Screening Fetal Hemoglobin Inducing Compounds in Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells

Background: Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells-2 (HUDEP-2) cells are an immortalized human CD34+ hematopoietic stem and progenitor cell (HSPC)-derived erythroid precursor cell line that expresses BCL11A and β-globin. HUDEP-1 cells are an immortalized human CD34+ HSPC-derived erythroid precursor cell line that does not express BCL11A, predominantly expresses γ-globin, and exhibits an increase in γ-globin after differentiation. High baseline γ-globin and difficulty in distinguishing between true γ-globin induction and changes in HUDEP-1 differentiation, which increases g-globin, combined with the lack of β-globin expression, make HUDEP-1 cells a suboptimal system in which to study hemoglobin switching. HUDEP-2 cells have been used successfully to demonstrate HbF induction in several gene editing experiments involving deletion of BCL11A enhancer regions and substitution mutations in the γ-globin locus. HUDEP-2 also express very low levels of γ-globin; this has led to the hope that potential HbF inducing compounds can be screened in HUDEP-2 cells, causing them to express significant amounts of γ-globin, and potentially a reduction in β-globin expression, demonstrating hemoglobin switching.

Objectives: Determine if HUDEP-2 cell lines are suitable systems in which to examine pharmacologic hemoglobin switching. We will determine if γ-globin induction can be achieved in HUDEP-2 cells from hydroxyurea, metformin, piceatannol, decitabine, or pomalidomide at doses that induce HbF in human HSPCs and raise γ-globin expression in HUDEP-1 cells.

Methods: We performed drug treatment on differentiated HUDEP-1 andHUDEP-2 cells as well as hematopoietic stem and progenitor cells (HSPCs) from SCD patients with hydroxyurea, metformin, piceatannol, decitabine and pomalidomide at different doses. The effect of the drugs on HUDEP-1 differentiation was determined by measurement of Band3 by quantitative western blot. After 7 days of drug treatment, HbF was measured by western blot and HPLC in HSPCs, and by RT-qPCR (gamma globin expression) and western blot in HUDEP-1 and HUDEP-2.

Results: Hydroxyurea, metformin, piceatannol, decitabine and pomalidomide all significantly increased γ-globin expression in HUDEP-1 cells, and HbF in HSPCs derived from patients with SCD. However, metformin was shown to increase HUDEP-1 differentiation, as measured by a rise in Band 3, which could explain the rise in γ-globin expression. HPLC analysis of the culture of HSPCs derived from patients with SCD showed that drug treatment with 30 µM hydroxyurea, 100 µM Metformin, 25 µM piceatannol or 200 nM decitabine produced a 2.3 fold, 2.1 fold, 3.1 fold, and 2.9 fold increase in HbF respectively. No change was observed in γ-globin expression or HbF in HUDEP-2 cells with any of the 5 drugs tested.

Conclusions: γ-globin is not inducible in HUDEP-2 cells using hydroxyurea, metformin, piceatannol, decitabine and pomalidomide, known HbF inducing drugs that are believed to act through different pathways and mechanisms. It is therefore unlikely that HUDEP-2 cells will be effective in screening drug compounds for HbF induction activity. HUDEP-1 cells do show increased γ -globin levels in response to these agents, but care must be taken to show that the rise in γ-globin is not due to further differentiation of HUDEP-1 cells.