Mechanisms and therapeutic prospects of thrombopoietin receptor agonists

The Cost-Effectiveness of Avatrombopag Versus Eltrombopag and Romiplostim in the Treatment of Patients with Immune Thrombocytopenia in the UK

BACKGROUND

Thrombopoietin receptor agonists-romiplostim, eltrombopag and avatrombopag-are commonly used as second-line treatments for immune thrombocytopenia (ITP).

METHODS

A Markov model was developed to estimate the cost effectiveness of the three TPO-RAs in adults with insufficient response to previous treatment from the perspective of the UK National Health Service (NHS). The model considered the effects of bleeding events, concomitant ITP medications, rescue therapies and treatment related adverse events over a lifetime horizon. Model inputs for effectiveness were based on a network meta-analysis and other published literature on ITP management. Other model inputs included costs (e.g., drug acquisition and administration) and healthcare resource utilisation.

RESULTS

Avatrombopag was associated with higher quality-adjusted life-years (QALYs) (10.979) than romiplostim (10.628) and eltrombopag (10.085), producing incremental QALYs of -0.351 and -0.894, respectively. Avatrombopag was associated with lower total costs (GBP £319,334) compared with romiplostim (GBP 406,361 [cost saving of GBP 87,027]) and higher total costs compared with eltrombopag (GBP 313,987 [incremental cost of GBP 5347]). Avatrombopag therefore dominated romiplostim (more effective and less expensive) and was cost-effective versus eltrombopag (incremental cost-effectiveness ratio of GBP 5982 per QALY).

CONCLUSIONS

Avatrombopag is a cost-effective treatment compared with romiplostim and eltrombopag for the second-line treatment of adults with ITP from the perspective of the UK NHS.

Safety analysis of romiplostim, eltrombopag, and avatrombopag post-market approval: a pharmacovigilance study based on the FDA Adverse Event Reporting System

BACKGROUND

Romiplostim, eltrombopag, and avatrombopag, as new-generation thrombopoietin receptor agonists (TPO-RAs), have been widely used in the treatment of immune thrombocytopenia (ITP). Given their similar efficacy, a comprehensive evaluation of their safety is crucial for optimizing treatment choices. This study aims to explore the potential safety issues of three major drugs for treating ITP: romiplostim, eltrombopag, and avatrombopag, thereby providing references and research directions for subsequent high-quality clinical studies.

METHODS

We retrieved data from the FDA Adverse Event Reporting System (FAERS) database from the first quarter of 2018 to the second quarter of 2023. Using reporting odds ratio (ROR), proportional reporting ratio (PRR), bayesian confidence propagation neural network (BCPNN), and multiple gamma poisson shrinkage (MGPS), we mined and analyzed adverse events (AEs) associated with romiplostim, eltrombopag, and avatrombopag. The Designated Medical Event (DME) list from the European Medicines Agency (EMA) was used to screen out the DME of three drugs. Venn analysis was used to screen the specific AEs of each drug.

RESULTS

The study included 2,851 cases of romiplostim, 10,297 cases of eltrombopag, and 973 cases of avatrombopag. Venn analysis revealed nine common AEs across the three drugs. The number of significant specific AEs associated with romiplostim, eltrombopag, and avatrombopag were 58, 98, and 15 respectively. DMEs for romiplostim included autoimmune haemolytic anaemia (ROR = 6.1, n = 3), haemolytic anaemia (ROR = 8.13, n = 7), sudden hearing loss (ROR = 5.24, n = 3), haemolysis (ROR = 3.89, n = 3). DMEs for eltrombopag included hepatic infection (ROR = 9.56, n = 6), granulocytopenia (ROR = 2.91, n = 4), autoimmune haemolytic anaemia (ROR = 3.03, n = 5), haemolytic anaemia (ROR = 3.46, n = 10), haemolysis (ROR = 4.65, n = 12), hepatic failure (ROR = 2.51, n = 23). Not a single DME was found for avatrombopag.

CONCLUSION

This study indicates that eltrombopag manifests significant safety signals within the hepatic system. This implies that monitoring liver function during treatment is advisable. Avatrombopag shows relatively lower hepatotoxicity signals; however, further large-scale studies are needed to validate these observations. Moreover, both romiplostim and eltrombopag therapies may be linked to a risk of sudden hearing loss or deafness, which merits clinical attention. These findings offer crucial safety references for clinical drug use. Nevertheless, the causal relationship between the drugs and AEs necessitates further in-depth investigation.

