Suramin induces deoligomerization of human tumor necrosis factor alpha

Suramin inhibits the biological activity of human tumor necrosis factor alpha (TNF) through a direct action on the ligand rather than on its receptors (Grazioli, L., Alzani, R., Ciomei, M., Mariani, M., Restivo, A., Cozzi, E., and Marcucci, F. (1992) Int. J. Immunopharmacol. 14, 637-642). In order to clarify the mechanism whereby suramin leads to inhibition of TNF, we investigated the possibility that suramin might modify the quaternary structure of TNF which is biologically active as a trimer. For this purpose we used a new assay (double streptavidin sandwich assay) designed for the rapid detection of oligomer-monomer conversion of proteins. Taking advantage of this assay we observed, upon incubation with suramin, dissociation of TNF. Suramin-induced dissociation of TNF was confirmed by gel filtration chromatography. Under conditions of partial dissociation, two molecular species were separated. One of higher molecular weight, corresponding to trimeric TNF, was biologically active, whereas the other, corresponding to monomeric TNF, was inactive. These results are at variance with others recently reported, where suramin has been shown to induce microaggregation of several polypeptides (Middaugh, C. R., Mach, H., Burke, C. J., Volkin, D. B., Dabora, J. M., Tsai, P. K., Bruner, M. W., Ryan, J. A., and Marfia, K. E. (1992) Biochemistry 31, 9016-9024). This suggests that suramin inhibits the bioactivity of different protein molecules through opposite effects on their quaternary structure. The present results are, to our knowledge, the first demonstration of a drug inhibiting a target molecule through dissociation of its quaternary structure.