Receptor Type IIA Research Articles

Elritercept, a modified activin receptor IIA ligand trap, increased erythropoiesis and thrombopoiesis in a phase 1 trial

AbstractThe transforming growth factor β (TGF-β) superfamily plays a crucial role in regulating biological processes of virtually every tissue and system in the body, including hemostasis and hematopoiesis. Elritercept (KER-050) is an investigational, modified activin receptor type IIA ligand trap designed to bind and inhibit activin A and other select TGF-β superfamily ligands, including activin B, growth differentiation factor 8 (GDF-8), and GDF-11. The objectives of this phase 1 randomized, placebo-controlled study of elritercept were to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamic markers of activin inhibition and hematopoiesis in healthy postmenopausal women (N = 48). This study comprised 2 parts: single ascending doses ranging from 0.05 to 4.5 mg/kg; and multiple (up to 2 doses) ascending doses of 0.75 mg/kg administered subcutaneously (SC) every 4 weeks. Elritercept was generally well tolerated at all dose levels, with no dose-limiting toxicities observed. There were no severe or serious adverse events nor clinically significant changes in safety laboratory measures. Serum concentrations increased in dose-proportional manner after single SC doses, with peak concentrations achieved in 4.5 to 6 days and a mean elimination half-life of 12 days. These parameters were comparable after multiple doses. Elritercept elicited rapid, sustained, and dose-dependent increases in reticulocytes, red blood cells, hemoglobin, and platelets without eliciting detrimental changes in white blood cells such as neutrophils and lymphocytes. The time course and duration of changes in these cell populations supported a differentiated pharmacologic profile that is consistent with the stimulation of both early- and late-stage hematologic pathways. The trial was registered at www.anzctr.org.au/ as #ACTRN12619000318189.

Mechanisms and treatment of pulmonary arterial hypertension.

Substantial progress has been made in the management of pulmonary arterial hypertension (PAH) in the past 25 years, but the disease remains life-limiting. Established therapies for PAH are mostly limited to symptomatic relief by correcting the imbalance of vasoactive factors. The tyrosine kinase inhibitor imatinib, the first predominantly non-vasodilatory drug to be tested in patients with PAH, improved exercise capacity and pulmonary haemodynamics compared with placebo but at the expense of adverse events such as subdural haematoma. Given that administration by inhalation might reduce the risk of systemic adverse effects, inhaled formulations of tyrosine kinase inhibitors are currently in clinical development. Other novel therapeutic approaches for PAH include suppression of activin receptor type IIA signalling with sotatercept, which has shown substantial efficacy in clinical trials and was approved for use in the USA in 2024, but the long-term safety of the drug remains unclear. Future advances in the management of PAH will focus on right ventricular function and involve deep phenotyping and the development of a personalized medicine approach. In this Review, we summarize the mechanisms underlying PAH, provide an overview of available PAH therapies and their limitations, describe the development of newer, predominantly non-vasodilatory drugs that are currently being tested in phase II or III clinical trials, and discuss future directions for PAH research.

Ker-050 Treatment Reduced Iron Overload and Increased Bone Specific Alkaline Phosphatase in Participants with Lower-Risk MDS Supporting Potential to Restore Balance to the Osteohematopoietic Niche

Background: Iron overload (IO) in myelodysplastic syndromes (MDS) contributes to the deterioration of the osteohematopoietic niche (OHN), where hematopoietic and osteogenic precursors interact to regulate hematopoiesis and bone metabolism. Excess iron exacerbates ineffective hematopoiesis, inflammation, and bone loss via direct effects on resident hematopoietic and osteogenic precursors. Iron chelation therapy (ICT) is associated with improved event-free survival in patients with MDS but does not address the underlying cause of IO and introduces patient burden due to tolerability and cost. KER-050 is an investigational, modified activin receptor type IIA ligand trap designed to inhibit select TGF-β superfamily ligands (activins A, B, GDFs 8, 11) and promote differentiation and maturation of erythroid and megakaryocytic precursors. KER-050 has potential to reduce dependence on red blood cell transfusions and increase iron utilization via erythropoiesis, possibly mitigating IO at its source. As previously reported from an ongoing Phase 2 study (NCT04419649), KER-050 treatment in participants with lower-risk (LR) MDS resulted in rates of modified IWG 2006 Hematological Improvement-Erythroid (HI-E) and transfusion independence (TI) of 51.4% and 42.3%, respectively, with a mean decrease in ferritin (322 ng/mL at Week 24) among HI-E and/or TI responders. KER-050 treatment also demonstrated effects on osteogenic precursors, including prevention of bone loss in a mouse model of MDS and dose-dependent increases in bone specific alkaline phosphatase (BSAP), a marker of bone formation, observed in healthy postmenopausal women. Thus, KER-050 has potential to address the multifaceted pathogenesis of MDS, including IO. Here, we present new data from the ongoing Phase 2 study in MDS, exploring the potential of KER-050 to provide benefit beyond hematologic responses and to ameliorate IO in MDS. Methods: This ongoing Phase 2 study is evaluating KER-050 in participants with LR MDS. Data from exploratory assessments of markers of IO, hematopoiesis, and bone turnover are presented as of a cutoff date of April 3, 2023, for all participants who had received the recommended Part 2 dose (RP2D; 3.75-5 mg/kg q4wks). Results: Baseline ferritin levels in RP2D participants (N=59) were generally elevated, while levels of mean corpuscular hemoglobin and reticulocyte hemoglobin were in the normal range (Table 1). After KER-050 treatment, sustained decreases in serum ferritin were observed among participants with baseline levels ≥1000 ng/mL (Figure 1), likely driven in part by reduced transfusion burden in responders. Concomitant increases observed in soluble transferrin receptor (sTfR; Figure 1) suggest that increased erythropoiesis may also have contributed. Mean decreases in ferritin observed in non-transfused (NT) participants (-228 ng/mL at Week 24, n=7) indicate potential for KER-050 to affect iron homeostasis by mechanisms other than transfusion reduction. In 1 NT participant receiving ICT, the baseline ferritin of 1632 ng/mL decreased to <500 ng/mL over 32 weeks, leading to ICT discontinuation and coinciding with an increase in hemoglobin (Hgb) from 9.2 g/dL at baseline to 11.3 g/dL over the same period. In another NT participant not receiving ICT, ferritin decreased from 1094 ng/mL at baseline to 884 ng/mL and 583 ng/mL at Weeks 24 and 68, respectively, while Hgb gradually increased from 9.94 g/dL at baseline to 10.7 and 12.2 g/dL at Weeks 24 and 68. KER-050 treatment was also associated with increases in BSAP, a new finding in this MDS population that is consistent with prior observations in preclinical and healthy volunteer studies. Despite some heterogeneity, mean increases of 8.47% (n=23) and 10.4% (n=13) were observed at Weeks 24 and 48, respectively; 3 participants with erythroid responses had increases in BSAP of ≥30% at these time points. Summary: Exploratory data indicate potential for KER-050 to drive meaningful decreases in ferritin in participants with LR MDS, particularly among those with IO. While transfusion reduction likely contributes, observations in NT participants highlight the potential for enhancement of erythropoiesis to improve IO, irrespective of transfusions. Observed changes in BSAP suggest that KER-050 is also acting on osteogenic precursors, with the potential to provide functional improvements within the OHN. Updated results will be provided at the presentation.

