How acute myeloid leukemia (AML) escapes from FMS-related tyrosine kinase 3 (FLT3) inhibitors? Still an overrated complication?

Inhibition of FLT3-induced signalling in refractory acute myeloid leukaemia

Mutations in FLT3 make this receptor tyrosine kinase overactive. Such mutations found in ∼30 % of the patients who suffer from acute myeloid leukaemia (AML). FLT3 mediates signalling networks that lead to cell proliferation and survival. FLT3 inhibitors are used to treat AML but patients who are treated with them typically become resistant. Such resistance often emerges through secondary mutations which either restore the activity of FLT3 in the presence of drugs or activate a key player in a signalling network such as NRAS. We had developed AML-specific cell lines resistant to two advanced FLT3 inhibitors: gilteritinib and FF-10101. Resistance in these cell lines proceeds though different mechanisms. In this study, we followed on the efficacy of five FLT3 inhibitors (gilteritinib, FF-10101 and three promising inhibitors that are being developed), two pan-PI3K inhibitors (one of which also inhibits mTOR) and two c-KIT inhibitors in order to examine the significance of different signalling cascades in FLT3+-AML. In addition, we used molecular modelling and quantum chemistry calculations to explain why specific FLT3 mutations affect some inhibitors more than others. Two novel FLT3 inhibitors were found to be only weakly affected by resistance mutations against gilteritinib and FF-10101. The efficacy of most FLT3 inhibitors was only weakly (or not at all) affected by the NRAS/G12C activating mutation. Finally, no non-FLT3 inhibitor has shown sufficient efficacy in the cells, suggesting the central role of FLT3 in FLT3-mutated AML.

Gene Mutation Characteristics and Prognostic Significance in Acute Myeloid Leukemia Patients From Northeast China

A great part of studies on the correlation between gene mutations and prognosis in acute myeloid leukemia (AML) patients are based on Western populations. To profile the genomic landscape of AML patients in Northeast China, we retrospectively analyzed the clinical data of 377 newly diagnosed AML patients in Shengjing Hospital of China Medical University from 2016 to 2022 and compared them with data from other populations with different genetic backgrounds. The mutation status of NPM1, FLT3-ITD, FLT3-TKD, CEBPA (CCAT enhancer binding protein alpha), ASXL1, TET2, KIT, DNMT3A (DNA methyltransferase 3A), IDH1, IDH2, EZH2 (enhancer of zeste 2), RUNX1, TP53, NRAS, and GATA2 was acquired by next-generation sequencing (NGS) technology; meanwhile, the clinical data of the patients were collected. The Cox regression model was used to analyze factors affecting patient survival and the impact of CEBPA and DNMT3A mutation on prognosis, and the results were different from those in other populations. Seventy-seven of 377 patients (20.4%) were detected with CEBPA mutations, which was higher than the 2%-6% in the Caucasian population. In the CEBPAdm patients who did not receive bone marrow transplantation, the prognosis of male patients (n = 18) was significantly better than that of female patients (n = 21) (p = 0.0242). Sixty-three of 377 patients (16.7%) carried the DNMT3A mutation, which was lower than the mutation frequency of 20.9% in the German-Austrian population, and the prognosis of these patients was significantly poorer (p = 0.0052). In addition, the prognostic evaluation value of the DNMT3A mutation in AML patients was not affected regardless of the presence of the NPM1 and FLT3-ITD comutation (p > 0.05), nor the mutation site of DNMT3A. In conclusion, for the Northeastern Chinese population, the prognosis of male patients with CEBPAdm was more favorable than that of female patients, and the DNMT3A mutation serves as an independent predictor of poor prognosis in AML. These results highlighted the central role of genetic background in precision medicine strategies and further emphasized the importance of the clinical characteristics of AML gene mutations in the Chinese population.

Salvage Therapy with Second-Generation Inhibitors for FLT3 Mutated Acute Myeloid Leukemia: A Real-World Study by the CETLAM and PETHEMA Groups

BACKGROUND/OBJECTIVES

Patients with relapsed/refractory (R/R) AML with FLT3 mutation (FLT3mut) have a dismal prognosis. FLT3mut offers a target for therapy in these patients. Gilteritinib (gilter) and quizartinib (quizar) have demonstrated efficacy as single agents in two phase 3 clinical trials.

METHODS

We retrospectively analyzed the characteristics, treatments, and outcomes of 50 patients with R/R FLT3mut AML who received gilter or quizar as monotherapy in 27 Spanish centers before their commercial availability. Forty-four patients were treated with gilter and six with quizar.

