The role of Aurora-A inhibitors in cancer therapy

Identification of chemical inhibitors targeting long noncoding RNA through gene signature-based high throughput screening

Scalable methods for functionally high-throughput screening of RNA-targeting small molecules are currently limited. Here, an RNA knockdown gene signature and high-throughput sequencing-based high-throughput screening (HTS2) were integrated to identify RNA-targeting compounds. We first generated a gene signature characterizing the knockdown of the long non-coding RNA LINC00973. Then, screening of 8199 compounds by HTS2 assay identified that treatments of Hesperadin and GSK1070916 significantly mimic the expression pattern of the LINC00973 knockdown gene signature. Functionally, cell phenotype changes after treatments of these two compounds also mimic the losing function of LINC00973 in multiple types of cancer cells. Mechanistically, the inhibitory action of these two compounds on LINC00973 primarily operates via the AURKB-mediated MAPK signaling pathway, resulting in reduced expression of the transcription factor c-Jun. Consequently, this leads to the suppression of LINC00973 transcription. Moreover, these two compounds significantly inhibit xenograft tumor growth in vivo. Clinically, we further found that breast tumors with high expression of LINC00973 also show relatively high expression of AURKB or JUN, and vice versa. In summary, we established a novel high-throughput screening strategy to identify small molecules capable of targeting RNA, provided two promising compounds targeting LINC00973 and further shed light on the underlying transcriptional upregulation mechanism of LINC00973 within cancer cells.

Recent advancements in mechanistic research, therapeutic potential, and structure-activity relationships of aurora kinase inhibitors in cancer therapies

Aurora kinases (AURKs)-a family of serine/threonine protein kinases consisting of AURK-A, AURK-B, and AURK-C, are critical regulators of chromosomal segregation, centrosome maturation, and cytokinesis during the cell cycle. Each kinase is activated via phosphorylation at unique threonine residues: Thr288 (AURK-A), Thr232 (AURK-B), and Thr195 (AURK-C). Activation of AURK-A and AURK-B through phosphorylation triggers a series of downstream signaling pathways, including RalA, NF-κB, p53, PLK1, BRCA1/BRCA2, H2AX, and Kif2C, as well as multiple transmembrane kinase receptors. Dysregulation of these pathways has been implicated in cancer development and progression, positioning AURKs as pivotal targets for anticancer drug research. Inhibition of AURKs has demonstrated significant efficacy in tumor growth suppression and induction of cancer cell death, thereby focusing recent research on the development of potent AURK inhibitors. This review provides an in-depth exploration of AURK inhibitors, discussing their biological activities, structure-activity relationships, selectivity profiles, and mechanisms of action. Notably, compounds 6, 27, and 16 exhibit potent AURK-A inhibition with IC50 values of 1.7 nM, 11.83 nM, and 15 nM, respectively. Similarly, compounds 28, 16, and 7 demonstrate strong AURK-B inhibitory activity, with IC50 values of 10.5 nM, 12 nM, and 14.09 nM, respectively. This comprehensive overview aims to support medicinal chemists in developing more potent, selective, and safe AURK inhibitors as potential anticancer therapeutics.

Machine learning based androgen receptor regulatory gene-related random forest survival model for precise treatment decision in prostate cancer

Background

It has been demonstrated that aberrant androgen receptor (AR) signaling contributes to the pathogenesis of prostate cancer (PCa). To date, the most efficacious strategy for the treatment of PCa remains to target the AR signaling axis. However, numerous PCa patients still face the issue of overtreatment or undertreatment. The establishment of a precise risk prediction model is urgently needed to distinguish patients with high-risk and select appropriate treatment modalities.

Methods

In this study, a consensus AR regulatory gene-related signature (ARS) was developed by integrating a total of 101 algorithm combinations of 10 machine learning algorithms. We evaluated the value of ARS in predicting patient prognosis and the therapeutic effects of the various treatments. Additionally, we conducted a screening of therapeutic targets and agents for high-risk patients, followed by the verification in vitro and in vivo.

Results

ARS was an independent risk factor for biochemical recurrence and distant metastasis in PCa patients. The enhanced and consistent prognostic predictive capability of ARS across various platforms was confirmed when compared with 44 previously published signatures. More importantly, PCa patients in the ARShigh group benefit more from PARP inhibitors and immunotherapy, while chemotherapy, radiotherapy, and AR-targeted therapy are more effective for ARSlow patients. The results of in silico screening suggest that AURKB could potentially serve as a promising therapeutic target for ARShigh patients.

Conclusions

Collectively, this prediction model based on AR regulatory genes holds great clinical translational potential to solve the dilemma of treatment choice and identify potential novel therapeutic targets in PCa.

AURKAIP1 actuates tumor progression through stabilizing DDX5 in triple negative breast cancer

Aurora-A kinase interacting protein 1 (AURKAIP1) has been proved to take an intermediary role in cancer by functioning as a negative regulator of Aurora-A kinase. However, it remains unclear whether and how AURKAIP1 itself would directly engage in regulating malignancies. The expression levels of AURKAIP1 were detected in triple negative breast cancer (TNBC) by immunohistochemistry and western blots. The CCK8, colony formation assays and nude mouse model were conducted to determine cell proliferation whereas transwell and wound healing assays were performed to observe cell migration. The interaction of AURKAIP1 and DEAD-box helicase 5 (DDX5) were verified through co-immunoprecipitation and successively western blots. From the results, we found that AURKAIP1 was explicitly upregulated in TNBC, which was positively associated with tumor size, lymph node metastases, pathological stage and unfavorable prognosis. AURKAIP1 silencing markedly inhibited TNBC cell proliferation and migration in vitro and in vivo. AURKAIP1 directly interacted with and stabilized DDX5 protein by preventing ubiquitination and degradation, and DDX5 overexpression successfully reversed proliferation inhibition induced by knockdown of AURKAIP1. Consequently, AURKAIP1 silencing suppressed the activity of Wnt/β-catenin signaling in a DDX5-dependent manner. Our study may primarily disclose the molecular mechanism by which AURKAIP1/DDX5/β-catenin axis modulated TNBC progression, indicating that AURKAIP1 might serve as a therapeutic target as well as a TNBC-specific biomarker for prognosis.

Identification of miRNAs and target genes associated with lymph node metastasis in cervical cancer using bioinformatics analysis

This study was designed to identify the differentially expressed miRNAs (DEMs) and genes (DEGs) in metastatic cervical cancer using bioinformatic tools. In this study, fifty-seven DEMs (48 downregulated and 9 upregulated) were identified, among which miR-4459 and miR-3195 expression was negatively associated with overall survival of cervical cancer patients. Then, 476 target DEGs were determined, and protein-protein interaction (PPI) network was constructed. Seventeen hub genes (LONRF2, CCNE2, AURKA, SYT1, NEGR1, PPP1R12B, GABRP, RAD51, CDK1, FBLN5, PRKG1, CDC6, CACNA1C, MEOX2, ANLN, MYLK, and EDNRB) were finally selected to construct the miRNA-hub gene network. Overall, our study discovered the key miRNAs and mRNAs related to lymph node metastasis (LNM) in cervical cancer, which helps discover candidate therapeutic targets for cervical cancer.

Aurora kinase inhibitor VX-680 enhances sensitivity of esophageal squamous cell carcinoma cells to cisplatin chemotherapy

Esophageal squamous cell carcinoma (ESCC) is malignant cancer with a high mortality rate. Cisplatin is one of the most potent chemotherapy agents used in the treatment of ESCC. However, chemoresistance and severe adverse effects of cisplatin become major obstacles to clinical utility. The combination treatment with molecule-targeted drugs and chemotherapy agents is a promising treatment strategy for cancer to improve antineoplastic responses. VX-680 is a potent inhibitor of Aurora kinases. This study was performed to investigate if VX-680 and cisplatin can synergistically inhibit the malignant behavior of ESCC cells. The results obtained from 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide assay and combination index analysis demonstrated that the combination of VX-680 and cisplatin synergistically enhanced cytotoxic effects in ESCC cells. 2-(4-Amidinophenyl)-6-indolecarbamidine dihydrochloride staining and western blot analysis suggested that VX-680 increased cisplatin-mediated cell apoptosis. Further analysis revealed that VX-680 combined with cisplatin could attenuate cell migration and angiogenesis confirmed by wound-healing assay and tube formation assay. Subsequently, VX-680 and cisplatin combined treatment significantly promoted cell-cell cohesion, and reduced cell-extracellular matrix interaction, as analyzed by the cell dissociation assay and cell-matrix attachment assay. In addition, the combination of VX-680 and cisplatin markedly decreased the expressions of matrix metalloproteinases-2 (MMP-2), vascular endothelial growth factor (VEGF), p-extracellular signal-regulated protein kinase and p-RAC-α serine/threonine-protein kinase compared to VX-680 or cisplatin only treatment. Altogether, these findings strongly suggest that the combination of VX-680 and cisplatin could exert a synergistic antitumor effect in ESCC cells and this combination might represent a promising therapeutic strategy against ESCC.