Durable Clinical Benefit with Ker-050 Treatment: Findings from an Ongoing Phase 2 Study in Participants with Lower-Risk MDS

Background: In myelodysplastic syndromes (MDS), defects occur at multiple stages of hematopoiesis. Available Erythropoiesis Stimulating or Erythroid Maturation Agents (ES/EMAs) target early or late stages of erythropoiesis, respectively, and are only effective in subsets of patients. For patients with high transfusion burden (HTB) who have diminished erythropoietic capacity and a worse prognosis, ES/EMAs show limited efficacy and durability of response (DOR). KER-050 is an investigational, modified activin receptor type IIA ligand trap designed to inhibit select TGF-β superfamily ligands (activins A, B, GDFs 8, 11) that is being evaluated in diseases with ineffective hematopoiesis (IH), including MDS and myelofibrosis. Preclinical studies demonstrated that KER-050 increased erythropoiesis and thrombopoiesis and acted on early- and late-stage erythropoietic and megakaryocyte progenitors. By eliciting effects on hematopoiesis across multiple differentiation stages and cell lineages, KER-050 has the potential to address the complex nature of IH and to provide robust and sustained hematological improvement in patients with MDS who have limited treatment options, including those with HTB or non-ring sideroblast (RS) MDS. Methods: Analyses evaluating KER-050 at the recommended Part 2 dose (RP2D; 3.75 - 5 mg/kg q4wk) in participants with lower-risk (LR), RS+ or non-RS MDS from an ongoing Phase 2 study (NCT04419649) are presented as of a data cutoff date of April 3, 2023. The primary endpoint evaluates the safety and tolerability of KER-050. Secondary endpoints of modified IWG 2006 Hematological Improvement-Erythroid (HI-E) and transfusion independence (TI) ≥8 weeks are presented for participants who received ≥24 weeks of treatment or discontinued. DOR and changes in hematological parameters for participants with ongoing TI are presented for the first time. Results: At baseline, most participants receiving KER-050 at the RP2D (74.6%) required regular transfusions (≥2 RBC units/8 weeks); 52.5% of RP2D participants had HTB (≥4 RBC units/8 weeks) and 20.3% had ≥8 RBC units/8 weeks (Table 1). The median treatment duration was 166 days (range 6 to 649). Most participants (89.8%) had at least 1 treatment-emergent adverse event (TEAE), and 32.2% had TEAEs considered treatment-related (Table 1). The most frequently observed TEAEs in ≥15% of participants were fatigue (22.0%), nausea and diarrhea (18.6% each), epistaxis (16.9%), and COVID-19 and dyspnea (15.3% each). A minority of participants (10.2%) had TEAEs that led to treatment discontinuation. Consistent with prior data, rates of TI for ≥8 weeks were similar regardless of baseline transfusion burden or RS status (Table 1). Among TI responders, 72.7% maintained TI for ≥24 weeks (data not shown), and the median DOR was not yet evaluable as more than half (6/11) had ongoing TI as of the cutoff date (Figure 1). Five of the 6 (83.3%) participants with ongoing TI had HTB at baseline, including one participant with a baseline transfusion burden of 11 RBC units/8 weeks, and all 3 responders with ongoing TI for >60 weeks. One participant with HTB and non-RS MDS had ongoing TI for >72 weeks with a steady increase in hemoglobin from 8.4 to 11.8 g/dL. Erythroid responses were not at the expense of other cell lineages, as levels of platelets and neutrophils generally did not decrease (Figure 1). In fact, 44.1% of participants overall experienced a sustained (≥8 weeks) mean increase in platelet count of ≥30 x 10 9 within the first 24 weeks. Sustained decreases in ferritin were observed in parallel with increases in soluble transferrin receptor (Table 1), and for 3 participants, iron chelator therapy (ICT) was able to be discontinued. Investigation into changes in serum ferritin and ICT with KER-050 treatment will continue as cohorts of participants with MDS and iron overload are enrolled. Summary: Updated findings from this ongoing Phase 2 study in LR MDS continue to show that KER-050 is generally well-tolerated and has potential to elicit sustained hematological improvements in a broad population of participants with LR MDS, including those with HTB. New data reveal an encouraging DOR, with observed preservation or improvement of multilineage hematopoiesis and sustained decreases in ferritin manifesting clinically with discontinuation of ICT. The study is ongoing and an update with the latest data will be provided at the time of presentation.

