Activin Receptor-Ligand Trap for the Treatment of ß-thalassemia: A Serendipitous Discovery.

ß-thalassemia is a hereditary disorder caused by defective production of ß-globin chains of hemoglobin (Hb) that leads to an increased α/ß globins ratio with subsequent free α-globins. Alpha globin excess causes oxidative stress, red blood cells membrane damage, premature death of late-stage erythroid precursors, resulting in ineffective erythropoiesis. The transforming growth factor ß (TGF-ß) superfamily signaling acts on biological processes, such as cell quiescence, apoptosis, proliferation, differentiation, and migration, and plays an essential role in regulating the hematopoiesis. This pathway can lose its physiologic regulation in pathologic conditions, leading to anemia and ineffective erythropoiesis. Activin receptor-ligand trap molecules such as Sotatercept and Luspatercept downregulate the TGF-ß pathway, thus inhibiting the Smad2/3 cascade and alleviating anemia in patients with ß-thalassemia and myelodysplastic syndromes. In this review, we describe in extenso the TGF-ß pathway, as well as the molecular and biological basis of activin receptors ligand traps, focusing on their role in various ß-thalassemia experimental models. The most recent results from clinical trials on sotatercept and luspatercept will also be reviewed.

The autophagy-activating kinase ULK1 mediates clearance of free α-globin in ß-thalassemia.

In ß-thalassemia, accumulated free α-globin forms intracellular precipitates that impair erythroid cell maturation and viability. Protein quality control systems mitigate ß-thalassemia pathophysiology by degrading toxic free α-globin, although the associated mechanisms are poorly understood. We show that loss of the autophagy-activating Unc-51-like kinase 1 (Ulk1) gene in ß-thalassemic mice reduces autophagic clearance of α-globin in red blood cell precursors and exacerbates disease phenotypes, whereas inactivation of the canonical autophagy-related 5 (Atg5) gene has relatively minor effects. Systemic treatment with the mTORC1 inhibitor rapamycin reduces α-globin precipitates and lessens pathologies in ß-thalassemic mice via an ULK1-dependent pathway. Similarly, rapamycin reduces free α-globin accumulation in erythroblasts derived from CD34+ cells of ß-thalassemic individuals. Our findings define a drug-regulatable pathway for ameliorating ß-thalassemia.

2'-O-methoxyethyl splice-switching oligos correct splicing from IVS2-745 ß-thalassemia patient cells restoring HbA production and chain rebalance.

ß-thalassemia is a disorder caused by altered hemoglobin protein synthesis and affects individuals worldwide. Severe forms of the disease, left untreated, can result in death before the age of 3 years (1). The standard of care consists of chronic and costly palliative treatment by blood transfusion combined with iron chelation. This dual approach suppresses anemia and reduces iron-related toxicities in patients. Allogeneic bone marrow transplant is an option, but limited by the availability of a highly compatible HSC donor. While gene therapy is been explored in several trials, its use is highly limited to developed regions with centers of excellence and well-established healthcare systems (2). Hence, there remains a tremendous unmet medical need to develop alternative treatment strategies for ß-thalassemia (3). Occurrence of aberrant splicing is one of the processes that affects ß-globin synthesis in ß-thalassemia. The (C>G) IVS-2-745 is a splicing mutation within intron 2 of the ß-globin gene. It leads to an aberrantly spliced mRNA that incorporates an intron fragment. This results in an in-frame premature termination codon that inhibits ß-globin production. Here, we propose the use of uniform 2'-O-methoxyethyl (2'-MOE) splice switching oligos (SSOs) to reverse this aberrant splicing in the pre-mRNA. With these lead SSOs we show aberrant to wild type splice switching. This switching leads to an increase of adult hemoglobin (HbA) up to 80% in erythroid cells from patients with the IVS-2-745 mutation. Furthermore, we demonstrate a restoration of the balance between ß-like- and α-globin chains, and up to an 87% reduction in toxic α-heme aggregates. While examining the potential benefit of 2'-MOE-SSOs in a mixed sickle-thalassemic phenotypic setting, we found reduced HbS synthesis and sickle cell formation due to HbA induction. In summary, 2'-MOE-SSOs are a promising therapy for forms of ß-thalassemia caused by mutations leading to aberrant splicing.

Genetic variability of TMPRSS6 and its association with iron deficiency anaemia.

Transmembrane Protease, Serine 6 (TMPRSS6) has an important role in iron homeostasis and its mutations, performed in TMPRSS6-deficient mice, have been recently associated with iron-refractory iron deficiency anaemia (IRIDA). Several variants of TMPRSS6 have been already identified; however the role of polymorphisms and TMPRSS6 haplotypes, causing iron deficiency anaemia, have not yet been investigated. This study sequenced the TMPRSS6 gene in 16 subjects with IRIDA phenotype and identified 27 DNA polymorphisms. Eight single nucleotide polymorphisms and four haplotypes were significantly associated with iron-refractory anaemia (P < 0·001). Our preliminary results suggest a possible association between specific haplotypes of TMPRSS6 and IRIDA.

Mutation analysis of hepcidin and ferroportin genes in Italian prospective blood donors with iron overload.

