Anti-angiogenesis is a promising strategy for cancer therapy currently evaluated in clinical trials. The aim of the study was to investigate the effects of an antiangiogenic combination therapy inhibiting alpha(v)-integrins by a c(yclic)RGD-peptide (EMD270179) and blocking VEGFR-2 by SU5416 on tumor angiogenesis and progression in vivo. Experiments were performed in dorsal skinfold chamber preparations of Syrian golden hamsters (60 +/- 5 g) bearing A-Mel-3 tumors. From day 3-10 after tumor-cell implantation, animals (n = 6 per group) were treated by monotherapies using the cRGD-peptide (114 mg/kg/day; i.p.), the VEGFR-2 antagonist (6 mg/kg/day; i.p.) or by the combination of both monotherapies. A control group received only the solvent DMSO. Using intravital microscopy parameters of intratumoral microcirculation were analyzed on day 5, 7 and 10. In separate experiments subcutaneous tumor growth and metastasis formation was evaluated starting therapy on day 0. Functional vessel density was significantly reduced by the combination therapy compared to that by all other groups on day 10. Although intratumoral red blood cell velocity and vessel diameters were less affected, blood flow in vessel segments and the microcirculatory perfusion index were lower after combined therapy compared to controls. In addition, we observed a significantly stronger inhibition of subcutaneous tumor growth and metastasis formation using the combination therapy. These data clearly support the concept of antiangiogenic combination therapy and demonstrate that it may especially be effective when scheduled as an early or prophylactic treatment regimen, thus avoiding angiogenesis-dependent tumor and metastasis initiation or tumor recurrence.
2006 Wiley-Liss, Inc.