Development of novel fetal hemoglobin inducers using targeted protein degradation

The major β-hemoglobinopathies, sickle cell disease (SCD) and β-thalassemia, are two of the most common monogenetic diseases. β-thalassemia describes a heterogenous set of mutations, insertions, deletions, or substitutions of the β-globin gene, HBB, that result in no or decreased β-globin synthesis. SCD on the other hand is an autosomal recessive disorder that has a well-defined missense point mutation in the HBB gene, that changes a glutamic acid to valine residue at the sixth position in the polypeptide sequence. This mutation causes adult erythroid cells to express βs-globin and synthesize an abnormal form of hemoglobin, HbS, that is prone to polymerizing. Patients with β-hemoglobinopathies cannot synthesize normal β-globin, and thus cannot form normally functioning adult hemoglobin, HbA, the predominant form in mature erythroid cells. Elevating levels of fetal hemoglobin, HbF, in patients with β-hemoglobinopathies can alleviate clinical symptoms. Compared to HbA, which is composed of globin subunits α2β2, HbF is composed of α2γ2 subunits. After birth, hematopoiesis shifts from fetal hemoglobin expression in fetal liver to the bone marrow where adult erythrocytes are produced and express adult hemoglobin. The transition from fetal to adult hemoglobin, from γ-globin to β-globin expression, requires several critical transcription factors (TFs), namely BCL11A and ZBTB7A, that recruit the Nucleosome Remodeling and Deacetylase, NuRD, complex, and its catalytic component, CHD4, to the globin locus and repress γ-globin expression. A third TF, ZNF410, was recently found to be a unique activator of CHD4 expression. CRISPR/Cas9 knockout or shRNA knockdown of each of these three TFs induces HbF expression, and targeted therapies against these factors might offer a new therapeutic avenue for β-hemoglobinopathies. Immunomodulatory drugs (IMiDs) have been shown to recruit Cys2-His2 zinc-finger (C2H2-ZF) TFs to cereblon, the substrate recognition component for the Cullin-4 E3 ubiquitin ligase (CRL4) complex, for targeted protein degradation. The three TFs of interest all contain various numbers of tandem C2H2-ZF domains, and therefore, I hypothesize that IMiD-induced targeted protein degradation of one or a combination of BCL11A, ZBTB7A, or ZNF410, will lead to reactivation of the γ-globin gene and increase levels of HbF. Using a 1122 compound IMiD library built by the Crews lab, Aim 1 will determine which compounds from the library can serve as lead hit compounds that will be optimized by iterative rounds of structure-activity relationship studies and characterized in cellulo for target TF degradation. Aim 2 will examine the ability of these optimized compounds to reactivate γ-globin expression and induce HbF synthesis in HUDEP-2 and primary erythroid progenitor cells. Completion of this proposal will provide the preclinical framework to assess the therapeutic potential of targeted protein degradation against TFs critical in the γ-globin to β-globin switch as a novel treatment avenue for the major β-hemoglobinopathies.