Identification of genes that confer tumor cell resistance to the aurora B kinase inhibitor, AZD1152

The multidrug resistance transporter P-glycoprotein confers resistance to ferroptosis inducers

Aim: Ferroptosis is a non-apoptotic form of cell death caused by lethal lipid peroxidation. Several small molecule ferroptosis inducers (FINs) have been reported, yet little information is available regarding their interaction with the ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp, ABCB1) and ABCG2. We thus sought to characterize the interactions of FINs with P-gp and ABCG2, which may provide information regarding oral bioavailability and brain penetration and predict drug-drug interactions. Methods: Cytotoxicity assays with ferroptosis-sensitive A673 cells transfected to express P-gp or ABCG2 were used to determine the ability of the transporters to confer resistance to FINs; confirmatory studies were performed in OVCAR8 and NCI/ADR-RES cells. The ability of FINs to inhibit P-gp or ABCG2 was determined using the fluorescent substrates rhodamine 123 or purpuin-18, respectively. Results: P-gp overexpression conferred resistance to FIN56 and the erastin derivatives imidazole ketone erastin and piperazine erastin. P-gp-mediated resistance to imidazole ketone erastin and piperazine erastin was also reversed in UO-31 renal cancer cells by CRISPR-mediated knockout of ABCB1. The FINs ML-162, GPX inhibitor 26a, and PACMA31 at 10 µM were able to increase intracellular rhodamine 123 fluorescence over 10-fold in P-gp-expressing MDR-19 cells. GPX inhibitor 26a was able to increase intracellular purpurin-18 fluorescence over 4-fold in ABCG2-expressing R-5 cells. Conclusion: Expression of P-gp may reduce the efficacy of these FINs in cancers that express the transporter and may prevent access to sanctuary sites such as the brain. The ability of some FINs to inhibit P-gp and ABCG2 suggests potential drug-drug interactions.

The Multidrug Resistance Transporter P-glycoprotein Confers Resistance to Ferroptosis Inducers

Ferroptosis is a form of cell death caused by direct or indirect inhibition of glutathione peroxidase 4 that leads to lethal lipid peroxidation. Several small molecule ferroptosis inducers (FINs) have been reported, yet little information is available regarding resistance mechanisms, particularly their interaction with the ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp, ABCB1) and ABCG2. Given the role that ABC transporters play in absorption, distribution, and excretion of many drugs, characterizing these interactions could provide information regarding oral bioavailability and brain penetration and may predict drug-drug interactions. Using ferroptosis-sensitive A673 cells transfected to express P-gp or ABCG2, we found that P-gp overexpression was able to confer resistance to FIN56 and the erastin derivatives imidazole ketone erastin and piperazine erastin. Results were confirmed with OVCAR8-derived NCI/ADR-RES cells that overexpress P-gp, where the P-gp inhibitor valspodar completely inhibited resistance to the FINs. P-gp-mediated resistance to imidazole ketone erastin and piperazine erastin was also reversed in UO-31 renal cancer cells by CRISPR-mediated knockout of ABCB1. At a concentration of 10 μM, the FINs ML-162, GPX inhibitor 26a, and PACMA31 were able to increase intracellular rhodamine 123 fluorescence over 10-fold in P-gp-expressing MDR-19 cells and GPX inhibitor 26a was able to increase intracellular purpurin-18 fluorescence over 4-fold in ABCG2-expressing R-5 cells. Expression of P-gp may reduce the efficacy of these FINs in cancers that express the transporter and may prevent access to sanctuary sites such as the brain. The ability of some FINs to inhibit P-gp and ABCG2 suggests potential drug-drug interactions.

Design of new disubstituted imidazo[1,2-b]pyridazine derivatives as selective Haspin inhibitors. Synthesis, binding mode and anticancer biological evaluation

Haspin is a mitotic protein kinase required for proper cell division by modulating Aurora B kinase localisation and activity as well as histone phosphorylation. Here a series of imidazopyridazines based on the CHR-6494 and Structure Activity Relationship was established. An assessment of the inhibitory activity of the lead structures on human Haspin and several other protein kinases is presented. The lead structure was rapidly optimised using a combination of crystal structures and effective docking models, with the best inhibitors exhibiting potent inhibitory activity on Haspin with IC₅₀ between 6 and 100 nM in vitro. The developed inhibitors displayed anti-proliferative properties against various human cancer cell lines in 2D and spheroid cultures and significantly inhibited the migration ability of osteosarcoma U-2 OS cells. Notably, we show that our lead compounds are powerful Haspin inhibitors in human cells, and did not block G2/M cell cycle transition due to improved selectivity against CDK1/CyclinB.

