Novel chemical-structure TPOR agonist, TMEA, promotes megakaryocytes differentiation and thrombopoiesis via mTOR and ERK signalings

BACKGROUND

Non-peptide thrombopoietin receptor (TPOR) agonists are promising therapies for the mitigation and treatment of thrombocytopenia. However, only few agents are available as safe and effective for stimulating platelet production for thrombocytopenic patients in the clinic.

PURPOSE

This study aimed to develop a novel small molecule TPOR agonist and investigate its underlying regulation of function in megakaryocytes (MKs) differentiation and thrombopoiesis.

METHODS

A potential active compound that promotes MKs differentiation and thrombopoiesis was obtained by machine learning (ML). Meanwhile, the effect was verified in zebrafish model, HEL and Meg-01 cells. Next, the key regulatory target was identified by Drug Affinity Responsive Target Stabilization Assay (DARTS), Cellular Thermal Shift Assay (CETSA), and molecular simulation experiments. After that, RNA-sequencing (RNA-seq) was used to further confirm the associated pathways and evaluate the gene expression induced during MK differentiation. In vivo, irradiation (IR) mice, C57BL/6N-TPOR^em1cyagen (Tpor^-/-) mice were constructed by CRISPR/Cas9 technology to examine the therapeutic effect of TMEA on thrombocytopenia.

RESULTS

A natural chemical-structure small molecule TMEA was predicted to be a potential active compound based on ML. Obvious phenotypes of MKs differentiation were observed by TMEA induction in zebrafish model and TMEA could increase co-expression of CD41/CD42b, DNA content, and promote polyploidization and maturation of MKs in HEL and Meg-01 cells. Mechanically, TMEA could bind with TPOR protein and further regulate the PI3K/AKT/mTOR/P70S6K and MEK/ERK signal pathways. In vivo, TMEA evidently promoted platelet regeneration in mice with radiation-induced thrombocytopenia but had no effect on Tpor^-/- and C57BL/6 (WT) mice.

CONCLUSION

TMEA could serve as a novel TPOR agonist to promote MKs differentiation and thrombopoiesis via mTOR and ERK signaling and could potentially be created as a promising new drug to treat thrombocytopenia.

Elucidating the Mechanism of Action of the Attributed Immunomodulatory Role of Eltrombopag in Primary Immune Thrombocytopenia: An In Silico Approach

Eltrombopag is a thrombopoietin receptor (MPL) agonist approved for the treatment of primary immune thrombocytopenia (ITP). Recent evidence shows that some patients may sustain platelet counts following eltrombopag discontinuation. The systemic immunomodulatory response that resolves ITP in some patients could result from an increase in platelet mass, caused either by the direct action of eltrombopag on megakaryocytes through MPL stimulation, or potential MPL-independent actions on other cell types. To uncover the possible mechanisms of action of eltrombopag, in silico analyses were performed, including a systems biology-based approach, a therapeutic performance mapping system, and structural analyses. Through manual curation of the available bibliography, 56 key proteins were identified and integrated into the ITP interactome analysis. Mathematical models (94.92% mean accuracy) were obtained to elucidate potential MPL-dependent pathways in non-megakaryocytic cell subtypes. In addition to the effects on megakaryocytes and platelet numbers, the results were consistent with MPL-mediated effects on other cells, which could involve interferon-gamma, transforming growth factor-beta, peroxisome proliferator-activated receptor-gamma, and forkhead box protein P3 pathways. Structural analyses indicated that effects on three apoptosis-related proteins (BCL2L1, BCL2, BAX) from the Bcl-2 family may be off-target effects of eltrombopag. In conclusion, this study proposes new hypotheses regarding the immunomodulatory functions of eltrombopag in patients with ITP.

Hematologic recovery induced by eltrombopag in Japanese patients with aplastic anemia refractory or intolerant to immunosuppressive therapy

Eltrombopag, an oral thrombopoietin-receptor agonist, stimulates hematopoiesis in patients with acquired aplastic anemia (AA) and has higher exposure in patients of East Asian origin. We evaluated the pharmacokinetics, efficacy, and safety of eltrombopag in Japanese patients with AA refractory or intolerant to immunosuppressive therapy (IST). Twenty-one patients (15 with non-severe AA, six with severe AA) with platelet counts < 30,000/µL received eltrombopag in a dose-escalation fashion (25, 50, 75, or 100 mg once daily) depending on individual platelet responses; the responders continued eltrombopag treatment beyond 6 months. The primary endpoint was hematologic response at 6 months, defined as improvements in blood counts or transfusion requirements. Ten (48%) patients achieved hematologic responses in at least one lineage at 6 months. Six patients achieved tri- and/or bi-lineage responses with continuation of eltrombopag treatment, with two patients no longer requiring eltrombopag treatment. The most common adverse events were nasopharyngitis and abnormal hepatic function, with the majority being grade 1 or 2. Cytogenetic abnormalities were observed in three patients; however, no progression to myelodysplastic syndrome/other malignancy was observed. Eltrombopag can safely restore multi-lineage hematopoiesis in Japanese patients with AA refractory or intolerant to IST.Clinical Trial registration NCT02148133.

