4-Aminoquinazoline Analogs: A Novel Class of Anticancer Agents
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4-Aminoquinazoline analogs have been identified as a new class of cancer chemotherapeutic agents with significant therapeutic efficacy against solid tumors. They are potent and highly selective inhibitors of tyrosine kinase (TK) and epidermal growth factor receptor (EGFR). Till date various 4-aminoquinazoline analogs have been synthesized and evaluated for anticancer activity. This review is an attempt to compile the medicinal chemistry of various synthesized 4-aminoquinazoline analogs. Keywords: 4-Aminoquinazoline, antitumor, apoptosis, cytotoxic, epidermal growth factor receptor, tyrosine kinase.Because conventional chemotherapy is not specific for cancer cells leading to toxic side effects there is a need for novel agents with high grade antitumor specificity. The major prerequisite to develop such drugs is to understand the targets that these agents should attack. In recent years a number of promising new anticancer drugs have been developed which target intracellular pathways or extracellular cell molecules. The clinically most effective compounds function as tyrosine kinase inhibitors. In the past, various tyrosine kinase receptors have been identified as regulators of tumor or tumor vessel growth. Having shown their expression characteristics in different tumor entities, specific inhibitors of the ATP binding sites of these receptors or antibodies were developed and entered clinical trials. The pathognomonic role of the tyrosine kinase defines the way of action of the inhibiting drug, whereas the amount of expression in tumor tissue defines the rationale to use the inhibitor to treat a specific protein. The future will define indications for such drugs by tumor kinase profiles instead of tumor entities. Gleevec, inhibiting the BCR-ABL tyrosine kinase; Iressa, inhibiting the EGF-receptor tyrosine kinase, Herceptin, inhibiting the Her2 / neu tyrosine kinase and PTK787 / ZK222584, inhibiting the VEGF-receptor tyrosine kinase will be discussed as representatives of selective tyrosine kinase inhibitors whereas ZD6474 and SU6668 will be discussed as representatives of multitarget tyrosine kinase inhibitors. Keywords: tyrosine kinases, receptor tyrosine kinase, anti cancer, vegf-receptor, egf-receptor
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Tyrosine kinases have significant roles in cell growth, apoptosis, development, and disease. To explore the use of zebrafish as a vertebrate model for tyrosine kinase signaling and to better understand their roles, we have identified all of the tyrosine kinases encoded in the zebrafish genome and quantified RNA expression of selected tyrosine kinases during early development. Using profile hidden Markov model analysis, we identified 122 zebrafish tyrosine kinase genes and proposed unambiguous gene names where needed. We found them to be organized into 39 nonreceptor and 83 receptor type, and 30 families consistent with human tyrosine kinase family assignments. We found five human tyrosine kinase genes (epha1, bmx, fgr, srm, and insrr) with no identifiable zebrafish ortholog, and one zebrafish gene (yrk) with no identifiable human ortholog. We also found that receptor tyrosine kinase genes were duplicated more often than nonreceptor tyrosine kinase genes in zebrafish. We profiled expression levels of 30 tyrosine kinases representing all families using direct digital detection at different stages during the first 24 hours of development. The profiling experiments clearly indicate regulated expression of tyrosine kinases in the zebrafish, suggesting their role during early embryonic development. In summary, our study has resulted in the first comprehensive description of the zebrafish tyrosine kinome.
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Abstract : Receptor tyrosine kinases are important in cell signal transduction and proliferation. Abnormal expression of tyrosine kinases often leads to malignant transformation. C-met is a tyrosine kinase receptor and its ligand is hepatocyte growth factor (HGF). HGF/c-met plays diverse role in regulation of cell growth, shape and movement. Constitutively activated met, such as tpr-met, is a potent oncogene in vitro, but its carcinogenic role in vivo remains unclear. Our study demonstrates that expression of tpr-met leads to development of mammary tumors and other malignancies in transgenic mice, and suggests that deregulated met expression may be involved in mammary carcinogenesis.
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Receptor Protein-Tyrosine Kinases
Malignant Transformation
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Purpose of review Extensive evidence indicates that receptor tyrosine kinases and nonreceptor tyrosine kinases underlie vascular damage in hypertension. However, recent clinical studies using vascular endothelial growth factor (VEGF) receptor inhibitors (bevacizumab, axitinib) revealed the unexpected finding of increased blood pressure. Whether this is a generalized receptor tyrosine kinase phenomenon or a VEGF receptor-specific effect is unclear. The present review focuses on current findings regarding the role of tyrosine kinases and signaling in vascular pathobiology of hypertension. Recent findings Multiple complex and interacting signaling pathways activated by receptor and nonreceptor tyrosine kinases are upregulated and have been implicated in vascular alterations associated with high blood pressure. Experimental evidence suggests that receptor tyrosine kinase activation by direct ligand binding as well as by ligand-independent mechanisms through transactivation by G protein-coupled receptors plays a role in vascular signaling and cardiovascular diseases. Summary Cellular mechanisms and signaling pathways mediated by tyrosine kinases involved in hypertensive vascular damage are currently the subject of intensive investigation. The unexpected finding of hypertension as a side effect in patients treated with VEGF receptor inhibitors suggests that some tyrosine kinases negatively regulate vascular function. Further characterization of these processes will provide greater understanding of the role of tyrosine kinases in vascular pathobiology in hypertension and should provide new insights on novel therapeutic targets.