Rker-050, a Modified Activin Receptor Type Iia Ligand Trap, Promoted Erythropoiesis in a Murine Model of Myelofibrosis

Myelofibrosis (MF) is one of several myeloproliferative neoplasms most often associated with anemia due to ineffective hematopoiesis, inflammation, aberrant bone metabolism and progressive fibrosis in the bone marrow (BM). As a compensatory mechanism, extramedullary hematopoiesis is initiated in the spleen, resulting in splenomegaly. Megakaryocyte hyperplasia/dysplasia are thought to be one of the main drivers of MF disease progression. Evidence also suggests that dysregulated TGF-β superfamily activity contributes to ineffective hematopoiesis. KER-050 and its research form, RKER-050, are investigational modified activin receptor type IIA ligand traps designed to inhibit specific TGF-β superfamily ligands, including activin A, activin B, growth and differentiation factor (GDF) 8 and GDF11, to promote erythropoiesis and thrombopoiesis. Additionally, the KER-050 target ligands promoted fibrosis and bone resorption in preclinical studies. Therefore, by inhibiting these ligands, KER-050 could potentially rebalance the bone marrow microenvironment, including reducing fibrosis, allowing restoration of hematopoiesis and alleviating extramedullary hematopoiesis and associated splenomegaly. To investigate the potential of RKER-050 to reverse ineffective hematopoiesis in MF, a hypomorphic Gata1 MF mouse model (Gata1Low; MF mice) was utilized which presents similar characteristics to human MF, including ineffective hematopoiesis, cytopenias, extramedullary hematopoiesis, defective bone deposition and BM fibrosis. this study, we also observed aberrant bone growth in the cortex of the hind limb long bones which inappropriately extended into the bone marrow, resulting in limited BM compartment space and demonstrating a severe disease state in these mice. Anemia status of MF mice was confirmed at the start of the treatment. MF mice showed a 16% reduction in hemoglobin (Hgb) compared to WT control mice. After 12 weeks of treatment, MF+VEH mice continued to exhibit a significant or trending decrease in red blood cells (RBCs; -19%), Hgb (-20%), and hematocrit (Hct; -10%) compared to WT mice. In contrast, MF+050 mice had a significant recovery of RBCs (+31%), Hgb (+24%) and Hct (+20%), compared to MF+VEH mice, demonstrating that RKER-050 reversed anemia in this advanced disease MF model. To assess the mechanism of action of RKER-050, we evaluated erythroid precursor populations in the BM. While MF+VEH mice showed a significant reduction in erythroid progenitors compared to WT mice, These data support increased BM erythropoiesis with RKER-050 treatment. In addition, we evaluated the effect of RKER-050 on thrombopoiesis. MF+VEH mice were severely thrombocytopenic and had significantly increased megakaryocyte progenitors (MkP; +591%) compared to WT mice. Although RKER-050 significantly reduced MkP (-33%; MF+050), suggesting RKER-050 may positively influence the megakaryocyte lineage, this did not translate to improvements in thrombocytopenia, and platelet counts remained similar to MF+VEH. Additional data will be presented that investigates the potential of RKER-050 treatment in (6-month vs 10-month-old mice, where disease is less severe) to further evaluate the potential to impact cytopenias, extramedullary hematopoiesis and BM fibrosis. Overall, in the context of severe disease, our results suggest RKER-050 can promote erythropoiesis and reverse anemia in the BM in by rebalancing hematopoiesis in the BM niche. Reestablishing BM hematopoiesis could obviate the need for compensatory extramedullary hematopoiesis in the spleen, the major driver of splenomegaly in MF patients. In conclusion, KER-050 represents a potentially promising approach for patients with MF and other hematological diseases where ineffective hematopoiesis occurs.

Modulation of TGF-β Superfamily Signaling By Ker-050 Demonstrated Potential to Treat Myelofibrosis and Mitigate Ruxolitinib-Associated Cytopenia