Thrombocytopenia after liver transplantation: Should we care?

Transient thrombocytopenia is a common phenomenon after liver transplantation. After liver transplantation (LT), platelet count decreases and reaches a nadir on postoperative days 3-5, with an average reduction in platelet counts of 60%; platelet count recovers to preoperative levels approximately two weeks after LT. The putative mechanisms include haemodilution, decreased platelet production, increased sequestration, medications, infections, thrombosis, or combination of these processes. However, the precise mechanisms remain unclear. The role of platelets in liver transplantation has been highlighted in recent years, and particular attention has been given to their effects beyond hemostasis and thrombosis. Previous studies have demonstrated that perioperative thrombocytopenia causes poor graft regeneration, increases the incidence of postoperative morbidity, and deteriorates the graft and decreases patient survival in both the short and long term after liver transplantation. Platelet therapies to increase perioperative platelet counts, such as thrombopoietin, thrombopoietin receptor agonist, platelet transfusion, splenectomy, and intravenous immunoglobulin treatment might have a potential for improving graft survival, however clinical trials are lacking. Further studies are warranted to detect direct evidence on whether thrombocytopenia is the cause or result of poor-graft function and postoperative complications, and to determine who needs platelet therapies in order to prevent postoperative complications and thus improve post-transplant outcomes.

Phenotypic Screening for Inhibitors of a Mutant Thrombopoietin Receptor

An inhibitor for the thrombopoietin receptor (TpoR) would be more specific for the treatment of myeloproliferative neoplasms (MPNs) due to constitutively active mutant TpoR compared to the current treatment approach of inhibiting Janus kinase 2 (JAK2). We describe a cell-based high-throughput phenotypic screening approach to identify inhibitors for constitutively active mutant TpoR. A stepwise elimination process is used to differentiate generally cytotoxic compounds from compounds that specifically inhibit growth of cells expressing wild-type TpoR and/or mutant TpoR. We have systematically optimized the phenotypic screening assay and documented in this chapter critical parameters for a successful phenotypic screen, such as cell growth and seeding optimization, plate reproducibility and uniformity studies, and an assay robustness analysis with a pilot screen.

Thrombopoietin Receptor Agonist Mitigates Hematopoietic Radiation Syndrome and Improves Survival after Whole-Body Ionizing Irradiation Followed by Wound Trauma

Ionizing radiation combined with trauma tissue injury (combined injury, CI) results in greater mortality and H-ARS than radiation alone (radiation injury, RI), which includes thrombocytopenia. The aim of this study was to determine whether increases in numbers of thrombocytes would improve survival and mitigate H-ARS after CI. We observed in mice that WBC and platelets remained very low in surviving RI animals that were given 9.5 Gy 60Co-γ-photon radiation, whereas only lymphocytes and basophils remained low in surviving CI mice that were irradiated and then given skin wounds. Numbers of RBC and platelets, hemoglobin concentrations, and hematocrit values remained low in surviving RI and CI mice. CI induced 30-day mortality higher than RI. Radiation delayed wound healing by approximately 14 days. Treatment with a thrombopoietin receptor agonist, Alxn4100TPO, after CI improved survival, mitigated body-weight loss, and reduced water consumption. Though this therapy delayed wound-healing rate more than in vehicle groups, it greatly increased numbers of platelets in sham, wounded, RI, and CI mice; it significantly mitigated decreases in WBC, spleen weights, and splenocytes in CI mice and decreases in RBC, hemoglobin, hematocrit values, and splenocytes and splenomegaly in RI mice. The results suggest that Alxn4100TPO is effective in mitigating CI.

Thrombocytopenia and Anemia with Anti-c-Mpl antibodies Effectively Treated with Cyclosporine in a Patient with Rheumatoid Arthritis and Chronic Renal Failure

A 61-year-old woman with rheumatoid arthritis who was undergoing hemodialysis for end-stage renal failure was transferred to our hospital due to severe thrombocytopenia and anemia. A bone marrow biopsy showed the complete absence of megakaryocytes and erythroblasts. Cyclosporine treatment resulted in the improvement of her megakaryocyte and erythroblast levels, and a decrease in her serum level of anti-c-Mpl (thrombopoietin receptor) antibodies. After this initial improvement, her anemia progressively worsened, despite the continuous administration of immunosuppressive therapy with cyclosporine. Her platelet and leukocyte counts remained stable. This is the first report of a probable case of anti-c-Mpl antibody-associated pure red cell aplasia and acquired amegakaryocytic thrombocytopenic purpura.

