The Molecular Basis of Class Side Effects Due to Treatment with Inhibitors of the VEGF/VEGFR Pathway

Vascular Endothelial Growth Factor (VEGF) is considered to be one of the most important regulators of angiogenesis and a new key target in anti-cancer treatment. Various clinical trials have validated the clinical importance of anti- VEGF or anti-VEGF receptor (VEGFR) therapy. Currently the humanized monoclonal antibody bevacizumab (blocks VEGF-A), and the tyrosine kinase inhibitors sunitinib and sorafenib (inhibit VEGFRs) are approved for patients with various malignancies and several others are expected in the coming years. Unfortunately, anti-VEGF/VEGFR treatment is not void of side effects. An array of unexpected side effects is now seen in clinical practice. Management of these side effects is extremely important in the development of the various anti-VEGF/VEGFR therapies and their optimal use. This review provides an overview of the toxicity profile of this class of agents, the molecular basis behind these side effects and indicates potential options for management.

VEGF and its receptors play an important role in normal tissues and are widely expressed. It is likely that interference with this pathway induces an array of side effects due to the lack of normal function of VEGF. A consistent pattern of side effects is now emerging. Hypertension, gastro-intestinal toxicity, hypothyroidism, proteinuria, coagulation disorders and neurotoxicity are side effects observed with both anti-VEGF and anti-VEGFR inhibitors. For these side effects the role of VEGF/VEGFR pathway in normal tissue was reviewed in order to provide a molecular mechanism that linked side effect with physiological activity of VEGF/VEGFR. Insight into the molecular basis may aid specific supportive care measures to ensure optimal use of this class of agents.

Conclusion: Inhibiting the VEGF/VEGFR pathway is an effective approach to treat cancer. It has also provided new insight into the physiological role of this pathway in various organs. Integrating the knowledge in daily oncological practice will be a challenge for the future.