Background: Myelofibrosis (MF) is a disorder characterized by unrestrained proliferation of myeloid precursors and dysfunctional Janus kinase (JAK) signaling. Fibroblast proliferation, bone remodeling, and marrow fibrosis within the osteohematopoietic niche (OHN) result in ineffective and extramedullary hematopoiesis. Clinical manifestations include anemia, splenomegaly, and often disabling symptoms. JAK inhibitors, such as ruxolitinib, have been shown to improve spleen size and symptoms but are associated with dose-limiting cytopenia, reducing their utility for many patients. KER-050 is an investigational, modified activin receptor type IIA ligand trap designed to inhibit select TGF-β superfamily ligands (activins A, B, GDFs 8, 11) to address ineffective hematopoiesis by promoting differentiation of erythroid and megakaryocytic precursors. Here, we present new data from an ongoing Phase 2 study (NCT05037760) evaluating KER-050 as a monotherapy and in combination with ruxolitinib in participants with MF. Methods: This ongoing Phase 2 study is evaluating the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and efficacy of KER-050 administered with or without ruxolitinib in participants with anemia and primary MF, post-essential thrombocythemia MF, or post-polycythemia vera MF. Part 1 involves parallel dose escalation arms (1A: monotherapy, 1B: combination with ruxolitinib) to identify the dose(s) of KER-050 to be evaluated in Part 2. Data are presented as of the data cutoff date of April 3, 2023. Results: A total of 24 participants were enrolled (n=12 in Arm 1A and n=12 in 1B). One participant recently enrolled in Arm 1B at dose level III (3.0 mg/kg) had limited exposure at the time of data cutoff and is not included in the PD findings reported below. All participants met the criteria for higher-risk disease by DIPSS and 41.7% met IWG 2013 transfusion-dependent (TD) criteria (Table 1). The median duration of KER-050 treatment was 116 days (range 26 to 474), with 62.5% of participants ongoing as of the cutoff date. Most participants (91.7%) had at least 1 treatment-emergent adverse event (TEAE). No dose-limiting toxicities and no treatment-related severe or serious TEAEs have been observed. Most frequently observed TEAEs in ≥15% of participants were fatigue (including asthenia) (37.5%), and diarrhea (20.8%). Mean increases in hemoglobin (Hgb), reticulocytes, and soluble transferrin receptor (sTfR) were observed over the first 12 weeks of treatment in non-TD (NTD) participants for whom changes in markers of erythropoiesis were less confounded by ongoing transfusions (Figure 1). Overall, 7 of 13 (53.8%) NTD participants achieved a mean Hgb increase of ≥1.0 g/dL over the first 12 weeks and 2 of 13 (15.4%) achieved an increase of ≥1.5 g/dL. Increases in Hgb were also observed among TD participants, with 3/10 (30%) having a Hgb increase ≥1 g/dL over the first 12 weeks and one participant achieving a transfusion reduction ≥50% over at least 12 weeks (data not shown). For this participant (dose level I, Arm 1B), transfusion burden decreased from 9 red blood cell (RBC) units/12 weeks at baseline to 2 RBC units/12 weeks. Another participant (dose level I, Arm 1B), who received 4 RBC units/12 weeks at baseline, achieved a 20-week transfusion-free period with concomitant increases in Hgb, sTfR and platelets. Across treatment arms, platelet values were generally maintained if not increased. Additionally, for one participant receiving KER-050 monotherapy (dose level I), spleen size decreased by 38% from 2569 cm 3 at baseline to 1592 cm 3 at 24 weeks, coinciding with a 55% reduction in MF-SAF-TSS score from 56 to 25. Summary: Preliminary data from this ongoing Phase 2 study suggest that KER-050 is generally well tolerated and support the potential of KER-050 to improve key aspects of MF, including cytopenia, spleen size, and symptoms. Despite data being limited thus far to the 2 lowest dose levels, encouraging increases in markers of hematopoiesis have been observed as well as an initial case of reduced spleen size in a participant receiving KER-050 monotherapy. Updated analyses available at the time of presentation will provide further insight into the potential of KER-050 to treat MF and mitigate ruxolitinib-associated cytopenia.

Is sotatercept, which traps activins and growth differentiation factors, a new dawn in treating pulmonary arterial hypertension (PAH)?

ABSTRACT Introduction Although the prevalence of pulmonary arterial hypertension (PAH) is low, mortality is high. In PAH, there is a down-regulation of the bone morphogenetic protein receptor type 2 pathway, leading to a prominence of the upregulation pathway that is mediated by activins and growth differentiation factors acting at the receptor type IIA (ActRIIA). Sotatercept is an ActRIIA fusion protein. STELLAR was a phase 3 study of sotatercept for the treatment of PAH. Areas covered STELLAR. The primary endpoint of STELLAR was change from baseline at 24 weeks in the 6-minute walking distance, which was increased by 34.4 m by sotatercept compared to 1 m in the placebo group. Epistaxis/nosebleed, telangiectasia, and dizziness were more common with sotatercept than placebo. Expert opinion By targeting the remodeling in PAH, sotatercept is providing a new approach to the treatment of PAH and has the potential to slow or reverse cardiovascular remodeling in other conditions, e.g. left heart failure. However, the development of sotatercept for the treatment of PAH still requires a consideration of the appropriate dose and a longer-term assessment of the benefits and safety. If sotatercept becomes available for self-administration, it will be of interest to assess whether this affects adherence and benefits.

Modeling of clinical phenotypes in systemic lupus erythematosus based on the platelet transcriptome and FCGR2a genotype

BackgroundThe clinical heterogeneity of SLE with its complex pathogenesis remains challenging as we strive to provide optimal management. The contribution of platelets to endovascular homeostasis, inflammation and immune regulation highlights their potential importance in SLE. Prior work from our group showed that the Fcγ receptor type IIa (FcγRIIa)–R/H131 biallelic polymorphism is associated with increased platelet activity and cardiovascular risk in SLE. The study was initiated to investigate the platelet transcriptome in patients with SLE and evaluate its association across FcγRIIa genotypes and distinct clinical features.MethodsFifty-one patients fulfilling established criteria for SLE (mean age = 41.1 ± 12.3, 100% female, 45% Hispanic, 24% black, 22% Asian, 51% white, mean SLEDAI = 4.4 ± 4.2 at baseline) were enrolled and compared with 18 demographically matched control samples. The FCGR2a receptor was genotyped for each sample, and RNA-seq was performed on isolated, leukocyte-depleted platelets. Transcriptomic data were used to create a modular landscape to explore the differences between SLE patients and controls and various clinical parameters in the context of FCGR2a genotypes.ResultsThere were 2290 differentially expressed genes enriched for pathways involved in interferon signaling, immune activation, and coagulation when comparing SLE samples vs controls. When analyzing patients with proteinuria, modules associated with oxidative phosphorylation and platelet activity were unexpectedly decreased. Furthermore, genes that were increased in SLE and in patients with proteinuria were enriched for immune effector processes, while genes increased in SLE but decreased in proteinuria were enriched for coagulation and cell adhesion. A low-binding FCG2Ra allele (R131) was associated with decreases in FCR activation, which further correlated with increases in platelet and immune activation pathways. Finally, we were able to create a transcriptomic signature of clinically active disease that performed significantly well in discerning SLE patients with active clinical disease form those with inactive clinical disease.ConclusionsIn aggregate, these data demonstrate the platelet transcriptome provides insight into lupus pathogenesis and disease activity, and shows potential use as means of assessing this complex disease using a liquid biopsy.

