Haematologia, Vol. 30, No. 3, pp. 167–176 (2000)  VSP 2000.

Paper

Synthetic cytokines containing interleukin-3 exert potent megakaryopoietic activity

N. AHMED, M. A. KHOKHER and H. T. HASSAN ∗ Division of Biomedical Sciences, School of Health Sciences, University of Wolverhampton, United Kingdom

Abstract—The shared properties of haematopoietic cytokines and their receptors have enabled the genetically engineered construction of several synthetic cytokines with increased haematopoietic ac- tivity and/or more desirable pharmacological characteristics. Thrombocytopenia remains a signifi- cant cause of morbidity in cancer patients undergoing allogeneic or autologous bone marrow/blood stem cell transplantation after myeloablative therapy including total body irradiation. Several in vitro, in vivo and preliminary clinical studies have demonstrated the efficacy of synthetic cytokines con- taining interleukin-3 in accelerating platelet recovery after radiotherapy-induced myelosuppression, enhancing G-CSF-mobilisation of CD34 positive cells for transplantation and increasing the ex-vivo expansion of myeloid and megakaryocytic progenitor cells. More randomised controlled clinical tri- als are needed to study the efficacy of the pre-transplant platelet mobilisation and the acceleration of the post-transplant platelet recovery. This also applies to cohort in vitro studies for expanding the production of CD41+ megakaryocytes from human bone marrow, mobilised peripheral blood and cord blood CD34 positive cells using myelopoietin as the only accepted synthetic cytokine containing interleukin-3.

Key words: Cytokine; ex-vivo expansion; haematopoiesis; interleukin; mobilisation.

INTRODUCTION Human haematopoiesis, the complex biologic process responsible for the produc- tion of billions of mature blood cells each day, is regulated by many pleiotropic glyco-proteins named haematopoietic cytokines in the bone marrow. These cy- tokines are both survival and growth factors for haematopoietic stem, progenitor, precursor and mature cells [1]. The shared properties of these cytokines and their receptors have allowed the genetically engineered construction of several synthetic

∗ Correspondence to be addressed to: Dr. H. T. Hassan, MD, PhD, Senior Lecturer of Haematology, School of Health Sciences, University of Wolverhampton, 62-68 Lichfield Street, Wolverhampton, WV1 1DJ, England, UK. Phone: +44-1902-321154, Fax: +44-1902-321161. 168 N. Ahmed et al.

Table 1. Synthetic haematopoietic cytokines

Engineered cytokine Properties Refer- ence SINGLE: Erythropoietin Receptor Agonist (EMP1) One-eighth the size of Erythropoietin and [2] (20-amino acid small peptide) has the same erythropoietic activity Thrombopoietin Receptor Agonist 1/25 of the size of Thrombopoietin and [3] (14-amino acid small peptide) has the same thrombopoietic activity lnterleukin-3 Receptor Agonist has 20-fold greater haematopoietic activity and [4] (Daniplestim, SC-55494) only 2-fold more inflammatory priming than IL-3 Stem Cell Factor Receptor Agonist has greater haematopoietic activity but not [5] (SAF-9, c-kit ligand analogue) mast cell stimulation activity COMBINED: (Fusion, Chimeric) PIXY321 (Pixykine) Fusion protein in which GM-CSF is linked to IL-3 [6] Myelopoietin (Leridistim, MPO) Dual IL-3 receptor agonist and G-CSF [7] receptor agonist Promegapoietin (PMP) Dual IL-3 receptor agonist and Thrombopoietin [8] (TPO) receptor agonist Progenipoietin (ProGP) Dual Flt3 ligand receptor agonist and G-CSF [9] receptor agonist TPOG Linked mutant truncated versions of G-CSF [10] and TPO with multilineage haematopoietic activity TFLOG Linked mutant truncated versions of G-CSF, [10] flt-3 ligand and TPO with multilineage haematopoietic activity Hyper Interleukin-6 Fusion protein containing shortened interleukin-6 [11] receptor linked to interleukin-6 cytokines with increased haematopoietic activity and/or more desirable pharmaco- logical characteristics. Table 1 lists the single and combined synthetic cytokines generated during the last five years. Both daniplestim and pixykine were used in phase III clinical trials to mobilise CD34 positive cells for transplantation. Also, myelopoietin and daniplestim plus G-CSF were used in phase I/II clinical trials to mobilise CD34 positive cells for transplantation. The other synthetic cytokines are undergoing both in vivo studies in non-human primates for haematopoietic reconstitution or mobilisation after cancer chemotherapy and in vitro studies for expansion of CD34 positive cells.

INTERLEUKIN-3 RECEPTOR AGONIST Daniplestim is a synthetic, genetically engineered, interleukin-3 receptor agonist with a 20-fold greater in vitro clonogenic multi-lineage haematopoietic activity and only 2-fold greater inflammatory priming effect compared to recombinant human