A Phase I Trial Of Zileuton In Sickle Cell Disease

Sickle cell disease (SCD) is associated with a high prevalence of airway hyperreactivity (AHR) and chronic inflammation at a steady state in the absence of infection or acute sickle events; SCD patients have also been reported to have increased circulating leukotrienes (LT) (Setty et al, 2002; Jennings et al, 2008): both the pro-inflammatory LT-B4 and cysteinyl leukotrienes (cys-LTs; LT-C4, -D4 and -E4), known to promote AHR. We sought to explore the mechanisms of increased AHR in SCD. Five-lipoxygenase (5LO) is a key enzyme in LT-B4 and cysLT synthesis, we have recently reported that expression of 5LO is significantly increased in blood mononuclear cells (MNCs) in patients with SCD (Patel et al 2009). Zileuton is a specific inhibitor of 5LO that decreases LT production, is licensed for asthma and is now available in BID dosing (Zyflo CR, Cornerstone Therapeutics), but has never been tested in patients with SCD. We performed a phase 1 clinical trial to determine the safety and pharmacodynamics (PK) of twice daily administration of ZL (Zyflo CR, the study drug was provided by Cornerstone Therapeutics) in patients with SCD after obtaining an IND from the FDA. The primary objective of this study was to determine a safe and tolerable dose of ZL using a 3x3 dose escalation design of twice daily ZL for 6 weeks, with monitoring of blood counts, serum and urine chemistries, echo, EKG and clinical events. Patients 7-30 years of age with SCD at steady state that were not on hydroxyurea or chronic transfusions were enrolled. A total of 14 subjects were consented and screened for the ZL trial; 4 failed screening and 11 subjects received the study drug; 2 subjects were withdrawn due to acute sickle events. The 1200 mg BID dose that is approved for asthma was well tolerated by 3 patients; the dose was then escalated to 3000 mg/day. We found that 1800 mg alternating with 1200 mg of ZL was a safe and clinically well tolerated dose in 6 patients. No clinically significant changes of any of the clinical/laboratory safety parameters were observed from baseline values that were attributable to ZL. PK, another primary objective of this study was performed using a D-optimal sampling strategy (day 1 through week 6) and data analyzed by nonlinear mixed effects modeling (NONMEM). ZL plasma concentrations were determined by validated LC-MS/MS assay. The Cmax of ZL were 2445 ± 795 ng/ml and 2510 ± 489 ng/ml at 2400 mg/d and 3000 mg/d and the minimum zileuton exposure as measured by predose troughs were 445.0 ± 137.7 ng/ml and 703.7 ± 172.2 ng/ml at 2400 mg/d and 3000 mg/d respectively. PK details will be presented. The secondary objective was to determine the pharmacodynamics (PD) of ZL in patients with SCD. PD end points were 1. CysLT levels before and after ZL administration for 6 weeks, 2. circulating levels of inflammatory biomarkers: sVCAM, sICAM, IL-6, IL-13 and macrophage chemoattractant protein-1 (MCP-1), 3. Methacholine challenge test (MCT) for AHR and 4. fetal hemoglobin. MCT was negative in 5 of 9 of patients; It is to be noted that exclusion of patients on hydroxyurea and chronic transfusions excluded the majority of patients with moderate to severe SCD that predominantly have AHR; 4 patients had a positive MCT, 2 of them became negative after receiving ZL while there was no change in the other 2 patients. LT and inflammatory markers are under analysis. There was no increase in HbF, F cells/F-retics in any of the patients, unlike results reported in vitro in erythroid cultures (Haynes et al, Blood 2004). Our study shows the safety and PK of ZL in SCD and that a higher dose of ZL (than used for asthma) was safely tolerated by SCD patients with good compliance. This phase I trial may form the basis of a phase II/III trial of zileuton in SCD. Clinicaltrial.gov # NCT01136941.