Effects of Ker-050 on Iron Metabolism: Exploratory Analyses from an Ongoing Phase 2 Study in Patients with Myelodysplastic Syndromes

Background: Iron overload (IO) is an important clinical consequence of transfusion-dependent myelodysplastic syndromes (MDS). For patients with high transfusion burden (HTB), limited treatment options are available to effectively treat anemia and reduce transfusion dependence. Transfusion dependence is an independent predictor of poor prognosis in MDS. It is associated with IO and elevated ferritin, a marker of intracellular iron storage that also predicts poor prognosis in MDS. When adjusting for transfusion burden, each 500 µg/L increase in ferritin above 1000 µg/L is associated with a 30% greater risk of death (Malcovati et al. 2006). IO also disrupts osteoprogenitors and erythroid precursors within the osteohematopoietic niche, leading to abnormal bone turnover and ineffective erythropoiesis (Bulycheva 2015). While iron chelators have shown some efficacy in managing IO, they introduce toxicities and have little effect on transfusion burden. Unmet need remains for treatments that effectively address anemia, IO, and reduce transfusion dependence in patients with MDS, especially those with HTB. KER-050 is designed to alter signaling of TGF-β superfamily ligands, restoring balance to the osteohematopoietic niche, and promoting differentiation of erythroid and megakaryocytic precursors. It is a modified activin receptor type IIA ligand trap that inhibits TGF-β superfamily ligands, including activins A and B and growth and differentiation factors (GDFs) 8 and 11. To date, clinical data indicate that KER-050 induces sustained increases in reticulocytes and hemoglobin. Preliminary findings also show potential for KER-050 to induce erythroid response and reduce transfusion burden in patients with MDS, including those with HTB (Tan et al., 2022). KER-050 may also impact iron metabolism and this presentation explores the effects of KER-050 on indices of IO. Methods: This Phase 2 study is evaluating KER-050 in participants with very low- to intermediate-risk MDS. Data presented are from Part 1 Dose Escalation which included 16 weeks of KER-050 treatment across 5 cohorts (0.75 to 5 mg/kg). Iron chelator therapy was permitted at the discretion of the investigator provided patients had been on a stable dose for 8 weeks prior to C1D1. Markers of IO and hematopoiesis were assessed as exploratory endpoints over the 16-week treatment period. Analyses presented evaluate the effect of KER-050 on these markers. Baseline markers of bone turnover were also assessed. Results: A total of 31 patients were enrolled in Part 1 Dose Escalation; 26 were transfusion dependent, 18 with HTB (≥ 4 RBC units in 8 weeks prior to day 1). Seven HTB patients (38.9%) received iron chelator therapy. Baseline differences were noted in measures of iron status, erythropoiesis and bone turnover for non-transfused (NT), low transfusion burden (LTB), and HTB patients (Table 1). HTB patients had the highest baseline serum iron and ferritin levels. Preliminary findings indicate that KER-050 treatment was associated with decreases in serum ferritin for patients both with and without iron chelator therapy. Patients achieving transfusion independence (TI) experienced a 39.5% reduction (mean change: -619.4 ng/ml, range: -2118.4 to +243 ng/mL) in serum ferritin at Week 12 that was generally sustained at Week 16 and 20 (Figure 1). Similarly, over the same time period, serum iron and transferrin saturation (TSAT) decreased by 4.03 µmol/L (8.38%) and 5.3%, respectively, in patients achieving TI. Soluble transferrin receptor (sTfR) increased by 32.2% and remained elevated at subsequent visits. Summary: Preliminary data from the 16-week Dose Escalation in this ongoing phase 2 study reveal differences in baseline iron biomarkers indicative of increasing iron overload with increasing transfusion burden. While nearly half of HTB patients received iron chelator therapy, this group had markedly elevated ferritin compared to NT and LTB patients at baseline. KER-050 treatment was associated with reductions in serum ferritin, irrespective of the use of iron chelation. Patients achieving TI experienced decreases in ferritin, iron and TSAT concurrent with increases in sTfR that were generally maintained through follow-up. The data suggest that, in addition to improving hematopoiesis and transfusion burden in MDS patients, KER-050 may reduce iron overload, a serious clinical complication impacting the survival of these patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Modulation of TGF-β Superfamily Signaling to Treat Myelofibrosis and Mitigate JAK Inhibitor Toxicity: A Report on the Phase 2 Study of Ker-050 in Participants with Myelofibrosis

