Calmodulin inhibitors improve erythropoiesis in Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a rare hematopoietic disease characterized by a block in red cell differentiation. Most DBA cases are caused by mutations in ribosomal proteins and characterized by higher than normal activity of the tumor suppressor p53. Higher p53 activity is thought to contribute to DBA phenotypes by inducing apoptosis during red blood cell differentiation. Currently, there are few therapies available for patients with DBA. We performed a chemical screen using zebrafish ribosomal small subunit protein 29 (rps29) mutant embryos that have a p53-dependent anemia and identified calmodulin inhibitors that rescued the phenotype. Our studies demonstrated that calmodulin inhibitors attenuated p53 protein amount and activity. Treatment with calmodulin inhibitors led to decreased p53 translation and accumulation but does not affect p53 stability. A U.S. Food and Drug Administration–approved calmodulin inhibitor, trifluoperazine, rescued hematopoietic phenotypes of DBA models in vivo in zebrafish and mouse models. In addition, trifluoperazine rescued these phenotypes in human CD34+ hematopoietic stem and progenitor cells. Erythroid differentiation was also improved in CD34+ cells isolated from a patient with DBA. This work uncovers a potential avenue of therapeutic development for patients with DBA.

Modeling Diamond Blackfan Anemia and p53 Activation in the Zebrafish

Marrow dysplasias are pre-leukemic conditions that include ribosomopathies, a group of rare genetic diseases, or myelodysplasia preceded by clonal expansion in older adults with somatic mutations. To discover novel therapies for ribosomopathies, we performed two chemical suppressor screens using a ribosomal protein mutant zebrafish and human induced pluripotent stem cells (iPSCs) derived from ribosomopathy patients. In the zebrafish screen, we found calmodulin inhibitors rescued the anemia in zebrafish and also rescued the erythroid defect of the mouse (in vivo) and human (in vitro) models of marrow failure. The screen in RPS19 mutant human iPSCs identified a compound, SMER28, which enhanced erythropoiesis in anemia models through an autophagy-dependent mechanism. The compounds identified in our chemicals screens have provided new insight into the etiology of marrow failure, and calmodulin inhibitors will soon be studied in a clinical trial with adult Diamond-Blackfan anemia patients. To study the abnormal clonal hematopoiesis associated with myelodysplasia, we have generated a new system using the zebrafish in which single stem cells and their progeny express unique combinations of fluorescent proteins, allowing them to be tracked over time by their specific color. Mosaic mutagenesis induced by clustered regularly interspaced short palindromic repeats /cas9 and/or gene overexpression in this system led to expansion of specifically colored blood, modeling the clonal hematopoiesis of human myelodysplasia. Our studies should provide new insight into the ribosomopathies and myelodysplasia. Disclosures Zon: Marauder Therapeutics: Equity Ownership, Other: Founder; Scholar Rock: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Fate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder.