Avatrombopag for the treatment of immune thrombocytopenia and thrombocytopenia of chronic liver disease

Use of romiplostim for antineoplastic therapy-induced thrombocytopenia in gynecologic and breast cancers

Objective

Romiplostim is used to treat chemotherapy-induced thrombocytopenia in a variety of tumor types; however, few studies have examined its use in breast and gynecologic cancers. We evaluated platelet response and durability of response to romiplostim in patients with gynecologic or breast cancer complicated by chemotherapy-induced thrombocytopenia.

Methods

We retrospectively identified 33 patients with gynecologic or breast cancer who received romiplostim between 07/1/2021-07/31/2022 at an academic cancer center.

Results

Thirty-three patients met inclusion criteria; 26 (79 %) had breast cancer, 4 (12 %) had ovarian cancer, and 3 (9 %) had endometrial cancer. Twenty patients (61 %) experienced treatment delays and 12 (36 %) required dose reductions prior to starting romiplostim for chemotherapy-induced thrombocytopenia, with some patients experiencing both. Eleven patients (33 %) did not undergo a dose reduction or delay prior to initiation of romiplostim. Median platelet count prior to romiplostim therapy was 53 k/mcL (range, 40.5-78.8). Median platelet count within 3 weeks following initiation of romiplostim was 147 k/mcL (range, 31-562). Twenty-one patients (64 %) achieved platelet correction within 3 weeks, of whom 10 (48 %) resumed anticancer therapy and maintained platelet levels above 100 k/mcL at 8 weeks. Twelve patients did not achieve platelet correction within 3 weeks of romiplostim initiation; 4 (33 %) required a treatment change secondary to persistent thrombocytopenia, 3 (25 %) required a treatment dose reduction, 3 (25 %) were deemed too ill to continue therapy, and 2 (17 %) required a treatment delay.

Conclusions

Romiplostim facilitated the resumption of anticancer therapy in 64 % of patients with gynecologic or breast cancer complicated by chemotherapy-induced thrombocytopenia.

Herombopag for the treatment of persistent thrombocytopenia following hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) stands as a pivotal treatment for hematologic malignancies, often considered the sole effective treatment option. A frequent complication following allo-HSCT is poor graft function (PGF), with one of its primary manifestations being persistent thrombocytopenia (PT), comprising prolonged isolated thrombocytopenia (PIT) and secondary failure of platelet recovery (SFPR). Conventional treatment methods have had poor efficacy and a high transplantation-associated mortality rate. In recent years, the efficacy of eltrombopag has been reported in the treatment of post-transplantation PT, and additional thrombopoietin receptor agonists (TPO-RA) have been developed. Herombopag is a next-generation TPO-RA which has strong proliferation-promoting effects on human TPO-R-expressing cells (32D-MPL) and hematopoietic progenitor cells in vitro. We reviewed eighteen patients with transplantation-associated thrombocytopenia who received herombopag when eltrombopag was ineffective or poorly tolerated and evaluated its efficacy including effects on survival. Herombopag was administered at a median time of 197 days post-transplantation. Six patients achieved complete response (CR), with a median time to CR of 56 days. Five patients achieved partial response (PR), and the median time to PR was 43 days. Seven patients were considered to have no response (NR). The overall response (OR) rate was 61.1%, and the cumulative incidence (CI) of OR was 90.2%. No patients developed herombopag-associated grade 3-4 toxicity. The median follow-up period was 6.5 months. Twelve patients survived and six patients died, with an overall survival rate of 66.7%. This is the first study to demonstrate the efficacy and safety of herombopag in transplantation-associated thrombocytopenia after failing eltrombopag, introducing a new approach in the treatment of PT following allo-HSCT.

Avatrombopag for adults with early versus chronic immune thrombocytopenia

Avatrombopag is a newer thrombopoietin receptor agonist (TPO-RA) currently approved to treat chronic ITP (duration >12 months). No studies have yet evaluated the safety and effectiveness of avatrombopag in newly diagnosed ITP (duration <3 months) or persistent ITP (duration 3-12 months), and so its use in these populations is presently off-label worldwide. We hypothesize that avatrombopag has similar safety and effectiveness irrespective of ITP disease phase. To evaluate this, we performed a multicenter observational cohort study of adults with ITP treated with avatrombopag, comparing patient outcomes by disease phase (newly diagnosed/persistent versus chronic). Seventy-five patients were included, 23 with newly diagnosed/persistent ITP (17.7 patient-years of avatrombopag treatment) and 52 with chronic ITP (65.3 patient-years of avatrombopag treatment). On avatrombopag, 91% of newly diagnosed/persistent patients versus 96% of chronic patients (p = .58) achieved a platelet response (≥50 × 109 /L) and 86% versus 81% of patients (p = .78) achieved a complete response (≥100 × 109 /L). Median platelet counts on avatrombopag were similar between the two groups (165 × 109 /L vs. 129 × 109 /L, p = .57). Response durability was high and similar in both groups. No patients in the newly diagnosed/persistent group had a major bleeding event, thromboembolic event or avatrombopag discontinuation for adverse events, compared with 4, 1, and 2, respectively, in the chronic group. Thrombocytosis (platelets ≥400 × 109 /L) incidence was similar in the two groups. No other drug-related adverse events occurred in either group. Avatrombopag was safe and effective in patients with newly diagnosed and persistent ITP, with outcomes numerically, statistically, and clinically similar to patients receiving avatrombopag for chronic ITP.

