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

DNA damage response pathways and cell cycle checkpoints in colorectal cancer: current concepts and future perspectives for targeted treatment

Although several drugs have been designed in the last few years to target specific key pathways and functions in colorectal cancer (CRC), the backbone of CRC treatment is still made up of compounds which rely on DNA damage to accomplish their role. DNA damage response (DDR) and checkpoint pathways are intertwined signaling networks that arrest cell cycle, recognize and repair genetic mistakes which arise during DNA replication and transcription, as well as through the exposure to chemical and physical agents that interact with nucleic acids. The good but highly variable activity of DNA damaging agents in the treatment of CRC suggests that intrinsic alterations in DDR pathways and cell cycle checkpoints may contribute differentially to the way cancer cells react to DNA damage. In the present review, our aim is to depict the recent advances in understanding the molecular basis of the activity of DNA damaging agents used for the treatment of CRC. We focus on the known and potential drug targets that are part of these complex and intertwined pathways. We describe the potential role of the checkpoints in CRC, and how their pharmacological manipulation could lead to chemopotentiation or synergism with currently used drugs. Novel therapeutic agents playing a role in DDR and checkpoint inhibition are assessed. We discuss the possible rationale for combining PARP inhibition with DNA damaging agents, and we address the link between DDR and EGFR pathways in CRC.

Phase I study of aurora A kinase inhibitor MLN8237 in advanced solid tumors: safety, pharmacokinetics, pharmacodynamics, and bioavailability of two oral formulations

PURPOSE

This phase I study evaluated the safety, pharmacokinetics, pharmacodynamics, and efficacy of the investigational oral drug MLN8237 (alisertib), a small-molecule Aurora A kinase (AAK) inhibitor, in 87 adult patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Sequential cohorts of patients received MLN8237 5 to 150 mg orally once daily or twice daily for 7, 14, or 21 days, followed by 14 days' rest per cycle. MLN8237 pharmacokinetics was characterized, and the relative bioavailability of an enteric-coated tablet (ECT) formulation was evaluated in reference to the original powder-in-capsule (PIC) formulation. Pharmacodynamic effects of MLN8237 on inhibition of AAK activity were evaluated in skin biopsies. Tolerability and response to treatment were assessed.

RESULTS

Common toxicities included fatigue, nausea, and neutropenia. Plasma exposures increased dose proportionally (5-150 mg/d), and were similar for PIC and ECT. The terminal half-life was 23 hours. At the maximum tolerated dose of 50 mg twice daily on the 7-day schedule, the mitotic index of the skin basal epithelium was increased within 24 hours after MLN8237 administration on days 1 and 7, a finding consistent with AAK inhibition. One (1%) patient achieved a partial response lasting for more than 1 year and received MLN8237 for 51 cycles; 20 (23%) patients achieved stable disease for ≥3 months.

CONCLUSIONS

This first-in-human trial of MLN8237 showed tolerability and favorable pharmacokinetics in this patient population. The recommended phase II dose of MLN8237 is 50 mg twice daily orally for 7 days in 21-day cycles, which is being evaluated further in the treatment of various solid tumors and hematologic malignancies.

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.

Tanshinones inhibit the growth of breast cancer cells through epigenetic modification of Aurora A expression and function

The objectives of this study were to evaluate the effects of tanshinones from a Chinese herb Salvia Miltiorrhiza on the growth of breast cancer cells, and to elucidate cellular and molecular mechanisms of action. Tanshinones showed the dose-dependent effect on the growth inhibition of breast cancer cells in vitro, with tanshinone I (T1) the most potent agent. T1 was also the only tanshinone to have potent activity in inhibiting the growth of the triple-negative breast cancer cell line MDA-MB231. T1 caused cell cycle arrests of both estrogen-dependent and estrogen-independent cell lines associated with alterations of cyclinD, CDK4 and cyclinB, and induced breast cancer cell apoptosis associated with upregulation of c-PARP and downregulation of survivin and Aurora A. Among these associated biomarkers, Aurora A showed the most consistent pattern with the anti-growth activity of tanshinones. Overexpression of Aurora A was also verified in breast tumors. The gene function assay showed that knockdown of Aurora A by siRNA dramatically reduced the growth-inhibition and apoptosis-induction activities of T1, suggesting Aurora A as an important functional target of T1 action. On the other hand, tanshinones had much less adverse effects on normal mammary epithelial cells. Epigenetic mechanism studies showed that overexpression of Aurora A gene in breast cancer cells was not regulated by gene promoter DNA methylation, but by histone acetylation. T1 treatment significantly reduced acetylation levels of histone H3 associated with Aurora A gene. Our results supported the potent activity of T1 in inhibiting the growth of breast cancer cells in vitro in part by downregulation of Aurora A gene function. Our previous studies also demonstrated that T1 had potent anti-angiogenesis activity and minimal side effects in vivo. Altogether, this study warrants further investigation to develop T1 as an effective and safe agent for the therapy and prevention of breast cancer.

