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Aurora kinases.

Aurora kinases A (also known as Aurora, Aurora-2, AIK, AIR-1, AIRK1, AYK1, BTAK, Eg2, MmIAK1 and STK15), Aurora B (also known as Aurora-1, AIM-1, AIK2, AIR-2, AIRK-2, ARK2, IAL-1 and STK12) and Aurora C (also known as AIK3) participate in several biological processes, including cytokinesis and dysregulated chromosome segregation. These important regulators of mitosis are over-expressed in diverse solid tumors. One member of this family of serine-threonine kinases, human Aurora A, has been proposed as a drugable target in pancreatic cancer. The recent determination of the three-dimensional structure of Aurora A has shown that Aurora kinases exhibit unique conformations around the activation loop region. This property has boosted the search and development of inhibitors of Aurora kinases, which might also function as novel antioncogenic agents.

Amino Acid Sequence↗

Characterization of a splicing variant of plant Aurora kinase.

Aurora kinases play a key role in chromosome segregation and cytokinesis. In plants, three Aurora kinases (AtAUR1-AtAUR3) have been identified in Arabidopsis thaliana. Here, we report an AtAUR2 splicing variant (AtAUR2S), which lacks the fourth exon encoding a part of the kinase domain of AtAUR2. AtAUR2S was shown to have lost its kinase activity to phosphorylate histone H3 at Ser10; however, it maintained its ability to bind to histone H3. The localization pattern of AtAUR2S was the same as that of AtAUR2. The findings suggest that AtAUR2S affects cell division by competing with AtAUR2.

Amino Acid Sequence↗

Structure-based design of novel anti-cancer agents targeting aurora kinases.

Aurora kinases are a family of mitotic serine-threonine kinases (S/T kinases), that functions as a class of novel oncogenes and are over-expressed in several solid tumors including breast, ovary, prostate, pancreas and colorectal cancer. To validate human ARK1 (Aurora2, STK15, HsAIRK1) as a drugable target in pancreatic cancer, we undertook a structure-based approach to design specific inhibitors utilizing homology modeling, affinity docking and an in vitro kinase assay in an iterative process. In this review, we discuss the biology, rationale for targeting and approaches taken to inhibit this family of protein kinases, implicated in dysregulated chromosome segregation and cytokinesis.

Animals↗

The in vitro and in vivo effects of JNJ-7706621: a dual inhibitor of cyclin-dependent kinases and aurora kinases.

Modulation of aberrant cell cycle regulation is a potential therapeutic strategy applicable to a wide range of tumor types. JNJ-7706621 is a novel cell cycle inhibitor that showed potent inhibition of several cyclin-dependent kinases (CDK) and Aurora kinases and selectively blocked proliferation of tumor cells of various origins but was about 10-fold less effective at inhibiting normal human cell growth in vitro. In human cancer cells, treatment with JNJ-7706621 inhibited cell growth independent of p53, retinoblastoma, or P-glycoprotein status; activated apoptosis; and reduced colony formation. At low concentrations, JNJ-7706621 slowed the growth of cells and at higher concentrations induced cytotoxicity. Inhibition of CDK1 kinase activity, altered CDK1 phosphorylation status, and interference with downstream substrates such as retinoblastoma were also shown in human tumor cells following drug treatment. Flow cytometric analysis of DNA content showed that JNJ-7706621 delayed progression through G1 and arrested the cell cycle at the G2-M phase. Additional cellular effects due to inhibition of Aurora kinases included endoreduplication and inhibition of histone H3 phosphorylation. In a human tumor xenograft model, several intermittent dosing schedules were identified that produced significant antitumor activity. There was a direct correlation between total cumulative dose given and antitumor effect regardless of the dosing schedule. These results show the therapeutic potential of this novel cell cycle inhibitor and support clinical evaluation of JNJ-7706621.

Animals↗

[Aurora kinases and cancer].