Avatrombopag for the Treatment of Immune Thrombocytopenia and Periprocedural Thrombocytopenia Associated With Chronic Liver Disease

Objective: To review the pharmacology, pharmacokinetics, clinical efficacy, safety, dosing and administration, and place in therapy of avatrombopag for the treatment of immune thrombocytopenia and chronic liver disease-associated thrombocytopenia. Summary: Avatrombopag is an orally administered thrombopoietin receptor agonist approved for the treatment of immune thrombocytopenia and is the first oral thrombopoietin receptor agonist approved for the treatment of perioperative thrombocytopenia associated with chronic liver disease in adults. The efficacy and safety of avatrombopag has been demonstrated in a multicenter, randomized, double blind, placebo-controlled phase III study in the setting of immune thrombocytopenia and in 2 identically designed, multicenter, randomized, double blind, placebo-controlled phase III trials in the setting of thrombocytopenia associated with chronic liver disease. The most common adverse events reported in the clinical trials were headache, fatigue, and gastrointestinal toxicities. The incidence of bleeding events was comparable between the avatrombopag and placebo treatment groups in each study. Avatrombopag has not been shown to be associated with hepatoxicity and does not require food restriction like the other oral thrombopoietin receptor agonist for immune thrombocytopenia, eltrombopag. Also, unlike eltrombopag for immune thrombocytopenia, it can be dosed less frequently than once daily. Conclusion: Avatrombopag offers another safe and effective oral option for the treatment of immune thrombocytopenia without food restrictions and an alternative, transfusion-sparing option for thrombocytopenia associated with chronic liver disease patients undergoing surgery.

Optimal management of chemotherapy-induced thrombocytopenia with thrombopoietin receptor agonists

Chemotherapy-induced thrombocytopenia (CIT) is a common complication of antineoplastic therapy, resulting in antineoplastic therapy dose reductions, treatment delays, treatment discontinuation, and morbid bleeding events. Despite several decades of research into thrombopoietic growth factors in CIT, there are presently no available U.S. FDA- or EMA-approved agents to treat CIT. However, a respectable body of evidence has been published evaluating the thrombopoietin receptor agonists (TPO-RAs) for the management and prevention of CIT in patients with solid tumors, and critical studies are ongoing with the TPO-RAs romiplostim and avatrombopag. When employed in the appropriate patient population and used properly, TPO-RAs can successfully and safely manage CIT for extended periods of time with minimal apparent risks. This comprehensive review discusses the evidence for TPO-RAs in CIT in patients with solid tumors, provides detailed guidance for their use in the clinic, and discusses ongoing essential clinical trials in management of CIT.

Avatrombopag, a promising novel thrombopoietin receptor agonist for refractory/relapsed/intolerant non-severe aplastic anemia: a phase 2 single-arm clinical trial

INTRODUCTION

The therapeutic options for thrombocytopenia in non-severe aplastic anaemia (NSAA) are limited. Avatrombopag (AVA) is prescribed for thrombocytopenic diseases but not for NSAA.

METHODS

Herein, we conducted a phase 2, non-randomized, single-arm trial to explore the efficacy and safety of AVA in refractory/relapsed/intolerant NSAA. AVA dose was initiated at 20 mg/d and titrated to a maximum of 60 mg/d. The primary endpoint was the haematological response at 3 months.

RESULTS

Twenty-five patients were analyzed. The overall response rate (ORR) at 3 months was 56% (14/25), with 12% (3/25) achieving a complete response (CR). At a median follow-up of 7 (3-10) months, the OR and CR rates were 52% and 20%, respectively. Responders had a shorter duration of diagnosis of AVA administration than non-responders (10 (6-80) vs 37 (6-480) months, p = 0.027) and belonged to the relapsed/intolerant NSAA type (71% vs 27%, p = 0.047); 44% (8/18) patients previously treated with eltrombopag before enrollment responded at 3 months, with an average prior eltrombopag dose of median 72.5 (50-100) mg/d and an average AVA dose for a response of median 43.5 (20-60) mg/d. 3-month ORR had no significant correlation with eltrombopag exposure (p = 0.09), prior eltrombopag length (R²=0.11), or cumulative eltrombopag dose (R²=0.30). Only one patient relapsed after stopping AVA for 1 month. No serious AVA-related side effects or clone evolution were detected.

CONCLUSION

AVA is effective and well-tolerated in NSAA patients who are refractory, relapsed, or intolerant to CsA/tacrolimus ± eltrombopag. Earlier treatment and relapsed/intolerant AA may show a better short-term response rate. More studies are needed to define the optimal dose and the long-term efficacy (NCT04728789).

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.

