3182 – PHARMACOLOGICAL INHIBITION OF NEMO-LIKE KINASE RESCUES MTOR-MEDIATED TRANSLATION AND ERYTHROPOIESIS IN PRE-CLINICAL MODELS OF DIAMOND BLACKFAN ANEMIA

Diamond Blackfan Anemia (DBA) is associated with anemia, congenital abnormalities, and cancer. Current therapies for DBA have undesirable side effects, including iron overload from repeated transfusions or infections from immunosuppressive drugs and stem cell transplantation. Nemo-like Kinase (NLK) is hyperactivated in erythroid progenitors in murine and human models as well as DBA patients. In an RPS19-insufficient human model, genetic silencing of NLK increased erythroid expansion by 2.2 fold, indicating that aberrant NLK activation contributes to disease pathogenesis. A high-throughput inhibitor screen identified a compound that inhibits NLK (IC50:440nM) and increased erythroid expansion in murine (5.4 fold) and human (6.3 fold) models of DBA with no effect on wild type erythropoiesis (EC50: 0.7 µM). Virtually identical results were observed in CD34+ progenitors from 3 DBA patient bone marrow aspirates with 2.3, 1.9 and 2.1 fold increases in CD235+ erythroblast generation. In erythroid progenitors, RPS19 insufficiency increased phosphorylation of the mTORC1 component Raptor, reducing mTOR activity by 82%. This was restored to basal levels upon inhibition of NLK. To compensate for a reduction in ribosomes, stimulating mTOR activity with leucine has been proposed to increase translational efficiency in DBA patients. Probably due to NLK phosphorylation of raptor, DBA patients did not respond as anticipated. While leucine treatment mildly increased mTOR activity in both control and RPS19-insufficiency, combining leucine with NLK inhibition increased mTOR activity to 142% of control and significantly improved erythroid expansion. Identification of aberrantly activated enzymes, such as NLK, offer therapeutic promise used alone, or in combination with existing therapies, as druggable targets in the clinical management of DBA.