Identification of a potent 5-phenyl-thiazol-2-ylamine-based inhibitor of FLT3 with activity against drug resistance-conferring point mutations

Developments of Fms-like Tyrosine Kinase 3 Inhibitors as Anticancer Agents for AML Treatment

BACKGROUND

FMS-like tyrosine kinase 3 (FLT3) is a commonly mutated gene in acute myeloid leukemia. As a receptor tyrosine kinase (RTK), FLT3 plays a role in the proliferation and differentiation of hematopoietic stem cells. As the most frequent molecular alteration in AML, FLT3 has drawn the attention of many researchers, and a lot of small molecule inhibitors targeting FLT3 have been intensively investigated as potential drugs for AML therapy.

METHODS

In this paper, PubMed and SciFinder® were used as a tool; the publications about "FLT3 inhibitor" and "Acute myeloid leukemia" were surveyed from 2014 to the present with an exclusion of those published as patents.

RESULTS

In this study, the structural characterization and biological activities of representative FLT3 inhibitors were summarized. The major challenges and future directions for further research are discussed.

CONCLUSION

Recently, numerous FLT3 inhibitors have been discovered and employed in FLT3-mutated AML treatment. In order to overcome the drug resistance caused by FLT3 mutations, screening multitargets FLT3 inhibitors has become the main research direction. In addition, the emergence of irreversible FLT3 inhibitors also provides new ideas for discovering new FLT3 inhibitors.

Small Molecule c-KIT Inhibitors for the Treatment of Gastrointestinal Stromal Tumors: A Review on Synthesis, Design Strategies, and Structure-Activity Relationship (SAR)

The proto-oncogenic protein, c-KIT, plays a crucial role in regulating cellular transformation and differentiation processes, such as proliferation, survival, adhesion, and chemotaxis. The overexpression of, and mutations, in c-KIT can lead to its dysregulation and promote various human cancers, particularly gastrointestinal stromal tumors (GISTs); approximately 80-85% of cases are associated with oncogenic mutations in the KIT gene. Inhibition of c-KIT has emerged as a promising therapeutic target for GISTs. However, the currently approved drugs are associated with resistance and significant side effects, highlighting the urgent need to develop highly selective c-KIT inhibitors that are not affected by these mutations for GISTs. Herein, the recent research efforts in medicinal chemistry aimed at developing potent small-molecule c-KIT inhibitors with high kinase selectivity for GISTs are discussed from a structure-activity relationship perspective. Moreover, the synthetic pathways, pharmacokinetic properties, and binding patterns of the inhibitors are also discussed to facilitate future development of more potent and pharmacokinetically stable small-molecule c-KIT inhibitors.

Small molecules in targeted cancer therapy: advances, challenges, and future perspectives

Due to the advantages in efficacy and safety compared with traditional chemotherapy drugs, targeted therapeutic drugs have become mainstream cancer treatments. Since the first tyrosine kinase inhibitor imatinib was approved to enter the market by the US Food and Drug Administration (FDA) in 2001, an increasing number of small-molecule targeted drugs have been developed for the treatment of malignancies. By December 2020, 89 small-molecule targeted antitumor drugs have been approved by the US FDA and the National Medical Products Administration (NMPA) of China. Despite great progress, small-molecule targeted anti-cancer drugs still face many challenges, such as a low response rate and drug resistance. To better promote the development of targeted anti-cancer drugs, we conducted a comprehensive review of small-molecule targeted anti-cancer drugs according to the target classification. We present all the approved drugs as well as important drug candidates in clinical trials for each target, discuss the current challenges, and provide insights and perspectives for the research and development of anti-cancer drugs.

Potent and orally active purine-based fetal hemoglobin inducers for treating β-thalassemia and sickle cell disease

Reactivation of fetal hemoglobin (HbF) expression by therapeutic agents has been suggested as an alternative treatment to modulate anemia and the related symptoms of severe β-thalassemia and sickle cell disease (SCD). Hydroxyurea (HU) is the first US FDA-approved HbF inducer for treating SCD. However, approximately 25% of the patients with SCD do not respond to HU. A previous study identified TN1 (1) as a small-molecule HbF inducer. However, this study found that the poor potency and oral bioavailability of compound 1 limits the development of this inducer for clinical use. To develop drug-like compounds, further structure-activity relationship studies on the purine-based structure of 1 were conducted. Herein, we report our discovery of a more potent inducer, compound 13a, that can efficiently induce γ-globin gene expression at non-cytotoxic concentrations. The molecular mechanism of 13a, for the regulation HbF expression, was also investigated. In addition, we demonstrated that oral administration of 13a can ameliorate anemia and the related symptoms in SCD mice. The results of this study suggest that 13a can be further developed as a novel agent for treating hemoglobinopathies, such as β-thalassemia and SCD.

Small-Molecule Fms-like Tyrosine Kinase 3 Inhibitors: An Attractive and Efficient Method for the Treatment of Acute Myeloid Leukemia

Fms-like tyrosine kinase 3 (FLT3) is an important member of the class III receptor tyrosine kinase (RTK) family, which is involved in the proliferation of hematopoietic cells and lymphocytes. In recent years, increasing evidence have demonstrated that the activation and mutation of FLT3 is closely implicated in the occurrence and development of acute myeloid leukemia (AML). The exploration of small-molecule inhibitors targeting FLT3 has aroused wide interest of pharmaceutical chemists and is expected to bring new hope for AML therapy. In this review, we specifically highlighted FLT3 mediated JAK/STAT, RAS/MAPK, and PI3K/AKT/mTOR signaling. The structural properties and biological activities of representative FLT3 inhibitors reported from 2014 to the present were also summarized. In addition, the major challenges in the current advance of novel FLT3 inhibitors were further analyzed, with the aim to guide future drug discovery.

