GDF11 is not the target of luspatercept

Combination of a TGF-β ligand trap (RAP-GRL) and TMPRSS6-ASO is superior for correcting β-thalassemia

A recently approved drug that induces erythroid cell maturation (luspatercept) has been shown to improve anemia and reduce the need for blood transfusion in non-transfusion-dependent as well as transfusion-dependent β-thalassemia (BT) patients. Although these results were predominantly positive, not all the patients showed the expected increase in hemoglobin (Hb) levels or transfusion burden reduction. Additional studies indicated that administration of luspatercept in transfusion-dependent BT was associated with increased erythropoietic markers, decreased hepcidin levels, and increased liver iron content. Altogether, these studies suggest that luspatercept may necessitate additional drugs for improved erythroid and iron management. As luspatercept does not appear to directly affect iron metabolism, we hypothesized that TMPRSS6-ASO could improve iron parameters and iron overload when co-administered with luspatercept. We used an agent analogous to murine luspatercept (RAP-GRL) and another novel therapeutic, IONIS TMPRSS6-LRx (TMPRSS6-ASO), a hepcidin inducer, to treat non-transfusion-dependent BT-intermedia mice. Our study shows that RAP-GRL alone improved red blood cell (RBC) production, with no or limited effect on splenomegaly and iron parameters. In contrast, TMPRSS6-ASO improved RBC measurements, ameliorated splenomegaly, and improved iron overload most effectively. Our results provide pre-clinical support for combining TMPRSS6-ASO and luspatercept in treating BT, as these drugs together show potential for simultaneously improving both erythroid and iron parameters in BT patients.

Bone marrow Tfr2 deletion improves the therapeutic efficacy of the activin-receptor ligand trap RAP-536 in β-thalassemic mice

β-thalassemia is a disorder characterized by anemia, ineffective erythropoiesis (IE), and iron overload, whose treatment still requires improvement. The activin receptor-ligand trap Luspatercept, a novel therapeutic option for β-thalassemia, stimulates erythroid differentiation inhibiting the transforming growth factor β pathway. However, its exact mechanism of action and the possible connection with erythropoietin (Epo), the erythropoiesis governing cytokine, remain to be clarified. Moreover, Luspatercept does not correct all the features of the disease, calling for the identification of strategies that enhance its efficacy. Transferrin receptor 2 (TFR2) regulates systemic iron homeostasis in the liver and modulates the response to Epo of erythroid cells, thus balancing red blood cells production with iron availability. Stimulating Epo signaling, hematopoietic Tfr2 deletion ameliorates anemia and IE in Hbbth3/+ thalassemic mice. To investigate whether hematopoietic Tfr2 inactivation improves the efficacy of Luspatercept, we treated Hbbth3/+ mice with or without hematopoietic Tfr2 (Tfr2BMKO/Hbbth3/+) with RAP-536, the murine analog of Luspatercept. As expected, both hematopoietic Tfr2 deletion and RAP-536 significantly ameliorate IE and anemia, and the combined approach has an additive effect. Since RAP-536 has comparable efficacy in both Hbbth3/+ and Tfr2BMKO/Hbbth3/+ animals, we propose that the drug promotes erythroid differentiation independently of TFR2 and EPO stimulation. Notably, the lack of Tfr2, but not RAP-536, can also attenuate iron-overload and related complications. Overall, our results shed further light on the mechanism of action of Luspatercept and suggest that strategies aimed at inhibiting hematopoietic TFR2 might improve the therapeutic efficacy of activin receptor-ligand traps.

Anemia in patients receiving anticancer treatments: focus on novel therapeutic approaches

Anemia is common in cancer patients and impacts on quality of life and prognosis. It is typically multifactorial, often involving different pathophysiological mechanisms, making treatment a difficult task. In patients undergoing active anticancer treatments like chemotherapy, decreased red blood cell (RBC) production due to myelosuppression generally predominates, but absolute or functional iron deficiency frequently coexists. Current treatments for chemotherapy-related anemia include blood transfusions, erythropoiesis-stimulating agents, and iron supplementation. Each option has limitations, and there is an urgent need for novel approaches. After decades of relative immobilism, several promising anti-anemic drugs are now entering the clinical scenario. Emerging novel classes of anti-anemic drugs recently introduced or in development for other types of anemia include activin receptor ligand traps, hypoxia-inducible factor-prolyl hydroxylase inhibitors, and hepcidin antagonists. Here, we discuss their possible role in the treatment of anemia observed in patients receiving anticancer therapies.

