Aurora kinase inhibitors: progress towards the clinic

Effects of selective inhibitors of Aurora kinases on anaplastic thyroid carcinoma cell lines

Aurora kinases are serine/threonine kinases that play an essential role in cell division. Their aberrant expression and/or function induce severe mitotic abnormalities, resulting in either cell death or aneuploidy. Overexpression of Aurora kinases is often found in several malignancies, among which is anaplastic thyroid carcinoma (ATC). We have previously demonstrated the in vitro efficacy of Aurora kinase inhibitors in restraining cell growth and survival of different ATC cell lines. In this study, we sought to establish which Aurora might represent the preferential drug target for ATC. To this end, the effects of two selective inhibitors of Aurora-A (MLN8237) and Aurora-B (AZD1152) on four human ATC cell lines (CAL-62, BHT-101, 8305C, and 8505C) were analysed. Both inhibitors reduced cell proliferation in a time- and dose-dependent manner, with IC50 ranges of 44.3-134.2 nM for MLN8237 and of 9.2-461.3 nM for AZD1152. Immunofluorescence experiments and time-lapse videomicroscopy yielded evidence that each inhibitor induced distinct mitotic phenotypes, but both of them prevented the completion of cytokinesis. As a result, poliploidy increased in all AZD1152-treated cells, and in two out of four cell lines treated with MLN8237. Apoptosis was induced in all the cells by MLN8237, and in BHT-101, 8305C, and 8505C by AZD1152, while CAL-62 exposed to AZD1152 died through necrosis after multiple rounds of endoreplication. Both inhibitors were capable of blocking anchorage-independent cell growth. In conclusion, we demonstrated that either Aurora-A or Aurora-B might represent therapeutic targets for the ATC treatment, but inhibition of Aurora-A appears more effective for suppressing ATC cell proliferation and for inducing the apoptotic pathway.

Aurora kinases as targets in drug-resistant neuroblastoma cells

Aurora kinase inhibitors displayed activity in pre-clinical neuroblastoma models. Here, we studied the effects of the pan-aurora kinase inhibitor tozasertib (VX680, MK-0457) and the aurora kinase inhibitor alisertib (MLN8237) that shows some specificity for aurora kinase A over aurora kinase B in a panel of neuroblastoma cell lines with acquired drug resistance. Both compounds displayed anti-neuroblastoma activity in the nanomolar range. The anti-neuroblastoma mechanism included inhibition of aurora kinase signalling as indicated by decreased phosphorylation of the aurora kinase substrate histone H3, cell cycle inhibition in G2/M phase, and induction of apoptosis. The activity of alisertib but not of tozasertib was affected by ABCB1 expression. Aurora kinase inhibitors induced a p53 response and their activity was enhanced in combination with the MDM2 inhibitor and p53 activator nutlin-3 in p53 wild-type cells. In conclusion, aurora kinases are potential drug targets in therapy-refractory neuroblastoma, in particular for the vast majority of p53 wild-type cases.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

Discovery of (7-aryl-1,5-naphthyridin-2-yl)ureas as dual inhibitors of ERK2 and Aurora B kinases with antiproliferative activity against cancer cells

A novel series of (7-aryl-1,5-naphthyridin-2-yl)ureas was discovered as dual ERK2 and Aurora B kinases inhibitors. Several analogues were active at micromolar and submicromolar range against ERK2 and Aurora B, associated with very promising antiproliferative activity toward various cancer cell lines. Synthesis, structure activity relationship and docking study are reported. In vitro ADME properties and safety data are also discussed.

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.

An overview of the spindle assembly checkpoint status in oral cancer

Abnormal chromosome number, or aneuploidy, is a common feature of human solid tumors, including oral cancer. Deregulated spindle assembly checkpoint (SAC) is thought as one of the mechanisms that drive aneuploidy. In normal cells, SAC prevents anaphase onset until all chromosomes are correctly aligned at the metaphase plate thereby ensuring genomic stability. Significantly, the activity of this checkpoint is compromised in many cancers. While mutations are rather rare, many tumors show altered expression levels of SAC components. Genomic alterations such as aneuploidy indicate a high risk of oral cancer and cancer-related mortality, and the molecular basis of these alterations is largely unknown. Yet, our knowledge on the status of SAC components in oral cancer remains sparse. In this review, we address the state of our knowledge regarding the SAC defects and the underlying molecular mechanisms in oral cancer, and discuss their therapeutic relevance, focusing our analysis on the core components of SAC and its target Cdc20.

