Related Receptor Tyrosine Kinases Research Articles

Establishment of a cellular model to study TrkC-dependent neuritogenesis.

The rat PC12 cell line has become a widely used research tool for many aspects of neurobiology. Nerve growth factor (NGF)-responsive PC12 cells were engineered to drive expression of doxycycline (Dox)-induced gene of interest in the Tet-On expression system that resulted in obtaining PC12-Tet-On cells. TrkA and TrkC are neurotrophin receptors derived from the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases. TrkA receptor binds and is activated mainly by NGF, while TrkC receptor binds and is activated by neurotrophin 3 (NT3). The purpose of this research was to design and describe PC12-based neuronal cell model to study TrkC-triggered versus TrkA-triggered neurite outgrowth. The second-generation tetracycline-responsive promoter (P tight) was used in order to provide low basal expression in the absence of Dox and high-level Dox-induced expression of TrkC. The main advantage of presented model system is dependence of TrkC level on Dox concentration. It also allows to compare activation of intracellular signaling proteins and neurite outgrowth following activation of TrkA and TrkC receptors by NGF and NT3, respectively, in the context of the same quality and quantity of intracellular adaptor proteins, Ras proteins, protein kinases and phosphatases, and phospholipase Cγ1, as a difference in the activation of intracellular signaling network by these two distinct although related receptor tyrosine kinases is expected. The results of our studies suggest that despite slightly weaker activation of ERK1/2 mitogen-activated protein kinases, NT3-triggered TrkC seems to provide apparently stronger than NGF-triggered TrkA signal for neurite elongation in differentiating PC12 cells.

Development of EGFR family small molecule inhibitors for anticancer intervention: an overview of approved drugs and clinical candidates.

The epidermal growth factor receptor (EGFR) family includes four structurally related receptor tyrosine kinases, termed as HER1 (EGFR, erbB1), HER2 (erbB2), HER3 (erbB3), and HER4 (erbB4). Given its intimate role in the development of several solid tumors, excessive HER signaling provides a unique opportunity for anticancer intervention. Along with extensive pharmacological studies validating the therapeutic potential of targeting the EGFR family for cancer therapy, kinase inhibitors of this family are continuously coming up and entering clinical studies. Herein, we review the EGFR family small molecule kinase inhibitors which have been approved or progressed into clinical studies, mainly focusing on their mechanisms of action, structure-activity relationships, binding modes, synthetic routes, and clinical status.

Idiopathic basal ganglia calcification-associated PDGFRB mutations impair the receptor signalling.

Platelet-derived growth factors (PDGF) bind to two related receptor tyrosine kinases, which are encoded by the PDGFRA and PDGFRB genes. Recently, heterozygous PDGFRB mutations have been described in patients diagnosed with idiopathic basal ganglia calcification (IBGC or Fahr disease), a rare inherited neurological disorder. The goal of the present study was to determine whether these mutations had a positive or negative impact on the PDGFRB activity. We first showed that the E1071V mutant behaved like wild-type PDGFRB and may represent a polymorphism unrelated to IBGC. In contrast, the L658P mutant had no kinase activity and failed to activate any of the pathways normally stimulated by PDGF. The R987W mutant activated Akt and MAP kinases but did not induce the phosphorylation of signal transducer and activator of transcription 3 (STAT3) after PDGF stimulation. Phosphorylation of phospholipase Cγ was also decreased. Finally, we showed that the R987W mutant was more rapidly degraded upon PDGF binding compared to wild-type PDGFRB. In conclusion, PDGFRB mutations associated with IBGC impair the receptor signalling. PDGFRB loss of function in IBGC is consistent with recently described inactivating mutations in the PDGF-B ligand. These results raise concerns about the long-term safety of PDGF receptor inhibition by drugs such as imatinib.

