FLT3

Overview

FLT3 (FMS-like tyrosine kinase 3), also known as CD135, is a receptor tyrosine kinase encoded by the FLT3 gene and expressed primarily on hematopoietic progenitor cells. It plays an important role in normal blood cell development by transmitting signals that regulate proliferation, survival, and differentiation. In acute myeloid leukemia (AML), FLT3 is one of the most clinically important signaling proteins because activating alterations can drive malignant growth and are associated with aggressive disease biology.

Pathogenic FLT3 alterations include internal tandem duplication (FLT3-ITD) and other activating mutations that lead to constitutive kinase signaling. These aberrations can promote downstream pathways such as STAT5A, MAPK1, and Akt1, contributing to leukemic cell survival and expansion. Because of this central role in AML pathogenesis, FLT3 has become a major therapeutic target, and multiple FLT3 inhibitors are used or investigated in mutation-defined AML subsets.

Focus of Latest Publications

Recent publications on FLT3 have focused heavily on acute myeloid leukemia, especially FLT3-ITD–positive disease, and on the development or evaluation of therapies that directly inhibit FLT3 or exploit FLT3-associated biology. Several studies reported new small-molecule inhibitors or optimized analogues with improved binding and antileukemic activity. Nintedanib was identified as a putative FLT3 inhibitor through drug-sensitivity analysis and was shown by docking, cellular thermal shift, and kinase assays to engage FLT3, suppress FLT3 autophosphorylation, and inhibit downstream STAT5, ERK, and Akt signaling in FLT3-ITD-mutant cells. It retained activity against resistance mutations, including F691L, and showed in vivo efficacy in a Ba/F3 FLT3-ITD-F691L mouse model. In parallel, rational design studies generated modified FLT3 inhibitors with improved docking scores, conformational stability, and predicted pharmacokinetic properties, and a separate medicinal chemistry program identified staurosporine-type indolocarbazole glycoalkaloids, especially compound 35, as potent and selective FLT3-ITD inhibitors that blocked FLT3 phosphorylation and downstream signaling, induced G2/M arrest, and triggered apoptosis.

Other recent work examined FLT3 in combination strategies and in translational treatment settings. A preclinical triplet regimen combining the p300/CBP bromodomain inhibitor inobrodib with venetoclax and gilteritinib was reported to virtually eliminate leukemia stem cells in a DNMT3A/FLT3-mutant AML model by impairing pro-oncogenic survival and proliferation factors. A dual SYK-HDAC inhibitor, compound 14, was also described as having strong activity in MV4-11 cells harboring FLT3-ITD mutations and significant antitumor efficacy in a FLT3-ITD-positive AML xenograft model, with approximately an 80% reduction in tumor mass and a favorable safety profile. In the clinical and real-world setting, gilteritinib was discussed as an established FLT3 inhibitor used in relapsed or refractory AML, including maintenance after allogeneic transplantation, while post-marketing surveillance of quizartinib in Japan found a safety profile consistent with prior knowledge, with QT prolongation manageable under current risk minimization measures.

FLT3 expression itself was also evaluated as a prognostic biomarker. In de novo AML, high CD135 (FLT3 receptor) expression was associated with distinct blast immunophenotypes, a higher frequency of NPM1 and DNMT3A mutations, lower induction response rates, and independently poorer overall and progression-free survival. In the subgroup with high CD135 expression and FLT3-ITD mutations, treatment with a tyrosine kinase inhibitor plus chemotherapy was associated with better overall survival. A prognostic nomogram incorporating CD135 expression showed good performance in both development and validation cohorts, supporting its use as a marker that links molecular pathogenesis with clinical outcome.

Mechanistic and structural studies further expanded the FLT3 literature. One report mapped the ATP-binding pockets of FLT3 and TAK1 and showed that several clinically used FLT3 inhibitors also bind TAK1, revealing a structural basis for off-target cross-reactivity confirmed by enzymatic and in silico analyses. This work suggested that chronic TAK1 inhibition by FLT3 inhibitors may help explain aspects of their in vivo safety and tolerability. Together, these publications emphasize FLT3 as both a therapeutic target and a clinically relevant biomarker in AML, with ongoing efforts to improve inhibitor potency, overcome resistance, refine combination therapy, and better define prognostic value.