Repositioning: the fast track to new anti-malarial medicines?

BACKGROUND

Repositioning of existing drugs has been suggested as a fast track for developing new anti-malarial agents. The compound libraries of GlaxoSmithKline (GSK), Pfizer and AstraZeneca (AZ) comprising drugs that have undergone clinical studies in other therapeutic areas, but not achieved approval, and a set of US Food and Drug Administration (FDA)-approved drugs and other bio-actives were tested against Plasmodium falciparum blood stages.

METHODS

Molecules were tested initially against erythrocytic co-cultures of P. falciparum to measure proliferation inhibition using one of the following methods: SYBR®I dye DNA staining assay (3D7, K1 or NF54 strains); [(3)H] hypoxanthine radioisotope incorporation assay (3D7 and 3D7A strain); or 4',6-diamidino-2-phenylindole (DAPI) DNA imaging assay (3D7 and Dd2 strains). After review of the available clinical pharmacokinetic and safety data, selected compounds with low μM activity and a suitable clinical profile were tested in vivo either in a Plasmodium berghei four-day test or in the P. falciparum Pf3D7(0087/N9) huSCID 'humanized' mouse model.

RESULTS

Of the compounds included in the GSK and Pfizer sets, 3.8% (9/238) had relevant in vitro anti-malarial activity while 6/100 compounds from the AZ candidate drug library were active. In comparison, around 0.6% (24/3,800) of the FDA-approved drugs and other bio-actives were active. After evaluation of available clinical data, four investigational drugs, active in vitro were tested in the P. falciparum humanized mouse model: UK-112,214 (PAF-H1 inhibitor), CEP-701 (protein kinase inhibitor), CEP-1347 (protein kinase inhibitor), and PSC-833 (p-glycoprotein inhibitor). Only UK-112,214 showed significant efficacy against P. falciparum in vivo, although at high doses (ED90 131.3 mg/kg [95% CI 112.3, 156.7]), and parasitaemia was still present 96 hours after treatment commencement. Of the six actives from the AZ library, two compounds (AZ-1 and AZ-3) were marginally efficacious in vivo in a P. berghei model.

CONCLUSIONS

Repositioning of existing therapeutics in malaria is an attractive proposal. Compounds active in vitro at μM concentrations were identified. However, therapeutic concentrations may not be effectively achieved in mice or humans because of poor bio-availability and/or safety concerns. Stringent safety requirements for anti-malarial drugs, given their widespread use in children, make this a challenging area in which to reposition therapy.

STK31 is a cell-cycle regulated protein that contributes to the tumorigenicity of epithelial cancer cells

Serine/threonine kinase 31 (STK31) is one of the novel cancer/testis antigens for which its biological functions remain largely unclear. Here, we demonstrate that STK31 is overexpressed in many human colorectal cancer cell lines and tissues. STK31 co-localizes with pericentrin in the centrosomal region throughout all phases of the cell cycle. Interestingly, when cells undergo mitosis, STK31 also localizes to the centromeres, central spindle, and midbody. This localization behavior is similar to that of chromosomal passenger proteins, which are known to be the important players of the spindle assembly checkpoint. The expression of STK31 is cell cycle-dependent through the regulation of a putative D-box near its C-terminal region. Ectopically-expressed STK31-GFP increases cell migration and invasive ability without altering the proliferation rate of cancer cells, whereas the knockdown expression of endogenous STK31 by lentivirus-derived shRNA results in microtubule assembly defects that prolong the duration of mitosis and lead to apoptosis. Taken together, our results suggest that the aberrant expression of STK31 contributes to tumorigenicity in somatic cancer cells. STK31 might therefore act as a potential therapeutic target in human somatic cancers.