Discovery and Synthesis of a Pyrimidine-Based Aurora Kinase Inhibitor to Reduce Levels of MYC Oncoproteins

The A-type Aurora kinase is upregulated in many human cancers, and it stabilizes MYC-family oncoproteins, which have long been considered an undruggable target. Here, we describe the design and synthesis of a series of pyrimidine-based derivatives able to inhibit Aurora A kinase activity and reduce levels of cMYC and MYCN. Through structure-based drug design of a small molecule that induces the DFG-out conformation of Aurora A kinase, lead compound 13 was identified, which potently (IC₅₀ < 200 nM) inhibited the proliferation of high-MYC expressing small-cell lung cancer (SCLC) cell lines. Pharmacokinetic optimization of 13 by prodrug strategies resulted in orally bioavailable 25, which demonstrated an 8-fold higher oral AUC (F = 62.3%). Pharmacodynamic studies of 25 showed it to effectively reduce cMYC protein levels, leading to >80% tumor regression of NCI-H446 SCLC xenograft tumors in mice. These results support the potential of 25 for the treatment of MYC-amplified cancers including SCLC.

The impact of Aurora kinase A genetic polymorphisms on cervical cancer progression and clinicopathologic characteristics

The aims of this study were to explore the involvement of Aurora kinase A (AURKA) gene single nucleotide polymorphisms (SNPs) in uterine cervical cancer that has not yet been investigated. One hundred and six patients with cervical invasive cancer and 94 patients with precancerous lesions, and 302 Taiwanese female individuals were included. AURKA SNPs rs2273535, rs6024836, rs2064863 and rs1047972 were analyzed for genotypic distributions using real-time polymerase chain reaction. There were no statistically significant differences in the genetic frequencies of AURKA SNPs among patients with invasive cancer and those with precancerous lesions of uterine cervix and control women. There were no associations among AURKA SNPs and clinicopathologcal variables and recurrence and survival events. However, in a multivariate analysis, cervical cancer patients with adenocarcinoma (HR: 3.18, 95% CI: 1.23-8.23; p=0.017) and larger tumor (HR: 5.61, 95% CI: 2.10-14.95; p=0.001) had poorer recurrence-free survival. In conclusion, tumor size and pelvic lymph node status rather than AURKA SNPs were the most obvious independent parameter that could significantly predict 5 years survival rate in Taiwanese women with cervical cancer.

Kinase-Based Screening of Marine Natural Extracts Leads to the Identification of a Cytotoxic High Molecular Weight Metabolite from the Mediterranean Sponge Crambe tailliezi

Regulated cell death (RCD) results from the activation of one or more signal transduction modules both in physiological or pathological conditions. It is now established that RCD is involved in numerous human diseases, including cancer. As regulated cell death processes can be modulated by pharmacological tools, the research reported here aims to characterize new marine compounds acting as RCD modulators. Protein kinases (PKs) are key signaling actors in various RCDs notably through the control of either mitosis (e.g., the PKs Aurora A and B) or necroptosis (e.g., RIPK1 and RIPK3). From the primary screening of 27 various extracts of marine organisms collected in the Mediterranean Sea, an extract and subsequently a purified high molecular weight compound dubbed P3, were isolated from the marine sponge Crambe tailliezi and characterized as a selective inhibitor of PKs Aurora A and B. Furthermore, P3 was shown to induce apoptosis and to decrease proliferation and mitotic index of human osteosarcoma U-2 OS cells.

A new role for Drosophila Aurora-A in maintaining chromosome integrity

Aurora-A is a conserved mitotic kinase overexpressed in many types of cancer. Growing evidence shows that Aurora-A plays a crucial role in DNA damage response (DDR) although this aspect has been less characterized. We isolated a new aur-A mutation, named aur-A⁹⁴⁹, in Drosophila, and we showed that it causes chromosome aberrations (CABs). In addition, aur-A⁹⁴⁹ mutants were sensitive to X-ray treatment and showed impaired γ-H2Av foci dissolution kinetics. To identify the pathway in which Aur-A works, we conducted an epistasis analysis by evaluating CAB frequencies in double mutants carrying aur-A⁹⁴⁹ mutation combined to mutations in genes related to DNA damage response (DDR). We found that mutations in tefu (ATM) and in the histone variant H2Av were epistatic over aur-A⁹⁴⁹ indicating that Aur-A works in DDR and that it is required for γ-H2Av foci dissolution. More interestingly, we found that a mutation in lig4, a gene belonging to the non-homologous end joining (NHEJ) repair pathway, was epistatic over aur-A⁹⁴⁹. Based on studies in other systems, which show that phosphorylation is important to target Lig4 for degradation, we hypothesized that in aur-A⁹⁴⁹ mutant cells, there is a persistence of Lig4 that could be, in the end, responsible for CABs. Finally, we observed a synergistic interaction between Aur-A and the homologous recombination (HR) repair system component Rad 51 in the process that converts chromatid deletions into isochromatid deletions. Altogether, these data indicate that Aur-A depletion can elicit chromosome damage. This conclusion should be taken into consideration, since some anticancer therapies are aimed at reducing Aurora-A expression.

New Cell Cycle Inhibitors Target Aneuploidy in Cancer Therapy

Aneuploidy is a hallmark of cancer. Defects in chromosome segregation result in aneuploidy. Multiple pathways are engaged in this process, including errors in kinetochore-microtubule attachments, supernumerary centrosomes, spindle assembly checkpoint (SAC) defects, and chromosome cohesion defects. Although aneuploidy provides an adaptation and proliferative advantage in affected cells, excessive aneuploidy beyond a critical level can be lethal to cancer cells. Given this, enhanced chromosome missegregation is hypothesized to limit survival of aneuploid cancer cells, especially when compared to diploid cells. Based on this concept, proteins and pathways engaged in chromosome segregation are being exploited as candidate therapeutic targets for aneuploid cancers. Agents that induce chromosome missegregation and aneuploidy now exist, including SAC inhibitors, those that alter centrosome fidelity and others that are under active study in preclinical and clinical contexts. This review explores the therapeutic potentials of such new agents, including the benefits of combining them with other antineoplastic agents.

Analysis of tissue and circulating microRNA expression during metaplastic transformation of the esophagus

Genetic changes involved in the metaplastic progression from squamous esophageal mucosa toward Barrett's metaplasia and adenocarcinoma are almost unknown. Several evidences suggest that some miRNAs are differentially expressed in Barrett's esophagus (BE) and esophageal adenocarcinoma. Among these, miR-143, miR-145, miR-194, miR-203, miR-205, miR-215 appear to have a key role in metaplasia and neoplastic progression. The aim of this study was to analyze deregulated miRNAs in serum and esophageal mucosal tissue biopsies to identify new biomarkers that could be associated with different stages of esophageal disease. Esophageal mucosal tissue biopsies and blood samples were collected and analyzed for BE diagnosis. Quantitative Real-time PCR was used to compare miRNA expression levels in serum and 60 disease/normal-paired tissues from 30 patients diagnosed with esophagitis, columnar-lined oesophagus (CLO) or BE. MiRNA expression analysis showed that miR-143, miR-145, miR-194 and miR-215 levels were significantly higher, while miR-203 and miR-205 were lower in BE tissues compared with their corresponding normal tissues. Esophageal mucosa analysis of patients with CLO and esophagitis showed that these miRNAs were similarly deregulated but to a lesser extent keeping the same trend and CLO appeared as intermediate step between esophagitis and BE. Analysis on circulating miRNA levels confirmed that miR-194 and miR-215 were significantly upregulated in both BE and CLO compared to esophagitis, while miR-143 was significantly upregulated only in the Barrett group. These findings suggest that miRNAs may be involved in neoplastic/metaplastic progression and miRNA analysis might be useful for progression risk prediction as well as for monitoring of BE/CLO patients.