Role of thrombopoietin receptor agonists in chemotherapy-induced thrombocytopenia: A meta-analysis

INTRODUCTION

Chemotherapy-induced thrombocytopenia (CIT) is a significant challenge in cancer treatment, often leading to dose reductions and reduced number of cycles. The limited effectiveness of platelet transfusions in managing CIT highlights the need for alternative treatments. Thrombopoietin receptor agonists (TPO-RA), including romiplostim, eltrombopag and avatrombopag, have shown potential in increasing platelet counts in CIT patients, necessitating a comprehensive analysis of their efficacy.

METHODS

This meta-analysis followed the Preferred Reporting Items for Systemic Reviews and Meta-analysis guidelines, searching Ovid databases up to 5 October 2023. The primary metric of interest was platelet count changes post-TPO-RA administration in CIT patients.

RESULTS

From the initial 867 studies obtained, 7 studies were selected based on the inclusion criteria. The analysis included 348 patients. A significant association was found between TPO-RA administration and platelet count increase, with a combined-effect increase of 69.52 ± 2.24 × 109/l. Subgroup analysis based on Romiplostim use suggested an increase of approximately 70.11 ± 39.07 × 109/l, while non-Romiplostim TPO-RAs showcased an increase of about 68.09 ± 82.58 × 109/l.

CONCLUSIONS

The meta-analysis demonstrates the effectiveness of TPO-RAs in managing CIT. Further research comparing platelet increases across standardised TPO-RA regimens is recommended to refine treatment strategies. This analysis provides valuable insights for clinicians in tailoring CIT treatment using TPO-RAs.

Let It Grow: The Role of Growth Factors in Managing Chemotherapy-Induced Cytopenia

Chemotherapy-induced cytopenia (CIC) is characterized by neutropenia, anemia, and thrombocytopenia, which are common and serious complications in cancer treatment. These conditions affect approximately 60% of patients undergoing chemotherapy and can significantly impact quality of life, treatment continuity, and overall survival. The use of growth factors, including granulocyte colony-stimulating factors (GCSFs), erythropoietin-stimulating agents (ESAs), and thrombopoietin receptor agonists (TPO-RAs), has emerged as a promising strategy for managing CIC. However, the use of these growth factors must be approached with caution. This review provides an overview of the mechanisms, efficacy, and safety of growth factors in the management of CIC. Additionally, we discuss predictive markers for treatment response, potential risks, and highlight areas for future research.

Thrombopoietin receptor agonists regulate myeloid-derived suppressor cell-mediated immunomodulatory effects in ITP

TPO receptor agonists (TPO-RAs) are a class of clinical second-line regimens for the treatment of primary immune thrombocytopenia (ITP). It can promote megakaryocyte maturation and increase platelet production, but its effect on immunosuppressive cells in patients with ITP has not been explored. Sixty-two ITP patients and 34 healthy controls (HCs) were included in this study. The proportion and functions of myeloid-derived immunosuppressive cells (MDSCs) in ITP patients and HCs were investigated. We found that the proportion and function of MDSCs in ITP patients treated with TPO-RAs were significantly higher than those treated with glucocorticoids (GCs), which was correlated with the clinical efficacy. The proportion and function of cytotoxic Th1 cells and CD8+T cells decreased, while the proportion and immunosuppressive function of Treg cells increased in ITP patients treated with TPO-RAs. We further proved, through MDSC depletion tests, that the inhibitory effect of MDSCs on Th1 cells and the promotion of Treg cells in the original immune micro-environment of GCs-treated ITP patients were impaired; however, these MDSCs' functions were improved in TPO-RAs-treated patients. Finally, we found that the KLF9 gene in MDSCs cells of ITP patients treated with TPO-RAs was down-regulated, which contribute to the higher mRNA expression of GADD34 gene and improved function of MDSCs. These results demonstrate a novel mechanism of TPO-RAs for the treatment of ITP through the assessment of MDSCs and their subsequent impact on T cells, which provides a new basis for TPO-RAs as first-line treatment approach to the treatment of ITP.