The aurora kinases in cell cycle and leukemia

The Aurora kinases, which include Aurora A (AURKA), Aurora B (AURKB) and Aurora C (AURKC), are serine/threonine kinases required for the control of mitosis (AURKA and AURKB) and meiosis (AURKC). Since their discovery nearly 20 years ago, Aurora kinases have been studied extensively in cell and cancer biology. Several early studies found that Aurora kinases are amplified and overexpressed at the transcript and protein level in various malignancies, including several types of leukemia. These discoveries and others provided a rationale for the development of small-molecule inhibitors of Aurora kinases as leukemia therapies. The first generation of Aurora kinase inhibitors did not fare well in clinical trials, owing to poor efficacy and high toxicity. However, the creation of second-generation, highly selective Aurora kinase inhibitors has increased the enthusiasm for targeting these proteins in leukemia. This review will describe the functions of each Aurora kinase, summarize their involvement in leukemia and discuss inhibitor development and efficacy in leukemia clinical trials.

New resistance mechanisms for small molecule kinase inhibitors of Abl kinase

Mutations in the kinase domain of Bcr-Abl are the most common cause of resistance to therapy with Imatinib in patients with chronic myelogenous leukaemia (CML). Second generation Bcr-Abl inhibitors, such as Nilotinib and Dasatinib, are able to overcome most Imatinib- resistant mutants, with the exception of the T315I substitution. Structural studies of Abl wild-type and T315I mutant have provided better understanding of how this mutation leads to resistance and have been used to support the drug design process for the development of inhibitors able to target the T315I substitution.

CDKN1A-mediated responsiveness of MLL-AF4-positive acute lymphoblastic leukemia to Aurora kinase-A inhibitors

Overexpression of Aurora kinases is largely observed in many cancers, including hematologic malignancies. In this study, we investigated the effects and molecular mechanisms of Aurora kinase inhibitors in acute lymphoblastic leukemia (ALL). Western blot analysis showed that both Aurora-A and Aurora-B are overexpressed in ALL cell lines and primary ALL cells. Both VE-465 and VX-680 effectively inhibited Aurora kinase activities in nine ALL cell lines, which exhibited different susceptibilities to the inhibitors. Cells sensitive to Aurora kinase inhibitors underwent apoptosis at an IC50 of ∼10-30 nM and displayed a phenotype of Aurora-A inhibition, whereas cells resistant to Aurora kinase inhibitors (with an IC50 more than 10 μM) accumulated polyploidy, which may have resulted from Aurora-B inhibition. Drug susceptibility of ALL cell lines was not correlated with the expression level or activation status of Aurora kinases. Interestingly, RS4;11 and MV4;11 cells, which contain the MLL-AF4 gene, were both sensitive to Aurora kinase-A inhibitors treatment. Complementary DNA (cDNA) microarray analysis suggested that CDKN1A might govern the drug responsiveness of ALL cell lines in a TP53-independent manner. Most importantly, primary ALL cells with MLL-AF4 and CDKN1A expression were sensitive to Aurora kinase inhibitors. Our study suggests CDKN1A could be a potential biomarker in determining the drug responsiveness of Aurora kinase inhibitors in ALL, particularly in MLL-AF4-positive patients.

A new aurora in anaplastic thyroid cancer therapy

Anaplastic thyroid cancers (ATC) are among the most aggressive human neoplasms with a dire prognosis and a median survival time of few months from the diagnosis. The complete absence of effective therapies for ATC renders the identification of novel therapeutic approaches sorely needed. Chromosomal instability, a feature of all human cancers, is thought to represent a major driving force in thyroid cancer progression and a number of mitotic kinases showing a deregulated expression in malignant thyroid tissues are now held responsible for thyroid tumor aneuploidy. These include the three members of the Aurora family (Aurora-A, Aurora-B, and Aurora-C), serine/threonine kinases that regulate multiple aspects of chromosome segregation and cytokinesis. Over the last few years, several small molecule inhibitors targeting Aurora kinases were developed, which showed promising antitumor effects against a variety of human cancers, including ATC, in preclinical studies. Several of these molecules are now being evaluated in phase I/II clinical trials against advanced solid and hematological malignancies. In the present review we will describe the structure, expression, and mitotic functions of the Aurora kinases, their implications in human cancer progression, with particular regard to ATC, and the effects of their functional inhibition on malignant cell proliferation.