Avatrombopag increased platelet count in a patient with chronic immune thrombocytopenia refractory to multiple lines of treatment

We present a case of a 30-year-old man suffering from chronic refractory immune thrombocytopenia (ITP) from early childhood. The patient was treated with all the therapeutic methods available in Poland, without platelet response: corticosteroids, intravenous immunoglobulins, splenectomy, cyclophosphamide, vinblastine, azathioprine, mycophenolate mofetil, rituximab, ciclosporin A, romiplostim, and eltrombopag. He continued to function persistently with deep thrombocytopenia, symptoms of hemorrhagic diathesis, and one episode of spontaneous subarachnoid bleeding. In April 2022, at the age of 29, the patient received avatrombopag. Within 4 weeks of starting avatrombopag 20 mg daily for 2 weeks and then 40 mg daily, he reached a platelet (PLT) count of 67 x 10 9 /l. In the next month, platelets fell below 30 x 10 9 /l, but subsequently the count increased to 47 x 10 9 /l, then to 52 x 10 9 /l, and remained stable. The symptoms of cutaneous hemorrhage diathesis have resolved completely since avatrombopag was introduced and did not reappear despite the decrease in PLT count.

Thrombopoietin receptor agonist antibody for treating chemotherapy-induced thrombocytopenia

BACKGROUND

Thrombocytopenia is a common complication in cancer patients undergoing chemotherapy. Chemotherapy-induced thrombocytopenia (CIT) leads to dose reduction and treatment delays, lowering chemotherapy efficacy and survival rate. Thus, rapid recovery and continuous maintenance of platelet count during chemotherapy cycles are crucial in patients with CIT. Thrombopoietin (TPO) and its receptor, myeloid proliferative leukemia (MPL) protein, play a major role in platelet production. Although several MPL agonists have been developed to regulate thrombopoiesis, none have been approved for the management of CIT due to concerns regarding efficacy or safety. Therefore, the development of effective MPL agonists for treating CIT needs to be further expanded.

METHODS

Anti-MPL antibodies were selected from the human combinatorial antibody phage libraries using phage display. We identified 2R13 as the most active clone among the binding antibodies via cell proliferation assay using BaF3/MPL cells. The effect of 2R13 on megakaryocyte differentiation was evaluated in peripheral blood CD34⁺ cells by analyzing megakaryocyte-specific differentiation markers (CD41a⁺ and CD42b⁺) and DNA ploidy using flow cytometry. The 2R13-induced platelet production was examined in 8- to 10-week-old wild-type BALB/c female mice and a thrombocytopenia mouse model established by intraperitoneal injection of 5-fluorouracil (150 mg/kg). The platelet counts were monitored twice a week over 14 days post-initiation of treatment with a single injection of 2R13, or recombinant human TPO (rhTPO) for seven consecutive days.

RESULTS

We found that 2R13 specifically interacted with MPL and activated its signaling pathways. 2R13 stimulated megakaryocyte differentiation, evidenced by increasing the proportion of high-ploidy (≥ 8N) megakaryocytes in peripheral blood-CD34⁺ cells. The platelet count was increased by a single injection of 2R13 for up to 14 days. Injection of 5-fluorouracil considerably reduced the platelet count by day 4, which was recovered by 2R13. The platelets produced by 2R13 sustained a higher count than that achieved using seven consecutive injections of rhTPO.

CONCLUSIONS

Our findings suggest that 2R13 is a promising therapeutic agent for CIT treatment.

Emerging data on thrombopoietin receptor agonists for management of chemotherapy-induced thrombocytopenia

INTRODUCTION

Chemotherapy-induced thrombocytopenia (CIT) is a common complication of cancer treatment, frequently leading to reduced relative dose intensity, and is associated with reduced survival. Given the lack of FDA-approved therapies for CIT, thrombopoietin receptor agonists (TPO-RAs) have received significant attention for treatment and prevention of CIT.

AREAS COVERED

This review will summarize the development of prior agents for treatment of CIT, discuss the existing literature investigating the use of TPO-RAs in CIT primarily in patients with solid tumor malignancies, and offer insights on the future direction of TPO-RAs and other therapeutics for CIT.

EXPERT OPINION

In alignment with NCCN guidelines, we recommend that patients with CIT participate in a clinical trial for consideration of TPO-RA treatment or consider off-label use of romiplostim when participation in clinical trials is not possible. The literature to date supports the use of TPO-RAs for treatment of persistent CIT. Further data is needed to describe the long-term efficacy, safety, and prescribing practices of TPO-RAs in a diverse patient population with a variety of tumor types and chemotherapy regimens in addition to exploring the underlying biology of CIT.

Small Molecule Drugs That Inhibit Phagocytosis

In our initial publication on the in vitro testing of more than 200 compounds, we demonstrated that small molecules can inhibit phagocytosis. We therefore theorized that a small molecule drug discovery-based approach to the treatment of immune cytopenias (ITP, AIHA, HTR, DHTR) is feasible. Those earlier studies showed that small molecules with anti-phagocytic groups, such as the pyrazole core, are good models for producing efficacious phagocytosis inhibitors with low toxicity. We recently screened a chemical library of 80 compounds containing pyrazole/isoxazole/pyrrole core structures and found four hit molecules for further follow-up, all having the pyrazole core structure. Subsequent evaluation via MTT viability, LDH release, and apoptosis, led to the selection of two lead compounds with negligible toxicity and high efficacy. In an in vitro assay for inhibition of phagocytosis, their IC₅₀ values were 2-4 µM. The rational development of these discoveries from hit to lead molecule stage, viz. independent synthesis/scale up of hit molecules, and in vivo activities in mouse models of autoimmune disease, will result in the selection of a lead compound(s) for further pre-clinical evaluation.

Avatrombopag for the treatment of thrombocytopenia induced by chemotherapy in patients with solid tumors: A multicenter, open-label, single-arm trial

Objective: To explore the effect and safety of avatrombopag for chemotherapy-induced thrombocytopenia (CIT).

