HUMAN INTERLEUKIN-6 RECEPTOR SUPER-ANTAGONISTS WITH HIGH POTENCY AND WIDE SPECTRUM ON MULTIPLE-MYELOMA CELLS

Interleukin-6 (IL-6) is the major growth factor for myeloma cells and is believed to participate in the pathogenesis of chronic autoimmune d iseases and postmenopausal osteoporosis. IL-6 has been recently shown to possess three topologically distinct receptor binding sites: site 1 for binding to the subunit specific chain IL-6R alpha and sites 2 and 3 for the interaction with two subunits of the signaling chain gp130, We have generated a set of IL-6 variants that behave as potent cytoki ne receptor super-antagonists carrying substitutions that abolish inte raction with gp130 at either site 2 alone (site 2 antagonist) or at bo th sites 2 and 3 (site 2 + 3 antagonist). In addition, substitutions h ave been introduced in site 1 that lead to variable increases in bindi ng for IL-6R alpha up to 70-fold. IL-6 super-antagonists inhibit wild- type cytokine activity with efficacy proportional to the increase in r eceptor binding on a variety of human cell lines of different origin, and the most potent molecules display full antagonism at low molar exc ess to wild-type IL-6, When tested on a representative set of IL-6-dep endent human myeloma cell lines, although site 2 super-antagonists wer e in general quite effective, only the site 2 + 3 antagonist Sant7 sho wed antagonism on the full spectrum of cells tested. In conclusion, IL -6 super-antagonists are a useful tool for the study of myeloma in vit ro and might constitute, in particular Sant7, effective IL-6 blocking agents in vivo. (C) 1996 by The American Society of Hematology.