Luspatercept stimulates erythropoiesis, increases iron utilization, and redistributes body iron in transfusion-dependent thalassemia

Luspatercept, a ligand-trapping fusion protein, binds select TGF-β superfamily ligands implicated in thalassemic erythropoiesis, promoting late-stage erythroid maturation. Luspatercept reduced transfusion burden in the BELIEVE trial (NCT02604433) of 336 adults with transfusion-dependent thalassemia (TDT). Analysis of biomarkers in BELIEVE offers novel physiological and clinical insights into benefits offered by luspatercept. Transfusion iron loading rates decreased 20% by 1.4 g (~7 blood units; median iron loading rate difference: -0.05 ± 0.07 mg Fe/kg/day, p< .0001) and serum ferritin (s-ferritin) decreased 19.2% by 269.3 ± 963.7 μg/L (p < .0001), indicating reduced macrophage iron. However, liver iron content (LIC) did not decrease but showed statistically nonsignificant increases from 5.3 to 6.7 mg/g dw. Erythropoietin, growth differentiation factor 15, soluble transferrin receptor 1 (sTfR1), and reticulocytes rose by 93%, 59%, 66%, and 112%, respectively; accordingly, erythroferrone increased by 51% and hepcidin decreased by 53% (all p < .0001). Decreased transfusion with luspatercept in patients with TDT was associated with increased erythropoietic markers and decreasing hepcidin. Furthermore, s-ferritin reduction associated with increased erythroid iron incorporation (marked by sTfR1) allowed increased erythrocyte marrow output, consequently reducing transfusion needs and enhancing rerouting of hemolysis (heme) iron and non-transferrin-bound iron to the liver. LIC increased in patients with intact spleens, consistent with iron redistribution given the hepcidin reduction. Thus, erythropoietic and hepcidin changes with luspatercept in TDT lower transfusion dependency and may redistribute iron from macrophages to hepatocytes, necessitating the use of concomitant chelator cover for effective iron management.

From bench to bedside: The promise of sotatercept in hematologic disorders

Sotatercept (ACE-011) is an activin receptor IIA-Fc (ActRIIA-Fc) fusion protein currently under investigation for its potential in the treatment of hematologic diseases. By impeding the activities of the overexpressed growth and differentiation factor 11 (GDF11), activin A, and other members of the transforming growth factor-β (TGF-β) superfamily, commonly found in hematologic disorders, sotatercept aims to restore the normal functioning of red blood cell maturation and osteoblast differentiation. This action is anticipated to enhance anemia management and hinder the progression of myeloma. Simultaneously, comprehensive research is ongoing to investigate sotatercept's pharmacokinetics and potential adverse reactions, thus laying a robust foundation for its prospective clinical use. In this review, we provide a detailed overview of TGF-β pathways in physiological and hematologic disorder contexts, outline the potential mechanism of sotatercept, and delve into its pharmacokinetics and clinical research advancements in various hematologic diseases. A particular emphasis is given to the relationship between sotatercept dosage and its efficacy or associated adverse reactions.

Luspatercept, a two-edged sword in beta-thalassemia-associated paravertebral extramedullary hematopoietic masses (EHMs)

Paravertebral extramedullary hematopoietic masses (EHMs) account for up to 15% of extramedullary pseudotumors in beta-thalassemia (BT) and are most likely related to compensatory hematopoiesis. In most cases, pseudotumors are incidentally detected, as the majority of patients are asymptomatic. Since June 2020, luspatercept is approved for the treatment of patients with BT who require regular red blood cell transfusions. Data addressing the safety and efficacy of luspatercept in patients with BT-associated EHMs are pending. To date (May 2022), paravertebral EHMs were observed in two asymptomatic patients out of currently 43 adult patients with BT registered at the Adult Hemoglobinopathy Outpatient Unit of the University Hospital Essen, Germany. In one of them, a paravertebral EHM was diagnosed for more than 10 years prior to referral. Throughout observation time, treatment with luspatercept was associated with a clinically significant reduction in transfusion burden while allowing to maintain a baseline hemoglobin concentration of ≥10 g/dl aiming to suppress endogenous (ineffective) erythropoiesis associated with BT. Considering the rarity of paravertebral EHMs in BT, luspatercept might potentially represent a novel therapeutic option for these often-serious disease-associated complications. However, appropriate follow-up investigations are recommended to detect (early) treatment failures secondary to an undesired luspatercept-associated erythroid expansion.

