“FLipping” the Story: FLT3-Mutated Acute Myeloid Leukemia and the Evolving Role of FLT3 Inhibitors

FLT3 targeting in the modern era: from clonal selection to combination therapies

Fms-like tyrosine kinase 3 (FLT3) is the most frequently mutated gene in acute myeloid leukemia (AML). Modern targeting of FLT3 with inhibitors has improved clinical outcomes and FLT3 inhibitors have been incorporated into the treatment of AML in all phases of the disease, including the upfront, relapsed/refractory and maintenance settings. This review will discuss the current understanding of FLT3 biology, the clinical use of FLT3 inhibitors, resistance mechanisms and emerging combination treatment strategies.

Shikonin Exerts an Antileukemia Effect against FLT3-ITD Mutated Acute Myeloid Leukemia Cells via Targeting FLT3 and Its Downstream Pathways

INTRODUCTION

Acute myeloid leukemia (AML) with internal tandem duplication (ITD) mutations in Fms-like tyrosine kinase 3 (FLT3) has an unfavorable prognosis. Recently, using newly emerging inhibitors of FLT3 has led to improved outcomes of patients with FLT3-ITD mutations. However, drug resistance and relapse continue to be significant challenges in the treatment of patients with FLT3-ITD mutations. This study aimed to evaluate the antileukemic effects of shikonin (SHK) and its mechanisms of action against AML cells with FLT3-ITD mutations in vitro and in vivo.

METHODS

The CCK-8 assay was used to analyze cell viability, and flow cytometry was used to detect cell apoptosis and differentiation. Western blotting and real-time polymerase chain reaction were used to examine the expression of certain proteins and genes. Leukemia mouse model was created to evaluate the antileukemia effect of SHK against FLT3-ITD mutated leukemia in vivo.

RESULTS

After screening a series of leukemia cell lines, those with FLT3-ITD mutations were found to be more sensitive to SHK in terms of proliferation inhibition and apoptosis induction than those without FLT3-ITD mutation. SHK suppresses the expression and phosphorylation of FLT3 receptors and their downstream molecules. Inhibition of the NF-κB/miR-155 pathway is an important mechanism through which SHK kills FLT3-AML cells. Moreover, a low concentration of SHK promotes the differentiation of AML cells with FLT3-ITD mutations. Finally, SHK could significantly inhibit the growth of MV4-11 cells in leukemia bearing mice.

CONCLUSION

The findings of this study indicate that SHK may be a promising drug for the treatment of FLT3-ITD mutated AML.

FLT3 inhibitors and novel therapeutic strategies to reverse AML resistance: An updated comprehensive review

FMS-like tyrosine kinase 3 (FLT3) mutations occur in almost 30% of acute myeloid leukemia (AML) patients. Despite the initial clinical efficacy of FLT3 inhibitors, many treated AML patients with mutated FLT3 eventually relapse. This review critically discusses the opportunities and challenges of FLT3-targeted therapies and sheds light on their drug interactions as well as potential biomarkers. Furthermore, we focus on the molecular mechanisms underlying the resistance of FLT3 internal tandem duplication (FLT3-ITD) AMLs to FLT3 inhibitors alongside novel therapeutic strategies to reverse resistance. Notably, dynamic heterogeneous patterns of clonal selection and evolution contribute to the resistance of FLT3-ITD AMLs to FLT3 inhibitors. Ongoing preclinical research and clinical trials are actively directed towards devising rational "personalized" or "patient-tailored" combinatorial therapeutic regimens to effectively treat patients with FLT3 mutated AML.

From Fruit Waste to Medical Insight: The Comprehensive Role of Watermelon Rind Extract on Renal Adenocarcinoma Cellular and Transcriptomic Dynamics