A De Novo Frameshift Mutation in RPL5 with Classical Phenotype Abnormalities and Worsening Anemia Diagnosed in a Young Adult-A Case Report and Review of the Literature

Diamond-Blackfan anemia (DBA) is a congenital bone marrow failure syndrome associated with malformations. DBA is related to defective ribosome biogenesis, which impairs erythropoiesis, causing hyporegenerative macrocytic anemia. The disease has an autosomal dominant inheritance and is commonly diagnosed in the first year of life, requiring continuous treatment. We present the case of a young woman who, at the age of 21, developed severe symptomatic anemia. Although, due to malformations, a congenital syndrome had been suspected since birth, a confirmation diagnosis was not made until the patient was referred to our center for an evaluation of her anemia. In her neonatal medical history, she presented with anemia that required red blood cell transfusions, but afterwards remained with a stable, mild, asymptomatic anemia throughout her childhood and adolescence. Her family history was otherwise unremarkable. To explain the symptomatic anemia, vitamin deficiencies, autoimmune diseases, bleeding causes, and myeloid and lymphoid neoplasms were investigated and ruled out. A molecular investigation showed the RPL5 gene variant c.392dup, p.(Asn131Lysfs*6), confirming the diagnosis of DBA. All family members have normal blood values and none harbored the mutation. Here, we will discuss the unusual evolution of this case and revisit the literature.

Safety of non‑peptide thrombopoietin receptor agonists in patients with immune thrombocytopenia: A systematic review and meta‑analysis of short‑term double‑blind randomized clinical trials

The aim of the present study was to analyze the safety of non-peptide thrombopoietin receptor agonists (TPO-RAs) for immune thrombocytopenia (ITP) treatment. All studies reporting adverse events (AEs) in relation to ITP treatment with eltrombopag, avatrombopag, and hetrombopag were retrieved from PubMed, Web of Science, and Embase databases. RevMan 5.4.1 was used for meta-analysis, heterogeneity and bias analyses. A total of 1,078 patients from seven eligible studies were enrolled. In the enrolled clinical trials, the double-blind period was between 6 weeks and 6 months. The results revealed that the chances of any AEs [relative risk (RR)=1.16; 95% confidence interval (CI), 0.90-1.51; I²=78%; P=0.26], grade 3/4 AEs (RR=1.07; 95% CI, 0.63-1.80; I²=0%; P=0.81), elevated transaminase levels (RR=1.09; 95% CI, 0.68-1.74; I²=0%; P=0.72), thrombosis (RR=1.92; 95% CI, 0.55-6.66; I²=0%; P=0.31) and cataracts (RR=0.83; 95% CI, 0.38-1.83; I²=0%; P=0.65) were not significantly higher in patients with ITP that received non-peptide TPO-RAs compared with patients with ITP treated with a placebo. The present study indicated that non-peptide TPO-RAs were relatively safe for patients with ITP, at least within 6 months of administration.

Sustained response off treatment in eltrombopag for children with persistent/chronic primary immune thrombocytopenia: A multicentre observational retrospective study in China

Eltrombopag (ELT) is effective and safe in adult persistent/chronic immune thrombocytopenia (p/cITP); a proportion could achieve a sustained response off treatment (SRoT); however, data on children are lacking. We attempted to analyse SRoT of ELT in children with p/cITP in this study. A multicentre retrospective observational study was performed in November 2022 for children with p/cITP who used ELT alone for >2 months between January 2017 and November 2021. Clinical data of pre-, during and post-ELT were collected. SRoT was defined as maintaining a platelet count of ≥30 × 10⁹ /L without rescue therapy for at least 6 months off ELT. There were 143 patients enrolled; 69.2% (99/143) achieved an overall response of 43.3% and 25.9% achieved complete response (CR) and response (R). Among the 35 patients analysed from whom ELT was withdrawn, 71.4% (25/35) showed SRoT after discontinuing ELT without additional ITP therapy, with a median follow-up of 0.94 (range, 0.53-3.8) years, equal to 17.5% (25/143) in all patients treated with ELT. Compared with the patients with relapse (n = 10), the SRoT patients (n = 25) had a higher rate of CR (80% [20/25] vs. 40% [4/10]), shorter interval time from initiation to taper (6.4 months vs. 9.4 months), longer time from taper to withdrawal (1.1 years vs. 0.3 years) and a longer duration of ELT treatment (1.6 years vs. 0.5 years) with p < 0.05. Patients who achieved CR could attain SRoT more easily (p = 0.02). ELT had a response in 69.2% of children with p/cITP and 17.5% of them attained SRoT with good tolerance. The patients who achieved CR and began ELT treatment as early as possible, with a longer treatment duration and slower tapering, had a higher probability of SRoT.