Design strategies, SAR, and mechanistic insight of Aurora kinase inhibitors in cancer

Aurora kinases (AURKs) are serine/threonine protein kinases that play a critical role during cell proliferation. Three isoforms of AURKs reported in mammals include AURKA, AURKB, AURKC, and all share a similar C-terminal catalytic domain with differences in their subcellular location, substrate specificity, and function. Recent research reports indicate an elevated expression of these kinases in several cancer types highlighting their role as oncogenes in tumorigenesis. Inhibition of AURKs is an attractive strategy to design potent inhibitors modulating this target. The last few years have witnessed immense research in the development of AURK inhibitors with few FDA approvals. The current clinical therapeutic regime in cancer is associated with severe side-effects and emerging resistance to existing drugs. This has been the key driver of research initiatives toward designing more potent drugs that can potentially circumvent the emerging resistance. This review is a comprehensive summary of recent research on AURK inhibitors and presents the development of scaffolds, their synthetic schemes, structure-activity relationships, biological activity, and enzyme inhibition potential. We hope to provide the reader with an array of scaffolds that can be selected for further research work and mechanistic studies in the development of new AURK inhibitors.

Aurora Kinase B Inhibition: A Potential Therapeutic Strategy for Cancer

Aurora kinase B (AURKB) is a mitotic serine/threonine protein kinase that belongs to the aurora kinase family along with aurora kinase A (AURKA) and aurora kinase C (AURKC). AURKB is a member of the chromosomal passenger protein complex and plays a role in cell cycle progression. Deregulation of AURKB is observed in several tumors and its overexpression is frequently linked to tumor cell invasion, metastasis and drug resistance. AURKB has emerged as an attractive drug target leading to the development of small molecule inhibitors. This review summarizes recent findings pertaining to the role of AURKB in tumor development, therapy related drug resistance, and its inhibition as a potential therapeutic strategy for cancer. We discuss AURKB inhibitors that are in preclinical and clinical development and combination studies of AURKB inhibition with other therapeutic strategies.

Overexpression of human ATP-binding cassette transporter ABCG2 contributes to reducing the cytotoxicity of GSK1070916 in cancer cells

The emergence of multidrug resistance (MDR) is one of the main factors that impair therapeutic outcome in cancer therapy. Among all the factors that contribute to MDR, overexpression of ABCG2 transporter has been described as a key factor. GSK1070916 is a potent Aurora kinase inhibitor with broad anticancer effects. The robust efficacy shown in preclinical studies allowed the drug progress to clinical investigation. However, the potential mechanisms of acquired resistance to GSK1070916 remain inconclusive. Since several Aurora kinase inhibitors were reported to be transported substrates of ABCG2, we aimed to identify the potential interaction of GSK1070916 with ABCG2. Our data showed that ABCG2-overexpressing cells demonstrated high resistance-fold to GSK1070916 compared to the parental cells. In addition, combination of GSK1070916 with an ABCG2 inhibitor was able to restore its sensitivity. The multicellular tumor spheroid assay supported this finding by demonstrating attenuated growth inhibition in ABCG2-overexpressing tumor spheroids. In addition, the ABCG2 ATPase assay and computational modeling suggested that GSK1070916 could bind to ABCG2 substrate-binding site. The HPLC assay provided another direct evidence that ABCG2-overexpressing cells showed attenuated intracellular accumulation of GSK1070916, and such phenomenon was abolished by Ko143, a known ABCG2 inhibitor. Furthermore, GSK1070916 was able to hinder the efflux activity of ABCG2, indicating possible drug-drug interactions with other ABCG2 substrate drugs. In summary, we revealed that overexpression of ABCG2 can cause GSK1070916 resistance in cancer cells. The combination of an ABCG2 inhibitor with GSK1070916 may be a rational strategy to overcome the drug resistance and should be considered for clinical investigation.