Cancer researchers are fascinated by the chemistry of diverse natural products that show exciting potential as anticancer agents. In this study, we aimed to investigate the anticancer properties of watermelon rind extract (WRE) by examining its effects on cell proliferation, apoptosis, senescence, and global gene expression in human renal cell adenocarcinoma cells (HRAC-769-P) in vitro. Our metabolome data analysis of WRE exhibited untargeted phyto-constituents and targeted citrulline (22.29 µg/mg). HRAC-769-P cells were cultured in RPMI-1640 media and treated with 22.4, 44.8, 67.2, 88.6, 112, 134.4, and 156.8 mg·mL-1 for 24, 48, and 72 h. At 24 h after treatment, (88.6 mg·mL-1 of WRE) cell proliferation significantly reduced, more than 34% compared with the control. Cell viability decreased 48 and 72 h after treatment to 45% and 37%, respectively. We also examined poly caspase, SA-beta-galactosidase (SA-beta-gal), and wound healing activities using WRE. All treatments induced an early poly caspase response and a significant reduction in cell migration. Further, we analyzed the transcript profile of the cells grown at 44.8 mg·mL-1 of WRE after 6 h using RNA sequencing (RNAseq) analysis. We identified 186 differentially expressed genes (DEGs), including 149 upregulated genes and 37 downregulated genes, in cells treated with WRE compared with the control. The differentially expressed genes were associated with NF-Kappa B signaling and TNF pathways. Crucial apoptosis-related genes such as BMF, NPTX1, NFKBIA, NFKBIE, and NFKBID might induce intrinsic and extrinsic apoptosis. Another possible mechanism is a high quantity of citrulline may lead to induction of apoptosis by the production of increased nitric oxide. Hence, our study suggests the potential anticancer properties of WRE and provides insights into its effects on cellular processes and gene expression in HRAC-769-P cells.

A Review of FLT3 Kinase Inhibitors in AML

Acute myeloid leukemia (AML) is a highly aggressive illness distinguished by the accumulation of abnormal hematopoietic precursors in both the bone marrow and peripheral blood. The prevalence of FLT3 gene mutations is high and escalates the probability of relapse and mortality. The survival rates for AML patients, particularly those over 65, are low. FLT3 mutation screening at diagnosis is mandatory, and FLT3 inhibitors are crucial in treating AML patients with mutations. There are two categories of FLT3 mutations: FLT3-ITD located in the juxtamembrane domain and FLT3-TKD in the tyrosine kinase domain. FLT3-ITD is the most common type, affecting nearly a quarter of patients, whereas FLT3-TKD only affects 6-8% of patients. FLT3 inhibitors are now crucial in treating AML patients with FLT3 mutations. When dealing with FLT3-mutated AML, the recommended course of treatment typically involves chemotherapy and midostaurin, followed by allogeneic hematopoietic cell transplantation (HCT) to maximize the likelihood of success. Maintenance therapy can lower the risk of relapse, and gilteritinib is a better option than salvage chemotherapy for relapsed or refractory cases. Clinical trials for new or combined therapies are the most effective approach. This review discusses treatment options for patients with FLT3-mutated AML, including induction chemotherapy and options for relapsed or refractory disease. Additional treatment options may become available as more studies are conducted based on the patient's condition and susceptibility.

Relapsed pediatric acute myeloid leukaemia: state-of-the-art in 2023

Although outcomes of children and adolescents with newly diagnosed acute myeloid leukemia (AML) have improved significantly over the past two decades, more than one-third of patients continue to relapse and experience suboptimal long-term outcomes. Given the small numbers of patients with relapsed AML and historical logistical barriers to international collaboration including poor trial funding and drug availability, the management of AML relapse has varied among pediatric oncology cooperative groups with several salvage regimens utilized and a lack of universally defined response criteria. The landscape of relapsed pediatric AML treatment is changing rapidly, however, as the international AML community harnesses collective knowledge and resources to characterize the genetic and immunophenotypic heterogeneity of relapsed disease, identify biological targets of interest within specific AML subtypes, develop new precision medicine approaches for collaborative investigation in early-phase clinical trials, and tackle challenges of universal drug access across the globe. This review provides a comprehensive overview of progress achieved to date in the treatment of pediatric patients with relapsed AML and highlights modern, state-of-the-art therapeutic approaches under active and emerging clinical investigation that have been facilitated by international collaboration among academic pediatric oncologists, laboratory scientists, regulatory agencies, pharmaceutical partners, cancer research sponsors, and patient advocates.

A Multicenter, Open-Label, Phase I/II Study of FN-1501 in Patients with Advanced Solid Tumors

BACKGROUND

FN-1501, a potent inhibitor of receptor FMS-like tyrosine kinase 3 (FLT3) and CDK4/6, KIT, PDGFR, VEGFR2, ALK, and RET tyrosine kinase proteins, has demonstrated significant in vivo activity in various solid tumor and leukemia human xenograft models. Anomalies in FLT3 have an established role as a therapeutic target where the gene has been shown to play a critical role in the growth, differentiation, and survival of various cell types in hematopoietic cancer and have shown promise in various solid tumors. An open-label, Phase I/II study (NCT03690154) was designed to evaluate the safety and PK profile of FN-1501 as monotherapy in patients (pts) with advanced solid tumors and relapsed, refractory (R/R) AML.