Abstract 3007: Heterogeneity of vascular endothelial growth factor receptors 1, 2, and 3 in primary human colorectal adenocarcinoma

Abstract The Vascular Endothelial Growth Factor (VEGF) pathway plays an important role in the genesis, growth and progression of human cancer, including colorectal carcinomas (CRC). The key mediators of VEGF signaling are VEGFR1, VEGFR2, and VEGFR3, part of a family of related receptor tyrosine kinases. The relative expression, activity, or interplay among these receptors may determine the response of CRC patients to anti-angiogenic therapies. Using high-affinity, specific monoclonal primary anti-VEGFR1, 2 3 antibodies, we have developed robust imunohistochemical assays in our laboratory to quantify VEGFR1, 2 and 3 in archival human tissues. Using a well-annotated CRC tissue microarray (TMA), we carried out comprehensive comparative evaluation of immunohistochemical (IHC) expression of the three VEGFRs in archival primary CRC tissues (n=84). VEGFR1 immunoreactivity was reported as H-score (range 0-300); VEGFR2 positive vessels were counted and normalized to the number of CD34-positive vessels and reported as vascular positivity index (VEGFR2-VPI) and VEGFR3-positive vessels were counted in each core by the same solid tumor immunopathologist, who was blinded to the clinico-pathologic details. Based on immunoreactivity for VEGFRs, each case was scored as negative, low, medium or high. Thresholds were selected based on the overall range of expression of each receptor in the CRC tissues examined: 0, 1-50, 51-100, >100 (VEGFR1 H-scores); 0, 1-25, 26-49, 50-100 (VEGFR2-VPI); 0, 1-5, 6-10, >10 (VEGFR3+ vascular count). Based on VEGFR (1,2,3) expression, a set of eight VEGFR staining profiles were noted: Triple VEGFR positive (n=9, 11%), VEGFR1 predominant (17, 20%), VEGFR2 predominant (7, 8%), VEGFR3 predominant (1, 1%), VEGFR1/2 predominant (42, 50%), VEGFR1/3 predominant (2, 2%), VEGFR2/3 predominant (3, 4%), and triple VEGFR negative (3, 4%). These new data provide original insights on the distribution, subcellular localization and heterogeneity of expression of VEGFRs in human CRC stromal vessels and tumor cells. The proposed human CRC sub-classification, based on the observed differential VEGFR 1, 2, 3 expression profiles, has identified various subsets of human CRCs. Clinical trials incorporating IHC profiling would be required to test whether these subsets show differential responsiveness to targeted agents in the VEGF/VEGFR2 family. Citation Format: Timothy R. Holzer, Leslie A. O'Neill, Drew M. Nedderman, Angie D. Fulford, Beverly L. Falcon, Mark T. Uhlik, Laura E. Benjamin, Andrew E. Schade, Aejaz Nasir. Heterogeneity of vascular endothelial growth factor receptors 1, 2, and 3 in primary human colorectal adenocarcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3007. doi:10.1158/1538-7445.AM2014-3007

Thioaryl naphthylmethanone oxime ether analogs as novel anticancer agents.

Employing a rational design of thioaryl naphthylmethanone oxime ether analogs containing functional properties of various anticancer drugs, a series of compounds were identified that displayed potent cytotoxicity toward various cancer cells, out of which 4-(methylthio)phenyl)(naphthalen-1-yl)methanone O-2-(diethylamino)ethyl oxime (MND) exhibited the best safety profile. MND induced apoptosis, inhibited migration and invasion, strongly inhibited cancer stem cell population on a par with salinomycin, and demonstrated orally potent tumor regression in mouse MCF-7 xenografts. Mechanistic studies revealed that MND strongly abrogated EGF-induced proliferation, migration, and tyrosine kinase (TK) signaling in breast cancer cells. However, MND failed to directly inhibit EGFR or other related receptor TKs in a cell-free system. Systematic investigation of a putative target upstream of EGFR revealed that the biological effects of MND could be abrogated by pertussis toxin. Together, MND represents a new nonquinazoline potential drug candidate having promising antiproliferative activity with good safety index.

The regulation of reproductive neuroendocrine function by insulin and insulin-like growth factor-1 (IGF-1).

