Antiangiogenic effect of metronomic paclitaxel treatment in prostate cancer and non-tumor tissue in the same animals: a quantitative study.

Well-tolerated continuous or metronomic chemotherapy can exert a marked antiangiogenic and thus superior antitumor effect compared with conventional high-dose, temporarily spaced-out chemotherapy, as shown in preclinical studies. There is, however, no means of directly assessing the antiangiogenic effect in a tumor, a serious impediment to assessing the effects of putative antiangiogenic chemotherapeutics or treatments. In an attempt to circumvent or minimize this impediment we studied the antiangiogenic effect of well-tolerated metronomic paclitaxel therapy in a surrogate tumor-free tissue that allows true quantitative analysis as well as in syngeneic At-1 prostate cancer in the same rat. This novel model allows an accurate comparison of the angiogenesis-modulating effect of chemotherapy in the two tissues to be made. The effect of chemotherapy on VEGF-A-mediated angiogenesis, a characteristic of most tumors, was assessed truly quantitatively by microscopic morphometry and image analysis in the tumor-free mesentery. The chemotherapy significantly suppressed VEGF-A-mediated angiogenesis in the mesentery to an extent that closely mirrored the significant increase in tumor necrosis measured morphometrically and the significant decrease in tumor growth rate. This finding opens an avenue to study quantitatively and systematically the antiangiogenic effect of chemotherapeutic modalities and treatments that approximately mirror their antiangiogenic effect in the At-1 tumor.