Final Results of a Phase 2 Study of Sotatercept (ACE-011) for Anemia of MPN-Associated Myelofibrosis
Authors: Bose Prithviraj , Masarova Lucia , Pemmaraju Naveen , Bledsoe Sharon D. , Daver Naval , Jabbour Elias J. , Kadia Tapan M. , Estrov Zeev E. , Kornblau Steven M. , Andreeff Michael , Cortes Jorge E. , Jain Nitin , Borthakur Gautam , Alvarado Yesid , Huynh-Lu Julie , Nguyen-Cao Madeleine M. , Richie Mary Ann , Dobbins Mackenzie H. , McCrackin Selene Andrea , Zhou Lingsha , Pierce Sherry A. , Wang Xuemei , Pike Allison M. , Garcia-Manero Guillermo , Kantarjian Hagop , Verstovsek Srdan 
Published: November 2021

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 &lt;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 &lt;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 &lt;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 &lt;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 & Lymphoma Society (LLS), German Research Council; 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: Research Funding; Incyte: Research Funding; Genentech: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Aprea Therapeutics: Research Funding; Adaptive Biotechnologies: Honoraria, Research Funding; Servier: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Pharmacyclics: Research Funding. Borthakur: Ryvu: Research Funding; Protagonist: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Astex: Research Funding; University of Texas MD Anderson Cancer Center: Current Employment; Takeda: Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy; ArgenX: Membership on an entity's Board of Directors or advisory committees. Alvarado: MEI Pharma: Research Funding; Astex Pharmaceuticals: Research Funding; Sun Pharma: Consultancy, Research Funding; Daiichi-Sankyo: Research Funding; FibroGen: Research Funding; BerGenBio: Research Funding; CytomX Therapeutics: Consultancy; Jazz Pharmaceuticals: Research Funding. Huynh-Lu: Incyte Corporation: Speakers Bureau. Nguyen-Cao: Incyte Corporation: Speakers Bureau. Kantarjian: AbbVie: Honoraria, Research Funding; Jazz: Research Funding; Astellas Health: Honoraria; Precision Biosciences: Honoraria; NOVA Research: Honoraria; Taiho Pharmaceutical Canada: Honoraria; Immunogen: Research Funding; Ipsen Pharmaceuticals: Honoraria; Novartis: Honoraria, Research Funding; Ascentage: Research Funding; Daiichi-Sankyo: Research Funding; Aptitude Health: Honoraria; Astra Zeneca: Honoraria; Pfizer: Honoraria, Research Funding; BMS: Research Funding; KAHR Medical Ltd: Honoraria; Amgen: Honoraria, Research Funding. Verstovsek: NS Pharma: Research Funding; Incyte Corporation: Consultancy, Research Funding; Promedior: Research Funding; PharmaEssentia: Research Funding; AstraZeneca: Research Funding; Blueprint Medicines Corp: Research Funding; Genentech: Research Funding; Ital Pharma: Research Funding; Gilead: Research Funding; Roche: Research Funding; Protagonist Therapeutics: Research Funding; Celgene: Consultancy, Research Funding; CTI BioPharma: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy.

OffLabel Disclosure:
Sotatercept is an activin receptor ligand trap. This trial evaluates sotatercept for the treatment of anemia in patients with MPN-associated myelofibrosis.