Suramin Alters Phosphoinositide Synthesis and Inhibits Growth Factor Receptor Binding in HT-29 Cells¹

Initiation of cell growth frequently involves activation of growth factor receptor-coupled tyrosine kinases and stimulation of the phosphoinositide second messenger system. The antitrypanosomal and antifiliarial drug suramin has been shown to exert antiproliferative activities by inhibition of growth factor receptor binding. We therefore investigated the effect of suramin on epidermal growth factor receptor-binding characteristics and, additionally, searched for effects on basal or cholinergically stimulated phospholipid metabolism in HT-29 cells.

Suramin caused a dose-dependent and noncompetitive inhibition of ¹²⁵I-epidermal growth factor binding (concentration producing 50% inhibition, 44.2 µg/ml) but did not alter muscarinic receptor binding. Suramin did not affect the basal ³²P incorporation into phosphoinositides at concentrations of <200 µg/ml suramin. In contrast, the carbachol-stimulated enhancement of ³²P incorporation into phosphatidic acid, phosphatidylinositol, and polyphosphoinositides was reduced by 48–95% in the presence of 100 µg/ml suramin. Thus, phosphoinositide and diacylglycerol kinases involved in basal and receptor-stimulated phosphoinositide metabolism may be localized in different subcellular compartments, which can be dissociated by the use of suramin. Direct measurements of phosphatidylinositol kinase and diacylglycerol kinase activities showed a potent inhibition when treated with suramin. Suramin did not affect the stimulation of phospholipase C by carbachol, determined by release of [³H]inositol phosphates in [³H]myoinositol-prelabeled cells.

Our data indicate that suramin potently inhibits phosphoinositide resynthesis under stimulated conditions. Additionally, we confirm the inhibitory effects of suramin on epidermal growth factor receptor binding in a human intestinal cell line. The inhibitory effects of suramin on phospholipid metabolism may play a role in the antiproliferative actions of this drug.