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-TPORem1cyagen (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.

Chemotherapy-induced thrombocytopenia: literature review

Chemotherapy-induced thrombocytopenia (CIT) is a common condition that frequently results in reduced chemotherapy dosages, postponed treatment, bleeding, and unfavorable oncological outcomes. At present, there is no clear suggestions for preventing or treating CIT. Thrombopoietin (TPO) replacement therapy has been invented and used to treat CIT to promote the production of megakaryocytes and stimulate the formation of platelets. However, this treatment is limited to the risk of immunogenicity and cancer progression. Therefore, an unmet need exists for exploring alternatives to TPO to address the clinical issue of CIT. Application of appropriate therapeutic drugs may be due to understanding the potential mechanisms of CIT. Studies have shown that chemotherapy significantly affects various cells in bone marrow (BM) microenvironment, reduces their ability to support normal hematopoiesis, and may lead to BM damage, including CIT in cancer patients. This review focuses on the epidemiology and treatment of cancer patients with CIT. We also introduce some recent progress to understand the cellular and molecular mechanisms of chemotherapy inhibiting normal hematopoiesis and causing thrombocytopenia.

Eltrombopag increases the hematopoietic supporting ability of mesenchymal stem/stromal cells

Background

Eltrombopag (EP) is a small molecule that acts directly on hematopoietic stem cells (HSCs) and megakaryocytes to stimulate the hematopoietic process. Mesenchymal stem/stromal cells (MSCs) are key hematopoietic niche regulators.

Objectives

We aimed to determine whether EP has any effect on MSC function and properties (especially on their hematopoietic-supporting ability) and if so, what changes (e.g. genome-wide transcriptomic alterations) are induced in MSC after EP treatment.

Design/Methods

MSCs were isolated from 12 healthy donors and treated with 15 µM and 50 µM of EP for 24 h. The toxicity of the drug on MSCs and their differentiation ability were analyzed, as well as the transcriptomic profile, reactive oxygen species (ROS) and DNA damage and the changes induced in the clonogenic capacity of HSCs.

Results

The results show that EP also modifies MSC functions, decreasing their adipogenic differentiation, increasing the expression of genes involved in hypoxia and other pathways related to oxygen homeostasis, and enhancing their ability to support hematopoiesis in vitro.

Conclusion

Our findings support the use of EP in cases where hematopoiesis is defective, despite its well-known direct effects on hematopoietic cells. Our findings suggest that further studies on the effects of EP on MSCs from patients with aplastic anemia are warranted.

Effect of thrombopoietin receptor agonist on health-related quality of life and platelet transfusion burden for patients with myelodysplastic syndromes: a systematic review and meta-analysis

Thrombocytopenia is a common and unsolved problem in myelodysplastic syndrome (MDS) patients; we aimed to summarize the evidence of TPO-RA treatment for heath-related quality of life (HRQoL) and platelet transfusion burden of MDS patients. We searched Pubmed, Web of Science, EMBASE, and CENTRAL for randomized clinical trials (RCTs) comparing TPO-RA to placebo in MDS published until July 31, 2021. A random-effect model was used. Eight RCTs with 908 patients were identified. Only three RCTs involving eltrombopag reported HRQoL, and all three studies treated HRQoL as a secondary outcome. In these three RCTs, the HRQoL instruments used in each study were different. However, this outcome cannot be meta-analyzed because some studies did not provide complete data. Subsequent clinical trials should pay more attention to this. Compared to placebo, TPO-RA did not affect platelet transfusion incidence 0.83 (95% CI 0.60-1.15). There was no evidence for subgroup differences in the analyses of different types of TPO-RA, different additional agent, and different types of MDS risk groups. However, platelet transfusion units (RR = 0.68, 95% CI 0.53 to 0.84) were significantly decreased. The RR of patients who did not require platelet transfusion for 56 or more consecutive days was not different between groups (RR = 0.98, 95% CI 0.41 to 2.34). TPO-RA may decrease platelet transfusion units in MDS patients with thrombocytopenia. But the significance of this finding should be interpreted with caution, because too few studies were meta-analyzed.

