Identification of sulfated oligosaccharide-based inhibitors of tumor growth and metastasis using novel in vitro assays for angiogenesis and heparanase activity

Inhibitors of tumor angiogenesis and metastasis are rapidly emerging as imp ortant new drug candidates for cancer therapy. To facilitate the identifica tion of such drugs, we recently developed novel and rapid in vitro assays f or human angiogenesis and for the extracellular matrix-degrading enzyme hep aranase, which has been implicated in tumor metastasis. In this study, sulf ated oligosaccharides, which are structural mimics of heparan sulfate, were investigated as drug candidates because these compounds may interfere with heparan sulfate recognition by many angiogenic growth factors and may inhi bit cleavage of heparan sulfate by heparanase. In the preliminary screening studies, it was found that inhibitory activity in both assay systems was c ritically dependent on chain length and degree of sulfation, highly sulfate d linear oligosaccharides of five or more monosaccharides in length being t he most active. However, two sulfated oligosaccharides stood out as potenti al antitumor drugs, phosphomannopentaose sulfate (PI-88) and maltohexaose s ulfate, both of these compounds having the important property of simultaneo usly being potent inhibitors of in vitro angiogenesis and heparanase activi ty. Due to the ease of manufacture of the starting material, phosphomannope ntaose, PI-88 was studied in more detail. PI-88 was shown to inhibit the pr imary tumor growth of the highly invasive rat mammary adenocarcinoma 13762 MAT by similar to 50%, inhibit metastasis to the draining popliteal lymph n ode by similar to 40%, and reduce the vascularity of tumors by similar to 3 0%, all of these effects being highly significant. Acute hematogenous metas tasis assays also demonstrated that PI-88 was a potent (>90%) inhibitor of blood-borne metastasis. Thus, by the use of novel in vitro screening proced ures, we have identified a promising antitumor agent.