Targeting nuclear kinases in cancer: development of cell cycle kinase inhibitors

Cellular proliferation is a tightly controlled set of events that is regulated by numerous nuclear protein kinases. The proteins involved include checkpoint kinases (CHK), cyclin-dependent kinases (CDK), which regulate the cell cycle and aurora kinases (AURK) and polo-like kinases (PLK), which regulate mitosis. In cancer, these nuclear kinases are often dysregulated and cause uncontrolled cell proliferation and growth. Much work has gone into developing novel therapeutics that target each of these protein kinases in cancer but none have been approved in patients. In this review we provide an overview of the current compounds being developed clinically to target these nuclear kinases involved in regulating the cell cycle and mitosis.

Targeting GD2 ganglioside and aurora A kinase as a dual strategy leading to cell death in cultures of human neuroblastoma cells

The mechanism of the inhibitory effect of anti-GD2 ganglioside (GD2) 14G2a mouse monoclonal antibody (mAb) on human neuroblastoma cells survival was studied in vitro. It was recently shown in IMR-32 cells that death induced by this antibody exhibited several characteristics typical of apoptosis. In this study we used cytotoxixity assays, qRT-PCR and immunoblotting to evaluate the response of several human neuroblastoma cell lines to the anti-GD2 14G2a mAb. We showed that the mAb decreases all three aurora kinases expression and phosphorylation in IMR-32 and LA-N-1 cells. Most importantly, we show, that MK-5108 specific aurora A kinase inhibitor decreases neuroblastoma cell survival, and when used in combination with the mAb, significantly potentiates cytotoxicity against IMR-32, CHP-134, and LA-N-5 neuroblastoma cells in vitro. It was shown that downregulation of aurora A kinase by the therapeutic antibody is associated with decreased levels of MYCN protein in cytoplasm, and induced expression of PHLDA1 and P53 proteins.

The σ2 receptor: a novel protein for the imaging and treatment of cancer

The σ2 receptor is an important target for the development of molecular probes in oncology because of its 10-fold higher density in proliferating tumor cells compared with that in quiescent tumor cells and because of the observation that σ2 receptor agonists are able to kill tumor cells via apoptotic and nonapoptotic mechanisms. Although recent evidence indicates that the σ2 receptor binding site is localized within the progesterone receptor membrane component 1 (PGRMC1), most information regarding this protein has been obtained using either radiolabeled or fluorescent receptor-based probes and from biochemical analysis of the effect of σ2 selective ligands on cells grown in culture. This article reviews the development of σ2 receptor ligands and presents an overview of how they have been used in vitro and in vivo to increase our understanding of the role of the σ2 receptor in cancer and proliferation.

A review of targeted therapies evaluated by the pediatric preclinical testing program for osteosarcoma

Osteosarcoma, the most common malignant bone tumor of childhood, is a high-grade primary bone sarcoma that occurs mostly in adolescence. Standard treatment consists of surgery in combination with multi-agent chemotherapy regimens. The development and approval of imatinib for Philadelphia chromosome-positive acute lymphoblastic leukemia in children and the fully human monoclonal antibody, anti-GD2, as part of an immune therapy for high-risk neuroblastoma patients have established the precedent for use of targeted inhibitors along with standard chemotherapy backbones. However, few targeted agents tested have achieved traditional clinical endpoints for osteosarcoma. Many biological agents demonstrating anti-tumor responses in preclinical and early-phase clinical testing have failed to reach response thresholds to justify randomized trials with large numbers of patients. The development of targeted therapies for pediatric cancer remains a significant challenge. To aid in the prioritization of new agents for clinical testing, the Pediatric Preclinical Testing Program (PPTP) has developed reliable and robust preclinical pediatric cancer models to rapidly screen agents for activity in multiple childhood cancers and establish pharmacological parameters and effective drug concentrations for clinical trials. In this article, we examine a range of standard and novel agents that have been evaluated by the PPTP, and we discuss the preclinical and clinical development of these for the treatment of osteosarcoma. We further demonstrate that committed resources for hypothesis-driven drug discovery and development are needed to yield clinical successes in the search for new therapies for this pediatric disease.