Possibility of the use of public microarray database for identifying significant genes associated with oral squamous cell carcinoma

There are lots of studies attempting to identify the expression changes in oral squamous cell carcinoma. Most studies include insufficient samples to apply statistical methods for detecting significant gene sets. This study combined two small microarray datasets from a public database and identified significant genes associated with the progress of oral squamous cell carcinoma. There were different expression scales between the two datasets, even though these datasets were generated under the same platforms - Affymetrix U133A gene chips. We discretized gene expressions of the two datasets by adjusting the differences between the datasets for detecting the more reliable information. From the combination of the two datasets, we detected 51 significant genes that were upregulated in oral squamous cell carcinoma. Most of them were published in previous studies as cancer-related genes. From these selected genes, significant genetic pathways associated with expression changes were identified. By combining several datasets from the public database, sufficient samples can be obtained for detecting reliable information. Most of the selected genes were known as cancer-related genes, including oral squamous cell carcinoma. Several unknown genes can be biologically evaluated in further studies.

Bioactive tanshinone I inhibits the growth of lung cancer in part via downregulation of Aurora A function

Lung cancer is the leading cause of cancer death in the world, and the searching for novel efficacious and safe agents for lung cancer prevention remains the top priority of lung cancer research. In the present study, we evaluated the effect of bioactive tanshinones from a Chinese herb Salvia miltiorrhiza, cryptotanshinone (CT), tanshinone I (T1) and tanshinone IIA (T2A), on the proliferation inhibition of lung cancer cell lines. Tanshinones inhibited the lung cancer cell proliferation in vitro, with T1 the most potent, via cell cycle arrest and apoptosis induction. Gene function assay showed that Aurora A knockdown by siRNA dramatically eliminated the T1 activity in vitro, suggesting that Aurora A is an important functional target for T1. We further evaluated the effectiveness of T1 on the growth of H1299 nonsmall lung cancer cell in a mouse model. Tanshinone I inhibited the growth of H1299 lung tumor in a dose-dependent manner. Tanshinone I at 200 mg/kg body weight significantly reduced final tumor weight by 34% (P < 0.05) associated with inhibiting proliferation and inducing apoptosis of lung cancer cells by 54% (P < 0.001) and 193% (P < 0.001), respectively, inhibiting lung tumor angiogenesis by 72% (P < 0.001), and reducing Aurora A expression by 67% (P < 0.001). On the other hand, T1 did not significantly alter food intake or body weight. Our results provided experimental evidence to suggest that T1 may be an efficacious and safe agent for the prevention of lung cancer progression and Aurora A may be an important molecular target for T1 action against lung cancer.

Aurora kinase B/C inhibition impairs malignant glioma growth in vivo

Inhibition of Aurora kinase B has been evaluated as a therapy to block solid tumor growth in breast cancer, hepatocellular carcinoma, lung adenocarcinoma, and colorectal cancer models. Aurora kinase inhibitors are in early clinical trials for the treatment of leukemia. We hypothesized that Aurora B inhibition would reduce malignant glioma cell viability and result in impaired tumor growth in vivo. Aurora B expression is greater in cultured malignant glioma U251 cells compared to proliferating normal human astrocytes, and expression is maintained in U251 flank xenografts. Aurora B inhibition with AZD1152-HQPA blocked cell division in four different p53-mutant glioma cell lines (U251, T98G, U373, and U118). AZD1152-HQPA also inhibited Aurora C activation loop threonine autophosphorylation at the effective antiproliferative concentrations in vitro. Reduction in cell viability of U251 (p53(R273H)) cells was secondary to cytokinesis blockade and apoptosis induction following endoreplication. AZD1152-HQPA inhibited the growth of U251 tumor xenografts and resulted in an increase in tumor cell apoptosis both in vitro and in vivo. Subcutaneous administration of AZD1152-HQPA (25 mg/kg/day × 4 days; 2 cycles spaced 7 days apart) resulted in a prolongation in median survival after intracranial inoculation of U251 cells in mice (P = 0.025). This is the first demonstration that an Aurora kinase inhibitor can inhibit malignant glioma growth in vivo at drug doses that are clinically relevant.

