Program: Oral and Poster Abstracts
Session: 112. Thalassemia and Globin Gene Regulation: Molecular Mechanisms of Thalassemia
We identified potent antisense oligonucleotides (ASOs) against mouse TMPRSS6. Downregulation of TMPRSS6 with ASO treatment results in dose-dependent hepcidin upregulation, which leads to dramatic reductions in serum iron and transferrin saturation. This in turn ameliorated the anemia and iron overload phenotypes in a mouse model of beta-thalassemia (th3/+ mice), which recapitulates beta-thalassemia intermedia in humans (Guo et al. J Clin Invest. 2013; 123(4):1531-41). Moreover, this ASO can be combined efficiently with iron chelators for the management of iron overload and anemia in non-transfusion-dependent thalassemia (Casu et al. Haematologica. 2016; 101(1):e8-e11).
TMPRSS6 is predominantly expressed in hepatocytes, for which we have developed a targeted delivery approach with triantennary N-acetyl galactosamine (GalNAc). With GalNAc-conjugated ASOs, a ~10-fold improvement in potency is observed for many liver targets (Prakash et al. Nucleic Acids Res. 2014; 42(13):8796-807). In order to characterize GalNAc-conjugated TMPRSS6 ASO, we treated normal mice with both parent ASO and its conjugated counterpart. As expected, the conjugated ASO demonstrated a ~10-fold improvement in ED50 (25 mg/kg/week versus 2.5 mg/kg/week for parent and conjugated ASOs, respectively). Next, we treated th3/+ mice for six weeks with 10 mg/kg/week GalNAc-conjugated TMPRSS6 ASO or a control ASO of the same chemistry. Compared to the control ASO treatment group, we observed >95% reduction of TMPRSS6 mRNA levels and >3-fold up-regulation of hepcidin mRNA levels in the liver. This resulted in a ~40% reduction in serum iron and ~50% reduction in transferrin saturation. In addition, anemia phenotypes were significantly improved as shown by a significant increase in hemoglobin and red blood cells (from 7.0 g/dL to 8.9 g/dL and from 5.8 to 7.5x10^6 cells/µl in the control ASO treatment group and in the TMPRSS6 ASO treatment group, respectively). Furthermore, there was an approximately 50% reduction in spleen weight. Improved erythroid maturation was indicated by a significant reduction in reticulocyte number and a normalized proportion between the pool of erythroblasts and enucleated erythroid cells.
A GalNAc-conjugated human TMPRSS6 clinical candidate was identified. Similar to mouse TMPRSS6, GalNAc-conjugated ASO demonstrated superior potency in human primary hepatocyte culture, in human TMPRSS6 transgenic mice and in cynomolgus monkey. Collectively, our data demonstrate that GalNAc-conjugated TMPRSS6 ASO could be an effective therapeutic for patients with beta-thalassemia and related disorders. A Phase 1 clinical trial is planned to initiate in 2017.
Disclosures: Aghajan: Ionis Pharmaceuticals: Employment, Equity Ownership. Booten: Ionis Pharmaceuticals: Employment, Equity Ownership. Monia: Ionis Pharmaceuticals: Employment, Equity Ownership. Guo: Ionis Pharmaceuticals: Employment, Equity Ownership.
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