Aurora kinases are highly conserved in eukaryotes and involved in many processes during cell division. Three Aurora kinases have been identified in humans and designated as Aurora-A, -B, and -C. Aurora A regulates centrosome function during M phase through its interactions with various cell cycle regulators including TACC, chTOG, Ajuba, BRCA1, LATS2, and p53. Aurora-B localizes at the kinetochore from G2 to metaphase, and relocates to the midbody after anaphase. Aurora-B plays roles in spindle dynamics, chromosome condensation, and cytokinesis by interacting with many proteins such as INCENP, Survivin, CENP-A, MgcRacGAP, and intermediate filaments. Overexpression of both Aurora-A and -B proteins is frequently observed in various human cancer tissues, and a common coding region polymorphism in aurora-A affects the risk of breast or esophageal cancer. Ectopic overexpression of Aurora-A or -B protein leads to aneuploid cells. The cells overexpressing active Aurora A or wildtype Aurora-B are tumorigenic in nude mice.

Animals↗

Characterization of plant Aurora kinases during mitosis.

The Aurora kinase family is a well-characterized serine/threonine protein kinase family that regulates different processes of mitotic events. Although functions of animal and yeast Aurora kinases have been analyzed, plant aurora kinases were not identified and characterized. We identified three Aurora kinase orthologs in Arabidopsis thaliana and designated these as AtAUR1, AtAUR2, and AtAUR3. These AtAURs could phosphorylate serine 10 in histone H3, in vitro. Dynamic analyses of GFP-fused AtAUR proteins revealed that AtAUR1 and AtAUR2 localized at the nuclear membrane in interphase and located in mitotic spindles during cell division. AtAUR1 also localized in the cell plates. AtAUR3 showed dot-like distribution on condensed chromosomes at prophase and then localized at the metaphase plate. At late anaphase, AtAUR3 is evenly localized on chromosomes. The localization of AtAUR3 during mitosis is very similar to that of phosphorylated histone H3. Interestingly, an overexpression of AtAUR3 induces disassembly of spindle microtubules and alteration of orientation of cell division. Our results indicate that plant Aurora kinases have different characters from that of Aurora kinases of other eukaryotes.

Amino Acid Sequence↗

Phospho-regulation of kinetochore-microtubule attachments by the Aurora kinase Ipl1p.

The Aurora kinase Ipl1p plays a crucial role in regulating kinetochore-microtubule attachments in budding yeast, but the underlying basis for this regulation is not known. To identify Ipl1p targets, we first purified 28 kinetochore proteins from yeast protein extracts. These studies identified five previously uncharacterized kinetochore proteins and defined two additional kinetochore subcomplexes. We then used mass spectrometry to identify 18 phosphorylation sites in 7 of these 28 proteins. Ten of these phosphorylation sites are targeted directly by Ipl1p, allowing us to identify a consensus phosphorylation site for an Aurora kinase. Our systematic mutational analysis of the Ipl1p phosphorylation sites demonstrated that the essential microtubule binding protein Dam1p is a key Ipl1p target for regulating kinetochore-microtubule attachments in vivo.

Amino Acid Sequence↗

Expression of Aurora kinases A and B in normal, hyperplastic, and malignant human endometrium: Aurora B as a predictor for poor prognosis in endometrial carcinoma.

Aurora kinases such as Aurora A and Aurora B are key regulators of mitosis and have been reported to be overexpressed in various malignancies. However, the expression and localization of Aurora kinases in normal and neoplastic endometrial tissues remain undetermined. In the present study, immunohistochemical expression of Aurora A and B was examined in 40 normal, 30 hyperplastic, and 73 malignant endometria. The data were compared with the expression of Ki-67 and patient survivals. The expression of Aurora A and B at protein and messenger RNA levels was also examined using Western blotting and the reverse transcriptase polymerase chain reaction. The expression of Aurora A in normal endometrium was observed mainly in the proliferative phase and was decreased in the secretory phase. The Aurora A expression was significantly increased in carcinomas compared with normal proliferative endometrium; however, there was no correlation of Aurora A expression with Ki-67 expression or patient survival. The expression of Aurora B in normal endometrium was significantly higher in the proliferative phase than in the secretory phase. In endometrial carcinomas, the expression of Aurora B was correlated with Ki-67 expression and was significantly increased in high-grade tumors. In addition, patients with Aurora B-positive carcinoma showed poor prognosis compared with those with Aurora B-negative carcinoma (P = .0135). Accordingly, the present study indicates the aberrant expression of Aurora A and Aurora B in endometrial carcinomas and the clinical importance of Aurora B expression in relationship to patient prognosis.

