New treatment regimen for acute megakaryoblastic leukemia with BCR-ABL positive: case report and literature review

Acute megakaryocytic leukemia (AMKL) is a rare type of acute myeloid leukemia (AML), which is characterized by its effect on megakaryocytes in bone marrow. Despite standard doses of anthracycline plus cytarabine based regimen, AMKL is notorious for its poor prognosis. With the continuous development of targeted drugs, the choice of chemotherapy regimens for AML patients has been gradually enriched. However, as far as we known, there is little data with this regimen in AMKL with decitabine and Bcl-2 inhibitor combined with imatinib. Herein, we reported the first case of adult AMKL with BCR-ABL positive successfully treated with decitabine and venetoclax combined with imatinib.

First reported case of acute megakaryoblastic leukemia successfully treated with decitabine and venetoclax combined with imatinib

Acute megakaryocytic leukemia (AMKL) is a rare type of acute myeloid leukemia (AML), which is characterized by its effect on megakaryocytes in bone marrow. Despite standard doses of anthracycline plus cytarabine based regimen, AMKL is notorious for its poor prognosis. With the continuous development of targeted drugs, the choice of chemotherapy regimens for AML patients has been gradually enriched. However, as far as we known, there is little data with this regimen in AMKL with decitabine and Bcl-2 inhibitor combined with imatinib. Herein, we reported the first case of adult AMKL with BCR-ABL positive successfully treated with decitabine and venetoclax combined with imatinib.

Acute Megakaryocytic Leukemia with or Without Acquired Trisomy 21 in 15 Pediatric Patients

The knowledge of clinical characteristics and prognosis of pediatric acute megakaryocytic leukemia (AMKL) with or without acquired +21 was limited. We reported 15 AMKL pediatric patients without Down Syndrome (four cases with acquired +21 and 11 cases without acquired +21) with the clinical manifestations, laboratory data, and prognosis. The clinical features and laboratory data between patients with acquired +21 and patients without acquired +21 are similar. As for prognosis, three of the 11 cases without acquired +21 obtained complete remission (CR) after 1st induction. The median follow-up time of the 11 cases was 9 months. Among four cases with acquired +21, one case gave up treatment during 1st induction, one obtained CR after 1st induction and was still alive after 49 months of follow-up. One case obtained CR after 2nd induction and was still alive for 15 months of follow-up after bone marrow transplantation, the other patient was planning for allogeneic hematopoietic stem cell transplantation (HSCT) without CR. The median follow-up time of the four cases was 12 months. None relapsed in our study. In conclusion, acquired trisomy 21 may not be an indicator for poor prognosis. Cytogenetics analysis can help us for diagnosis stratification, prognostic judgment and individualized treatment of AMKL.

A Monocentric Clinical Observation of Haploidientical Transplantation in 27 Patients with Acute Megakaryocytic Leukemia

Background Acute Megakaryocytic Leukemia (AMKL) accounts for approximately 10% of childhood AML and 1% of adult AML cases. Although AMKL with Down syndrome has a good prognosis, the prognosis for non-DS-AMKL is quite poor with a 3-years survival rate of less than 40%. At present, only allogeneic HSCT is curative. In our study, we followed 27 patients with AMKL who received a modified Bu/Cy/Mel protocol and underwent hematopoietic stem cell transplantation. The patients were then followed up with monocentric clinical observation. Methods From August 2015 to July 2020, 27 AMKL patients (14 males, 13 females, all non-Down-AMKL) with a median age of 2 years (range: 1-9 years) were continuously treated in our hospital (Hebei Yanda Lu Daopei Hospital) including 18 cases of chromosome abnormality including 3 cases of CBFA2T3/GLIS2 gene fusion (11.1%). Gene mutation included WT1(8), EVI1(5), JAK2(5): 18.51%, TET2(4), ASXL1(4), PTPN11(4): 14.81%, GATA1(2), GATA2(2): 7.4%. Bone marrow status before transplantation: 19 complete remission (CR) cases, 3 partial response (PR) cases, and 5 no response (NR) cases. There were 24 haploidentical transplants (including one patient going through 3 transplants), one transplant from a HLA-identical sibling donor and two from matched unrelated donors. Source of donor stem cells: parents in 23 cases, brothers in 2 cases, non-blood relationship in 2 cases, and none from offspring. HLA matching between the donor and recipient: 21 cases with HLA 5/10, 6 cases with ≥HLA 6/10. Haplo stem cells all came from BM+PBSC, with a median MNC input of 20.32x108/kg (10.1-26.7), CD34+ 11.68106/kg (4.05-22.44), and CD3+ 4.66x108/kg (2.11-11.29). Pre-treatment protocol: 27 patients received a modified Bu/Cy/Mel and were treated with graft-versus-host disease (GVHD) to prevent CsA+MMF+sMTX. Results During a median follow-up period of 10 months (range: 2-48 months), the 27 patients remained alive, with a median of +13 days (range: 9-21 days) to leukocyte transplantation and a median of +9 days (range: 4-38 days) to platelet transplantation. One month following transplantation, the bone marrow of all patients was 100% donor type. The overall survival (OS) rate was 63.0%, event-free survival (EFS) was 59.3%. OS was 84.2%, 33.3%, and 0% in the CR, PR, and NR groups, respectively (P<0.001). There were 7 cases of relapse and 10 deaths, among which 4 were caused by GVHD and 5 due to relapse. Incidence of acute GVHD (aGVHD) was 59.25% Grade I-IV and 18.51% Grade III-IV. Incidence of chronic GVHD (cGVHD) was 56%, with cystitis accounting for 14.81% of cases, 29.62% cytomegalovirus (CMV), 3.7% EBV, 0% thrombotic microangiopathy (TMA) and 18.51% infection. Conclusion For high-risk AMKL patients with poor long-term prognosis, the application of a modified Bu/Cy/Mel pretreatment significantly improves the efficacy of haploid transplantation without increasing pretreat-related death. For non-Down syndrome AMKL, we conclude that it is feasible to perform hematopoietic stem cell transplantation in CR status patients. Additional studies and multicenter and large-scale clinical studies with long-term follow-up are still needed to confirm these results. Disclosures No relevant conflicts of interest to declare.

