Sickle cell disease (SCD) is a genetic blood disorder affecting approximately 100,000 people in the United States, 90% of whom are African American. This disorder causes abnormal hemoglobin production due to defects in the beta-globin protein. As a result, oxygen transport by erythrocytes (a type of erythroid cell) is hindered, leading to severe symptoms and complications.

Current treatments for this disorder have limited effectiveness and/or accessibility and often have side effects. Recent studies, however, suggest that fetal hemoglobin (HbF) can compensate for the defective adult hemoglobin in SCD patients. HbF is naturally inhibited throughout adulthood by several transcription factors, including ZBTB7A. While transcription factors have historically been deemed “undruggable,” new advancements in therapeutic modalities, like molecular glue degraders, have spurred interest in targeting them.

We previously identified and characterized SH6, a novel small molecule degrader, to induce gamma-globin (a component of HbF) through ZBTB7A degradation. It is still unclear, though, if SH6 is as effective as other gamma-globin inducers (e.g., thalidomide, decitabine, and hydroxyurea) or if SH6’s action can be amplified with them.

HUDEP-2 cells were treated with 0.05%-0.2% DMSO, pomalidomide (an analog of thalidomide), decitabine, hydroxyurea, SH6, or SH6 with decitabine or pomalidomide during their 5-day long differentiation phase. qPCR was then conducted to measure gamma-globin mRNA expression. HUDEP-2 cells without a combination treatment were also accessed via flow cytometry for gamma-globin protein production. Singlet cells were selected based on FSC/SSC, while CD235+ bright differentiated erythroid cells were gated.

SH6 had a stronger gamma globin induction effect on both mRNA and protein levels than other non-combination treatments. Synergistic effects were also seen between SH6 and decitabine, with mRNA gamma-globin expression increasing 4-fold compared to SH6 alone and 9-fold compared to decitabine alone.

So, although some gamma-globin inducers are available in the market or are in clinical trials, they are less effective than SH6 in HUDEP-2 cells. However, HUDEP-2 cells differentiate into normal erythrocytes and thus are not representative of erythrocytes found in SCD patients. SH6-mediated gamma-globin induction would need further investigation using SCD patient-derived iPSCs or CD34+ cells to ensure SH6’s efficacy in SCD physiological conditions. Despite the limited realm within which it has been studied, SH6 shows promising pre-clinical results as a potential therapy for sickle cell disease.