Luspatercept (Reblozyl)

CADTH recommends that Reblozyl should be reimbursed by public drug plans for the treatment of adult patients with very low- to intermediate-risk myelodysplastic syndromes (MDS)-associated anemia who have ring sideroblasts and require red blood cell (RBC) transfusions, if certain conditions are met. Reblozyl should only be covered to treat patients who have failed or are not suitable for erythropoietin-based therapy. Reblozyl should only be reimbursed if prescribed by a specialist in MDS and if the cost of Reblozyl is reduced. Reimbursement should only be renewed if Reblozyl shows benefit to the patient such that the patient no longer requires RBC transfusions.

Health-Related Quality of Life Outcomes in Patients with Myelodysplastic Syndromes with Ring Sideroblasts Treated with Luspatercept in the MEDALIST Phase 3 Trial

Patients with myelodysplastic syndromes (MDS) often experience chronic anemia and long-term red blood cell transfusion dependence associated with significant burden on clinical and health-related quality of life (HRQoL) outcomes. In the MEDALIST trial (NCT02631070), luspatercept significantly reduced transfusion burden in patients with lower-risk MDS who had ring sideroblasts and were refractory to, intolerant to, or ineligible for prior treatment with erythropoiesis-stimulating agents. We evaluated the effect of luspatercept on HRQoL in patients enrolled in MEDALIST using the EORTC QLQ-C30 and the QOL-E questionnaire. Change in HRQoL was assessed every 6 weeks in patients receiving luspatercept with best supportive care (+ BSC) and placebo + BSC from baseline through week 25. No clinically meaningful within-group changes and between-group differences across all domains of the EORTC QLQ-C30 and QOL-E were observed. On one item of the QOL-E MDS-specific disturbances domain, patients treated with luspatercept reported marked improvements in their daily life owing to the reduced transfusion burden, relative to placebo. Taken together with previous reports of luspatercept + BSC reducing transfusion burden in patients from baseline through week 25 in MEDALIST, these results suggest luspatercept may offer a treatment option for patients that reduces transfusion burden while providing stability in HRQoL.

Ineffective erythropoiesis and its treatment

The erythroid marrow and circulating red blood cells (RBCs) are the key components of the human erythron. Abnormalities of the erythron that are responsible for anemia can be distinguished into 3 major categories, that is, erythroid hypoproliferation, ineffective erythropoiesis, and peripheral hemolysis. Ineffective erythropoiesis is characterized by erythropoietin-driven expansion of early-stage erythroid precursors, associated with apoptosis of late-stage precursors. This mechanism is primarily responsible for anemia in inherited disorders like β-thalassemia, inherited sideroblastic anemias, and congenital dyserythropoietic anemias, as well as in acquired conditions like some subtypes of myelodysplastic syndromes (MDS). The inherited anemias due to ineffective erythropoiesis are also defined as iron loading anemias because of the associated parenchymal iron loading caused by the release of erythroid factors that suppress hepcidin production. Novel treatments specifically targeting ineffective erythropoiesis are being developed. Iron restriction through enhancement of hepcidin activity or inhibition of ferroportin function has been shown to reduce ineffective erythropoiesis in murine models of β-thalassemia. Luspatercept is a TGF-β ligand trap that inhibits SMAD2/3 signaling. Based on pre-clinical and clinical studies, this compound is now approved for the treatment of anemia in adult patients with β-thalassemia who require regular RBC transfusions. Luspatercept is also approved for the treatment of transfusion-dependent anemia in patients with MDS with ring sideroblasts, most of whom carry a somatic SF3B1mutation. While long-term efficacy and safety of luspatercept need to be evaluated both in β-thalassemia and MDS, defining the molecular mechanisms of ineffective erythropoiesis in different disorders might allow the discovery of new effective compounds.

