SCT800 Seen as Safe, Effective for Hemophilia A in Phase 3 Trial

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by Margarida Maia |

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SCT800, a replacement therapy containing a man-made form of clotting factor VIII (FVIII), appears to be safe and effective at treating and preventing bleeds in adolescents and adults with severe hemophilia A, a study has found.

The study, “Pharmacokinetic, efficacy and safety evaluation of B-domain-deleted recombinant FVIII (SCT800) for prophylactic treatment in adolescent and adult patients with severe haemophilia A,” was published in the journal Haemophilia by a team of researchers from China.

Treatment with concentrated FVIII — the clotting protein that is missing or defective in people with hemophilia A — remains the mainstay option for managing hemophilia in many countries.

In China, both plasma-derived and recombinant FVIII products are popular. However, recombinant products are costly, which calls for the development of more affordable alternatives.

“Currently, plasma-derivedFVIII (pdFVIII) is the most commonly used FVIII in China. Only a few recombinant FVIII (rFVIII) products (i.e., AdvateXyntha and Kovaltry) are available in China, and impose relatively high cost burdens to patients,” the researchers wrote.

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SCT800, a recombinant FVIII developed in China, could provide a less costly alternative, since it can be produced without requiring “human or animal plasma-derived protein at any stage of the preparation.” Early studies in mice, as well as in humans, suggested that SCT800 is capable of stopping bleeds, safe, and well tolerated.

Researchers reported the findings of an open-label Phase 3 study (NCT03815318) assessing the efficacy, safety, and pharmacological properties of SCT800 as a preventive, or prophylactic, therapy in patients with severe hemophilia A, ages 12 and older, who had previously received treatment with FVIII.

The study enrolled 73 patients (23 adolescents and 50 adults) at 12 centers in China between January 2019 and January 2020. Study participants had a median age of 19 (range: 12–48).

In the three months prior to the study’s start, 55 patients (75%) exclusively received on-demand therapy with a FVIII concentrate to stop bleeds, while 18 (25%) had been on a routine prophylactic regimen to prevent bleeds.

After entering the study, patients received a first injection containing 50 international units of SCT800 per kilogram of body weight (IU/kg). All then received SCT800 at a dose of 25–50 IU/kg, once every other day or three times weekly for 24 weeks (about six months). Of the 73 patients enrolled, 71 (97%) completed the study.

During the study, the therapy’s dose and frequency could be adjusted according to bleed frequency. Five patients adjusted the therapy’s dose, and two of them also adjusted its frequency. Overall, the mean dose of SCT800 used was 34.8 IU/kg.

Annualized bleeding rate, which measures the number of bleeding events occurring within a year, was 2.82 for both adolescents and adults.

Of the 71 patients who completed the study, 32 (45%) did not experience any bleeds. The remaining 39 (55%) had a total of 94 bleeding episodes, most of which (89%) were controlled with one or two injections of SCT800 at a mean dose of 41.9 IU/kg.

The therapy was considered successful; that is, it provided an excellent or good response in 93% of the 94 bleeding episodes. Almost all bleeds (98%) were mild or moderate, and there were no life-threatening episodes.

A total of 39 patients (53%) had at least one treatment-related side effect. The most common were respiratory infections in 17 (23%) patients, high levels of uric acid in the blood (hyperuricemia) in six (8%), cough in five (7%), and common cold (nasopharyngitis) in four (6%).

One patient interrupted prophylactic treatment with SCT800 once due to an upper respiratory tract infection. 

Four minor adverse events were considered to be related to SCT800 in three patients (4%). These included diarrhea in two patients, and somnolence and increased blood pressure, each in one patient. According to researchers, adverse events of SCT800 observed in this study were similar to those of other FVIII replacement therapies, “but lower in frequency.”

No one developed FVIII inhibitors, or neutralizing antibodies against FVIII, and no other safety concerns were identified. Likewise, none of the patients withdrew from the study prematurely due to adverse events.

Among the 18 patients for whom data about pharmacokinetics (the movement of a medicine into, through, and out of the body) were available, SCT800 showed similar profiles both after the first injection and later after repeated dosing.

Researchers also used the hemophilia joint health score (HJHS) and the three-level version of the European Quality of Life with five dimensions (EQ-5D-3L) to evaluate changes in joint health and quality of life. Patients’ life quality was found to improve after 24 weeks of treatment, but no meaningful changes were evident in HJHS scores.

Based on these findings, investigators stated that SCT800 may be “an excellent choice for prophylaxis and treatment” of people with hemophilia A.