Adenocarcinoma↗

Phosphorylation by aurora kinase A induces Mdm2-mediated destabilization and inhibition of p53.

Aurora kinase A (also called STK15 and BTAK) is overexpressed in many human cancers. Ectopic overexpression of aurora kinase A in mammalian cells induces centrosome amplification, chromosome instability and oncogenic transformation, a phenotype characteristic of loss-of-function mutations of p53. Here we show that aurora kinase A phosphorylates p53 at Ser315, leading to its ubiquitination by Mdm2 and proteolysis. p53 is not degraded in the presence of inactive aurora kinase A or ubiquitination-defective Mdm2. Destabilization of p53 by aurora kinase A is abrogated in the presence of mutant Mdm2 that is unable to bind p53 and after repression of Mdm2 by RNA interference. Silencing of aurora kinase A results in less phosphorylation of p53 at Ser315, greater stability of p53 and cell-cycle arrest at G2-M. Cells depleted of aurora kinase A are more sensitive to cisplatin-induced apoptosis, and elevated expression of aurora kinase A abolishes this response. In a sample of bladder tumors with wild-type p53, elevated expression of aurora kinase A was correlated with low p53 concentration. We conclude that aurora kinase A is a key regulatory component of the p53 pathway and that overexpression of aurora kinase A leads to increased degradation of p53, causing downregulation of checkpoint-response pathways and facilitating oncogenic transformation of cells.

Apoptosis↗

The Aurora kinases: role in cell transformation and tumorigenesis.

Aurora kinases representing a novel family of serine/threonine kinases have been identified as key regulators of the mitotic cell division process. The three members of this kinase family, identified so far, referred to as Aurora-A, Aurora-B and Aurora-C kinases, are close homologues of the prototypic yeast Ipll and Drosophila aurora kinases, which are known to be involved in the regulation of centrosome function, bipolar spindle assembly and chromosome segregation processes. All three members of the mammalian kinase family have a catalytic domain that is highly conserved with a short C-terminal domain and an N-terminal domain of varying sizes. Following their discovery about five years ago, extensive research has focused on understanding the biological roles of these kinases and elucidation of their pathways, which regulate cell proliferation and maintenance of normal cellular phenotypes. Significant interest in the subject was generated since all three Aurora kinases family members were reported to be overexpressed in many human cancers, and elevated expression has been correlated with chromosomal instability and clinically aggressive disease in some instances. Ectopic overexpression of one member of the family, Aurora-A, was shown to induce oncogenic transformation in cells. Unlike most other putative oncogenes identified, so far, members of this kinase family are expressed and active at the highest level during G2-M phase of the cell cycle. Aurora kinases are localized at the centrosomes of interphase cells, at the poles of the bipolar spindle and in the midbody of the mitotic apparatus. Substrates identified for the Aurora-A and Aurora-B kinases, include a kinesin-like motor protein, spindle apparatus proteins, histone H3 protein, kinetochore protein and the tumor suppressor protein p53. Identification of Aurora kinases as RasGAP Src homology 3 domain binding protein, also implicates these kinases as potential effectors in the Ras pathway relevant to oncogenesis. Abnormal elevated expression of Aurora kinases detected in human cancer cells could help explain the underlying biological mechanisms responsible for the development of many cellular phenotypes associated with malignant cells. Identification of these mechanisms offers the possibility of designing novel targeted therapies for cancer in the future.

Amino Acid Sequence↗

PHA-680632, a novel Aurora kinase inhibitor with potent antitumoral activity.

