Safety, Pharmacokinetics and Pharmacodynamics of Hetrombopag Olamine, a Novel TPO-R Agonist, in Healthy Individuals

Avatrombopag for the Treatment of Immune Thrombocytopenia

Avatrombopag, a second-generation thrombopoietin receptor agonist (TPO-RA), represents a significant advancement in the treatment of chronic immune thrombocytopenic purpura (cITP) and a potential therapeutic option for other thrombocytopenic disorders. Approved in both the USA and Europe, avatrombopag offers a convenient oral dosing regimen, initiated at 20 mg daily with food, to achieve and maintain platelet counts ≥ 50 × 109/L. Its favorable safety profile, characterized by minimal hepatic toxicity and the absence of dietary restrictions, distinguishes it from older TPO-RAs such as eltrombopag and romiplostim. Clinical trials and real-world data support its efficacy, with over 90% of patients that fail to standard first- and second-line treatments or become unresponsive, achieving target platelet counts, and its hepatotoxicity-free profile makes it particularly advantageous for patients with liver disease or complex comorbidities. Economic evaluations, including a budget impact analysis for the Italian National Health Service, have projected significant healthcare cost savings associated with avatrombopag use, reinforcing its value as a cost-effective therapeutic option. However, challenges remain, including limited data on long-term safety. In this review, we aim to provide a comprehensive synthesis of clinical evidence and real-world data on avatrombopag's efficacy, safety, and pharmacological advantages, while exploring its current and potential therapeutic applications, such as chemotherapy-induced thrombocytopenia and aplastic anemia.

Thrombopoietin Receptor Agonists in Post-Hematopoietic Cell Transplantation Complicated by Prolonged Thrombocytopenia: A Comprehensive Review

Hematopoietic cell transplantation (HCT) is a well-established procedure that has become a therapeutic mainstay for various hematological conditions. Prolonged thrombocytopenia following HCT is associated with a significant risk of morbidity and mortality, yet no universally recognized treatment protocol exists for such a complication. First-generation thrombopoietin receptor (TpoR) agonists as well as second-generation agents are known for their role in enhancing platelet production, and their use is expanding across various thrombocytopenic conditions. Therefore, we conducted this comprehensive review of the literature to provide an updated evaluation of the use of TpoR agonists and explore their efficacy and safety in the treatment of extended post-HCT thrombocytopenia. The literature search was conducted using PubMed database from 1996 through December 2023, using a predefined strategy with medical subject headings terms. We identified 64 reports on the utility of TpoR agonists, five of them were randomized controlled trials and the rest were retrospective observational studies and case series, with a total number of 1730 patients. Second-generation TpoR agonists appear more convenient than subcutaneous recombinant human thrombopoietin (rhTpo) as they can be orally administered and exhibit similar efficacy in platelet recovery, as indicated by recent trial results. Among these agents, avatrombopag, unlike eltrombopag, does not require any dietary restrictions, which could be more favorable for patients. However, eltrombopag remains the most extensively studied agent. TpoR agonists had promising effects in the treatment of post-HCT thrombocytopenia with a good safety profile so far, highlighting the potential benefit of their use.

Update on the Use of Thrombopoietin-Receptor Agonists in Pediatrics

This review summarizes the rationale and current data on the use of thrombopoietin receptor agonists (TPO-RAs) for treating severe thrombocytopenia in infants, children, and adolescents. It focuses on substances that have been approved by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) for pediatric patients. Romiplostim and eltrombopag are already established as second-line treatment for persistent or chronic immune thrombocytopenia (ITP). As in adults, TPO-RAs are currently also evaluated in severe aplastic anemia (SAA), chemotherapy-induced thrombocytopenia (CIT), myelodysplastic syndromes (MDS), and poor engraftment after hematopoietic stem cell transplantation in pediatric and adolescent patients. Moreover, studies on the implication of TPO-RA in treating rare inherited thrombocytopenias, such as Wiskott-Aldrich syndrome (WAS), congenital amegakaryocytic thrombocytopenia (CAMT), or MYH9-associated thrombocytopenia, deserve future attention. Current developments include testing of avatrombopag and lusutrombopag that are approved for the treatment of thrombocytopenia associated with chronic liver disease (CLD) in adult patients. In pediatric and adolescent medicine, we expect in the near future a broader use of TPO-RAs as first-line treatment in primary ITP, thereby considering immunomodulatory effects that increase the rate of sustained remission off-treatment, and a selective use in rare inherited thrombocytopenias based on current clinical trials.

