Preliminary Results of a Phase II Study to Determine the Safety of Defibrotide in Children and Adolescents with Sickle Cell Disease-Associated Acute Chest Syndrome (IND 127812)

Background: Sickle cell disease (SCD) is a vasculopathy resulting in recurrent vaso-occlusive crises leading to endothelial dysfunction, chronic end-organ damage, poor quality of life, early mortality and the major curative therapy to date is allogeneic stem cell transplantation (AlloSCT) (Talano/Cairo, EJH, 2015). Acute chest syndrome (ACS) can result in pulmonary hypertension and is the leading cause of morbidity and mortality in patients with SCD (Gladwin et al, NEJM, 2008). ACS accounts for 25% of deaths (Vichinsky et al, Blood, 1997). Clinical definition of ACS is chest pain, fever, cough, dyspnea, and new pulmonary infiltrate on chest radiography. Defibrotide was approved in the US for the treatment of severe sinusoidal obstructive syndrome (SOS) with renal or pulmonary dysfunction following HSCT (Cairo et al, BJH, 2020). Defibrotide primarily targets endothelium in microvascular beds and has anti-inflammatory and anti-coagulant activity, which can treat the underlying pathophysiology of ACS (Falanga et al, Leukemia, 2003 and Scallia et al, Clin Pharm, 1996 and Pescador et al, Vasc Pharm, 2013).

Objective: To determine the safety and toxicity of defibrotide in children, adolescents, and young adults with SCD-associated ACS.

Design/Methods: Patients with SCD aged 2 to 40 years meeting ACS criteria (at least two of the following: fever, chest pain, cough, dyspnea, tachypnea, pulmonary infiltrate on chest imaging, decreased oxygen saturation with or without supplemental oxygen requirements) and eligibility were enrolled within 72 hours of diagnosis after consent was obtained (NCT03805581). Baseline studies comprised of chest radiograph, CT chest angiogram, echocardiography with TRJ velocity and brachial artery reactivity, pulmonary function tests, and biomarkers (IFN-a and -g, TNF-a, IL-6, 8, and 10, sCD163, TSP-1, secretory phospholipase A(2), sVCAM-1, sTNFR1, Ang2, sTei-2, PAI-1, sICAM-1, sP-and sE-selectin, sPECAM-1, VEGF-A, C, D and sVEGFR1 and 2). Defibrotide was administered at 6.25mg/kg IV q6 hours and continued for 7 days or until time of discharge, whichever occurred earlier and patients were followed until day +30 following defibrotide. Dose limiting toxicities include Grade III/IV infusion/allergic reaction or hemorrhage probably or directly related to defibrotide.

Results: We have enrolled thirteen patients aged 3 to 18 years with a gender ratio (M/F) of 4/9. Patients' genotypes are as follows: hemoglobin SS disease in nine patients, hemoglobin SC disease in two patients, and hemoglobin Sb0/+ thalassemia in two patients. Presenting symptoms included fever, chest pain, cough, dyspnea, tachypnea, pulmonary infiltrate on imaging, and hypoxia.Eight patients completed seven days of treatment, one patient received 6 days of treatment, three patients were discharged after three days of treatment, and one patient withdrew due to recurrent fevers unrelated to defibrotide. All but one patient had resolution of fevers prior to end of treatment. Patients required an average of 1.15 days of oxygen support, with one patient requiring high flow nasal cannula, and no patients required mechanical ventilation. There were no adverse events possibly, probably, or directly related to defibrotide. There was no evidence of hemorrhage in any patient despite four patients receiving concomitant ketorolac or ibuprofen. Of the eleven patients who had pulmonary infiltrates on imaging, eight were evaluated on day +30, two had complete resolution of infiltrate, five had improvements, and one had no change. Seven patients did not follow-up for echocardiography or pulmonary function testing and two of those patients were unable to be evaluated at day +30 due to COVID-19.

Discussion: The preliminary data suggest defibrotide is safe and well tolerated in patients with SCD-related ACS. All patients at diagnosis have had baseline studies, which included biomarkers; however, only eight of the thirteen patients have completed all required observations due to poor compliance. After four patients were enrolled and three failed to follow-up, changes to appointment schedules were made with detailed information on all follow-ups. Efforts at improving compliance post therapy are ongoing. Further accrual is needed to determine clinical significance of improvements in cardiac and/or pulmonary function. This study was funded in part by a grant from Jazz Pharmaceuticals.