Preparation and related properties of melanin iron supplement

In this study, BM-Fe (black sesame melanin-iron complex) was prepared and characterized. The results showed that the carboxyl hydroxyl group of BSM (black sesame melanin) participated in the chelation of iron ions. EDS (energy dispersive spectroscopy) and XPS (X-ray photoelectron spectroscopy) results confirmed the presence of iron ions in BM-Fe. The results of DLS (dynamic light scattering) showed that the average particle sizes of BSM and BM-Fe were 844.9 nm and 294.3 nm, respectively, indicating that the structure of BM-Fe with a smaller particle size was formed after the binding of iron ions with the active group on BSM. Finally, the in vitro iron dissolution, iron ion identification, in vitro iron ion reduction, antioxidant activity, cytotoxicity and moisture resistance properties of BM-Fe and FST (ferrous sulfate tablets, a commonly used iron supplement) were comprehensively compared. The results showed that BSM combined with iron instead of physically mixing, and BM-Fe was easily reduced in the gastrointestinal environment. BM-Fe had good bioavailability and retained the excellent characteristics (such as oxidation resistance and biocompatibility) of BSM, and had the potential to be applied in the treatment of iron-deficiency-related diseases. In summary, BM-Fe prepared in this study not only retained the excellent characteristics of BSM but also had a good effect on iron supplementation, high bioavailability and low side effects. Comprehensive analysis showed that the performance of BM-Fe prepared in this study was similar to or even better than that of the control (FST). Thus, BM-Fe is expected to become a new comprehensive multi-functional iron supplement and has a broad developmental prospect.

Luspatercept as a therapy for myelodysplastic syndromes with ring sideroblasts

INTRODUCTION

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell diseases characterized by cell dysplasia, ineffective hematopoiesis and risk of transformation to acute myeloid leukemia (AML). The median age of 75 years at diagnosis is associated with the presence of comorbidities, which preclude intensive therapies like allogeneic hematopoietic stem cell transplantation in most MDS patients. Risk stratification using the (Revised) International Prognostic Scoring System (IPSS/IPSS-R) is necessary to plan individualized treatment.

AREAS COVERED

Luspatercept (ACE-536), a specific activin receptor fusion protein, promotes late-stage erythropoiesis. Two clinical trials, PACE-MDS (phase 2) and MEDALIST (phase 3), yielded positive results in terms of improved hemoglobin levels and loss of transfusion dependence, with hardly any side effects. A phase 3 trial to compare luspatercept to ESAs (COMMANDS study) is ongoing.

EXPERT OPINION

Luspatercept is a promising alternative to ESAs for a subset of transfusion-dependent patients with lower risk MDS, namely those with a sideroblastic phenotype who are either not suitable for or have already failed erythropoietin-based treatment. The favorable safety profile and convenient subcutaneous administration every 3 weeks are more conducive to patients' quality of life than chronic red blood cell transfusion therapy.

The use of luspatercept for thalassemia in adults

Luspatercept is an activin receptor ligand trap that has been shown to enhance late-stage erythropoiesis in animal models of β-thalassemia. A multicenter, international, phase 2 dose-finding study was initiated in adult patients with β-thalassemia, either non-transfusion-dependent thalassemia (NTDT) or transfusion-dependent thalassemia (TDT). Positive results of the phase 2 study paved the way to a randomized phase 3 clinical trial (BELIEVE) to assess the efficacy and safety of luspatercept. The BELIEVE trial is a randomized, double-blind, placebo-controlled phase 3 trial. Three hundred thirty-six patients aged ≥18 years with TDT (regularly transfused, 6-20 red blood cell units within 24 weeks before randomization) were included in the trial. Patients received luspatercept or placebo subcutaneously every 21 days for ≥48 weeks and best supportive care. Forty-eight of 224 patients (21.4%) in the luspatercept group achieved the primary end points (≥33% reduction in transfusion burden) compared with those in the placebo group (4.5%; P < .001). Moreover, more patients had a ≥33% reduction in transfusion burden during any rolling 12-week interval (70.5% vs 29.5%) or any 24-week interval (41.1% vs 2.7%) with luspatercept than with the placebo. Transfusion independence was achieved by 11% of patients in the luspatercept group. Transient adverse events were more frequent with luspatercept than with placebo, but were manageable. Luspatercept was approved by the US Food and Drug Administration in 2019 and by the European Medicines Agency in 2020. The luspatercept trial is registered on www.clinicaltrials.gov at #NCT01749540 and the BELIEVE trial at #NCT02604433.

The role of activin: the other side of chronic kidney disease-mineral bone disorder?