Switching from eltrombopag to hetrombopag in patients with primary immune thrombocytopenia: a post-hoc analysis of a multicenter, randomized phase III trial

While studies have explored the feasibility of switching between various thrombopoietin receptor agonists in treating immune thrombocytopenia (ITP), data on the switching from eltrombopag to hetrombopag remains scarce. This post-hoc analysis of a phase III hetrombopag trial aimed to assess the outcomes of ITP patients who switched from eltrombopag to hetrombopag. In the original phase III trial, patients initially randomized to the placebo group were switched to eltrombopag. Those who completed this 14-week eltrombopag were eligible to switch to a 24-week hetrombopag. Treatment response, defined as a platelet count of ≥ 50 × 109/L, and safety were evaluated before and after the switch. Sixty-three patients who completed the 14-week eltrombopag and switched to hetrombopag were included in this post-hoc analysis. Response rates before and after the switch were 66.7% and 88.9%, respectively. Among those with pre-switching platelet counts below 30 × 109/L, eight out of 12 patients (66.7%) responded, while eight out of nine patients (88.9%) with pre-switching platelet counts between 30 × 109/L and 50 × 109/L responded post-switching. Treatment-related adverse events were observed in 50.8% of patients during eltrombopag treatment and 38.1% during hetrombopag treatment. No severe adverse events were noted during hetrombopag treatment. Switching from eltrombopag to hetrombopag in ITP management appears to be effective and well-tolerated. Notably, hetrombopag yielded high response rates, even among patients who had previously shown limited response to eltrombopag. However, these observations need to be confirmed in future trials.

Hetrombopag for the management of chemotherapy-induced thrombocytopenia in patients with advanced solid tumors: a multicenter, randomized, double-blind, placebo-controlled, phase II study

Background

Chemotherapy-induced thrombocytopenia (CIT) increases the risk of bleeding, necessitates chemotherapy dose reductions and delays, and negatively impacts prognosis.

Objectives

This study aimed to evaluate the efficacy and safety of hetrombopag for the management of CIT in patients with advanced solid tumors.

Design

A multicenter, randomized, double-blind, placebo-controlled, phase II study.

Methods

Patients with advanced solid tumors who experienced a chemotherapy delay of ⩾7 days due to thrombocytopenia (platelet count <75 × 109/L) were randomly assigned (1:1) to receive oral hetrombopag at an initial dose of 7.5 mg once daily or a matching placebo. The primary endpoint was the proportion of treatment responders, defined as patients resuming chemotherapy within 14 days (platelet count ⩾100 × 109/L) and not requiring a chemotherapy dose reduction of ⩾15% or a delay of ⩾4 days or rescue therapy for two consecutive cycles.

Results

Between 9 October 2021 and 5 May 2022, 60 patients were randomized, with 59 receiving ⩾1 dose of assigned treatment (hetrombopag/placebo arm, n = 28/31). The proportion of treatment responders was significantly higher in the hetrombopag arm than in the placebo arm [60.7% (17/28) versus 12.9% (4/31); difference of proportion: 47.6% (95% confidence interval (CI): 26.0-69.3); odds ratio = 10.44 (95% CI: 2.82-38.65); p value (nominal) based on the Cochran-Mantel-Haenszel: <0.001)]. During the double-blind treatment period, grade 3 or higher adverse events (AEs) occurred in 35.7% (10/28) of patients with hetrombopag and 38.7% (12/31) of patients on placebo. The most common grade 3 or higher AEs were decreased neutrophil count [35.7% (10/28) versus 35.5% (11/31)] and decreased white blood cell count [17.9% (5/28) versus 19.4% (6/31)]. Serious AEs were reported in 3.6% (1/28) of patients with hetrombopag and 9.7% (3/31) of patients with placebo.

