Termination was due to significant challenges associated with study enrollment in a genetic subset of fit participants in the front-line acute myeloid leukemia (AML) setting and other challenges associated with post-COVID impacts.

The primary objective of this study is to evaluate the efficacy of entospletinib (ENTO) compared to placebo when added to chemotherapy in previously untreated nucleophosmin-1 mutated (NPM1-m) acute myeloid leukemia (AML), as defined by the rate of molecularly defined measurable residual disease (MRD).

This is a multi-center, international, double-blind, placebo-controlled study in previously untreated participants with acute myeloid leukemia (AML) harboring nucleophosmin-1 (NPM1) mutations. Upon fulfillment of all eligibility criteria, participants were randomized 1:1 to receive intensive chemotherapy in combination with either the spleen tyrosine kinase (SYK) inhibitor entospletinib (ENTO), or placebo. The study consisted of Screening, Induction, Consolidation, End-of-Treatment, and Long-term Follow-up phases.

Inclusion Criteria:

1. Adults 18 to 74 years with previously untreated de novo acute myeloid leukemia (AML), AML with myelodysplastic syndromes (MDS) features, or therapy-related AML, who were candidates for intensive induction therapy.

2. Nucleophosmin-1 (NPM1)-mutated disease documented in a local or the Sponsor's central testing facility.

   Note: Participants with local test results for nucleophosmin-1 mutated (NPM1-m) (and/or FMS-like tyrosine kinase 3 mutational status) may enroll, provided appropriate samples were sent to the Sponsor's central testing facility for NPM1-m companion diagnostic development.

3. Eastern Cooperative Oncology Group Performance Status (ECOG PS) score of 0, 1, or 2.

4. Adequate hepatic and renal function defined as:

   1. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) < 2.5 times the upper limit of normal (ULN), except those with hepatic involvement by AML, as documented by either computed tomography (CT) or ultrasound, in whom levels of AST and ALT < 5 times ULN are acceptable; total bilirubin < 1.5 times ULN unless elevated due to Gilbert's Disease or hemolysis.
   2. Calculated creatinine clearance > 40 mL/min or serum creatinine < 1.5 times ULN.

5. Prothrombin time (PT), activated partial thromboplastin time (aPTT), and international normalized ratio (INR) ≤ 1.5 x ULN unless receiving therapeutic anticoagulation.

6. Left ventricular ejection fraction ≥ 45% confirmed by echocardiogram (ECHO) or multi-gated acquisition (MUGA) scan.

Exclusion Criteria:

1. Isolated myeloid sarcoma (ie, participants must had peripheral blood and/or bone marrow involvement by AML) or acute promyelocytic leukemia.

2. Concurrent FLT3 mutation (either tyrosine kinase domain or internal tandem duplication).

3. Known central nervous system (CNS) involvement with leukemia.

4. Was a candidate for more intensive treatment than specified in this protocol.

5. Either not a candidate for any anthracycline therapy or a candidate for induction therapy with a higher dose of daunorubicin (eg. 90 mg/m^2).

6. Was a candidate for daily doses of cytarabine > 100 mg/m^2 in Induction Cycle 1.

7. Active infection with hepatitis B, C, or uncontrolled human immunodeficiency virus (HIV).

8. Known active coronavirus disease 2019 (COVID-19) either symptomatic or asymptomatic, as determined by nasopharyngeal swab for severe acute respiratory syndrome (SARS) coronavirus 2 (SARS CoV-2) ribonucleic acid (RNA) or antigen.

   Note: Participants with a history of SARS-CoV-2 nasopharyngeal carriage (either with or without symptoms), who had subsequently tested negative on follow-up nasopharyngeal swab and were without signs or symptoms of COVID-19 might enroll. Participants who were fully vaccinated against SARS-CoV-2 might enroll.

9. Disseminated intravascular coagulation with active bleeding or signs of thrombosis.

10. History of prior allogeneic hematopoietic stem cell transplant or solid organ transplant.

11. Treatment with proton pump inhibitors (PPIs) from 7 days prior to enrollment until 48 hours after completion of entospletinib (ENTO) or placebo.

    Note: PPIs were likely to interfere with ENTO absorption, thus requiring a 7-day washout period prior to the initiation of study medication. For management of acute gastrointestinal bleeding during the study treatment period (such as that related to chemotherapy), short term concurrent use of PPIs was permitted for up to 10 consecutive days. If longer durations of PPI exposure were required, participants should discontinue study medication. Histamine (H2) receptor antagonists and antacids were allowed throughout the study treatment period.

12. Ongoing immunosuppressive therapy, including systemic chemotherapy for treatment of leukemia.

    Note: Participants may not receive AML-directed therapy prior to enrollment other than hydroxyurea or leukapheresis for acute management of hyperleukocytosis.

13. Clinical signs/symptoms of leukostasis that had failed therapy including hydroxyurea and/or leukapheresis of at least 3 days duration.

14. Clinically significant heart disease defined as:

    1. New York Heart Association Class 3 or 4 congestive heart failure,
    2. Acute myocardial infarction ≤ 6 months before enrollment,
    3. Symptomatic cardiac ischemia/unstable angina ≤ 3 months before enrollment,
    4. History of clinically significant arrhythmias (eg, ventricular tachycardia or fibrillation; Torsades de Pointe) including Mobitz type II 2nd degree or 3rd degree heart block without a permanent pacemaker in place.

15. Participants with a corrected congenital long measure between Q wave and T wave in the electrocardiogram (QT) interval (using the Fredericia formula, Fridericia correction of the QT measure [QTcF]) > 480 msec or Long QT Syndrome.

16. Evidence of ongoing, uncontrolled systemic bacterial, fungal, or viral infection at the time of study treatment initiation, including but not limited to persistent fever or positive cultures in the setting of appropriate antimicrobial therapy.

17. Unable to swallow tablets or concurrent disease affecting gastrointestinal function such as, malabsorption syndrome, gastric or small bowel resection, bariatric surgery, inflammatory bowel disease, or bowel obstruction.