CBFA2T3-GLIS2 Fusion Gene Cause Dismal Clinical Course in Acute Megakaryocytic Leukemia of Down Syndrome

[Introduction] Acute megakaryocytic leukemia of Down syndrome (DS-AMKL) is characterized by excellent outcome with chemotherapy in contrast to non-Down syndrome-related AMKL (non-DS-AMKL). DS-AMKL and non-DS-AMKL have distinct genetic features which may underlie their different clinical characteristics. DS-AMKL is initiated by a GATA1 mutation in the transient abnormal myelopoiesis (TAM) phase and developed with further mutations of other regulators, while non-DS-AMKL is a heterogeneous group which occasionally carry chimeric oncogenes. CBFA2T3-GLIS2 fusion gene is identified in about 30% of children with non-DS-AMKL, and reported as a strong poor prognostic factor in pediatric AMKL. However, CBFA2T3-GLIS2 has never been reported in DS-AMKL and adult AMKL patients. We performed genomic analysis of DS-AMKL including atypical case with difficult clinical course. This is the first report of DS-AMKL harboring the CBFA2T3-GLIS2 fusion gene. [Case] The patient is a 1-year-old female of DS-AMKL with no prior episode of TAM. G-banding analysis revealed the karyotype both of the leukemic cells and normal tissue sample; 47, XX, +21. Chimeric genes of AML1-MTG8, CBFB-MYH, DEK-CAN, MLL-LTG4, MLL-LTG9, MLL-ENL and abnormalities of KIT and FLT3 were not detected. The chemotherapy according to the Japanese Pediatric Leukemia / Lymphoma Study Group AML-D05 protocol, gemtuzumab ozogamicin, IDA-FLAG regimen (idarubicin, fludarabine, cytarabine, filgrastim) and clofarabine-based regimen were tried, but all of them failed to achieve complete remission (CR). She underwent umbilical cord blood transplantation and relapsed on day 35 after transplantation. Once she showed a response to azacitidine, but finally she died on day 293 after transplantation. [Materials and Methods] We performed whole transcriptome sequencing (RNAseq), SNP array analysis, mutational analysis of GATA1 in 6 DS-AMKL samples, which included this refractory sample and five DS-AMKL samples with GATA1 mutations. To analyze gene expression profiling, we applied the hierarchical clustering method and principal component analysis. [Results] RNA sequencing analysis identified a fusion gene involving exon 10 of CBFA2T3 and exon 2 of GLIS2 gene in this refractory sample. This fusion gene was a result of a cryptic inversion on chromosome 16 and the in-frame fusion of both genes. The fusion transcript was validated by reverse transcription-polymerase chain reaction (RT-PCR) followed by Sanger sequencing. Though SNP array analysis confirmed 21 trisomy, it did not identify other copy number aberrations. PCR analysis did not detect GATA1 mutation in this refractory sample, which can be identified in other DS-AMKL samples. Expression analysis elucidated DS-AMKL with CBFA2T3-GLIS2 fusion had distinct expression profile from DS-AMKL with GATA1 mutations. [Discussion] CBFA2T3-GLIS2 fusion is the most common chimeric oncogene identified in non-DS-AMKL children, but has never been detected in DS-AMKL patients. Patients with non-DS-AMKL, especially holding CBFA2T3-GLIS2 fusion gene, have poorer outcomes than DS-AMKL. DS-AMKL patients generally have GATA1 mutations, show high sensitivity to chemotherapy, and can be treated with less intensive chemotherapy. However, our case had no GATA1 mutation and could not achieve CR despite intensive chemotherapy and transplantation. Thus, it is suggested this fusion gene caused the resistance to chemotherapies including hematopoietic stem cell transplantation in our case. Therefore, our case suggests patients with DS-AMKL should be surveyed genomic investigations including RNAseq and mutational analysis of GATA1 to identify their molecular biological subtypes before treatments are initiated. In case that fusion genes are detected in DS-AMKL patients, they must undergo highly intense chemotherapies, looking ahead to transplantation from the beginning of the treatment. Moreover, in case of harboring CBFA2T3-GLIS2 fusion gene, some potential therapies have been proposed, so that efficacy of such new therapies should be validated in a cell line-derived xenograft or patient-derived xenograft model. [Conclusion] DS-AMKL is generally known to show superior outcome, but DS-AMKL without GATA1 mutation and with CBFA2T3-GLIS2 fusion gene shows resistance to chemotherapies. For DS-AMKL patients, it is desirable to perform genomic analysis including RNAseq before chemotherapy. Disclosures No relevant conflicts of interest to declare.