Restoring Treatment Response in Colorectal Cancer Cells by Targeting MACC1-Dependent ABCB1 Expression in Combination Therapy

Treatment failure of solid cancers, represented by the development of drug resistance in the primary tumor or later outgrowth of drug resistant metastases, is the major cause of death for cancer patients. It represents an urgent clinical need for predictive biomarkers which indicate the success or failure of standard treatment regimens. Besides treatment prediction, interfering with cellular processes associated with drug resistance might improve treatment response by applying combination therapies. Metastasis-associated in colon cancer (MACC) 1 was identified in our group as a prognostic biomarker in human colorectal cancer, and has been established as key player, prognostic, and predictive biomarker for tumor progression and metastasis in a variety of solid cancers. Besides increased cell proliferation and motility, subsequently contributing to growth and metastatic spread of the primary tumor, MACC1 has also been shown to dysregulate apoptosis and is contributing to treatment resistance. Here we report the MACC1 dependent treatment resistance of colorectal cancer (CRC) cells to standard therapeutics like doxorubicin by upregulating ATP-binding cassette subfamily B member 1 (ABCB1) protein. Overexpression of MACC1 in CRC cells increased both its presence on the ABCB1 promoter and its transcriptional activity, resulting in elevated ABCB1 expression and thus treatment resistance to standard therapeutics. In contrast, depleting MACC1 increased intracellular drug concentrations, leading to better treatment response. We already identified the first MACC1 transcriptional inhibitors, such as lovastatin, by high-throughput screening of clinically approved small molecule drugs. These compounds inhibited cell motility in vitro but also restricted metastasis development in xenograft mouse models by reducing MACC1 expression. Here we report, that treating high MACC1 expressing CRC cells with a combination of statins and standard therapeutics increased the rate of cytotoxicity and resulted in higher treatment response.

Anti-mitotic agents: Are they emerging molecules for cancer treatment?

Mutations in cancer cells frequently result in cell cycle alterations that lead to unrestricted growth compared to normal cells. Considering this phenomenon, many drugs have been developed to inhibit different cell-cycle phases. Mitotic phase targeting disturbs mitosis in tumor cells, triggers the spindle assembly checkpoint and frequently results in cell death. The first anti-mitotics to enter clinical trials aimed to target tubulin. Although these drugs improved the treatment of certain cancers, and many anti-microtubule compounds are already approved for clinical use, severe adverse events such as neuropathies were observed. Since then, efforts have been focused on the development of drugs that also target kinases, motor proteins and multi-protein complexes involved in mitosis. In this review, we summarize the major proteins involved in the mitotic phase that can also be targeted for cancer treatment. Finally, we address the activity of anti-mitotic drugs tested in clinical trials in recent years.

Recent advances in the development of Aurora kinases inhibitors in hematological malignancies

Over the last two decades, since the discovery of Drosophila mutants in 1995, much effort has been made to understand Aurora kinase biology. Three mammalian subtypes have been identified thus far which include the Aurora A, B and C kinases. These regulatory proteins specifically work at the cytoskeleton and chromosomal structures between the kinetochores and have vital functions in the early phases of the mitotic cell cycle. Today, there are multiple phase I and phase II clinical trials as well as numerous preclinical studies taking place looking at Aurora kinase inhibitors in both hematologic and solid malignancies. This review focuses on the preclinical and clinical development of Aurora kinase inhibitors in hematological malignancy and discusses their therapeutic potential.

ABCG2 impairs the activity of the aurora kinase inhibitor tozasertib but not of alisertib

BACKGROUND

Recently, we have shown that the ATP-binding cassette (ABC) transporter ABCB1 interferes with the anti-cancer activity of the pan-aurora kinase inhibitor tozasertib (VX680, MK-0457) but not of the aurora kinase A and B inhibitor alisertib (MLN8237). Preliminary data had suggested tozasertib also to be a substrate of the ABC transporter ABCG2, another ABC transporter potentially involved in cancer cell drug resistance. Here, we studied the effect of ABCG2 on the activity of tozasertib and alisertib.

