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

Aurora-A amplification associated with BRCA2 mutation in breast tumours

Potential interaction of Aurora-A amplification and BRCA2 mutation was examined in breast tumours from BRCA2 999del5 mutation carriers (n=20) and non-carriers (n=41). Aurora-A amplification studied by FISH was significantly more common in breast tumours from BRCA2 mutation carriers (p=0.0005). Extensive Aurora-A amplification was also detected on metaphase chromosomes in three breast epithelial cell lines with the same BRCA2 mutation. In addition, significant association was found between Aurora-A amplification and TP53 mutations in non-BRCA2 mutation carrier tumours (p=0.007). These results suggest that breast tumours with mutations in BRCA2 or TP53 could be promising candidates for Aurora-A targeted treatment.

Discovery, synthesis, and in vivo activity of a new class of pyrazoloquinazolines as selective inhibitors of aurora B kinase

The Aurora kinases have been the subject of considerable interest as targets for the development of new anticancer agents. While evidence suggests inhibition of Aurora B kinase gives rise to the more pronounced antiproliferative phenotype, the most clinically advanced agents reported to date typically inhibit both Aurora A and B. We have discovered a series of pyrazoloquinazolines, some of which show greater than 1000-fold selectivity for Aurora B over Aurora A kinase activity, in recombinant enzyme assays. These compounds have been designed for parenteral administration and achieve high levels of solubility by virtue of their ability to be delivered as readily activated phosphate derivatives. The prodrugs are comprehensively converted to the des-phosphate form in vivo, and the active species have advantageous pharmacokinetic properties and safety pharmacology profiles. The compounds display striking in vivo activity, and compound 5 (AZD1152) has been selected for clinical evaluation and is currently in phase 1 clinical trials.

Chk1 is required for spindle checkpoint function

The spindle checkpoint delays anaphase onset in cells with mitotic spindle defects. Here, we show that Chk1, a component of the DNA damage and replication checkpoints, protects vertebrate cells against spontaneous chromosome missegregation and is required to sustain anaphase delay when spindle function is disrupted by taxol, but not when microtubules are completely depolymerized by nocodazole. Spindle checkpoint failure in Chk1-deficient cells correlates with decreased Aurora-B kinase activity and impaired phosphorylation and kinetochore localization of BubR1. Furthermore, Chk1 phosphorylates Aurora-B and enhances its catalytic activity in vitro. We propose that Chk1 augments spindle checkpoint signaling and is required for optimal regulation of Aurora-B and BubR1 when kinetochores produce a weakened signal. In addition, Chk1-deficient cells exhibit increased resistance to taxol. These results suggest a mechanism through which Chk1 could protect against tumorigenesis through its role in spindle checkpoint signaling.

Aurora-A regulation of nuclear factor-kappaB signaling by phosphorylation of IkappaBalpha

The Aurora-A/STK15 gene encodes a kinase that is frequently amplified in cancer. Overexpression of Aurora-A in mammalian cells leads to centrosome amplification, genetic instability, and transformation. In this study, we show that Aurora-A activates nuclear factor-kappaB (NF-kappaB) via IkappaBalpha phosphorylation. Inhibition of endogenous Aurora-A reduces tumor necrosis factor alpha (TNFalpha)-induced IkappaBalpha degradation. We analyzed primary human breast cancers, and 13.6% of samples showed Aurora-A gene amplification, all of which exhibited nuclear localization of NF-kappaB. We propose that this subgroup of patients with breast cancer might benefit from inhibiting Aurora-A. We also show that down-regulation of NF-kappaB via Aurora-A depletion can enhance cisplatin-dependent apoptosis. These data define a new role for Aurora-A in regulating IkappaBalpha that is critical for the activation of NF-kappaB-directed gene expression and may be partially responsible for the oncogenic effect of Aurora-A when the gene is amplified and overexpressed in human tumors.

Structural investigation of PAP derivatives by CoMFA and CoMSIA reveals novel insight towards inhibition of Bcr-Abl oncoprotein

Molecular modeling by 3D-QSAR comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were employed on a series of phenylaminopyrimidine-based (PAP) Bcr-Abl inhibitors. The chemical structures of 63 PAP analogues were aligned using a template extracted from the crystal structure of STI571 bound to Abl kinase. Subsequently, the structures built were divided into training and test sets that include 53 and 10 compounds, respectively. Statistical results showed that the 3D-QSAR models generated from CoMSIA were superior to CoMFA (CoMSIA; q2=0.66, r2=0.94, N=3, F=139.09, r2pred=0.64 while CoMFA; q2=0.53, r2=0.73, N=3, F=43.53, r2pred=0.61). Based on the contour interpretation, the attachment of hydrophobic and bulky groups to the phenyl and pyrrolidine (D- and E-ring of NS-187, respectively) along with highly electronegative groups around the D-ring are important structural features for the design of second-generation Bcr-Abl inhibitors. The generated models are predictive based on reproducible values of the predicted compared with experimental activities in the test set. Further, the complementary analysis of contour maps to the Bcr-Abl binding site suggested the anchor points for binding affinity.

Roles of Aurora kinases in mitosis and tumorigenesis

Aurora kinases, which have been implicated in several vital events in mitosis, represent a protein kinase family highly conserved during evolution. The activity of Aurora kinases is delicately regulated, mainly by phosphorylation and degradation. Deregulation of Aurora kinase activity can result in mitotic abnormality and genetic instability, leading to defects in centrosome function, spindle assembly, chromosome alignment, and cytokinesis. Both the expression level and the kinase activity of Aurora kinases are found to be up-regulated in many human cancers, indicating that these kinases might serve as useful targets for the development of anticancer drugs. This review focuses on recent progress on the roles of Aurora kinases in mitosis and tumorigenesis.

Aurora B expression correlates with aggressive behaviour in glioblastoma multiforme

Chromosomal abnormalities and genomic instability are common features of, and possible driving forces in, tumorigenesis. Recently, several mitotic proteins that are critical to proper chromosome segregation have been identified. Members of the Aurora kinase family have been identified as having important roles in mitosis; overexpression induces multicellularity and fosters polyploidy. As aneuploidy is a common feature of malignant gliomas, particularly glioblastomas (GBMs), we examined 25 prospectively collected GBMs to assess the role that overexpression of one member of this family, Aurora B, might have in the clinical behaviour of GBMs. Aurora B expression levels were markedly correlated with a shortened survival. Aurora B expression was not directly related to age, tumour proliferation status or to several common molecular changes found in GBMs. These results suggest that Aurora B may be a prognostic feature of impaired survival and a novel therapeutic target in some patients.

