Novel Epigenetic Modulators That Promote Fetal Hemoglobin Production for the Prevention of Sickle Cell Disease Related Complications

Background: Sickle cell disease (SCD) is the most common inherited blood disorder in the United States.  Affected patients are at risk of multi-organ complications, significant morbidity and early mortality with an average age at death of 42 and 48 years for men and women, respectively.  Complications include acute and chronic pain due to vascular occlusion, end organ damage, acute chest syndrome and increased risk of sepsis.  SCD is caused by a point mutation on chromosome 11, which codes for the beta chain of adult hemoglobin.  Fetal hemoglobin is not affected by the mutation. Persons with SCD who maintain persistent  fetal hemoglobin demonstrate a decreased number of pain crises and acute chest episodes along with a decreased risk of mortality compared to other patients with SCD.  The only FDA approved fetal hemoglobin inducer, Hydroxyurea, remains highly underutilized due to the risk of complications and unwanted side effects. The discovery of a new agent that promotes re-expression of fetal hemoglobin could revolutionize the care of affected patients by reducing morbidity and mortality. Epigenetic modulation is one possible mechanistic approach to accomplish this goal.  Recent studies with lysine specific demethylase-1 (LSD1) inhibitors, including tranylcypromine (TCP) have shown promising results.  Unfortunately, TCP also affects monoamine oxidase and thus has significant side effects.  Developing a molecule with high specificity, low cross reactivity and negligible toxicity would increase desired effects while reducing unwanted side effects.

Objectives: To discover small-molecule inhibitors of LSD1 that exhibit high selectivity for LSD1 and low in-vivo toxicity that can be used to promote re-expression of fetal hemoglobin in SCD patients.

Design/Methods: Our laboratory at the Medical University of South Carolina has recently described a library of potent, non-toxic LSD1 inhibitors.  Our preliminary results suggest that these inhibitors show promise as fetal hemoglobin inducers.  Using K562 cells, an erythroleukemic cell line known to model in-vivo hemoglobin production, we are screening this library to identify the most effective compounds using Western blotting for the gamma globin chain that is unique to fetal hemoglobin.  Following identification of the most effective compounds in initial screens, we will confirm results with RT-qPCR.  Subsequent studies will involve culturing and treating erythroid progenitor cells from healthy subject samples and from patients with SCD obtained through bone marrow sampling.  HPLC will be used for identification and quantification of hemoglobin chains, including fetal hemoglobin, after ex-vivo treatment with selected compounds.

Results: Initial results from Western blots for fetal hemoglobin  (gamma globin protein) demonstrate that TCP, as well as the experimental compounds C1, 107-3 and 107-15, promote the re-expression of fetal hemoglobin in K562 cells.  Experimental compounds were compared to DMSO as negative control, and hemin (10 mM) and hydroxyurea (200 mM) as positive controls.  All experimental compounds evaluated are significantly less toxic than hydroxyurea, and do not impact cell viability in trypan blue exclusion studies. 

Conclusion: Initial studies show promising results for fetal hemoglobin production using these novel LSD-1 inhibitors.  Viability data is also encouraging. Continued investigation is warranted to further investigate the efficacy of these compounds.