Protamine inhibits angiogenesis and growth of C6 rat glioma; a synergistic effect when combined with carmustine

Abstract

Protamine inhibits angiogenesis and blocks endothelial, fibroblast and platelet growth factors. Human and experimental gliomas spread and grow in response to both paracrine and autocrine release of these factors. Our objective was to study the effect of protamine administration on cell proliferation, angiogenesis and tumoral growth of C6 glioma. Additionally, we compared the antitumoral effect of protamine with that of another inhibitor of angiogenesis, suramin, and investigated a potential synergistic antitumoral action of low doses of protamine combined with the antineoplastic carmustine. C6 glioma cells were implanted subcutaneously in Wistar rats. A highly malignant glioma developed in 80% of animals; when the tumour reached a diameter of 1.5 cm, either protamine, suramin, carmustine or protamine plus carmustine were administered in various doses. Tumour parameters were measured and compared between groups. In a dose-dependent manner, protamine reduced tumour volume (P < 0.001), mitotic index (P < 0.05), vascular density (P < 0.05) and cell viability (P < 0.005) of C6 glioma. An ultrastructural study demonstrated membranous inclusions in the cytoplasm of 28% of tumoral and endothelial cells of tumours from animals treated with protamine. The inhibition of tumoral growth produced by moderate doses of protamine was similar to that produced by toxic doses of suramin. The combination of protamine and carmustine had a synergistic curtailing effect on tumoral growth (P < 0.001). Our results indicate that protamine is an effective agent against glioblastoma; in non-toxic doses it could potentiate the antineoplastic effect of nitrosoureas for the treatment of glial tumours.