COPENHAGEN—Results from a pair of phase 2 trials suggest luspatercept can produce erythroid responses and enable transfusion independence in patients with lower-risk myelodysplastic syndromes (MDS).
In a 3-month base study, 51% of patients treated with luspatercept had an erythroid response, and 35% achieved transfusion independence.
In an ongoing extension study, 81% of luspatercept-treated patients have had an erythroid response, and 50% have achieved transfusion independence.
The majority of adverse events in both trials were grade 1 and 2.
Uwe Platzbecker, MD, of the University Hospital in Dresden, Germany, presented these results at the 21st Congress of the European Hematology Association (abstract S131*). The studies were sponsored by Acceleron Pharma, Inc.
Luspatercept (formerly ACE-536) is a modified activin receptor type IIB fusion protein that increases red blood cell (RBC) levels by targeting molecules in the TGF-β superfamily. Acceleron and Celgene are developing luspatercept to treat anemia in patients with rare blood disorders.
The phase 2 base study was a dose-escalation trial in which MDS patients received luspatercept for 3 months. In the ongoing extension study, patients from the base study are receiving luspatercept for an additional 24 months.
In both studies, patients with high transfusion burden (≥4 RBC units/8 weeks) and those with low transfusion burden (<4 RBC units/8 weeks) received luspatercept once every 3 weeks.
Base study
This study included 58 patients with a median age of 71.5 (range, 27-90). Their median time since diagnosis was 2.4 years (range, 0-14). Seventeen percent of patients had prior lenalidomide treatment, and 66% had previously received erythropoiesis-stimulating agents (ESAs).
In patients with low transfusion burden (n=19), the median hemoglobin at baseline was 8.7 g/dL (range, 6.4-10.1). In patients with high transfusion burden (n=39), the median number of RBC units transfused per 8 weeks was 6 (range, 4-18).
Patients received luspatercept subcutaneously every 3 weeks for up to 5 doses. The study included 7 dose-escalation cohorts (n=27, 0.125 to 1.75 mg/kg) and an expansion cohort (n=31, 1.0 to 1.75 mg/kg).
The primary outcome measure was the proportion of patients who had an erythroid response. In non-transfusion-dependent patients, an erythroid response was defined as a hemoglobin increase of at least 1.5 g/dL from baseline for at least 14 days.
In transfusion-dependent patients, an erythroid response was defined as a reduction of at least 4 RBC units transfused or a reduction of at least 50% of RBC units transfused compared to pretreatment.
Fifty-one percent (25/49) of patients treated at the higher dose levels had an erythroid response. And 35% (14/40) of transfused patients treated at the higher dose levels were transfusion independent for at least 8 weeks.
Extension study
This study includes 32 patients with a median age of 71.5 (range, 29-90). Their median time since diagnosis was 2.9 years (range, 0-14). Nineteen percent of patients had prior lenalidomide treatment, and 59% had previously received ESAs.
In patients with low transfusion burden (n=13), the median hemoglobin at baseline was 8.5 g/dL (range, 6.4-10.1). In patients with high transfusion burden (n=19), the median number of RBC units transfused per 8 weeks was 6 (range, 4-14).
In this ongoing study, patients are receiving luspatercept (1.0 to 1.75 mg/kg) subcutaneously every 3 weeks for an additional 24 months.
At last follow-up (March 4, 2016), 81% (26/32) of patients had an erythroid response. And 50% (11/22) of patients who were transfused prior to study initiation achieved transfusion independence for at least 8 weeks (range, 9-80+ weeks).
Dr Platzbecker noted that, in both studies, erythroid responses were observed whether or not patients previously received ESAs and regardless of patients’ baseline erythropoietin levels.
Safety
There were three grade 3 adverse events that were possibly or probably related to luspatercept—an increase in blast cell count, myalgia, and worsening of general condition.
Adverse events that were possibly or probably related to luspatercept and occurred in at least 2 patients were fatigue (7%, n=4), bone pain (5%, n=3), diarrhea (5%, n=3), myalgia (5%, n=3), headache (3%, n=2), hypertension (3%, n=2), and injection site erythema (3%, n=2).
Dr Platzbecker said luspatercept was generally safe and well-tolerated in these studies. And the results of these trials supported the initiation of a phase 3 study (MEDALIST, NCT02631070) in patients with lower-risk MDS.
*Data in the abstract differ from data presented at the meeting.