Final Results of a Phase 2 Study of Sotatercept (ACE-011) for Anemia of MPN-Associated Myelofibrosis

Abstract Background Anemia is common in patients (pts) with myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF). Furthermore, anemia is an on-target effect of therapeutic Janus kinase 2 (JAK2) inhibition, and is a frequent cause of ruxolitinib (rux) discontinuation (d/c) in clinical practice (Kuykendall, Ann Hematol 2018). Current therapies for anemia of MF (erythropoietin and analogs, danazol, IMiDs®) are unsatisfactory. Sotatercept (ACE-011) is a first-in-class, activin receptor type IIA ligand trap that may improve anemia by sequestering stromal transforming growth factor beta superfamily ligands that suppress terminal erythropoiesis (Iancu-Rubin, Exp Hematol 2013). Methods This is a phase 2, investigator-initiated, open-label, single institution study of sotatercept, administered subcutaneously every 3 weeks, in 2 cohorts of anemic pts (Hgb 10 g/dl on every determination for 12 w or transfusion-dependent (TD) per IWG-MRT criteria (Tefferi, Blood 2013)) with MF: as a single agent, and in combination with a stable dose of rux. Pts on rux must have been on it for ≥6 months with a stable dose for the preceding ≥8 weeks, and receive sotatercept at a dose of 0.75 mg/kg. Monotherapy pts receive either 0.75 or 1 mg/kg of sotatercept. In both cohorts, anemia response is defined as achievement of transfusion independence (TI) in TD pts, or an increase in Hgb level from baseline of ≥1.5 g/dl sustained for ≥12 wks in non-TD pts (Gale, Leuk Res 2011). Pts must be on-study for ≥12 w (84 d) to be response-evaluable. Results A total of 56 pts have been treated; one pt received only 0.3 mg/kg of sotatercept and is not considered further. Thirty four pts received sotatercept alone and 21 in combination with rux. Baseline characteristics appear in Table 1, panel A. Seventeen TD and 17 non-TD pts received sotatercept alone for a median of 11 (3-73) cycles. Sixteen pts received 0.75 mg/kg and 18, 1 mg/kg. Eight of 27 (30%) evaluable pts responded. Of these, 5 were anemia responses; 3 TD pts achieved TI. Six responses occurred at the 0.75 mg/kg dose, and 2 at the 1 mg/kg dose. Median time to response (TTR) was 19 (1-22) days and median duration of response (DOR), 23.3 (3.9-68.4) months. Seven pts (21%) were on-study for 84 d and hence not response-evaluable: 2 because of stem cell transplant (SCT), 2 due to logistical (travel) issues, and 1 each d/ced sotatercept because of hypertension (HTN), unrelated medical problems and pt decision. Two pts continue on study. Reasons for d/c include lack or loss of response (14), progressive MF (6), SCT (4), travel logistics (3), patient decision (2), hypertension (1), unrelated medical complications (1) and transformation to AML (1). The combination cohort comprised 15 non-TD pts and 6 TD pts. Median rux dose at study entry was 10 (5-25) mg bid. Median number of cycles was 25 (2-49). Six of 19 (32%) evaluable pts in the combination cohort responded, all non-TD pts. Median TTR was 14 (6-147) days and median DOR, 18.2 (3.7-56.8) months. Two pts (10%) were on-study for 84 d and hence not response-evaluable, 1 due to SCT and 1 due to loss of insurance. Two pts remain on study. Reasons for d/c include lack or loss of response (8), SCT (4), progressive MF (3), travel logistics (2), loss of insurance (1) and pt decision (1). Several non-response-evaluable pts in both cohorts achieved ≥1.5 g/dl increments in Hgb from baseline that were not sustained for ≥12 w because of early d/c from the study. An additional pt in the combination cohort required a rux dose increase, leading to failure to sustain a ≥1.5 g/dl Hgb improvement for ≥12 w. Across both cohorts, several responding pts required multiple protocol-specified drug holidays because of Hgb levels ≥11.5 g/dl, with resumption of sotatercept once Hgb was 11 g/dl. Sotatercept was well-tolerated (Table 1, panel B). Grade 3 adverse events possibly related to sotatercept were HTN (n=7) and limb (bone/muscle/joint) or back pain (n=2). Conclusions Sotatercept is safe and effective against anemia of MPN-associated MF, both in non-TD and TD pts, with a response rate of 30% when used alone and 32% when used in conjunction with a stable dose of rux. All responses in the rux cohort occurred in non-TD pts. The trial (NCT01712308) has been closed to new pt enrollment. Figure 