Radiobiology and vascular targeting in glioma

This review examines the emerging role of agents that target tumour blood vessels in the treatment of glioma. It addresses the important issue of how these agents may best be combined with conventional radiation based therapies to optimize their effects, and reviews recent experimental and clinical data on which future treatment policies may be developed.

Two main classes of agents can be used to influence tumour growth through their actions on the vasculature. Antiangiogenic agents prevent the formation of new tumour blood vessels, whereas vascular targeting agents destroy existing tumour blood vessels. Based on an improved understanding of the biology of tumour vasculature, many new agents are being developed that exhibit these effects in preclinical models. Several agents are also entering clinical trials. At the same time, new evidence is emerging that the effect of conventional therapies, particularly radiotherapy, may exert important antitumour effects through actions on the vasculature as well as through cytotoxic effects on tumour clonogens. Preclinical data suggest that the combination of these agents may not act in a straightforward synergistic manner, suggesting that careful consideration of scheduling will be required to optimize their effects.

Agents that act at the tumour vasculature provide a powerful new potential strategy in tumour treatment. However, these agents will need to be used in combination with conventional treatment strategies, and optimal combinations need to be defined in preclinical studies. This will depend on gaining a more thorough understanding of the effects of other modalities on tumour vasculature.