Sickle cell disease (SCD) is an autosomal recessive blood disorder affecting 50,000-100,000 people in the United States (Brawley et. al. 2008).  In the US, those with SCD have an average mortality in their 40s and aggregate direct hospital costs in excess of $500 million per year (Steiner and Miller 2004).  In addition to the increased mortality of the disease, patients often experience a reduced quality of life, suffering frequent episodes of severe bone pain, vaso-occlusive crises, and hospital admissions, reducing their ability to participate in physical activities, affecting their social and economic advancement and producing a fear of early death (Artiz et al. 2009).
     The only disease-modifying drug is the anti-cancer drug hydroxyurea (HU) that was approved for use in adult patients with SCD in 1998.  A multicenter clinical study showed that approximately 44% of patients on HU therapy had an annual reduction in the rate of painful episodes (Charache et. al. 1995). HU has clearly helped some patients, but not all patients respond to it. HU can be poorly tolerated causing various undesirable side effects, including dose-limiting myelosuppression, and requires frequent monitoring for the life-threatening side effects which have limited its use (Platt 2008).  Research over several decades has shown little progress in the development of additional disease modifying agents. Therefore, safer and more effective therapeutic antisickling agents are needed to treat patients with SCD, particularly children, which is the focus of this grant application.
     In SCD, the altered beta globin protein of hemoglobin (ß^S-globin) has decreased solubility when not bound to oxygen and can self-polymerize forming long rigid deoxy-Hb S fibers inside the red blood cells (RBCs) that result in a rigid sickle shape, hence the name sickle cell disease.  Under conditions of low partial oxygen pressure, a condition found in capillaries, the RBCs sickle and can block capillary blood flow. The deformed RBCs can cause an increase in blood viscosity and the altered RBCs can interact with vascular endothelium causing inflammation and occlusion of larger blood vessels.
     The interruption of blood flow causes infarctions and ischemic necrosis in tissues and organs (Steinberg 1999).  If such occlusions take place in organs such as the brain or lungs, the patients may die. Cumulative ischemic tissue damage and fibrosis can result in chronic pain, and over 50% of SCD patients experience chronic pain (Smith et. al. 2008).  SCD pain can last from a few minutes to days or even weeks requiring hospitalization. Splenic sequestration, common in children, is one of the most serious complications and is second only to infection as a cause of death in infants with SCD. Stroke is one of the most devastating aspects of SCD and is most prevalent in childhood and adolescence, where it is estimated that 11% of SCD patients under the age of 20 will have a stroke (Adams et. al. 1998).  Recently, it was reported that one third of adult SCD patients have pulmonary arterial hypertension (PAH), which may worsen with age and be a prognostic indicator for early death (Gladwin et. al. 2004).
     In an attempt to find new therapeutic agents, various drugs are being tested in clinical trials though to date the results have been disappointing.  Some drugs increase the affinity of Hb for oxygen (Cerami 1978; Arya et. al. 1996), delay or inhibit deoxy-HbS polymerization (Eaton and Hofrichter 1983). Some drugs promote hydration/prevent dehydration of RBCs or increase vasodilation, e.g. nitric oxide (NO) or its inducers (Head et. al 1997), or some drugs  reduce adhesion of the RBCs and white blood cells (WBCs) to the endothelium (Schechter and Gladwin 2002), e.g. a p-selectin receptor blocker. A trial testing a p-selectin inhibitor recently failed.  Some drugs being tested work by inducing the production of more fetal hemoglobin (HbF) similar to the mechanism of hydroxyurea.  Short chain fatty acids (Atweh et. al. 1998), azacitidine (Vidaza) or its deoxy derivative decitibine (Dacogen) have shown some promise in increasing HbF (Gilbert et. al. 2004).  These drugs, however, cause epigenetic changes by altering the acylation and methylation of DNA and may be inappropriate for children as they might disrupt a child’s genetic developmental program.  Increasing the hydration of RBCs with magnesium or blocking the Gardos channel in RBCs has been tried (De Franceschi et. al. 1997; Ataga et. al. 2008) and though increasing the hydration of RBCs is a mechanism of action for reducing sickling, these drugs have not shown a clinical benefit.