Anti-VEGF therapy is a promising approach to the treatment and prevention of human cancers, but thus far only modest clinical activity has been reported. Optimal dosing of anti-VEGF compounds will be one key to maximizing clinical efficacy while minimizing toxicity. Recently several anti-VEGF class related toxicities have emerged, including hypertension, proteinuria, thrombosis, and bleeding. Unless anti-VEGF mechanisms are understood, treatments for these side effects may be inefficient or may even interfere with anti-tumor effects. Accumulating evidence points to a role for nitric oxide (NO) as a mediator of VEGF effects in addition to NO's known role in the regulation of vascular tone and many other endothelial functions. Thus, nitric oxide mechanisms may also mediate the efficacy and toxicity of anti-VEGF therapy either directly or indirectly via other co- and counter-regulatory pathways. We propose to use several novel approaches and the unique clinical setting of anti-VEGF therapy to evaluate the clinical effects of anti-VEGF treatment on several known VEGF/NO dependent processes. These include regulation of blood pressure, endothelial cell vasoreactivity, wound angiogenesis, and platelet function. We will also determine if these effects are mediated by nitric oxide by measuring plasma and urine nitrite/nitrate and exhaled NO. We will employ low nitrite/nitrate diets and administration of sublingual nitroglycerin to improve the sensitivity and specificity of these approaches. Brachial reactivity will be used to assess NO dependent vasoreactivity. A novel wound angiogenesis model will allow clinical correlation of anti-angiogenic effects with changes in tissue VEGF/VEGFR-2 phosphorylation, and nitric oxide synthase. Other NO mediated events will also be evaluated in an exploratory fashion. Since bevacizumab is the anti-VEGF compound furthest along in clinical development, the proposal will focus on this compound. Intense biomarker evaluations will be performed pre/post the first month of anti-VEGF treatment. However, to allow for potential clinical benefit, patients will be permitted to receive ongoing anti-VEGF therapy as deemed appropriate by their physician.