The induction of polyploidy or apoptosis by the Aurora A kinase inhibitor MK8745 is p53-dependent

Aurora kinases are mitotic serine/threonine protein kinases and are attractive novel targets for anticancer therapy. Many small-molecule inhibitors of Aurora kinases are currently undergoing clinical trials. Aurora A kinase is essential for successful mitotic transition. MK8745 is a novel and selective small-molecule inhibitor of Aurora A kinase. MK8745 induced apoptotic cell death in a p53-dependent manner when tested in vitro in cell lines of multiple lineages. Cells expressing wild-type p53 showed a short delay in mitosis followed by cytokinesis, resulting in 2N cells along with apoptosis. However, cells lacking or with mutant p53 resulted in a prolonged arrest in mitosis followed by endoreduplication and polyploidy. Cytokinesis was completely inhibited in p53-deficient cells, as observed by the absence of 2N cell population. The induction of apoptosis in p53-proficient cells was associated with activation of caspase 3 and release of cytochrome c but was independent of p21. Exposure of p53 wild-type cells to MK8745 resulted in the induction of p53 phosphorylation (ser15) and an increase in p53 protein expression. p53-dependent apoptosis by MK8745 was further confirmed in HCT 116 p53(-/-) cells transfected with wild-type p53. Transient knockdown of Aurora A by specific siRNA recapitulated these p53- dependent effects, with greater percent induction of apoptosis in p53 wild-type cells. In conclusion, our studies show p53 as a determining factor for induction of apoptosis vs. polyploidy upon inhibition of Aurora A.

An integrated genomic approach to identify predictive biomarkers of response to the aurora kinase inhibitor PF-03814735

PF-03814735 is a novel, reversible inhibitor of Aurora kinases A and B that finished a phase I clinical trial for the treatment of advanced solid tumors. To find predictive biomarkers of drug sensitivity, we screened a diverse panel of 87 cancer cell lines for growth inhibition upon PF-03814735 treatment. Small cell lung cancer (SCLC) and, to a lesser extent, colon cancer lines were very sensitive to PF-03814735. The status of the Myc gene family and retinoblastoma pathway members significantly correlated with the efficacy of PF-03814735. Whereas RB1 inactivation, intact CDKN2A/p16, and normal CCND1/Cyclin D1 status are hallmarks of SCLC, activation or amplification of any of the three Myc genes (MYC, MYCL1, and MYCN) clearly differentiated cell line sensitivity within the SCLC panel. By contrast, we found that expression of Aurora A and B were weak predictors of response. We observed a decrease in histone H3 phosphorylation and polyploidization of sensitive lines, consistent with the phenotype of Aurora B inhibition. In vivo experiments with two SCLC xenograft models confirmed the sensitivity of Myc gene-driven models to PF-03814735 and a possible schedule dependence of MYC/c-Myc-driven tumors. Altogether our results suggest that SCLC and other malignancies driven by the Myc family genes may be suitable indications for treatment by Aurora B kinase inhibitors.

The flavonoid eupatorin inactivates the mitotic checkpoint leading to polyploidy and apoptosis

The spindle assembly checkpoint (SAC) is a conserved mechanism that ensures the fidelity of chromosome distribution in mitosis by preventing anaphase onset until the correct bipolar microtubule-kinetochore attachments are formed. Errors in SAC function may contribute to tumorigenesis by inducing numerical chromosome anomalies (aneuploidy). On the other hand, total disruption of SAC can lead to massive genomic imbalance followed by cell death, a phenomena that has therapeutic potency. We performed a cell-based high-throughput screen with a compound library of 2000 bioactives for novel SAC inhibitors and discovered a plant-derived phenolic compound eupatorin (3',5-dihydroxy-4',6,7-trimethoxyflavone) as an anti-mitotic flavonoid. The premature override of the microtubule drug-imposed mitotic arrest by eupatorin is dependent on microtubule-kinetochore attachments but not interkinetochore tension. Aurora B kinase activity, which is essential for maintenance of normal SAC signaling, is diminished by eupatorin in cells and in vitro providing a mechanistic explanation for the observed forced mitotic exit. Eupatorin likely has additional targets since eupatorin treatment of pre-mitotic cells causes spindle anomalies triggering a transient M phase delay followed by impaired cytokinesis and polyploidy. Finally, eupatorin potently induces apoptosis in multiple cancer cell lines and suppresses cancer cell proliferation in organotypic 3D cell culture model.