RESULTS

The tozasertib concentration that reduces cell viability by 50% (IC50) was dramatically increased in ABCG2-transduced UKF-NB-3(ABCG2) cells (48.8-fold) compared to UKF-NB-3 cells and vector-transduced control cells. The ABCG2 inhibitor WK-X-34 reduced tozasertib IC50 to the level of non-ABCG2-expressing UKF-NB-3 cells. Furthermore, ABCG2 depletion from UKF-NB-3(ABCG2) cells using another lentiviral vector expressing an shRNA against the bicistronic mRNA of ABCG2 and eGFP largely re-sensitised these cells to tozasertib. In contrast, alisertib activity was not affected by ABCG2 expression.

CONCLUSIONS

Tozasertib but not alisertib activity is affected by ABCG2 expression. This should be considered within the design and analysis of experiments and clinical trials investigating these compounds.

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.

Sinapine as an active compound for inhibiting the proliferation of Caco-2 cells via downregulation of P-glycoprotein

Sinapine, an alkaloid from seeds of the cruciferous species, shows favorable biological activities such as antioxidant and radio-protective activities. However, the inhibitory effect of sinapine on tumors, and the molecular mechanisms have not been completely understood thus far. In this study, we determined anti-proliferative effects of sinapine. We examined the anti-tumor effects of the combination of sinapine and doxorubicin. The results of the MTT assay and apoptosis showed that sinapine increased the sensitivity of Caco-2 cells to doxorubicin in a dose-dependent manner, whereas no or less effect was observed in the cells treated with doxorubicin alone. The combination of sinapine and doxorubicin had a synergistic effect and increased the cytotoxicity of doxorubicin against Caco-2 cells. Doxorubicin accumulation assay showed that sinapine increased the intracellular accumulation of doxorubicin in dose-dependent manner. Immunoblotting and QT-PCR analysis showed that sinapine suppressed P-glycoprotein (P-gp) expression via ubiquitination. A significant correlation was observed between the expression of p-ERK1/2 and P-gp. These results indicated that sinapine played an important role in the down-regulation of P-gp expression through suppression of FGFR4-FRS2α-ERK1/2 signaling pathway. To our knowledge, this is the first study to show that sinapine can be used as an effective natural compound for chemo-resistance.

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.

Canine osteosarcoma cells exhibit resistance to aurora kinase inhibitors

We evaluated the effect of Aurora kinase inhibitors AZD1152 and VX680 on canine osteosarcoma cells. Cytotoxicity was seen in all four cell lines; however, half-maximal inhibitory concentrations were significantly higher than in human leukaemia and canine lymphoma cells. AZD1152 reduced Aurora kinase B phosphorylation, indicating resistance was not because of failure of target recognition. Efflux mediated by ABCB1 and ABCG2 transporters is one known mechanism of resistance against these drugs and verapamil enhanced AZD1152-induced apoptosis; however, these transporters were only expressed by a small percentage of cells in each line and the effects of verapamil were modest, suggesting other mechanisms contribute to resistance. Our results indicate that canine osteosarcoma cells are resistant to Aurora kinase inhibitors and suggest that these compounds are unlikely to be useful as single agents for this disease. Further investigation of these resistance mechanisms and the potential utility of Aurora kinase inhibitors in multi-agent protocols is warranted.

Preclinical characterization of ABT-348, a kinase inhibitor targeting the aurora, vascular endothelial growth factor receptor/platelet-derived growth factor receptor, and Src kinase families

