Immunomodulation in Primary Immune Thrombocytopenia: A Possible Role of the Fc Fragment of Romiplostim?

Immune thrombocytopenia: Pathophysiology and impacts of Romiplostim treatment

Immune thrombocytopenia (ITP) is an autoimmune bleeding disease caused by immune-mediated platelet destruction and decreased platelet production. ITP is characterized by an isolated thrombocytopenia (<100 × 109/L) and increased risk of bleeding. The disease has a complex pathophysiology wherein immune tolerance breakdown leads to platelet and megakaryocyte destruction. Therapeutics such as corticosteroids, intravenous immunoglobulins (IVIg), rituximab, and thrombopoietin receptor agonists (TPO-RAs) aim to increase platelet counts to prevent hemorrhage and increase quality of life. TPO-RAs act via stimulation of TPO receptors on megakaryocytes to directly stimulate platelet production. Romiplostim is a TPO-RA that has become a mainstay in the treatment of ITP. Treatment significantly increases megakaryocyte maturation and growth leading to improved platelet production and it has recently been shown to have additional immunomodulatory effects in treated patients. This review will highlight the complex pathophysiology of ITP and discuss the usage of Romiplostim in ITP and its ability to potentially immunomodulate autoimmunity.

Romiplostim for Treatment of Children and Young Adults With Severe Aplastic Anemia and Myelodysplastic Syndrome

Thrombopoietin receptor agonists (TPO-RAs) induce trilineage hematopoiesis under conditions with acquired hematopoietic failure. We evaluated safety, tolerability, and preliminary efficacy of a TPO-RA, romiplostim (Nplate), with or without standard-of-care immunosuppressive therapy (±IST) for children (ages < 21 y) with newly diagnosed and relapsed/refractory severe aplastic anemia (SAA) and myelodysplastic syndrome (MDS). Data were collected from an observational study and a single arm interventional pilot study. The safety outcome was treatment-related adverse events (AEs). Efficacy was evaluated by complete hematopoietic response (CHR) at week 24. Romiplostim was commenced at 5 µg/kg/week, with dose escalation of 2.5 µg/kg/week (maximum, 20 µg/kg/dose) based on platelet response. Romiplostim was continued until CHR was observed. Ten subjects (SAA, 9 [IST, 4; without IST, 5]; MDS, 1) completed the study (median age: 9.2 y). Median romiplostim dose was 10 µg/kg/week (range: 5 to 17.5 µg/kg/week). The cumulative incidence of CHR was 70.4% (95% CI, 20.2%-92.6%). Among 21 AEs (Grade 1 to 3), 3 were attributed to romiplostim. At a median posttherapy follow-up of 10.9 months (range: 0.7 to 77.5), no clonal evolution, bone marrow fibrosis or mortality was reported. This proof-of-concept study provides data about short-term safety, tolerability, and preliminary efficacy of romiplostim (±IST) for treatment of pediatric SAA/MDS.

Immunomodulation with romiplostim as a second-line strategy in primary immune thrombocytopenia: The iROM study

Thrombopoietin receptor agonists (TPO-RAs) stimulate platelet production, which might restore immunological tolerance in primary immune thrombocytopenia (ITP). The iROM study investigated romiplostim's immunomodulatory effects. Thirteen patients (median age, 31 years) who previously received first-line treatment received romiplostim for 22 weeks, followed by monitoring until week 52. In addition to immunological data, secondary end-points included the sustained remission off-treatment (SROT) rate at 1 year, romiplostim dose, platelet count and bleedings. Scheduled discontinuation of romiplostim and SROT were achieved in six patients with newly diagnosed ITP, whereas the remaining seven patients relapsed. Romiplostim dose titration was lower and platelet count response was stronger in patients with SROT than in relapsed patients. In all patients, regulatory T lymphocyte (Treg) counts increased until study completion and the counts were higher in patients with SROT. Interleukin (IL)-4, IL-9 and IL-17F levels decreased significantly in all patients. FOXP3 (Treg), GATA3 (Th2) mRNA expression and transforming growth factor-β levels increased in patients with SROT. Treatment with romiplostim modulates the immune system and possibly influences ITP prognosis. A rapid increase in platelet counts is likely important for inducing immune tolerance. Better outcomes might be achieved at an early stage of autoimmunity, but clinical studies are needed for confirmation.

