apoptosis (type I programmed cell death) as compared to the highly cellular centre of the tumor, and this may contribute to their resistance to conventional pro-apoptotic chemotherapy and radiotherapy. Resistance to apoptosis results from changes at the genomic, transcriptional and post-transcriptional level of proteins, protein kinases and their transcriptional factor effectors. The PTEN/ PI3K/Akt/mTOR/NF-kappaB and the Ras/Raf/MEK/ERK signaling cascades play critical roles in the regulation of gene expression and prevention of apoptosis. Components of these pathways are mutated or aberrantly expressed in human cancer, notably glioblastomas. Monoclonal antibodies and low molecular-weight kinase inhibitors of these pathways are the most common classes of agents in targeted cancer treatment. However, most clinical trials of these agents as monotherapies have failed to demonstrate survival benefit. Despite resistance to apoptosis being closely linked to tumorigenesis, tumor cells can still be induced to die by non-apoptotic mechanisms such as necrosis, senescence, autophagy (type II programmed cell death) and mitotic catastrophe. Temozolomide brings significant therapeutic benefits in glioblastoma treatment. Part of temozolomide cytotoxic activity is exerted through pro-autophagic processes and also through the induction of late apoptosis. Autophagy, type II programmed cell death, represents an alternative mechanism to overcome, at least partly, the dramatic resistance of many cancers to pro-apoptotic-related therapies. Another way to potentially overcome apoptosis resistance is to decrease the migration of malignant glioma cells in the brain, which then should restore a level of sensitivity to pro-apoptotic drugs. Recent series of studies have supported the concept that malignant gliomas might be seen as an orchestration of cross-talks between cancer cells, microenvironment, vasculature and cancer stem cells. The present chapter focuses on (i) the major signaling pathways making glioblastomas resistant to apoptosis, (ii) the signaling pathways distinctly activated by pro-autophagic drugs as compared to pro-apoptotic ones, (iii) autophagic cell death as an alternative to combat malignant gliomas, (iv) the major scientific data already obtained by researchers to prove that temozolomide is actually a pro-autophagic and pro-apoptotic drug, (v) the molecular and cellular therapies and local drug delivery which could be used to complement conventional treatments, and a review of some of the currently ongoing clinical trials, (vi) the fact that reducing the levels of malignant glioma cell motility can restore pro-apoptotic drug sensitivity, (vii) the observation that inhibiting the sodium pump activity reduces both glioma cell proliferation and migration, (viii) the brain tumor stem cells as a target to complement conventional treatment.