Suramin inhibits binding and degradation of platelet-derived growth factor in arterial smooth muscle cells but does not interfere with autocrine stimulation of DNA synthesis.

During in vitro culture arterial smooth muscle cells of adult rats are able to produce a platelet-derived growth factor (PDGF)-like protein and to promote their own growth in an autocrine manner. Here, this process has been studied using suramin, a polyanionic drug that has been reported to interfere with the cellular binding of several growth factors. Our results indicate that suramin speeds up the transition of the cells from a contractile to a synthetic phenotype early in primary culture. It inhibits the binding of PDGF to the cells, displaces PDGF bound to the cell surface, and slows down the degradation of PDGF internalized by the cells. It reduces the specific activities of the lysosomal enzymes acid phosphatase, beta-N-acetylglucosaminidase and beta-glucuronidase, and gives rise to an accumulation of lysosomes with myelin-like inclusions. It blocks PDGF- and serum-induced DNA synthesis and cellular proliferation in secondary cultures, but lacks a distinct inhibitory effect on DNA synthesis in primary cultures under serum-free conditions. The results suggest that the PDGF-like protein produced by the smooth muscle cells under the latter conditions may bind to its receptor and exert its autocrine effect intracellularly, without prior release into the pericellular space.