Dual inhibition of SRC and Aurora kinases induces postmitotic attachment defects and cell death

Increased activity of SRC family kinases promotes tumor invasion and metastasis, and overexpression of the mitotic regulator Aurora kinase A (AURKA) drives tumor aneuploidy and chromosomal instability. These functions nominate SRC and AURKA as valuable therapeutic targets for cancer, and inhibitors for SRC and Aurora kinases are now being used in the clinic. In this study, we demonstrate potent synergy between multiple inhibitors of Aurora and SRC kinases in ovarian and colorectal cancer cell lines, but not in normal ovarian epithelial cell lines. Combination of Aurora and SRC inhibitors selectively killed cells that have undergone a preceding aberrant mitosis, and was associated with a postmitotic reattachment defect, and selective removal of aneuploid cell populations. Combined inhibition of Aurora kinase and SRC potentiated dasatinib-dependent loss of activated (Y(416)-phosphorylated) SRC. SRC and AURKA share a common interaction partner, NEDD9, which serves as a scaffolding protein with activities in cell attachment and mitotic control, suggesting SRC and AURKA might interact directly. In vitro, we observed physical interaction and mutual cross-phosphorylation between SRC and AURKA that enhanced SRC kinase activity. Together, these findings suggest that combination of SRC and Aurora-targeting inhibitors in the clinic may be a productive strategy.

Inhibition of mitotic kinase Aurora suppresses Akt-1 activation and induces apoptotic cell death in all-trans retinoid acid-resistant acute promyelocytic leukemia cells

BACKGROUND

Aurora kinase ensures accurate chromosome segregation during cell cycle, maintaining genetic integrity in cell division. VX-680, a small-molecule Aurora kinase inhibitor, interferes with mitotic entry and formation of bipolar spindles. Here, we evaluated VX-680 as a potential agent for treatment of all-trans retinoid acid (ATRA)-resistant acute promyelocytic leukemia (APL) in vitro.

METHODS

CD11b expression was utilized to assess cell differentiation by flow cytometry. Immunofluorescence staining was conducted to analyze formation of cell monopolar spindle. Cell proliferation was evaluated by MTT assay. Sub-G1 population and Annexin V/PI staining were used to measure cell apoptosis. Hoechst 33342 staining was applied for identifying morphological changes in nucleus of apoptotic cell. Aurora-A (Aur-A) activation and the signaling pathways involved in apoptosis were detected by Western blot. JC-1 probe was employed to measure mitochondrial depolarization.

RESULTS

VX-680 inhibited Aur-A by reducing autophosphorylation at the activation site, Thr288, accompanied by producing monopolar mitotic spindles in APL cell line NB4-R2 that was resistant to ATRA. In addition, we found that VX-680 inhibited cell proliferation as assessed by MTT assay. Flow cytometry showed that VX-680 led to apoptotic cell death in both dose- and time-dependent manners by either Sub-G1 or Annexin V/PI analysis. Hoechst 33342 staining represented typical apoptotic cells with nuclear fragmentation in VX-680 treated cells. Importantly, VX-680 inhibition of Aurora kinase suppressed Akt-1 activation and induced mitochondrial depolarization, which eventually resulted in apoptosis by activation of caspase pathway, as indicated by increasing proteolytic cleavage of procaspase-3 and poly ADP ribose polymerase (PARP) in NB4-R2 cells.

CONCLUSIONS

Our study suggested potential clinical use of mitotic Aurora kinase inhibitor in targeting ATRA-resistant leukemic cells.

MLN8054, a small molecule inhibitor of aurora kinase a, sensitizes androgen-resistant prostate cancer to radiation

PURPOSE

To determine whether MLN8054, an Aurora kinase A (Aurora-A) inhibitor causes radiosensitization in androgen-insensitive prostate cancer cells in vitro and in vivo.

METHODS AND MATERIALS

In vitro studies consisted of culturing PC3 and DU145 prostate cancer cells and then immunoblotting Aurora A and phospho-Aurora A after radiation and/or nocodazole with MLN8054. Phases of the cell cycle were measured with flow cytometry. PC3 and DU145 cell lines were measured for survival after treatment with MLN8054 and radiation. Immunofluorescence measured γ-H2AX in the PC3 and DU145 cells after treatment. In vivo studies looked at growth delay of PC3 tumor cells in athymic nude mice. PC3 cells grew for 6 to 8 days in mice treated with radiation, MLN8054, or combined for 7 more days. Tumors were resected and fixed on paraffin and stained for von Willebrand factor, Ki67, and caspase-3.