The mammalian reproductive hormone axis regulates gonadal steroid hormone levels and gonadal function essential for reproduction. The neuroendocrine control of the axis integrates signals from a wide array of inputs. The regulatory pathways important for mediating these inputs have been the subject of numerous studies. One class of proteins that have been shown to mediate metabolic and growth signals to the CNS includes Insulin and IGF-1. These proteins are structurally related and can exert endocrine and growth factor like action via related receptor tyrosine kinases. The role that insulin and IGF-1 play in controlling the hypothalamus and pituitary and their role in regulating puberty and nutritional control of reproduction has been studied extensively. This review summarizes the in vitro and in vivo models that have been used to study these neuroendocrine structures and the influence of these growth factors on neuroendocrine control of reproduction.

Classifying the adverse mitogenic mode of action of insulin analogues using a novel mechanism-based genetically engineered human breast cancer cell panel

Insulin analogues are widely used in clinical practice. Modifications on the insulin molecular structure can affect the affinity and activation towards two closely related receptor tyrosine kinases: the insulin receptor (INSR) and the insulin-like growth factor 1 receptor (IGF1R). A switch towards higher IGF1R affinity is likely to emphasize mitogenesis rather than glucose metabolism. Relevant well-validated experimental tools to address the insulin analogue activation of either INSR or IGF1R are missing. We have established a panel of human MCF-7 breast cancer cell lines either ectopically expressing the INSR (A or B isoform) in conjunction with a stable knockdown of the IGF1R or ectopically expressing the IGF1R in conjunction with a stable knockdown of the INSR. In these cell lines, we systematically evaluated the INSR and IGF1R receptor activation and downstream mitogenic signalling of all major clinical relevant insulin analogues in comparison with insulin and IGF1R. While most insulin analogues primarily activated the INSR, the mitogenic activation pattern of glargine was highly similar to IGF1 and insulin AspB10, known to bind IGF1R and induce carcinogenesis. Yet, in a long-term proliferation assay, the proliferative effect of glargine was not much different from regular insulin or other insulin analogues. This was caused by the rapid enzymatic conversion into its two metabolic active metabolites M1 and M2, with reduced mitogenic signalling through the IGF1R. In summary, based on our new cell models, we identified a similar mitogenic potency of insulin glargine and AspB10. However, rapid enzymatic conversion of glargine precludes a sustained activation of the IGF1R signalling pathway.

Epithelial mesenchymal transition status is associated with anti-cancer responses towards receptor tyrosine-kinase inhibition by dovitinib in human bladder cancer cells

BackgroundDovitinib (TKI-258) is a receptor tyrosine kinase (RTK) inhibitor targeting fibroblast growth factor receptor (FGFR) and further related RTKs. TKI-258 is under investigation as anticancer drug for the treatment of various cancers including bladder cancer with aberrant RTK signaling. Here, we analyzed the responses of ten human bladder cancer cell lines towards TKI-258 treatment in relation to the epithelial mesenchymal transition (EMT) status of the cells.MethodsExpression of epithelial marker E-cadherin as well as mesenchymal markers N-cadherin and vimentin was determined by quantitative RT-PCR and Western-blot in RNA and protein extracts from the cultured cell lines. The cell responses were analyzed upon addition of TKI-258 by viability/proliferation (XTT assay) and colony formation assay for measurement of cell contact independent growth.ResultsThe investigated bladder cancer cell lines turned out to display quite different EMT patterns as indicated by the abundance of E-cadherin or N-cadherin and vimentin. Protein and mRNA levels of the respective components strongly correlated. Based on E-cadherin and N-cadherin mRNA levels that were expressed approximately mutual exclusively, an EMT-score was calculated for each cell line. A high EMT-score indicated mesenchymal-like cells and a low EMT-score epithelial-like cells. Then, we determined the IC50 values for TKI-258 by dose response curves (0-12 μM TKI-258) in XTT assays for each cell line. Also, we measured the clonogenic survival fraction after adding TKI-258 (1 μM) by colony formation assay. We observed significant correlations between EMT-score and IC50 values (r = 0.637, p = 0.0474) and between EMT-score and clonogenic survival fraction (r = 0.635, p = 0.0483) as analyzed by linear regression analyses.ConclusionsIn sum, we demonstrated that the EMT status based on E-cadherin and N-cadherin mRNA levels may be useful to predict responses towards TKI-258 treatment in bladder cancer.

