Cluster of differentiation antigen 135 (CD135) also known as fms like tyrosine kinase 3 (FLT-3 with fms standing for "feline McDonough sarcoma"), receptor-type tyrosine-protein kinase FLT3, or fetal liver kinase-2 (Flk2) is a protein that in humans is encoded by the FLT3 gene. FLT3 is a cytokine receptor which belongs to the receptor tyrosine kinase class III. CD135 is the receptor for the cytokine Flt3 ligand (FLT3L).
It is expressed on the surface of many hematopoietic progenitor cells. Signalling of FLT3 is important for the normal development of haematopoietic stem cells and progenitor cells.
The FLT3 gene is one of the most frequently mutated genes in acute myeloid leukemia (AML). [5] High levels of wild-type FLT3 have been reported for blast cells of some AML patients without FLT3 mutations. These high levels may be associated with worse prognosis.
FLT3 is composed of five extracellular immunoglobulin-like domains, an extracellular domain, a transmembrane domain, a juxtamembrane domain and a tyrosine-kinase domain consisting of 2 lobes that are connected by a tyrosine-kinase insert. Cytoplasmic FLT3 undergoes glycosylation, which promotes localization of the receptor to the membrane. [6]
CD135 is a class III receptor tyrosine kinase. When this receptor binds to FLT3L a ternary complex is formed in which two FLT3 molecules are bridged by one (homodimeric) FLT3L. [7] The formation of such complex brings the two intracellular domains in close proximity to each other, eliciting initial trans-phosphorylation of each kinase domain. This initial phosphorylation event further activates the intrinsic tyrosine kinase activity, which in turn phosphorylates and activates signal transduction molecules that propagate the signal in the cell. Signaling through CD135 plays a role in cell survival, proliferation, and differentiation. CD135 is important for lymphocyte (B cell and T cell) development.
Two cytokines that down modulate FLT3 activity (& block FLT3-induced hematopoietic activity) are:
TGF-beta especially, decreases FLT3 protein levels and reverses the FLT3L-induced decrease in the time that hematopoietic progenitors spend in the G1-phase of the cell cycle. [6]
Cluster of differentiation (CD) molecules are markers on the cell surface, as recognized by specific sets of antibodies, used to identify the cell type, stage of differentiation and activity of a cell. In mice, CD135 is expressed on several hematopoietic (blood) cells, including long- and short-term reconstituting hematopoietic stem cells (HSC) and other progenitors like multipotent progenitors (MPPs) and common lymphoid progenitors (CLP). [8]
CD135 is a proto-oncogene, meaning that mutations of this protein can lead to cancer. [9] Mutations of the FLT3 receptor can lead to the development of leukemia, a cancer of bone marrow hematopoietic progenitors. Internal tandem duplications of FLT3 (FLT3-ITD) are the most common mutations associated with acute myelogenous leukemia (AML) and are a prognostic indicator associated with adverse disease outcome.
Gilteritinib, a dual FLT3-AXL tyrosine kinase inhibitor [10] has completed a phase 3 trial of relapsed/refractory acute myeloid leukemia in patients with FLT3 ITD or TKD mutations. [11] In 2017, gilteritinib gained FDA orphan drug status for AML. [12] In November 2018, the FDA approved gilteritinib (Xospata) for treatment of adult patients with relapsed or refractory acute myeloid leukemia (AML) with a FLT3 mutation as detected by an FDA-approved test. [13]
In July 2023, quizartinib (Vanflyta) was also approved for the treatment of newly diagnosed AML with FLT3 internal tandem duplication (ITD)-positive, as detected by an FDA-approved test. [14] Precisely, it should be used with standard cytarabine and anthracycline induction and cytarabine consolidation, and as maintenance monotherapy following consolidation chemotherapy. [14]
Midostaurin was approved by the FDA in April 2017 for the treatment of adult patients with newly diagnosed AML who are positive for oncogenic FLT3, in combination with chemotherapy. [15] The drug is approved for use with a companion diagnostic, the LeukoStrat CDx FLT3 Mutation Assay, which is used to detect the FLT3 mutation in patients with AML.