Roles of Embryonic Lethal Abnormal Vision-Like RNA Binding Proteins in Cancer and Beyond

Embryonic lethal abnormal vision-like (ELAVL) proteins are RNA binding proteins that were originally discovered as indispensable regulators of the development and functioning of the nervous system. Subsequent studies have shown that ELAVL proteins not only exist in the nervous system, but also have regulatory effects in other tissues. ELAVL proteins have attracted attention as potential therapeutic targets because they stabilize multiple mRNAs by binding within the 3′-untranslated region and thus promote the development of tumors, including hepatocellular carcinoma, pancreatic cancer, ovarian cancer, breast cancer, colorectal carcinoma and lung cancer. Previous studies have focused on these important relationships with downstream mRNAs, but emerging studies suggest that ELAVL proteins also interact with non-coding RNAs. In this review, we will summarize the relationship of the ELAVL protein family with mRNA and non-coding RNA and the roles of ELAVL protein family members in a variety of physiological and pathological processes.

Eltrombopag inhibits TET dioxygenase to contribute to hematopoietic stem cell expansion in aplastic anemia

Eltrombopag, an FDA-approved non-peptidyl thrombopoietin receptor agonist, is clinically used for the treatment of aplastic anemia, a disease characterized by hematopoietic stem cell failure and pancytopenia, to improve platelet counts and stem cell function. Eltrombopag treatment results in a durable trilineage hematopoietic expansion in patients. Some of the eltrombopag hematopoietic activity has been attributed to its off-target effects, including iron chelation properties. However, the mechanism of action for its full spectrum of clinical effects is still poorly understood. Here, we report that eltrombopag bound to the TET2 catalytic domain and inhibited its dioxygenase activity, which was independent of its role as an iron chelator. The DNA demethylating enzyme TET2, essential for hematopoietic stem cell differentiation and lineage commitment, is frequently mutated in myeloid malignancies. Eltrombopag treatment expanded TET2-proficient normal hematopoietic stem and progenitor cells, in part because of its ability to mimic loss of TET2 with simultaneous thrombopoietin receptor activation. On the contrary, TET inhibition in TET2 mutant malignant myeloid cells prevented neoplastic clonal evolution in vitro and in vivo. This mechanism of action may offer a restorative therapeutic index and provide a scientific rationale to treat selected patients with TET2 mutant-associated or TET deficiency-associated myeloid malignancies.

Repurposing Eltrombopag as an Antimicrobial Agent Against Methicillin-Resistant Staphylococcus aureus

Because of the excessive use of antibiotics, methicillin-resistant Staphylococcus aureus (MRSA) has become prevalent worldwide. Moreover, the formation of S. aureus biofilms often cause persistence and relapse of infections. Thus, the discovery of antibiotics with excellent antimicrobial and anti-biofilm activities is urgently needed. In the present study, eltrombopag (EP), a classic thrombopoietin receptor agonist, exhibited potential antimicrobial activity against S. aureus and its biofilms. Through our mechanistic studies, EP was found to interfere with proton motive force in S. aureus. The in vivo anti-infective efficacy of EP was further confirmed in the wound infection model, thigh infection model and peritonitis model by MRSA infection. In addition, the cytotoxicity of EP against mammalian cells and the in vivo toxicity of EP in animal models were not observed at the tested concentrations. Collectively, these results indicate that EP could be considered a potential novel antimicrobial agent against recalcitrant infections caused by MRSA.

