Vascular-targeting agents and radiation therapy in lung cancer: where do we stand in 2005?

With recent Food and Drug Administration approval of the anti-vascular endothelial growth factor (VEGF) antibody for the treatment of colon cancer, it may be possible to achieve similar progress in the treatment of locally advanced lung cancer. Antiangiogenic therapies in the clinic are a reality, and it is important to demonstrate that they can be used safely with conventional modalities, including radiation therapy (RT). Strategies under scrutiny in preclinical and clinical studies include the use of endogenous inhibitors of angiogenesis, use of agents that target VEGF and VEGF receptor signaling, targeting endothelial-related integrins during angiogenesis, and targeting the preexisting immature vessels growing within tumors (ie, vascular targeting). Regardless of the approach, it is necessary to address whether angiogenesis is a consistent phenomenon within the lung parenchyma around a cancer and a relevant target and whether inhibiting angiogenesis will improve current lung cancer therapies without increasing toxicity. Vascular-targeting agents (VTAs) are an interesting class of agents that have the potential to enhance RT, but their clinical promise has yet to be realized. In preclinical models, these agents selectively destroy the tumor vasculature, initiating a rapid centralized necrosis within established tumors. Characteristically, after treatment with VTAs, a rim of viable tumor cells remains at the periphery of the tumor, which remains well perfused and should therefore be relatively sensitive to radiation-induced cytotoxicity. This review will focus on VTAs in the treatment of lung cancer and includes a discussion of combination studies with RT in the laboratory and some of the hurdles in the clinical application of these agents.