Methods: This multicenter, open-label, single-arm trial enrolled CIT patients in eight centers from October 2020 to April 2021. The participants received avatrombopag tablets 60 mg once a day for 5–10 days. The main endpoint was the proportion of patients with platelet count ≥100×10⁹/L or increased by ≥ 50×10⁹/L or increased by ≥ 100% in the cycle after the start of treatment.

Results: Seventy-four participants were enrolled with a mean age of 59.8 ± 11.62.2% were males. The cumulative effective rate (any criteria) was 70.3% at 4 weeks. 42 (56.8%) achieved platelet count ≥100×10⁹/L, 44 (59.5%) increased by ≥ 50×10⁹/L, and 27 (36.5%) increase by ≥ 100% from baseline. The duration of grade III and IV platelet reduction was 4.2 ± 5.3 days. The time of PLT recovery to ≥75×10⁹/L was 9.4 ± 6.6 days. The time of PLT recovery to ≥100×10⁹/L was 10.2 ± 6.4 days. The platelet count nadir was 57.9 ± 45.3×10⁹/L. The most common adverse events were nausea (8.1%), fatigue (5.4%), and abdominal pain (1.4%). There were no cases of fever, headache, or peripheral edema.

Conclusion: Although it was a single-arm trial without a control group, the application of avatrombopag in patients with CIT can increase the platelet count of the patients compared with baseline. Avatrombopag is safe and tolerable.

Clinical Trial Registration:https://clinicaltrials.gov/ct2/show/NCT04609891?term=04609891&draw=2&rank=1, identifier [NCT04609891]

An updated evaluation of avatrombopag for the treatment of chronic immune thrombocytopenia

INTRODUCTION

Multiple agents are available for the management of chronic immune thrombocytopenia (ITP), including thrombopoietin-receptor agonists (TPO-RAs), rituximab, and fostamatinib. Although TPO-RAs are often selected as treatments for chronic ITP, when choosing between the TPO-RAs, clinicians must balance safety profile, dosing restrictions, and method of administration incorporating patient preference.

AREAS COVERED

We provide an overview of the thrombopoietin receptor agonists with a particular focus on avatrombopag, the newest agent in this class. In phase II and III clinical trials, avatrombopag was shown to offer durable improvement in platelet counts. We also include recent real-world evidence describing avatrombopag effectiveness in patients with poor response to prior treatments (including other TPO-RAs).

EXPERT OPINION

Compared with other TPO-RAs used to treat ITP, avatrombopag offers practical oral dosing with a single pill strength, does not require long-term dietary restrictions, and has no warning for hepatotoxicity. It is frequently effective after use of other TPO-RAs in ITP. The primary downside with avatrombopag use at present is the lack of longer-term safety data in ITP that presently exists for romiplostim and eltrombopag.

Romiplostim for chemotherapy‐induced thrombocytopenia: Efficacy and safety of extended use

Background

Chemotherapy‐induced thrombocytopenia (CIT) is common during treatment with antineoplastic therapies and may adversely impact chemotherapy dose intensity. There is no approved therapy for CIT. In our recent phase II randomized study, romiplostim led to correction of platelet counts in 85% of treated patients and allowed resumption of chemotherapy, with low rates of recurrent CIT in the first two cycles or 8 weeks of chemotherapy. However, there is a lack of long‐term data on the efficacy and safety of romiplostim in CIT.

Objectives

To analyze efficacy and safety of romiplostim in the patients in the phase 2 study, who received romiplostim for ≥1 year.

Patients/Methods

Twenty‐one patients remained on romiplostim for ≥1 year. We analyzed the effect of romiplostim on platelet counts, absolute neutrophil counts, and hemoglobin, as well as impact on ongoing chemotherapy. We also tracked venous or arterial thrombotic events.

Results

During the study period, romiplostim was effective in preventing reduction of chemotherapy dose intensity due to CIT. Fourteen of the 20 (70%) analyzable patients experienced no episode of CIT, 4 subjects experienced a single chemotherapy dose delay due CIT, and 2 patients required a chemotherapy dose reduction. Platelet counts were preserved throughout the duration of the extension analysis. One patient experienced a proximal deep vein thrombosis, and one patient experienced multiple tumor‐related ischemic events.

Conclusions

Long‐term use of romiplostim for treatment of CIT was effective and safe, with no evidence of resistance or increased risk of thrombosis.

Dualistic role of platelets in living donor liver transplantation: Are they harmful?

Platelets are anucleate fragments mainly involved in hemostasis and thrombosis, and there is emerging evidence that platelets have other nonhemostatic potentials in inflammation, angiogenesis, regeneration and ischemia/reperfusion injury (I/R injury), which are involved in the physiological and pathological processes during living donor liver transplantation (LDLT). LDLT is sometimes associated with impaired regeneration and severe I/R injury, leading to postoperative complications and decreased patient survival. Recent studies have suggested that perioperative thrombocytopenia is associated with poor graft regeneration and postoperative morbidity in the short and long term after LDLT. Although it is not fully understood whether thrombocytopenia is the cause or result, increasing platelet counts are frequently suggested to improve posttransplant outcomes in clinical studies. Based on rodent experiments, previous studies have identified that platelets stimulate liver regeneration after partial hepatectomy. However, the role of platelets in LDLT is controversial, as platelets are supposed to aggravate I/R injury in the liver. Recently, a rat model of partial liver transplantation (LT) was used to demonstrate that thrombopoietin-induced thrombocytosis prior to surgery accelerated graft regeneration and improved the survival rate after transplantation. It was clarified that platelet-derived liver regeneration outweighed the associated risk of I/R injury after partial LT. Clinical strategies to increase perioperative platelet counts, such as thrombopoietin, thrombopoietin receptor agonist and platelet transfusion, may improve graft regeneration and survival after LDLT.