Conclusion

Hetrombopag is an effective and well-tolerated alternative for managing CIT in patients with solid tumors.

Trial registration

ClinicalTrials.gov identifier: NCT03976882.

Synthetic Approaches to the New Drugs Approved During 2022

In 2022, 23 new small molecule chemical entities were approved as drugs by the United States FDA, European Union EMA, Japan PMDA, and China NMPA. This review describes the synthetic approach demonstrated on largest scale for each new drug based on patent or primary literature. The synthetic routes highlight practical methods to construct molecules, sometimes on the manufacturing scale, to access the new drugs. Ten additional drugs approved in 2021 and one approved in 2020 are included that were not covered in the previous year's review.

Thrombopoietin-receptor agonists for adult patients with immune thrombocytopenia: a narrative review and an approach for managing patients fasting intermittently

Introduction

Thrombopoietin-receptor agonist (TPO-RAs) currently represent the state of art for treating immune thrombocytopenia. Their different molecular structures contribute to the difference in their pharmacodynamics and pharmacokinetics. This narrative review aims to provide an overview of the current TPO-RAs approved for primary immune thrombocytopenia (romiplostim, eltrombopag, avatrombopag) and the effect of intermittent fasting in adult patients receiving TPO-RAs.

Areas covered

Literature was searched with no limits on date or language, using various combinations of keywords. Data on the pharmacokinetics, pharmacodynamics, efficacy, and safety of TPO-RAs and the effect of intermittent fasting were summarized.

Expert opinion

Switching between TPO-RAs is a useful strategy to tackle some associated limitations. Romiplostim and avatrombopag have an advantage over eltrombopag as they do not require any dietary restrictions. In cases where romiplostim and avatrombopag are unavailable, patients should be educated on the appropriate administration, possible interactions, and dietary restrictions before initiating eltrombopag.

Simultaneous analysis of avatrombopag, eltrombopag, and hetrombopag in human plasma by UPLC-MS/MS for therapeutic drug monitoring

Avatrombopag, eltrombopag, and hetrombopag are three oral thrombopoietin receptor agonists used to treat thrombocytopenia. To investigate the pharmacokinetic properties, a fast and robust UPLC-MS/MS method was developed and validated for simultaneous determination of avatrombopag, eltrombopag, and hetrombopag in human plasma. Chromatographically separation was achieved on an Acquity BEH C18 column using a gradient elution of methanol-water (20:80, v/v) and acetonitrile containing 0.1% formic acid at a flow rate of 0.4 mL/min within 4.5 min. The linearity was assessed over the range of 7.5-1500 ng/mL for avatrombopag, 50-10,000 ng/mL for eltrombopag, and 5-1000 ng/mL for hetrombopag. This method was validated with adequate results in terms of selectivity, precision (intra- and inter-day CV from 4.2% to 12.2%), accuracy (RE from -6.6% to 7.5%), dilution integrity, carryover, recovery, matrix effects, as well as stability of the analytes under various conditions. The developed approach has been successfully applied to the therapeutic drug monitoring of avatrombopag, eltrombopag, and hetrombopag in patients with immune thrombocytopenia.

Hetrombopag plus recombinant human thrombopoietin for chemotherapy-induced thrombocytopenia in patients with solid tumors

BACKGROUND

Chemotherapy-induced thrombocytopenia (CIT) is a common hematological complication in patients with cancer. Hetrombopag is a novel thrombopoietin receptor agonist that has shown an additive effect in stimulating platelet production when combined with recombinant human thrombopoietin (rhTPO).

OBJECTIVES

This multicenter retrospective cohort study aimed to evaluate the efficacy and safety of hetrombopag plus rhTPO compared with rhTPO alone for CIT.

METHODS

A total of 294 patients with solid tumors and CIT (platelet count, <50 × 109/L) who received either rhTPO plus hetrombopag (146 patients) or rhTPO alone (148 patients) at 3 centers from January to December 2022 were included in the study. The primary outcome was a platelet count at least 50 × 109/L higher than the baseline value within 14 days. Chemotherapy dose reductions/delays, bleeding, and adverse events were reported.

