Dxo-1801, a liver-targeted siRNA, attenuates inflammation-driven iron restriction and enhances erythropoiesis in non-human primates

Abstract DXO-1801, a Liver-Targeted siRNA, Attenuates Inflammation-Driven Iron Restriction and Enhances Erythropoiesis in Non-Human Primates Background. Anemia of inflammation (AI) is a serious complication of chronic conditions (such as inflammatory bowel and autoimmune diseases), chronic kidney disease, advanced solid tumors and hematological malignancies (such as myelofibrosis). AI is driven by elevated pro-inflammatory cytokine triggered increase in hepcidin levels that limit iron availability for erythropoiesis, by reducing dietary iron absorption and restricting its mobilization from tissue stores. Hepcidin is primarily produced by hepatocytes and is regulated by iron-sensing and inflammatory pathways. DXO-1801 is a fully chemically stabilized, liver targeted and highly specific GalNAc-conjugated siRNA, silencing the expression of one of the key genes in the hepcidin-regulatory pathway in hepatocytes. Methods. Safety and pharmacodynamic (PD) effects of DXO-1801 were evaluated in cynomolgus macaques. For PD evaluation, animals (n=3 per group) received a single subcutaneous dose of DXO-1801 (1 or 5 mg/kg) and were followed for up to 22 weeks. To model inflammation-driven anemia, animals were challenged with intravenous IL-6, 14 days before and 28 days after DXO-1801administration. PD readouts included target mRNA expression (RT-qPCR), serum hepcidin, serum iron, transferrin saturation (TSAT) levels, and hematologic markers of erythropoiesis. For safety evaluation, other animals (n=2-3 per group) received a range of DXO-1801 doses up to 300 mg/kg. Results. DXO-1801 was well tolerated at all dose levels, including 300 mg/kg. No complement activation, cytokine elevation or coagulation abnormalities were observed. Transient and minor post-dose liver enzyme elevation was seen at the higher doses, consistent with a class effect observed for GalNAc-conjugated siRNA molecules. In the liver, DXO-1801 induced robust, dose-dependent and durable target mRNA knockdown: up to 90% by week 6 (p<0.0001) that was sustained at 77% (p<0.01) through week 22 in the 5 mg/kg dose group. Serum hepcidin declined markedly by week 3 and remained suppressed for over 8 weeks. Corresponding increases in serum iron and TSAT (2–3 fold) peaked at week 4 and remained elevated through week 16. Early increases in reticulocyte hemoglobin and mean corpuscular hemoglobin were followed by elevations in hematocrit and hemoglobin. Whereas the first IL-6 challenge (14 days prior to DXO-1801 administration) induced an acute hepcidin surge and deep hypoferremia, the serum hepcidin increase post second IL-6 challenge (28 days post DXO-1801 administration) was significantly reduced. Accordingly, the resulting hypoferremia was significantly and dose dependently, attenuated. Conclusions. A single administration of DXO-1801 was well tolerated up to the highest tested dose of 300 mg/kg. Doses as low as 1 or 5 mg/kg durably and deeply suppressed the target gene mRNA expression in the liver, leading to modulation of the hepcidin-iron axis that resulted in enhanced iron availability and improved erythropoiesis. These observations, together with DXO-1801-mediated attenuation of IL-6-induced hypoferremia, support its therapeutic potential for treating inflammation-driven anemia. Further preclinical studies are ongoing in support of planned first in human study.