Suramin is a polysulfonated naphthylurea with various biological activities. Suramin is a DNA topoisomerase II inhibitor with an IC50 of 5 μM. IC50: 5 μM (DNA topoisomerase II) Suramin inhibits cell proliferation and DNA synthesis in cultured HeLa cells. The replication of SV40 DNA is completely abolished by 40 μM suramin. DNA polymerase α is sensitive to lower concentrations of suramin (IC50=8 µM) than is DNA polymerase δ (IC50=36 µM), whereas DNA polymerase β is relatively insensitive to the drug (IC50 of 90 µM). Suramin is a potent inhibitor of DNA strand exchange and ATPase activities of bacterial RecA proteins. Suramin inhibits RecA-catalysed proteolytic cleavage of the LexA repressor. The mechanism underlying such inhibitory actions of suramin involves its ability to disassemble RecA-single-stranded DNA filaments. Suramin is a potent inhibitor of the nuclear enzyme DNA topoisomerase II. Suramin inhibits purified yeast topoisomerase II with an IC50 of about 5 μM. Treatment with suramin shows lower values for pulmonary artery pressure, right ventricular hypertrophy, and distal vessel muscularization on day 21 compared to control rats. Suramin treatment suppresses PA-SMC proliferation and attenuates both the inflammatory response and the deposition of collagen.