Background: Myelofibrosis (MF) is a disorder characterized by unrestrained proliferation of myeloid precursors and dysfunctional Janus kinase (JAK) signaling. Hyperplastic and dysplastic megakaryocyte expansion in MF releases inflammatory cytokines. These cytokines promote fibroblast proliferation, bone remodeling, and marrow fibrosis, disrupting the osteohematopoietic niche and leading to ineffective and extramedullary hematopoiesis (Vainchenker et al. 2017). Clinical manifestations include splenomegaly, anemia, and often disabling constitutional symptoms. JAK inhibitors, such as ruxolitinib, have been shown to improve spleen size and symptoms, but are associated with dose-limiting anemia and thrombocytopenia, reducing their utility for many patients (Verstovsek et al. 2012). KER-050 is an investigational product designed to alter signaling of TGF-β superfamily ligands, restoring balance to the osteohematopoietic niche and promoting differentiation of erythroid and megakaryocytic precursors. It is a modified activin receptor type IIA ligand trap that inhibits TGF-β superfamily ligands, including activins A and B and growth and differentiation factors (GDFs) 8 and 11. Preclinical studies have demonstrated that KER-050 induces erythropoiesis, increases platelet counts, improves bone mass, and prevents fibrosis. A preclinical study previously presented demonstrated that RKER-050 can reverse ruxolitinib-associated reductions in hemoglobin, hematocrit, and red blood cell count, indicating potential for KER-050 to mitigate ruxolitinib toxicity. In two clinical studies, including an ongoing study in participants with myelodysplastic syndromes (MDS), KER-050 has been well-tolerated. Accumulated clinical data demonstrate that KER-050 can stimulate erythropoiesis and thrombopoiesis in both healthy post-menopausal women and MDS participants with ineffective hematopoiesis. Here we present data from the first clinical study of KER-050 in participants with MF (NCT05037760). The objective of this study is to evaluate the potential of KER-050 as monotherapy and in combination with ruxolitinib to treat the underlying pathology of MF and mitigate JAK inhibitor-associated cytopenias. Methods: This ongoing Phase 2 open-label study is evaluating the safety, tolerability, pharmacokinetics PK), pharmacodynamics (PD), and efficacy of KER-050 administered with or without ruxolitinib in participants with primary myelofibrosis (PMF), post-essential thrombocythemia myelofibrosis (post-ET MF), and post-polycythemia vera myelofibrosis (post-PV MF) who have anemia (hemoglobin ≤ 10 g/dL or receiving transfusions). Part 1 involves parallel dose escalation arms (1A: monotherapy, 1B: combination with ruxolitinib) to evaluate the safety and tolerability of KER-050 and identify the dose(s) of KER-050 to be evaluated in Part 2 (Figure 1). Changes in hemoglobin, transfusion burden, spleen size, the Myelofibrosis Symptom Assessment Form Total Symptom Score (MF-SAF-TSS), PK and incidence of accelerated MF and acute myeloid leukemia are assessed as secondary endpoints. This study is also evaluating markers of multilineage hematopoiesis, bone remodeling, iron metabolism, inflammation, and marrow fibrosis. Frequency of ruxolitinib dose modification and quality of life will be explored. Results: Preliminary results from Part 1 will be presented. At the time of this writing, 5 patients have received KER-050 on study, 3 in Arm 1A and 2 in Arm 1B. Three participants have completed the dose-limiting toxicity (DLT) assessment period and no DLTs have been experienced. Data evaluated to date indicate a PD effect consistent with previous preclinical and clinical studies of KER-050. Summary: KER-050 is designed to alter TGF-β superfamily signaling, restoring balance to the osteohematopoietic niche and promoting multilineage hematopoietic differentiation. Here we present data from the first study of KER-050 in participants with MF evaluating the potential for KER-050 to impact key aspects of the MF disease state (anemia, spleen size, symptoms, progression), as monotherapy and in combination with ruxolitinib. The potential for KER-050 to mitigate ruxolitinib toxicity and related dose-reductions is being investigated. Exploratory analyses of the KER-050 impact on inflammation, bone remodeling, iron metabolism, and marrow fibrosis, as available, will be shared. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

ALK2 Inhibition and a Modified Activin Receptor Type Iia Ligand Trap Cotherapy Maximized Hematologic Improvements in a Mouse Model of Anemia of Inflammation

Introduction: Anemia of inflammation (AI) is commonly seen in patients with chronic diseases, including chronic kidney disease (CKD). Current therapeutic options to mitigate anemia in AI include treating the underlying inflammatory disease, oral or intravenous iron supplementation, erythropoietin, and blood transfusions. The persistent release of inflammatory cytokines in AI not only induces the iron regulator hepcidin to inhibit iron absorption and recycling, but also directly impacts the marrow to suppress erythropoiesis, further worsening the ineffective, iron-restricted erythropoiesis. Therefore, targeting both iron and erythropoiesis could comprehensively address anemia in AI. We previously showed that ALK2 inhibition was sufficient to reduce serum hepcidin and improve hemoglobin in a CKD mouse model. We also demonstrated that a modified activin receptor IIA ligand trap RKER-050 increased hemoglobin and red blood cell production by promoting erythroid differentiation in mice. Here, we explored the potential of additive improvements in hematologic parameters that could be achieved with a combination of hepcidin suppression by ALK2 inhibition and increased hematopoiesis with RKER-050 in a mouse model of AI. Methods: C57BL/6 mice were fed a control or 0.2% adenine with 40 ppm iron diet (Ade 40) for 5 weeks to induce CKD. After confirming anemia, CKD mice were subcutaneously treated with 3 mg/kg isotype control or KTI-m216, a neutralizing antibody against ALK2, twice a week for 4 weeks while continuing the Ade 40 diet or switching to a 0.2% adenine with 3 ppm low iron diet (Ade 3). Combination therapy was evaluated in CKD mice on Ade 40 diet receiving biweekly isotype or KTI-m216 and also received either weekly PBS or 7.5 mg/kg RKER-050 intraperitoneally for 4 weeks. Results: CKD mice developed impaired kidney function and characteristics of AI, including increased serum IL-6 and hepcidin, hypoferremia, tissue iron retention, and anemia compared to control mice. Serum hepcidin was reduced >95% in KTI-m216 treated mice on both Ade diets compared to mice receiving isotype control (CKD control). Transferrin saturation (TSAT) increased 65% in KTI-m216 treated mice on Ade 40 diet, with a similar trend in mice on Ade 3 diet. When compared to CKD control of the same diet, KTI-m216 treated mice had similar hematologic improvements: hemoglobin (+2.2 g/dL), hematocrit (+5.4%), red blood cells (+1.1 M/μl), and reticulocyte hemoglobin (CHr, +1.8 pg). These data support that increased circulating iron by KTI-m216 mediated hepcidin suppression can increase erythropoiesis in CKD mice. Data also suggest that dietary iron contribution is negligible in supporting erythropoiesis in this context. With combination therapy, mice receiving KTI-m216 alone (KTI-m216 and PBS) and a combined KTI-m216 and RKER-050 therapy had a similar reduction in serum hepcidin (>91%) and a similar increase in TSAT (>1.7-fold), compared to mice receiving vehicle (isotype and PBS) controls. Mice treated with KTI-m216 alone increased hemoglobin to 11.4 g/dL compared to vehicle treated mice with hemoglobin of 8.0 g/dL. Treatment with a combined KTI-m216 and RKER-050 therapy showed a further increase in hemoglobin to 13.5 g/dL. Additionally, red blood cell production was 6.4 M/μl in mice given vehicle controls and increased to 8.3 M/μl in KTI-m216 alone and 9.8 M/μl in combined KTI-m216 and RKER-050; hematocrit was 23.4% in vehicle control, 32.5% in KTI-m216 alone and 38.7% in combined KTI-m216 and RKER-050. Although hematocrit was not fully rescued, hemoglobin and red blood cells in mice receiving a combined KTI-m216 and RKER-050 therapy were not different from the non-CKD controls. Conclusion: These data illustrate that inhibition of ALK2 with KTI-m216 could potentially release sufficient iron from the recycling pathway to ameliorate anemia, but not restore RBC parameters to normal levels. Combined treatment with activin receptor ligand trap, RKER-050 and KTI-m216 normalized the RBC production in this preclinical model. These data support that increasing erythropoiesis with RKER-050 combined with iron mobilization with KTI-m216 has the potential to achieve the maximal amelioration of anemia in AI.