Transcriptional repression of Aurora-A gene by wild-type p53 through directly binding to its promoter with histone deacetylase 1 and mSin3a

In this study, we firstly showed that p53 transcriptionally represses Aurora-A gene expression through directly binding to its promoter. DNA affinity precipitation assay and chromatin immunoprecipitation assay indicated that p53 physically bound to the Aurora-A promoter. Moreover, the in vitro and in vivo assays showed that p53 directly bound to the Aurora-A promoter together with histone deacetylase 1 (HDAC1) and mSin3a as corepressors. Furthermore, we identified that the nucleotides -360 to -354 (CCTGCCC), upstream of the Aurora-A transcriptional start site, was responsible for the p53-mediated repression. Mutation within this site disrupted its interaction with p53, mSin3a and HDAC1, as well as attenuated the repressive effect of p53 on Aurora-A promoter activity. Treatment with trichostatin A (TSA), a HDAC1 inhibitor, disrupted the interaction of p53-HDAC1-mSin3a complex with the nucleotides -365∼-345 region, and enhanced the Aurora-A promoter activity and gene expression. Additionally, knockdown of p53 or mSin3a also drastically blocked the formation of p53-HDAC1-mSin3a repressive complex onto this promoter region and elevated the Aurora-A promoter activity and gene expression. Moreover, the p53-HDAC1-mSin3a repressive complex also involved in the inhibition of Aurora-A gene expression upon cisplatin treatment. Finally, the clinical investigation showed that Aurora-A and p53 exhibited an inverse correlation in both the expression level and prognostic status, and the low p53/high Aurora-A showed the poorest prognosis of NSCLC patients. Our findings showed novel regulatory mechanisms of p53 in regulating Aurora-A gene expression in NSCLC cells.

Reversine Induced Multinucleated Cells, Cell Apoptosis and Autophagy in Human Non-Small Cell Lung Cancer Cells

Reversine, an A3 adenosine receptor antagonist, has been shown to induce differentiated myogenic-lineage committed cells to become multipotent mesenchymal progenitor cells. We and others have reported that reversine has an effect on human tumor suppression. This study revealed anti-tumor effects of reversine on proliferation, apoptosis and autophagy induction in human non-small cell lung cancer cells. Treatment of these cells with reversine suppressed cell growth in a time- and dosage-dependent manner. Moreover, polyploidy occurred after reversine treatment. In addition, caspase-dependent apoptosis and activation of autophagy by reversine in a dosage-dependent manner were also observed. We demonstrated in this study that reversine contributes to growth inhibition, apoptosis and autophagy induction in human lung cancer cells. Therefore, reversine used as a potential therapeutic agent for human lung cancer is worthy of further investigation.

Combination of Eribulin and Aurora A Inhibitor MLN8237 Prevents Metastatic Colonization and Induces Cytotoxic Autophagy in Breast Cancer

Recent findings suggest that the inhibition of Aurora A (AURKA) kinase may offer a novel treatment strategy against metastatic cancers. In the current study, we determined the effects of AURKA inhibition by the small molecule inhibitor MLN8237 both as a monotherapy and in combination with the microtubule-targeting drug eribulin on different stages of metastasis in triple-negative breast cancer (TNBC) and defined the potential mechanism of its action. MLN8237 as a single agent and in combination with eribulin affected multiple steps in the metastatic process, including migration, attachment, and proliferation in distant organs, resulting in suppression of metastatic colonization and recurrence of cancer. Eribulin application induces accumulation of active AURKA in TNBC cells, providing foundation for the combination therapy. Mechanistically, AURKA inhibition induces cytotoxic autophagy via activation of the LC3B/p62 axis and inhibition of pAKT, leading to eradication of metastases, but has no effect on growth of mammary tumor. Combination of MLN8237 with eribulin leads to a synergistic increase in apoptosis in mammary tumors, as well as cytotoxic autophagy in metastases. These preclinical data provide a new understanding of the mechanisms by which MLN8237 mediates its antimetastatic effects and advocates for its combination with eribulin in future clinical trials for metastatic breast cancer and early-stage solid tumors. Mol Cancer Ther; 15(8); 1809-22. ©2016 AACR.

Aurora B expression and histone variant H1.4S27 phosphorylation are no longer coordinated during metaphase in aneuploid colorectal carcinomas

Experimental model systems identified phosphorylation of linker histone variant H1.4 at Ser 27 (H1.4S27p) as a novel mitotic mark set by Aurora B kinase. Here, we examined expression of Aurora B and H1.4S27p in colorectal carcinoma (CRC) cell lines (HCT116, DLD1, Caco-2, HT29) and tissue specimens (n = 36), in relation to microsatellite instability (MSI) status and ploidy. In vitro, Aurora B (pro-/meta-/anaphase) and H1.4S27p (pro-/metaphase) were localized in mitotic figures. The proportion of labeled mitoses was significantly different between cell lines for Aurora B (p = 0.019) but not for H1.4S27p (p = 0.879). For Aurora B, these differences were not associated with an altered Aurora B gene copy number (FISH) or messenger RNA (mRNA) expression level (qRT-PCR). Moreover, Aurora B expression and H1.4S27 phosphorylation were no longer coordinated during metaphase in aneuploid HT29 cells (p = 0.039). In CRCs, immunoreactivity for Aurora B or H1.4S27p did not correlate with T- or N-stage, grade, or MSI status. However, metaphase labeling of H1.4S27p was significantly higher in diploid than in aneuploid CRCs (p = 0.011). Aurora B was significantly correlated with H1.4S27p-positive metaphases in MSI (p = 0.010) or diploid (p = 0.003) CRCs. Finally, combined classification of MSI status and ploidy revealed a significant positive correlation of Aurora B with H1.4S27p in metaphases of diploid/MSI (p = 0.010) and diploid/microsatellite-stable (MSS; p = 0.031) but not of aneuploid/MSS (p = 0.458) CRCs. The present study underlines the functional link of Aurora B expression and H1.4S27p during specific phases of mitosis in diploid and/or MSI-positive CRCs in vitro and in situ. Importantly, the study shows that the coordination between Aurora B expression and phosphorylation of H1.4 at Ser 27 is lost in cycling aneuploid CRC cells.

Aurora kinase A has a significant role as a therapeutic target and clinical biomarker in endometrial cancer

Aurora kinase A (AURKA) regulates the cell cycle checkpoint and maintains genomic integrity. AURKA is overexpressed in various malignant tumors and its upregulation induces chromosomal instability, which leads to aneuploidy and cell transformation. To investigate the role of AURKA in endometrial cancer, we evaluated the association of immunohistochemical expression of AURKA with clinicopathological factors. Furthermore, we examined the effects of AURKA inhibition by transfected siRNA in HEC-1B cells on colony-forming ability, invasion and migration capacity, and chemosensitivity. Immunohistochemical staining showed that overexpression of AURKA was significantly associated with tumor grade (P<0.05) and poor histologic differentiation (P<0.05). The recurrence rate also tended to be high in cases with overexpression of AURKA (P<0.1) and these cases also had a tendency for shorter disease-free survival (DFS) (P<0.1). AURKA inhibition in endometrial cancer cell lines significantly decreased cell growth, invasion and migration (P<0.05), and increased chemosensitivity to paclitaxel. We also evaluated the efficacy of a combination of AURKA siRNA and paclitaxel against subcutaneous tumors formed in a nude mouse. After treatment, the tumor volume shrank significantly compared to treatment with paclitaxel only (P<0.05). To our knowledge, this is the first study in endometrial carcinoma to show a correlation between overexpression of AURKA and tumor grade, histological type and sensitivity to paclitaxel. AURKA is a promising therapeutic target in endometrial cancer and the combination therapy with AURKA inhibitors and paclitaxel could be effective for endometrial cancer that is resistant to conventional treatment and has a poor prognosis.