Adults with immune thrombocytopenia who switched to avatrombopag following prior treatment with eltrombopag or romiplostim: A multicentre US study

Patients with immune thrombocytopenia (ITP) may respond to one thrombopoietin receptor agonist (TPO-RA) but not another. Limited data are available describing outcomes in patients who switched from romiplostim or eltrombopag to avatrombopag, a newer oral TPO-RA. We performed a retrospective observational study of adults with ITP who switched from eltrombopag or romiplostim to avatrombopag at four US tertiary ITP referral centres. Forty-four patients were included, with a mean ITP duration of 8.3 years and a median (range) of four prior ITP treatments. On avatrombopag, 41/44 patients (93%) achieved a platelet response (≥50 × 10⁹ /l) and 38/44 patients (86%) achieved a complete response (≥100 × 10⁹ /l). In all patients, the median platelet count on eltrombopag or romiplostim was 44 × 10⁹ /l vs 113 × 10⁹ /l on avatrombopag (p < 0.0001); in patients switched for ineffectiveness of romiplostim/eltrombopag, it was 28 × 10⁹ /l on romiplostim/eltrombopag vs 88 × 10⁹ /l on avatrombopag (p = 0.025). Fifty-seven percent of patients receiving concomitant ITP medications before switching discontinued them after switching, including 63% of patients receiving chronic corticosteroids. In a heavily pretreated chronic ITP population, avatrombopag was effective following therapy with romiplostim or eltrombopag, with high response rates even in patients with inadequate response to a prior TPO-RA.

The efficacy and safety of thrombopoietin receptor agonists in patients with chronic liver disease undergoing elective procedures: a systematic review and meta-analysis

Thrombopoietin receptor agonists (TPO-RAs) can mitigate preprocedural thrombocytopenia in patients with chronic liver disease (CLD) however their effects on procedural outcomes is unclear. In this meta-analysis, we aimed to better define the efficacy, thrombotic risk and bleeding mitigation associated with the use of preoperative TPO-RAs in patients with CLD. We performed a systematic review and meta-analysis of randomized placebo-controlled clinical trials to assess the use of preprocedural TPO-RAs in patients with CLD, searching MEDLINE, EMBASE and the Cochrane library database. Six publications comprising eight randomized trials (1229 patients; 717 received TPO-RAs, 512 received placebo) and three unique TPO-RAs were retrieved. The majority of the included procedures were endoscopic. TPO-RAs were significantly more likely to result in a preoperative platelet count greater than 50 x 109/L (72.1% vs 15.6%, RR 4.8, 95% CI 3.6-6.4 p < .00001. NNT 1.8) and reduced the incidence of platelet transfusions (22.5% vs 67.8%, RR 0.33, 95% CI 0.3-0.4 p < .00001. NNT 2.2). Total periprocedural bleeding was decreased in patients who received TPO-RAs (11.6% vs 15.6%, RR 0.64, 95% CI 0.5-0.9 p = .01. NNT 24.7) and there was no increase in the rate of thrombosis (2.2% vs 1.8% RR 1.25, 95% CI 0.6-2.9 p = .60. NNH 211.1). In patients with CLD the use of preprocedural TPO-RAs resulted in significant increased platelet counts, and decreased the incidence of platelet transfusions as compared to placebo. TPO use likewise decreased the incidence of total periprocedural bleeding without increasing the rate of thrombosis.

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.

Immune thrombocytopenia

INTRODUCTION

Primary immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count (<100 × 10⁹/L) with an increased risk of bleeding. Recent (2019) guidelines from the International Consensus Report (ICR) expert panel and the American Society of Hematology (ASH) provide updated recommendations for the diagnosis and management of ITP.

AREAS COVERED

The 2019 ICR and ASH guidelines are reviewed, and differences and similarities highlighted. Clinical approaches to the treatment of ITP are discussed, including the role of fostamatinib which is an approved treatment option in adult patients who are refractory to other treatments.

EXPERT OPINION

The 2019 ICR and ASH guidelines reflect recent changes in the management of ITP. Current treatment approaches for ITP are more rational and evidence-based than in the past. Patients should be treated based on their needs rather than on disease stage, and patient-specific outcomes, (e.g. quality of life) should be considered. Whilst corticosteroids are the mainstay of initial ITP treatment their use should be limited. For subsequent treatment, the use of thrombopoietin receptor agonist (TPO-RA) agents, fostamatinib and rituximab in adults is supported by robust evidence. Rituximab and recently approved fostamatinib offer viable alternatives to splenectomy.

