Granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein versus granulocyte-macrophage colony-stimulating factor after autologous bone marrow transplantation for non-Hodgkin's lymphoma: results of a randomized double-blind trial

Cytokines for the Treatment of Thrombocytopenia

Multiple cytokines affect the cellular processes that occur during the transition of a hematopoietic stem cell (HSC) to a platelet. Thrombopoietin (TPO) is the physiological regulator of thrombopoiesis. Although a number of cytokines (interleukin [IL]-1, IL-3, and IL-6) were first evaluated for their ability to lessen the degree of thrombocytopenia occurring during a variety of clinical scenarios, their clinical development was abandoned due to their limited effectiveness or excessive toxicity. Clinical results with TPO and a truncated pegylated form of TPO, megakaryocyte growth and development factor (MGDF), were more promising, but the repeated use of MGDF resulted in the development of neutralizing antibodies. This adverse event halted the further clinical development of not only MGDF but also TPO. IL-11 also affects various stages of megakaryocytopoiesis and thrombopoiesis and its use has been shown to shorten the duration of chemotherapy-induced thrombocytopenia, which led to its approval by the US Food and Drug Administration (FDA). A growing number of new non-immunogenic peptides and non-peptide TPO agonists recently have entered clinical trials. These small molecules appear to be effective therapies and have acceptable toxicity, but additional clinical evaluation will be required prior to their approval for clinical use.

High-level expression of human stem cell factor fused with erythropoietin mimetic peptide in Escherichia coli

Stem cell factor (SCF) and erythropoietin are essential for normal erythropoiesis and induce proliferation and differentiation synergistically for erythroid progenitor cells. Here, we report our work on construction of SCF/erythropoietin mimetic peptide (EMP) fusion protein gene, in which human SCF cDNA (1-165aa) and EMP sequence (20aa) were connected using a short (GGGGS) or long (GGGGSGGGGGS) linker sequence. The SCF/EMP gene was cloned into the pBV220 vector and expressed in the Escherichia coli DH5alpha strain. The expression level of the fusion protein was about 30% of total cell protein. The resulting inclusion bodies were solubilized with 8 M urea, followed by dilution refolding. The renatured protein was subsequently purified by Q-Sepharose FF column. The final product was >95% pure by SDS-PAGE and the yield of fusion protein was about 40 mg/L of culture. UT-7 cell proliferation and human cord blood cell colony-forming assays showed that the fusion proteins exhibited more potent activity than recombinant human SCF, suggesting a new strategy to enhance biological activities of growth factors.

Myeloid growth factors in oncology

Within the last decade haemopoietic growth factors have become established in the pharmacopoeia of oncology. In the form of granulocyte colony-stimulating factor (G-CSF), and to a lesser extent granulocyte-macrophage colony-stimulating factor (GM-CSF), these proteins are routinely used to accelerate restoration of neutrophil count after chemotherapy or bone marrow transplant. Their main advance has been the development of mobilisation protocols. Peripheral blood progenitor cells are induced to egress from the bone marrow and re-transfusion after myelosuppressive chemotherapy allows for a simple and more rapid form of autologous transplantation than bone marrow transplantation. This review will give a brief overview of the biology of haemopoiesis in relation to growth factors and the potential lines of further research. Although the established clinical uses of G-CSF will be discussed the main focus will be on the developmental applications, such as ex vivo haemopoiesis, dose intensification schedules and the application of growth factors in the therapy of haematological malignancies. The relevance of novel or more recently introduced recombinant haemopoietic growth factors will also be discussed in relation to these indications.

Thrombopoietic Factors in Chronic Bone Marrow Failure States: The Platelet Problem Revisited: Table 1

Thrombocytopenia is a serious clinical problem in several different clinical settings. In chronic bone marrow failure states, which include aplastic anemia, myelodysplastic syndrome, and graft failure, the prolonged nature of thrombocytopenia often leads to alloimunization after repeated platelet transfusions, the consequence of which is a platelet-refractory state and enhanced risk of bleeding. Despite the introduction of several thrombopoietic factors into clinical trials, an effective way to alleviate thrombocytopenia has been elusive, and the problem in chronic bone marrow failure states has remained poorly addressed by clinical investigations. Even so, several studies by our group and others suggest that a subset of patients suffering from chronic bone marrow failure can respond to appropriate growth factor therapy. The temporal pace of response appears, however, to be much slower than that observed after administering growth factors which act on neutrophils. On the other hand, durable responses can be secured in some patients given thrombopoietic factors for long periods of time. Herein, we provide an overview of the clinical research investigations of thrombopoietic factors in chronic bone marrow failure, and the emerging insights these studies provide for understanding the process of thrombopoiesis and its therapy in this setting.

