Romiplostim for therapy-related thrombocytopenia in pediatric malignancies

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.

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.

Thrombopoietin receptor agonists for chemotherapy-induced thrombocytopenia: a new solution for an old problem

Chemotherapy-induced thrombocytopenia (CIT) is common, resulting in increased bleeding risk and chemotherapy delays, dose reduction, and treatment discontinuation, which can negatively affect oncologic outcomes. The only agent approved by the US Food and Drug Administration to manage CIT (oprelvekin) was voluntarily withdrawn from the market by the manufacturer, leaving few options for patients. Therefore, patients experiencing CIT present a significant clinical challenge in daily practice. The availability of thrombopoietin receptor agonists has led to formal clinical trials describing efficacy in CIT as well as a rather extensive body of published observational data from off-label use in this setting but no formal regulatory indications for CIT to date. The accumulated data, however, have affected National Comprehensive Cancer Network guidelines, which now recommend consideration of TPO-RA clinical trials as well as off-label use of romiplostim. This review article details the evidence to date for the management of CIT with thrombopoietin receptor agonists (TPO-RAs), discussing the efficacy data, the specific circumstances when treatment is warranted (and when it is generally unnecessary), and safety considerations. Specific recommendations regarding patient selection, initiation, dosing, titration, and discontinuation for TPO-RA therapy in CIT are given, based on published data and expert opinion where evidence is lacking.

Chemotherapy-induced thrombocytopenia in Ewing sarcoma: Implications and potential for romiplostim supportive care

BACKGROUND

Maintaining dose-dense, interval-compressed chemotherapy improves survival in patients with Ewing sarcoma but is limited by myelosuppression. Romiplostim is a thrombopoietin receptor agonist that may be useful in the treatment of chemotherapy-induced thrombocytopenia (CIT).

METHODS

Patients aged between 3 and 33 years with Ewing sarcoma from 2010 to 2020 were reviewed. CIT was defined as a failure to achieve 75,000 platelets per microliter by day 21 after the start of any chemotherapy cycle. Fisher's exact test was used for univariate analysis and Pearson's correlation coefficient was used for the association between continuous variables.

RESULTS

Twenty-seven out of 42 patients (64%) developed isolated CIT, delaying one to four chemotherapy cycles per patient. CIT occurred during consolidation therapy in 24/27(88.9%) and with ifosfamide/etoposide cycles in 24/27 (88.9%). Univariate analysis failed to identify risk factors for CIT. The use of radiation approached significance (p-value = .056). Ten patients received romiplostim. The median starting dose was 3 μg/kg (range 1-5). Doses were escalated weekly by 1-2 to 4-10 μg/kg and continued throughout chemotherapy. A higher romiplostim dose was associated with a higher change in average platelet counts from baseline, r = .73 (p = .04). No romiplostim-related adverse events were identified aside from mild headache.

CONCLUSIONS

CIT is the primary reason for the inability to maintain treatment intensity in Ewing sarcoma. The concurrent use of romiplostim with chemotherapy was safe and feasible, and efficacy was associated with higher romiplostim doses.

Radiation countermeasures for hematopoietic acute radiation syndrome: growth factors, cytokines and beyond

PURPOSE

The intent of this article is to report the status of some of the pharmaceuticals currently in late stage development for possible use for individuals unwantedly and acutely injured as a result of radiological/nuclear exposures. The two major questions we attempt to address here are: (a) What medicinals are currently deemed by regulatory authorities (US FDA) to be safe and effective and are being stockpiled? (b) What additional agents might be needed to make the federal/state/local medicinal repositories more robust and useful in effectively managing contingencies involving radiation overexposures?