Antitumor activity of MLN8054, an orally active small-molecule inhibitor of Aurora A kinase

Increased Aurora A expression occurs in a variety of human cancers and induces chromosomal abnormalities during mitosis associated with tumor initiation and progression. MLN8054 is a selective small-molecule Aurora A kinase inhibitor that has entered Phase I clinical trials for advanced solid tumors. MLN8054 inhibits recombinant Aurora A kinase activity in vitro and is selective for Aurora A over the family member Aurora B in cultured cells. MLN8054 treatment results in G(2)/M accumulation and spindle defects and inhibits proliferation in multiple cultured human tumor cells lines. Growth of human tumor xenografts in nude mice was dramatically inhibited after oral administration of MLN8054 at well tolerated doses. Moreover, the tumor growth inhibition was sustained after discontinuing MLN8054 treatment. In human tumor xenografts, MLN8054 induced mitotic accumulation and apoptosis, phenotypes consistent with inhibition of Aurora A. MLN8054 is a selective inhibitor of Aurora A kinase that robustly inhibits growth of human tumor xenografts and represents an attractive modality for therapeutic intervention of human cancers.

The small-molecule inhibitor BI 2536 reveals novel insights into mitotic roles of polo-like kinase 1

BACKGROUND

The mitotic kinases, Cdk1, Aurora A/B, and Polo-like kinase 1 (Plk1) have been characterized extensively to further understanding of mitotic mechanisms and as potential targets for cancer therapy. Cdk1 and Aurora kinase studies have been facilitated by small-molecule inhibitors, but few if any potent Plk1 inhibitors have been identified.

RESULTS

We describe the cellular effects of a novel compound, BI 2536, a potent and selective inhibitor of Plk1. The fact that BI 2536 blocks Plk1 activity fully and instantaneously enabled us to study controversial and unknown functions of Plk1. Cells treated with BI 2536 are delayed in prophase but eventually import Cdk1-cyclin B into the nucleus, enter prometaphase, and degrade cyclin A, although BI 2536 prevents degradation of the APC/C inhibitor Emi1. BI 2536-treated cells lack prophase microtubule asters and thus polymerize mitotic microtubules only after nuclear-envelope breakdown and form monopolar spindles that do not stably attach to kinetochores. Mad2 accumulates at kinetochores, and cells arrest with an activated spindle-assembly checkpoint. BI 2536 prevents Plk1's enrichment at kinetochores and centrosomes, and when added to metaphase cells, it induces detachment of microtubules from kinetochores and leads to spindle collapse.

CONCLUSIONS

Our results suggest that Plk1's accumulation at centrosomes and kinetochores depends on its own activity and that this activity is required for maintaining centrosome and kinetochore function. Our data also show that Plk1 is not required for prophase entry, but delays transition to prometaphase, and that Emi1 destruction in prometaphase is not essential for APC/C-mediated cyclin A degradation.

Experimental therapy in myelofibrosis with myeloid metaplasia

Myelofibrosis with myeloid metaplasia (MMM) is a Philadelphia chromosome-negative myeloproliferative disorder that is characterised by constitutional symptoms, progressive anaemia and extramedullary haematopoiesis. There are no curative therapies available for patients with MMM apart from stem cell transplantation, which is associated with significant morbidity and mortality, and for which most patients are not suitable candidates. Traditional pharmacological therapy of MMM has focused on the palliation of symptoms associated with myeloproliferation and correction of cytopoenias. Recently, new findings regarding the molecular basis of MMM and the pathogenesis of the associated bone marrow stromal reaction have provided both basic and clinical researchers with invaluable tools to develop effective targeted therapies for patients with MMM. Several novel treatment strategies are being investigated including antiangiogenic agents, signal transduction inhibitors, inhibitors of fibrogenesis and small-molecule inhibitors of the JAK2(V617F )mutation. This article reviews the current status of experimental novel therapies for MMM.

Novel targets for anticancer treatment development in colorectal cancer

Despite recent advances in the treatment of metastatic colorectal cancer (CRC), the prognosis of patients with this malignancy remains poor. An emerging understanding of the molecular pathways that characterize cell growth, cell cycle, apoptosis, angiogenesis, and invasion has provided novel targets in cancer therapy. Numerous proteins have been implicated as having a crucial role in CRC. There are different targets according to their cellular localization such as membrane receptor targets, intracellular signaling targets, and other protein kinases that regulate cell division. Emerging data from the clinical development of new drugs directed to these targets are providing novel opportunities in the treatment of patients with CRC that will probably translate into an efficacy advantage in the years to come. In this article, we review the current developmental status of some of the most advanced targeted therapies in the treatment of CRC.

Frequent overexpression of aurora B kinase, a novel drug target, in non-small cell lung carcinoma patients

The serine/threonine protein kinase aurora B, a key regulator of mitosis, is emerging as a novel drug target for cancer treatment. Aurora B overexpression has been previously documented by immunohistochemistry in several types of human tumors. We assessed aurora B expression in a series of 160 non-small cell lung cancer (NSCLC) samples (60% stage I, 21% stage II, 11% stage III, and 8% stage IV). In addition, we determined the expression of survivin and p16, two molecules also involved in cell cycle control. Aurora B was expressed selectively in tumor cells compared with normal epithelium. Aurora B expression was significantly correlated with expression of survivin in the nucleus (P < 0.0001), but not with expression of p16 (P = 0.134). High aurora B expression levels were significantly associated with older age (P = 0.012), male sex (P = 0.013), squamous cell carcinoma histology (P = 0.001), poor tumor differentiation grade (P = 0.007), and lymph node invasion (P = 0.037), in the subset of radically resected patients in our series. In addition, aurora B expression predicted shorter survival for the patients with adenocarcinoma histology, at both univariate (P = 0.020) and multivariate (P = 0.012) analysis. Survivin expression levels were neither associated with patient clinicopathologic characteristics nor with survival. However, expression of survivin in the nucleus was preferentially detected in stage I and II than in stage III and IV (P = 0.007) in the overall series of NSCLC samples. Taken together, our results suggest that aurora B may represent a valid target in NSCLC.

1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles: identification of a potent Aurora kinase inhibitor with a favorable antitumor kinase inhibition profile

The optimization of a series of 5-phenylacetyl 1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole derivatives toward the inhibition of Aurora kinases led to the identification of compound 9d. This is a potent inhibitor of Aurora kinases that also shows low nanomolar potency against additional anticancer kinase targets. Based on its high antiproliferative activity on different cancer cell lines, favorable chemico-physical and pharmacokinetic properties, and high efficacy in in vivo tumor models, compound 9d was ultimately selected for further development.