Experts' review: the emerging roles of romiplostim in immune thrombocytopenia (ITP)

INTRODUCTION

The management of ITP has in recent years been transformed from reliance on immunosuppressants and splenectomy to targeted therapy with thrombopoietin receptor agonists (TPO-RA) that directly stimulate platelet production in the bone marrow. This has reduced the long-term infective complications and toxicities associated with the use of potent immunosuppressants and splenectomy. The welltolerated romiplostim, itself a novel drug construct called peptibody, has established itself, alongside other TPO-RA as the preferred 2nd line therapy in major international guidelines on treatment of ITP.

AREAS COVERED

This review summarizes the data from early licensing trials of romiplostim and discusses the real-world experience to date, the unexpected emerging data on treatment-free long-term remission achieved using TPO-RA, and the case for its early introduction in the therapeutic pathway. The emerging risk of thrombosis is also discussed.

EXPERT OPINION

The use of romiplostim and other TPO-RA will be increasingly brought forward in the management pathway of ITP with the prospect of modifying the long-term outcome of the disease by increasing sustained treatment-free remission. With the prospect of several new targeted therapies been introduced into clinical practice, TPO-RA will likely be a key component of future combination therapies for difficult cases.

Management of Adult Patients with Immune Thrombocytopenia (ITP): A Review on Current Guidance and Experience from Clinical Practice

Immune thrombocytopenia (ITP) is an autoimmune process resulting in increased destruction and inadequate production of platelets that can result in bleeding, fatigue, and reduced health-related quality of life. While treatment is not required for many patients with ITP, the occurrence of bleeding manifestations, severe thrombocytopenia, and requirement for invasive procedures are among the reasons necessitating initiation of therapy. Corticosteroids, intravenous immunoglobulin, and anti-RhD immune globulin are typical first-line and rescue treatments, but these agents typically do not result in a durable remission in adult patients. Most patients requiring treatment therefore require subsequent line therapies, such as thrombopoietin receptor agonists (TPO-RAs), rituximab, fostamatinib, splenectomy, or a number of other immunosuppressive agents. In this focused review, we discuss management of adult ITP in the acute and chronic settings.

Improving Outcomes of Chemotherapy: Established and Novel Options for Myeloprotection in the COVID-19 Era

Chemotherapy-induced damage of hematopoietic stem and progenitor cells (HPSCs) often results in myelosuppression that adversely affects patient health and quality of life. Currently, chemotherapy-induced myelosuppression is managed with chemotherapy dose delays/reductions and lineage-specific supportive care interventions, such as hematopoietic growth factors and blood transfusions. However, the COVID-19 pandemic has created additional challenges for the optimal management of myelosuppression. In this review, we discuss the impact of this side effect on patients treated with myelosuppressive chemotherapy, with a focus on the prevention of myelosuppression in the COVID-19 era. During the COVID-19 pandemic, short-term recommendations on the use of supportive care interventions have been issued with the aim of minimizing the risk of infection, reducing the need for hospitalization, and preserving limited blood supplies. Recently, trilaciclib, an intravenous cyclin-dependent kinase 4 and 6 inhibitor, was approved to decrease the incidence of myelosuppression in adult patients when administered prior to platinum/etoposide-containing or topotecan-containing chemotherapy for extensive-stage small cell lung cancer (ES-SCLC). Approval was based on data from three phase 2 placebo-controlled clinical studies in patients with ES-SCLC, showing that administering trilaciclib prior to chemotherapy significantly reduced multilineage myelosuppression, with patients receiving trilaciclib having fewer chemotherapy dose delays/reductions and myelosuppression/sepsis-related hospitalizations, and less need for supportive care interventions, compared with patients receiving placebo. Several other novel agents are currently in clinical development for the prevention or treatment of multilineage or single-lineage myelosuppression in patients with various tumor types. The availability of treatments that could enable patients to maintain standard-of-care chemotherapy regimens without the need for additional interventions would be valuable to physicians, patients, and health systems.

Thrombopoietin Receptor Agonists (TPO-RAs): Drug Class Considerations for Pharmacists

The thrombopoietin receptor agonists (TPO-RAs) romiplostim, eltrombopag, avatrombopag, and lusutrombopag carry unique US Food and Drug Administration (US FDA)- and European Medicines Agency (EMA)-approved indications and may be used to increase platelet counts in a variety of conditions. Current indications for available TPO-RAs include treatment of chronic immune thrombocytopenia (ITP) in cases of insufficient response to prior treatment (avatrombopag, eltrombopag, romiplostim), management of thrombocytopenia in adult patients with chronic liver disease who are scheduled to undergo a procedure (avatrombopag, lusutrombopag), management of severe aplastic anemia (eltrombopag), and management of thrombocytopenia associated with interferon-based therapy for hepatitis C (eltrombopag). Across current indications, pharmacists can assist in stabilizing platelet counts and help to reduce large undulations commonly seen when starting, stopping, or transitioning between these agents. If therapy modifications may benefit the patient, pharmacists should discuss possible changes with the patient's treatment team or treating physician. When used for ITP, romiplostim, eltrombopag, and avatrombopag stimulate TPO receptors on hematopoietic stem cells (also known as c-Mpl, or CD110) to promote platelet production; however, romiplostim is the only TPO-RA that binds at the same site as endogenous TPO. These subtle mechanistic differences may explain why switching TPO-RA may be clinically advantageous in some situations. As pharmacists are called to counsel patients on TPO-RA use, a deep understanding of potential adverse events and management strategies, as well as appropriate monitoring, will increase the likelihood that patients meet their goals of therapy in the shortest timeframe. Other uses of TPO-RAs are also discussed in this review, including use following hematopoietic stem cell transplant, use in myelodysplastic syndrome, and use in chemotherapy-induced thrombocytopenia.