Issues in interpreting the in vivo activity of Aurora-A

INTRODUCTION

Based on its role as a mitotic regulatory kinase, overexpressed and associated with aneuploidy in cancer, small-molecule inhibitors have been developed for Aurora-A (AURKA) kinase. In preclinical and clinical assessments, these agents have shown efficacy in inducing stable disease or therapeutic response. In optimizing the use of Aurora-A inhibitors, it is critical to have robust capacity to measure the kinase activity of Aurora-A in tumors.

AREAS COVERED

We provide an overview of molecular mechanisms of mitotic and non-mitotic activation of Aurora-A kinase, and interaction of Aurora-A with its regulatory partners. Typically, Aurora-A activity is measured by use of phospho-antibodies targeting an autophosphorylated T288 epitope. However, recent studies have identified alternative means of Aurora-A activation control, including allosteric regulation by partners, phosphorylation on alternative activating residues (S51, S98), dephosphorylation on inhibitory sites (S342) and T288 phosphorylation by alternative kinases such as Pak enzymes. Additional work has shown that the relative abundance of Aurora-A partners can affect the activity of Aurora-A inhibitors, and that Aurora-A activation also occurs in interphase cells.

EXPERT OPINION

Taken together, this work suggests the need for comprehensive analysis of Aurora-A activity and expression of Aurora-A partners in order to stratify patients for likely therapeutic response.

Aurora kinase inhibitor patents and agents in clinical testing: an update (2011 - 2013)

INTRODUCTION

Aurora kinase A, B and C, members of serine/threonine kinase family, are key regulators of mitosis. As Aurora kinases are overexpressed in many of the human cancers, small-molecule inhibitors of Aurora kinase have emerged as a possible treatment option for cancer.

AREAS COVERED

In 2009 and 2011, the literature pertaining to Aurora kinase inhibitors and their patents was reviewed. Here, the aim is to update the information for Aurora kinase inhibitors in clinical trials and the patents filed between the years 2011 and 2013. Pubmed, Scopus®, Scifinder®, USPTO, EPO and www.clinicaltrials.gov databases were used for searching the literature and patents for Aurora kinase inhibitors.

EXPERT OPINION

Even though both Aurora sub-type selective as well as pan-selective inhibitors show preclinical and clinical efficacy, so far no Aurora kinase inhibitor has been approved for clinical use. Particularly, dose-limiting toxicity (neutropenia) is a key issue that needs to be addressed. Preliminary evidence suggests that the use of selective Aurora A inhibitors could avoid Aurora B-mediated neutropenia in clinical settings. Also, use of adjunctive agents such as granulocyte stimulating factor to overcome neutropenia associated with Aurora B inhibition could be an answer to overcome the toxicity and bring Aurora inhibitors to market in the future.

NEDD9 regulates actin dynamics through cortactin deacetylation in an AURKA/HDAC6-dependent manner

The prometastatic protein NEDD9 (neural precursor cell expressed, developmentally downregulated 9) is highly expressed in many cancers and is required for mesenchymal individual cell migration and progression to the invasive stage. Nevertheless, the molecular mechanisms of NEDD9-driven migration and the downstream targets effecting metastasis are not well defined. In the current study, knockdown of NEDD9 in highly metastatic tumor cells drastically reduces their migratory capacity due to disruption of actin dynamics at the leading edge. Specifically, NEDD9 deficiency leads to a decrease in the persistence and stability of lamellipodial protrusions similar to knockdown of cortactin (CTTN). Mechanistically, it was shown that NEDD9 binds to and regulates acetylation of CTTN in an Aurora A kinase (AURKA)/HDAC6-dependent manner. The knockdown of NEDD9 or AURKA results in an increase in the amount of acetylated CTTN and a decrease in the binding of CTTN to F-actin. Overexpression of the deacetylation mimicking (9KR) mutant of CTTN is sufficient to restore actin dynamics at the leading edge and migration proficiency of the tumor cells. Inhibition of AURKA and HDAC6 activity by alisertib and Tubastatin A in xenograft models of breast cancer leads to a decrease in the number of pulmonary metastases. Collectively, these findings identify CTTN as the key downstream component of NEDD9-driven migration and metastatic phenotypes.

IMPLICATIONS

This study provides a mechanistic platform for therapeutic interventions based on AURKA and HDAC6 inhibition for patients with metastatic breast cancer to prevent and/or eradicate metastases.

Computational methods in drug discovery

Computer-aided drug discovery/design methods have played a major role in the development of therapeutically important small molecules for over three decades. These methods are broadly classified as either structure-based or ligand-based methods. Structure-based methods are in principle analogous to high-throughput screening in that both target and ligand structure information is imperative. Structure-based approaches include ligand docking, pharmacophore, and ligand design methods. The article discusses theory behind the most important methods and recent successful applications. Ligand-based methods use only ligand information for predicting activity depending on its similarity/dissimilarity to previously known active ligands. We review widely used ligand-based methods such as ligand-based pharmacophores, molecular descriptors, and quantitative structure-activity relationships. In addition, important tools such as target/ligand data bases, homology modeling, ligand fingerprint methods, etc., necessary for successful implementation of various computer-aided drug discovery/design methods in a drug discovery campaign are discussed. Finally, computational methods for toxicity prediction and optimization for favorable physiologic properties are discussed with successful examples from literature.

Preclinical validation of Aurora kinases-targeting drugs in osteosarcoma

Background:

Aurora kinases are key regulators of cell cycle and represent new promising therapeutic targets in several human tumours.

Methods:

Biological relevance of Aurora kinase-A and -B was assessed on osteosarcoma clinical samples and by silencing these genes with specific siRNA in three human osteosarcoma cell lines. In vitro efficacy of two Aurora kinases-targeting drugs (VX-680 and ZM447439) was evaluated on a panel of four drug-sensitive and six drug-resistant human osteosarcoma cell lines.

Results:

Human osteosarcoma cell lines proved to be highly sensitive to both drugs. A decreased drug sensitivity was observed in doxorubicin-resistant cell lines, most probably related to ABCB1/MDR1 overexpression. Both drugs variably induced hyperploidy and apoptosis in the majority of cell lines. VX-680 also reduced in vitro cell motility and soft-agar cloning efficiency. Drug association experiments showed that VX-680 positively interacts with all conventional drugs used in osteosarcoma chemotherapy, overcoming the cross-resistance observed in the single-drug treatments.

Conclusion:

Aurora kinase-A and -B represent new candidate therapeutic targets for osteosarcoma. In vitro analysis of the Aurora kinases inhibitors VX-680 and ZM447439 indicated in VX-680 a new promising drug of potential clinical usefulness in association with conventional osteosarcoma chemotherapeutic agents.

HIF-1 is involved in the negative regulation of AURKA expression in breast cancer cell lines under hypoxic conditions

Numerous microarray-based gene expression studies performed on several types of solid tumors revealed significant changes in key genes involved in progression and regulation of the cell cycle, including AURKA that is known to be overexpressed in many types of human malignancies. Tumor hypoxia is associated with poor prognosis in several cancer types, including breast cancer (BC). Since hypoxia is a condition that influences the expression of many genes involved in tumorigenesis, proliferation, and cell cycle regulation, we performed a microarray-based gene expression analysis in order to identify differentially expressed genes in BC cell lines exposed to hypoxia. This analysis showed that hypoxia induces a down-regulation of AURKA expression. Although hypoxia is a tumor feature, the molecular mechanisms that regulate AURKA expression in response to hypoxia in BC are still unknown. For the first time, we demonstrated that HIF-1 activation downstream of hypoxia could drive AURKA down-regulation in BC cells. In fact, we found that siRNA-mediated knockdown of HIF-1α significantly reduces the AURKA down-regulation in BC cells under hypoxia. The aim of our study was to obtain new insights into AURKA transcriptional regulation in hypoxic conditions. Luciferase reporter assays showed a reduction of AURKA promoter activity in hypoxia. Unlike the previous findings, we hypothesize a new possible mechanism where HIF-1, rather than inducing transcriptional activation, could promote the AURKA down-regulation via its binding to hypoxia-responsive elements into the proximal region of the AURKA promoter. The present study shows that hypoxia directly links HIF-1 with AURKA expression, suggesting a possible pathophysiological role of this new pathway in BC and confirming HIF-1 as an important player linking an environmental signal to the AURKA promoter. Since AURKA down-regulation overrides the estrogen-mediated growth and chemoresistance in BC cells, these findings could be important for the development of new possible therapies against BC.