Important Therapeutic Targets in Chronic Myelogenous Leukemia

PURPOSE

Review the state-of-art knowledge of the biology and therapy of chronic myelogenous leukemia (CML).

EXPERIMENTAL DESIGN

A review of the literature was undertaken to summarize current information on the pathophysiology of CML and to update data of imatinib mesylate therapy, mechanisms of resistance, and in vitro and clinical data with the new tyrosine kinase inhibitors.

RESULTS

Imatinib, which targets the ABL kinase activity of BCR-ABL, has prolonged survival in CML. Despite the efficacy of imatinib, some patients in chronic phase and more in advanced phases of CML develop resistance, frequently as a result of BCR-ABL tyrosine kinase domain mutants that impair imatinib binding but retain enzymatic activity. New tyrosine kinase inhibitors inhibit BCR-ABL more potently than imatinib and maintain activity against an array of imatinib-resistant BCR-ABL mutants. The IC(50) values of nilotinib and dasatinib are at least 10- to 100-fold lower for BCR-ABL compared with imatinib. Phase I-II trials of nilotinib and dasatinib showed high activity in imatinib-resistant CML and Philadelphia chromosome-positive ALL. Dasatinib also inhibits members of the Src family of kinases (SFKs); nilotinib does not. Whether SFKs have a critical role in imatinib resistance or BCR-ABL-mediated oncogenesis is unresolved. Agents that target signals downstream of BCR-ABL (e.g. Ras/Raf and phosphatidylinositol 3-kinase) are under investigation.

CONCLUSIONS

Understanding the pathophysiology of CML and mechanisms of resistance has produced effective targeted strategies for imatinib-resistant CML.

Diazonamide toxins reveal an unexpected function for ornithine delta-amino transferase in mitotic cell division

We have studied a naturally occurring small-molecule antimitotic called diazonamide A. Diazonamide A is highly effective at blocking spindle assembly in mammalian cell culture and does so through a unique mechanism. A biotinylated form of diazonamide A affinity purifies ornithine delta-amino transferase (OAT), a mitochondrial enzyme, from HeLa cell and Xenopus egg extracts. In the latter system, the interaction between diazonamide A and OAT is regulated by RanGTP. We find that specific OAT knockdown in human cervical carcinoma and osteosarcoma cells by RNA interference blocks cell division and causes cell death, the effects largely phenocopying diazonamide A treatment in these cell lines. Our experiments reveal an unanticipated, paradoxical role for OAT in mitotic cell division and identify the protein as a target for chemotherapeutic drug development.

Mechanisms of mitotic cell death induced by chemotherapy-mediated G2 checkpoint abrogation

The novel concept of anticancer treatment termed "G(2) checkpoint abrogation" aims to target p53-deficient tumor cells and is currently explored in clinical trials. The anticancer drug UCN-01 is used to abrogate a DNA damage-induced G(2) cell cycle arrest leading to mitotic entry and subsequent cell death, which is poorly defined as "mitotic cell death" or "mitotic catastrophe." We show here that UCN-01 treatment results in a mitotic arrest that requires an active mitotic spindle checkpoint, involving the function of Mad2, Bub1, BubR1, Mps1, Aurora B, and survivin. During the mitotic arrest, hallmark parameters of the mitochondria-associated apoptosis pathway become activated. Interestingly, this apoptotic response requires the spindle checkpoint protein Mad2, suggesting a proapoptotic function for Mad2. However, although survivin and Aurora B are also required for the mitotic arrest, both proteins are part of an antiapoptotic pathway that restrains the UCN-01-induced apoptosis by promoting hyperphosphorylation of Bcl-2 and by inhibiting the activation of Bax. Consequently, inhibition of the antiapoptotic pathway by genetic ablation of survivin or by pharmacologic inhibitors of Aurora B or cyclin-dependent kinase 1 lead to a significant enhancement of apoptosis and therefore act synergistically with UCN-01. Thus, by defining the mechanism of cell death on G(2) checkpoint abrogation we show a highly improved strategy for an anticancer treatment by the combined use of UCN-01 with abrogators of the survivin/Aurora B-dependent antiapoptotic pathway that retains the selectivity for p53-defective cancer cells.

Comparing Aurora A and Aurora B as molecular targets for growth inhibition of pancreatic cancer cells

To address the increased need to understand the similarities and differences in targeting Aurora A or Aurora B for the treatment of cancer, we systematically evaluated the relative importance of Aurora A and/or Aurora B as molecular targets using antisense oligonucleotides. It was found that perturbations in Aurora A and Aurora B signaling result in growth arrest and apoptosis preferentially in cancer cells. The biological fingerprints of Aurora A and Aurora B inhibition were compared and contrasted in efforts to identify the superior therapeutic target. Due to the different biological responses, we conclude that each Aurora kinase should be treated as autonomous drug targets, which can be targeted independently or in combination. We observed no advantages to targeting both kinases simultaneously and feel that an Aurora A-targeted therapy may have some beneficial consequences over an Aurora B-targeted therapy, such as mitotic arrest and the rapid induction of apoptosis.

Analysis of mitotic phosphorylation of borealin

Background

The main role of the chromosomal passenger complex is to ensure that Aurora B kinase is properly localized and activated before and during mitosis. Borealin, a member of the chromosomal passenger complex, shows increased expression during G2/M phases and is involved in targeting the complex to the centromere and the spindle midzone, where it ensures proper chromosome segregation and cytokinesis. Borealin has a consensus CDK1 phosphorylation site, threonine 106 and can be phosphorylated by Aurora B Kinase at serine 165 in vitro.

Results

Here, we show that Borealin is phosphorylated during mitosis in human cells. Dephosphorylation of Borealin occurs as cells exit mitosis. The phosphorylated form of Borealin is found in an INCENP-containing complex in mitosis. INCENP-containing complexes from cells in S phase are enriched in the phosphorylated form suggesting that phosphorylation may encourage entry of Borealin into the chromosomal passenger complex. Although Aurora B Kinase is found in complexes that contain Borealin, it is not required for the mitotic phosphorylation of Borealin. Mutation of T106 or S165 of Borealin to alanine does not alter the electrophoretic mobility shift of Borealin. Experiments with cyclohexamide and the phosphatase inhibitor sodium fluoride suggest that Borealin is phosphorylated by a protein kinase that can be active in interphase and mitosis and that the phosphorylation may be regulated by a short-lived phosphatase that is active in interphase but not mitosis.