Effect of avatrombopag in the management of severe and refractory chemotherapy-induced thrombocytopenia (CIT) in patients with solid tumors

Chemotherapy-induced thrombocytopenia (CIT) is a common complication in cancer patients, especially after multiple cycles of chemotherapy, which leads to the delayed treatment or reduced dosage. The treatment of CIT is limited for refractory and severe cases. Herein we reported a single-center study of avatrombopag, a type of thrombopoietin receptor agonist (TPO-RA), for the treatment of severe and refractory (S/R) CIT who failed from multi-line treatments. A total of 13 cancer patients with S/R CIT were enrolled at the First Affiliated Hospital of Zhejiang Chinese Medical University from September 2020 to February 2021. All the patients were administered oral avatrombopag at an initial dose of 60 mg/day, which could be decreased as needed, over a period of 8 weeks. Eight (8/13, 61.5%) patients responded to avatrombopag (with a platelet count ≥50 × 10⁹/L and transfusion independent), with a median response time of 27.5 (11-50) days, and the median cumulative day of platelet response was 79 (20-167). Ten of 13 patients (76.9%) no longer required platelet transfusion at the study endpoint. The predictor of response was the level of hemoglobin (HB) at study entry, patients with an HB over 90 g/L achieved a response rate of 88.9%. In addition, platelet count showed 87.5% sensitivity and 100% specificity to predict the treatment response at a cutoff value of 25.5× 10⁹/L at the end of the third week management. No drug-related side effects were noticed during administration. Our study showed that avatrombopag could be a novel and effective drug for the treatment of severe and refractory CIT, especially for those with hemoglobin above 90 g/L. This study was registered at chictr.org.cn as # ChiCTR2100050646.

Risk of thrombosis with thrombopoietin receptor agonists for ITP patients: a systematic review and meta-analysis

One possible side effect of thrombopoietin receptor agonists in immune thrombocytopenia is thrombosis. Our aim is to systematically review whether patients with ITP that were treated with a TPO-RA have an increased risk for thrombosis as compared to ITP patients without TPO-RA. Patients in the intervention group were required to receive TPO-RA therapy. The primary outcome was the incidence of thromboembolic events. Eleven studies were included in the pooled analysis. More thromboembolic events were noted in the TPO-RA group than in the control group: 25 compared to 4. Ten out of 11 studies showed a relative risk greater than 1. However, none of these individual risk ratios was statistically significant. The meta-analysis showed a RR of 1.82 [95% CI 0.78-4.24]. Our findings indicate there is a non-significant higher chance of thrombosis in ITP patients with TPO-RA treatments versus ITP patients without TPO-RA treatment.

Thrombocytopenia in Chronic Liver Disease: Challenges and Treatment Strategies

Thrombocytopenia is a common hematologic complication seen in patients with chronic liver disease (CLD). The pathophysiology of thrombocytopenia in CLD is multifactorial, primarily stemming from platelet sequestration and decreased platelet production. This review focuses on the pathophysiology and current treatment options in the treatment of thrombocytopenia in chronic liver disease. While platelet transfusions are the gold standard of treatment, considerations ought to be given to CLD patients who can benefit from transjugular intrahepatic portosystemic shunt and splenic artery embolization. Finally, the recent approval of thrombopoietin receptor agonists for use in CLD patients paves a way for a safe and effective alternative method of improving platelet levels and reducing the need for recurrent platelet transfusions.

A Review of Romiplostim Mechanism of Action and Clinical Applicability

Thrombocytopenia results from a variety of conditions, including radiation, chemotherapy, autoimmune disease, bone marrow disorders, pathologic conditions associated with surgical procedures, hematopoietic stem cell transplant (HSCT), and hematologic disorders associated with severe aplastic anemia. Immune thrombocytopenia (ITP) is caused by immune reactions that accelerate destruction and reduce production of platelets. Thrombopoietin (TPO) is a critical component of platelet production pathways, and TPO receptor agonists (TPO-RAs) are important for the management of ITP by increasing platelet production and reducing the need for other treatments. Romiplostim is a TPO-RA approved for use in patients with ITP in the United States, European Union, Australia, and several countries in Africa and Asia, as well as for use in patients with refractory aplastic anemia in Japan and Korea. Romiplostim binds to and activates the TPO receptor on megakaryocyte precursors, thus promoting cell proliferation and viability, resulting in increased platelet production. Through this mechanism, romiplostim reduces the need for other treatments and decreases bleeding events in patients with thrombocytopenia. In addition to its efficacy in ITP, studies have shown that romiplostim is effective in improving platelet counts in various settings, thereby highlighting the versatility of romiplostim. The efficacy of romiplostim in such disorders is currently under investigation. Here, we review the structure, mechanism, pharmacokinetics, and pharmacodynamics of romiplostim. We also summarize the clinical evidence supporting its use in ITP and other disorders that involve thrombocytopenia, including chemotherapy-induced thrombocytopenia, aplastic anemia, acute radiation syndrome, perisurgical thrombocytopenia, post-HSCT thrombocytopenia, and liver disease.

