Granulocyte-macrophage colony-stimulating factor and interleukin-3 in combination: a potent and consistent myelodysplastic syndrome bone marrow stimulant in vitro

Approval of tagraxofusp-erzs for blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and clinically challenging hematologic malignancy with dismal outcomes. With a median age of ∼70 years, the majority of patients with BPDCN have experienced historically suboptimal responses with intensive chemotherapy regimens. The major scientific breakthrough in this field was the recognition of overexpression of a surface receptor, CD123/interleukin 3 (IL-3) receptor α, in all patients. Importantly, a novel therapeutic agent consisting of a truncated diphtheria toxin (DT) payload fused to recombinant human IL-3 was being developed, one that targeted CD123, initially known as DT-IL-3 (later known as SL401; tagraxofusp; tagraxofusp-erzs [Elzonris]). The identification of this agent, and subsequent clinical trials specifically dedicated to patients with BPDCN (including a pilot study, followed by a larger phase 1/2 multicenter study [90% overall response rate [ORR] in frontline and 67% ORR in relapsed/refractory setting]), in part led to approval of tagraxofusp-erzs on 21 December 2018. Tagraxofusp-erzs was the first agent approved for BPDCN (for patients ages 2 years and older), and importantly, established this drug as the first CD123-targeted agent ever approved. The most notable toxicity of tagraxofusp-erzs is occurrence of the capillary leak syndrome, which occurs frequently at all grades, and has also been observed to be life-threatening, appropriately leading to a US Food and Drug Administration "black box" warning in the package insert. The preclinical and clinical aspects of drug development of tagraxofusp-erzs as monotherapy leading to drug approval are reviewed herein, with discussion of future directions of this novel agent, including consideration for rational combinations in BPDCN and beyond.

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.

New treatment approaches for myelodysplastic syndrome and secondary leukaemias

Allogeneic BMT is the treatment of choice for patients with MDS or sAML, offering a good chance of long-term disease-free survival if the transplant is performed in an early stage of disease or if the patient receives the transplant in complete remission after polychemotherapy. The transplant is limited to a minority of relatively young patients (aged below 55 years) with an HLA-identical sibling. Allogeneic BMT may also be considered when a closely- or fully-matched unrelated donor has been identified for a young and fit patient. All patients, including those without an excess of blasts, should be conditioned with bone marrow ablative therapy rather than an immune suppressive regime, such as cyclophosphamide alone. For the majority of patients there is no standard therapy other than appropriate supportive care. Relatively young patients below the age of 60 years with poor risk features can be considered for treatment with combination chemotherapy. Maintaining remission after remission-induction chemotherapy is a difficult issue. Patients not eligible for allogeneic BMT could be treated with post-remission chemotherapy or autologous BMT in the framework of prospective studies. Older patients can be considered for treatment with haematopoietic growth factors alone or in combination with differentiating agents such as low-dose Ara-C. This treatment should be delivered within the context of carefully designed and conducted trials.

Myelodysplastic syndromes in childhood--classification, epidemiology, and treatment

Much of the applied terminology of myelodysplastic syndromes (MDS) in childhood is confusing and not mutually exclusive. It is therefore proposed that the FAB classification of MDS is used in children in order to improve diagnostic precision and to facilitate epidemiologic, clinical, and therapeutic comparisons. The true incidence of childhood MDS is unknown but the rate may approximate the incidence of acute myelogenous leukemia. A pooled analysis of eight larger series representing 110 children less than 15 years old at diagnosis with de novo MDS classified according to the FAB recommendations showed that the more aggressive subtypes dominated, which partly may reflect that the less advanced cases are underdiagnosed. The median age at presentation was 6.0 years. The male/female ratio was 1.6. Monosomy 7 was the most frequent cytogenetic abnormality. The median survival was 13 months and the probability of survival three years from diagnosis was 16%. Spontaneous remission may be observed very infrequently. Allogeneic bone marrow transplantation (BMT) represents the only potentially curative treatment. The survival rate three years after BMT is about 50%. Major differences between childhood and adult MDS exist with respect to the distribution of FAB subgroups, the rate of progression, and the cytogenetic findings. The literature on MDS in children is still sparse and there is an obvious need for more studies designed to determine the incidence, clinical and laboratory characteristics, the natural course, and the efficacy of contemporary treatment options.

Southwestern Internal Medicine Conference: clinical use of hematopoietic growth factors

The hematopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), have been cloned, produced in bacteria and yeast, and approved for clinical use in the treatment of neutropenia. Both factors stimulate the proliferation and maturation of neutrophil progenitors and enhance the effector functions of mature cells by interaction with specific receptors on the cell surface. Serum levels of G-CSF correlate inversely with the neutrophil count, suggesting that G-CSF may be the normal homeostatic regulator of the neutrophil count, while GM-CSF is generally undetectable in the serum and appears under normal physiologic conditions to act locally at inflammatory sites. Phase I and II clinical trials with these factors demonstrated minimal toxicity for G-CSF and mild to moderate dose-dependent toxicity for GM-CSF. Recent clinical trials, including double-blind, randomized studies, support a role for these growth factors in the treatment of chronic neutropenias, such as Kostmann's syndrome, acquired immune deficiency syndrome (AIDS), aplastic anemia, and myelodysplasia, as well as in acute neutropenias, such as cyclic neutropenia, chemotherapy-induced neutropenia, and bone marrow transplantation.

Interleukin-3 in the treatment of myelodysplastic syndromes

Patients with myelodysplastic syndromes frequently present with anemia, leukopenia and thrombocytopenia due to defective maturation of bone marrow cells. Clinical studies with hematopoietic growth factors, including interleukin-3 (IL-3), have been undertaken to evaluate the possibility to reverse cytopenia. In initial phase I/II trials, treatment with IL-3 has resulted in an increase of neutrophil counts in 59%, of platelet counts in 34%, and in reticulocyte counts in 25% of the patients. Adverse effects were rather mild but in individual patients a reversible decrease in platelet counts and in the number of blast cells in blood and bone marrow were observed. Further clinical trials should concentrate on the combination of an early acting cytokine like IL-3 and later acting hemopoietic growth factors like erythropoietin and granulocyte colony-stimulating factor.