Non-cytotoxic augmentation of fetal hemoglobin and bone marrow reserves

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ABSTRACT SCD patients require erythropoiesis >10-fold over normal to barely sustain hemoglobin levels compatible with life, and dwindling compensatory capacity is a major cause of early death. Therefore, our overall goal in Project 3 is to develop methods of inducing HbF that are non-cytotoxic and preserve or even increase marrow reserves. Biologically undergirding our approach is the `maturational switch': the switch of the shared enhancer from γ- globin (HBG) to the adult β-globin gene (HBB) during non-fetal erythropoiesis, a switch that first requires acquisition of repressive marks at HBG. As examined in Project 1, the repressive marks are catalyzed by druggable enzymes, e.g. DNMT1, and inhibiting these enzymes favors the LCR interaction with HBG, producing significant HbF increases even in patients with severe, HU-refractory SCD. Moreover, as examined in Project 2, treatments that retard erythroid maturation can potentially widen the maturation-stage window for inhibition of repressing enzymes, enabling greater HbF inductions while simultaneously increasing RBC output per progenitor, relieving some of the demands on dwindling and precious marrow stem cell reserve. This highly innovative but rational concept is evaluated clinically for the first time in Aim 1, by combining nicotinamide (vit.B3), which retards hematopoietic maturation but not proliferation, is very well-tolerated, and is a major mediator of the benefits of glutamine supplementation in SCD, with THU-decitabine, a novel orally bioavailable non-cytotoxic drug that targets DNMT1. Aim 2 addresses a more obvious concept, that although any HbF induction is potentially beneficial, achieving maximum protection with HbF ~30% may require combining inhibitors of individual HBG repressing enzymes. The culmination of chromatin remodeling for repression is nucleosome repositioning that physically denies access to the basal transcription machinery. This energetically expensive work is executed by ISWI family enzymes, e.g., CHD4 (Project 1). CHD4 inhibition should hence offer corresponding potency for HbF induction. We have therefore screened for and optimized through structure-aided design a first-in-class CHD4 inhibitor - we will evaluate this inhibitor for HbF inducing potency and drive toward IND-enabling. Aim 1: Conduct a proof-of-concept study of oral nicotinamide (vitamin B3) and oral THU- decitabine, alone and in combination, to treat severe SCD. This proof-of-concept study of combination non- cytotoxic oral therapy to both induce HbF and augment bone marrow reserves will randomize adult SCD patients at risk of early death to nicotinamide or oral THU-decitabine alone. Aim 2: Determine the HbF inducing potency of small molecule CHD4 inhibition in vitro and in vivo, to justify IND-enabling studies. We will employ primary cell ex vivo systems to compare the HbF inducing potency of the novel drug vs established agents, followed by evaluation in SCD mice (Project 1), and finally in non-human primate models (Project 2). Hence, candidate molecular targets for simultaneous induction of HbF and augmentation of bone marrow reserve, identified and validated in Projects 1 & 2, are translated into or toward the clinic by Project 3.