Dose effects of continuous vinblastine chemotherapy on mammalian angiogenesis mediated by VEGF-A.
Low-dose continuous or metronomic chemotherapy with several agents can exert significant antiangiogenic effects, as shown in preclinical studies. Therapy of this kind is generally well tolerated compared with conventional chemotherapy with high, temporally spaced out bolus doses. A critical point emerges when the effects on angiogenesis of low-toxic metronomic doses of chemotherapeutics in preclinical studies are to be transferred to clinical protocols, as there is a risk that a virtually non-toxic dose might also be ineffective; clearly, dose-effect data are important. We therefore sought to investigate whether a dose-dependent response exists in metronomic vinblastine chemotherapy. The surrogate tumor-free rat mesentery model, allowing the study of antiangiogenic effects per se, was used. Following systemically administered metronomic chemotherapy, it closely reflects the indirectly assessed antiangiogenic and growth-retarding effects in a syngenic cancer model. VEGF-A, which is a central proangiogenic factor in most tumors, was administered i.p. to induce angiogenesis in the mesenteric test tissue and, using morphometry, the angiogenesis-modulating effects of vinblastine were assessed in terms of objective quantitative variables. We report that continuous vinblastine treatment with an apparently non-toxic dose (1.0 mg/kg/week or 0.143 mg/kg/day) for 10 days, and a dose that substantially inhibited the physiologic body-weight gain (2.0 mg/kg/week or 0.286 mg/kg/day) for 6 days, demonstrates a dose-response relationship; the high dose significantly suppresses angiogenesis. To our knowledge, no previous study has reported on a dose-dependent antiangiogenic effect by continuous or metronomic vinblastine treatment in a mammalian in vivo model.