Clinical experience with antiangiogenic therapy in leukemia

The pathological role of bone marrow angiogenesis in human leukemias has been clearly established. Bone marrow neoangiogenesis is mediated by several growth factors, such as VEGF-A, VEGF-C, angiopoietin-1 and -2, FGF, HGF, TGF-β and others secreted by leukemic cells. The prognostic relevance of microvessel density, and expression of VEGF-A and -C has been demonstrated especially in acute myeloid leukemia. In the last years, several classes of angiogenesis inhibitors have been developed blocking several angiogenic pathways. These include drugs that inhibit the VEGF (with or without blockade of FLT3) and the mTor signalling cascade. Besides, thalidomide and lenalidomide although possessing a pleiotrophic mode of action including antiangiogenic properities have been evaluated in the treatment of human leukemias. In the current review we analyze the results of clinical trials employing these antiangiogenic drugs. Since the clinical efficacy of these compounds used as monotherapy is often limited, confined to certain subgroups of patients and frequently short lived, several trials combining standard chemotherapy with these agents have been initiated in order to demonstrate an additional benefit to standard therapy. Furthermore the introduction of new antiangiogenic drugs such as inhibitors of the angiopoietin and HGF/cMET pathway is on the horizon. Utilizing cocktails of inhibitors of several angiogenic pathways may represent a new possibility to augment the efficacy of antiangiogenic therapy in the future.