Clinical challenges and promising therapies for chemotherapy-induced thrombocytopenia

Introduction: Chemotherapy-induced thrombocytop enia (CIT) is a common complication of cancer treatment causing chemotherapy delays, dose reductions, and treatment discontinuation, negatively impacting treatment outcomes and putting patients at risk for bleeding complications. There is no FDA-approved agent available to manage CIT.Areas covered: This article covers the diagnosis, definitions, and clinical challenges of CIT, and then focuses on the therapeutics developed to manage CIT. The first-generation thrombopoietic agents (oprelvekin and recombinant human thrombopoietins) are reviewed for critical background and context, followed by a detailed discussion of the data for the thrombopoietin receptor agonists (TPO-RAs) to manage CIT. Efficacy of TPO-RAs in treatment and prevention of CIT, as well as safety concerns such as the risk of thromboembolic complications, are reviewed in detail. For this review, a PubMed/MEDLINE literature search was undertaken for relevant articles published from 1995-2021.Expert opinion: After over two decades of drug development for CIT, multiple clinical trials and observational studies have found TPO-RAs, in particular romiplostim, to be safe and effective agents to manage patients with CIT, although no agent is yet FDA-approved for this indication. Active management of CIT with TPO-RAs is likely to improve oncologic outcomes, although additional data are needed. Phase 3 trials are ongoing.

Repurposing Pharmaceuticals Previously Approved by Regulatory Agencies to Medically Counter Injuries Arising Either Early or Late Following Radiation Exposure

The increasing risks of radiological or nuclear attacks or associated accidents have served to renew interest in developing radiation medical countermeasures. The development of prospective countermeasures and the subsequent gain of Food and Drug Administration (FDA) approval are invariably time consuming and expensive processes, especially in terms of generating essential human data. Due to the limited resources for drug development and the need for expedited drug approval, drug developers have turned, in part, to the strategy of repurposing agents for which safety and clinical data are already available. Approval of drugs that are already in clinical use for one indication and are being repurposed for another indication is inherently faster and more cost effective than for new agents that lack regulatory approval of any sort. There are four known growth factors which have been repurposed in the recent past as radiomitigators following the FDA Animal Rule: Neupogen, Neulasta, Leukine, and Nplate. These four drugs were in clinic for several decades for other indications and were repurposed. A large number of additional agents approved by various regulatory authorities for given indications are currently under investigation for dual use for acute radiation syndrome or for delayed pathological effects of acute radiation exposure. The process of drug repurposing, however, is not without its own set of challenges and limitations.

Platelets Stimulate Liver Regeneration in a Rat Model of Partial Liver Transplantation

Living donor liver transplantation (LDLT) is sometimes associated with impaired regeneration and severe ischemia/reperfusion injury (IRI) in the graft, resulting in small-for-size syndrome (SFSS). Platelets were previously reported to stimulate liver regeneration in models of hepatectomy, but the evidence in partial liver transplantation (LT) is lacking. In this study, a rat model of partial LT was used, and the impact of thrombopoietin (TPO)-induced perioperative thrombocytosis on graft regeneration, IRI, and survival was investigated. In experiment 1, a 30% partial LT was performed. Under thrombocytosis, SFSS was attenuated, as shown by decreased levels of serum aminotransferases, bilirubin, and ascites. Serum hepatocyte regeneration-related cytokines, including insulin-like growth factor-1, hepatocyte growth factor, interleukin 6 (IL6), and tumor necrosis factor α (TNF-α), were elevated. In addition, the proliferative signaling pathways, Ki-67-labeling index, proliferating cell nuclear antigen (PCNA)-labeling index, mitotic index, and liver/body weight ratio were increased under thrombocytosis. The platelet-induced regeneration was independent of TPO because increases in the Ki-67-labeling and PCNA-labeling indexes were eliminated after reducing platelet counts by antiplatelet serum in rats administered with TPO. For IRI, thrombocytosis did not aggravate oxidative stress or downstream signaling pathways, necrosis, or apoptosis in the graft. After Kupffer cell (KC) depletion, the platelet-induced attenuation of serum aminotransferases, increased serum levels of IL6 and TNF-α, and proliferation-related signaling pathways were eliminated. Moreover, platelet accumulation in the graft decreased substantially. In experiment 2, a 20% partial LT was performed, and thrombocytosis improved postoperative survival. In conclusion, our results suggested that thrombocytosis stimulated graft regeneration and prolonged survival without aggregating IRI after partial LT, and KCs vitally contributed to platelet-derived regeneration. Platelet therapies to increase perioperative platelet counts may improve the outcomes after LDLT.