PURPOSE: Aurora kinases play critical roles during mitosis in chromosome segregation and cell division. The aim of this study was to determine the preclinical profile of a novel, highly selective Aurora kinase inhibitor, PHA-680632, as a candidate for anticancer therapy. EXPERIMENTAL DESIGN: The activity of PHA-680632 was assayed in a biochemical ATP competitive kinase assay. A wide panel of cell lines was evaluated for antiproliferative activity. Cell cycle analysis. Immunohistochemistry, Western blotting, and Array Scan were used to follow mechanism of action and biomarker modulation. Specific knockdown of the targets by small interfering RNA was followed to validate the observed phenotypes. Efficacy was determined in different xenograft models and in a transgenic animal model of breast cancer. RESULTS: PHA-680632 is active on a wide range of cancer cell lines and shows significant tumor growth inhibition in different animal tumor models at well-tolerated doses. The mechanism of action of PHA-680632 is in agreement with inhibition of Aurora kinases. Histone H3 phosphorylation in Ser10 is mediated by Aurora B kinase, and our kinetic studies on its inhibition by PHA-680632 in vitro and in vivo show that phosphorylation of histone H3 is a good biomarker to follow activity of PHA-680632. CONCLUSIONS: PHA-680632 is the first representative of a new class of Aurora inhibitors with a high potential for further development as an anticancer therapeutic. On treatment, different cell lines respond differentially, suggesting the absence of critical cell cycle checkpoints that could be the basis for a favorable therapeutic window.

Animals↗

Targeting aurora kinases as therapy in multiple myeloma.

The aurora kinases facilitate transit from G2 through cytokinesis and, thus, are targets in cancer therapy. Multiple myeloma (MM) is a malignancy characterized by genetic instability, suggesting a disruption of checkpoints that arrest cells at G2M when injury to the mitotic machinery occurs. Since deficient checkpoints would prevent cell cycle arrest and may render cells susceptible to apoptosis in mitosis and since aurora kinases are intermediaries in checkpoint pathways, we tested antimyeloma effects of 2 agents that inhibit aurora kinases. Both inhibited growth of MM lines and primary myeloma samples at nanomolar concentrations while having less of an effect on proliferating lymphocytes and hematopoietic cells. MM cells were not protected by IL-6 or activating mutations of Ras. Antimyeloma effects included induction of tetraploidy followed by apoptosis. Apoptosis correlated with inhibition of aurora activity as shown by reduction of histone 3B phosphorylation. Ectopic expression of aurora A protected MM cells against aurora inhibitors but had no effect on apoptosis induced by bortezomib. As expression of RHAMM in MM contributes to genetic instability, we tested effects of RHAMM. RHAMM overexpression enhanced sensitivity to apoptosis and RHAMM silencing decreased sensitivity. These results suggest potential for aurora kinase inhibitors in MM especially in patients in whom RHAMM is overexpressed.

Antineoplastic Agents↗

A Ran signalling pathway mediated by the mitotic kinase Aurora A in spindle assembly.

The activated form of Ran (Ran-GTP) stimulates spindle assembly in Xenopus laevis egg extracts, presumably by releasing spindle assembly factors, such as TPX2 (target protein for Xenopus kinesin-like protein 2) and NuMA (nuclear-mitotic apparatus protein) from the inhibitory binding of importin-alpha and -beta. We report here that Ran-GTP stimulates the interaction between TPX2 and the Xenopus Aurora A kinase, Eg2. This interaction causes TPX2 to stimulate both the phosphorylation and the kinase activity of Eg2 in a microtubule-dependent manner. We show that TPX2 and microtubules promote phosphorylation of Eg2 by preventing phosphatase I (PPI)-induced dephosphorylation. Activation of Eg2 by TPX2 and microtubules is inhibited by importin-alpha and -beta, although this inhibition is overcome by Ran-GTP both in the egg extracts and in vitro with purified proteins. As the phosphorylation of Eg2 stimulated by the Ran-GTP-TPX2 pathway is essential for spindle assembly, we hypothesize that the Ran-GTP gradient established by the condensed chromosomes is translated into the Aurora A kinase gradient on the microtubules to regulate spindle assembly and dynamics.

Animals↗

Expression of Aurora kinases in human thyroid carcinoma cell lines and tissues.

