Eltrombopag can overcome the anti-megakaryopoietic effects of lenalidomide without increasing proliferation of the malignant myelodysplastic syndrome/acute myelogenous leukemia clone

Oral therapy for myelodysplastic syndromes/neoplasms and acute myeloid leukemia: a revolution in progress

INTRODUCTION

Patients with myeloid neoplasms such as myelodysplastic syndromes/neoplasms (MDS) and acute myeloid leukemia (AML) are generally older, and many are not eligible for curative intent intensive therapies and/or allogeneic hematopoietic stem cell transplantation. While lower intensity, hypomethylating agent (HMA)-based therapies such as azacitidine+venetoclax have improved patient outcomes significantly, responses are not durable, and most patients die from disease-related complications. The approvals of oral HMAs such as cedazuridine-decitabine (C-DEC) and oral azacitidine (CC-486) have kindled the hope that myeloid malignancies may soon be treated with total oral therapy.

AREAS COVERED

We review all-oral therapies including the approvals of C-DEC and CC-486 in MDS and AML, respectively, in addition to emerging all-oral therapies, both monotherapy and combination, in higher-risk (HR) MDS and AML.

EXPERT OPINION

Oral HMAs have the potential to be a convenient and efficacy-equivalent treatment option for patients with HR-MDS or AML and improve their quality of life by reducing clinic visits for medication administration. Total-oral therapy combinations, largely including an oral HMA 'backbone,' are in the early phases of clinical development, and it is our hope that well-designed trials employing these agents may soon allow the identification of optimal regimens that deliver effective disease-directed therapy with good tolerability.

Lenalidomide and Eltrombopag for Treatment of Low- or Intermediate-Risk Myelodysplastic Syndrome: Result of a Phase II Clinical Trial

PURPOSE

Thrombocytopenia is a serious complication of myelodysplastic syndromes (MDS) associated with an increased bleeding risk and worse prognosis. Eltrombopag (ELT), a thrombopoietin receptor agonist, can increase platelet counts and reverse anti-megakaryopoietic effects of lenalidomide (LEN) in preclinical studies. We hypothesized ELT would reduce the incidence of thrombocytopenia in MDS.

PATIENTS AND METHODS

We conducted a Phase II multicenter trial of ELT and LEN in adult patients with low- or intermediate-1-risk MDS with symptomatic or transfusion-dependent anemia or thrombocytopenia (NCT01772420). Thrombocytopenic patients were started on ELT and subsequently treated with LEN after platelets were increased. Patients without thrombocytopenia were started on LEN monotherapy and treated with ELT if they became thrombocytopenic.

RESULTS

Fifty-two patients were enrolled; mean age was 71 years (range 34-93). Overall response rate (ORR) in the intention-to-treat population was 35% (18/52). ELT monotherapy led to ORR of 33.3% (7/21), 29% achieving hematologic improvement (HI)-Platelets, and 24% bilineage responses. LEN monotherapy had 38% ORR (6/16) with all responders achieving HI-Erythroid. Fifteen patients received both ELT and LEN with ORR of 33.3%, 20% achieved HI-Erythroid, and 20% HI-Platelets with 13% bilineage responses. Median duration of response was 40 weeks for ELT (range 8-ongoing), 41 weeks (25-ongoing) for LEN, and 88 weeks (8.3-ongoing) for ELT/LEN. Non-hematologic grade 3-4 treatment-related adverse events were infrequent. Among patients on ELT, 2 had major bleeding events, 1 had a reversible increase in peripheral blasts, and 1 developed marrow fibrosis after 6 years on ELT.

CONCLUSIONS

ELT and LEN are well tolerated and effective in achieving hematologic improvement in patients with low-/intermediate-risk MDS.

Mechanisms and therapeutic prospects of thrombopoietin receptor agonists

The second-generation thrombopoietin (TPO) receptor agonists eltrombopag and romiplostim are potent activators of megakaryopoiesis and represent a growing treatment option for patients with thrombocytopenic hematological disorders. Both TPO receptor agonists have been approved worldwide for the treatment of children and adults with chronic immune thrombocytopenia. In the EU and USA, eltrombopag is approved for the treatment of patients with severe aplastic anemia who have had an insufficient response to immunosuppressive therapy and in the USA for the first-line treatment of severe aplastic anemia in combination with immunosuppressive therapy. Eltrombopag has also shown efficacy in several other disease settings, for example, chemotherapy-induced thrombocytopenia, selected inherited thrombocytopenias, and myelodysplastic syndromes. While both TPO receptor agonists stimulate TPO receptor signaling and enhance megakaryopoiesis, their vastly different biochemical structures bestow upon them markedly different molecular and functional properties. Here, we review and discuss results from preclinical and clinical studies on the functional and molecular mechanisms of action of this new class of drug.

