Phase I Trial of Zileuton CR in Children and Adults With Sickle Cell Disease

Inflammation is now recognized as central to the pathophysiology of sickle cell disease (SCD), and is manifest as leukocytosis, elevated levels of inflammatory cytokines, and activation of monocytes, polymorphonuclear leukocytes (PMN) and endothelial cells. It is present at steady state and is strongly associated with acute events, acute chest and early mortality. Inflammation contributes to endothelial cell dysfunction, potentiates vaso-occlusion, and may also give rise to the airway hyper-reactivity (AHR) that often accompanies SCD. A spectrum of lung disease is seen in this patient population, from AHR and obstructive lung disease in children, to restrictive lung disease and pulmonary vascular remodeling in adults.

Evidence from our laboratory suggests that a specific angiogenic cytokine, Placenta Growth Factor that is produced by hyperplastic erythroid marrow cells and elevated in SCD, contributes to activation of monocytes and endothelial cells by inducing a key leukotriene (LT) synthetic enzyme, 5-Lipoxygenase (5LO). 5LO increases production of LT. LT are among the most potent inflammatory mediators known. LT-B4 is a very potent chemoattractant and activator of PMN and enhances endothelial cell activation, and cysteinyl LT produce airway smooth muscle constriction and inflammation in lung. Elevated LT-B4 and cysteinyl LT, and a high incidence of AHR are observed in patients with SCD. Zileuton (ZL) is a specific inhibitor of 5LO that decreases LT production, and is FDA-approved for treatment of asthma for individuals 12 years of age or older. In the context of SCD, ZL reduced adhesion of PMN and sickle RBC to rat pulmonary vasculature. In vitro data shows that ZL also increased fetal hemoglobin (HbF) production from erythroid cells in vitro, and could have additive/synergistic effects with hydroxyurea (HU). Thus, ZL may be beneficial in SCD by reducing inflammation, mitigating AHR, and increasing HbF.

We hypothesize that inhibition of 5LO activity with ZL will be safe, feasible; will significantly reduce leukotrienes and biomarkers of inflammation, will decrease AHR; and will induce HbF in patients with SCD.

We will test this hypothesis in a Phase I study of ZL in SCD. First, we will establish a safe dose of ZL and its pharmacokinetics in patients with SCD. The secondary objectives will be to determine its pharmacodynamic effects on biological endpoints and compliance to twice daily ZL administration.