Real-world use of thrombopoietin receptor agonists in elderly patients with primary immune thrombocytopenia

The efficacy and safety of thrombopoietin-receptor agonists (TRAs) in elderly patients with primary immune thrombocytopenia (ITP) is uncertain. In 384 ITP patients treated with TRAs when aged ≥60 years, we investigated TRAs response and switch, thrombotic/hemorrhagic risk, and sustained responses off-treatment (SROT). After 3 months, 82.5% and 74.3% of eltrombopag and romiplostim-treated patients achieved a response, respectively (p=0.09); 66.7% maintained the response (median follow-up: 2.7 years). Eighty-five (22.2%) patients switched to the alternative TRA; while no cross-toxicity was observed, 83.3% of resistant patients had a response after the switch. During TRA, 34 major thromboses (3 fatal) and 14 major hemorrhages (none fatal) occurred in 18 and 10 patients, respectively, and were associated with thrombosis history (SHR: 2.04, p=0.05) and platelet count <20x109/L at TRA start (SHR: 1.69, p=0.04), respectively. A recurrent event occurred in 15.6% of patients surviving thrombosis, in all cases but one during persisting TRA treatment (incidence rate: 7.7 per 100 patient-years). All recurrences occurred in the absence of adequate antithrombotic secondary prophylaxis. Sixty-two (16.5%) responding patients discontinued TRA; 53 (13.8%) patients maintained SROT, which was associated with TRA discontinuation in complete response (p<0.001). Very old age (≥75, 41.1%) was associated with more frequent TRAs start in persistent/acute phase but not with response or thrombotic/hemorrhagic risk. TRAs are effective in elderly ITP patients, with no fatal haemorrhages and with SROT in a significant portion of patients; in patients with thrombosis history caution is warranted and a careful risk/benefit balance should be carried out.

Role of Thrombopoietin Receptor Agonists in Inherited Thrombocytopenia

In the last decade, improvements in genetic testing have revolutionized the molecular diagnosis of inherited thrombocytopenias (ITs), increasing the spectrum of knowledge of these rare, complex and heterogeneous disorders. In contrast, the therapeutic management of ITs has not evolved in the same way. Platelet transfusions have been the gold standard treatment for a long time. Thrombopoietin receptor agonists (TPO-RA) were approved for immune thrombocytopenia (ITP) ten years ago and there is evidence for the use of TPO-RA not only in other forms of ITP, but also in ITs. We have reviewed in the literature the existing evidence on the role of TPO-RAs in ITs from 2010 to February 2021. A total of 24 articles have been included, 4 clinical trials, 3 case series and 17 case reports. A total of 126 patients with ITs have received TPO-RA. The main diagnoses were Wiskott–Aldrich syndrome, MYH9-related disorder and ANKRD26-related thrombocytopenia. Most patients were enrolled in clinical trials and were treated for short periods of time with TPO-RA as bridging therapies towards surgical interventions, or other specific approaches, such as hematopoietic stem cell transplantation. Here, we have carried out an updated and comprehensive review about the efficacy and safety of TPO-RA in ITs.