The synergistic antileukemic effects of eltrombopag and decitabine in myeloid leukemia cells

Background

Hypomethylating agents (HMAs), such as decitabine (DAC), are currently used as first-line therapy for patients with high-risk myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML) not eligible for standard chemotherapies. Exacerbation of thrombocytopenia is one of the prevalent complications after HMA treatment. Eltrombopag (EP), an oral thrombopoietin receptor agonist, can efficiently stimulate megakaryopoiesis and elevate platelet counts in MDS/AML patients. However, the significance of combining EP with HMAs in patients with high-risk MDS/AML has not been determined.

Purpose

To explore the impacts and mechanisms of EP and/or DAC on leukemia cell growth and to explore whether EP exhibits antileukemic effects in the context of DAC treatment in human myeloid leukemia cell lines.

Methods

In our study, we assessed the anti-leukemic effect of EP in the context of DAC treatment by measuring cell proliferation, apoptosis, cell-cycle distribution, and intracellular reactive oxygen species (ROS) levels.

Results

Our results showed that the combination of EP and DAC had a more obvious antiproliferative effect than that of DAC as a single agent. EP mainly induced S or G0/G1 phase cell cycle arrest, and DAC arrested the cell cycle in the S or G2/M phase. The combination of EP and DAC had a synergistic effect on cell cycle arrest. Furthermore, single-agent treatment with EP or DAC induced a change in intracellular ROS levels, and the combination of EP and DAC had a synergistic effect on ROS levels, exacerbating leukemia cell death.

Conclusion

Our study provides in vitro evidence of the synergistic antileukemic effect and potential mechanisms of the combination of DAC and EP on myeloid leukemia cells.

Thrombocytopenia in MDS: epidemiology, mechanisms, clinical consequences and novel therapeutic strategies

Thrombocytopenia is commonly seen in myelodysplastic syndrome (MDS) patients, and bleeding complications are a major cause of morbidity and mortality. Thrombocytopenia is an independent factor for decreased survival and has been incorporated in newer prognostic scoring systems. The mechanisms of thrombocytopenia are multifactorial and involve a differentiation block of megakaryocytic progenitor cells, leading to dysplastic, hypolobated and microscopic appearing megakaryocytes or increased apoptosis of megakaryocytes and their precursors. Dysregulated thrombopoietin (TPO) signaling and increased platelet destruction through immune or nonimmune mechanisms are frequently observed in MDS. The clinical management of patients with low platelet counts remains challenging and approved chemotherapeutic agents such as lenalidomide and azacytidine can also lead to a transient worsening of thrombocytopenia. Platelet transfusion is the only supportive treatment option currently available for clinically significant thrombocytopenia. The TPO receptor agonists romiplostim and eltrombopag have shown clinical activity in clinical trials in MDS. In addition to thrombopoietic effects, eltrombopag can inhibit leukemic cell proliferation via TPO receptor-independent effects. Other approaches such as treatment with cytokines, immunomodulating drugs and signal transduction inhibitors have shown limited activity in selected groups of MDS patients. Combination trials of approved agents with TPO agonists are ongoing and hold promise for this important clinical problem.

Treatment of myelodysplastic syndrome with thrombomimetic drugs

Myelodysplastic syndromes (MDS) are clinically, genetically, and molecularly heterogeneous neoplastic diseases characterized by ineffective hematopoiesis leading to peripheral cytopenias. The severity of cytopenias influences oucome and is considered in prognostic scoring systems; thrombocytopenia, although not the most frequently observed at disease onset, is estimated to affect 40%-80% of MDS patients. As thrombocytopenia in MDS is determined by premature marrow destruction and programmed cell death, the use of thrombomimetic agents has been proposed in order to stimulate megakaryocyte differentation and proliferation. After early attempts of therapy of thrombocytopenic MDS patients with thrombopoietin and interleukin (IL)-11, clinical trials testing the activity of romiplostim and eltrombopag have been recently designed and have demonstrated good tolerability and efficacy in re-inducing megakaryocytopoiesis and in lowering the number of hemorragic events. The number of MDS patients receiving such treatments is still limited and a broader evaluation of the long-term effects and safety of these agents is ongoing.