Anti-Angiogenic Cancer Therapy Based on Integrin αvβ3 Antagonism

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is a fundamental process during cancer progression. Anti-angiogenic strategies have been pursued for cancer treatment and prevention of cancer recurrence and metastasis. Integrins are a family of cell adhesion molecules consisting of two non-covalently bound transmembrane subunits (α3 and β). Much research has demonstrated that integrin signaling plays a key role in tumor angiogenesis and metastasis. Integrin αvβ3 is highly expressed on activated endothelial cells and tumor cells but is not present in resting endothelial cells and most normal organ systems, which makes it a suitable target for anti-angiogenic cancer therapy. In this review we will focus on cancer therapy targeting integrin αvβ3 while other integrins (such as α5β1, αIIbβ3, αvβ5, α6β4) will only be briefly mentioned when relevant. MEDI-522 (a humanized anti-human integrin avb3 monoclonal antibody) and Cilengitide (cyclic peptidic integrin αvβ3 /αvβ5 antagonist) are currently in clinical trials for anti-angiogenic cancer therapy. Small interfering RNA (siRNA) that specifically silences integrin αv and/or β3 was reported to cause tumor shrinkage in preclinical xenograft models. Combination of anti-integrin αvβ3 therapy and other therapeutic approaches (such as chemotherapy, radiotherapy and gene therapy) has also been applied for cancer treatment. Mounting evidence suggests that there is potentially synergistic effect of combined therapeutic approaches over single modality alone. Lastly, integrin targeted delivery (drugs, genes, and radioisotopes) and imaging (optical, MRI, ultrasound, SPECT, and PET) is discussed in detail.