RESULTS

One hundred twenty patients (82.2%) in the rhTPO-hetrombopag group vs 100 patients (67.6%) in the rhTPO group achieved the primary outcome (P = .005). This significant difference persisted in adjusted analysis (odds ratio, 2.01; 95% CI, 1.12-3.60). A total of 115 patients (78.8%) in the rhTPO-hetrombopag group and 101 patients (68.2%) in the rhTPO group avoided chemotherapy dose reductions/delays (P = .041). There was no significant difference in bleeding rates, and adverse events were mild and similar between the 2 groups. No deaths occurred.

CONCLUSION

Compared to rhTPO alone, our findings suggest that the combination of hetrombopag and rhTPO is safe and more effective in patients with CIT.

A phase I, single-sequence, open-label study to evaluate the drug-drug interaction between hetrombopag and cyclosporine in healthy Chinese subjects

AIMS

This study aims to evaluate the drug-drug interaction (DDI) between hetrombopag and cyclosporine in healthy Chinese subjects.

METHODS

Twenty-six eligible subjects enrolled in this single-centre, single-sequence, open-label, DDI study with 3 treatment periods, receiving 5 mg hetrombopag once on Day 1, 100 mg cyclosporine twice daily from Day 11 to Day 15 and 5 mg hetrombopag + 100 mg cyclosporine on Day 16. Serial blood samples were collected for pharmacokinetic evaluation. Adverse events were monitored throughout the study.

RESULTS

The plasma hetrombopag geometric mean ratios (90% confidence interval) of maximum plasma concentration, area under the plasma concentration-time curve (AUC) from predose to time of last quantifiable sample and AUC to infinity of coadministration of hetrombopag with cyclosporine vs. hetrombopag alone were 95.97% (70.08-131.43%), 105.75% (75.04-149.04%) and 104.19% (74.71-145.32%), respectively, indicating multiple doses of cyclosporine had minimal effects on hetrombopag exposure. The geometric mean ratios (90% confidence interval) of maximum blood concentration and AUC at steady state during a dosing interval for blood cyclosporine of coadministration vs. cyclosporine alone were 100.49% (91.89-109.89%) and 100.81% (107.88-103.82%), respectively, suggesting a single dose of hetrombopag had no impact on the exposure of cyclosporine. Coadministration of hetrombopag with cyclosporine was generally well tolerated.

CONCLUSION

No clinically significant DDI was observed when coadministration of hetrombopag with cyclosporine. The results of this study will inform the appropriate use of this combination therapy both in clinical trials and clinical settings.

Novel Therapies to Address Unmet Needs in ITP

Primary immune thrombocytopenia (ITP) is an autoimmune disorder that causes low platelet counts and subsequent bleeding risk. Although current corticosteroid-based ITP therapies are able to improve platelet counts, up to 70% of subjects with an ITP diagnosis do not achieve a sustained clinical response in the absence of treatment, thus requiring a second-line therapy option as well as additional care to prevent bleeding. Less than 40% of patients treated with thrombopoietin analogs, 60% of those treated with splenectomy, and 20% or fewer of those treated with rituximab or fostamatinib reach sustained remission in the absence of treatment. Therefore, optimizing therapeutic options for ITP management is mandatory. The pathophysiology of ITP is complex and involves several mechanisms that are apparently unrelated. These include the clearance of autoantibody-coated platelets by splenic macrophages or by the complement system, hepatic desialylated platelet destruction, and the inhibition of platelet production from megakaryocytes. The number of pathways involved may challenge treatment, but, at the same time, offer the possibility of unveiling a variety of new targets as the knowledge of the involved mechanisms progresses. The aim of this work, after revising the limitations of the current treatments, is to perform a thorough review of the mechanisms of action, pharmacokinetics/pharmacodynamics, efficacy, safety, and development stage of the novel ITP therapies under investigation. Hopefully, several of the options included herein may allow us to personalize ITP management according to the needs of each patient in the near future.

A multicenter phase II study on the efficacy and safety of hetrombopag in patients with severe aplastic anemia refractory to immunosuppressive therapy

Background:

In this single-arm phase II study (NCT03557099), we evaluated the efficacy and safety of hetrombopag, a small molecule thrombopoietin (TPO) receptor agonist, in patients with severe aplastic anemia (SAA) who were refractory to standard first-line immunosuppressive therapy (IST).