METHODS

Pts received FN-1501 IV three times a week for 2 weeks, followed by 1 week off treatment in continuous 21-day cycles. Dose escalation followed a standard 3 + 3 design. Primary objectives include the determination of the maximum tolerated dose (MTD), safety, and recommended Phase 2 dose (RP2D). Secondary objectives include pharmacokinetics (PK) and preliminary anti-tumor activity. Exploratory objectives include the relationship between pharmacogenetic mutations (e.g., FLT3, TP53, KRAS, NRAS, etc.), safety, and efficacy; as well as an evaluation of the pharmacodynamic effects of treatment with FN-1501. Dose expansion at RP2D further explored the safety and efficacy of FN-1501 in this treatment setting.

RESULTS

A total of 48 adult pts with advanced solid tumors (N = 47) and AML (N = 1) were enrolled at doses ranging from 2.5 to 226 mg IV three times a week for two weeks in 21-day cycles (2 weeks on and 1 week off treatment). The median age was 65 years (range 30-92); 57% were female and 43% were male. The median number of prior lines of treatment was 5 (range 1-12). Forty patients evaluable for dose-limiting toxicity (DLT) assessment had a median exposure of 9.5 cycles (range 1-18 cycles). Treatment-related adverse events (TRAEs) were reported for 64% of the pts. The most common treatment-emergent adverse events (TEAEs), defined as those occurring in ≥20% of pts, primarily consisted of reversible Grade 1-2 fatigue (34%), nausea (32%), and diarrhea (26%). The most common Grade ≥3 events occurring in ≥5% of pts consisted of diarrhea and hyponatremia. Dose escalation was discontinued due to DLTs of Grade 3 thrombocytopenia (N = 1) and Grade 3 infusion-related reaction (N = 1) occurring in 2 pts. The maximum tolerated dose (MTD) was determined to be 170 mg.

CONCLUSIONS

FN-1501 demonstrated reasonable safety, tolerability, and preliminary activity against solid tumors in doses up to 170 mg. Dose escalation was terminated based on 2 DLTs occurring at the 226 mg dose level.

Targeting Proliferation Signals and the Cell Cycle Machinery in Acute Leukemias: Novel Molecules on the Horizon

Uncontrolled proliferative signals and cell cycle dysregulation due to genomic or functional alterations are important drivers of the expansion of undifferentiated blast cells in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) cells. Therefore, they are largely studied as potential therapeutic targets in the field. We here present the most recent advancements in the evaluation of novel compounds targeting cell cycle proteins or oncogenic mechanisms, including those showing an antiproliferative effect in acute leukemia, independently of the identification of a specific target. Several new kinase inhibitors have been synthesized that showed effectiveness in a nanomolar to micromolar concentration range as inhibitors of FLT3 and its mutant forms, a highly attractive therapeutic target due to its driver role in a significant fraction of AML cases. Moreover, we introduce novel molecules functioning as microtubule-depolymerizing or P53-restoring agents, G-quadruplex-stabilizing molecules and CDK2, CHK1, PI3Kδ, STAT5, BRD4 and BRPF1 inhibitors. We here discuss their mechanisms of action, including the downstream intracellular changes induced by in vitro treatment, hematopoietic toxicity, in vivo bio-availability and efficacy in murine xenograft models. The promising activity profile demonstrated by some of these candidates deserves further development towards clinical investigation.

Inhibition of Mcl-1 Synergistically Enhances the Antileukemic Activity of Gilteritinib and MRX-2843 in Preclinical Models of FLT3-Mutated Acute Myeloid Leukemia

FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (FLT3-ITD) mutations occur in about 25% of all acute myeloid leukemia (AML) patients and confer a poor prognosis. FLT3 inhibitors have been developed to treat patients with FLT3-mutated AML and have shown promise, though the acquisition of resistance occurs, highlighting the need for combination therapies to prolong the response to FLT3 inhibitors. In this study, we investigated the selective Mcl-1 inhibitor AZD5991 in combination with the FLT3 inhibitors gilteritinib and MRX-2843. The combinations synergistically induce apoptosis in AML cell lines and primary patient samples. The FLT3 inhibitors downregulate c-Myc transcripts through the suppression of the MEK/ERK and JAK2/STAT5 pathways, resulting in the decrease in c-Myc protein. This suppression of c-Myc plays an important role in the antileukemic activity of AZD5991. Interestingly, the suppression of c-Myc enhances AZD5991-inudced cytochrome c release and the subsequent induction of apoptosis. AZD5991 enhances the antileukemic activity of the FLT3 inhibitors gilteritinib and MRX-2843 against FLT3-mutated AML in vitro, warranting further development.