Conclusion

Borealin is phosphorylated during mitosis. Neither residue S165, T106 nor phosphorylation of Borealin by Aurora B Kinase is required to generate the mitotic, shifted form of Borealin. Suppression of phosphorylation during interphase is ensured by a labile protein, possibly a cell cycle regulated phosphatase.

Structural basis for potent inhibition of the Aurora kinases and a T315I multi-drug resistant mutant form of Abl kinase by VX-680

The small molecule inhibitor of the Aurora-family of protein kinases VX-680 or MK-0457, demonstrates potent anti-cancer activity in multiple in vivo models and has recently entered phase II clinical trials. Although VX-680 shows a high degree of enzyme selectivity against multiple kinases, it unexpectedly inhibits both Flt-3 and Abl kinases at low nanomolar concentrations. Furthermore VX-680 potently inhibits Abl and the Imatinib resistant mutant (T315I) that is commonly expressed in refractory CML and ALL. We describe here the crystal structure of VX-680 bound to Aurora-A and show that this inhibitor exploits a centrally located hydrophobic pocket in the active site that is only present in an inactive or "closed" kinase conformation. A tight association of VX-680 with this hydrophobic pocket explains its high affinity for the Aurora kinases and also provides an explanation for its selectivity profile, including its ability to inhibit Abl and the Imatinib-resistant mutant (T315I).

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.

DNA methylation promotes Aurora-B-driven phosphorylation of histone H3 in chromosomal subdomains

Confinement of enzymatic reactions to nuclear and chromosomal subdomains regulates functional organization of the nucleus. Aurora-B kinase regulates cell-cycle-dependent phosphorylation of chromosomal substrates through sequential localization to a series of sites on chromosomes and the mitotic spindle. In G2 nuclei, Aurora-B recruitment to heterochromatin restricts histone H3S10 phosphorylation to a domain around centromeres (pericentromeres). However, no intrinsic chromosomal determinants have been implicated in Aurora-B recruitment to interphase pericentromeres. Using cyclin B1 as a cell-cycle marker, we found that the great majority of nuclei exhibiting H3S10 phosphorylated foci were positive for cyclin B1, thus revealing that H3S10 phosphorylation arises at pericentromeres during late S phase and persists in G2. By immunofluorescent in situ hybridization, Aurora-B and H3S10 phosphorylated foci were found more frequently at larger pericentromeres than at smaller ones, revealing a preferential phosphorylation of pericentromeres, exhibiting a high density of methyl cytosines. Disruption of DNA methylation inhibited pericentromeric Aurora-B targeting and H3S10 phosphorylation in G2 nuclei, thus demonstrating the role of DNA methylation in Aurora-B targeting to pericentromeres. These results favour the idea that DNA methylation maintains a local environment essential for regulating the functional properties of sub-chromosomal domains during S-G2 progression.

Dynamic survivin in head and neck cancer: Molecular mechanism and therapeutic potential

Although disease management of head and neck squamous cell carcinomas (HNSCC) has improved significantly, therapy resistance leading to tumor recurrence still counteracts improvement of long-term survival. Consequently, identification of molecular markers that signal increased risk of treatment failure or, which can be exploited by targeted therapy, is urgently needed. Survivin is strongly expressed in HNSCC, and its proposed dual role as an apoptosis inhibitor and a mitotic effector positioned survivin in the front line of cancer research. Notably, survivin is detected as a cytoplasmic and as a nuclear protein in HNSCC patients, which stimulated numerous studies to investigate and to speculate on the functional and prognostic significance of its dynamic localization. This review focuses on our current understanding of the molecular mechanisms regulating survivin's intracellular localization and discusses its potential prognostic and therapeutic relevance for head and neck cancer.

Analysis of kinetochore assembly and function in Caenorhabditis elegans embryos and human cells

All eukaryotes rely on multi-protein assemblies, called kinetochores, to direct the segregation of their chromosomes in mitosis. The list of known kinetochore components has been growing rapidly in the post-genomic era: in animal cells, there are presently more than 80 proteins that show either exclusive or partial localization at kinetochores during mitosis. The future challenge is to elucidate how these proteins contribute to kinetochore structure, spindle microtubule attachment, regulation of microtubule dynamics, and the detection, signaling, and correction of microtubule attachment errors. Cultured human tumor cells, especially HeLa cells, are widely used for the study of kinetochores. Recently, the experimental advantages offered by the nematode Caenorhabditis elegans have been exploited for functional analysis of kinetochore components in the first embryonic division. Here, we discuss basic methods, largely based on fluorescence imaging, to study kinetochore structure and function in these two metazoan model systems.

Computational proteomics of biomolecular interactions in the sequence and structure space of the tyrosine kinome: Deciphering the molecular basis of the kinase inhibitors selectivity

Understanding and predicting the molecular basis of protein kinases specificity against existing therapeutic agents remains highly challenging and deciphering this complexity presents an important problem in discovery and development of effective cancer drugs. We explore a recently introduced computational approach for in silico profiling of the tyrosine kinases binding specificity with a class of the pyrido-[2,3-d]pyrimidine kinase inhibitors. Computational proteomics analysis of the ligand-protein interactions using parallel simulated tempering with an ensemble of the tyrosine kinases crystal structures reveals an important molecular determinant of the kinase specificity. The pyrido-[2,3-d]pyrimidine inhibitors are capable of dynamically interacting with both active and inactive forms of the tyrosine kinases, accommodating structurally different kinase conformations with a similar binding affinity. Conformational tolerance of the protein tyrosine kinases binding with the pyrido[2,3-d]pyrimidine inhibitors provides the molecular basis for the broad spectrum of potent activities and agrees with the experimental inhibition profiles. The analysis of the pyrido[2,3-d]pyrimidine sensitivities against a number of clinically relevant ABL kinase mutants suggests an important role of conformational adaptability of multitargeted kinase inhibitors in developing drug resistance mechanisms. The presented computational approach may be useful in complementing proteomics technologies to characterize activity signatures of small molecules against a large number of potential kinase targets.