Design and Synthesis of New Sulfonamides-Based Flt3 Inhibitors

Background:

Flt3 is an oncogenic kinase involved in different leukemias. It is most prominently associated with acute myeloid leukemia (AML). Flt3-specific inhibitors have shown promising results in interfering with AML.

Methods:

The crystallographic structures of two inhibitors complexed within Flt3, namely, quizartinib and F6M, were used to guide the synthesis of new sulfonamide-based Flt3 inhibitors.

Results:

One of the prepared compounds showed low micromolar anti-Flt3 bioactivity, and interestingly, low micromolar bioactivity against the related oncogenic kinase VEGFR2.

Conclusion:

Sulfonamides were successfully used as privileged scaffolds for the synthesis of novel Flt3 inhibitors of micromolar potencies.

MEK inhibition enhances the response to tyrosine kinase inhibitors in acute myeloid leukemia

FMS-like tyrosine kinase 3 (FLT3) is a key driver of acute myeloid leukemia (AML). Several tyrosine kinase inhibitors (TKIs) targeting FLT3 have been evaluated clinically, but their effects are limited when used in monotherapy due to the emergence of drug-resistance. Thus, a better understanding of drug-resistance pathways could be a good strategy to explore and evaluate new combinational therapies for AML. Here, we used phosphoproteomics to identify differentially-phosphorylated proteins in patients with AML and TKI resistance. We then studied resistance mechanisms in vitro and evaluated the efficacy and safety of rational combinational therapy in vitro, ex vivo and in vivo in mice. Proteomic and immunohistochemical studies showed the sustained activation of ERK1/2 in bone marrow samples of patients with AML after developing resistance to FLT3 inhibitors, which was identified as a common resistance pathway. We examined the concomitant inhibition of MEK-ERK1/2 and FLT3 as a strategy to overcome drug-resistance, finding that the MEK inhibitor trametinib remained potent in TKI-resistant cells and exerted strong synergy when combined with the TKI midostaurin in cells with mutated and wild-type FLT3. Importantly, this combination was not toxic to CD34+ cells from healthy donors, but produced survival improvements in vivo when compared with single therapy groups. Thus, our data point to trametinib plus midostaurin as a potentially beneficial therapy in patients with AML.

Discovery of N-(4-(6-Acetamidopyrimidin-4-yloxy)phenyl)-2-(2-(trifluoromethyl)phenyl)acetamide (CHMFL-FLT3-335) as a Potent FMS-like Tyrosine Kinase 3 Internal Tandem Duplication (FLT3-ITD) Mutant Selective Inhibitor for Acute Myeloid Leukemia

Most of the current FMS-like tyrosine kinase 3 (FLT3) inhibitors lack selectivity between FLT3 kinase and cKIT kinase as well as the FLT3 wt and internal tandem duplication (ITD) mutants. We report a new compound 27, which displays GI₅₀ values of 30-80 nM against different ITD mutants and achieves selectivity over both FLT3 wt (8-fold) and cKIT kinase in the transformed BaF3 cells (>300-fold). 27 potently inhibits the proliferation of the FLT3-ITD-positive acute myeloid leukemia cancer lines through suppression of the phosphorylation of FLT3 kinase and downstream signaling pathways, induction of apoptosis, and arresting the cell cycle into the G0/G1 phase. 27 also displays potent antiproliferative effect against FLT3-ITD-positive patient primary cells, whereas it does not apparently affect FLT3 wt primary cells. In addition, it also exhibits a good therapeutic window to PBMC compared to PKC412. In the in vivo studies, 27 demonstrates favorable PK profiles and suppresses the tumor growth in the MV4-11 cell inoculated mouse xenograft model.

Design, synthesis and biological evaluation of indolin-2-one-based derivatives as potent, selective and efficacious inhibitors of FMS-like tyrosine kinase3 (FLT3)

Activating mutations of FMS-like tyrosine kinase 3 (FLT3) are present in approximately one third of acute myeloid leukemia (AML) patients, which has been proposed as a promising drug target for AML therapy. A series of indolin-2-one derivatives bearing different groups at the solvent interface position based on sunitinib as FLT3 inhibitors were designed, synthesized and evaluated in FLT3-dependent human AML cell line MV4-11. Structure-activity relationship (SAR)analysis showed that heterocyclic alkane at the solvent interface position could significantly increase the potency for the inhibition of proliferation of MV4-11 cell line. Compound 10a and 10d exhibited better efficacy (MV4-11, IC₅₀: 14.7 nM for 10a and 24.8 nM for 10d) than positive control sunitinib (MV4-11, IC₅₀: 38.5 nM). The kinase and cellular inhibition assay exhibited that 10d (FLT3, IC₅₀: 5.3 nM) was a potent and selective FLT3 inhibitor. Furthermore, the pharmacokinetic experiments showed that 10d had good properties of oral bioavailability, C_max, T_max, T_1/2 and AUC in mice, respectively. The in vivo study indicated that 10d could significantly suppress tumor growth in MV4-11 xenografts nude mice model and occupied with a commendable therapeutic window compared to sunitinib.