AB8939, a Microtubule-Destabilizing Agent with Potential to Overcome Multidrug Resistance, Is Active across the Range (M0-M7) of Acute Myeloid Leukemia Subtypes

Compound AB8939 is a structurally novel, small chemical molecule, synthesized tubulin inhibitor that can circumvent two of the major resistance mechanisms in acute myeloid leukemia (AML), namely P-glycoprotein (Pgp) and myeloperoxidase (MPO) mediated resistance, thereby conferring an important advantage over traditional tubulin inhibitors. A series of ex vivo and in vivo studies provide proof-of-concept that AB8939 has broad anti-proliferative activity across the breath of acute myeloid leukemia (AML) subtypes, i.e. M0 through M7 of the French-American-British AML classification. Acute myeloid leukemia blasts were isolated from patients' peripheral blood and/or bone marrow samples, collected either at the time of diagnosis or following relapse, and also from patient derived xenograft (PDX) models. After purification, mononuclear cells were treated for 48 hours with various concentrations of AB8939 or cytarabine (Ara-C) and analyzed in a cell proliferation/viability assay. AB8939 produced a strong anti-proliferative action against blasts isolated from AML patients with a majority of IC50 values ranging from 1.4 nM to 1.0 µM. Two-thirds of AML patients had nanomolar sensitivity to AB8939 (IC50 ≤ 500 nM), while 44% where very sensitive (IC50 ≤ 100 nM) and 11% were highly sensitive (IC50 ≤ 10 nM). The potential of AB8939 to overcome Ara-C-resistance was also evident with 66% of Ara-C-resistant blasts (i.e. IC50 >5 µM) being sensitive to AB8939. Notably, AB8939 demonstrated activity across the entire spectrum of AML subtypes, according to the French-American-British (FAB) AML classification, with an IC50 of < 50 nM in M0, M1, M4, M5 and M6 subtypes, corresponding to over 90% of the AML patient population. A slightly lower sensitivity was observed for the M3 subtype (IC50 = 1.25 µM). Additionally, potent AB8939 activity was also seen in Ara-C-insensitive biphenotypic and mixed-phenotype acute leukemia samples. All FAB categories other than M7 were tested in the abovementioned ex vivo assessment. Acute megakaryocytic leukemia (FAB AML subtype M7) is a rare form of adult AML, accounting for only 1% of cases, and is associated with resistance to standard treatment and poor prognosis. The effect of AB8939 in this subtype was assessed in vivo using an AMKL26 model, an NSG mouse model based on cells isolated from a patient with an aggressive acute megakaryocytic leukemia presenting the ETO2-GLIS2 fusion oncogene. Following post graft detection of blasts, single agent AB8939 was administered intravenously at a dose of 2 mg/kg for three consecutive days per week (3 ON / 4 OFF) for 2 weeks and then at 5 mg/kg for three consecutive days per week (3 ON / 4 OFF) for 1 week. At the end of the 3-week treatment period, blast detection in bone marrow was performed via bioluminescence imaging with comparison to vehicle-treated controls. As seen in the figure below, single agent AB8939 showed strong anti-leukemic activity in this AMKL26 mouse model as evidenced by the near eradication of blasts. No blasts could be detected in 6 out of 8 mice treated with AB8939. At the described dosing schedule, AB8939 was well-tolerated with no toxicity-related deaths and no impact on animal body weight or behavior. These findings provide preclinical proof of concept for the development of AB8939 as a next-generation tubulin inhibitor for AML, in particular for poor-prognosis AML subsets and relapse/refractory AML; i.e. patients that currently have very limited therapeutic options and represent the highest unmet medical need. Disclosures Goubard: AB Science: Employment. Humbert:AB Science: Employment. Mansfield:AB Science: Employment, Patents & Royalties. Hermine:AB Science: Membership on an entity's Board of Directors or advisory committees. AB8939 Study Group:AB Science: Consultancy, Employment.