Longitudinal Safety of Luspatercept in the Treatment of Anemia in Patients with Myelofibrosis: Results from the ACE-536-MF-001 Study

Abstract

Introduction Luspatercept (LUSPA) is approved for the treatment of anemia in some adults with β-thalassemia or myelodysplastic syndrome who require red blood cell transfusion and has a well characterized safety profile for these indications. The primary readout from the phase 2 ACE-536-MF-001 study (NCT03194542) demonstrated manageable safety and promising efficacy of LUSPA for treatment of myelofibrosis (MF)-related anemia with 19.0%-31.6% of patients (pts) achieving transfusion independence (defined as 84 consecutive days transfusion free), and 18.2%-21.4% of non-transfusion-dependent (NTD) pts achieving anemia response (defined as 84 consecutive days ≥ 1.5 g/dL hemoglobin increase from baseline without transfusion) in the entire treatment period (Gerds ASCO 2023 7016). To characterize further the safety profile of LUSPA in MF and provide data on adverse event (AE) management, we present a detailed longitudinal safety analysis of the MF-001 study. Methods Pts were enrolled into 4 cohorts based on transfusion dependence (TD) and stable ruxolitinib (RUX) treatment - cohort 1: NTD, no RUX; cohort 2: TD, no RUX; cohort 3A: NTD, RUX; cohort 3B: TD, RUX. All pts received LUSPA 1.0 mg/kg subcutaneously with titration up to 1.75 mg/kg in 21-day cycles; the starting dose was 1.33 mg/kg in the cohort 3B expansion group. Response was assessed at day 169 (24 weeks), with treatment extended for pts showing clinical benefit. The primary endpoint was anemia response; AEs alongside LUSPA and RUX dosing were also assessed. On dosing days, seated blood pressure was assessed prior to LUSPA administration. In the case of ≥ grade 3 hypertension (systolic ≥ 160 mmHg, diastolic ≥ 100 mmHg), dosing was delayed until hypertension had resolved to ≤ grade 1 or baseline, followed by dose reduction by 1 dose level. If ≥ 2 dose reductions were implemented due to any suspected treatment-related AE (TRAE), LUSPA was discontinued. Results In the safety population (N = 95; cohort 1, n = 22; cohort 2, n = 14; cohort 3A, n = 21; cohort 3B, n = 38), the most frequently used prior medications for anemia treatment were erythropoiesis-stimulating agents (23.2%, most frequently epoetin alfa [14.7%]), followed by danazol (11.6%), lenalidomide (2.1%), and thalidomide (1.1%). Prior history of hypertension was recorded in 50.5% of pts. Median follow-up duration was 546 days. A total of 47.4% of pts had ≥ 1 TRAE; the most common were hypertension (17.9%), bone pain (7.4%), and diarrhea (6.3%). Incidence of treatment-related grade ≥ 3 diarrhea was low (2.1%). Overall, 13.7% of pts received concomitant antidiarrheals. LUSPA was discontinued in 9 pts due to AEs; 1 event of cerebral toxoplasmosis was considered treatment related by the investigator. Among pts receiving RUX (cohorts 3A/3B), hypertension was the most frequently occurring grade ≥ 3 TRAE ( Table 1) and 5 pts had LUSPA dose modifications related to hypertension events; considered related to LUSPA in 4 pts ( Table 2). In contrast, among pts not receiving RUX (cohorts 1/2), no pts experienced grade ≥ 3 hypertension events. Hypertension was manageable with clinical intervention; during the study the most frequent concomitant medications for hypertension were angiotensin-converting enzyme inhibitors (26.3%), beta-blocking agents (selective, 23.2%; non-selective, 3.2%), and angiotensin II receptor blockers (alone, 20.0%; plus diuretics, 5.3%). Among NTD pts (cohort 3A), there were no changes in RUX dose. Among TD pts (cohort 3B), 25 (65.8%) pts maintained their RUX dose and 6 (15.8%) pts had ≥ 1 dose increase. Overall, 9 deaths occurred during treatment; none were considered treatment related. Causes of death were pneumonia, septic shock, intracranial hemorrhage, ischemic stroke, organ dysfunction, post-procedural hemorrhage, myelofibrosis, renal failure, and pneumonitis (n = 1 each). Conclusions The safety profile of LUSPA in the ACE-536-MF-001 study was consistent with previous studies in other indications, and AEs were mostly low grade. In addition to benefits in anemia, the safety profile of LUSPA allowed most pts receiving RUX to maintain or increase their RUX dose, supporting maintenance of Janus kinase inhibitor therapy for adequate disease control of MF. Study support: Bristol Myers Squibb.