RESULTS

The median age was 62.5 years, and 52% were women. Most patients presented with FLT3-ITD mutations (80%); 46% had refractory disease and 54% had relapsed disease at treatment initiation. First-line treatment was chemotherapy in 80% of patients, with 40% of these also receiving midostaurin. Twenty-five patients (50%) had previously received FLT3 inhibitor, and twenty-eight (56%) had received more than one line treatment before starting gilter/quizar. The rates of complete remission (CR), CR without hematological recovery (CRi), and partial remission were 22%, 18%, and 16%, respectively. The median overall survival (OS) and disease-free survival were 4.74 months and 2.99 months, respectively. We observed a significant improvement in OS in patients who had received only one prior line of therapy compared to those who had received two or more therapies (10.77 months vs. 4.24 months, p = 0.016). Multivariate analysis identified failure to achieve CR/CRi, receiving more than one prior line of therapy, age, and white blood cells count as independent prognostic factors for OS. The most common toxicities were febrile neutropenia, liver function abnormalities, and QT interval prolongation.

CONCLUSIONS

Gilter/quizar monotherapy are effective and tolerable options for patients with R/R FLT3mut AML in a real-world setting. Response and toxicity rates are similar to those reported in the phase 3 trials, despite the more heterogeneous nature of the study population.

Advances in the pathogenesis of FLT3 -mutated acute myeloid leukemia and targeted treatments

PURPOSE OF REVIEW

FLT3 mutations are among the most common myeloid drivers identified in adult acute myeloid leukemia (AML). Their identification is crucial for the precise risk assessment because of the strong prognostic significance of the most recurrent type of FLT3 alterations, namely internal tandem duplications (ITDs). Recent advances in the pathogenesis and biology of FLT3 -mutated AML have opened an opportunity for development and application of selective inhibition of FLT3 pathway.

RECENT FINDINGS

In the last decade, at least three targeted treatments have been approved by regulatory agencies and several others are currently under investigations. Here, we review the latest advance in the role of FLT3 mutations in AML, providing an outline of the available therapeutic strategies, their mechanisms of actions and of resistance, as well as routes for potential improvement.

SUMMARY

The availability of FLT3 inhibitors has improved outcomes in AML harboring such mutations, currently also reflected in disease stratification and recommendations. Newer inhibitors are under investigations, and combinations with chemotherapy or other targeted treatments are being explored to further improve disease outcomes.

Enhancing Therapeutic Efficacy of FLT3 Inhibitors with Combination Therapy for Treatment of Acute Myeloid Leukemia

FMS-like tyrosine kinase 3 (FLT3) mutations are genetic changes found in approximately thirty percent of patients with acute myeloid leukemia (AML). FLT3 mutations in AML represent a challenging clinical scenario characterized by a high rate of relapse, even after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The advent of FLT3 tyrosine kinase inhibitors (TKIs), such as midostaurin and gilteritinib, has shown promise in achieving complete remission. However, a substantial proportion of patients still experience relapse following TKI treatment, necessitating innovative therapeutic strategies. This review critically addresses the current landscape of TKI treatments for FLT3+ AML, with a particular focus on gilteritinib. Gilteritinib, a highly selective FLT3 inhibitor, has demonstrated efficacy in targeting the mutant FLT3 receptor, thereby inhibiting aberrant signaling pathways that drive leukemic proliferation. However, monotherapy with TKIs may not be sufficient to eradicate AML blasts. Specifically, we provide evidence for integrating gilteritinib with mammalian targets of rapamycin (mTOR) inhibitors and interleukin-15 (IL-15) complexes. The combination of gilteritinib, mTOR inhibitors, and IL-15 complexes presents a compelling strategy to enhance the eradication of AML blasts and enhance NK cell killing, offering a potential for improved patient outcomes.

RAS mutations in myeloid malignancies: revisiting old questions with novel insights and therapeutic perspectives

NRAS and KRAS activating point mutations are present in 10-30% of myeloid malignancies and are often associated with a proliferative phenotype. RAS mutations harbor allele-specific structural and biochemical properties depending on the hotspot mutation, contributing to variable biological consequences. Given their subclonal nature in most myeloid malignancies, their clonal architecture, and patterns of cooperativity with other driver genetic alterations may potentially have a direct, causal influence on the prognosis and treatment of myeloid malignancies. RAS mutations overall tend to be associated with poor clinical outcome in both chronic and acute myeloid malignancies. Several recent prognostic scoring systems have incorporated RAS mutational status. While RAS mutations do not always act as independent prognostic factors, they significantly influence disease progression and survival. However, their clinical significance depends on the type of mutation, disease context, and treatment administered. Recent evidence also indicates that RAS mutations drive resistance to targeted therapies, particularly FLT3, IDH1/2, or JAK2 inhibitors, as well as the venetoclax-azacitidine combination. The investigation of novel therapeutic strategies and combinations that target multiple axes within the RAS pathway, encompassing both upstream and downstream components, is an active field of research. The success of direct RAS inhibitors in patients with solid tumors has brought renewed optimism that this progress will be translated to patients with hematologic malignancies. In this review, we highlight key insights on RAS mutations across myeloid malignancies from the past decade, including their prevalence and distribution, cooperative genetic events, clonal architecture and dynamics, prognostic implications, and therapeutic targeting.

