Targeted Therapy of FLT3 in Treatment of AML-Current Status and Future Directions

Simvastatin Preferentially Targets FLT3/ITD Acute Myeloid Leukemia by Inhibiting MEK/ERK and p38-MAPK Signaling Pathways

BACKGROUND

The FLT3/ITD mutation exists in many acute myeloid leukemia (AML) patients and is related to the poor prognosis of patients. In this study, we attempted to evaluate the antitumor activity of simvastatin, a member of the statin class of drugs, in vitro and in vivo models of FLT3/ITD AML and to identify the potential mechanisms.

METHODS

Cell Counting Kit-8 (CCK-8) and Annexin V/propidium iodide (PI) staining kits were used to detect cell viability and apoptosis, respectively. Subsequently, Western blot and rescue experiment were applied to explore the potential molecular mechanism. In vivo anti-leukemia activity of simvastatin was evaluated in xenograft mouse models.

RESULTS

In vitro experiments revealed that simvastatin inhibited AML progression in a dose- and time-dependent manner, while in vivo experiments showed that simvastatin significantly reduced tumor burden in FLT3/ITD xenograft mouse models. After simvastatin treatment of FLT3/ITD AML cells, intracellular Rap1 was downregulated and the phosphorylation levels of its downstream targets MEK, ERK and p38 were significantly inhibited. The rescue experiment showed that mevalonate, an intermediate product of the metabolic pathway of mevalonate, and its downstream geranylgeranyl pyrophosphate (GGPP) played a key role in this process. Finally, we demonstrate that simvastatin can induce apoptosis of primary AML cells, while having no effect on peripheral blood mononuclear cells from normal donors.

CONCLUSIONS

Simvastatin can selectively and effectively eradicate FLT3/ITD AML cells in vitro and in vivo, and its mechanism may be related to the disruption of the HMG-CoA reductase pathway and the downregulation of the MEK/ERK and p38-MAPK signaling pathways.

Melatonin enhances sorafenib-induced cytotoxicity in FLT3-ITD acute myeloid leukemia cells by redox modification

Acute myeloid leukemia (AML) with an internal tandem duplication in Fms-related tyrosine kinase 3 (FLT3-ITD) is identified as a subgroup with poor outcome and intrinsic resistance to chemotherapy and therefore urgent need for development of novel therapeutic strategies. Methods: The antitumor effects of melatonin alone or combined with sorafenib were evaluated via flow cytometry and immunoblotting assays in FLT-ITD AML cells. Also, the ex vivo and in vivo models were used to test the synergistic effects of melatonin and sorafenib against leukemia with FLT3/ITD mutation. Results: Our study shows for the first time that melatonin inhibits proliferation and induces apoptosis in FLT3/ITD-positive leukemia cells. Mechanistically, melatonin preferentially causes overproduction of reactive oxygen species (ROS) and ultimately massive cell death in FLT3-ITD AML cells. Moreover, melatonin significantly enhances the cytotoxicity induced by the FLT3 tyrosine kinase inhibitor sorafenib in AML cells with FLT3/ITD through redox modification. Importantly, combination of melatonin and sorafenib exhibited highly synergistic therapeutic activity in MV4-11 xenografts and a murine model bearing FLT3/ITD leukemia. Conclusion: This study indicates that melatonin, alone or in combination with sorafenib, has potential to improve the therapeutic outcome of AML patients with FLT3-ITD mutation that merits further investigation.

Turning Stem Cells Bad: Generation of Clinically Relevant Models of Human Acute Myeloid Leukemia through Gene Delivery- or Genome Editing-Based Approaches

Acute myeloid leukemia (AML), the most common acute leukemia in the adult, is believed to arise as a consequence of multiple molecular events that confer on primitive hematopoietic progenitors unlimited self-renewal potential and cause defective differentiation. A number of genetic aberrations, among which a variety of gene fusions, have been implicated in the development of a transformed phenotype through the generation of dysfunctional molecules that disrupt key regulatory mechanisms controlling survival, proliferation, and differentiation in normal stem and progenitor cells. Such genetic aberrations can be recreated experimentally to a large extent, to render normal hematopoietic stem cells "bad", analogous to the leukemic stem cells. Here, we wish to provide a brief outline of the complementary experimental approaches, largely based on gene delivery and more recently on gene editing, employed over the last two decades to gain insights into the molecular mechanisms underlying AML development and progression and on the prospects that their applications offer for the discovery and validation of innovative therapies.

