Jun Liu, MD PhD: No financial relationships to disclose
Background/Case Studies: Beta-globinopathies, such as β-thalassemia and sickle cell disease, present significant global health challenges. Existing treatments, including γ-globin inducers, blood transfusions, gene therapies, and bone marrow transplantation, face hurdles of cost, efficacy, and tolerability. Recent research underscores the crucial role of ZBTB7A/LRF, a transcriptional factor, in suppressing γ-globin during the erythroid globin switch. While transcription factors have historically been deemed "undruggable”, recent advancements in therapeutic modalities, like molecular glue degraders, have spurred interest in targeting them. Leveraging nearly two decades of expertise in transcription factor biology, access to compound libraries, and collaborations, we identified and characterized a novel degrader of ZBTB7A, a known γ-globin repressor.
Study
Design/Methods: Through in silico and phenotypic screens, we discovered SH6, a novel small molecule ZBTB7A degrader. The globin induction effect of SH6 was evaluated using various erythroid cell models, including HUDEP2, sickle cell patient iPSC-derived erythroid cells, and normal CD34 cell-derived erythroid cells. γ-globin induction was assessed by qPCR, flow cytometry, and clinical grade HPLC. Mechanistic studies explored SH6's dependence on the proteasome machinery and the Cereblon E3 ligase system. Synergistic effects with other disease-modifying agents, such as hydroxyurea, decitabine, and pomalidomide, were investigated.
Results/Findings: Treatment with SH6 (0.25uM) led to a 6-fold increase in γ-globin expression in HUDEP2 cells compared to DMSO, surpassing other γ-globin-inducing treatments (Fig 1A-C). Preliminary evidence suggests SH6's potential efficacy in hydroxyurea-unresponsive sickle cell patients, with a near doubling of γ-globin expression observed with flow cytometry (Fig 1D-E). In healthy donor CD34 stem cell-derived erythroid cells, SH6 induced significant functional hemoglobin F without affecting differentiation (11% vs 34% HbF, compared to DMSO) (Fig 1F). SH6 effectively degraded ZBTB7A in a proteasome-dependent manner within 24 hours of treatment (Fig 1G), and its effect is abrogated in a CRBN-E3 ligase knockout HUDEP2 cell line. Synergistic effects with Decitabine were notable, showing a 4-fold increase in mRNA expression compared to SH6 alone and a 9-fold increase compared to Decitabine alone. Additionally, SH6 demonstrated the unique ability to reactivate "primitive" forms of globins, epsilon and zeta globins, suggesting potential relevance for treating alpha and beta thalassemia.
Conclusions: We have identified SH6, a novel small molecule degrader of the ZBTB7A transcriptional repressor, which significantly activates γ- and epsilon globins in relevant erythroid cell line systems. Further research is warranted to elucidate SH6's mechanism, extend treatment to β-thalassemia cell lines and primary patient cells, and conduct IND-enabling animal studies.
