The Phase IIa multi-center, open-label study enrolled 32 subjects and was conducted at 12 US sites. Study patients received 6R-BH4 at 2.5mg/kg, 5mg/kg, 10mg/kg and 20mg/kg for four weeks each in a 16-week dose-escalation study. A total of 21 patients completed the baseline and final assessments.
The primary objective in the study was to evaluate the safety of oral 6R-BH4 administered in escalating doses in patients with sickle cell disease. The secondary objective was to evaluate changes in physiological and biochemical markers of endothelial function which underlie some key aspects of sickle cell disease (SCD). Peripheral arterial tonometry (PAT) scores were measured at the end of each four week dose period and compared to the baseline PAT score for statistical purposes.
Oral administration of 6R-BH4 was associated with an improvement in endothelial dysfunction in sickle cell disease patients. The study showed that endothelial dysfunction, measured using the EndoPAT device to assess PAT, was common in the sickle cell disease patient population.
At baseline, 56% of the patients in the trial had endothelial dysfunction (PAT score less than or equal to 1.67), consistent with prior studies using other methods for measuring endothelial function. Endothelial dysfunction in SCD patients treated with escalating doses of 6R-BH4 showed improvement at week eight (5mg/kg; p=0.042), week 12 (10mg/kg; p=0.003) and week 16 (20mg/kg; p=0.075).
SCD patients with an abnormal PAT scores of less than or equal to 1.67 at baseline demonstrated greater improvement at all dose levels (2.5, 5, 10 and 20mg/kg). The mean endothelial function PAT score improved from the abnormal to the normal range (>1.67) in SCD patients with an abnormal PAT score at baseline. Improvement in endothelial dysfunction appeared to be dose-dependent. 6R-BH4 was well-tolerated in sickle cell disease patients.