No KRAS mutations found in gastrointestinal stromal tumors (GISTs): molecular genetic study of 514 cases

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. A great majority of GISTs is driven by pathological activation of KIT or platelet-derived growth factor receptor-α (PDGFRA), two closely related receptor tyrosine kinases. However, other genetic changes including gain-of-function BRAF mutations and loss of succinate dehydrogenase (SDH) complex activity have been identified in the subsets of KIT-, PDGFRA-wild type tumors. Genetic mutations affecting KIT, PDGFRA, BRAF and SDH complex functions are believed to be mutually exclusive events. Recently, KRAS codon 12 and 13 mutations were reported in a small subset of KIT or PDGFRA mutant GISTs. Moreover, in in vitro experiments, KIT mutants with concurrent KRAS mutation showed resistance to imatinib, a receptor tyrosine kinase inhibitor used in GIST treatment. The aim of this study was to evaluate a large cohort of GISTs to define frequency and clinical significance of KRAS mutations in this type of cancer. A well-characterized cohort of 514 GISTs was screened for KRAS mutations using Sanger sequencing (n=450) and pyrosequencing (n=64). In all, 350 gastric, 100 intestinal and 64 primary disseminated GISTs were analyzed. No KRAS mutations were found. In GIST, KRAS mutations are extremely rare if they exist (<0.2%). Thus, mutational activation of KRAS does not seem to play any significant role in the development and progression of this type of cancer.

Abstract A291: A highly selective dual insulin receptor (IR)/insulin-like growth factor 1 receptor (IGF-1R) inhibitor derived from an ERK inhibitor.

Abstract Dual inhibitors of the closely related receptor tyrosine kinases insulin-like growth factor 1 receptor (IGF-1R) and insulin receptor (IR) are promising therapeutic agents in cancer. Here we report an unusually selective class of dual inhibitors of IGF-1R and IR identified in a parallel screen of known kinase inhibitors against a panel of 300 human protein kinases. Biochemical and structural studies indicate that this class achieves its high selectivity by binding to the ATP-binding pocket of inactive, unphosphorylated IGF-1R/IR and stabilizing the activation loop in a native-like inactive conformation. One member of this compound family was originally reported as an inhibitor of the serine/threonine kinase ERK, a kinase that is distinct in the structure of its unphosphorylated/inactive form from IR/IGF-1R. Remarkably, this compound binds to the ATP-binding pocket of ERK in an entirely different conformation to that of IGF-1R/IR, explaining the potency against these two structurally distinct kinase families. These findings suggest a novel approach to polypharmacology in which two or more unrelated kinases are inhibited by a single compound that targets different conformations of each target kinase. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A291. Citation Format: Krisna C. Duong-Ly, Theonie Anastassiadis, Sean W. Deacon, Alec Lafontant, Haiching Ma, Karthik Devarajan, Roland L. Dunbrack, Jinhua Wu, Jeffrey R. Peterson. A highly selective dual insulin receptor (IR)/insulin-like growth factor 1 receptor (IGF-1R) inhibitor derived from an ERK inhibitor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A291.