1 Figure 1. Disclosures Bose: Sierra Oncology: Honoraria; NS Pharma: Research Funding; Astellas: Research Funding; Pfizer: Research Funding; Constellation Pharmaceuticals: Research Funding; Blueprint Medicines: Honoraria, Research Funding; Celgene Corporation: Honoraria, Research Funding; Incyte Corporation: Honoraria, Research Funding; CTI BioPharma: Honoraria, Research Funding; Novartis: Honoraria; BMS: Honoraria, Research Funding; Kartos Therapeutics: Honoraria, Research Funding; Promedior: Research Funding. Pemmaraju: Dan's House of Hope: Membership on an entity's Board of Directors or advisory committees; Stemline Therapeutics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Novartis Pharmaceuticals: Consultancy, Other: Research Support, Research Funding; HemOnc Times/Oncology Times: Membership on an entity's Board of Directors or advisory committees; Cellectis S.A. ADR: Other, Research Funding; Sager Strong Foundation: Other; CareDx, Inc.: Consultancy; Plexxicon: Other, Research Funding; Aptitude Health: Consultancy; DAVA Oncology: Consultancy; Celgene Corporation: Consultancy; MustangBio: Consultancy, Other; Roche Diagnostics: Consultancy; ASH Communications Committee: Membership on an entity's Board of Directors or advisory committees; LFB Biotechnologies: Consultancy; Abbvie Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Samus: Other, Research Funding; Incyte: Consultancy; Daiichi Sankyo, Inc.: Other, Research Funding; ASCO Leukemia Advisory Panel: Membership on an entity's Board of Directors or advisory committees; Springer Science + Business Media: Other; Affymetrix: Consultancy, Research Funding; Protagonist Therapeutics, Inc.: Consultancy; Clearview Healthcare Partners: Consultancy; Blueprint Medicines: Consultancy; Bristol-Myers Squibb Co.: Consultancy; ImmunoGen, Inc: Consultancy; Pacylex Pharmaceuticals: Consultancy. Daver: Trovagene: Consultancy, Research Funding; Trillium: Consultancy, Research Funding; Glycomimetics: Research Funding; Novimmune: Research Funding; FATE Therapeutics: Research Funding; Astellas: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Novartis: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Hanmi: Research Funding; ImmunoGen: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Data Monitoring Committee member; Genentech: Consultancy, Research Funding; Sevier: Consultancy, Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Dava Oncology (Arog): Consultancy; Celgene: Consultancy; Syndax: Consultancy; Shattuck Labs: Consultancy; Agios: Consultancy; Kite Pharmaceuticals: Consultancy; SOBI: Consultancy; STAR Therapeutics: Consultancy; Karyopharm: Research Funding; Newave: Research Funding. Jabbour: Amgen, AbbVie, Spectrum, BMS, Takeda, Pfizer, Adaptive, Genentech: Research Funding. Kadia: BMS: Other: Grant/research support; Amgen: Other: Grant/research support; Aglos: Consultancy; AbbVie: Consultancy, Other: Grant/research support; Novartis: Consultancy; AstraZeneca: Other; Astellas: Other; Genfleet: Other; Ascentage: Other; Jazz: Consultancy; Liberum: Consultancy; Dalichi Sankyo: Consultancy; Genentech: Consultancy, Other: Grant/research support; Cure: Speakers Bureau; Pfizer: Consultancy, Other; Pulmotech: Other; Sanofi-Aventis: Consultancy; Cellonkos: Other. Andreeff: Karyopharm: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Glycomimetics: Consultancy; Syndax: Consultancy; ONO Pharmaceuticals: Research Funding; Novartis, Cancer UK; Leukemia NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Medicxi: Consultancy; AstraZeneca: Research Funding; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Aptose: Consultancy; Breast Cancer Research Foundation: Research Funding; Oxford Biomedica UK: Research Funding; Amgen: Research Funding; Senti-Bio: Consultancy. Cortes: Bristol Myers Squibb, Daiichi Sankyo, Jazz Pharmaceuticals, Astellas, Novartis, Pfizer, Takeda, BioPath Holdings, Incyte: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Sun Pharma: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Bio-Path Holdings, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding. Jain: ADC Therapeutics: Honoraria, Research Funding; Precision Biosciences: Honoraria, Research Funding; Janssen: Honoraria; Fate Therapeutics: Research Funding; Beigene: Honoraria; Cellectis: Honoraria, Research Funding; TG Therapeutics: Honoraria; AstraZeneca: Honoraria, Research Funding; Pfizer: