Immunomodulatory effects of anti-angiogenic drugs

Much progress and significant therapeutic changes have been made in the field of tumor therapy in the past decades. Besides chemotherapy and radiotherapy, a special focus was laid on targeted therapies such as small molecule tyrosine kinase inhibitors (TKIs) and other immunomodulatory drugs, which have become standard therapies and important combination partners in a variety of malignancies. In contrast to the widely established use of these often anti-angiogenic drugs, many functional molecular mechanisms are yet not completely understood. Recent analyses focused not only on their direct anti-tumor responses, but also on their influence on tumor microenvironment, as well as on their effects on malignant and healthy cells. Different anti-angiogenic compounds targeting the vascular endothelial growth factor (VEGF) or platelet-derived growth factor pathways seem to be capable of modulating immune responses, in a positive, as well as apparently harmful manner. For an optimal clinical anti-cancer treatment, a better understanding of these immunomodulatory effects is necessary. Here we summarize recent reports on the immunomodulatory function of lately introduced clinically applied anti-angiogenic compounds, such as the humanized monoclonal antibody against VEGF bevacizumab, the small molecule TKIs sunitinib, sorafenib, imatinib, dasatinib, nilotinib and the proteasome inhibitor bortezomib.