Sorafenib has been reported to show significant activity against Flt3-ITD positive acute myelogenous leukemia. [16] [17]
Sunitinib also inhibits Flt3.
Lestaurtinib is in clinical trials.
A paper published in Nature in April 2012 studied patients who developed resistance to FLT3 inhibitors, finding specific DNA sites contributing to that resistance and highlighting opportunities for future development of inhibitors that could take into account the resistance-conferring mutations for a more potent treatment. [18]
The Philadelphia chromosome or Philadelphia translocation (Ph) is a specific genetic abnormality in chromosome 22 of leukemia cancer cells. This chromosome is defective and unusually short because of reciprocal translocation, t(9;22)(q34;q11), of genetic material between chromosome 9 and chromosome 22, and contains a fusion gene called BCR-ABL1. This gene is the ABL1 gene of chromosome 9 juxtaposed onto the breakpoint cluster region BCR gene of chromosome 22, coding for a hybrid protein: a tyrosine kinase signaling protein that is "always on", causing the cell to divide uncontrollably by interrupting the stability of the genome and impairing various signaling pathways governing the cell cycle.
Acute myeloid leukemia (AML) is a cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal cells that build up in the bone marrow and blood and interfere with normal blood cell production. Symptoms may include feeling tired, shortness of breath, easy bruising and bleeding, and increased risk of infection. Occasionally, spread may occur to the brain, skin, or gums. As an acute leukemia, AML progresses rapidly, and is typically fatal within weeks or months if left untreated.
The interleukin-3 receptor (CD123) is a molecule found on cells which helps transmit the signal of interleukin-3, a soluble cytokine important in the immune system.
Bruton's tyrosine kinase, also known as tyrosine-protein kinase BTK, is a tyrosine kinase that is encoded by the BTK gene in humans. BTK plays a crucial role in B cell development.
Acute monocytic leukemia is a type of acute myeloid leukemia. In AML-M5 >80% of the leukemic cells are of monocytic lineage. This cancer is characterized by a dominance of monocytes in the bone marrow. There is an overproduction of monocytes that the body does not need in the periphery. These overproduced monocytes interfere with normal immune cell production which causes many health complications for the affected individual.
Proto-oncogene c-KIT is the gene encoding the receptor tyrosine kinase protein known as tyrosine-protein kinase KIT, CD117 or mast/stem cell growth factor receptor (SCFR). Multiple transcript variants encoding different isoforms have been found for this gene. KIT was first described by the German biochemist Axel Ullrich in 1987 as the cellular homolog of the feline sarcoma viral oncogene v-kit.
CD22, or cluster of differentiation-22, is a molecule belonging to the SIGLEC family of lectins. It is found on the surface of mature B cells and to a lesser extent on some immature B cells. Generally speaking, CD22 is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases.
Acute myeloblastic leukemia with maturation (M2) is a subtype of acute myeloid leukemia (AML).
ETV6 protein is a transcription factor that in humans is encoded by the ETV6 gene. The ETV6 protein regulates the development and growth of diverse cell types, particularly those of hematological tissues. However, its gene, ETV6 frequently suffers various mutations that lead to an array of potentially lethal cancers, i.e., ETV6 is a clinically significant proto-oncogene in that it can fuse with other genes to drive the development and/or progression of certain cancers. However, ETV6 is also an anti-oncogene or tumor suppressor gene in that mutations in it that encode for a truncated and therefore inactive protein are also associated with certain types of cancers.
Fms-related tyrosine kinase 3 ligand (FLT3LG) is a protein which in humans is encoded by the FLT3LG gene.