ABT-348 [1-(4-(4-amino-7-(1-(2-hydroxyethyl)-1H-pyrazol-4-yl)thieno[3,2-c]pyridin-3-yl)phenyl)-3-(3-fluorophenyl)urea] is a novel ATP-competitive multitargeted kinase inhibitor with nanomolar potency (IC(50)) for inhibiting binding and cellular autophosphorylation of Aurora B (7 and 13 nM), C (1 and 13 nM), and A (120 and 189 nM). Cellular activity against Aurora B is reflected by inhibition of phosphorylation of histone H3, induction of polyploidy, and inhibition of proliferation of a variety of leukemia, lymphoma, and solid tumor cell lines (IC(50) = 0.3-21 nM). In vivo inhibition of Aurora B was confirmed in an engrafted leukemia model by observing a decrease in phosphorylation of histone H3 that persisted in a dose-dependent manner for 8 h and correlated with plasma concentration of ABT-348. Evaluation of ABT-348 across a panel of 128 kinases revealed additional potent binding activity (K(i) < 30 nM) against vascular endothelial growth factor receptor (VEGFR)/platelet-derived growth factor receptor (PDGFR) families and the Src family of cytoplasmic tyrosine kinases. VEGFR/PDGFR binding activity correlated with inhibition of autophosphorylation in cells and inhibition of vascular endothelial growth factor (VEGF)-stimulated endothelial cell proliferation (IC(50) ≤ 0.3 nM). Evidence of on-target activity in vivo was provided by the potency for blocking VEGF-mediated vascular permeability and inducing plasma placental growth factor. Activity against the Src kinase family was evident in antiproliferative activity against BCR-ABL chronic myeloid leukemia cells and cells expressing the gleevec-resistant BCR-ABL T315I mutation. On the basis of its unique spectrum of activity, ABT-348 was evaluated and found effective in representative solid tumor [HT1080 and pancreatic carcinoma (MiaPaCa), tumor stasis] and hematological malignancy (RS4;11, regression) xenografts. These results provide the rationale for clinical assessment of ABT-348 as a therapeutic agent in the treatment of cancer.

Aurora kinase inhibitors: progress towards the clinic

The Aurora kinases (serine/threonine kinases) were discovered in 1995 during studies of mutant alleles associated with abnormal spindle pole formation in Drosophila melanogaster. They soon became the focus of much attention because of their importance in human biology and association with cancer. Aurora kinases are essential for cell division and are primarily active during mitosis. Following their identification as potential targets for cancer chemotherapy, many Aurora kinase inhibitors have been discovered, and are currently under development. The binding modes of Aurora kinase inhibitors to Aurora kinases share specific hydrogen bonds between the inhibitor core and the back bone of the kinase hinge region, while others parts of the molecules may point to different parts of the active site via noncovalent interactions. Currently there are about 30 Aurora kinase inhibitors in different stages of pre-clinical and clinical development. This review summarizes the characteristics and status of Aurora kinase inhibitors in preclinical, Phase I, and Phase II clinical studies, with particular emphasis on the mechanisms of action and resistance to these promising anticancer agents. We also discuss the validity of Aurora kinases as oncology targets, on/off-target toxicities, and other important aspects of overall clinical performance and future of Aurora kinase inhibitors.

A novel Aurora kinase A inhibitor MK-8745 predicts TPX2 as a therapeutic biomarker in non-Hodgkin lymphoma cell lines

Selective small-molecule kinase inhibitors have encouraging clinical efficacy in several malignancies. These agents are still limited to a subset of patients, indicating the need to develop therapeutic biomarkers that influence clinical benefit. In this study, we demonstrate that treatment with MK-8745, a novel Aurora-A specific inhibitor, leads to cell cycle arrest at the G2/M phase with accumulation of tetraploid nuclei followed by cell death in non-Hodgkin lymphoma (NHL) cell lines. The sensitivity of the cell lines to MK-8745 is correlated with the expression level of Aurora-A activator. The siRNA knockdown of Aurora-A activator TPX2 (targeting protein for Xenopus kinase-like protein 2) increased MK-8745 sensitivity in less-MK-8745-sensitive NHL cell lines, whereas overexpression of TPX2 in high-MK-8745-sensitive NHL cell lines increased drug resistance. Our results indicate that TPX2 may serve as a biomarker for identifying subpopulations of patients sensitive to Aurora-A inhibitor treatment.

Aurora kinase inhibitor patents and agents in clinical testing: an update (2009-10)

INTRODUCTION

Mitosis is a key step in the cell cycle and is controlled by several cell cycle regulators, including aurora kinases. Aurora family members A, B and C are essential for spindle assembly, centrosome maturation, chromosomal segregation and cytokinesis. Overexpression/amplification of aurora kinases has been implicated in oncogenic transformation, including the development of chromosomal instability in cancer cells. Hence, the use of aurora kinase small molecule inhibitors as a potential molecular-targeted therapeutic intervention for cancer is being pursued by various researchers.