The prognostic value of Her4 receptor isoform expression in triple-negative and Her2 positive breast cancer patients

BackgroundNot only four but rather seven different human epidermal growth factor receptor related (Her) receptor tyrosine kinases (RTKs) have been described to be expressed in a variety of normal and neoplastic tissues: Her1, Her2, Her3, and additionally four Her4 isoforms have been identified. A differential expression of Her4 isoforms does not, however, play any role in either the molecular diagnostics or treatment decision for breast cancer patients. The prognostic and predictive impact of Her4 expression in breast cancer is basically unclear.MethodsWe quantified the Her4 variants JM-a/CYT1, JM-a/CYT2, JM-b/CYT1, and JM-b/CYT2 by isoform-specific polymerase chain reaction (qPCR) in (i) triple-negative, (ii) Her2 positive breast cancer tissues and (iii) in benign breast tissues.ResultsIn all three tissue collectives we never found the JM-b/CYT1 or the JM-b/CYT2 isoform expressed. In contrast, the two JM-a/CYT1 and JM-a/CYT2 isoforms were always simultaneously expressed but at different ratios. We identified a positive prognostic impact on overall survival (OS) in triple-negative and event-free survival (EFS) in Her2 positive patients. This finding is independent of the absolute JM-a/CYT1 to JM-a/CYT2 expression ratio. In Her2 positive patients, Her4 expression only has a favorable effect in estrogen-receptor (ER)-positive but not in ER-negative individuals.ConclusionIn summary, JM-a/CYT1 and JM-a/CYT2 but not JM-b isoforms of the Her4 receptor are simultaneously expressed in both triple-negative and Her2 positive breast cancer tissues. Although different expression ratios of the two JM-a isoforms did not reveal any additional information, Her4 expression basically indicates a prolonged EFS and OFS. An extended expression analysis that takes all Her receptor homologs, including the Her4 isoforms, into account might render more precisely the molecular diagnostics required for the development of optimized targeted therapies.

A Highly Selective Dual Insulin Receptor (IR)/Insulin-like Growth Factor 1 Receptor (IGF-1R) Inhibitor Derived from an Extracellular Signal-regulated Kinase (ERK) Inhibitor

Dual inhibitors of the closely related receptor tyrosine kinases insulin-like growth factor 1 receptor (IGF-1R) and insulin receptor (IR) are promising therapeutic agents in cancer. Here, we report an unusually selective class of dual inhibitors of IGF-1R and IR identified in a parallel screen of known kinase inhibitors against a panel of 300 human protein kinases. Biochemical and structural studies indicate that this class achieves its high selectivity by binding to the ATP-binding pocket of inactive, unphosphorylated IGF-1R/IR and stabilizing the activation loop in a native-like inactive conformation. One member of this compound family was originally reported as an inhibitor of the serine/threonine kinase ERK, a kinase that is distinct in the structure of its unphosphorylated/inactive form from IR/IGF-1R. Remarkably, this compound binds to the ATP-binding pocket of ERK in an entirely different conformation to that of IGF-1R/IR, explaining the potency against these two structurally distinct kinase families. These findings suggest a novel approach to polypharmacology in which two or more unrelated kinases are inhibited by a single compound that targets different conformations of each target kinase.

Update on HER1–3 in Advanced Non–Small-Cell Lung Cancer

Update on HER1–3 in Advanced Non–Small-Cell Lung Cancer

Differential expression of RON in small and non–small cell lung cancers

RON is a MET related receptor tyrosine kinase (RTK) and its natural ligand is macrophage stimulating protein (MSP). RON plays a very important role in the regulation of inflammation. Several studies have previously reported overexpression of RON in a variety of cancers including lung and identified numerous RON alternate splice forms that very likely contribute to tumor growth and metastasis. Here, we have analyzed the expression of total RON protein as well as its kinase-active form (phospho-RON) in 175 archival lung tumor FFPE (formalin fixed paraffin embedded) samples that included non-small-cell lung cancer (NSCLC) and small cell lung cancer (SCLC), and their metastatic forms. The frequency and intensity of RON protein expression was much higher in lung tumors of neuroendocrine origin such as SCLC and in secondary tumors that metastasized to brain. In addition, the majority of the expressed RON protein was phospho-RON. We also identified 62, and 30 kDa isoforms of RON (GenBank accession numbers are JN689381 and JN689382) using RNA isolated from pooled lung cancer cell lines and RT-PCR. A majority of the NSCLC cell lines expressed a 150 kDa band that corresponded to the RON β chain and 120 kDa band in the panel of SCLC cell lines tested. RON was expressed on the cell surface in NSCLC cell lines. Finally, knock down of RON expression resulted in a significant loss in viability as well as motility in lung cancer cells suggesting that RON is a potential therapeutic target.