CONCLUSIONS

A limited number (precisely four) of medicinals have been deemed safe and effective, and are approved by the US FDA for the 'hematopoietic acute radiation syndrome (H-ARS).' These agents are largely recombinant growth factors (e.g. rhuG-CSF/filgrastim, rhuGM-CSF/sargramostim) that target and stimulate myeloid progenitors within bone marrow. Romiplostim, a small molecular agonist that enhances platelet production via stimulation of bone marrow megakaryocytes, has been recently approved and indicated for H-ARS. It is critical that additional agents for other major sub-syndromes of ARS (gastrointestinal-ARS) be approved. Future success in developing such medicinals will undoubtedly entail some form of a polypharmaceutical strategy, or perhaps novel, bioengineered chimeric agents with multiple, radioprotective/radiomitigative functionalities.

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.

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.

Up-front Treatment With Romiplostim in Children With Acquired Bone Marrow Failure: A Single Institutional Pediatric Case Series

BACKGROUND

Thrombopoietin receptor agonists are emerging as a therapeutic option for patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS). We report our experience of treating children with AA/MDS with romiplostim, thrombopoietin receptor agonist.

OBSERVATIONS

Three children (AA, 2; MDS, 1) received romiplostim treatment at a median dose of 10 μg/kg/week (starting dose: 5 μg/kg/wk; 2.5 μg/kg/wk increment). Trilineage hematopoietic recovery occurred at a median of 13 weeks (range: 13 to 16 wk) without adverse events. Hematopoiesis continued to improve after therapy discontinuation (median follow-up: 2.8 y; range: 0.5 to 3.0).

CONCLUSION

Our experience supports the short-term safety and efficacy of romiplostim in children with AA/MDS.

Romiplostim for the management of pediatric immune thrombocytopenia: drug development and current practice

Since successful cloning of thrombopoietin (TPO) in 1994, significant advances have been made in the development of recombinant TPO receptor agonists. The US Food and Drug Administration (FDA) has approved 2 agents for use in patients with immune thrombocytopenia (ITP): eltrombopag and romiplostim. Romiplostim is a once-weekly subcutaneous injection that has been shown to increase the platelet count, lessen bleeding, and reduce concurrent medication use in adults with ITP. In December 2018, the US FDA approved romiplostim for use in pediatric patients ≥1 year of age with ITP of >6 months' duration and insufficient response to corticosteroids, immunoglobulins, or splenectomy, based on similarly favorable clinical trial data. In addition, romiplostim is well tolerated, making it an attractive option for the treatment of children. Expansion of off-label romiplostim use is being reported in children for ITP <6 months, neonatal thrombocytopenia, hereditary thrombocytopenias, and chemotherapy- and bone marrow transplant-associated thrombocytopenia. We review here the development of romiplostim with a focus on pediatric use.

Pharmacological management of ionizing radiation injuries: current and prospective agents and targeted organ systems

Introduction: There is a limited array of currently available medicinals that are useful for either the prevention, mitigation or treatment of bodily injuries arising from ionizing radiation exposure.Area covered: In this brief article, the authors review those pharmacologic agents that either are currently being used to counter the injurious effects of radiation exposure, or those that show promise and are currently under development.Expert opinion: Although significant, but limited progress has been made in the development and fielding of safe and effective pharmacotherapeutics for select types of acute radiation-associated injuries, additional effort is needed to broaden the scope of drug development so that overall health risks associated with both short- and long-term injuries in various organ systems can be reduced and effectively managed. There are several promising radiation countermeasures that may gain regulatory approval from the government in the near future for use in clinical settings and in the aftermath of nuclear/radiological exposure contingencies.

Romiplostim for Immune Thrombocytopenia in Neuroblastoma Patients Receiving Chemotherapy

Thrombocytopenia, a serious complication of myelosuppressive chemotherapy in cancer patients, is managed with platelet transfusions until recovery of platelet counts. However, children receiving chemotherapy can rarely develop immune thrombocytopenia (ITP) that is refractory to transfused platelets. This limits the ability to achieve adequate platelet counts and administer further myelosuppressive chemotherapy safely, especially if first-line ITP therapy is ineffective. We report 2 cases of intravenous immunoglobulin refractory ITP in children receiving chemotherapy for high-risk neuroblastoma. ITP was successfully treated with the thrombopoietin-receptor-agonist romiplostim, allowing safe and timely continuation of antineuroblastoma therapies in these high-risk patients.