Targeting the untargetable: recent advances in the selective chemical modulation of protein phosphatase-1 activity

Protein phosphatase-1 (PP1) has long been neglected as a potential drug target owing to its misinterpreted unselective nature. However, growing evidence demonstrates that PP1 is highly selective in complex with regulatory proteins at the holoenzyme level, each of which is involved in different essential cellular signaling events. Here we summarize promising approaches to specifically activate or inhibit PP1 activity, and discuss remaining challenges and potential solutions. The summarized chemical tools pave the way for a better understanding of PP1's role in signaling networks, and the effects resulting from their application suggest their potential as future therapeutic candidates.

A phase I schedule dependency study of the aurora kinase inhibitor MSC1992371A in combination with gemcitabine in patients with solid tumors

INTRODUCTION

MSC1992371A is an aurora kinase inhibitor with potential antitumor activity.

METHODS

This trial established the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs) of oral MSC1992371A given before or after gemcitabine (1,000 mg/m(2)) in a 21-day cycle in patients with advanced malignancies. In schedule 1 (n = 31), gemcitabine was administered on days 1 and 8 followed by escalating doses of MSC1992371A on days 2 and 9. In schedule 2 (n = 35), MSC1992371A was given on days 1 and 8 followed by gemcitabine on days 2 and 9. Patients had a range of solid tumors, the most frequent of which was colorectal (n = 19).

RESULTS

In both schedules, the 37 mg/m(2) dose level was defined as the MTD. The main DLT was grade 4 neutropenia. Adverse events consisted of neutropenia, thrombocytopenia, asthenia, fatigue, nausea, vomiting, anorexia, and diarrhea. Administration of MSC1992371A prior to gemcitabine had no effect on the metabolism or elimination of gemcitabine. Time to reach maximum plasma concentration and area under the plasma concentration-time curve for MSC1992371A increased proportionally with dose. Exploration of drug-target-related and tumor biomarkers did not identify predictors of biologic activity or response. Two patients (1 with lung carcinoma and 1 with hepatocellular carcinoma) had durable partial responses in schedule 2, and 5 patients had stable disease (SD) lasting 6 - 14 months.

CONCLUSION

Oral MSC1992371A can be administered at a MTD of 37 mg/m(2) in combination with the standard 1,000 mg/m(2) dose of gemcitabine, but hematologic toxicity requires careful monitoring. Preliminary signs of efficacy were indicated by durable responses and SD.

Targeting Aurora kinase A suppresses the growth of human oral squamous cell carcinoma cells in vitro and in vivo

OBJECTIVES

Oncogene addiction has provided therapeutic opportunities in many human malignancies, but molecular targeted therapy for oral squamous cell carcinoma (OSCC) is not yet available. In this study, we attempted to identify an appropriate target molecule for treatment of patients with OSCC.

MATERIALS AND METHODS

Microarray analysis was performed to determine the gene expression profiles in nine human OSCC cell lines and a non-neoplastic keratinocyte cell line. The expression levels of Aurora kinase A (AURKA) mRNA and protein in human OSCC cells and tissues were examined. We investigated the effect of small interfering RNAs specific for AURKA (siAURKAs) and MLN8237, an AURKA selective inhibitor on the growth of OSCC cells in vitro and in vivo. We also analyzed clinical significance in AURKA mRNA expression levels in OSCC.

