Inhibition of endothelial cell proliferation and tumor-induced angiogenesis by pentoxifylline

Purpose: In this study we investigated the effect of pentoxifylline (PTX) o n tumor-induced neovascularization as well as on different steps involved i n the angiogenic process. Methods: To assess angiogenesis inhibition, we in jected intradermally (i.d.) 10(6) B16-F10 melanoma cells into C57BL/6J mice which were subsequently intraperitoneally (i.p.) inoculated with PTX or sa line. On day 7 the number of blood vessels converging to the remnant of inj ected material was counted and the volumes of incipient tumors were calcula ted in each case. In vitro growth inhibition by PTX was evaluated in two di fferent cell lines of endothelial origin and in human umbilical vein endoth elial cells. Motility assays, as well as zymographic assays carried out to analyze gelatinolytic metalloproteinases and urokinase-type plasminogen act ivator, were performed in one of the endothelial cell lines. Results: A sig nificant inhibition of tumor-induced angiogenesis was observed in C57B1/6 m ice i.p. inoculated with PTX, that paralleled reduced incipient tumor volum es. The endothelial cells derived from different sources were inhibited in a dose-response manner by PTX in vitro. Non-cytotoxic PTX concentrations as sayed in one of the endothelial cell lines did not inhibit its in vitro cel l motility nor its gelatinase secretion, but its low molecular weight uroki nase-type plasminogen activator expression. Conclusions: Our findings sugge st that the inhibitory effect of PTX on tumor angiogenesis is related to an tiproliferative action on endothelial cells, as well as to down regulation of u-PA secreted by them.