The Serine Threonine Kinase Inhibitor Ots-167 Improves Erythropoiesis through Suppression of Nlk Activity in Diamond Blackfan Anemia Models

Diamond Blackfan Anemia (DBA) is associated with a hypoproliferative anemia, congenital abnormalities, and cancer. The disease typically presents within the first year of life with the majority of patients carrying mutations in one of at least 17 ribosomal proteins, with RPS19 being the most common. Current therapies for DBA have undesirable side effects, including iron overload from repeated red cell transfusions, chronic effects from long term corticosteroid use, or complications from stem cell transplantation.

The serine threonine kinase Nemo-like Kinase (NLK) is an atypical member of the MAP kinase family of enzymes and has been shown to be chronically hyper-activated in RPS19- and RPL11-haploinsufficient murine and human models of DBA, as well as in erythroid progenitors from DBA patients. In RPS19-insufficient human hematopoietic stem and progenitor cells, genetic silencing of NLK by shRNA increased erythroid expansion by 220.3% (SD = 6.6%), indicating that aberrant NLK activation may contribute to the pathogenesis of the disease and is a potential target for DBA therapy.

A number of clinically approved or advanced compounds have been developed to inhibit MAP kinases with various degrees of cross reactivity among its family members. We therefore screened a number of compounds that inhibit NLK as an off-target and found that these NLK inhibitors improved erythroid expansion in DBA models. Of these inhibitors, OTS-167 performed optimally, improving erythropoiesis by 2-fold at 300nM, with an EC50 of 146nM.

Previous studies of OTS-167 in xenograft models of neuroblastoma for one month did not result in neutropenia, suggesting very little to no toxicity to myeloid cells. The goal in treating DBA patients with NLK inhibitors is to sufficiently raise the hemoglobin to prevent the need for chronic red cell transfusions or treatment with steroids. Our results suggest that pharmacologic inhibition of NLK is a potential approach to treat patients with DBA. We are currently investigating other NLK inhibitors in preclinical models for future clinical application.