Distinct Involvement of the Gab1 and Grb2 Adaptor Proteins in Signal Transduction by the Related Receptor Tyrosine Kinases RON and MET

Although the signal transduction mechanisms of the receptor tyrosine kinase MET are well defined, less is known about its close relative RON. MET initiates intracellular signaling by autophosphorylation on specific cytoplasmic tyrosines that form docking sites for the adaptor proteins Grb2 and Gab1. Grb2 binds directly and is essential for all of the biological activities of MET. Gab1 docks either directly or indirectly via Grb2 and controls only a subset of MET functions. Because MET and RON possess similar adaptor binding sites, it was anticipated that their adaptor interactions would be conserved. Here we show that in contrast to MET, RON relies primarily on Gab1 for signal transmission. Surprisingly, disruption of the Grb2 docking site of RON or Grb2 depletion augments activity, whereas enhancement of Grb2 binding attenuates Gab1 recruitment and signaling. Hence, RON and MET differ in their adaptor interactions; furthermore, Grb2 performs a novel antagonistic role in the context of RON signaling.

An open-label, multicenter biomarker-oriented phase II trial of sunitinib for patients with chemo-refractory advanced gastric cancer

Background: Tumour angiogenesis, growth, and metastasis can be inhibited by blocking receptor tyrosine kinases (RTKs) overexpressed in human advanced gastric cancer (AGC), including vascular endothelial growth factor receptors (VEGFRs), epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptors (PDGFRs). Sunitinib malate, an oral, multi-targeted tyrosine kinase inhibitor of VEGFR1, -2, and -3, PDGFR-α and -β, and several other related RTKs was investigated Sunitinib in pretreated patients with AGC. Preplanned analyses of tumour biomarkers on treatment outcome were performed.

Abstract 3130: The short form of the receptor tyrosine kinase Ron is expressed in acute myeloid leukemia, regulated by methylation and sensitizes leukemic cells to c-Met inhibitors

Abstract Acute myeloid leukemia (AML) are heterogeneous hematopoietic disorders characterized by an accumulation of immature leukemic cells and by a block in cell differentiation. In spite of recent therapeutical advances and frequent complete remission, all patients shortly relapse leading to an urgent need for more specific targeted treatments. Beside the development of epigenetic and differentiation therapies for AML, therapeutic strategies targeting protein tyrosine kinases are also attractive and promising. Here we report a novel oncogenic activity of the cMet related receptor tyrosine kinase Ron (Recepteur d'Origine Nantais) in AML. Ron is expressed in most epithelial tissues as well as in normal hematopoietic CD34+ cells and macrophages. Its oncogenic properties have been documented in solid tumors and a truncated form of Ron (short form of Ron, sf-Ron) lacking most of the Ron receptor extracellular domain but retaining the whole transmembrane and intracellular domains has been detected in several tissues and in KG1 AML cell line. We found that sf-Ron was expressed in 44% of AML patients cells (n=87), whereas 38% of patient cells did not express neither fl-Ron nor sf-Ron. Interestingly only fl-Ron is expressed in CD34+ normal cells suggesting that sf-Ron could be specific of leukemic cells. Accordingly, sf-Ron was found to be active in AML samples unlike the fl-Ron. Inhibition of sf-Ron activity by either the dual c-Met/Ron inhibitor SU-11274 or a specific siRNA approach inhibited clonogenic properties and induced apoptosis only in sf-RON positive AML cells. Moreover, the leukemic compartment CD34+CD38-CD123+ often associated with the chemoresistance and clinical relapse, was also sensitive to this treatment. Additionally, we observed an original link between sfRon and the tyrosine kinase Lyn previously described to be strongly deregulated in AML cells. Indeed, we showed that sf-Ron is associated with Lyn and these two tyrosine kinases activate each other. Finally, a recent study described an epigenetic mechanism of expression regulation of Ron and sf-Ron, showing the existence of two distinct CpG islands. Indeed, 5-Azacytidine treatment of AML cells led to a marked down-regulation of sf-Ron in AML cells. This effect was accompanied by a strong reduction of Lyn activity. In conclusion, our study suggests that targeting sf-Ron activity might be of therapeutic value in AML and uncovers novel mechanisms by which hypomethylating agents would act on AML and myelodysplastic syndromes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3130. doi:10.1158/1538-7445.AM2011-3130