A cell-penetrating ARF peptide inhibitor of FoxM1 in mouse hepatocellular carcinoma treatment

The forkhead box m1 (Foxm1) transcription factor is essential for initiation of carcinogen-induced liver tumors; however, whether FoxM1 constitutes a therapeutic target for liver cancer treatment remains unknown. In this study, we used diethylnitrosamine/phenobarbital treatment to induce hepatocellular carcinomas (HCCs) in either WT mice or Arf(-/-)Rosa26-FoxM1b Tg mice, in which forkhead box M1b (FoxM1b) is overexpressed and alternative reading frame (ARF) inhibition of FoxM1 transcriptional activity is eliminated. To pharmacologically reduce FoxM1 activity in HCCs, we subjected these HCC-bearing mice to daily injections of a cell-penetrating ARF(26-44) peptide inhibitor of FoxM1 function. After 4 weeks of this treatment, HCC regions displayed reduced tumor cell proliferation and angiogenesis and a significant increase in apoptosis within the HCC region but not in the adjacent normal liver tissue. ARF peptide treatment also induced apoptosis of several distinct human hepatoma cell lines, which correlated with reduced protein levels of the mitotic regulatory genes encoding polo-like kinase 1, aurora B kinase, and survivin, all of which are transcriptional targets of FoxM1 that are highly expressed in cancer cells and function to prevent apoptosis. These studies indicate that ARF peptide treatment is an effective therapeutic approach to limit proliferation and induce apoptosis of liver cancer cells in vivo.

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.

Activation of CDCA1-KNTC2, members of centromere protein complex, involved in pulmonary carcinogenesis

We found cotransactivation of cell division associated 1 (CDCA1) and kinetochore associated 2 (KNTC2), members of the evolutionarily conserved centromere protein complex, in non-small cell lung carcinomas (NSCLC). Immunohistochemical analysis using lung cancer tissue microarray confirmed high levels of CDCA1 and KNTC2 proteins in the great majority of lung cancers of various histologic types. Their elevated expressions were associated with poorer prognosis of NSCLC patients. Knockdown of either CDCA1 or KNTC2 expression with small interfering RNA significantly suppressed growth of NSCLC cells. Furthermore, inhibition of their binding by a cell-permeable peptide carrying the CDCA1-derived 19-amino-acid peptide (11R-CDCA1(398-416)) that correspond to the binding domain to KNTC2 effectively suppressed growth of NSCLC cells. As our data imply that human CDCA1 and KNTC2 seem to fall in the category of cancer-testis antigens, and that their simultaneous up-regulation is a frequent and important feature of cell growth/survival of lung cancer, selective suppression of CDCA1 or KNTC2 activity and/or inhibition of the CDCA1-KNTC2 complex formation could be a promising therapeutic target for treatment of lung cancers.

Array CGH identifies distinct DNA copy number profiles of oncogenes and tumor suppressor genes in chromosomal- and microsatellite-unstable sporadic colorectal carcinomas

DNA copy number changes represent molecular fingerprints of solid tumors and are as such relevant for better understanding of tumor development and progression. In this study, we applied genome-wide array comparative genomic hybridization (aCGH) to identify gene-specific DNA copy number changes in chromosomal (CIN)- and microsatellite (MIN)-unstable sporadic colorectal cancers (sCRC). Genomic DNA was extracted from microdissected, matching normal colorectal epithelium and invasive tumor cells of formalin-fixed and paraffin-embedded tissues of 22 cases with colorectal cancer (CIN = 11, MIN = 11). DNA copy number changes were determined by aCGH for 287 target sequences in tumor cell DNAs, using pooled normal DNAs as reference. aCGH data of tumor cell DNAs was confirmed by fluorescence in situ hybridization (FISH) for three genes on serial tissues as those used for aCGH. aCGH revealed DNA copy number changes previously described by metaphase CGH (gains 7, 8q, 13q, and 20q; losses 8p, 15q, 18q, and 17p). However, chromosomal regions 20q, 13q, 7, and 17p were preferentially altered in CIN-type tumors and included DNA amplifications of eight genes on chromosome 20q (TOP1, AIB1, MYBL2, CAS, PTPN1, STK15, ZNF217, and CYP24), two genes on chromosome 13q (BRCA2 and D13S25), and three genes on chromosome 7 (IL6, CYLN2, and MET) as well as DNA deletions of two genes on chromosome 17p (HIC1 and LLGL1). Finally, additional CIN-tumor-associated DNA amplifications were identified for EXT1 (8q24.11) and MYC (8q24.12) as well as DNA deletions for MAP2K5 (15q23) and LAMA3 (18q11.2). In contrast, distinct MIN-tumor-associated DNA amplifications were detected for E2F5 (8p22-q21.3), GARP (11q13.5-q14), ATM (11q22.3), KAL (Xp22.3), and XIST (Xq13.2) as well as DNA deletions for RAF1 (3p25), DCC (18q21.3), and KEN (21q tel). aCGH revealed distinct DNA copy number changes of oncogenes and tumor suppressor genes in CIN- and MIN-type sporadic colorectal carcinomas. The identified candidate genes are likely to have distinct functional roles in the carcinogenesis and progression of CIN- and MIN-type sporadic CRCs and may be involved in the differential response of CIN- and MIN-type tumor cells to (adjuvant) therapy, such as 5-fluorouracil.

Anaplastic Thyroid Carcinoma: Expression Profile of Targets for Therapy Offers New Insights for Disease Treatment

BACKGROUND

Anaplastic thyroid cancer is an endocrine malignancy. Its rare and rapidly lethal disease course has made it challenging to study. Little is known regarding the expression by anaplastic tumors of molecular targets for new human anticancer agents that have been studied in the preclinical or clinical setting. The objective of this work was to evaluate the expression profile of anaplastic thyroid tumors for molecular targets for treatment.

METHODS

Of the 94 cases of anaplastic thyroid cancers diagnosed and treated in British Columbia, Canada over a 20-year period (1984-2004), 32 cases (34%) had adequate archival tissue available for evaluation. A tissue microarray was constructed from these anaplastic thyroid tumors and immunohistochemistry was utilized to evaluate expression of 31 molecular markers. The markers evaluated were: epidermal growth factor receptor (EGFR), HER2, HER3, HER4, ER, PR, uPA-R, clusterin, E-cadherin, beta-catenin, AMF-R, c-kit, VEGF, ILK, aurora A, aurora B, aurora C, RET, CA-IX, IGF1-R, p53, MDM2, p21, Bcl-2, cyclin D1, cyclin E, p27, calcitonin, MIB-1, TTF-1, and thyroglobulin.

RESULTS

A single tumor with strong calcitonin expression was identified as a poorly differentiated medullary carcinoma and excluded from the study cohort. The mean age of the anaplastic cohort was 66 years; 16 patients (51%) were females, and the median patient survival was 23 weeks. A wide range in molecular marker expression was observed by the anaplastic thyroid cancer tumors (0-100%). The therapeutic targets most frequently and most strongly overexpressed by the anaplastic tumors were: beta-catenin (41%), aurora A (41%), cyclin E (67%), cyclin D1 (77%), and EGFR (84%).