Detection of activin receptor type IIA and IIB-Fc fusion proteins by automated capillary immunoassay.

Activin receptor type IIA and type IIB fusion protein have been designed to sequester circulating molecules of the transforming growth factor-β (TGF-β) superfamily and inactivate their actions. Members of this superfamily have been reported as essential regulators of erythropoiesis by triggering the formation of activated ternary complexes containing different combinations of type I and type II receptors, which can limit RBC production by accelerating erythroid differentiation and inhibiting erythroid progenitor expansion. The recent approval of Luspatercept for the treatment of anemia associated to transfusion-dependent MDS and Beta-thalassemia in afflicted patients means that it can now pose a real threat of being abused in sport for its ability to stimulate erythropoiesis. Several methods for the detection of these molecules in blood have been proposed for the purpose of sport antidoping control. Here we propose the detection of the ActRIIA-Fc and ActRIIB-Fc fusion proteins by automated capillary Western immunoassay (Simple Western). The use of these immunoassays for the detection of protein targets has become widespread in the recent years. The work presented here demonstrates that this methodology enables a versatile, rapid, and sensitive detection of activin ligand traps in blood samples: plasma, serum, or dried blood spots (DBS). Preliminary results indicate that detection in urine samples is also possible. The option to use different antibodies allows the possibility to use this method as an initial testing procedure as well as a confirmation procedure. Finally, results coming from an administration study confirm that the method is suitable for routine analysis.

New treatment for myelodysplastic syndromes: luspatercept and oral hypomethylating agents

Several novel myelodysplastic syndromes (MDS) treatment drugs are being developed, and luspatercept and oral hypomethylating medicines have already been licensed in the United States and other countries. Luspatercept is a ligand trap that inhibits SMAD2/3 signals by combining the extracellular domain of the activin type IIA receptor with the human immunoglobulin G1 Fc domain. In the phase 2 study for low-risk MDS, the hematological improvement-erythroid (HI-E) was found in 63% of patients, and in the phase 3 study for transfusion-dependent low-risk MDS with ring sideroblasts, 38% of patients achieved transfusion independence. A combination of oral decitabine with oral cedazuridine, an inhibitor of cytidine deaminase, which metabolizes decitabine, demonstrated pharmacological equivalence with intravenous decitabine and has overall response rates of 60% and 43% for high-risk MDS in phase 2 and 3 trials, respectively. Furthermore, oral azacitidine and its combination with oral cedazuridine have been under development.

Abstract 13985: Targeting the Activin Receptor Type IIA for Therapeutics in Atrial Fibrillation

Introduction: Atrial fibrillation (AF) is the most common cardiac arrhythmia and a leading cause of stroke and heart failure. However, limited treatment options are available. The adipo-fibrokine Activin-A has been associated with AF in humans, and genome-wide association studies have implicated the Activin receptor type IIA (ActRIIA) in AF. Hypothesis: Our aim was to investigate the potential functional role of ActRIIA in AF pathophysiology. Methods: We used an Activin-A overexpression murine model (AOE) to determine if Activin-A/ActRII signaling increases AF inducibility and explored potential mechanisms by performing RNA sequencing. Comparative studies between the Activin-A binding receptors, ActRIIA and ActRIIB, were then conducted in vitro using siRNA knockdown (KD) in isolated cardiomyocytes and in vivo using cardiac specific ActRIIA or ActRIIB mouse knockouts (KO) in a high fat diet (HFD)-induced model of AF. Results: AOE mice displayed increased cardiac ActRII signaling, including increased FSTL3 mRNA expression (3.4-fold; p=0.005) and SMAD3 phosphorylation (2.7-fold; p=0.005). AF inducibility was markedly increased in AOE mice (75% versus 0% in controls), and was associated with decreased atrial conduction velocity (RA: 0.46±0.07 vs 0.61±0.09 m/s, p=0.005; LA: 0.54±0.18 vs 0.73±0.14 m/s, p=0.06). Pathway analysis of the cardiac transcriptome in AOE mice identified gap junctions as one of the most downregulated pathways (normalized enrichment score -2.8, FDR<0.001) with 50% decreased expression of the AF-associated connexin, CX43 (p adj =1.2x10 -9 ). Conversely, ActRIIA KD increased CX43 expression in cardiomyocytes (mRNA: 2-fold; p=0.005; protein: 1.8-fold; p=0.07), which was not observed with ActRIIB KD (mRNA: 1-fold; p=0.9; protein: 0.9-fold; p=0.3). ActRIIA KO mice also displayed lower AF inducibility rates (67%) to HFD, compared to ActRIIB KO mice (80%) and controls (αMHCcre 83%, ActRIIA flox/flox 89%, ActRIIB flox/flox 100%). Conclusions: Activin-A/ActRII signaling increases AF inducibility in part by decreasing cardiomyocyte CX43 expression and atrial conduction. This effect is specifically mediated through the ActRIIA, not ActRIIB, suggesting Activin receptor specificity in AF pathophysiology.