AREA COVERED

This review provides an update on aurora kinase inhibitors based on developments from 2009 to 2010. The medicinal chemistry aspects of aurora kinase inhibitors, with a particular emphasis on the patent literature, are reviewed. Databases such as PubMed, SCOPUS®, Scifinder® and www.clinicaltrials.gov database were used to search for literature in the preparation of this review.

EXPERT OPINION

Around a dozen aurora kinase inhibitors are currently undergoing various Phase I-II evaluations for different human cancers. Instead of being applied as a monotherapy, combinations of aurora kinase inhibitors and existing chemotherapeutic compounds seem to give better therapeutic outcomes and are, therefore, a promising future cancer therapy.

BPR1K653, a novel Aurora kinase inhibitor, exhibits potent anti-proliferative activity in MDR1 (P-gp170)-mediated multidrug-resistant cancer cells

Background

Over-expression of Aurora kinases promotes the tumorigenesis of cells. The aim of this study was to determine the preclinical profile of a novel pan-Aurora kinase inhibitor, BPR1K653, as a candidate for anti-cancer therapy. Since expression of the drug efflux pump, MDR1, reduces the effectiveness of various chemotherapeutic compounds in human cancers, this study also aimed to determine whether the potency of BPR1K653 could be affected by the expression of MDR1 in cancer cells.

Principal Findings

BPR1K653 specifically inhibited the activity of Aurora-A and Aurora-B kinase at low nano-molar concentrations in vitro. Anti-proliferative activity of BPR1K653 was evaluated in various human cancer cell lines. Results of the clonogenic assay showed that BPR1K653 was potent in targeting a variety of cancer cell lines regardless of the tissue origin, p53 status, or expression of MDR1. At the cellular level, BPR1K653 induced endo-replication and subsequent apoptosis in both MDR1-negative and MDR1-positive cancer cells. Importantly, it showed potent activity against the growth of xenograft tumors of the human cervical carcinoma KB and KB-derived MDR1-positive KB-VIN10 cells in nude mice. Finally, BPR1K653 also exhibited favorable pharmacokinetic properties in rats.

Conclusions and Significance

BPR1K653 is a novel potent anti-cancer compound, and its potency is not affected by the expression of the multiple drug resistant protein, MDR1, in cancer cells. Therefore, BPR1K653 is a promising anti-cancer compound that has potential for the management of various malignancies, particularly for patients with MDR1-related drug resistance after prolonged chemotherapeutic treatments.

P-glycoprotein and breast cancer resistance protein in acute myeloid leukaemia cells treated with the aurora-B kinase inhibitor barasertib-hQPA

BACKGROUND

Aurora kinases play an essential role in orchestrating chromosome alignment, segregation and cytokinesis during mitotic progression, with both aurora-A and B frequently over-expressed in a variety of human malignancies. Over-expression of the ABC drug transporter proteins P-glycoprotein (Pgp) and Breast cancer resistance protein (BCRP) is a major obstacle for chemotherapy in many tumour types with Pgp conferring particularly poor prognosis in acute myeloid leukaemia (AML). Barasertib-hQPA is a highly selective inhibitor of aurora-B kinase that has shown tumouricidal activity against a range tumour cell lines including those of leukaemic AML origin.

METHODS

Effect of barasertib-hQPA on the pHH3 biomarker and cell viability was measured in a panel of leukaemic cell lines and 37 primary AML samples by flow cytometry. Pgp status was determined by flow cytometry and BCRP status by flow cytometry and real-time PCR.