Early immunomodulation in immune thrombocytopenia-A report of the ICIS meeting in Lenzerheide, Switzerland 2022

The only way to prevent immune thrombocytopenia (ITP) from becoming refractory would be to restore tolerance to platelets at an early phase of the disease. Numerous immune alterations probably accumulate in chronic ITP; thus, the chances of cure decrease significantly with time. Currently, sustained remission off treatment (SROT) is a clinical definition describing patients who can discontinue their ITP treatment without risk and maintain a state of remission. Different treatment strategies are presently being evaluated with the goal of attaining SROT, mostly combining drugs targeting the innate and/or the adaptive immune system, the inflammation state, so as increasing the platelet load. In this sense, thrombopoietin receptor agonists (TPO-RAs) have shown promising results if used as upfront treatment. TPO-RAs seem to exhibit immunomodulation and immune tolerance properties, increasing not only the platelet antigen mass but also increasing the transforming growth factor-β concentration, and stimulating regulatory T and B lymphocytes. However, more immunological studies are needed to establish accurate molecular alterations in ITP that are potentially reversed with treatments.

Engineering an Fc-Fusion of a Capsule Degrading Enzyme for the Treatment of Anthrax

Polymers of d-glutamic acid (PDGA) form the capsule of the highly virulent Ames strain of B. anthracis. PDGA is antiphagocytic and weakly immunogenic; it enables the bacteria to evade the innate immune responses. CapD is an enzyme that catalyzes the covalent anchoring of PDGA. CapD is an Ntn-amido hydrolase that utilizes an internal Thr-352 as its nucleophile and general acid and base. An internal cleavage produces a free N-terminal Thr-352 and a short and long polypeptide chain. The chains were circularly permuted (CP) to move Thr-352 to the N-terminus of the polypeptide. We previously showed that a branched PEG-CapD^S334C-CP could protect mice (80% survival) against a 5 LD₅₀ challenge with B. anthracis Ames without the use of antibiotics, monoclonals, or vaccines. In attempts to improve the in vivo circulation time of CapD and enhance its avidity to its polymeric substrate, an Fc-domain of a mouse IgG1 was fused to CapD^S334C-CP and the linker length and sequence were optimized. The resulting construct, Fc-CapD^S334C-CP, then was pegylated with a linear 2 kDa mPEG at S334C to produce mPEG-Fc-CapD^S334C-CP. Interestingly, the fusion of the Fc-domain and incorporation of the S334C mutation imparted acid stability, but slightly reduced the k_cat (∼ 2-fold lower). In vivo, the measured protein concentration in sera was higher for the Fc-fusion constructs compared to the mPEG-Fc-CapD^S334C-CP. However, the exposure calculated from measured sera enzymatic activity was higher for the mPEG-CapD^S334C-CP. The pegylated Fc-fusion was less active than the PEG-CapD^S334C-CP, but detectable in sera at 24 h by immunoblot. Here we describe the engineering of a soluble, active, pegylated Fc-fusion of B. anthracis CapD (mPEG-Fc-CapD-CP) with activity in vitro, in serum, and on encapsulated bacteria.

Refractory primary immune thrombocytopenia (ITP): current clinical challenges and therapeutic perspectives

Chronic primary immune thrombocytopenia (ITP) can today benefit from multiple therapeutic approaches with proven clinical efficacy, including rituximab, thrombopoietin receptor agonists (TPO-RA), and splenectomy. However, some ITP patients are unresponsive to multiple lines of therapy with prolonged and severe thrombocytopenia. The diagnosis of refractory ITP is mainly performed by exclusion of other disorders and is based on the clinician's expertise. However, it significantly increases the risk of drug-related toxicity and of bleedings, including life-threatening events. The management of refractory ITP remains a major clinical challenge. Here, we provide an overview of the currently available treatment options, and we discuss the emerging rationale of new therapeutic approaches and their strategic combination. Particularly, combination strategies may target multiple pathogenetic mechanisms and trigger additive or synergistic effects. A series of best practices arising both from published studies and from real-life clinical experience is also included, aiming to optimize the management of refractory ITP.