The Aurora kinases are involved in the regulation of cell cycle progression, and alterations in their expression have been shown to associate with cell malignant transformation. In the present study, we demonstrated that human thyrocytes express all 3 Aurora kinases (A, B and C) at both protein and mRNA level and this expression is cell cycle-regulated. An increase in the protein level of the 3 kinases was found, with respect to normal human thyrocytes (HTU5), in the human cell lines derived from follicular (FTC-133), papillary (B-CPAP) and anaplastic (8305C) thyroid carcinomas, but not in cells derived from a follicular adenoma (HTU42). These observations were mirrored in RT-PCR experiments for Aurora-A and B. In contrast, Aurora-C mRNA levels were not significantly different among the different cell types analyzed, suggesting that posttranscriptional mechanism(s) modulate its expression. The expression at the protein level of all 3 Aurora kinases was significantly higher in 3 thyroid papillary carcinomas with respect to normal matched tissues obtained from the same patients. Similar modifications, at the mRNA level, could be observed in 7 papillary carcinoma tissues for Aurora-A and B, but not for Aurora-C. In conclusion, we demonstrated that normal human thyrocytes express all 3 members of the Aurora kinase family, and their expression is amplified in malignant thyroid cell lines and tissues. These results suggest that the Aurora kinases may play a relevant role in malignant thyroid cancers, and may represent a putative therapeutic target for thyroid neoplasms.

Adenocarcinoma, Follicular↗

Aurora kinase inhibitors: a new class of targeted drugs in cancer.

Aurora kinases (A, B, and C) are essential for spindle assembly, centrosome maturation, chromosomal segregation, and cytokinesis. Aurora kinases A and B are overexpressed in many cancers, including non-small-cell lung cancer and mesothelioma. Small-molecule inhibitors selective for aurora kinases have shown promising activity in preclinical tumor models. To date, phase I studies with aurora kinase inhibitors have shown that myelosuppression is the dose-limiting toxicity, and disease stabilization was achieved in a number of tumor types, including non-small-cell lung cancer. Phase II trials are under way in selected tumor types. This article reviews the biology of aurora kinases, their potential role in the treatment of lung cancer, and challenges in the clinical development of this unique class of antineoplastic agents.

Antineoplastic Agents↗

Therapeutic potential of Aurora kinase inhibitors in cancer.

Aurora kinases (AKs) represent a family of serine/threonine protein kinases that regulate mitotic processes during cell division. They are primarily involved in regulating the multiple steps of mitosis, including centrosome duplication, formation of bipolar mitotic spindle, chromosome alignment on the mitotic spindle, establishment and maintenance of the spindle checkpoint and cytokinesis. As AKs are key regulators of mitosis, several studies have indicated that they have a strong association with cancer and are overexpressed in numerous cancerous cell lines as well as human malignancies. Thus, AKs represent a promising therapeutic target for anticancer drug development. In this review, the role of AKs in cancer, and the current status and therapeutic potential of AK inhibitors is discussed.

Animals↗

Aurora kinases: new targets for cancer therapy.

The Aurora kinase family is a collection of highly related serine/threonine kinases that functions as a key regulator of mitosis. In mammalian cells, Aurora has evolved into three related kinases known as Aurora-A, Aurora-B, and Aurora-C. These kinases are overexpressed in a number of human cancers, and transfection studies have established Aurora-A as a bone fide oncogene. Because Aurora overexpression is associated with malignancy, these kinases have been targeted for cancer therapy. This article reviews the multiple functions of Aurora kinase in the regulation of mitosis and the mitotic checkpoint, the role of abnormal Aurora kinase activity in the development of cancer, the putative mechanisms of Aurora kinase inhibition and its antitumor effects, the development of the first generation of Aurora kinase inhibitors, and prospects for the future of Aurora kinase inhibition in the treatment of cancer.

Animals↗

VX-680, a potent and selective small-molecule inhibitor of the Aurora kinases, suppresses tumor growth in vivo.

The Aurora kinases are essential for the regulation of chromosome segregation and cytokinesis during mitosis. Aberrant expression and activity of these kinases occur in a wide range of human tumors, and lead to aneuploidy and tumorigenesis. Here we report the discovery of a highly potent and selective small-molecule inhibitor of Aurora kinases, VX-680, that blocks cell-cycle progression and induces apoptosis in a diverse range of human tumor types. This compound causes profound inhibition of tumor growth in a variety of in vivo xenograft models, leading to regression of leukemia, colon and pancreatic tumors at well-tolerated doses. Our data indicate that Aurora kinase inhibition provides a new approach for the treatment of multiple human malignancies.

Animals↗