Coordinated mis-splicing of TMEM14C and ABCB7 causes ring sideroblast formation in SF3B1-mutant myelodysplastic syndrome

SF3B1 splicing factor mutations are near-universally found in myelodysplastic syndromes (MDS) with ring sideroblasts, a clonal hematopoietic disorder characterized by abnormal erythroid cells with iron-loaded mitochondria. Despite this remarkably strong genotype-to-phenotype correlation, the mechanism by which mutant SF3B1 dysregulates iron metabolism to cause ring sideroblasts (RS) remains unclear due to an absence of physiological models of RS formation. Here, we report an induced pluripotent stem cell (iPSC) model of SF3B1-mutant MDS that for the first time recapitulates robust RS formation during in vitro erythroid differentiation. Mutant SF3B1 induces mis-splicing of ~100 genes throughout erythroid differentiation, including proposed RS driver genes TMEM14C, PPOX, and ABCB7. All three mis-splicing events reduce protein expression, notably occurring via 5' UTR alteration and reduced translation efficiency for TMEM14C. Functional rescue of TMEM14C and ABCB7, but not the non-rate-limiting enzyme PPOX, markedly decreased RS, and their combined rescue nearly abolished RS formation. Our study demonstrates that coordinated mis-splicing of mitochondrial transporters TMEM14C and ABCB7 by mutant SF3B1 sequesters iron in mitochondria, causing ring sideroblast formation.

Integrative Analysis of Primary SF3B1 mt Ring Sideroblasts Provides Fundamental Insights into MDS-RS Pathogenesis and Dyserythropoiesis

Myelodysplastic syndromes (MDS) constitute a heterogeneous group of clonal hematopoietic stem cell (HSC) disorders characterized by aberrant HSC differentiation, cytopenia, and an increased risk of progression to leukemia. The low-risk subtype MDS with ring sideroblasts (MDS-RS) is specifically characterized by expanded and ineffective erythropoiesis, with more than 80% of patients displaying mutations in the core spliceosome component SF3B1 (SF3B1 mt). A hallmark of the MDS-RS bone marrow (BM) is the progressive accumulation of ring sideroblasts (RS), erythroblasts displaying perinuclear mitochondria loaded with aberrant ferritin-iron complexes. Whilst several in vitro and in vivo model systems exist for studying the impact of SF3B1 mt on erythropoiesis and RS development, primary SF3B1 mt erythroid biology remains largely unexplored due to the inability to purify live SF3B1 mt cells or fully replicate BM conditions in vitro. To address this issue, we developed an innovative two-step method to isolate live ring sideroblasts from SF3B1 mt MDS-RS BM aspiration material with extremely high purity (as determined through droplet digital PCR-based genotyping [Fig. 1A] and morphology-based detection through Prussian blue staining [Fig. 1B,C]). Unexpectedly, evaluation of matching peripheral blood samples showed that circulating ring sideroblasts are strikingly common in MDS-RS (Fig. 1D), with their abundance being significantly positively associated with clinically-determined BM RS frequencies and serum erythropoietin levels, as well as negatively associated with hemoglobin levels. Through high-throughput Chromium 3'-based single-cell RNA sequencing (scRNAseq) analysis of purified RS, we then showed that these cells comprise a heterogeneous population encompassing all stages of the erythroid differentiation continuum, from early progenitors to orthochromatic erythroblasts (Fig. 1E). The RS transcriptome was shown to be dynamically regulated towards the maintenance of cell survival during late terminal erythroid differentiation (exemplified through parkin 1 [PINK1] expression), with SF3B1 K700E erythroblasts employing multiple strategies to preserve homeostasis despite undergoing extreme oxidative stress. These observations were confirmed through a parallel whole-transcript RNAseq investigation comprising CD34 + and GPA +-enriched samples obtained from normal bone marrow (NBM) donors and SF3B1 K700E MDS-RS patients, as well as purified RS samples. This bulk RNAseq experiment validated the RS transcriptomic signature observed in scRNAseq (Fig. 1F) and allowed for a detailed investigation of RNA splicing. SF3B1 K700E-associated alternative splicing in CD34 + and RS was consistent with previous literature, but also highly context-dependent and with substantial changes in scope and magnitude throughout erythroid differentiation (Fig. 1G-I). Finally, we substantiated these RNAseq results through Tandem Mass Tag-based semi-quantitative proteomic analysis of purified RS and GPA-enriched cells from NBM donors and MDS-RS patients. We confirmed that ring sideroblast survival is heavily dependent on redox balance modulation and suppression of ER stress via an increased dependence on glutamine, mirroring the molecular mechanisms observed in malignancy. Additionally, our data strongly indicate that the RS population is a major modulator of the MDS-RS BM microenvironment due to expression of stress factors (with particular emphasis on GDF15, erythroferrone and IL-18). In conclusion, our integrative analysis of primary RS constitutes a unique platform for the study of MDS-RS, with special interest for the investigation of potential drivers of disease severity or treatment avenues. Figure 1 Figure 1. Disclosures Kretzschmar: Vanadis Diagnostics, a PerkinElmer company.: Current Employment.

