Inhibition by pentosan polysulfate (PPS) of heparin-binding growth factors released from tumor cells and blockage by PPS of tumor growth in animals.

Abstract

In a proliferating tumor, locally secreted polypeptide growth factors, which have autocrine and paracrine functions, induce vascularization essential for tumor growth and metastasis. These growth factors may serve as targets for tumor therapy. We have shown that the heparinoid pentosan polysulfate (PPS) can block growth of subcutaneous human tumor xenografts in nude mice and angiogenesis induced by the heparin-binding, Kaposi's sarcoma-derived fibroblast growth factor (K-FGF). The purpose of this study was to determine whether PPS might also interfere with stimulation of endothelial cells by other growth factors released from tumor cells and whether the promising antitumor effects of PPS extend to other human tumor cell lines. We studied the effects of PPS on stimulation by heparin-binding growth factors released from seven human tumor cell lines in vitro and on tumors growing from these cell lines in athymic nude mice. Seven human cell lines established from breast, prostate, epidermoid, and lung carcinomas and rhabdomyosarcoma were used in in vivo as well as in vitro studies of the effects of PPS. We also studied in vitro the effects of PPS on growth factor-induced colony formation of normal rat kidney fibroblasts and human adrenal carcinoma cells. The tumor cell lines released growth factors into their media that stimulated growth of endothelial and epithelial cells as well as fibroblasts. Heparin-affinity chromatography showed that heparin-binding growth factors contributed substantially to this paracrine activity and that PPS inhibited this stimulus. Six of the seven tumor cell lines were resistant to PPS in soft-agar cloning assays and hence did not appear to depend on autocrine stimulation by the heparin-binding growth factors. In contrast to this in vitro resistance, subcutaneous growth of tumors from all cell lines in athymic nude mice was inhibited in a dose-dependent fashion by daily intraperitoneal injections of PPS. We conclude that heparin-binding growth factors contribute substantially to tumor growth in vivo and that PPS acts by blocking the paracrine effects of heparin-binding growth factors released from the tumor cells. PPS could become a novel treatment tool targeting tumor growth factors.