Methods:

SAA patients who were refractory to standard first-line IST were given hetrombopag orally at an initial dose of 7.5 mg once daily to a maximum of 15 mg once daily, for a total of 52 weeks. The primary endpoint was proportion of patients achieving hematologic responses in ⩾1 lineage at week 18.

Results:

A total of 55 eligible patients were enrolled and received hetrombopag treatment. This study met its primary endpoint, with 23 [41.8%, 95% confidence interval (CI) = 28.7–55.9] patients achieving hematologic response in ⩾1 lineage at week 18 after initiation of hetrombopag treatment. Twenty-four (43.6%, 95% CI = 30.3–57.7) and 27 (49.1%, 95% CI = 35.4–62.9) of the 55 patients responded in ⩾1 lineage at weeks 24 and 52, respectively. Median time to initial hematologic response was 7.9 weeks (range = 2.0–32.1). The responses were durable, with a 12-month relapse-free survival rate of 82.2% (95% CI = 62.2–92.2). Adverse events occurred in 54 (98.2%) patients, and 28 (50.9%) patients had treatment-related adverse events. Seventeen (30.9%) patients had adverse events of grade ⩾3. Serious adverse events occurred in 15 (27.3%) patients and three deaths (5.5%) were reported.

Conclusion:

Hetrombopag showed encouraging efficacy with durable hematologic responses in patients with SAA who were refractory to IST. Hetrombopag was well tolerant and safe for long-term use.

ClinicalTrials.gov identifier:

NCT03557099

The structure, function, and clinical use of the thrombopoietin receptor agonist avatrombopag

Thrombopoietin regulates platelet production through activation of the thrombopoietin receptor (TPO-R). TPO-R agonists (TPO-RAs) are available to treat thrombocytopenia in chronic immune thrombocytopenia (ITP), chronic liver disease (CLD) patients who are undergoing a procedure, severe aplastic anemia (SAA), and hepatitis C virus (HCV) infection. There are four TPO-RAs approved in the US and Europe: romiplostim (ITP), eltrombopag (ITP, SAA, HCV), avatrombopag (ITP, CLD), and lusutrombopag (CLD). It is important to understand pharmacological characteristics of these agents when evaluating treatment options. Avatrombopag interacts with the transmembrane domain of the TPO-RA and does not compete with endogenous thrombopoietin for TPO-R binding. Structural differences between avatrombopag and other TPO-RAs may impart differential downstream effects on cell signaling pathways, potentially resulting in clinically relevant differences in outcome. Avatrombopag has a favorable pharmacological profile with similar exposure in Japanese, Chinese, or Caucasian patients and no drug-drug interactions, food interactions, or potential for chelation.

Impact of target-mediated drug disposition on hetrombopag pharmacokinetics and pharmacodynamics in Chinese healthy subjects and patients with chronic idiopathic thrombocytopenic purpura

AIMS

The pharmacokinetics (PK) of hetrombopag were found to be nonlinear across evaluated dose ranges. The aim of this study was to develop a mechanism-based population pharmacokinetic/pharmacodynamic (PopPK/PD) model and to provide a reasonable expected therapeutic dose for a future confirmatory clinical study of hetrombopag.

METHODS

Nonlinear mixed-effects modelling was performed using pooled 2168 hetrombopag concentrations and 1526 platelet counts from 72 healthy subjects and 32 chronic idiopathic thrombocytopenic purpura (ITP) patients from two phase I studies and one phase II study. The final model was evaluated via goodness-of-fit plots, visual predictive check and nonparametric bootstrap. Simulations from the validated PopPK/PD model were used to devise an expected therapeutic dose for later confirmatory clinical study.

RESULTS

The pharmacokinetic data of hetrombopag were well described by a modified target-mediated drug disposition (TMDD) model with dual sequential first-order absorption. Mean parameter estimates (interindividual variability) were CL/F 7.66 L/h (63.5%), V_c /F 30.0 L (77.2%) and K_deg 0.693/h (87.1%). The pharmacodynamic profile was well described by a five-compartment lifespan model with four-transit and one-platelet compartments. Simulation results suggested that chronic ITP patients following 10 mg once-daily hetrombopag would able to achieve an ideal platelet count level (50-200 × 10⁹ /L).