Visualization of mitotic arrest of cell cycle with bioluminescence imaging in living animals

PURPOSE

Visualization of the cell cycle in living subjects has long been a big challenge. The present study aimed to noninvasively visualize mitotic arrest of the cell cycle with an optical reporter in living subjects.

PROCEDURES

An N-terminal cyclin B1-luciferase fusion construct (cyclin B-Luc) controlled by the cyclin B promoter, as a mitosis reporter, was generated. HeLa or HCT116 cells stably expressing cyclin B-Luc reporter were used to evaluate its cell cycle-dependent regulation and ubiquitination-mediated degradation. We also evaluated its feasibility to monitor the mitotic arrest caused by Taxotere both in vitro and in vivo.

RESULTS

We showed that the cyclin B-Luc fusion protein was regulated in a cell cycle-dependent manner and accumulated in the mitotic phase (M phase) in cellular assays. The regulation of cyclin B-Luc reporter was mediated by proteasome ubiquitination. In the present study, in vitro imaging showed that antimitotic reagents like Taxotere upregulated the reporter through cell cycle arrest in the M phase. Noninvasive longitudinal bioluminescence imaging further demonstrated an upregulation of the reporter consistent with mitotic arrest induced in tumor xenograft models. Induction of this reporter was also observed with a kinesin spindle protein inhibitor, which causes cell cycle blockage in the M phase.

CONCLUSIONS

Our results demonstrate that the cyclin B-Luc reporter can be used to image whether compounds are capable, in vivo, of causing an M phase arrest and/or altering cyclin B turnover. This reporter can also be potentially used in high-throughput screening efforts aimed at discovering novel molecules that will cause cell cycle arrest at the M phase in cultivated cell lines and animal models.

TTK/hMPS1 is an attractive therapeutic target for triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents a subgroup of breast cancers (BC) associated with the most aggressive clinical behavior. No targeted therapy is currently available for the treatment of patients with TNBC. In order to discover potential therapeutic targets, we searched for protein kinases that are overexpressed in human TNBC biopsies and whose silencing in TNBC cell lines causes cell death. A cohort including human BC biopsies obtained at Institut Curie as well as normal tissues has been analyzed at a gene-expression level. The data revealed that the human protein kinase monopolar spindle 1 (hMPS1), also known as TTK and involved in mitotic checkpoint, is specifically overexpressed in TNBC, compared to the other BC subgroups and healthy tissues. We confirmed by immunohistochemistry and reverse phase protein array that TNBC expressed higher levels of TTK protein compared to the other BC subgroups. We then determined the biological effects of TTK depletion by RNA interference, through analyses of tumorigenic capacity and cell viability in different human TNBC cell lines. We found that RNAi-mediated depletion of TTK in various TNBC cell lines severely compromised their viability and their ability to form colonies in an anchorage-independent manner. Moreover, we observed that TTK silencing led to an increase in H2AX phosphorylation, activation of caspases 3/7, sub-G1 cell population accumulation and high annexin V staining, as well as to a decrease in G1 phase cell population and an increased aneuploidy. Altogether, these data indicate that TTK depletion in TNBC cells induces apoptosis. These results point out TTK as a protein kinase overexpressed in TNBC that may represent an attractive therapeutic target specifically for this poor prognosis associated subgroup of breast cancer.

A comprehensive analysis of Aurora A; transcript levels are the most reliable in association with proliferation and prognosis in breast cancer

BACKGROUND

Aurora A kinase, a centrosomal serine/threonine kinase which plays an essential role in chromosome segregation during cell division, is commonly amplified and/or over expressed in human malignancies. Aurora A is suggested to be one of the proliferation parameters which is an independent prognostic factor for early invasive breast cancer patients; however the individual clinical or prognostic relevance of this gene has been a matter of debate.

METHODS

A comprehensive analysis of Aurora A at the levels of gene expression, gene copy number and protein expression was performed for 278 primary invasive breast cancer patients; and the correlation with clinical outcomes were investigated.

RESULTS

Aurora A gene expression level not only correlated with gene amplification, but was also significantly associated with several clinicopathological parameters and patient prognosis. Patients with higher nuclear grade, negative progesterone receptor status and higher Ki67 expressed higher levels of Aurora A mRNA, which was associated not only with poor relapse-free survival (RFS) but was also found to be a significant multivariate parameter for RFS. Aurora A protein expression was also significantly associated with clinicopathological characteristics; lymph node status, nuclear grade, estrogen receptor status and Ki67, but not with prognosis. By contrast, Aurora A gene amplification correlated with tumor size, nuclear grade and Ki67, and had no prognostic value.

CONCLUSION

Our data indicate that Aurora A gene expression is an effective tool, which defines both tumor proliferation potency and patient prognosis.

NEDD9 depletion destabilizes Aurora A kinase and heightens the efficacy of Aurora A inhibitors: implications for treatment of metastatic solid tumors

Aurora A kinase (AURKA) is overexpressed in 96% of human cancers and is considered an independent marker of poor prognosis. While the majority of tumors have elevated levels of AURKA protein, few have AURKA gene amplification, implying that posttranscriptional mechanisms regulating AURKA protein levels are significant. Here, we show that NEDD9, a known activator of AURKA, is directly involved in AURKA stability. Analysis of a comprehensive breast cancer tissue microarray revealed a tight correlation between the expression of both proteins, significantly corresponding with increased prognostic value. A decrease in AURKA, concomitant with increased ubiquitination and proteasome-dependent degradation, occurs due to depletion or knockout of NEDD9. Reexpression of wild-type NEDD9 was sufficient to rescue the observed phenomenon. Binding of NEDD9 to AURKA is critical for AURKA stabilization, as mutation of S296E was sufficient to disrupt binding and led to reduced AURKA protein levels. NEDD9 confers AURKA stability by limiting the binding of the cdh1-substrate recognition subunit of APC/C ubiquitin ligase to AURKA. Depletion of NEDD9 in tumor cells increases sensitivity to AURKA inhibitors. Combination therapy with NEDD9 short hairpin RNAs and AURKA inhibitors impairs tumor growth and distant metastasis in mice harboring xenografts of breast tumors. Collectively, our findings provide rationale for the use of AURKA inhibitors in treatment of metastatic tumors and predict the sensitivity of the patients to AURKA inhibitors based on NEDD9 expression.

Aurora kinase inhibitors: Potential molecular-targeted drugs for gynecologic malignant tumors

Chemotherapy and surgery are important treatment strategies for gynecologic malignant tumors such as ovarian, cervical and endometrial cancer. However, many anticancer drugs currently available are cytotoxic and cause strong adverse reactions in patients. Aurora kinases have attracted increasing attention in recent years as serine/threonine kinases with various roles in cell division, including chromosomal agglutination and segregation, functions of centromeres, centrosomal maturation, spindle formation and cytokinesis. Aurora kinases are overexpressed in a number of cancers and recent studies have shown that they are involved in onco genesis and cause an aberrant increase in centrosome number, emergence of polykaryocytes and failure of cancer inhibition mechanisms. Thus, drugs that inhibit Aurora kinases are likely to exert anticancer effects in various fields, including the gynecologic field. Aurora kinase inhibitors exert antitumor effects in monotherapy and synergistic effects in combination therapy with taxane-based anticancer agents for gynecologic tumors and are likely to increase the efficacy of existing anticancer drugs. Current Aurora kinase inhibitors include ZM447439, Hesperadin, VX-680/MK-0457, AT9283 and Barasertib, and clinical trials are ongoing to verify the effects of these inhibitors.

Reversine induces cell cycle arrest, polyploidy, and apoptosis in human breast cancer cells

BACKGROUND

Reversine, a small synthetic purine analogue, has been reported to be effective in tumor suppression. In the present study, we demonstrated an antitumor activity of reversine that could suppress cellular proliferation and induce cell cycle arrest and apoptosis in human breast cancer cell lines.