Final Results of a Phase 2 Study of Sotatercept (ACE-011) for Anemia of MPN-Associated Myelofibrosis

Final Results of a Phase 2 Study of Sotatercept (ACE-011) for Anemia of MPN-Associated Myelofibrosis

A Phase 2, Open-Label, Ascending Dose Study of Ker-050 for the Treatment of Anemia in Patients with Very Low, Low, or Intermediate Risk Myelodysplastic Syndromes

A Phase 2, Open-Label, Ascending Dose Study of Ker-050 for the Treatment of Anemia in Patients with Very Low, Low, or Intermediate Risk Myelodysplastic Syndromes

Type IIa RPTPs and Glycans: Roles in Axon Regeneration and Synaptogenesis.

Type IIa receptor tyrosine phosphatases (RPTPs) play pivotal roles in neuronal network formation. It is emerging that the interactions of RPTPs with glycans, i.e., chondroitin sulfate (CS) and heparan sulfate (HS), are critical for their functions. We highlight here the significance of these interactions in axon regeneration and synaptogenesis. For example, PTPσ, a member of type IIa RPTPs, on axon terminals is monomerized and activated by the extracellular CS deposited in neural injuries, dephosphorylates cortactin, disrupts autophagy flux, and consequently inhibits axon regeneration. In contrast, HS induces PTPσ oligomerization, suppresses PTPσ phosphatase activity, and promotes axon regeneration. PTPσ also serves as an organizer of excitatory synapses. PTPσ and neurexin bind one another on presynapses and further bind to postsynaptic leucine-rich repeat transmembrane protein 4 (LRRTM4). Neurexin is now known as a heparan sulfate proteoglycan (HSPG), and its HS is essential for the binding between these three molecules. Another HSPG, glypican 4, binds to presynaptic PTPσ and postsynaptic LRRTM4 in an HS-dependent manner. Type IIa RPTPs are also involved in the formation of excitatory and inhibitory synapses by heterophilic binding to a variety of postsynaptic partners. We also discuss the important issue of possible mechanisms coordinating axon extension and synapse formation.

Effect of Activin A on activation status of monocytes in acute-phase Kawasaki disease.

Kawasaki disease is a kind of self-limited systemic vasculitis involving middle and small arteries, which usually occurs in children under 5years old. Excessive inflammatory response caused by activation of monocytes is one of the important mechanisms of Kawasaki disease. Activated monocytes secrete large amounts of inflammatory mediators such as TNF-α and IL-1β. Activin A, a member of transforming growth factor-β superfamily, is a multifunctional growth and transforming factor. Several experimental evidences pinpoint that Activin A can regulate multiple biological function of the immune system. However, whether Activin A is involved in regulation of activation of monocytes in Kawasaki disease was not well characterized. Here, this study showed that the expression of Activin A in serum decreased in acute-phase Kawasaki disease. Furthermore, Activin A inhibits activin type IIA receptor, activin type IB receptor, CD86 and CD80 expression in over-activated monocytes. In addition, Activin A inhibited Smad3 expression and NF-κB signaling pathways. Specific function and mechanism of Activin A in acute-phase Kawasaki disease need further study.

Activin a suppresses peripheral CD8+ T lymphocyte activity in acute-phase Kawasaki disease

BackgroundKawasaki disease is an autoimmune disease characterized by systemic vasculitis of unknown aetiology and most commonly occurs in children under 5 years old. Previous studies have found that the over-activation of lymphocytes is an important mechanism of Kawasaki disease. Activin A, also known as immunosuppressive factor P, is a multifunctional growth and transforming factor. However, whether activin A is involved in the regulation of peripheral lymphocytes activity in Kawasaki disease is unclear. Thus, we aimed to investigate the effect of activin A on the activity of peripheral lymphocytes in acute-phase Kawasaki disease.MethodsSeven patients with Kawasaki disease and seven healthy controls were studied. Peripheral blood lymphocytes were isolated by Ficoll density gradient centrifugation. The activation of CD4+ and CD8+ T cells and CD19+ B cells was investigated by flow cytometry. The expression of activin type IIA receptors was investigated by flow cytometry.ResultsImmune imbalance in CD4 and CD8 lymphocytes were detected in acute-phase Kawasaki disease. The expression of activin type IIA receptors on CD8+ T cells and CD19+ B cells was increased in acute-phase Kawasaki disease and decreased following treatment with activin A. Activin A suppressed the expression of CD25 and CD69 on CD8+ T cells and the expression of CD69 on CD19+ B cells.ConclusionsThe expression of activin type IIA receptor was increased on CD8+ T cells and CD19+ B cells in Kawasaki disease. Activin A suppressed the expression of CD25, CD69 and activin type IIA receptors on peripheral CD8+ T lymphocyte. Activin A plays different roles in different lymphocyte subsets and suppresses peripheral CD8+ T lymphocyte activity in acute-phase Kawasaki disease.

Roles of type IIa receptor protein tyrosine phosphatases as synaptic organizers.

Neurons establish circuits for brain functions such as cognition, emotion, learning, and memory. Their connections are mediated by synapses, which are specialized cell-cell adhesions responsible for neuronal signal transmission. During neurodevelopment, synapse formation is triggered by interactions of cell adhesion molecules termed synaptic organizers or synapse organizers. Type IIa receptor protein tyrosine phosphatases (IIa RPTPs; also known as leukocyte common antigen-related receptor tyrosine phosphatases or LAR-RPTPs) play important roles in axon guidance and neurite extension, and also serve as presynaptic organizers. IIa RPTPs transsynaptically interact with multiple sets of postsynaptic organizers, mostly in a splicing-dependent fashion. Here, we review and update research progress on IIa RPTPs, particularly regarding their functional roles in vivo demonstrated using conditional knockout approach and structural insights into their extracellular and intracellular molecular interactions revealed by crystallography and other biophysical techniques. Future directions in the research field of IIa RPTPs are also discussed, including recent findings of the molecular assembly mechanism underlying the formation of synapse-specific nanostructures essential for synaptic functions.