RESULTS

In this study we report the creation of the cell line OCI-AML3DNR, which over-expresses Pgp but not BCRP or multidrug resistance-associated protein (MRP), through prolonged treatment of OCI-AML3 cells with daunorubicin. We demonstrate that Pgp (OCI-AML3DNR and KG-1a) and BCRP (OCI-AML6.2) expressing AML cell lines are less sensitive to barasertib-hQPA induced pHH3 inhibition and subsequent loss of viability compared to transporter negative cell lines. We also show that barasertib-hQPA resistance in these cell lines can be reversed using known Pgp and BCRP inhibitors. We report that barasertib-hQPA is not an inhibitor of Pgp or BCRP, but by using 14[C]-barasertib-hQPA that it is effluxed by these transporters. Using phosphoHistone H3 (pHH3) as a biomarker of barasertib-hQPA responsiveness in primary AML blasts we determined that Pgp and BCRP positive primary samples were less sensitive to barasertib-hQPA induced pHH3 inhibition (p = <0.001) than samples without these transporters. However, we demonstrate that IC50 inhibition of pHH3 by barasertib-hQPA was achieved in 94.6% of these samples after 1 hour drug treatment, in contrast to the resistance of the cell lines.

CONCLUSION

We conclude that Pgp and BCRP status and pHH3 down-regulation in patients treated with barasertib should be monitored in order to establish whether transporter-mediated efflux is sufficient to adversely impact on the efficacy of the agent.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

Update on Aurora Kinase Targeted Therapeutics in Oncology

INTRODUCTION: Mammalian cells contain three distinct serine/threonine protein kinases with highly conserved catalytic domains, including aurora A and B kinases that are essential regulators of mitotic entry and progression. Overexpression of aurora A and/or B kinase is associated with high proliferation rates and poor prognosis, making them ideal targets for anti-cancer therapy. Disruption of mitotic machinery is a proven anti-cancer strategy employed by multiple chemotherapeutic agents. Numerous small molecule inhibitors of the aurora kinases have been discovered and tested in vivo and in vitro, with a few currently in phase II testing. AREAS COVERED: This review provides the reader with updated results from both preclinical and human studies for each of the aurora kinase inhibitors (AKI) that are currently being investigated. The paper also covers in detail the late breaking and phase I data presented for AKIs thereby allowing the reader to compare and contrast individual and classrelated effects of AKIs. EXPERT OPINION: While the successful development and approval of an AKI for anti-cancer therapy remains unresolved, pre-clinical identification of resistant mechanisms would help design better early phase clinical trials where relevant combinations may be evaluated prior to phase II testing. The authors believe that aurora kinases are important anti-cancer targets that operate in collaboration with other oncogenes intimately involved in uncontrolled tumor proliferation and by providing a unique, targeted and complimentary anti-cancer mechanism, expand the available armamentarium against cancer.

Preclinical evaluation of AMG 900, a novel potent and highly selective pan-aurora kinase inhibitor with activity in taxane-resistant tumor cell lines

In mammalian cells, the aurora kinases (aurora-A, -B, and -C) play essential roles in regulating cell division. The expression of aurora-A and -B is elevated in a variety of human cancers and is associated with high proliferation rates and poor prognosis, making them attractive targets for anticancer therapy. AMG 900 is an orally bioavailable, potent, and highly selective pan-aurora kinase inhibitor that is active in taxane-resistant tumor cell lines. In tumor cells, AMG 900 inhibited autophosphorylation of aurora-A and -B as well as phosphorylation of histone H3 on Ser(10), a proximal substrate of aurora-B. The predominant cellular response of tumor cells to AMG 900 treatment was aborted cell division without a prolonged mitotic arrest, which ultimately resulted in cell death. AMG 900 inhibited the proliferation of 26 tumor cell lines, including cell lines resistant to the antimitotic drug paclitaxel and to other aurora kinase inhibitors (AZD1152, MK-0457, and PHA-739358), at low nanomolar concentrations. Furthermore, AMG 900 was active in an AZD1152-resistant HCT116 variant cell line that harbors an aurora-B mutation (W221L). Oral administration of AMG 900 blocked the phosphorylation of histone H3 in a dose-dependent manner and significantly inhibited the growth of HCT116 tumor xenografts. Importantly, AMG 900 was broadly active in multiple xenograft models, including 3 multidrug-resistant xenograft models, representing 5 tumor types. AMG 900 has entered clinical evaluation in adult patients with advanced cancers and has the potential to treat tumors refractory to anticancer drugs such as the taxanes.

hsa-miR-520h downregulates ABCG2 in pancreatic cancer cells to inhibit migration, invasion, and side populations

Background:

Expression of ABCG2 is normally absent or low in the pancreas, but high in human pancreatic cancer cells. The mechanism by which ABCG2 is altered in human cancers remains unknown.