CONCLUSION

TMDD was the primary reason leading to nonlinear PK profile of hetrombopag. Our PK/PD modelling and simulation results support 10 mg once-daily as the recommended therapeutic dose for chronic ITP patients in subsequent confirmatory clinical study of hetrombopag.

Novel therapies for immune thrombocytopenia

Current therapies for immune thrombocytopenia (ITP) are successful in providing a haemostatic platelet count in over two-thirds of patients. Still, some patients have an inadequate response and there is a need for other therapies. A number of novel therapies for ITP are currently being developed based upon the current pathophysiology of ITP. Many therapies are targetted at reducing platelet destruction by decreasing anti-platelet antibody production by immunosuppression with monoclonal antibodies targetted against CD40, CD38 and the immunoproteasome or physically reducing the anti-platelet antibody concentration by inhibition of the neonatal Fc receptor. Others target the phagocytic system by inhibiting FcγR function with staphylococcal protein A, hypersialylated IgG, polymeric Fc fragments, or Bruton kinase. With a recognition that platelet destruction is also mediated by complement, inhibitors of C1s are also being tested. Inhibition of platelet desialylation may also play a role. Other novel therapies promote platelet production with new oral thrombopoietin receptor agonists or the use of low-level laser light to improve mitochondrial activity and prevent megakaryocyte apoptosis. This review will focus on these novel mechanisms for treating ITP and assess the status of treatments currently under development. Successful new treatments for ITP might also provide a pathway to treat other autoimmune disorders.

Hetrombopag: First Approval

Hetrombopag (Hengqu^®), an oral nonpeptide thrombopoietin receptor agonist, is being developed by Jiangsu Hengrui Pharmaceutical for the treatment of thrombocytopenia and aplastic anaemia. On 16 June 2021, hetrombopag received its first approval in China as a second-line treatment for primary immune thrombocytopenia (ITP) and severe aplastic anaemia (SAA) in adults. The drug is also undergoing phase III development in China for the treatment of chemotherapy-induced thrombocytopenia. This article summarizes the milestones in the development of hetrombopag leading to this first approval for ITP and SAA.

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.

Thrombopoietin-receptor agonists in perioperative treatment of patients with chronic liver disease

Thrombocytopenia is a multifactorial disorder that is common in patients with chronic liver disease (CLD), leading to challenging perioperative planning. As thrombocytopenia in CLD is associated with thrombopoietin (TPO) deficiency, the use of TPO-receptor agonists (TPO-RAs) to increase platelet counts is a promising approach. This has led to the development of various TPO-RAs, including romiplostim, eltrombopag, avatrombopag, and lusutrombopag. Of these, only avatrombopag and lusutrombopag are approved by the United States Food and Drug Administration for the perioperative treatment of thrombocytopenia in patients with CLD. Platelet transfusion is commonly used for the clinical management of thrombocytopenia in patients with CLD undergoing invasive procedures. However, the limitations and possible risks of transfusion, including short duration of efficacy, development of antiplatelet antibodies, risk of infections and such complications as transfusion-related acute lung injury or circulatory overload, and possibility of refractoriness, limit its use. Moreover, there is no consensus among guidelines as to the platelet count at which transfusions are indicated. Results from studies using TPO-RAs perioperatively in patients with thrombocytopenia and CLD are promising and provide an alternative to platelet transfusions in the pre- and post-operative setting. These TPO-RAs are the subject of this review, with focus on their use in the perioperative setting in patients with thrombocytopenia, associated supporting clinical trials, efficacy and safety data, and their use with respect to platelet transfusions.

Effect of postdose fasting duration on hetrombopag olamine pharmacokinetics and pharmacodynamics in healthy volunteers

AIMS

Hetrombopag olamine is a novel small-molecule, nonpeptide thrombopoietin receptor agonist developed for immune thrombocytopenia treatment. This study aims to determine the safety and the effect of fasting duration after administration of hetrombopag on pharmacokinetics and pharmacodynamics in Chinese healthy subjects.