METHODS

To evaluate whether reversine could suppress cell growth of MCF-7 and MDA-MB-231 cells and induce cell death, the cell viability, cell cycle, and apoptosis were determined in this study.

RESULTS

Reversine treatment in human breast cancer cells reduced cell viability in a dose-dependent manner. Cell cycle accumulation at the G2/M phase in reversine-treated cells was also determined. Moreover, polyploidy was also found in reversine-treated cells. Apoptosis in reversine-treated cells was exhibited with PARP cleavage and caspase-3 and caspase-8 activation, but not caspase-9 activation, indicating that caspase-dependent apoptosis mediated by an extrinsic pathway took place in reversine-treated cells. Furthermore, reversine attenuated cell death in cells pretreated with a pan-caspase inhibitor before reversine treatment.

CONCLUSIONS

In the present study, we demonstrated that reversine contributes to growth inhibition in human breast cancer cells through cell cycle arrest, polyploidy, and/or apoptosis induction. The apoptosis mediated by reversine was induced by the mitochondria-independent pathway. Therefore, the potential role of reversine as a novel therapeutic agent for the treatment of breast cancer is worthy of further investigation.

p53 negatively regulates Aurora A via both transcriptional and posttranslational regulation

p53 plays an important role in mitotic checkpoint, but what its role is remains enigmatic. Aurora A is a Ser/Thr kinase involved in correcting progression of mitosis. Here, we show that p53 is a negative regulator for Aurora A. We found that p53 deficiency leads to Aurora A elevation. Ectopic expression of p53 or DNA damage-induced expression of p53 can suppress the expression of Aurora A. Mechanistic studies show that p53 is a negative regulator for Aurora A expression through both transcriptional and posttranslational regulation. p53 knockdown in cancer cells reduces the level of p21, which, in turn, increases the activity of CDK2 followed by induction of Rb1 hyperphosphorylation and its dissociation with transcriptional factor E2F3. E2F3 can bind to Aurora A gene promoter, potentiating Aurora A gene expression and p53 deficiency, enhancing the binding of E2F3 on Aurora A promoter. Also, p53 deficiency leads to decelerating Aurora A's turnover rate, due to the fact that p53 deficiency causes the downregulation of Fbw7α, a component of E3 ligase of Aurora A. Consistently, p53 knockdown-mediated Aurora A elevation is mitigated when Fbw7α is ectopically expressed. Thus, p53-mediated Aurora A degradation requires Fbw7α expression. Significantly, inverse correlation between p53 and Aurora A elevation is translated into the deregulation of centrosome amplification. p53 knockdown leads to high percentages of cells with abnormal amplification of centrosome. These data suggest that p53 is an important negative regulator of Aurora A, and that loss of p53 in many types of cancer could lead to abnormal elevation of Aurora A and dysregulated mitosis, which provides a growth advantage for cancer cells.

Ras-driven transcriptome analysis identifies aurora kinase A as a potential malignant peripheral nerve sheath tumor therapeutic target

PURPOSE

Patients with neurofibromatosis type 1 (NF1) develop malignant peripheral nerve sheath tumors (MPNST), which are often inoperable and do not respond well to current chemotherapies or radiation. The goal of this study was to use comprehensive gene expression analysis to identify novel therapeutic targets.

EXPERIMENTAL DESIGN

Nerve Schwann cells and/or their precursors are the tumorigenic cell types in MPNST because of the loss of the NF1 gene, which encodes the RasGAP protein neurofibromin. Therefore, we created a transgenic mouse model, CNP-HRas12V, expressing constitutively active HRas in Schwann cells and defined a Ras-induced gene expression signature to drive a Bayesian factor regression model analysis of differentially expressed genes in mouse and human neurofibromas and MPNSTs. We tested functional significance of Aurora kinase overexpression in MPNST in vitro and in vivo using Aurora kinase short hairpin RNAs (shRNA) and compounds that inhibit Aurora kinase.

RESULTS

We identified 2,000 genes with probability of linkage to nerve Ras signaling of which 339 were significantly differentially expressed in mouse and human NF1-related tumor samples relative to normal nerves, including Aurora kinase A (AURKA). AURKA was dramatically overexpressed and genomically amplified in MPNSTs but not neurofibromas. Aurora kinase shRNAs and Aurora kinase inhibitors blocked MPNST cell growth in vitro. Furthermore, an AURKA selective inhibitor, MLN8237, stabilized tumor volume and significantly increased survival of mice with MPNST xenografts.

CONCLUSION

Integrative cross-species transcriptome analyses combined with preclinical testing has provided an effective method for identifying candidates for molecular-targeted therapeutics. Blocking Aurora kinases may be a viable treatment platform for MPNST.

Aurora-A is an efficient marker for predicting poor prognosis in human nasopharyngeal carcinoma with aggressive local invasion: 208 cases with a 10-year follow-up from a single institution

Aurora-A kinase (Aur-A), a member of a family of mitotic serine/threonine kinases, is known to be amplified in epithelial malignancies. In this study, we focused our investigation on Aur-A expression and its prognostic significance in nasopharyngeal carcinoma (NPC). Immunohistochemical staining for Aur-A was performed on the paraffin sections of 208 patients with NPC. Data were subjected to statistical analysis with respect to clinicopathological variables, overall survival and disease-free survival. An immunohistochemical analysis showed that Aur-A was highly expressed in 132 (63.5%) of the 208 NPC tissues examined. Aur-A expression was significantly correlated with T classification (P=0.012), clinical stage (P=0.003) and skull base invasion (P=0.003). Statistical analysis showed that Aur-A expression was inversely correlated with the 10-year overall and disease-free survival rates of NPC patients. Results of the multivariate analysis revealed that Aur-A expression was an independent prognostic indicator for patient survival. More significantly, Aur-A was found to be a marker for poor survival, which was mainly attributed to its high expression in the subgroup of T(4) tumor classification with aggressive local invasion. These results indicated that Aur-A expression is inversely correlated with survival and directly correlated with the malignant status of NPC. Therefore, Aur-A may serve as a potential biological marker for poor prognosis in the T(4) subgroup of patients.

Ashwagandha derived withanone targets TPX2-Aurora A complex: computational and experimental evidence to its anticancer activity

Cancer is largely marked by genetic instability. Specific inhibition of individual proteins or signalling pathways that regulate genetic stability during cell division thus hold a great potential for cancer therapy. The Aurora A kinase is a Ser/Thr kinase that plays a critical role during mitosis and cytokinesis and is found upregulated in several cancer types. It is functionally regulated by its interactions with TPX2, a candidate oncogene. Aurora A inhibitors have been proposed as anticancer drugs that work by blocking its ATP binding site. This site is common to other kinases and hence these inhibitors lack specificity for Aurora A inhibition in particular, thus advocating the need of some alternative inhibition route. Previously, we identified TPX2 as a cellular target for withanone that selectively kill cancer cells. By computational approach, we found here that withanone binds to TPX2-Aurora A complex. In experiment, withanone treatment to cancer cells indeed resulted in dissociation of TPX2-Aurora A complex and disruption of mitotic spindle apparatus proposing this as a mechanism of the anticancer activity of withanone. From docking analysis, non-formation/disruption of the active TPX2-Aurora A association complex could be discerned. Our MD simulation results suggesting the thermodynamic and structural stability of TPX2-Aurora A in complex with withanone further substantiates the binding. We report a computational rationale of the ability of naturally occurring withanone to alter the kinase signalling pathway in an ATP-independent manner and experimental evidence in which withanone cause inactivation of the TPX2-Aurora A complex. The study demonstrated that TPX2-Aurora A complex is a target of withanone, a potential natural anticancer drug.

The novel protein suppressed in lung cancer down-regulated in lung cancer tissues retards cell proliferation and inhibits the oncokinase Aurora-A

INTRODUCTION

In an attempt to search for genes with abnormal expression in cancers, Suppressed in Lung Cancer (SLAN, also known as KIAA0256) is found underexpressed in human lung cancer tissues by quantitative real-time PCR (Q-RT-PCR). The study set out to characterize SLAN protein and explore its cellular functions.

