Role of anti-angiogenesis agents in treating NSCLC: focus on bevacizumab and VEGFR tyrosine kinase inhibitors.

Successful inhibition of angiogenesis with the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab has improved the efficacy seen with standard cytotoxic therapy in NSCLC. The addition of bevacizumab to first-line chemotherapy improved response rate and progression free survival and added 2 months to median overall survival for those patients with advanced stage NSCLC on the treatment arm of E4599. Bevacizumab is now a standard agent to add to frontline carboplatin and paclitaxel for patients with newly diagnosed NSCLC who meet the eligibility criteria from the landmark E4599 trial. Unfortunately about half of all patients are not eligible either because they have squamous histology, brain metastases, or are on anti-coagulation. Ongoing trials are further exploring the safety of bevacizumab in these patient populations, as well as in combination with other cytotoxic regimens. Exploration of other applications of bevacizumab in the second-line and adjuvant setting are ongoing as well. The largest class of drugs that block angiogenesis are the multi-targeted tyrosine kinase inhibitors (TKIs) that target the VEGF receptor (VEGFR). These drugs are still in development, and though two are now on the market for treating other malignancies, their role in NSCLC is under investigation. These agents have the advantages of hitting multiple targets, convenient oral administration, and potential for lower cost. Their lack of target specificity leads to unexpected toxicity, but also promising efficacy. For example, the overall objective response rate of 9.5% with single agent sunitinib compares similarly to that of pemetrexed or docetaxel in previously treated NSCLC patients, but toxicity, notably fatigue, lead to discontinuation in 38% of patients. Hypertension, hemorrhage and cavitation are common toxicities amongst this class of agents. Rash, fatigue, myalgia, and hand-foot syndrome are more specifically seen with TKIs. These compounds may also be synergistic or additive with traditional cytotoxic chemotherapy drugs and other novel compounds. In early trials sorafenib as a single agent has shown no clinical response in previously treated NSCLC patients, whereas clinical benefit in combination with erlotinib or chemotherapy has been seen in early studies. Vandetanib has demonstrated objective responses as a single agent and in combination with chemotherapy in previously treated NSCLC patients. A phase I trial of AZD2171 with carboplatin and paclitaxel in newly diagnosed advanced stage NSCLC also demonstrated promising results with 6 of 15 patients achieving partial responses. NSCLC specific trials are also underway, or in development for pazopanib, axitinib, AMG 706, XL647, enzastaurin, and other TKIs. Other anti-angiogenesis agents with different mechanisms of action include thalidomide and its derivatives, monoclonal antibodies to the VEGFRs, and VEGF Trap, a chimeric molecule which combines extracellular portions of VEGFR1 and VEGFR2 with the Fc portion of immunoglobulin G1 to form a molecule that binds and "traps" VEGF. Despite modest improvements, prognosis continues to be poor for patients with advanced NSCLC. Bevacizumab is a first step into the world of angiogenesis inhibitors for NSCLC and though it only offers a modest survival benefit in a limited patient population, it paves the way for the development of the next generation of anti-angiogenesis inhibitors. We can hope that further improvements in survival will follow.