Methods:

We investigated ABCG2 expression in four pancreatic cancer cell lines, and used three microRNA (miRNA) target prediction programmes, and information from the existing literature to predict and identify hsa-miR-520h as an miRNA that targets ABCG2. The function of this miRNA was investigated by transient transfection of the pancreatic cancer cell line PANC-1 with oligonucleotides that mimic hsa-miR-520h.

Results:

Results showed that both mRNA and protein levels of ABCG2 were reduced, indicating that it was a target of hsa-miR-520h. Introduction of hsa-miR-520h mimics into PANC-1 cells also resulted in inhibition of cell migration and invasion, and reduction of side population cells. Cell proliferation, cell cycle progression and apoptosis were not affected.

Conclusions:

We propose that the effects of hsa-miR-520h may be, at least in part, caused by its regulation of ABCG2. Thus, our findings provide a new insight into the function of miRNA in the regulation of ABCG2 expression in pancreatic cancer. Gene therapy using miRNA mimics may therefore be useful as a pancreatic cancer therapy.

Determinants for the efficiency of anticancer drugs targeting either Aurora-A or Aurora-B kinases in human colon carcinoma cells

The mitotic Aurora kinases, including Aurora-A and Aurora- B, are attractive novel targets for anticancer therapy, and inhibitory drugs have been developed that are currently undergoing clinical trials. However, the molecular mechanisms how these drugs induce tumor cell death are poorly understood. We have addressed this question by comparing the requirements for an efficient induction of apoptosis in response to MLN8054, a selective inhibitor of Aurora-A, and the selective Aurora-B inhibitor ZM447439 in human colon carcinoma cells. By using various isogenic knockout as well as inducible colon carcinoma cell lines, we found that treatment with MLN8054 induces defects in mitotic spindle assembly, which causes a transient spindle checkpoint-dependent mitotic arrest. This cell cycle arrest is not maintained due to the activity of MLN8054 to override the spindle checkpoint. Subsequently, MLN8054-treated cells exit from mitosis and activate a p53-dependent postmitotic G(1) checkpoint, which subsequently induces p21 and Bax, leading to G(1) arrest followed by the induction of apoptosis. In contrast, inhibition of Aurora-B by ZM447439 also interferes with normal chromosome alignment during mitosis and overrides the mitotic spindle checkpoint but allows a subsequent endoreduplication, although ZM447439 potently activates the p53-dependent postmitotic G(1) checkpoint. Moreover, the ZM447439-induced endoreduplication is a prerequisite for the efficiency of the drug. Thus, our results obtained in human colon carcinoma cells indicate that although both Aurora kinase inhibitors are potent inducers of tumor cell death, the pathways leading to the induction of apoptosis in response to these drugs are distinct.

Discovery and exploitation of inhibitor-resistant aurora and polo kinase mutants for the analysis of mitotic networks

The Aurora and Polo-like kinases are central components of mitotic signaling pathways, and recent evidence suggests that substantial cross-talk exists between Aurora A and Plk1. In addition to their validation as novel anticancer agents, small molecule kinase inhibitors are increasingly important tools to help dissect clinically relevant protein phosphorylation networks. However, one major problem associated with kinase inhibitors is their promiscuity toward "off-target" members of the kinome, which makes interpretation of data obtained from complex cellular systems challenging. Additionally, the emergence of inhibitor resistance in patients makes it clear that an understanding of resistance mechanisms is essential to inform drug design. In this study, we exploited structural knowledge of the binding modes of VX-680, an Aurora kinase inhibitor, and BI 2536, a Polo-like kinase inhibitor, to design and evaluate drug-resistant kinase mutants. Using inducible stable human cell lines, we authenticated mitotic targets for both compounds and demonstrated that Aurora A mutants exhibit differential cellular sensitivity toward the inhibitors VX-680 and MLN8054. In addition, we validated Aurora B as an important anti-proliferative target for VX-680 in model human cancer cells. Finally, this chemical genetic approach allowed us to prove that Aurora A activation loop phosphorylation is controlled by a Plk1-mediated pathway in human cells.