RESULTS

AURKA was overexpressed in human OSCC cell lines and tissues. All siAURKAs almost completely suppressed the expression of AURKA protein, and significantly inhibited the growth of OSCC cells by 31-89%. MLN8237 also reduced the cellular growth rate by 38-74%. Both siAURKA and MLN8237 significantly reduced the size of subcutaneously xenografted OSCC tumors by 66% and 40%. Knockdown of AURKA expression and MLN8237 induced the growth inhibition of primary cultured cells established from patients' OSCC tumors. Furthermore, we found a significant association between AURKA mRNA expression levels and histological differentiation and lymph node metastasis.

CONCLUSIONS

AURKA plays a critical role in the growth of human OSCC cells and targeting AURKA may be a useful therapeutic strategy for OSCC.

Basal aurora kinase B activity is sufficient for histone H3 phosphorylation in prophase

Histone H3 phosphorylation is the hallmark of mitosis deposited by aurora kinase B. Benzo[e]pyridoindoles are a family of potent, broad, ATP-competitive aurora kinase inhibitors. However, benzo[e]pyridoindole C4 only inhibits histone H3 phosphorylation in prophase but not in metaphase. Under the C4 treatment, the cells enter into mitosis with dephosphorylated histone H3, assemble chromosomes normally and progress to metaphase, and then to anaphase. C4 also induces lagging chromosome in anaphase but we demonstrated that these chromosome compaction defects are not related to the absence of H3 phosphorylation in prophase. As a result of C4 action, mitosis lasts longer and the cell cycle is slowed down.

We reproduced the mitotic defects with reduced concentrations of potent pan aurora kinase as well as with a specific aurora B ATP-competitive inhibitor; we therefore propose that histone H3 phosphorylation and anaphase chromosome compaction involve the basal activity of aurora kinase B. Our data suggest that aurora kinase B is progressively activated at mitosis entry and at anaphase onset. The full activation of aurora kinase B by its partners, in prometaphase, induces a shift in the catalytic domain of aurora B that modifies its affinity for ATP. These waves of activation/deactivation of aurora B correspond to different conformations of the chromosomal complex revealed by FRAP.

The presence of lagging chromosomes may have deleterious consequences on the daughter cells and, unfortunately, the situation may be encountered in patients receiving treatment with aurora kinase inhibitors.

Aurora A kinase (AURKA) in normal and pathological cell division

Temporally and spatially controlled activation of the Aurora A kinase (AURKA) regulates centrosome maturation, entry into mitosis, formation and function of the bipolar spindle, and cytokinesis. Genetic amplification and mRNA and protein overexpression of Aurora A are common in many types of solid tumor, and associated with aneuploidy, supernumerary centrosomes, defective mitotic spindles, and resistance to apoptosis. These properties have led Aurora A to be considered a high-value target for development of cancer therapeutics, with multiple agents currently in early-phase clinical trials. More recently, identification of additional, non-mitotic functions and means of activation of Aurora A during interphase neurite elongation and ciliary resorption have significantly expanded our understanding of its function, and may offer insights into the clinical performance of Aurora A inhibitors. Here we review the mitotic and non-mitotic functions of Aurora A, discuss Aurora A regulation in the context of protein structural information, and evaluate progress in understanding and inhibiting Aurora A in cancer.

Identification of an Aurora kinase inhibitor specific for the Aurora B isoform

Aurora kinases play an important role in chromosome alignment, segregation, and cytokinesis during mitosis. In the present study, we used a ligand docking method to explore the novel scaffold of potential Aurora B inhibitors. One thousand compounds from our in-house compound library were screened against the Aurora B structure and one compound, (E)-3-((E)-4-(benzo[d][1,3]dioxol-5-yl)-2-oxobut-3-en-1-ylidene)indolin-2-one (designated herein as HOI-07) was selected for further study. HOI-07 potently inhibited in vitro Aurora B kinase activity in a dose-dependent manner, without obvious inhibition of another 49 kinases, including Aurora A. This compound suppressed Aurora B kinase activity in lung cancer cells, evidenced by the inhibition of the phosphorylation of histone H3 on Ser10 in a dose- and time-dependent manner. This inhibition resulted in apoptosis induction, G(2)-M arrest, polyploidy cells, and attenuation of cancer cell anchorage-independent growth. Moreover, knocking down the expression of Aurora B effectively reduced the sensitivity of cancer cells to HOI-07. Results of an in vivo xenograft mouse study showed that HOI-07 treatment effectively suppressed the growth of A549 xenografts, without affecting the body weight of mice. The expression of phospho-histone H3, phospho-Aurora B, and Ki-67 was also suppressed in the HOI-07 treatment group. Taken together, we identified HOI-07 as a specific Aurora B inhibitor, which deserves further investigation.