Sequential interleukin 3 and granulocyte-macrophage-colony stimulating factor therapy in patients with bone marrow failure with long-term follow-up of responses

BACKGROUND

Interleukin-3 (IL-3) and granulocyte-macrophage-colony stimulating factor (GM-CSF) have synergistic, hematopoietic growth-promoting activity in preclinical studies. Because of the paucity of effective therapies for patients with chronic bone marrow failure states, the authors studied the biologic activity of sequential IL-3/GM-CSF in such patients.

METHODS

IL-3 was given subcutaneously for 5 days (at escalating doses of 0.15 microg/kg, 0.3 microg/kg, 0.6 microg/kg, 1.2 microg/kg, 2.5 microg/kg, 5.0 microg/kg, 10.0 microg/kg, or 15.0 microg/kg per day), and GM-CSF for was given subcutaneously for 9 days (at a dose of 5 microg/kg per day; Phase I 3 + 3 design) followed by 14 days of rest (total, 2 courses), then maintenance therapy.

RESULTS

The majority of 38 evaluable patients had aplastic anemia or myelodysplastic syndrome. Most patients (79%) had neutrophil responses. Ten patients (26%), all of whom were treated with IL-3 doses >/= 1.2 microg/kg per day, had platelet responses, with a median increase of 132 x 10(9)/L (range, 41-180 x 10(9)/L) over baseline in responders. Six patients (16%) had trilineage recovery, which could be durable (the longest ongoing at 6.5 years after therapy completion). The most common toxicities were low-grade fever, headache, and fatigue. The maximum tolerated doses were IL-3 at 10 microg/kg per day and GM-CSF at 5 microg/kg per day.

CONCLUSIONS

Sequential IL-3/GM-CSF effectively raised blood counts in some patients with bone marrow failure at doses that were tolerated well. These results indicate that early-acting growth factors can induce durable, multilineage responses in a subset of individuals with bone marrow failure.

Haemopoietic growth factors in paediatric oncology: a review of the literature

Recombinant haemopoietic growth factors (HGFs) are an attractive adjunct to reduce morbidity from chemotherapy regimens and their use has become widespread in paediatric oncology. Although patients receiving HGFs often have faster haematological recovery after intensive chemotherapy, this does not always translate into meaningful clinical benefits. This article reviews the clinical effectiveness of HGFs in a variety of different contexts. Most published studies have used granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) as prophylaxis to ameliorate the subsequent neutropenia following intensive chemotherapy. These 2 agents have also been used to mobilise peripheral blood stem cells for autologous transplantation. HGFs specific for anaemia and thrombocytopenia are currently in paediatric clinical trials and it is hoped that the proper context and administration strategy can be found to make their use clinically effective. This article also reviews data on toxicity, specifically focusing on differences between various formulations of growth factors. HGFs are expensive, and cost-benefit analyses reviewed in this article give an important perspective on the financial aspects of paediatric cancer care. Because HGFs do not benefit every child receiving chemotherapy and overuse increases costs and may result in unnecessary adverse effects, evidence-based guidelines for their rational use in paediatric oncology are proposed.

Pharmacologic treatment options in patients with thrombocytopenia

Thrombocytopenia that results from chemotherapy has become an increasingly important issue in the treatment of cancer and remains a difficult clinical problem. The identification of a safe and effective platelet growth factor could significantly improve the management of severe chemotherapy-induced thrombocytopenia. Over the past decade, a number of hematopoietic growth factors with thrombopoietic activity have been identified, including stem-cell factor (c-kit ligand), interleukin (IL)-1, IL-3, IL-6, and IL-11, as well as thrombopoietin (TPO) and its derivatives. Only a few of these agents have shown acceptable tolerability and sufficient ability to stimulate thrombopoiesis to justify testing in randomized clinical trials. Currently, IL-11 is the only cytokine licensed in the United States for treatment of chemotherapy-induced thrombocytopenia. However, its thrombopoietic activity is modest and its use is often associated with unfavorable side effects. Identification of TPO, the c-Mpl ligand, as the primary physiologic regulator of megakaryocyte and platelet development offers important promise for treatment of thrombocytopenia. Preliminary clinical studies of recombinant human TPO (rhTPO), a full-length glycosylated molecule, indicate that it is safe and biologically active in reducing severe chemotherapy-induced thrombocytopenia. In addition to rhTPO, the future may see the development of novel genetically engineered, high-affinity cytokine receptor agonists and c-Mpl ligand mimetic peptides.