Maintenance of iron balance is essential for humans and requires the coordinate regulation of iron transport into plasma from dietary sources in the duodenum, from recycled senescent red cells in macrophages, and from storage in hepatocytes. Hepcidin, a recently identified antimicrobial peptide produced in the liver, has been shown to play a central role in the homeostatic regulation of iron absorption and distribution [1]. It is a negative regulator of iron absorption in the small intestine and of iron release from macrophages engaged in the recycling of iron senescent erythrocytes [2]. The human hepcidin gene contains three exons that encode a 72-aa precursor (pro-hepcidin) with a characteristic furin cleavage site immediately N-terminal to the 25-aa major hepcidin species found in plasma and urine [3]. Recently, hepcidin has been shown to regulate iron homeostasis by interaction with ferroportin, an iron cellular exporter highly expressed in absorptive enterocytes, macrophages, hepatocytes, and placental cells [4].

Reversal of cardiac complications by deferiprone and deferoxamine combination therapy in a patient affected by a severe type of juvenile hemochromatosis (JH).

Juvenile hemochromatosis (JH) is a rare autosomal recessive disorder of iron metabolism, genetically heterogeneous. In JH, symptomatic organ involvement occurs as early as the second decade of life. Heart failure and/or arrhythmias are the most frequent causes of death. Phlebotomy is the safest, most effective, and most economic therapeutic approach in hemochromatosis patients but is not indicated during the treatment of severe congestive heart failure with unstable hemodynamic status. The treatment of iron overload in these prohibitive clinical situations has to be carried out using iron chelators. We report a case of heart failure in the setting of unrecognized juvenile hemochromatosis successfully treated by the simultaneous administration of deferoxamine and deferiprone. To our knowledge, this is the first patient affected by JH treated with combined chelation regimen.

Spectrum and haplotypes of the HFE hemochromatosis gene in Iran: H63D in beta-thalassemia major and the first E277K homozygous.

We present the molecular analysis of HFE gene in 400 Southwest Iranian individuals. We have studied 43 newborn, selected for the presence of HbBart's at birth, 203 normal adult and 154 transfused patients affected with beta-thalassemia. Mutation analysis consisted of amplification and direct sequencing using two different pairs of forward and reverse primers. The C282Y and S65C mutations were not found. The H63D mutation was present with an allele frequency of 0.10 in newborns, 0.082 in normal adults and 0.080 in the beta-thalassemia major populations, respectively. No differences were found between normal adults and thalassemia major patients suggesting that this mutation does not increase mortality in beta-thalassemia. The H63D mutation was found associated with haplotype VI in 41% of the chromosomes. Other haplotypes were found suggesting a multicentric origin rather than a single mutation of European origin. While sequencing exon 4, a G --> A transition was found in the proximity of the C282Y mutation. The effect of this single base substitution (E277K) previously reported in an Asian individual and now found in homozygous form in a young transfused and chelated homozygous beta-thalassemia patient is not yet known.

Frequency and spectrum of hemochromatosis mutations in Tunisia.

The occurrence of the C282Y and H63D mutations of the HFE gene, responsible for toxic iron overload in the liver (hereditary hemochromatosis), was still unknown in Tunisia. We report the screening of 194 chromosomes from 97 randomly collected cord blood samples. The mutations were analyzed by PCR followed by DNA sequencing. The mild H63D and the severe C282Y mutations were found in 17.5+/-5.34% and 0.5+/-0.97% of the alleles, respectively. The allele frequency of the IVS 2+4 T --> C polymorphism is high (46.4+/-7.01%) in this population. Risk for homozygosity for the severe C282Y mutation is present in the Tunisian population at a low theoretical incidence. However, due to the relatively high rate of consanguinity in the country, liver pathology due to HH is not to be disregarded.

Mutations of the hemochromatosis gene in Italian candidate blood donors with increased transferrin saturation.

The aim of this study was to analyze the role of HFE mutations in blood donors with iron parameters suggesting iron overload, taking into account the regional distribution of HFE mutations in Italy. We studied 5880 subjects undergoing evaluation for blood donation eligibility, from different areas of Italy. Abnormal iron parameters were defined as transferrin saturation (TS) >50% or >45% and serum ferritin (SF) >300 or >250 microg/ml in males and females, respectively. Subjects with increased TS and/or SF were re-tested and typed for HFE mutations C282Y and H63D. A total of 548 individuals had increased iron parameters at first testing. In total, 179/548 were available for retesting, and in 109 increased TS and/or SF were confirmed. Increased TS was confirmed in 25 individuals, among whom three were C282Y homozygotes and six were compound heterozygotes for C282Y and H63D. Increased TS was more frequent in northern Italy than in southern regions. In individuals with increased TS and/or SF, the frequency of C282Y and H63D was 0.13 and 0.21 in northern-Italy versus 0.05 and 0.45 in southern Italy (P=0.004 for H63D). Nine out of 10 individuals carrying hemochromatosis-associated genotypes (including compound heterozygosity for C282Y and H63D) originated from northern regions. Among controls, the allelic frequencies of C282Y and H63D were 0.037 and 0.16 in the northern regions and 0.015 and 0.16 in the southern regions. In conclusion, over one-third of individuals with persistently altered TS carried hemochromatosis-associated genotypes, confirming that a diagnostic approach based on TS and genotyping of selected cases may represent a viable screening procedure.