Bivalent binding and signaling characteristics of Leridistim, a novel chimeric dual agonist of interleukin-3 and granulocyte colony-stimulating factor receptors

Objective, Leridistim is a member of a novel family of engineered chimeric cytokines, myelopoietins, that contain agonists of both interleukin-3 (IL-3 ) receptors (IL-3R) and granulocyte colony-stimulating factor (G-CSF) recep tors (G-CSFR). Materials and Methods. To more clearly understand Leridistim's function at the molecular level, binding to both IL-3R and G-CSFR and subsequent signal ing characteristics have been delineated. Results. The affinity of Leridistim for the human G-CSFR was found to be co mparable to that of native G-CSF (IC50 = 0.96 nM and 1.0 nM, respectively). Both Leridistim and G-CSF induced receptor tyrosine phosphorylation to a s imilar maximal level. Compared with native recombinant human IL-3 (rhIL-3), Leridistim was found to possess higher affinity for the IL-3R alpha chain (IL-3R alpha) (IC50 = 85 nM and 162 nM, respectively). However, the increas e in Leridistim binding affinity to the functional, high-affinity heterodim eric IL-3R alpha beta (c) receptor is lower than that observed with rhIL-3 (85 nM and 14 nM vs 162 nM and 3.5 nM, respectively). Leridistim induced ty rosine phosphorylation of beta (c) to a level comparable to native IL-3, an d the level of JAK2 tyrosine phosphorylation in cells expressing both IL-3R and G-CSFR was comparable to that observed with IL-3 or G-CSF alone. The a bility of Leridistim to interact with IL-3R and G-CSFR simultaneously was d emonstrated using surface plasmon resonance analysis, These studies were ex tended to demonstrate that Leridistim exhibited a higher affinity for the I L-3R on cells that express both the IL-3R alpha beta (c), and the G-CSFR (I C50 = 2 nM) compared with cells that contain the IL-3R alpha beta (c) alone (IC50 = 14 nM). Conclusion. Leridistim binds to both IL-3R and G-CSFR simultaneously and ha s been shown to activate both receptors. The bivalent avidity may explain t he unique biologic effects and unexpected potency of Leridistim in hematopo ietic cells compared with rhIL-3 or G-CSF alone or in combination. (C) 2001 International Society for Experimental Hematology. Published by Elsevier S cience Inc.