Use of eltrombopag, a thrombopoietin receptor agonist, in post-transplantation thrombocytopenia

Persistent thrombocytopenia after stem cell transplantation can lead to increased morbidity and mortality [1,2]. The underlying causes are often multifactorial in this patient population [3,4]. In autologous transplantation, thrombocytopenia is usually a result of poor engraftment or a sign of impending disease relapse. In allogeneic stem cell transplantation, the etiology is often more complex with engraftment deficits, medication effects, graft versus host disease (GVHD), and other immunologic processes potentially contributing. Eltrombopag is an orally available nonpeptide thrombopoietin (TPO) receptor agonist which interacts with the transmembrane domain of the receptor on bone marrow megakaryocytes and upstream progenitor/stem cells. It has been studied in patients with chronic idiopathic thrombocytopenic purpura [5] and in patients with thrombocytopenia secondary to hepatitis C infection [6]. Unlike the case with recombinant human TPO, its use has not been associated with anti-platelet antibody production [7]. We report two cases of post-transplantation thrombocytopenia, one allogeneic and one autologous, where eltrombopag was given to treat prolonged thrombocytopenia. The use of eltrombopag in these two cases was effective in elevating platelet counts to levels that eliminated the need for platelet transfusions.

Eltrombopag. Idiopathic thrombocytopenic purpura after treatment failure: romiplostim is a better option

When corticosteroid therapy, immunoglobulin and splenectomy fail to control chronic idiopathic thrombocytopenic purpura and the risk of bleeding remains high, romiplostim is an acceptable option but close monitoring is needed to evaluate long-term risks. Eltrombopag (Revolade, GlaxoSmithKline) is a synthetic non-peptide agonist of endogenous receptors for thrombopoietin, a platelet growth factor. Clinical evaluation of eltrombopag in this setting is mainly based on a double-blind placebo-controlled trial in a heterogeneous group of 114 patients. The platelet count rose to at least 50,000/mm3 for five weeks in about one-quarter of patients receiving oral eltrombopag 50 mg/day. An indirect comparison providing weak evidence suggests that romiplostim is more effective. Clinical trials did not provide evidence that either drug reduced the frequency of bleeding. The haematological risks associated with eltrombopag are poorly evaluated, and mainly include: thrombosis, bone marrow disorders, and aggravation of thrombocytopenia after drug withdrawal. Aggravation of myelodysplastic syndrome cannot be ruled out in the long term. Hepatic disorders such as photosensitisation are frequent. The risk of cataract formation and renal impairment requires further study. There appears to be a high risk of pharmacokinetic interactions through a variety of mechanisms, including enzyme competition and cation binding, but this risk is not well documented. Eltrombopag is administered orally, making it more convenient than romiplostim, which necessitates weekly subcutaneous injections. In practice, when standard treatments fail in patients with chronic idiopathic thrombocytopenic purpura and a high risk of bleeding, it is better to use romiplostim, which appears to be somewhat more effective than eltrombopag. Eltrombopag also seems to carry a higher risk of non-haematological adverse effects and drug interactions.

TG101209, a small molecule JAK2-selective kinase inhibitor potently inhibits myeloproliferative disorder-associated JAK2V617F and MPLW515L/K mutations

JAK2V617F and MPLW515L/K represent recently identified mutations in myeloproliferative disorders (MPD) that cause dysregulated JAK-STAT signaling, which is implicated in MPD pathogenesis. We developed TG101209, an orally bioavailable small molecule that potently inhibits JAK2 (IC(50)=6 nM), FLT3 (IC(50)=25 nM) and RET (IC(50)=17 nM) kinases, with significantly less activity against other tyrosine kinases including JAK3 (IC(50)=169 nM). TG101209 inhibited growth of Ba/F3 cells expressing JAK2V617F or MPLW515L mutations with an IC(50) of approximately 200 nM. In a human JAK2V617F-expressing acute myeloid leukemia cell line, TG101209-induced cell cycle arrest and apoptosis, and inhibited phosphorylation of JAK2V617F, STAT5 and STAT3. Therapeutic efficacy of TG101209 was demonstrated in a nude mouse model. Furthermore, TG101209 suppressed growth of hematopoietic colonies from primary progenitor cells harboring JAK2V617F or MPL515 mutations.