Emerging Therapies in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a rare autoimmune disorder caused by peripheral platelet destruction and inappropriate bone marrow production. The management of ITP is based on the utilization of steroids, intravenous immunoglobulins, rituximab, thrombopoietin receptor agonists (TPO-RAs), immunosuppressants and splenectomy. Recent advances in the understanding of its pathogenesis have opened new fields of therapeutic interventions. The phagocytosis of platelets by splenic macrophages could be inhibited by spleen tyrosine kinase (Syk) or Bruton tyrosine kinase (BTK) inhibitors. The clearance of antiplatelet antibodies could be accelerated by blocking the neonatal Fc receptor (FcRn), while new strategies targeting B cells and/or plasma cells could improve the reduction of pathogenic autoantibodies. The inhibition of the classical complement pathway that participates in platelet destruction also represents a new target. Platelet desialylation has emerged as a new mechanism of platelet destruction in ITP, and the inhibition of neuraminidase could dampen this phenomenon. T cells that support the autoimmune B cell response also represent an interesting target. Beyond the inhibition of the autoimmune response, new TPO-RAs that stimulate platelet production have been developed. The upcoming challenges will be the determination of predictive factors of response to treatments at a patient scale to optimize their management.

Romiplostim in adults with newly diagnosed or persistent immune thrombocytopenia

Introduction: Three distinct phases are recognized in immune thrombocytopenia (ITP): newly diagnosed (≤3 months after diagnosis), persistent (>3-12 months after diagnosis), and chronic (>12 months). Several international guidelines/expert recommendations have been released in the past 2 years regarding the treatment of newly diagnosed/persistent ITP. Areas covered: Across the guidelines/expert recommendations, thrombopoietin receptor agonists (TPO-RAs), including romiplostim (the focus of this review), are recommended in newly diagnosed or persistent ITP for patients who fail to respond to corticosteroids or intravenous immunoglobulin (or where these are contraindicated). To identify data relating to romiplostim in adults with newly diagnosed or persistent ITP, we conducted a search of PubMed (with no time limit applied) and abstracts from 2019 EHA/ASH meetings using the term 'romiplostim.' Expert opinion: The findings from nine clinical trials, six real-world studies and ten case reports provide insight into the early use of romiplostim, which could help to reduce exposure to the adverse effects associated with prolonged corticosteroid use, as well as reduce the risk of severe bleeding. Additionally, given the durable responses observed in patients with newly diagnosed/persistent ITP, as well as the potential for treatment-free responses following discontinuation, romiplostim might help to avoid the need for subsequent treatment.

An evaluation of avatrombopag for the treatment of thrombocytopenia

Introduction: The thrombopoietin receptor agonists (TPO-RAs) are a class of drugs that have been FDA-approved for immune thrombocytopenia (ITP), periprocedural thrombocytopenia in patients with chronic liver disease (CLD), aplastic anemia, and thrombocytopenia associated with antiviral treatment of hepatitis C. Avatrombopag is a TPO-RA that is currently FDA-approved for ITP and periprocedural thrombocytopenia in patients with CLD and is currently undergoing evaluation for chemotherapy-induced thrombocytopenia (CIT) in an international phase III clinical trial. Areas covered: This paper summarizes the chemistry, pharmacodynamics, and pharmacokinetics of avatrombopag. In addition, the authors review the efficacy and safety of avatrombopag, covering clinical trials in patients with ITP and in patients with CLD scheduled to undergo a procedure. Expert opinion: Avatrombopag has demonstrated efficacy in patients with ITP. With its low side-effect burden, absence of hepatotoxicity, ease of use as an oral medication, and lack of food-drug interactions, avatrombopag is a favorable option for ITP, though there is a lack of long-term safety data. In periprocedural thrombocytopenia in patients with CLD, avatrombopag is comparable to lusutrombopag, another TPO-RA. Finally, the results of the study of avatrombopag in CIT are eagerly awaited, as there are no currently approved medications for this indication in the USA.

[Adult immune thrombocytopenia and thrombopoietin receptor agonist: Ten years later]

Ten years after their licence in France, the use of the two thrombopoietin receptor agonists (TPO-RA), eltrombopag and romiplostim, has deeply modified the landscape of immune thrombocytopenia (ITP) treatment. In this review, we summarise data on efficacy and safety of these treatments during ITP, as well as their use in clinical practice. Their place in therapeutic strategy, the recent description of persistant remission after discontinuation of TPO-RA, and future new thrombopoietic agents are also discussed. Their use has progressively increased and early use at a newly diagnosed stage of the disease is under evaluation. However physician have to keep in mind that thromboembolism rates appear to be higher with TPO-RA treatment in ITP patients at high risk of thrombosis, and that data from "real-life" studies with very long term follow up are not available. Finally, the cost of these treatments should also be evaluated in future therapeutic strategies comparisons.

The role of romiplostim for pediatric patients with immune thrombocytopenia

The thrombopoietin receptor agonists (TPO-RAs) are a class of platelet growth factors used to treat immune thrombocytopenia (ITP) in children and adults. Romiplostim is a peptide TPO-RA approved for over a decade to treat adults with ITP but was just recently US Food and Drug Administration approved to manage ITP in children 1 year of age and older who have had an inadequate response to corticosteroids, intravenous immunoglobulin, or splenectomy. Like the small molecule TPO-RA eltrombopag, romiplostim offers a high clinical response rate in pediatric patients with ITP, but requires use over an extended, and possibly indefinite, duration. This review is a critical appraisal of the role of romiplostim in pediatric ITP, discussing the safety and efficacy of this agent in clinical trials of children and adults and defining the patients most likely to benefit from romiplostim treatment. The treating hematologist is additionally provided guidance with treatment goals, dosing strategies, toxicity management, and indications for discontinuation.