An industry-funded phase II trial has shown that high doses of the experimental drug crizanlizumab significantly reduced the number of dangerous “pain crises” in subjects with sickle cell disease.

The median per-year rate of pain crises was 45.3% lower among those who took the high dose of crizanlizumab, compared with the placebo group (P = .01) More than a third of the subjects who took the high dose reported no pain crises during the treatment phase, more than double the rate among the placebo group.

The trial findings were released at the annual meeting of the American Society of Hematology and published simultaneously in the New England Journal of Medicine (doi: 10.1056/NEJMoa1611770).

The American Society of Hematology estimates that 70,000-100,000 people in the United States have sickle cell anemia and some patients are treated with hydroxyurea (Hydrea) are available. According to background material provided in the trial report, however, hydroxyurea has limited value, and some patients still face the prospect of pain crises which can lead to end-organ damage, and early death.

The SUSTAIN trial focuses on pain crises, also known as vaso-occlusive and sickle cell crises, which can occur without warning when sickle cells block blood flow and decrease oxygen delivery.

Researchers led by Kenneth I. Ataga, MB , of the University of North Carolina, Chapel Hill, recruited 198 subjects who had sickle cell disease and who had experienced 2-10 pain crises related to their condition over the past year. They randomly assigned 67 subjects to receive a low 2.5-mg/kg dose of crizanlizumab (also known as SelG1), 66 to a high 5.0-mg/kg dose, and 65 to a placebo. Crizanlizumab is an antibody against the molecule P-selectin, whose up-regulation in certain cells and platelets is thought to contribute to vaso-occlusion and sickle cell pain crises.

All the doses were administered intravenously 14 times over a year at sites in Brazil, the United States, and Jamaica. Risk groups for sickle cell include people of African and South American descent, among groups.

The first two doses were loading doses given at 2-week intervals, and the rest were given at 4-week intervals.

Subjects were aged 16-63 years; the median age was 29 for the two crizanlizumab groups and 26 for the placebo group. The percentage of black subjects ranged from 90% to 94% in each group, and the percentage of female subjects ranged from 52% to 58%.

Some subjects, but not all, were taking hydroxyurea. If they were taking the drug, they needed to have been on it for at least 6 months prior to the trial, and at least the last 3 months at a steady dose. Those who didn’t take hydroxyurea weren’t allowed to start taking it.

The researchers found that the median number of pain crises per year was 1.63 in the high-dose group, 2.01 in the low-dose group, and 2.98 in the placebo group. That translates to a 45.3% lower rate for the high-dose group than placebo (P = .01) and a 32.6% lower rate for low-dose than placebo (P = .18).

A total of 36% of the subjects in the high-dose group had no pain crises during the treatment phase, compared with 18% and 17% in the low-dose and placebo groups, respectively.

In a per-protocol analysis of 125 subjects, the researchers found similar numbers for median pain crises and no pain crises with one exception: The rate of annual pain crises was only 8.3% lower for the low-dose group than the placebo (P = .13).

Overall, the researchers wrote, the rates of adverse and serious adverse events were “similar” among all the subjects regardless of their randomized group.

Five patients died during the trial: two from the high dose group, one in the low dose group, and two in the placebo group. Among serious adverse events, pyrexia and pneumonia occurred more frequently in at least one of the crizanlizumab groups than in the placebo group, but their levels were low at zero to three cases of each event in the three groups.

The researchers noted that they didn’t detect any antibody response against crizanlizumab. However, “longer follow-up and monitoring are necessary to ensure that late neutralizing antibodies do not emerge that might limit the ability to administer crizanlizumab on a long-term basis.”

The study was funded by Selexys Pharmaceuticals, which received grants from the National Heart, Lung, and Blood Institute and the Food and Drug Administration’s Orphan Products Grant Program. Dr. Ataga reports personal fees from Selexys Pharmaceuticals. The other authors report various disclosures or none. The complete list of disclosures is available at