Luspatercept in MDS with Ring Sideroblasts: A Real-Life Multicenter Experience from a Named Patient Program

Background Low risk Myelodysplastic syndromes (LR MDS) are a heterogeneous group of clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis, peripheral cytopenias and relative increase of bone marrow blasts [List 2004]. The most common cytopenia is anemia, which occurs in 85-90% of cases (isolated in 35% of cases) [Fenaux 2013], and ranges from mild/asymptomatic to transfusion dependent. The standard of care for anemia remains supportive care and about 70% of cases benefits from erythropoiesis-stimulating agents (ESAs). According to the FAB classification, a low-risk group of MDS characterized by the presence of ring sideroblasts (RS) was recognized. In the 2017 WHO classification, the nosologic entities of MDS uni-linear and multi-linear dysplasia with RS (MDS-UD-RS, MDS-MD-RS) were established, to emphasize the importance of identifying forms with a potential therapeutic target [Arber 2016]. Luspatercept is a recombinant fusion protein consisting of the modified extracellular domain of human activin receptor type IIB (ActRIIB) linked to a domain of human immunoglobulin Fc G1. The drug showed efficacy in re-establishing erythropoiesis and was recently approved for the treatment of adult patients with very low- to intermediate-risk MDS-RS failing ESAs[Platzbecker 2017; Fenaux 2020]. Aims To retrospectively assess the efficacy and/or clinical benefit (defined as a reduction in red blood cells transfusions [RBCT] or increase in hemoglobin levels) of luspatercept in patients with LR MDS with RS in a real-life setting. Safety issues were also addressed and clinical and hematological predictors of outcome analyzed. Methods We considered all IPSS-R lower-risk MDS with RS patients with unsatisfactory response or unsuitable for ESAs, treated with luspatercept as monotherapy through an expanded access program since November 2020, in 2 tertiary hematologic centers in Milan, Italy. Luspatercept was administered according to the published schedule: starting dose 1,0 mg/kg every three weeks, with the possibility to increase up to 1,33 mg/kg and 1,75 mg/kg if patients did not reach transfusion independence or decreased transfusion burden after two consecutive infusions. Response to luspatercept was evaluated according to IWG 2018 criteria: Hb increase by > 1.5 g/dL and/or relevant reduction of units of RBC transfusions by an absolute number of at least 4 RBC transfusions/8 wk compared with the pretreatment transfusion number in the previous 8 wk. Results We included a total of 17 pts (70% males, 30% females), with a median age of 68 years (range 45-89). The median follow-up from the start of the Luspatercept was 4 months (range 3-6).According to WHO 2017 we included 13 MLD (76%) and 4 ULD (24%); in all of them SF3B1 mutations was confirmed. Moreover, According to IPSS-R classification: 5 (27%)cases were intermediate and 12 (73%) low risk. All patients received at least three doses of luspatercept. Nine patients (53%) needed a dose escalation to 1,33 mg/kg, and 7 (41%) required the maximal dose of 1,75 mg/kg. Interestingly, not all patients received a dose escalation, and 8 (47%) obtained prolonged efficacy with 1 mg/kg dose. Hemoglobin levels increased in 9 pts (53%): 4 (24%), 3 (18%) and 2 (12%) cases at 1 mg/Kg, 1,33 mg/kg and 1,75 mg/dl, respectively. Medina increase was 1,5 g/dl (range 0,2 - 2,2) and these levels were maintained for a median of 4 months (range 3-6). In addition, considering transfusion burden, the independence was reached in 3 pts (18%), after a median time of 6 weeks from treatment start. Importantly, off the 14 patients remaining transfusion-dependent, 6 (35%) reduced the transfusion burden. The most prominent toxicity was increased blood pressure (grade 2) occurring in 3 pts (18%), and dizziness (grade 2) in 2 pts (12%); though the drug was generally well tolerated. No serious adverse events (SAEs) were reported. Therefore, patients were treated as outpatients in all cases. At the last follow up, all patients are alive and free from leukemic evolution. Conclusions: Our real-world experience confirms the efficacy of luspatercept in improving erythropoiesis and decreasing transfusion dependency in very low, low or intermediate risk MDS with RS, with an acceptable toxicity profile. Disclosures Fattizzo: Amgen: Honoraria, Speakers Bureau; Apellis: Speakers Bureau; Annexon: Consultancy; Momenta: Honoraria, Speakers Bureau; Novartis: Speakers Bureau; Alexion: Speakers Bureau; Kira: Speakers Bureau. Barcellini: Agios: Honoraria, Research Funding; Bioverativ: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Alexion Pharmaceuticals: Honoraria; Novartis: Honoraria.