A Genome-Wide CRISPR Screen Identifies Genes Critical for Resistance to FLT3 Inhibitor AC220

Acute myeloid leukemia (AML) is a malignant hematopoietic disease and the most common type of acute leukemia in adults. The mechanisms underlying drug resistance in AML are poorly understood. Activating mutations in FMS-like tyrosine kinase 3 (FLT3) are the most common molecular abnormality in AML. Quizartinib (AC220) is a potent and selective second-generation inhibitor of FLT3. It is in clinical trials for the treatment of relapsed or refractory FLT3-ITD-positive and -negative AML patients and as maintenance therapy. To understand the mechanisms of drug resistance to AC220, we undertook an unbiased approach with a novel CRISPR-pooled library to screen new genes whose loss of function confers resistance to AC220. We identified SPRY3, an intracellular inhibitor of FGF signaling, and GSK3, a canonical Wnt signaling antagonist, and demonstrated reactivation of downstream FGF/Ras/ERK and Wnt signaling as major mechanisms of resistance to AC220. We confirmed these findings in primary AML patient samples. Expression of SPRY3 and GSK3A was dramatically reduced in AC220-resistant AML samples, and SPRY3-deleted primary AML cells were resistant to AC220. Intriguingly, expression of SPRY3 was greatly reduced in GSK3 knockout AML cells, which positioned SPRY3 downstream of GSK3 in the resistance pathway. Taken together, our study identified novel genes whose loss of function conferred resistance to a selective FLT3 inhibitor, providing new insight into signaling pathways that contribute to acquired resistance in AML. Cancer Res; 77(16); 4402-13. ©2017 AACR.

Prevalence and Clinical Significance of FLT3 Mutation Status in Acute Myeloid Leukemia Patients: A Multicenter Study

BACKGROUND AND AIMS

FLT3-ITD mutations in acute myeloid leukemia (AML) are associated with a poor prognosis. In Latin America, little epidemiological data exist about these mutations and their influence on clinical evolution and prognosis. Standardization and well-established clinical correlation make FLT3 mutational analysis by molecular methods an invaluable tool to decide among treatment options and to determine AML prognosis.

METHODS

We assessed the prevalence of FLT3-ITD mutations in 138 patients with AML at four hematology referral centers from Mexico and Colombia. Molecular methods based on polymerase chain reaction (PCR) were employed for determining FLT3-ITD status.

RESULTS

Mutations were present in 28 patients indicating a prevalence of 20.28%. Median age was 47 years (5-96). The FLT3 mutation positive group was older, had higher WBC and hemoglobin values and lower platelet counts but without statistical significance. A not previously described mutation in the FLT3 gene was found in one patient involving a nucleotide exchange of timine for cytosine at the 66608 position. A high mortality was found in the FLT3-mutated group, 67.8 vs. 42.72% in the non-mutated group and median survival was 4.9 months vs. 20.4 months, p = 0.009. A mutated FLT3 did not confer poor prognosis to those with M3 AML. The mutated FLT3 population had poor overall survival (OS) despite hematoprogenitor stem cell transplantation (HSCT).

CONCLUSION

Prevalence of FLT3-ITD mutation in AML was present in a proportion comparable to other populations and, when present, was associated with a very poor prognosis.

Hematopoietic stem cell transplantation for patients with AML in first complete remission

Postremission therapy in patients with acute myeloid leukemia (AML) may consist of continuing chemotherapy or transplantation using either autologous or allogeneic stem cells. Patients with favorable subtypes of AML generally receive chemotherapeutic consolidation, although recent studies have also suggested favorable outcome after hematopoietic stem cell transplantation (HSCT). Although allogeneic HSCT (alloHSCT) is considered the preferred type of postremission therapy in poor- and very-poor-risk AML, the place of alloHSCT in intermediate-risk AML is being debated, and autologous HSCT is considered a valuable alternative that may be preferred in patients without minimal residual disease after induction chemotherapy. Here, we review postremission transplantation strategies using either autologous or allogeneic stem cells. Recent developments in the field of alternative donors, including cord blood and haploidentical donors, are highlighted, and we discuss reduced-intensity alloHSCT in older AML recipients who represent the predominant category of patients with AML who have a high risk of relapse in first remission.