CONCLUSIONS

Anaplastic thyroid tumors exhibit considerable derangement of their cell cycle and multiple signal transduction pathways that leads to uncontrolled cellular proliferation and the development of genomic instability. This report is the first to comprehensively evaluate a panel of molecular targets for therapy of anaplastic thyroid cancer and supports the development of clinical trials with agents such as cetuximab, small-molecule tyrosine kinase inhibitors, and aurora kinase inhibitors, which may offer new hope for individuals diagnosed with this fatal thyroid malignancy.

Aurora kinase inhibition downregulates NF-kappaB and sensitises tumour cells to chemotherapeutic agents

We have identified that Aurora-A activates NF-kappaB via IkappaBalpha phosphorylation. Here, we analysed different human tumour cell types for their NF-kappaB activity. We found that there is an association between cell resistance to chemotherapeutic agents and NF-kappaB activation. A549 human lung adenocarcinoma cells and SKOV3 human ovarian cancer cells have high levels of NF-kappaB and are resistant to cytotoxic agents such as adriamycin and VP-16 (etoposide). We also found that in A549 and SKOV3 cells treated with a small molecule inhibitor towards Aurora kinases, the NF-kappaB activity was downregulated and the efficacy of cytotoxic drugs was enhanced. In addition, the transcriptional targets Bcl-XL and Bcl-2 were downregulated. This study provides evidence for a potential mechanism of chemoresistance and may be useful for the enhancement of certain chemotherapeutics regimens.

Structural basis for the inhibition of Aurora A kinase by a novel class of high affinity disubstituted pyrimidine inhibitors

The 2.25 A crystal structure of a complex of Aurora A kinase (AIKA) with cyclopropanecarboxylic acid-(3-(4-(3-trifluoromethyl-phenylamino)-pyrimidin-2-ylamino)-phenyl)-amide 1 is described here. The inhibitor binding mode is novel, with the cyclopropanecarboxylic acid moiety directed towards the solvent exposed region of the ATP-binding pocket, and several induced structural changes in the active-site compared with other published AIK structures. This structure provides context for the available SAR data on this compound class, and could be exploited for the design of analogs with increased affinity and selectivity for AIK.

Inhibition of Aurora kinases perturbs chromosome alignment and spindle checkpoint signaling in rat spermatocytes

In somatic cells, integrity of cell division is safeguarded by the spindle checkpoint, a signaling cascade that delays the separation of sister chromatids in the presence of misaligned chromosomes. Aurora kinases play important roles in this process by promoting centrosome maturation, chromosome bi-orientation, spindle checkpoint signaling, and cytokinesis. To investigate the functions of Aurora kinases in male meiosis, we applied a small molecule Aurora inhibitor, ZM447439, to seminiferous tubules in vitro. Primary and secondary spermatocytes exposed to ZM447439 exhibit defects in the spindle morphology and fail to align their chromosomes at the metaphase plate. Moreover, the treated spermatocytes undergo a forced exit from the meiotic M-phase without cytokinesis. These results suggest that the activities of Aurora kinases are required for normal spindle assembly as well as for establishment and maintenance of proper microtubule-kinetochore attachments and spindle checkpoint signaling in male mammalian meiosis.

The synthesis and SAR of 2-amino-pyrrolo[2,3-d]pyrimidines: A new class of Aurora-A kinase inhibitors

A new class of Aurora-A inhibitors have been identified based on the 2-amino-pyrrolo[2,3-d]pyrimidine scaffold. Here, we describe the synthesis and SAR of this novel series. We report compounds which exhibit nanomolar activity in the Aurora-A biochemical assay and are able to inhibit tumor cell proliferation. This study culminates in compound 30, an inhibitor with potent activity against Aurora A (IC50=0.008 microM), anti-proliferative activity against several tumor cell lines and induces polyploidy in H460 cells.

Development of new cancer therapeutic agents targeting mitosis

Targeting cellular proliferation persists as a mainstay of cancer therapeutic strategy. Although microtubule-targeting drugs (such as taxanes and vinca alkaloids) have been used successfully in the clinic to treat a variety of cancers, they carry substantial liabilities that have spurred drug companies to aggressively pursue new tubulin-targeting drug candidates with improved efficacy and toxicity profiles. The recent discoveries of new mitotic targets for cancer therapy (such as kinesin spindle protein, Aurora kinases and Polo-like kinase-1) have also stimulated intense work focused on identifying novel antimitotic drugs directed at these new targets. A number of novel antimitotic drugs have demonstrated encouraging activity in preclinical models and have progressed into clinical development. This review focuses on selected new antimitotic drugs under evaluation in clinical trials.

Identification of a lead small-molecule inhibitor of the Aurora kinases using a structure-assisted, fragment-based approach

Aurora A and Aurora B are potential targets for anticancer drug development due to their roles in tumorigenesis and disease progression. To identify small-molecule inhibitors of the Aurora kinases, we undertook a structure-based design approach that used three-dimensional structural models of the Aurora A kinase and molecular docking simulations of chemical entities. Based on these computational methods, a new generation of inhibitors derived from quinazoline and pyrimidine-based tricyclic scaffolds were synthesized and evaluated for Aurora A kinase inhibitory activity, which led to the identification of 4-(6,7-dimethoxy-9H-1,3,9-triaza-fluoren-4-yl)-piperazine-1-carbothioic acid [4-(pyrimidin-2-ylsulfamoyl)-phenyl]-amide. The lead compound showed selectivity for the Aurora kinases when it was evaluated against a panel of diverse kinases. Additionally, the compound was evaluated in cell-based assays, showing a dose-dependent decrease in phospho-histone H3 levels and an arrest of the cell cycle in the G(2)-M fraction. Although biological effects were observed only at relatively high concentrations, this chemical series provides an excellent starting point for drug optimization and further development.

