Cancer stem cells and malignant gliomas. From pathophysiology to targeted molecular therapy.

High grade gliomas, the most frequent and most malignant brain cancers, grow rapidly and infiltrate the cerebrospinal axis causing deficits in cognition, mobility, balance or speech and are typically resistant to radiation and chemotherapy. Despite recent progress, WHO grade III and IV gliomas still represent a great challenge in oncology, with overall poor outcomes and inevitable lethality. While radiotherapy and temozolomide are considered the standard first-line approach for therapy of newly diagnosed malignant gliomas, the treatment protocols for recurrent tumors remain ill-defined. Increasing evidence suggests that tumors of the central nervous system are derived from proliferatively active neural stem cells residing in defined neuropoietic niches of the adult brain. These cancer stem cells, also identified in other tumors, provide a reservoir of cells with self-renewal capabilities, can maintain the tumor by generating differentiated non-stem tumor cells and are responsible for recurrences after ablative neurosurgical therapy and chemoradiotherapy. The only way to successfully control recurrent malignant gliomas and even hope for a cure in the future is by combining standard chemotherapy with immunotherapy. Despite the apparent improvements of current treatments, it should be realized that the characteristic brain tumor niche may provide recurrent gliomas an "escape mechanism" from anticancer treatments. Thus, the use of targeted molecular therapy drugs may effectively inhibit or at least slow down cancer stem cell proliferation and stop the brain microenvironment from allowing furtive invasion and proliferation of highly aggressive malignant gliomas.

Metformin plus temozolomide-based chemotherapy as adjuvant treatment for WHO grade III and IV malignant gliomas.

PURPOSE: Glioblastoma multiforme (GBM) remains one of the most devastating diseases known to man and affects more than 17,000 patients in the United States alone every year. This malignancy infiltrates the brain early in its course and makes complete neurosurgical resection almost impossible. Recent years have brought significant advances in tumor biology, including the discovery that many cancers, including gliomas, appear to be supported by cells with stem-like properties. In the current study we have investigated the effects of combining metformin with the standard treatment-of-care, as this drug, already used in the treatment of diabetes mellitus, has shown surprising results in the treatment of breast cancer, being also associated with lower mortality in several other malignancies. METHODS: The subjects of the current study were 8 patients with newly diagnosed high-grade gliomas, operated at the Department of Neurosurgery - Clinical University Emergency Hospital, Cluj Napoca. Tumor tissue cultures were established and characterized using immunofluorescence microscopy and PCR analysis and the sensitivity to metformin, epidermal growth factor (EGF) and temozolomide (TMZ) was tested. Microvascular density (MVD) assay was performed on the tumor samples. RESULTS: Seven of the 8 cases had a positive correlation between the number of endothelial cells, the phenotype of isolated tumor cells and the response to adjuvant chemoradiotherapy. The isolated tumor cells had a stem-like behavior, being resistant to conventional drugs. In most cases there was no statistical significant difference between TMZ alone and TMZ plus EGF arms, but there was a important difference between TMZ alone and TMZ plus metformin arms in 6 of the cases. CONCLUSION: New drugs and targeted molecular therapies are important for future therapeutics, but sometimes we must not exclude drugs already used in the clinic that might have remarkable results. Such is the case of metformin, a drug used for decades in the treatment of type 2 diabetes mellitus that has proven to enhance the effect of TMZ in the treatment of breast cancer and, starting with this paper, of brain cancer.

Arsenic trioxide sensitizes cancer stem cells to chemoradiotherapy. A new approach in the treatment of inoperable glioblastoma multiforme.

PURPOSE: glioblastoma multiforme (GBM) still bears a very dismal prognosis even with complete resection followed by adjuvant chemoradiation. The aim of the current study was to evaluate in vitro the antitumor efficacy of arsenic trioxide (ATO) in combination with ionizing radiation plus temozolomide and bevacizumab against cultured glioblastoma stem-like cells, as possible way to increase the therapeutic index in patients diagnosed with recurrent, therapy-refractory GBM. METHODS: stem-like tumor cells isolated from a GBM biopsy were established by cell proliferation assays and upregulation of stem cell markers, as proven by reverse transcription - polymerase chain reaction (RT-PCR). Low concentrations of ATO were added prior to temozolomide, bevacizumab and ionizing irradiation. RESULTS: molecular analysis showed that cells expressed CXCR4, Oct-3/4 and GAPDH when compared to placental mesenchymal stem cells, as well as nestin, GFAP and neurofilament protein. Low concentrations of ATO led to morphologic differentiation, with fewer stem cells in Go state and differentiation-associated cytochemical features, like increased sensitivity to cytostatic drugs and radiotherapy. CONCLUSION: ATO exposure before conventional postoperative chemoradiotherapy for GBM might increase treatment efficacy. Further in vivo experiments on laboratory animals and analysis of absorption rate and side effects are required.

Functional and molecular characterization of glioblastoma multiforme-derived cancer stem cells.

PURPOSE: Brain tumors are the leading cause of cancer mortality in children and remain incurable despite advances in surgery and adjuvant therapies. The failure of malignant gliomas to respond to conventional treatment reflects the unique biology of these tumors, linked to a small population of stem-like precursors. This study describes the characteristics of stem cells isolated from glioblastoma multiforme (GM) and gives insight into the mechanism of brain tumorigenesis. METHODS: Tumor stem-like precursors were identified from primary human GM-derived cell culture using immunocytochemistry and reverse transcription polymerase chain reaction (RT-PCR). Cells were cultured in vitro in stem cell medium supplemented with growth factors and then the capacity of the surviving stem-like precursors to form tumor spheres and to continue to proliferate after chemoradiotherapy were tested. RESULTS: The tumor cells expressed the cellular markers CD133, CD105, CD90, Nanog, Oct 3/4, CXCR4, nestin, glial fibrillary acidic protein (GFAP), neurofilament protein (NF) and human glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Cells also displayed a high proliferative potential despite chemotherapy and irradiation and also had the ability to form spheroids in suspension. CONCLUSION: High grade gliomas contain stem-like precursors, which exhibit neural stem cell properties with tumorigenicity, establishing a novel developmental paradigm in the study of brain carcinogenesis and providing a powerful tool to develop patient-tailored therapy for this devastating disease.