Chronic kidney disease-mineral bone disorder (CKD-MBD) plays a pivotal role in the excess of cardiovascular morbidity and mortality associated with CKD. There is now a growing awareness that pathways involved in CKD-MBD, like canonical Wnt signalling, are activated from the earliest stages of CKD, playing a role in the development of adynamic bone disease with unknown consequences on vasculature. These changes occur before the classic changes in mineral metabolism: secondary hyperparathyroidism, calcitriol deficiency and hyperphosphataemia. Furthermore, vascular calcification is frequently associated and evolves with decreased bone mineral density and deranged bone turnover, while bone and arterial mineralization share common pathways. Therefore, results of clinical trials focused on mineral bone disorder, aimed at preserving bone and cardiovascular health, are considered unsatisfactory. In order to identify more effective therapeutic strategies, it is necessary to clarify the pathways modulating the cross-talk between bone and vasculature and identify new mediators involved in the pathogenesis of CKD-MBD. Much attention has been paid recently to the role of the transforming growth factor-beta superfamily members in renal disease, and in particular of activin A (ActA). Preclinical studies demonstrate an upgrade of ActA signalling in kidney, skeleton, vasculature and heart during CKD. This supports the idea that an endocrine factor produced in the kidney during renal disease, in addition to promoting the progression of kidney damage, deranges other organs' homoeostasis and participates in CKD-MBD. In this review, we analyse the contribution of ActA to kidney fibrosis and inflammation as well as its role in the development of CKD-MBD.

Controversies on the Consequences of Iron Overload and Chelation in MDS

Many patients with MDS are prone to develop systemic and tissue iron overload in part as a consequence of disease-immanent ineffective erythropoiesis. However, chronic red blood cell transfusions, which are part of the supportive care regimen to correct anemia, are the major source of iron overload in MDS. Increased systemic iron levels eventually lead to the saturation of the physiological systemic iron carrier transferrin and the occurrence of non-transferrin-bound iron (NTBI) together with its reactive fraction, the labile plasma iron (LPI). NTBI/LPI-mediated toxicity and tissue iron overload may exert multiple detrimental effects that contribute to the pathogenesis, complications and eventually evolution of MDS. Until recently, the evidence supporting the use of iron chelation in MDS was based on anecdotal reports, uncontrolled clinical trials or prospective registries. Despite not fully conclusive, these and more recent studies, including the TELESTO trial, unravel an overall adverse action of iron overload and therapeutic benefit of chelation, ranging from improved hematological outcome, reduced transfusion dependence and superior survival of iron-loaded MDS patients. The still limited and somehow controversial experimental and clinical data available from preclinical studies and randomized trials highlight the need for further investigation to fully elucidate the mechanisms underlying the pathological impact of iron overload-mediated toxicity as well as the effect of classic and novel iron restriction approaches in MDS. This review aims at providing an overview of the current clinical and translational debated landscape about the consequences of iron overload and chelation in the setting of MDS.

Luspatercept in Patients with Lower-Risk Myelodysplastic Syndromes

BACKGROUND

Patients with anemia and lower-risk myelodysplastic syndromes in whom erythropoiesis-stimulating agent therapy is not effective generally become dependent on red-cell transfusions. Luspatercept, a recombinant fusion protein that binds transforming growth factor β superfamily ligands to reduce SMAD2 and SMAD3 signaling, showed promising results in a phase 2 study.

METHODS

In a double-blind, placebo-controlled, phase 3 trial, we randomly assigned patients with very-low-risk, low-risk, or intermediate-risk myelodysplastic syndromes (defined according to the Revised International Prognostic Scoring System) with ring sideroblasts who had been receiving regular red-cell transfusions to receive either luspatercept (at a dose of 1.0 up to 1.75 mg per kilogram of body weight) or placebo, administered subcutaneously every 3 weeks. The primary end point was transfusion independence for 8 weeks or longer during weeks 1 through 24, and the key secondary end point was transfusion independence for 12 weeks or longer, assessed during both weeks 1 through 24 and weeks 1 through 48.

RESULTS

Of the 229 patients enrolled, 153 were randomly assigned to receive luspatercept and 76 to receive placebo; the baseline characteristics of the patients were balanced. Transfusion independence for 8 weeks or longer was observed in 38% of the patients in the luspatercept group, as compared with 13% of those in the placebo group (P<0.001). A higher percentage of patients in the luspatercept group than in the placebo group met the key secondary end point (28% vs. 8% for weeks 1 through 24, and 33% vs. 12% for weeks 1 through 48; P<0.001 for both comparisons). The most common luspatercept-associated adverse events (of any grade) included fatigue, diarrhea, asthenia, nausea, and dizziness. The incidence of adverse events decreased over time.

CONCLUSIONS

Luspatercept reduced the severity of anemia in patients with lower-risk myelodysplastic syndromes with ring sideroblasts who had been receiving regular red-cell transfusions and who had disease that was refractory to or unlikely to respond to erythropoiesis-stimulating agents or who had discontinued such agents owing to an adverse event. (Funded by Celgene and Acceleron Pharma; MEDALIST ClinicalTrials.gov number, NCT02631070; EudraCT number, 2015-003454-41.).