Phase II Trial of Eprenetapopt (APR-246) in Combination with Azacitidine (AZA) As Maintenance Therapy for TP53 Mutated AML or MDS Following Allogeneic Stem Cell Transplantation (SCT)

Background

Mutations in the tumor suppressor gene TP53 are found in up to 20% of patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). Allogeneic hematopoietic SCT remains the only potentially curative therapy however outcomes remain poor, with a 1-year relapse-free survival (RFS) of ~30% and median overall survival (OS) of ~8 months. Prior data on post-SCT maintenance therapies, including AZA, have failed to demonstrate improved post-SCT outcomes. Eprenetapopt, a small molecule p53 stabilizer, targets cellular redox balance resulting in tumor cell apoptosis and ferroptosis as well as immune modulation of the tumor microenvironment. Pre-clinical data demonstrates synergistic myeloid cell cytotoxicity in vitro and in vivo AML burden reduction when eprenetapopt is combined with AZA. Additionally, the known tolerability of this combination in AML/MDS patients makes it an attractive maintenance strategy.

Methods

This is a multi-center, open label, Phase II clinical trial to assess the safety and efficacy of eprenetapopt in combination with AZA as maintenance therapy after SCT for patients with TP53 mutant AML and MDS. Patients with MDS and AML with a known TP53 mutation were prescreened prior to SCT and protocol eligibility was confirmed post-SCT. Treatment consisted of up to 12 cycles of eprenetapopt 3.7 g/day Days 1-4 with AZA 36 mg/m ²/day IV/SC on Days 1-5 every 28 days.

The primary objectives of this study are to assess RFS and the safety and tolerability of the combination. Additional endpoints include OS, time to progression (TTP), non-relapse mortality (NRM) and cumulative incidence of acute and chronic graft-versus-host disease (GVHD).

Results

The study enrolled a total of 33 patients (19 MDS, 14 AML) for active therapy. Demographics across all patients included median age 65 years (range: 40-74), 64% males, and Karnofsky performance status of ≥ 80 in 79%. The majority (76%) received a reduced intensity conditioning regimen. At initial diagnosis, 97% (32) had TP53 mutations, 9% (3) had >1 TP53 mutation, 82% (27) had complex cytogenetics (>=3), 45% (15) had chromosome (chr) 17, 76% (25) had chr 5, and 45% (15) had chr 7 abnormalities. Among 25 patients with available molecular data from a pre-SCT sample, 22 (88%) patients had a residual detectable TP53 gene mutation, 8 (36%) had > 1 TP53 mutation, and 9 (36%) patients had non-TP53 gene mutations: ASXL1 (2 ), JAK2 (4), DNMT3A (3), IDH2 (2), IDH1 (2), NRAS (1) and SF3B1 (1). As of the data cutoff date of 22 June 2021, patients completed a median of 7 cycles (1,12) of study treatment with 6 patients (18.2%) remaining on study treatment. The primary reasons for study treatment discontinuation among 27 patients, were completion of 12 cycles of treatment (9) and disease relapse (9).

With median duration of RFS follow up of 413 days the median RFS was 368 days [95% CI (233-not evaluable)] and the 1-year RFS was 58%. With median duration of OS follow up of 429 days the median OS was 586 days [95% CI (369-not evaluable)] and 1-year OS 79%.

All-grade treatment emergent adverse events (TEAEs) occurring in ≥20% of patients included nausea (61%), platelet count decreased (49%), vomiting (46%), anemia, dizziness, and white blood cell count decreased (39% each), fatigue (36%), diarrhea and tremor (33% each), cough, neutrophil count decreased, pruritus, and pyrexia (24% each), abdominal pain, constipation, decreased appetite, headache and hypocalcemia (21% each). Grade ≥3 TEAEs in ≥10% of patients were platelet count decreased (36%), white blood cell count decreased (33%), anemia (27%), neutrophil count decreased (24%), thrombocytopenia and hypertension (12% each). SAEs in ≥2 patients were pyrexia (12%), febrile neutropenia and dyspnea (6% each). Two patients (6%) experienced TEAEs leading to discontinuation of study treatment. Acute and chronic GVHD events of any grade were reported in 12% and 30% of patients, respectively.

Conclusions

Post-SCT maintenance therapy with eprenetapopt in combination with AZA was safe and tolerable with favorable results in patients with TP53 mutant MDS and AML, with 9 patients completing 12 cycles of therapy at the data cutoff date and the majority of reported TEAEs comprising known complications of high-risk MDS and AML patients in the post-SCT period. In addition, the observed RFS and OS data are highly encouraging compared to the historical outcomes for this high-risk group of patients with unmet medical need.