Romiplostim in children with newly diagnosed or persistent primary immune thrombocytopenia

Immune thrombocytopenia (ITP) is a disease of heterogenous origin characterized by low platelet counts and an increased bleeding tendency. Three disease phases have been described: newly diagnosed (≤ 3 months after diagnosis), persistent (> 3-12 months after diagnosis), and chronic (> 12 months after diagnosis). The majority of children with ITP have short-lived disease and will not need treatment. For children with newly diagnosed ITP, who have increased bleeding symptoms, short courses of steroids are recommended. In children who do not respond to first-line treatment or who become steroid dependent, thrombopoietin receptor agonists (TPO-RAs) are recommended because of their efficacy and safety profiles. In this narrative review, we evaluate the available evidence on the use of the TPO-RA romiplostim to treat children with newly diagnosed or persistent ITP and identify data from five clinical trials, five real-world studies, and a case report. While the data are more limited for children with newly diagnosed ITP than for persistent ITP, the collective body of evidence suggests that romiplostim is efficacious in increasing platelet counts in children with newly diagnosed or persistent ITP and may result in long-lasting treatment-free responses in some patients. Furthermore, romiplostim was found to be well tolerated in the identified studies. Collectively, the data suggest that earlier treatment with romiplostim may help children to avoid the side effects associated with corticosteroid use and reduce the need for subsequent treatment.

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.

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.

Enhancing the Pharmacokinetics and Antitumor Activity of an α-Amanitin-Based Small-Molecule Drug Conjugate via Conjugation with an Fc Domain

Herein we describe the design and biological evaluation of a novel antitumor therapeutic platform that combines the most favorable properties of small-molecule drug conjugates (SMDCs) and antibody drug conjugates (ADCs). Although the small size of SMDCs, compared to ADCs, is an appealing feature for their application in the treatment of solid tumors, SMDCs usually suffer from poor pharmacokinetics, which severely limits their therapeutic efficacy. To overcome this limitation, in this proof-of-concept study we grafted an α-amanitin-based SMDC that targets prostate cancer cells onto an immunoglobulin Fc domain via a two-step "program and arm" chemoenzymatic strategy. We demonstrated the superior pharmacokinetic properties and therapeutic efficacy of the resulting Fc-SMDC over the SMDC in a prostate cancer xenograft mouse model. This approach may provide a general strategy toward effective antitumor therapeutics combining small size with pharmacokinetic properties close to those of an ADC.

Eltrombopag monotherapy can improve hematopoiesis in patients with low to intermediate risk-1 myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are a group of clonal myeloid disorders characterized by low blood counts and a propensity to develop acute myeloid leukemia. The management of lowerrisk (LR) MDS with persistent cytopenias remains suboptimal. Eltrombopag, a thrombopoietin-receptor agonist, can improve platelet counts in LR-MDS and trilineage hematopoiesis in aplastic anemia. We conducted a phase II dose modification study to investigate the safety and efficacy of eltrombopag in LR-MDS. The eltrombopag dose was escalated from 50 mg/day to a maximum of 150 mg/day over a period of 16 weeks. The primary efficacy endpoint was hematologic response at 16-20 weeks. Eleven of 25 (44%) patients responded; five and six patients had uni- or bi-lineage hematologic responses, respectively. The predictors of response were presence of a paroxysmal nocturnal hemoglobinuria clone, marrow hypocellularity, thrombocytopenia, and elevated plasma thrombopoietin levels at study entry. The safety profile was consistent with that found in previous eltrombopag studies in aplastic anemia; no patients discontinued the drug due to adverse events. Three patients developed reversible grade 3 liver toxicity and one patient had increased reticulin fibrosis. Ten patients discontinued eltrombopag after achieving a robust response (median time 16 months); four of them reinitiated eltrombopag because of declining blood counts, and all attained a second robust response. Six patients had disease progression not associated with expansion of mutated clones and no patient progressed to develop acute myeloid leukemia on study. In conclusion, eltrombopag was well-tolerated and effective in restoring hematopoiesis in some patients with low or intermediate-1 risk MDS. This study was registered at clinicaltrials.gov as #NCT00932156.

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.

Multidrug Therapy for Refractory Immune Thrombocytopenia in Pregnancy

BACKGROUND

Severe immune thrombocytopenia complicating pregnancy may require treatment beyond first-line medications (intravenous immunoglobulins or corticosteroids), but there is a paucity of literature on the use of such second-line agents in pregnancy.