METHODS

SLAN or its specific short hairpin RNA, full length or various deletion mutants were overexpressed in 293T or lung cancer cell lines, and cell proliferation, cell cycle, mitosis progression, and spindle configuration were surveyed.

RESULTS

SLAN and its deletion mutants are localized to many subcellular locations such as endoplasmic reticulum (ER), nucleus, nucleolus, spindle pole and midbody, suggesting SLAN may function as a multifunctional protein. Overexpression of SLAN per se or its short hairpin RNAs (shRNAs) inhibits or accelerates cell proliferation through prolonging or shortening mitosis. Time-lapse microscopic recording reveals that cells overexpressing exogenous SLAN are arrested in mitosis or cannot undergo cytokinesis. SLAN 2-551 mutants drastically arrest cells in mitosis, where α- and γ-tubulin are disorganized. SLAN employs C-terminal to interact with Aurora-A, a key mitosis regulator and an oncogenic kinase associated with a wide range of human cancers. SLAN negatively regulates the activity of Aurora-A by directly inhibiting kinase activity in vitro or reducing the level of active Aurora-A in cells. SLAN is frequently reduced in lung cancer tissues overexpressing Aurora-A, arguing for the necessity to suppress SLAN during the Aurora-A-associated cancer formation.

CONCLUSIONS

Taken together, we have identified a novel protein SLAN downregulated in lung caner, having multiple subcellular localization including spindle matrix and midbody, inhibiting cell proliferation and Aurora-A.

Synthesis and biological evaluation of novel pyrazole derivatives with anticancer activity

We synthesized thirty-six novel pyrazole derivatives and studied their antiproliferative activity in human ovarian adenocarcinoma A2780 cells, human lung carcinoma A549 cells, and murine P388 leukemia cells. Four of these substances were selected because of their higher antiproliferative activity and further analyses showed that they were all able to induce apoptosis, although to a different extent. The expression of p53 and p21(waf1), which induce apoptosis and cell cycle arrest, was evaluated by western blot analysis in cells treated with compound 12d. The analysis of the cell cycle showed that all the selected compounds cause a partial G2/M block and the formation of polyploid cells. Furthermore, the four selected compounds were tested for their interaction with the microtubular cytoskeletal system by docking analysis, tubulin polymerization assay and immunofluorescence staining, demonstrating that the compound 12d, unlike the other active derivatives, was able to significantly bind dimers of α- and β-tubulin, probably causing a molecular distortion resulting in the disassembly of microtubules.

Mitotic catastrophe: a mechanism for avoiding genomic instability

The improper distribution of chromosomes during mitosis compromises cellular functions and can reduce cellular fitness or contribute to malignant transformation. As a countermeasure, higher eukaryotes have developed strategies for eliminating mitosis-incompetent cells, one of which is mitotic catastrophe. Mitotic catastrophe is driven by a complex and poorly understood signalling cascade but, from a functional perspective, it can be defined as an oncosuppressive mechanism that precedes (and is distinct from) apoptosis, necrosis or senescence. Accordingly, the disruption of mitotic catastrophe precipitates tumorigenesis and cancer progression, and its induction constitutes a therapeutic endpoint.

Two TPX2-dependent switches control the activity of Aurora A

Aurora A is an important oncogenic kinase for mitotic spindle assembly and a potentially attractive target for human cancers. Its activation could be regulated by ATP cycle and its activator TPX2. To understand the activation mechanism of Aurora A, a series of 20 ns molecular dynamics (MD) simulations were performed on both the wild-type kinase and its mutants. Analyzing the three dynamic trajectories (Aurora A-ATP, Aurora A-ADP, and Aurora A-ADP-TPX2) at the residue level, for the first time we find two TPX2-dependent switches, i.e., switch-1 (Lys-143) and switch-2 (Arg-180), which are tightly associated with Aurora A activation. In the absence of TPX2, Lys-143 exhibits a "closed" state, and becomes hydrogen-bonded to ADP. Once TPX2 binding occurs, switch-1 is forced to "open" the binding site, thus pulling ADP away from Aurora A. Without facilitation of TPX2, switch-2 exits in an "open" conformation which accompanies the outward-flipping movement of P·Thr288 (in an inactive conformation), leading to the crucial phosphothreonine exposed and accessible for deactivation. However, with the binding of TPX2, switch-2 is forced to undergo a "closed" movement, thus capturing P·Thr288 into a buried position and locking its active conformation. Analysis of two Aurora A (K143A and R180A) mutants for the two switches further verifies their functionality and reliability in controlling Aurora activity. Our systems therefore suggest two switches determining Aurora A activation, which are important for the development of aurora kinase inhibitors.

AURKB-mediated effects on chromatin regulate binding versus release of XIST RNA to the inactive chromosome

How XIST RNA strictly localizes across the inactive X chromosome is unknown; however, prophase release of human XIST RNA provides a clue. Tests of inhibitors that mimic mitotic chromatin modifications implicated an indirect role of PP1 (protein phosphatase 1), potentially via its interphase repression of Aurora B kinase (AURKB), which phosphorylates H3 and chromosomal proteins at prophase. RNA interference to AURKB causes mitotic retention of XIST RNA, unlike other mitotic or broad kinase inhibitors. Thus, AURKB plays an unexpected role in regulating RNA binding to heterochromatin, independent of mechanics of mitosis. H3 phosphorylation (H3ph) was shown to precede XIST RNA release, whereas results exclude H1ph involvement. Of numerous Xi chromatin (chromosomal protein) hallmarks, ubiquitination closely follows XIST RNA retention or release. Surprisingly, H3S10ph staining (but not H3S28ph) is excluded from Xi and is potentially linked to ubiquitination. Results suggest a model of multiple distinct anchor points for XIST RNA. This study advances understanding of RNA chromosome binding and the roles of AURKB and demonstrates a novel approach to manipulate and study XIST RNA.

Aurora-A expression is independently associated with chromosomal instability in colorectal cancer

AURKA (the official symbol for Aurora-A, STK15, or BTAK) regulates the function of centrosomes, spindles, and kinetochores for proper mitotic progression. AURKA overexpression is observed in various cancers including colon cancer, and a link between AURKA and chromosomal instability (CIN) has been proposed. However, no study has comprehensively examined AURKA expression in relation to CIN or prognosis using a large number of tumors. Using 517 colorectal cancers in two prospective cohort studies, we detected AURKA overexpression (by immunohistochemistry) in 98 tumors (19%). We assessed other molecular events including loss of heterozygosity (LOH) in 2p, 5q, 17q, and 18q, the CpG island methylation phenotype (CIMP), and microsatellite instability (MSI). Prognostic significance of AURKA was evaluated by Cox regression and Kaplan-Meier method. In both univariate and multivariate logistic regressions, AURKA overexpression was significantly associated with CIN (defined as the presence of LOH in any of the chromosomal segments; multivariate odds ratio, 2.97; 95% confidence interval, 1.40-6.29; P = .0045). In multivariate analysis, AURKA was associated with cyclin D1 expression (P = .010) and inversely with PIK3CA mutation (P=.014), fatty acid synthase expression (P=.028), and family history of colorectal cancer (P = .050), but not with sex, age, body mass index, tumor location, stage, CIMP, MSI, KRAS, BRAF, BMI, LINE-1 hypomethylation, p53, p21, beta-catenin, or cyclooxygenase 2. AURKA was not significantly associated with clinical outcome or survival. In conclusion, AURKA overexpression is independently associated with CIN in colorectal cancer, supporting a potential role of Aurora kinase-A in colorectal carcinogenesis through genomic instability (rather than epigenomic instability).

Centrosome-associated regulators of the G(2)/M checkpoint as targets for cancer therapy

In eukaryotic cells, control mechanisms have developed that restrain cell-cycle transitions in response to stress. These regulatory pathways are termed cell-cycle checkpoints. The G(2)/M checkpoint prevents cells from entering mitosis when DNA is damaged in order to afford these cells an opportunity to repair the damaged DNA before propagating genetic defects to the daughter cells. If the damage is irreparable, checkpoint signaling might activate pathways that lead to apoptosis. Since alteration of cell-cycle control is a hallmark of tumorigenesis, cell-cycle regulators represent potential targets for therapy. The centrosome has recently come into focus as a critical cellular organelle that integrates G(2)/M checkpoint control and repairs signals in response to DNA damage. A growing number of G(2)/M checkpoint regulators have been found in the centrosome, suggesting that centrosome has an important role in G(2)/M checkpoint function. In this review, we discuss centrosome-associated regulators of the G(2)/M checkpoint, the dysregulation of this checkpoint in cancer, and potential candidate targets for cancer therapy.