Hydrosoluble benzo[e]pyridoindolones as potent inhibitors of aurora kinases

Aurora kinases play an essential role in mitotic progression and are potentially druggable targets in cancer therapy. We identified benzo[e]pyridoindoles (BePI) as powerful aurora kinase inhibitors. Their efficiency was demonstrated both in enzymatic inhibition studies and in cell culture assays. New BePI molecules were synthesized, and a structure-activity relationship study was conducted with the aim of improving the activity and solubility of the lead compound. Tetracyclic BePI derivatives are characterized by a particular curved shape, and the presence of an oxo group on the pyridine ring was found to be required for aurora kinase B inhibition. New hydrosoluble benzo[e]pyridoindolones were subsequently designed, and their efficacy was tested by a combination of cell-cycle analysis and time-lapse experiments in live cells. The most active BePI derivative, 13 b, inhibited the cell cycle, drove cells to polyploidy, and eventually induced apoptosis. It exhibited high antiproliferative activity in HeLa cells with an IC(50) value of 63 nM. Relative to compounds tested in clinical trials, this antiproliferative potency places 13 b among the top 10 aurora kinase inhibitors. Our results justify further in vivo evaluation in preclinical animal models of cancer.

Cancer cell resistance to aurora kinase inhibitors: identification of novel targets for cancer therapy

Drug resistance is the major obstacle to successful cancer therapy. Our study focuses on resistance to Aurora kinase inhibitors tested as anti-cancer drugs in clinical trials. We have used 2D electrophoresis in the pH ranges of 4-7 and 6-11 followed by protein identification using MALDI-TOF/TOF to compare the protein composition of HCT116 colon cancer cells either sensitive to CYC116 and ZM447439 inhibitors or resistant toward these drugs. The analysis also included p53(+/+) and p53(-/-) phenotypes of HCT116 cells. Our findings demonstrate that platelet-activating factor acetylhydrolase and GTP-binding nuclear protein Ran contribute to the development of resistance to ZM447439 only where resistance is related to p53. On the other hand, serine hydroxymethyltransferase was found to promote the tumor growth in cells resistant to CYC116 without the influence of p53. Computer modeling of interaction networks highlighted a direct link of the p53-independent mechanism of resistance to CYC116 with autophagy. Importantly, serine hydroxymethyltransferase, serpin B5, and calretinin represent the target proteins that may help overcome resistance in combination therapies. In addition, serpin B5 and calretinin appear to be candidate biomarkers that may be accessible in patients for monitoring of cancer therapy with ease.

Low concentration of arsenic-induced aberrant mitosis in keratinocytes through E2F1 transcriptionally regulated Aurora-A

Chronic exposure to low-concentration arsenic promotes cell proliferation and carcinogenesis both in vitro and in vivo. Centrosome amplification, the major cause of chromosome instability, occurs frequently in cancers. Aurora-A is a mitotic kinase and causes centrosome amplification and chromosome instability when overexpressed. Our previous study revealed that low-concentration arsenic induces Aurora-A overexpression in immortalized bladder cells. In this study, we hypothesized that low-concentration arsenic induces aberrant mitosis in keratinocytes due to Aurora-A overexpression. The specimen of Bowen's disease (BD) and squamous cell carcinoma obtained from arseniasis-endemic areas in Taiwan showed Aurora-A overexpression. The mRNA/protein levels and kinase activity of Aurora-A were increased in immortalized keratinocyte HaCaT cells after arsenic treatment at low concentration (< 1µM). Aberrant spindles, multiple centrosomes, and multinucleated cells were detected under fluorescent microscopy in HaCaT cells after arsenic treatment. These findings were associated with increased expression of Aurora-A. We further revealed that Aurora-A was regulated by arsenic-induced transcriptional factor E2F1 as demonstrated by chromosome immunoprecipitation, promoter activity, and small interfering RNA assays. Finally, in arsenic-treated HaCaT cells and in BD, a significant increase of dysfunctional p53 was found, and this event correlated with the increase in expression of Aurora-A. Altogether, our data suggest that low concentration of arsenic induces activation of E2F1-Aurora-A axis and results in aberrant mitosis of keratinocytes. Overexpression of Aurora-A and dysfunctional p53 may act synergistically to trigger skin tumor formation. Our findings suggest that Aurora-A may be a potential target for the prevention and treatment of arsenic-related cancers.