CCAAT/enhancer-binding protein alpha is a protein encoded by the CEBPA gene in humans. CCAAT/enhancer-binding protein alpha is a transcription factor involved in the differentiation of certain blood cells. For details on the CCAAT structural motif in gene enhancers and on CCAAT/Enhancer Binding Proteins see the specific page.
Colony stimulating factor 1 receptor (CSF1R), also known as macrophage colony-stimulating factor receptor (M-CSFR), and CD115, is a cell-surface protein encoded by the human CSF1R gene. CSF1R is a receptor that can be activated by two ligands: colony stimulating factor 1 (CSF-1) and interleukin-34 (IL-34). CSF1R is highly expressed in myeloid cells, and CSF1R signaling is necessary for the survival, proliferation, and differentiation of many myeloid cell types in vivo and in vitro. CSF1R signaling is involved in many diseases and is targeted in therapies for cancer, neurodegeneration, and inflammatory bone diseases.
Tyrosine-protein kinase receptor UFO is a protein that in human is encoded by the AXL gene. The gene was initially designated as UFO, in allusion to the unidentified function of this protein. However, in the years since its discovery, research into AXL's expression profile and mechanism has made it an increasingly attractive target, especially for cancer therapeutics. In recent years, AXL has emerged as a key facilitator of immune escape and drug-resistance by cancer cells, leading to aggressive and metastatic cancers.
Lestaurtinib is a tyrosine kinase inhibitor structurally related to staurosporine. This semisynthetic derivative of the indolocarbazole K252a was investigated by Cephalon as a treatment for various types of cancer. It is an inhibitor of the kinases fms-like tyrosine kinase 3 (FLT3), Janus kinase 2 (JAK2), tropomyosin receptor kinase (trk) A (TrkA), TrkB and TrkC.
Crenolanib besylate is an investigational inhibitor being developed by AROG Pharmaceuticals, LLC. The compound is currently being evaluated for safety and efficacy in clinical trials for various types of cancer, including acute myeloid leukemia (AML), gastrointestinal stromal tumor (GIST), and glioma. Crenolanib is an orally bioavailable benzimidazole that selectively and potently inhibits signaling of wild-type and mutant isoforms of class III receptor tyrosine kinases (RTK) FLT3, PDGFR α, and PDGFR β. Unlike most RTK inhibitors, crenolanib is a type I mutant-specific inhibitor that preferentially binds to phosphorylated active kinases with the ‘DFG in’ conformation motif.
Quizartinib, sold under the brand name Vanflyta, is an anti-cancer medication used for the treatment of acute myeloid leukemia.
Midostaurin, sold under the brand name Rydapt by Novartis, is a multi-targeted protein kinase inhibitor that has been investigated for the treatment of acute myeloid leukemia (AML), myelodysplastic syndrome (MDS) and advanced systemic mastocytosis. It is a semi-synthetic derivative of staurosporine, an alkaloid from the bacterium Streptomyces staurosporeus.
Clonal hypereosinophilia, also termed primary hypereosinophilia or clonal eosinophilia, is a grouping of hematological disorders all of which are characterized by the development and growth of a pre-malignant or malignant population of eosinophils, a type of white blood cell that occupies the bone marrow, blood, and other tissues. This population consists of a clone of eosinophils, i.e. a group of genetically identical eosinophils derived from a sufficiently mutated ancestor cell.
Gilteritinib, sold under the brand name Xospata, is an anti-cancer drug. It acts as an inhibitor of FLT3, hence it is a tyrosine kinase inhibitor.
Ivosidenib, sold under the brand name Tibsovo, is an anti-cancer medication for the treatment of acute myeloid leukemia (AML) and cholangiocarcinoma. It is a small molecule inhibitor of isocitrate dehydrogenase-1 (IDH1), which is mutated in several forms of cancer. Ivosidenib is an isocitrate dehydrogenase-1 inhibitor that works by decreasing abnormal production of the oncometabolite 2-hydroxyglutarate (2-HG), leading to differentiation of malignant cells.