The Aurora kinase inhibitor VX-680 induces endoreduplication and apoptosis preferentially in cells with compromised p53-dependent postmitotic checkpoint function

VX-680 is a potent inhibitor of Aurora kinases that induces the accumulation of cells with > or =4N DNA content, followed by cell death. Here, we define the role of p53 and p21(Waf1/Cip1) in cell cycle perturbations following exposure to VX-680. Endoreduplication and apoptosis in response to VX-680 are limited in A549 and MCF-7 cells expressing wild-type p53, and markedly enhanced in cells lacking p53, including those engineered to express the HPV16-E6 oncoprotein or short interfering RNA pools targeting p53. In contrast, endoreduplication and apoptosis occur in the p53 wild-type cell lines, RKO and U2OS. The difference in response to VX-680 among these cell lines correlates with the timing of induction of p21(Waf1/Cip1) and its ability to inhibit cyclin E-cdk2 activity. In A549 cells, VX-680 induces the expression of p53 and p21(Waf1/Cip1) within 24 hours, with consequent inhibition of cyclin E-cdk2, and reduction of retinoblastoma protein phosphorylation, limiting endoreduplication. In RKO and U2OS cells, the induction of p21(Waf1/Cip1) is delayed and associated with higher residual cyclin E-cdk2 kinase activity and retinoblastoma protein phosphorylation, followed by progressive endoreduplication and apoptosis. Abrogation of p21(Waf1/Cip1) expression by short interfering RNA targeting in A549 cells results in a substantial increase in the degree of endoreduplication, whereas inducible expression of p21(Waf1/Cip1) in p53-negative NCI-H1299 cells inhibits VX-680-induced endoreduplication and cell death. These data suggest that the integrity of the p53-p21(Waf1/Cip1)-dependent postmitotic checkpoint governs the response to Aurora kinase inhibition. Although cells with intact checkpoint function arrest with 4N DNA content, those with compromised checkpoint function are more likely to undergo endoreduplication followed by eventual apoptosis.

MK-0457, a novel kinase inhibitor, is active in patients with chronic myeloid leukemia or acute lymphocytic leukemia with the T315I BCR-ABL mutation

MK-0457 (VX-680) is a small-molecule aurora kinase (AK) inhibitor with preclinical antileukemia activity. The T315I BCR-ABL mutation mediates resistance to imatinib, nilotinib, and dasatinib. MK-0457 has in vitro activity against cells expressing wild-type or mutated BCR-ABL, including the T315I BCR-ABL mutation. Three patients with T315I abl-mutated chronic myeloid leukemia (CML) or Philadelphia chromosome (Ph)-positive acute lymphocytic leukemia (ALL) have achieved clinical responses to doses of MK-04547 that are not associated with adverse events. Higher MK-0457 dose levels were associated with clinical responses and down-regulation of CrkL phosphorylation in leukemia cells. The possible role of AK inhibition in these clinical responses requires further investigation. The currently reported cases are the first observed clinical activity of a kinase inhibitor against the T315I phenotype. The observation of responses in 3 patients with T315I phenotype-refractory CML or Ph-positive ALL, at doses of MK-0457 associated with no significant extramedullary toxicity, is very encouraging.

R-253 disrupts microtubule networks in multiple tumor cell lines

PURPOSE

The design and development of synthetic small molecules to disrupt microtubule dynamics is an attractive therapeutic strategy for anticancer drug discovery research. Loss of clinical efficacy of many useful drugs due to drug resistance in tumor cells seems to be a major hurdle in this endeavor. Thus, a search for new chemical entities that bind tubulin, but neither are a substrate of efflux pump, P-glycoprotein 170/MDR1, nor cause undesired side effects, would potentially increase the therapeutic index in certain cancer treatments.

EXPERIMENTAL DESIGN

A high-content cell-based screen of a compound library led to the identification of a new class of compounds belonging to a thienopyrimidine series, which exhibited significant antitumor activities. On structure-activity relationship analysis, R-253 [N-cyclopropyl-2-(6-(3,5-dimethylphenyl)thieno[3,2-d]pyrimidin-4-yl)hydrazine carbothioamide] emerged as a potent antiproliferative agent (average EC(50), 20 nmol/L) when examined in a spectrum of tumor cell lines.

RESULTS

R-253 is structurally unique and destabilizes microtubules both in vivo and in vitro. Standard fluorescence-activated cell sorting and Western analyses revealed that the effect of R-253 on cell growth was associated with cell cycle arrest in mitosis, increased select G(2)-M checkpoint proteins, and apoptosis. On-target activity of R-253 on microtubules was further substantiated by immunofluorescence studies and selected counter assays. R-253 competed with fluorescent-labeled colchicine for binding to tubulin, indicating that its binding site on tubulin could be similar to that of colchicine. R-253 neither is a substrate of P-glycoprotein 170/MDR1 nor is cytotoxic to nondividing human hepatocytes.

CONCLUSION

Both biochemical and cellular mechanistic studies indicate that R-253 could become a promising new tubulin-binding drug candidate for treating various malignancies.

Mitotic kinases: the key to duplication, segregation, and cytokinesis errors, chromosomal instability, and oncogenesis

Chromosomal instability (CIN) and aneuploidy are commonly observed in the vast majority of human solid tumors and in many hematological malignancies. These features are considered defining characteristics of human breast, bladder and kidney cancers since they markedly exceed a 50% aneuploidy frequency. The detection of persistent mitotic kinase over-expression, particularly the Aurora family, and centrosome amplification in precursor/pre-malignant stages, strongly implicate these molecular changes in precipitating the aneuploidy seen in many human neoplasms. Mitotic spindle checkpoint defects may also lead to aneuploid tumors. However, the sustained over-expression and activity of various members of the mitotic kinase families, including Aurora (Aur) (A, B, C), Polo-like (Plk1-4), and Nek (NIMA1-11) in diverse human tumors strongly indicate that these entities are intimately involved in the development of errors in centrosome duplication, chromosome segregation, and cytokinesis. Mitotic kinases have also been implicated in regulating the centrosome cycle, spindle checkpoint and microtubule-kinetochore attachment, spindle assembly, and chromosome condensation. These mitotic kinases are modulated by de-novo synthesis, stability factors, phosphorylation, and ubiquitin-dependent proteolysis. They, in turn, phosphorylate a myriad of centrosomal/mitotic protein substrates, and have the ability to behave as oncogenes (i.e. Aur-A, Plk-1), providing a compelling link between errors in mitosis and oncogenic processes. The recent development of selective small molecule inhibitors of Aurora kinases, in particular, will provide useful tools to ascertain more precisely their role in cancer development. Potent inhibitors of mitotic kinases, when fully developed, have the promise to be effective agents against tumor growth, and possibly, tumor prevention as well.

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.