METHODS

A randomized, open-label, single-dose, 3-period crossover, self-control trial was conducted. 15 eligible subjects were enrolled and received hetrombopag 7.5 mg at day 1 of each period followed by a standard meal 4 hours postdose (treatment A/fasting condition), or a high-calorie, high-fat meal 1 hour postdose (treatment B), or a high-calorie, high-fat meal 2 hours postdose (treatment C). The plasma concentrations of hetrombopag were determined by validated liquid chromatography-tandem mass spectrometry, platelet counts were quantified by blood test. Analysis was performed using a mixed model, including treatment, period as fixed effects and participant as a random effect.

RESULTS

Compared with treatment A, peak concentration and area under concentration-time curve extrapolated to infinity decreased by 56 and 74.6%, and 44 and 61% in treatments B and C, respectively. The mean platelet number on day 6 increased by 15.8, 6.96 and 10.26%, respectively, in treatments A, B and C in comparison with baseline platelet level. No severe adverse events happened in any of the 3 treatments.

CONCLUSION

Hetrombopag was well tolerated in healthy male subjects under fasted/fed conditions. The shorter fasting duration resulted in lower hetrombopag exposure, corresponding to a lower level of platelet elevation. Therefore, we recommended oral administration of hetrombopag on an empty stomach (fasting condition) or at least 2 hours before a meal to achieve maximum bioavailability.

Avatrombopag for the treatment of immune thrombocytopenia

INTRODUCTION

Thrombopoietin-receptor agonists (TPO-RAs) are the only American Society of Hematology (ASH) guideline-advocated, second-line treatment for immune thrombocytopenia (ITP) that have been validated by randomized, controlled trials with a placebo comparator. Avatrombopag is a new candidate in this class that has been investigated as a treatment option for the treatment of ITP. Areas covered: In this Drug Profile, we provide a review of the clinical data of avatrombopag, which was approved in May 2018 by the United States Food and Drug Administration (FDA) for the treatment of thrombocytopenia in patients with chronic liver disease undergoing an invasive procedure, and an opinion of its potential place in the current evidence-based ITP treatment landscape. Expert commentary: Avatrombopag induces doubling of platelet counts, increasing them to above 50 X 10⁹/L, and prevents the need for platelet transfusions while minimizing the need for rescue medications. Treatment-emergent adverse events (TEAEs) are comparable to placebo. Oral delivery, a 5-day dosing schedule and good tolerability (<1% discontinuation rate) with no clinically significant hepatoxicity make it a promising entrant as a potential second-line treatment for ITP. Further, data from a phase 3 study in patients with ITP supports its utility in the treatment of patients with ITP.

Pharmacological characterization of hetrombopag, a novel orally active human thrombopoietin receptor agonist

Nonpeptide thrombopoietin receptor (TPOR/MPL) agonists, such as eltrombopag, have been used to treat thrombocytopenia of various aetiologies. Here, we investigated the pharmacological properties of hetrombopag, a new orally active small‐molecule TPOR agonist, in preclinical models. Hetrombopag specifically stimulated proliferation and/or differentiation of human TPOR‐expressing cells, including 32D‐MPL and human hematopoietic stem cells, with low nanomolar EC₅₀ values through stimulation of STAT, PI3K and ERK signalling pathways. Notably, hetrombopag effectively up‐regulated G₁‐phase–related proteins, including p‐RB, Cyclin D1 and CDK4/6, normalized progression of the cell cycle, and prevented apoptosis by modulating BCL‐XL/BAK expression in 32D‐MPL cells. Moreover, hetrombopag and TPO acted additively in stimulating TPOR‐dependent signalling, promoting cell viability, and preventing apoptosis. Orally administered hetrombopag specifically promoted the viability and growth of 32D‐MPL cells in hollow fibres implanted into nude mice with much higher potency than that of the well‐known TPOR agonist, eltrombopag, in association with activation of TPOR‐dependent signal transduction in vivo. Taken together, our findings indicate that, given its favourable pharmacological characteristics, hetrombopag may represent a new, orally active, small‐molecule TPOR agonist for patients with thrombocytopenia.