Sovleplenib in patients with primary or secondary warm autoimmune haemolytic anaemia: results from phase 2 of a randomised, double-blind, placebo-controlled, phase 2/3 study.

Background: Spleen tyrosine kinase inhibitors are potential treatment options for warm autoimmune haemolytic anaemia. This study aimed to assess the preliminary efficacy and safety of sovleplenib-an oral spleen tyrosine kinase inhibitor-in patients with warm autoimmune haemolytic anaemia in China. Here we report on the phase 2 results.

Methods: This randomised, double-blind, placebo-controlled, phase 2 part from the phase 2/3 study was conducted at 13 centres in China. Eligible patients, aged 18-75 years, with an Eastern Cooperative Oncology Group (ECOG) performance status of no more than 2, had primary or secondary warm autoimmune haemolytic anaemia (stable underlying disease not requiring drug intervention) with no response to previous glucocorticoid treatment, haemoglobin of less than 100 g/L with active haemolysis, and a positive direct antiglobulin test. The study comprised two periods; patients were randomly assigned (3:1) to receive sovleplenib or placebo at 300 mg orally once a day in the 8-week double-blind period. Upon completion, all patients entered an open-label treatment period for at least 16 weeks and received sovleplenib 300 mg once a day until 24 weeks after the last patient was randomly assigned. The primary endpoint for phase 2 of the trial was overall haemoglobin response rate (haemoglobin ≥100 g/L with an increase of ≥20 g/L from baseline at least once, and haemoglobin not affected by rescue therapy, such as red blood cell transfusions, intravenous immunoglobulin, and glucocorticoids) by week 24. Efficacy analyses in the 0-8 week double-blind period included all patients who were randomly assigned, analysed by intention-to-treat. Safety analysis in the double-blind period included patients in the intention-to-treat population who received at least one dose of the study medication. This phase 2/3 study is registered with ClinicalTrials.gov, NCT05535933, and the phase 3 part is ongoing.

Findings: Between Sept 26, 2022, and May 9, 2023, 34 patients were screened and 21 patients (four [19%] male and 17 [81%] female) were enrolled in the study and randomly assigned to receive either sovleplenib (n=16) or placebo (n=5). All 21 patients completed the 0-8-week double-blind treatment and entered the open-label treatment period. The overall haemoglobin response rate was 67% (14 of 21 patients) by week 24, and durable haemoglobin response rate was 48% (ten of 21 patients) by week 24. During the 0-8-week double-blind treatment, 13 (81%) of 16 patients in the sovleplenib group versus five (100%) of five patients taking placebo reported treatment-emergent adverse events (TEAEs), and four (25%) of 16 patients versus four (80%) of five patients reported grade 3 adverse events. Although all 21 patients had a TEAE during the 24-week treatment with sovleplenib, only seven (33%) patients had grade 3 events. The most common grade 3 TEAE was anaemia (four [19%] patients), which was not related to treatment. There were no grade 4 or 5 TEAEs.

Interpretation: Sovleplenib treatment achieved an encouraging overall haemoglobin response in Chinese patients with warm autoimmune haemolytic anaemia and was well tolerated. The phase 3 part of the study (ESLIM-02) is currently ongoing to further substantiate the efficacy and safety of sovleplenib in this setting.

Funding: HUTCHMED.