Cladribine Combined with Homoharringtonine and Cytarabine Achieves a High Remission Rate in Adult Patients with De Novo Acute Myeloid Leukemia, Especially for Adverse-Risk Group: A Prospective, Single Center, Single-Arm, Phase 2 Study

Background: For adult de novo acute myeloid leukemia (AML), the standard 3+7 induction regimen has approximately 60% complete remission (CR) rate. Recently, BCL-2 inhibitor plus intensive chemotherapies as novel induction regimens have shown an above 90% composite complete remission (CRc) rate, however still have limited response effect in an adverse risk group, especially for patients with specific cytogenetic abnormalities such as KMT2A rearrangements, FLT3, RAS, and TP53 mutations. Multiple studies have shown that homoharringtonine (HHT) can target leukemia diseases that have switched their anti-apoptotic dependence from BCL-2 to MCL-1. We recently demonstrated that cladribine (CdA) could eradicate BCL-2 inhibitor-resistant monocytic leukemia stem cells driven by RAS mutants and KMT2A rearrangements. (Pei S, et al. Cancer Discovery. 2023) Together, these clinical and basic findings suggest a rationale for combining CdA with HHT to treat AML patients. In this study, we report the efficacy and safety of a newly designed "CHA" regimen composed of CdA, HHT, and cytarabine (AraC) in adult patients with de novo AML.

Methods: This is a prospective, single-center, single-arm phase 2 trial. Newly diagnosed AML patients aged 18-59 years were enrolled. The diagnosis, risk classification, and response evaluation were determined according to ELN 2022 criteria. All enrolled patients received the CHA regimen: CdA (5mg/m2, days 1-3), HHT (2mg/m2, days 1-5), and AraC (100mg/ m2, days 1-7) administered intravenously. The response was evaluated on day 28 via bone marrow routine and minimal residual disease (MRD) measurement by flow cytometry. The primary endpoint was CRc (CR plus CRi). Secondary endpoints were MRD, overall survival (OS), disease-free survival (DFS), event-free survival (EFS), and adverse events. Bone marrow (BM) samples on day 1 and 7 and peripheral blood (PB) samples on days 1-7 were collected for laboratory flow analysis to monitor the kinetics of leukemia reduction. We also treated primary AML specimens with single, dual, and triple combinations of CdA, HHT, and Ara-C to evaluate their anti-leukemic activity in vitro. Statistical analyses were carried out using SPSS 24.0. Survival curves were prepared using the Kaplan–Meier method. A two-tailed P value <0.05 was considered statistically significant. This trial is registered on ClinicalTrials.gov (NCT05906914).

Results: A total of 33 patients were enrolled from August 1, 2021, to April 15, 2023. The median age was 49 years. 33% (11/33) of patients were at favorable risk, 42% (14/33) were at intermediate risk, and 24% (8/24) were at adverse risk. After one course of CHA induction therapy, the CRc rate was 87% (27 of 31 patients), and the CR rate was 84% (26 of 31 patients). The CR rates in the favorable, intermediate, and adverse-risk groups were 82% (9 of 11 patients), 75% (9 of 12 patients), and 100% (8 of 8 patients), respectively. Notably, six out of six patients with KMT2A rearrangement and ten out of ten patients with RAS mutations achieved MRD-negative CR. The overall MRD negativity was 89% (24 of 27 patients with CRc). In 31 evaluable patients, four patients did not reach CR; three of them held FLT3 mutations. 30-days treatment-related mortality (TRM) was 6% (2 of 33 patients), and both died of sepsis. The median neutrophil recovery time (from the end of chemotherapy to the neutrophil counts ≥0.5×109/L) and platelets recovery time (from the end of chemotherapy to platelets counts ≥20×109/L) were both 11 days. With a median follow-up time of 13 months (IQR: 6-17 months), the one-year OS was 86%, 1-year DFS was 89%, and the 1-year EFS was 76%. Flow cytometry analysis of serially collected PB and BM samples from nine randomly selected patients revealed that an average of 91.0% and 94.7% of leukemia burden was cleared in the PB and BM by day 7, respectively, demonstrating a rapid and effective response induced by CHA. Finally, our in vitro assay demonstrated a synergistic effect of CdA, HHT, and Ara-C on primary AML specimens including three patients with adverse-risk.

Conclusion: We propose the CHA regimen as a novel, effective, and safe chemotherapy regimen for newly diagnosed adult AML patients with remarkable potency in treating adverse-risk group patients, especially those with KMT2A rearrangements and RAS mutations that are otherwise resistant to BCL-2 inhibitor-based therapies, but a limited effect on FLT3 mutated AML patients.