A Phase 2 Prospective Randomized Trial of Topical Sodium Nitrite in Patients with Sickle Cell Disease and Leg Ulcers

Background: Leg ulcers are a recurrent, painful and severe complication of sickle cell disease (SCD). Their occurrence significantly affects quality of life and is associated with decreased life expectancy. Although their pathophysiology is poorly defined, multiple studies have confirmed an association with anemia, hemolysis and systemic vasculopathy. We have previously reported in a dose escalation phase 1 study that treatment with topical sodium nitrate is safe and potentially effective, resulting in a significant increase of peri-wound cutaneous blood flow and a dose-dependent decrease in leg ulcer size and pain, with complete healing in three patients who received the highest dose. We now report the results of a prospective, double blinded, randomized study of the safety and efficacy of 10 weeks' treatment with 2% topical sodium nitrite in a placebo-controlled trial (NCT02863068).

Methods: Adults with SCD and leg ulcers were enrolled at 3 US sites and received 2% topical sodium nitrite cream or placebo twice weekly for 10 weeks. A run in period of standard wound care for at least 2 weeks was used to exclude patients who experienced a reduction of wound size by >25% during this time, as such improvement suggests an effect of wound care alone. Close monitoring of vital signs, methemoglobin, and overall health was performed. Ulcer surface area was measured from photos at baseline, after the run in period, at treatment mid-point, and at end of study. Quality of life questionnaires (ASCQ-Me), Brief Pain Inventory (BPI), PROMIS and Beck Depression Inventory (BDI) were administered before initial application and at the end of the study.

Statistical analyses were performed in SAS v9.4 (SAS Systems, Cary, NC). Frequency of categorical variables was assessed using PROC FREQ and median values for continuous variables were calculated using PROC UNIVARIATE. A matched pairs design was employed to test for changes in outcomes at baseline and end of study between treatment groups using a Wilcoxon signed rank test in PROC NPAR1WAY.

Results: We enrolled 23 subjects; 4 had a reduction of ulcer size by > 25% during the run in period and were not eligible for study-defined treatment. One individual withdrew consent. Eighteen individuals completed the study; 9 received placebo and 9 active cream. 12 were female (66.67%) and 15 (83.33%) self-identified as non-Hispanic Black race/ethnicity. Mean age was 44.5 years (range 33-52), and 17 (94.44%) subjects had HbSS genotype. At baseline, median ulcer size was 8.74 cm², the median number of ulcers per subject was 1.5, and the median ulcer duration was 28 months. No grade 3-4 AEs were observed, and there were no SAEs or dose-limiting side-effects. Methemoglobin mean levels were 1.64% at visit 3 and 1.71% at last time recorded, below the pre-specified toxicity level of 7.5%, with no significant increase in methemoglobin among those on study cream compared to placebo (p=0.3). No significant changes in BP were observed, and treatment was well tolerated.

Overall, we did not observe a significant reduction in ulcer size among subjects who received study cream compared to placebo (p=0.28). However, among subjects with younger ulcers (<6 months duration), those on study cream demonstrated a significant reduction in ulcer size compared to those on placebo, with subjects on study cream experiencing a 50% reduction in ulcer size, on average (p=0.05).

There was no change in SCD pain impact or pain frequency, but those on study cream had increased SCD pain but not leg ulcer pain compared to those on placebo (p=0.008). There were no significant changes in sleep, social functioning, or stiffness impact between those on study cream and those on placebo (p>0.05). There were no significant changes in BDI or PROMIS mental health scores between study cream and placebo (p's>0.05).

Conclusions: Our data demonstrate that twice weekly application of 2% topical sodium nitrite is safe and well tolerated. Unfortunately, due in part to Covid-19 pandemic, we were unable to enroll the planned 40 subjects that would have given us adequate statistical power. Despite these limitations, we identified a benefit, with about 50% reduction in ulcer size, in patients with ulcers of < 6 months duration. This is not surprising, as published data show that healing plateaus at about 6 months and becomes very unlikely thereafter. Overall, these data are promising and deserve further exploration.

Minniti:BluebirdBio: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Emmaus Life Science: Consultancy; Fulcrum: Consultancy; Guidepoint: Consultancy. Kato:CSL Behring: Current Employment, Patents & Royalties: named on the patent held by the US DHHS for formulation of topical sodium nitrite, granted Apr 30, 2019. Telen:Novo Nordisk: Research Funding; GBT/Pfizer: Research Funding; CSL Behring: Research Funding.