CASE

The patient is a 29-year-old woman with early-onset severe immune thrombocytopenia at 13 weeks of gestation. Maternal platelet counts reached a nadir of less than 5×10/L. The thrombocytopenia persisted despite first-line medications. Romiplostim, rituximab, and azathioprine were added to the therapeutic regimen. Platelet counts eventually stabilized at greater than 150×10/L before delivery. After delivery at term, the neonate had transient B-cell suppression, which was presumed to be secondary to rituximab, but was otherwise doing well and meeting all milestones at 7 months of age.

CONCLUSION

The addition of second-line agents was associated with sustained elevation in maternal platelet counts and may have obviated the need for splenectomy.

Therapeutic peptides for the treatment of systemic lupus erythematosus: a place in therapy

INTRODUCTION

Studies in vitro and in vivo have identified several peptides that are potentially useful in treating systemic lupus erythematosus (SLE). The rationale for their use lies in the cost-effective production, high potency, target selectivity, low toxicity, and a peculiar mechanism of action that is mainly based on the induction of immune tolerance. Three therapeutic peptides have entered clinical development, but they have yielded disappointing results. However, some subsets of patients, such as those with the positivity of anti-dsDNA antibodies, appear more likely to respond to these medications.

AREAS COVERED

This review evaluates the potential use of therapeutic peptides for SLE and gives an opinion on how they may offer advantages for SLE treatment.

EXPERT OPINION

Given their acceptable safety profile, therapeutic peptides could be added to agents traditionally used to treat SLE and this may offer a synergistic and drug-sparing effect, especially in selected patient populations. Moreover, they could temporarily be utilized to manage SLE flares, or be administered as a vaccine in subjects at risk. Efforts to ameliorate bioavailability, increase the half-life and prevent immunogenicity are ongoing. The formulation of hybrid compounds, like peptibodies or peptidomimetic small molecules, is expected to yield renewed treatments with a better pharmacologic profile and increased efficacy.

Deciphering predictive factors for choice of thrombopoietin receptor agonist, treatment free responses, and thrombotic events in immune thrombocytopenia

Very few data exist on when a particular thrombopoietin-receptor agonist (TPO-RA) is favored in clinical practice for the treatment of patients with immune thrombocytopenia (ITP), about novel risk factors for vascular events (VE) with these drugs, nor about predictive factors for therapy free responses (TFR). We conducted an observational, retrospective, long-term follow-up multicenter study from November 2016 to January 2018 of 121 adult ITP patients initiating TPO-RA between January 2012 to December 2014. Data reflected that a platelet count ≤25 × 10⁹/l at the time when the TPO-RA was initiated was associated with a 2.8 higher probability of receiving romiplostim vs. eltrombopag (P = 0.010). VE on TPO-RA was related to previous neoplasia in patients over 65 years (50% vs. 2.2%, P < 0.001), and to previous splenectomy in younger patients (100% vs. 33%, P = 0.001). Receiving romiplostim as first TPO-RA with no subsequent TPO-RA switching was associated with a 50% likelihood of TFR after 2.9 years of therapy (3.3 years in chronic ITP patients). These real-world data help deciphering some areas of uncertainty, and offer insight into some of the most relevant challenges of ITP which may help clinicians make appropriate treatment decisions in the management of adult ITP patients with TPO-RA.

Mechanisms and therapeutic prospects of thrombopoietin receptor agonists

The second-generation thrombopoietin (TPO) receptor agonists eltrombopag and romiplostim are potent activators of megakaryopoiesis and represent a growing treatment option for patients with thrombocytopenic hematological disorders. Both TPO receptor agonists have been approved worldwide for the treatment of children and adults with chronic immune thrombocytopenia. In the EU and USA, eltrombopag is approved for the treatment of patients with severe aplastic anemia who have had an insufficient response to immunosuppressive therapy and in the USA for the first-line treatment of severe aplastic anemia in combination with immunosuppressive therapy. Eltrombopag has also shown efficacy in several other disease settings, for example, chemotherapy-induced thrombocytopenia, selected inherited thrombocytopenias, and myelodysplastic syndromes. While both TPO receptor agonists stimulate TPO receptor signaling and enhance megakaryopoiesis, their vastly different biochemical structures bestow upon them markedly different molecular and functional properties. Here, we review and discuss results from preclinical and clinical studies on the functional and molecular mechanisms of action of this new class of drug.