Eltrombopag Improves Erythroid Differentiation in a Human Induced Pluripotent Stem Cell Model of Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is a congenital macrocytic anemia associated with ribosomal protein haploinsufficiency. Ribosomal dysfunction delays globin synthesis, resulting in excess toxic free heme in erythroid progenitors, early differentiation arrest, and pure red cell aplasia. In this study, DBA induced pluripotent stem cell (iPSC) lines were generated from blood mononuclear cells of DBA patients with inactivating mutations in RPS19 and subjected to hematopoietic differentiation to model disease phenotypes. In vitro differentiated hematopoietic cells were used to investigate whether eltrombopag, an FDA-approved mimetic of thrombopoietin with robust intracellular iron chelating properties, could rescue erythropoiesis in DBA by restricting the labile iron pool (LIP) derived from excessive free heme. DBA iPSCs exhibited RPS19 haploinsufficiency, reduction in the 40S/60S ribosomal subunit ratio and early erythroid differentiation arrest in the absence of eltrombopag, compared to control isogenic iPSCs established by CRISPR/Cas9-mediated correction of the RPS19 point mutation. Notably, differentiation of DBA iPSCs in the presence of eltrombopag markedly improved erythroid maturation. Consistent with a molecular mechanism based on intracellular iron chelation, we observed that deferasirox, a clinically licensed iron chelator able to permeate into cells, also enhanced erythropoiesis in our DBA iPSC model. In contrast, erythroid maturation did not improve substantially in DBA iPSC differentiation cultures supplemented with deferoxamine, a clinically available iron chelator that poorly accesses LIP within cellular compartments. These findings identify eltrombopag as a promising new therapeutic to improve anemia in DBA.

A Real-World Observation of Eltrombopag and Recombinant Human Thrombopoietin (rhTPO) in Lymphoma Patients With Chemotherapy Induced Thrombocytopenia

This real-world, observational study aimed to assess and compare the clinical efficacy and safety of eltrombopag with recombinant human thrombopoietin (rhTPO) in the treatment of chemotherapy induced thrombocytopenia (CIT) in patients with lymphoma. One hundred and fifty-three patients who experienced grade 3 or 4 thrombocytopenia after chemotherapy for lymphoma were enrolled, 51 of which were treated with eltrombopag, 50 with rhTPO, and 52 patients with no drug treatment were served as the control group. The lowest platelet level and mean platelet counts at Day 5, Day 7, and Day 10 were significantly higher in both the eltrombopag group (P=.041,.003,.000,.000) and rhTPO group (P=.005,.005,.000,.000) than the control, but there was no difference between treatment with eltrombopag and rhTPO. Similarly, days required for the recovery of platelet counts to ≥50×10⁹/L and ≥75×10⁹/L were not different between the two treatment groups but significantly higher than the control group (P <.05). Rates of bleeding and platelet transfusion were all significantly reduced in patients treated with eltrombopag (P=.031,.032) or rhTPO (P=.017,.009) when compared to the control. Treatment-related adverse events (AEs) were reported in 7 (13.7%) and 6 (12.0%) patients in the eltrombopag and rhTPO groups, respectively, all being mild and transient in nature. In conclusion, both eltrombopag and rhTPO were effective and safe in the treatment of thrombocytopenia after chemotherapy for lymphoma.

First-in-patient study of hetrombopag in patients with chronic idiopathic thrombocytopenic purpura

BACKGROUND

Idiopathic thrombocytopenic purpura (ITP) especially refractory and (or) relapsed ITP, is a serious and global health burden and its clinical treatment is far from being satisfied. Hetrombopag is a novel, small-molecule thrombopoietin receptor agonist for the treatment of chronic idiopathic thrombocytopenic purpura (CITP).

OBJECTIVES

This first-in-patient study aimed to investigate the safety, pharmacokinetics, and anticipated therapeutic dose of hetrombopag in CITP patients.

METHODS

In this multicenter, first-in-patient study, CITP patients received hetrombopag in a dose escalation (2.5 mg/day, 5 mg/day, or 7.5 mg/day) cohort. All patients received hetrombopag in fasting condition once daily for 2 weeks.

RESULTS

Of 44 patients screened, 32 were enrolled and treated. Most adverse events were graded 1 to 2 (ie, mild to moderate), and the incidence and severity were similar for three study cohorts. The pharmacokinetics of hetrombopag were found to be nonlinear with greater than dose-proportional: 12.5% of patients (1/8) in the 2.5 mg/d cohort, 58.3% of patients (7/12) in the 5 mg/d cohort, 66.7% of patients (8/12) in the 7.5 mg/d cohort reached the primary study endpoint of a platelet count exceeding 50 × 109 /L on day 28.

CONCLUSION

Hetrombopag was well tolerated and preliminarily efficacious. Efficacy, safety, and pharmacokinetic data suggest that 7.5 mg hetrombopag once daily was the anticipated therapeutic dose of hetrombopag in CITP patients and has been recommended for investigation in a later confirmatory clinical study of hetrombopag.