Therapeutic application of noncytotoxic molecular targeted therapy in gliomas: growth factor receptors and angiogenesis inhibitors

Growth factor receptors and angiogenesis play major roles in the oncogenesis of gliomas. Over the last several years, several noncytotoxic molecular targeted therapies have been developed against growth factor receptors and tumor angiogenesis. In gliomas, two main anti-growth factor receptor strategies have been evaluated in phase I/II clinical trials: (a) small molecule tyrosine kinase inhibitors (TKIs) and (b) monoclonal antibodies that target growth factors or growth factor receptors other than vascular endothelial growth factor (VEGF). Up to now, few glioma patients have responded to small TKIs (0%-14%) or monoclonal antibodies (three case reports) delivered as a single agent. Greater doses, combined therapies, as well as the identification of molecular biomarkers predictive of response and resistance are important in order to optimize drug delivery and improve efficacy. Antiangiogenic therapies are promising for the treatment of gliomas. Thalidomide and metronomic chemotherapy were the first antiangiogenic strategies evaluated, but they have shown only modest activity. Recent studies of bevacizumab, an anti-VEGF antibody, and irinotecan, a topoisomerase I inhibitor, have demonstrated a high response rate, suggesting that targeted antiangiogenic therapies may play a significant role in the management of high-grade gliomas in the future. However, the toxicity profiles of these agents are not fully defined and the radiological evaluation of possible tumor response is challenging. Clinical evaluation of several VEGF receptor TKIs is currently ongoing; one of these inhibitors, cediranib, has already demonstrated interesting activity as a single agent. The integrin inhibitor cilengitide represents another promising strategy.

Targeted therapy and blood-brain barrier

Due to defined molecular lesions and signaling pathway disruptions, brain tumors represent good candidates for targeted therapy. However, in brain tumors the blood-brain barrier may prevent the transfer of progress in the molecular neurosciences to the development of effective therapeutic strategies. In this article, the most advanced forms of targeted therapy for the treatment of brain tumors and their clinical results are presented.

Therapeutic advances in the treatment of glioblastoma: rationale and potential role of targeted agents

Despite advances in standard therapy, including surgical resection followed by radiation and chemotherapy, the prognosis for patients with glioblastoma multiforme (GBM) remains poor. Unfortunately, most patients die within 2 years of diagnosis of their disease. Molecular abnormalities vary among individual patients and also within each tumor. Indeed, one of the distinguishing features of GBM is its marked genetic heterogeneity. Nonetheless, recent developments in the field of tumor biology have elucidated signaling pathways and genes involved in the development of GBM, and several novel agents that target these signaling pathways are being developed. As new details on the genetic characteristics of this disease become available, innovative treatment regimens, including a variety of traditional treatment modalities such as surgery, radiation, and cytotoxic chemotherapy, will be combined with newer targeted therapies. This review introduces these new targeted therapies in the context of current treatment options for patients with GBM. It is hoped that this combined approach will overcome the current limitations in the treatment of patients with GBM and result in a better prognosis for these patients.

Emerging targeted treatments for malignant glioma

This paper focuses on the medical management of malignant gliomas, which is currently undergoing change. It suggests that as surgery and radiotherapy are of limited benefit in the treatment of these tumours, medical therapies may have the potential to offer a better alternative. The current therapies for glioma and the targeted agents in clinical trials are reviewed. There is a general acceptance that temozolomide in combination with radiotherapy is replacing radiotherapy alone as first-line therapy in high-grade astrocytic gliomas. Within the realms of clinical research, it can be seen that there is a shift away from therapies targeting the end effect of deregulated cell-cycle control, to targeting specific and individual genetic aberrations in tumours. Finally, the paper questions current clinical trial methodology and tentatively suggests ways in which this may be improved.