Inhibiting aurora kinases reduces tumor growth and suppresses tumor recurrence after chemotherapy in patient-derived triple-negative breast cancer xenografts

Triple-negative breast cancers (TNBC) have an aggressive phenotype with a relatively high rate of recurrence and poor overall survival. To date, there is no approved targeted therapy for TNBCs. Aurora kinases act as regulators of mammalian cell division. They are important for cell-cycle progression and are frequently overexpressed or mutated in human tumors, including breast cancer. In this study, we investigated the therapeutic potential of targeting Aurora kinases in preclinical models of human breast cancers using a pan-inhibitor of Aurora kinases, AS703569. In vitro, AS703569 was tested in 15 human breast cancer cell lines. TNBC cell lines were more sensitive to AS703569 than were other types of breast cancer cells. Inhibition of proliferation was associated with cell-cycle arrest, aneuploidy, and apoptosis. In vivo, AS703569 administered alone significantly inhibited tumor growth in seven of 11 patient-derived breast cancer xenografts. Treatment with AS703569 was associated with a decrease of phospho-histone H3 expression. Finally, AS703569 combined to doxorubicin-cyclophosphamide significantly inhibited in vivo tumor recurrence, suggesting that Aurora kinase inhibitors could be used both in monotherapy and in combination settings. In conclusion, these data indicate that targeting Aurora kinases could represent a new effective approach for TNBC treatment.

Phase I pharmacokinetic/pharmacodynamic study of MLN8237, an investigational, oral, selective aurora a kinase inhibitor, in patients with advanced solid tumors

PURPOSE

Aurora A kinase (AAK) is a key regulator of mitosis and a target for anticancer drug development. This phase I study investigated the safety, pharmacokinetics, and pharmacodynamics of MLN8237 (alisertib), an investigational, oral, selective AAK inhibitor, in 59 adults with advanced solid tumors.

EXPERIMENTAL DESIGN

Patients received MLN8237 once daily or twice daily for 7, 14, or 21 consecutive days, followed by 14 days recovery, in 21-, 28-, or 35-day cycles. Dose-limiting toxicities (DLT) and the maximum-tolerated dose (MTD) for the 7- and 21-day schedules were determined. Pharmacokinetic parameters were derived from plasma concentration-time profiles. AAK inhibition in skin and tumor biopsies was evaluated and antitumor activity assessed.

RESULTS

Neutropenia and stomatitis were the most common DLTs. The MTD for the 7- and 21-day schedules was 50 mg twice daily and 50 mg once daily, respectively. MLN8237 absorption was fast (median time to maximum concentration, 2 hours). Mean terminal half-life was approximately 19 hours. At steady state, pharmacodynamic effects were shown by accumulation of mitotic and apoptotic cells in skin, and exposure-related increases in numbers of mitotic cells with characteristic spindle and chromosomal abnormalities in tumor specimens, supporting AAK inhibition by MLN8237. Stable disease was observed and was durable with repeat treatment cycles, administered over 6 months, in 6 patients, without notable cumulative toxicity.

CONCLUSIONS

The recommended phase II dose of MLN8237 is 50 mg twice daily on the 7-day schedule, which is being evaluated further in a variety of malignancies, including in a phase III trial in peripheral T-cell lymphoma.