Foretinib Is Effective in Acute Myeloid Leukemia by Inhibiting FLT3 and Overcoming Secondary Mutations That Drive Resistance to Quizartinib and Gilteritinib

FLT3 internal tandem duplication (FLT3-ITD) mutations are one of the most prevalent somatic alterations associated with poor prognosis in patients with acute myeloid leukemia (AML). The clinically approved FLT3 kinase inhibitors gilteritinib and quizartinib improve the survival of patients with AML with FLT3-ITD mutations, but their long-term efficacy is limited by acquisition of secondary drug-resistant mutations. In this study, we conducted virtual screening of a library of 60,411 small molecules and identified foretinib as a potent FLT3 inhibitor. An integrated analysis of the BeatAML database showed that foretinib had a lower IC50 value than other existing FLT3 inhibitors in patients with FLT3-ITD AML. Foretinib directly bound to FLT3 and effectively inhibited FLT3 signaling. Foretinib potently inhibited proliferation and promoted apoptosis in human AML cell lines and primary AML cells with FLT3-ITD mutations. Foretinib also significantly extended the survival of mice bearing cell-derived and patient-derived FLT3-ITD xenografts, exhibiting stronger efficacy than clinically approved FLT3 inhibitors in treating FLT3-ITD AML. Moreover, foretinib showed potent activity against secondary mutations of FLT3-ITD that confer resistance to quizartinib and gilteritinib. These findings support the potential of foretinib for treating patients with AML with FLT3-ITD mutations, especially for those carrying secondary mutations after treatment failure with other FLT3 inhibitors.

SIGNIFICANCE

Foretinib exhibits superior efficacy to approved drugs in AML with FLT3-ITD mutations and retains activity in AML with secondary FLT3 mutations that mediate resistance to clinical FLT3 inhibitors.

Gilteritinib and the risk of intracranial hemorrhage: a case series of a possible, under-reported side effect

Gilteritinib is currently approved for patients with relapsed/refractory AML with FLT3 mutations, based on the positive results of the pivotal ADMIRAL study. In ADMIRAL trial, no increased risk of bleeding was reported, but in the previous dose finding study, a single event of intracranial hemorrhage (ICH) was registered after exposure to subtherapeutic doses of gilteritinib. Here, we report the first case series on five ICHs diagnosed in patients with FLT3-mutated AML, occurred within the first month of exposure to gilteritinib. Our cohort included 24 patients treated in three Italian centers. Most of these ICH cases were non-severe and self-limiting, while one was fatal. This link with ICHs remains in any case uncertain for the presence of active AML. We further reported that an analysis of the post-marketing surveillance data (EudraVigilance) retrieved other 11 cases of ICHs present in the database after gilteritinib treatment. A causality assessment was performed according to the Dx3 method to evaluate the possibility that ICHs might be an actual side effect of gilteritinib. In conclusion, further research is needed to elucidate the potential role of gilteritinib in the pathogenesis of ICHs.

AML under the Scope: Current Strategies and Treatment Involving FLT3 Inhibitors and Venetoclax-Based Regimens

Acute myeloid leukemia (AML) is a disease that mainly affects elderly patients who are more often unfit for intensive chemotherapy (median age of diagnosis is 68). The regimens, including venetoclax, a highly specific BCL-2 (B-cell lymphoma-2) inhibitor, are a common alternative because of their safer profile and fewer side effects. However, the resistance phenomenon of leukemic cells necessitates the search for drugs that would help to overcome the resistance and improve treatment outcomes. One of the resistance mechanisms takes place through the upregulation of MCL-1 and BCL-XL, preventing BAX/BAK-driven MOMP (mitochondrial outer membrane permeabilization), thus stopping the apoptosis process. Possible partners for BCL-2 inhibitors may include inhibitors from the FLT3i (FMS-like tyrosine kinase-3 inhibitor) group. They resensitize cancer cells through the downregulation of MCL-1 expression in the FLT3 mutated cells, resulting in the stronger efficacy of BCL-2 inhibitors. Also, they provide an additional pathway for targeting the clonal cell. Both preclinical and clinical data suggest that the combination might show a synergistic effect and improve patients' outcomes. The aim of this review is to determine whether the combination of venetoclax and FLT3 inhibitors can impact the therapeutic approaches and what other agents they can be combined with.