The t(4;9)(q11;q33) fuses CEP110 to KIT in a case of acute myeloid leukemia

KIT is a class III receptor tyrosine kinase (RTK) that has an important role in hemopoiesis, particularly with regard to stem cell maintenance and mast cell development. KIT is normally activated by engagement with its ligand, stem cell factor, but a variety of acquired KIT point mutations have been described in acute myeloid leukemia (AML) and systemic mastocytosis that result in constitutive, ligand-independent activation. In contrast to other related RTKs such as PDGFRA, PDGFRB and FLT3, constitutive activation of KIT by gene fusion has not been described.

Epithelial cell-directed efferocytosis in the post-partum mammary gland is necessary for tissue homeostasis and future lactation

BackgroundMammary glands harbor a profound burden of apoptotic cells (ACs) during post-lactational involution, but little is known regarding mechanisms by which ACs are cleared from the mammary gland, or consequences if this process is interrupted. We investigated AC clearance, also termed efferocytosis, during post-lactational remodeling, using mice deficient for MerTK, Axl, and Tyro3, three related receptor tyrosine kinases (RTKs) regulating macrophage-mediated efferocytosis in monocytes. MerTK expression, apoptosis and the accumulation of apoptotic debris were examined in histological sections of MerTK-deficient, Axl/Tyro3-deficient, and wild-type mammary glands harvested at specific time points during lactation and synchronized involution. The ability of primary mammary epithelial cells (MECs) to engulf ACs was assessed in culture. Transplant of MerTK-deficient mammary epithelium into cleared WT mammary fat pads was used to assess the contribution of WT mammary macrophages to post-lactational efferocytosis.ResultsACs induced MerTK expression in MECs, resulting in elevated MerTK levels at the earliest stages of involution. Loss of MerTK resulted in AC accumulation in post-lactational MerTK-deficient mammary glands, but not in Axl and Tyro3-deficient mammary glands. Increased vascularization, fibrosis, and epithelial hyperproliferation were observed in MerTK-deficient mammary glands through at least 60 days post-weaning, due to failed efferocytosis after lactation, but did not manifest in nulliparous mice. WT host-derived macrophages failed to rescue efferocytosis in transplanted MerTK-deficient mammary epithelium.ConclusionEfferocytosis by MECs through MerTK is crucial for mammary gland homeostasis and function during the post-lactational period. Efferocytosis by MECs thus limits pathologic consequences associated with the apoptotic load following lactation.

Discovery and selectivity-profiling of 4-benzylamino 1-aza-9-oxafluorene derivatives as lead structures for IGF-1R inhibitors

Recently the insuline-like growth factor receptor (IGF-1R) emerged as a promising target structure for the development of novel anti-cancer agents. IGF-1R plays a central role in both tumour progression and resistance development against anti-cancer drugs. We discovered 1-aza-9-oxafluorene derivatives as novel lead structures with submicromolar activities against IGF-1R. Structure-activity relationships (SARs) on a series of related receptor tyrosine kinases (RTKs) are discussed in the context of available crystal structures. A preliminary selectivity-profiling is demonstrated for the first compound series. Antiproliferative tumour cell line screening studies yielded one candidate as a promising cytostatic agent without significant toxic effects.