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Dimerized and enzymatically active epidermal growth factor receptor, in the presence of saturating epidermal growth factor (EGF), was passed over a column containing an immunoadsorbent for EGF. The immunoadsorbent removed both EGF free in solution and EGF bound to EGF receptor, while EGF receptor passed through unimpeded. Both the dimerization of EGF receptor and the activation of its tyrosine kinase were arrested in samples containing EGF receptor that had been mixed with saturating EGF and then immediately passed over the immunoadsorbent for EGF. The EGF receptor in these samples, however, dimerized completely, and its tyrosine kinase became fully active upon readdition of EGF. Samples of EGF receptor that were fully dimerized and enzymatically active prior to being passed over the immunoadsorbent for EGF remained dimerized and enzymatically active even in the absence of bound EGF. The first-order rate constant for the inactivation of the tyrosine kinase of EGF receptor depleted of EGF was estimated by subtracting the rate constant of inactivation of the tyrosine kinase in samples replenished with EGF from the rate constant of inactivation of the tyrosine kinase in samples that had been depleted of EGF. The rate constant of inactivation was found to be 0.26 +/- 0.06 h-1.
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Abstract Novel high-throughput analyses in molecular biology allow sensitive and rapid identification of disease-related genes and drug targets. We have used quantitative real-time reverse transcription-PCR reactions (n = 23,000) to analyze expression of all human receptor tyrosine kinases (n = 56) in malignant tumors (n = 313) of different origins and normal control samples (n = 58). The different tumor types expressed very different numbers of receptor tyrosine kinases: whereas brain tumors and testicular cancer expressed 50 receptor tyrosine kinases, acute myeloid leukemia (AML) samples expressed only 20 different ones. Specimens of similar tumor origin exhibited characteristic receptor tyrosine kinase expression patterns and were grouped together in hierarchical cluster analyses. When we focused on specific tumor entities, receptor tyrosine kinases were identified that were disease and/or stage specific. Leukemic blasts from AML bone marrow samples differed significantly in receptor tyrosine kinase expression compared with normal bone marrow and purified CD34+ cells. Among the differentially expressed receptor tyrosine kinases, we found FLT3, c-kit, CSF1 receptor, EPHB6, leukocyte tyrosine kinase, and ptk7 to be highly overexpressed in AML samples. Whereas expression changes of some of these were associated with altered differentiation patterns (e.g., CSF1 receptor), others, such as FLT3, were genuinely overexpressed in leukemic blasts. These data and the associated database (http://medweb.uni-muenster.de/institute/meda/research/) provide a comprehensive view of receptor tyrosine kinase expression in human cancer. This information can assist in the definition of novel drug targets.
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Abstract Receptor tyrosine kinases (RTKs) comprise a family of cell surface receptors that control many critical cellular processes. Various human diseases are caused by dysfunction in RTKs or in their intracellular signaling pathways. Stem Cell Factor (SCF) initiates its multiple cellular responses by binding to the extracellular region of the RTK KIT resulting in receptor dimerization and tyrosine kinase activation. We have determined the crystal structure of the entire extracellular region of KIT before and after SCF stimulation. The structures show that KIT dimerization is driven by SCF binding whose sole role is to bring two KIT molecules together. We have used X-ray crystallography, electron microscopy (EM) and biochemical experiments to determine the three dimensional structure of intact, SCF-stimulated KIT dimers. Several forms of dimeric KIT molecules with different asymmetric arrangements of the two tyrosine kinase domains were identified. These asymmetric contacts may represent specific interactions occurring between two KIT tyrosine kinase domains poised towards trans autophosphorylation. We propose that cooperative interactions mediated by multiple weak homotypic contacts between the extracellular, transmembrane and cytoplasmic regions of KIT are responsible for tyrosine kinase activation and cell signaling in normal and transformed cells. Sutent is a drug that blocks the tyrosine kinase activities of several RTKs including KIT and VEGFR2. Sutent has been approved by the FDA for the treatment of advanced kidney cancers, gastrointestinal tumors and for endocrine pancreatic cancers. A scaffold-based drug discovery approach was developed enabling the development of new families of inhibitors for protein kinases and other enzymes that play a role in cell signaling. V600E B-RAF mutant is an oncogenic mutation identified in approximately 50% of melanomas and in 4% of all solid tumors. By using a scaffold-based drug discovery approach, a potent inhibitor of V600E B-RAF mutant has been discovered designated PLX 4032 (Vemurafenib). Phase-I and-II clinical trials in multiple medical centers revealed 80% responses such as tumor shrinkage, delay in tumor progression and survival of melanoma patients harboring the B-RAF mutation. Primary endpoints of phase-III clinical trials in multiple medical centers were achieved to support Vemurafenib registration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr PL04-03. doi:1538-7445.AM2012-PL04-03
Cell Signaling
Proto-Oncogene Proteins c-kit
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