Potent antitumor activity of the anti-CD19 auristatin antibody drug conjugate hBU12-vcMMAE against rituximab-sensitive and -resistant lymphomas

Despite major advances in the treatment of non-Hodgkin lymphoma (NHL), including the use of chemotherapeutic agents and the anti-CD20 antibody rituximab, the majority of patients eventually relapse, and salvage treatments with non-cross-resistant compounds are needed to further improve patient survival. Here, we evaluated the antitumor effects of the microtubule destabilizing agent monomethyl auristatin E (MMAE) conjugated to the humanized anti-CD19 antibody hBU12 via a protease-sensitive valine-citrulline (vc) dipeptide linker. hBU12-vcMMAE induced potent tumor cell killing against rituximab-sensitive and -resistant NHL cell lines. CD19 can form heterodimers with CD21, and high levels of CD21 were reported to interfere negatively with the activity of CD19-targeted therapeutics. However, we observed comparable internalization, intracellular trafficking, and drug release in CD21(low) and CD21(high), rituximab-sensitive and -refractory lymphomas treated with hBU12-vcMMAE. Furthermore, high rates of durable regressions in mice implanted with these tumors were observed, suggesting that both rituximab resistance and CD21 expression levels do not impact on the activity of hBU12-vcMMAE. Combined, our data suggest that hBU12-vcMMAE may represent a promising addition to the treatment options for rituximab refractory NHL and other hematologic malignancies, including acute lymphoblastic leukemia.

Aurora A is essential for early embryonic development and tumor suppression

Aurora A is a serine/threonine kinase that functions in various stages of mitosis. Accumulating evidence has demonstrated that gene amplification and overexpression of Aurora A are linked to tumorigenesis, suggesting that Aurora A is an oncogene. In addition, Aurora A overexpression has been used as a negative prognostic marker, because it is associated with resistance to anti-mitotic agents commonly used for cancer therapy. To understand the physiological functions of Aurora A, we generated Aurora A knock-out mice. Aurora A null mice die early during embryonic development before the 16-cell stage. These Aurora A null embryos have defects in mitosis, particularly in spindle assembly, supporting critical functions of Aurora A during mitotic transitions. Interestingly, Aurora A heterozygosity results in a significantly increased tumor incidence in mice, suggesting that Aurora A may also act as a haploinsufficient tumor suppressor. Consistently, Aurora A heterozygous mouse embryonic fibroblasts have higher rates of aneuploidy. We further discovered that VX-680, an Aurora kinase inhibitor currently in phase II clinical trials for cancer treatment, could induce aneuploidy in wild type mouse embryonic fibroblasts. We conclude that a balanced Aurora A level is critical for maintaining genomic stability and one needs to be fully aware of the potential side effects of anti-cancer therapy based on the use of Aurora A-specific inhibitors.

Aurora-A and ch-TOG act in a common pathway in control of spindle pole integrity

Mitotic spindle assembly is a highly regulated process, crucial to ensure the correct segregation of duplicated chromosomes in daughter cells and to avoid aneuploidy, a common feature of tumors. Among the most important spindle regulators is Aurora-A, a mitotic centrosomal kinase frequently overexpressed in tumors. Here, we investigated the role of Aurora-A in spindle pole organization in human cells. We show that RNA interference-mediated Aurora-A inactivation causes pericentriolar material fragmentation in prometaphase, yielding the formation of spindles with supernumerary poles. This fragmentation does not necessarily involve centrioles and requires microtubules (MTs). Aurora-A-depleted prometaphases mislocalize the MT-stabilizing protein colonic hepatic tumor-overexpressed gene (ch-TOG), which abnormally accumulates at spindle poles, as well as the mitotic centromere-associated kinesin (MCAK), the major functional antagonist of ch-TOG, which delocalizes from poles. ch-TOG is required for extrapole formation in prometaphases lacking Aurora-A, because co-depletion of Aurora-A and ch-TOG mitigates the fragmented pole phenotype. These results indicate a novel function of Aurora-A, the regulation of ch-TOG and MCAK localization, and highlight a common pathway involving the three factors in control of spindle pole integrity.

Asymmetric stem cell division: lessons from Drosophila

Asymmetric cell division is an important and conserved strategy in the generation of cellular diversity during animal development. Many of our insights into the underlying mechanisms of asymmetric cell division have been gained from Drosophila, including the establishment of polarity, orientation of mitotic spindles and segregation of cell fate determinants. Recent studies are also beginning to reveal the connection between the misregulation of asymmetric cell division and cancer. What we are learning from Drosophila as a model system has implication both for stem cell biology and also cancer research.

Newer cytotoxic agents: attacking cancer broadly

The plasticity and instability of the cancer genome is impressive and is characterized by gene amplifications and deletions, rearrangements, and many silent and active mutations. Although targeted therapeutics have had effect in some diseases, there remains a large role for new cytotoxic agents that have the potential to be broadly active across multiple cancers. Platinum-based regimens are the basis for treatment of several common tumors. Satraplatin and picoplatin are newer platinum complexes that form bulkier lesions in DNA than their forerunners. Microtubules are a key target for anticancer agents. Vinca alkaloid and similar compounds fragment these critical structures, whereas taxanes stabilize them. Vinflunine is a new fluorinated Vinca alkaloid derivative with vascular disrupting effects, as well as antitumor effects. Epothilones are a new class of microtubule stabilizers. Mitosis has been targeted directly and indirectly by many anticancer agents. The aurora kinases are new targets in this class. Inhibitors of aurora kinases are likely to be cytotoxic. Finally, protein regulation is essential for cellular integrity. With the approval of bortezomib (Velcade, PS-341), the proteosome, a master protein regulator, has been validated as an anticancer target. The five articles in this issue of CCR Focus present the current status of these next generation cytotoxic agents.

MK615 inhibits pancreatic cancer cell growth by dual inhibition of Aurora A and B kinases

AIM: To investigate the anti-neoplastic effect of MK615, an anti-neoplastic compound isolated from Japanese apricot, against human pancreatic cancer cells in vitro.

METHODS: Three human pancreatic cancer cell lines PANC-1, PK-1, and PK45H were cultured with MK615 at concentrations of 600, 300, 150, and 0 &mgr;g/mL. Growth inhibition was evaluated by cell proliferation assay, and killing activity was determined by lactate dehydrogenase (LDH) assay. Expression of Aurora A and B kinases was detected by real-time polymerase chain reaction (PCR) and Western blotting. Cell cycle stages were evaluated by flow cytometry.

RESULTS: The growth inhibitory rates of MK615 at 150, 300, and 600 &mgr;g/mL were 2.3% ± 0.9%, 8.9% ± 3.2% and 67.1% ± 8.1% on PANC1 cells, 1.3% ± 0.3%, 8.7% ± 4.1% and 45.7 ± 7.6% on PK1 cells, and 1.2 ± 0.8%, 9.1% ± 2.1% and 52.1% ± 5.5% on PK45H cells, respectively (P <0.05). The percentage cytotoxicities of MK615 at 0, 150, 300, and 600 &mgr;g/mL were 19.6% ± 1.3%, 26.7% ± 1.8%, 25.5% ± 0.9% and 26.4% ± 0.9% in PANC1 cells, 19.7% ± 1.3%, 24.7% ± 0.8%, 25.9% ± 0.9% and 29.9% ± 1.1% in PK1 cells, and 28.0% ± 0.9%, 31.2% ± 0.9%, 30.4% ± 1.1% and 35.3 ± 1.0% in PK45H cells, respectively (P < 0.05). Real-time PCR and Western blotting showed that MK615 dually inhibited the expression of Aurora A and B kinases. Cell cycle analysis revealed that MK615 increased the population of cells in G2/M phase.

CONCLUSION: MK615 exerts an anti-neoplastic effect on human pancreatic cancer cells in vitro by dual inhibition of Aurora A and B kinases.