Phase III efficacy study of interleukin-3 after autologous bone marrow transplantation in patients with malignant lymphoma

We evaluated the efficacy of recombinant human interleukin-3 (rhIL-3) in reducing the number of platelet transfusions and major infections after autologous bone marrow transplantation (ABMT) in patients with malignant lymphoma. 198 patients with non-Hodgkin's lymphoma (NHL, n = 111) and Hodgkin's disease (HD, n = 87) were randomized to receive rhIL-3 10 microgram/kg/d (n = 130) or placebo (n = 68) for a maximum of 28 d after ABMT. Several well-known conditioning regimens were used. From day 1 after ABMT patients were treated with placebo or rhIL-3 at a dose of 10 microgram/kg/d by continuous i.v. infusion for 7 d and then by s.c. administration for 21 d or until platelet (50 x 109/l) and neutrophil (0.5 x 109/l) recovery had occurred. Treatment was completed in 54% of the patients in the rhIL-3 group versus 75% in the placebo group (P < 0.004). Adverse events were the main reason for premature discontinuation in the IL-3 group (23% IL-3 v 5% placebo). The median number of platelet transfusions was not significantly different between the IL-3 group and the placebo group (8.0 IL-3 v 6.0 placebo, P = 0.09). Platelet engraftment (>/= 20 x 109/l) was not significantly faster in the IL-3 group (28 d in the IL-3 and 27 d in the placebo group, P = 0.06) and the incidence of haemorrhagic complications was similar in both groups. In patients receiving the full intended dose of rhIL-3, platelet engraftment to >/= 20 x 109/l was delayed (P = 0.007). The median time to neutrophil engraftment was 23 d in the IL-3 and 25 d for the placebo group (P = 0.39). There was no difference in the incidence of major infections. We conclude that treatment with IL-3 has no clinical benefit in patients receiving ABMT for malignant lymphoma.

Development of a recombinant growth factor and fusion protein: lessons from GM-CSF

Several colony stimulating factors (CSFs) and cytokines have been successfully used to mobilize hematopoietic cells during myeloablative therapy, bone marrow failure, and transplantation and to provide supportive treatment during sepsis. The use of yeast-derived recombinant human granulocyte-macrophage CSF (rhuGM-CSF) and its interleukin-3 fusion protein, PIXY321, provides an example of issues associated with development programs for recombinant hematopoietic growth factors. Species specificity of rhuGM-CSF, different bioactivity of homologous molecules in mice, and production in laboratory animals of antibodies to human proteins limit preclinical evaluation of such molecules. In clinical trials, rhuGM-CSF was efficacious and well tolerated. The derivation of the recombinant molecule, optimal dosing, scheduling, and confounding effects of concurrent disease and treatments are factors that influence efficacy, adverse responses, and immunogenicity reported in patients treated with CSFs. In comparisons of yeast-derived with Escherichia coli-derived rhuGM-CS, the reduced severity and frequency of all adverse events, preponderance of low-grade adverse events, and similarity of positive clinical response versus adverse events reported for granulocyte CSF support safety and efficacy of yeast-derived rhuGM-CSE Enhanced pharmacoeconomic evaluations are beginning to limit and redirect clinical applications in this class of biological agents.

Thrombopoietic factors potentially useful in the treatment of acute leukemia

Thrombocytopenia is a major cause of morbidity following intensive chemotherapy for acute leukemia. Over recent years, there has been an increasing use of platelet transfusions which, although generally efficacious to prevent severe hemorrhage, have associated risks of transmitting blood-borne disease and of alloimmunization. Therefore, there is a clinical requirement for a drug that will reliably alleviate the thrombocytopenia associated with leukemia therapy. The c-mpl ligand thrombopoietin is the most interesting factor for the treatment of thrombocytopenia because of its lineage specificity. Phase I and II studies confirm its biological efficacy to induce rise in platelet count in patients with solid tumors and acute leukemia. Several other pleiotropic hematopoietic growth factors are also currently in clinical trials. These include interleukin-6, interleukin-3, interleukin-11, PIXY321 and stem cell factor. The effects of these cytokines appear to be modest at most and, with the exception of interleukin-11, their side effects are likely to limit their clinical application. Combinations of factors may prove more efficacious approaches to enhance platelet recovery.

Phase I/II trial of PIXY321 (granulocyte-macrophage colony stimulating factor/interleukin-3 fusion protein) for treatment of inherited and acquired marrow failure syndromes

Fourteen paediatric patients with advanced amegakaryocytic thrombocytopenia (AMT) or other bone marrow (BM) failure syndromes were enrolled on one of two phase I/II dose escalation studies of PIXY321. PIXY321 was administered subcutaneously in doses ranging from 250 to 750 mg/m2/d. No dose-limiting toxicity was observed. Peak absolute neutrophil count (ANC) was higher than baseline in all patients. Most transfusion-independent patients demonstrated elevation in haematocrit and/or platelet count. Trilineage haemopoietic responsiveness was evident in the three transfusion-independent patients. In these paediatric populations PIXY321 is well tolerated and merits consideration as a potential therapy.