Solid-phase immunoassays in mechanism-based drug discovery: their application in the development of inhibitors of the molecular chaperone heat-shock protein 90

High-throughput screening of chemical libraries and the subsequent rapid progress of hit compounds through an iterative developmental test cascade are essential parts of modern molecular mechanism-based drug discovery. These processes depend on the use of efficient assay technologies and equipment. Enzyme-linked immunosorbent assays have historically been carried out in 96-well microtitre plates. Improvements in reagents and assay technologies mean that solid-phase immunoassays can be adapted for higher throughput to play an important role in modern drug discovery. The molecular chaperone heat-shock protein (Hsp) 90 is an important anticancer drug target because it maintains the conformation, stability, and function of many important oncogenic client proteins, including those involved with signal transduction, cell proliferation, survival, differentiation, motility angiogenesis, and metastasis. Using the standard inhibitors of the adenosine triphosphatase (ATPase) activity of Hsp90, geldanamycin (GA) and 17-allylamino-17- demethoxygeldanamycin (17AAG), novel solid-phase immunoassays have been validated using a time-resolved fluorescence (TRF) end point. Their utility for confirming the mechanism of action of Hsp90 inhibition in secondary cell-based assays has been shown and applied to the novel Hsp90 inhibitor CCT018159. Adaptation of these assays for later studies using human tumour xenografts and samples obtained from a Phase 1 trial of 17AAG is also described. Finally, comparison is made between the use and applicability of this type of immunoassay and other techniques such as western blotting, immunohistochemistry, and flow cytometry analysis.

Validating Aurora B as an anti-cancer drug target

The Aurora kinases, a family of mitotic regulators, have received much attention as potential targets for novel anti-cancer therapeutics. Several Aurora kinase inhibitors have been described including ZM447439, which prevents chromosome alignment, spindle checkpoint function and cytokinesis. Subsequently, ZM447439-treated cells exit mitosis without dividing and lose viability. Because ZM447439 inhibits both Aurora A and B, we set out to determine which phenotypes are due to inhibition of which kinase. Using molecular genetic approaches, we show that inhibition of Aurora B kinase activity phenocopies ZM447439. Furthermore, a novel ZM compound, which is 100 times more selective for Aurora B over Aurora A in vitro, induces identical phenotypes. Importantly, inhibition of Aurora B kinase activity induces a penetrant anti-proliferative phenotype, indicating that Aurora B is an attractive anti-cancer drug target. Using molecular genetic and chemical-genetic approaches, we also probe the role of Aurora A kinase activity. We show that simultaneous repression of Aurora A plus induction of a catalytic mutant induces a monopolar phenotype. Consistently, another novel ZM-related inhibitor, which is 20 times as potent against Aurora A compared with ZM447439, induces a monopolar phenotype. Expression of a drug-resistant Aurora A mutant reverts this phenotype, demonstrating that Aurora A kinase activity is required for spindle bipolarity in human cells. Because small molecule-mediated inhibition of Aurora A and Aurora B yields distinct phenotypes, our observations indicate that the Auroras may present two avenues for anti-cancer drug discovery.

Expression of Late Cell Cycle Genes and an Increased Proliferative Capacity Characterize Very Early Relapse of Childhood Acute Lymphoblastic Leukemia

PURPOSE

In childhood acute lymphoblastic leukemia (ALL), approximately 25% of patients suffer from relapse. In recurrent disease, despite intensified therapy, overall cure rates of 40% remain unsatisfactory and survival rates are particularly poor in certain subgroups. The probability of long-term survival after relapse is predicted from well-established prognostic factors (i.e., time and site of relapse, immunophenotype, and minimal residual disease). However, the underlying biological determinants of these prognostic factors remain poorly understood.

EXPERIMENTAL DESIGN

Aiming at identifying molecular pathways associated with these clinically well-defined prognostic factors, we did gene expression profiling on 60 prospectively collected samples of first relapse patients enrolled on the relapse trial ALL-REZ BFM 2002 of the Berlin-Frankfurt-Münster study group.

RESULTS

We show here that patients with very early relapse of ALL are characterized by a distinctive gene expression pattern. We identified a set of 83 genes differentially expressed in very early relapsed ALL compared with late relapsed disease. The vast majority of genes were up-regulated and many were late cell cycle genes with a function in mitosis. In addition, samples from patients with very early relapse showed a significant increase in the percentage of S and G(2)-M phase cells and this correlated well with the expression level of cell cycle genes.

CONCLUSIONS

Very early relapse of ALL is characterized by an increased proliferative capacity of leukemic blasts and up-regulated mitotic genes. The latter suggests that novel drugs, targeting late cell cycle proteins, might be beneficial for these patients that typically face a dismal prognosis.

Tetraploidy/aneuploidy and stem cells in cancer promotion: The role of chromosome passenger proteins

While polyploidy, a state of having fully duplicated sets of chromosomes per cell, has been described in normally developing bone marrow megakaryocytes or as an adaptive response in other cell types, aneuploidy is never detected in normal cells. Tetraploidy or aneuploidy can be induced by several signals and it is highly prevalent in different forms of cancers, suggesting a role for this cell cycle state in promoting cellular transformation. Investigations suggested that loss of heterozygosity of cancer-related genes in stem cells might contribute to genetic instability in progeny cells and to subsequent cancer development. Deregulated expression of chromosome passenger proteins, such as Aurora kinases or Survivin, is a hallmark of various cancers, and experimentally induced changes in these regulators can promote tetraploidy or aneuploidy and loss of heterozygosity. Our studies described an induction of tetraploidy/aneuploidy by a stable form of Aurora-B, leading to acquisition of transformation properties. It is intriguing to speculate that in some cancers, tetraploidy/aneuploidy induced by deregulated expression of a mitotic regulator represents a primary event that leads to unbalanced expression of a cluster of crucial genes and to cellular transformation.

Targeting Aurora kinases in ovarian cancer

Although recurrent epithelial ovarian cancer initially responds well to current first-line adjuvant therapy, eventually the disease becomes resistant to chemotherapy. Novel strategies are needed to reverse chemoresistance in order to treat relapsed ovarian cancer effectively. One strategy is to target aberrant expression activation of Aurora kinases that are essential for the regulation of chromosome segregation and cytokinesis during mitosis and which play a role in tumourigenesis and progression in a wide range of human tumours, including ovarian cancer. The purpose of this article is to review Aurora kinases and their inhibitors in human epithelial ovarian cancer as an impetus to the development of effective and less toxic regimens for ovarian cancer. In addition, this review tries to define the differences between cytotoxic chemotherapeutic agents and molecular therapeutic agents: both groups of agents have either a single specific target or multiple specific targets, while their differences lie in their toxicity profiles and the way to determine their dosages for further studies. The authors propose that Aurora kinase inhibitors be developed as molecular therapeutic agents in order to minimise their toxicities and maximise their antitumour activities for ovarian cancer treatment.