Abstract
Increased fetal hemoglobin (HbF) levels lessen the severity of symptoms and increase the lifespan of patients with sickle cell disease (SCD). Hydroxyurea (HU), the only drug approved for the treatment of sickle cell disease, increases HbF levels, reduces pain crises, and increases the lifespan of patients. Because HU is not effective in a large proportion of patients, new pharmacological agents that increase HbF levels have long been sought. Recent studies identifying LSD-1 as a repressor of γ-globin expression led to experiments demonstrating that the LSD-1 inhibitor RN-1 increased γ-globin expression in SCD mice. As the arrangement and developmental stage-specific expression pattern of the β-like globin genes is highly conserved between man and baboon, the baboon remains the best predictor of the activity of HbF-inducing agents in man. Therefore, experiments were performed to test the effect of RN-1 on HbF in anemic baboons. Anemia (Hct=20) was induced by repeated phlebotomies for 14 days prior to administration of RN-1. Five anemic baboons were treated with varying doses of RN-1(0.125-2.5 mg/kg/d; 5d; sc). Dose-dependent increases in HbF, F cells, F retics, and γ-globin chain synthesis in reticulocytes were associated with decreased neutrophils and increased monocytes. Globin chain synthesis analysis following RN-1 treatment showed that the 5' Iγ and 3' Vγ-globin genes were expressed in the ratio characteristic of fetal development (5'Iγ/3'Vγ>2) rather than that induced in adults by erythropoietic stress (5'Iγ/3'Vγ<0.5) or decitabine treatment where changes in the Iγ/Vγ ratio are observed but the fetal ratio is not attained. RT-PCR analysis of pre-and post-treatment BM showed that RN-1 increased γ-globin mRNA nearly 5 fold (p<0.05) with no effect on ε-globin mRNA. ChIP analysis of pre- and post-treatment BM erythroid cells showed increased levels of pol II, H3K9ac, H3K4me2 and H3K4me3 associated with the γ-globin but not with the ε- or β-globin promoter and IVS II regions consistent with increased γ-globin transcription. Levels of H3K9me2 were increased at the β-globin promoter and IVSII regions. Bisulfite sequence analysis showed a small decrease in level of DNA methylation of the γ-globin promoter in post-treatment (0.68+0.07% total cytosine) compared to pre-treatment (0.79+0.05%; p<0.05). To investigate whether induction of γ-globin expression was dependent on erythropoietic stress, four normal, non-anemic baboons were treated with varying doses and schedules of RN-1 (0.2-0.5mg/kg/d; 5d/wk; 1-10wks; sc). The effect of RN-1 was measured by analysis of F cells and globin chain synthesis in peripheral blood. The results (Table) show that RN-1 increases γ-globin expression and F cells in normal, non-anemic baboons in a dose-dependent manner. Analysis of globin chain synthesis showed predominant synthesis of the Iγ-globin chain with an Iγ/Vγ ratio exceeding the fetal ratio in all individuals.
Effect of RN-1 in Normal, Non-Anemic Baboons Table.AnimalRN-1 Dose (mg/kg/d)ScheduleGlobin chain synthesis (γ/γ+β)Iγ/Vγ chain synthesisF cells (%)ANC (/μl)Plt(X103/μl)Mono(%)PrePostPrePostNadirNadirPeak85490.55d0.030.714.63NDND191016921.685490.255d0.010.264.47NDND191021914.586980.255d/wk/2 wks0.010.2020.12.09.21210687.986960.2-0.255d/wk/10 wksND0.106.633.526.81440646.1
Neutropenia following RN-1 treatment of anemic baboons (mean ANC nadir=746±156) was reduced in non-anemic animals (2 of 4 baboons >1500; mean ANC nadir=1617±350; p<0.02). Increased monocytes and decreased platelet counts were observed. Differences between anemic and non-anemic baboons may reflect perturbation of hematopoietic differentiation by phlebotomy. We conclude that RN-1 is a powerful in vivo inducer of HbF in both anemic and non-anemic baboons that preferentially increases synthesis of the 5' Iγ-globin gene and recapitulates the fetal pattern of hemoglobin synthesis. Our data predicts that RN-1 treatment will induce clinically relevant levels of HbF in SCD patients, although careful titration of dose may be required to minimize effects on hematopoiesis.
Disclosures
No relevant conflicts of interest to declare.
Absence of functional messenger RNA activity for beta globin chain synthesis in beta 0-thalassemia