Whole Transcriptome Analysis Identifies Distinct Gene Expression Profiles between SF3B1mut and SF3B1 wt Myelodysplastic Syndrome with Ring Sideroblasts

Background and aims - The 2016 revised WHO classification incorporated somatic mutation in SF3B1 spliceosome gene within the diagnostic criteria of myelodysplastic syndrome (MDS) with ring sideroblasts (RS). However, SF3B1wt MDS-RS display significantly different clinical features and outcome from those of SF3B1mut MDS-RS. Recently, the recognition of SF3B1-mutant MDS as a distinct nosologic entity has been proposed to overcome this limitation. Methods - To evaluate the biological relevance of this proposal, we studied a consecutive cohort of 132 MDS with RS >5% using a pangenomic approach (targeted-DNA sequencing, genome-wide copy number variation analysis and bulk RNA-sequencing of CD34+ bone marrow mononuclear cells). 16 age-matched healthy individuals and 43 MDS-SLD/MLD negative for both splicing mutation and RS were included in this study as controls. Results - Unsupervised clustering analysis based on mutation profiles identified two major clusters predicted by SF3B1 mutation (87 MDS-RS-SF3B1mut and 45 MDS-RS-SF3B1wt). The most recurrently mutated genes in MDS-RS-SF3B1wt were TP53(40%), SRSF2(38%), TET2 (33%), ASXL1 (21%) and DNMT3A (12%). SRSF2 and TP53 mutations were found to be mutually exclusive with SF3B1 (p-value <0.05), whereas no difference was found in TET2, DNMT3A and ASXL1 frequencies between MDS-RS-SF3B1 mutand MDS-RS-SF3B1wt subgroups. TP53-mutated MDS-RS exhibited shorter overall survival (median 1.3 years, log-rank p-value<0.0001) compared to SF3B1mut (median 7.6 years), SRSF2mut (median 3.4 years) and MDS-RS without the abovementioned aberrations (median 4.4 years). Notably, allelic imbalances analysis of oncogenic variants identified a significant enrichment of TP53 biallelic inactivation in MDS-RS-SF3B1wt (64% vs 0, p<0.01). Differential gene expression analysis results were incorporated into a specific expression signature highly predictive of MDS-RS-SF3B1 mutand MDS-RS-SF3B1wt subgroups (Figure 1). The resulting gene clusters were classified in RS-specific genes (cluster 1 and 2) and SF3B1-specific genes (cluster 3 and 4). RS-specific genes comprising heme and hypoxia genes were enriched (Figure 2AB) and correlated with RS percentage (p<0.01). Pathway analysis revealed a specific downregulation of adhesion molecules and an upregulation of G-protein coupled receptor signaling molecules in MDS-RS-SF3B1mut. Among SF3B1-specific genes (Figure 2CD), we confirmed ABCB7 downregulation and identified new molecular targets that may concur to the pathophysiology of SF3B1-driven myeloid neoplasms. Conclusions - This study contributes to unveil molecular features of SF3B1-mutant MDS and provides further evidence to support recognition of somatic SF3B1 mutation as a disease-defining genetic lesion. Disclosures Papaemmanuil: Isabl Technologies: Divested equity in a private or publicly-traded company in the past 24 months; Kyowa Hakko Kirin Pharma: Consultancy.