RESULTS

In vitro inhibition of Aurora-A by MLN8054 sensitized prostate cancer cells, as determined by dose enhancement ratios in clonogenic assays. These effects were associated with sustained DNA double-strand breaks, as evidenced by increased immunofluorescence for γ-H2AX and significant G2/M accumulation and polyploidy. In vivo, the addition of MLN8054 (30 mg/kg/day) to radiation in mouse prostate cancer xenografts (PC3 cells) significantly increased tumor growth delay and apoptosis (caspase-3 staining), with reduction in cell proliferation (Ki67 staining) and vascular density (von Willebrand factor staining).

CONCLUSION

MLN8054, a novel small molecule Aurora-A inhibitor showed radiation sensitization in androgen-insensitive prostate cancer in vitro and in vivo. This warrants the clinical development of MLN8054 with radiation for prostate cancer patients.

Response of experimental malignant melanoma models to the pan-Aurora kinase inhibitor VE-465

Aurora kinases represent promising novel cancer therapy targets. Genomic analyses of human cutaneous melanoma (CMM) models (N = 51, low passage) by classical and/or array CGH revealed frequent gains at chromosome 20q (65%, amplifications in 45%) repeatedly including the Aurora A gene locus. Accordingly, the majority of CMM cell cultures overexpressed Aurora A when compared to proliferating non-malignant cells. Moreover, CMM cells even when arrested in G1/S cell cycle phase contained readily detectable levels of Aurora A indicating incomplete degradation during mitosis. Already at low concentrations (10-100 nm), long-term (7-10 days) application of the pan-Aurora kinase inhibitor VE-465 completely prevented colony formation in all CMM models tested. In contrast, blockade of cell survival/proliferation and DNA synthesis as well as the induction of apoptosis by VE-465 distinctly differed in short-term experiments (up to 72 h exposure). Both cell cycle arrest and DNA synthesis blockade depended on the level of VE-465-mediated p53/p21 activation while p53/p21 unresponsiveness led to repetitive endoreduplication (>8n DNA content). In contrast, apoptosis induction by VE-465 and Aurora A siRNA did not correlate with p53/p21 responsiveness and DNA synthesis blockade. Moreover, application of the Aurora B-specific inhibitor ZM447439 and siRNA was less efficient to induce CMM cell death proofing that apoptosis induction by VE-465 depended predominantly on Aurora A targeting. In combination experiments with chemotherapeutic agents, VE-465 acted additive to antagonistic when applied concomitantly but in several cases even synergistic when applied consecutively. In summary, we suggest that the Aurora A kinase might represent a promising target of well-designed novel antimelanoma strategies.

Mitosis as an anti-cancer target

Most of the current drugs used to treat cancer can be classified as anti-proliferative drugs. These drugs perturb the proliferative cycle of tumor cells at diverse stages of the cell cycle. Examples of such drugs are DNA-damaging agents and inhibitors of cyclin-dependent kinases that arrest cell cycle progression at different stages of interphase. Another class of anti-proliferative drugs is the so-called anti-mitotic drugs, which selectively perturb progression through mitosis. Mitosis is the shortest and final stage in the cell cycle and has evolved to accurately divide the duplicated genome over the two daughter cells. This review deals with the different strategies that are currently considered to perturb mitotic progression in the treatment of cancer.

Mitotic drug targets

Mitosis is the key event of the cell cycle during which the sister chromatids are segregated onto two daughter cells. It is well established that abrogation of the normal mitotic progression is a highly efficient concept for anti-cancer treatment. In fact, various drugs that target microtubules and thus interfere with the function of the mitotic spindle are in clinical use for the treatment of various human malignancies for many years. However, since microtubule inhibitors not only target proliferating cells severe side effects limit their use. Therefore, the identification of novel mitotic drug targets other than microtubules have gained recently much attention. This review will summarize the latest developments on the identification and clinical evaluation of novel mitotic drug targets and will introduce novel concepts for chemotherapy that are based on recent progress in our understanding how mitotic progression is regulated and how anti-mitotic drugs induce tumor cell death.

Shared and separate functions of polo-like kinases and aurora kinases in cancer

Large numbers of inhibitors for polo-like kinases and aurora kinases are currently being evaluated as anticancer drugs. Interest in these drugs is fuelled by the idea that these kinases have unique functions in mitosis. Within the polo-like kinase family, the emphasis for targeted therapies has been on polo-like kinase 1 (PLK1), and in the aurora kinase family drugs have been developed to specifically target aurora kinase A (AURKA; also known as STK6) and/or aurora kinase B (AURKB; also known as STK12). Information on the selectivity of these compounds in vivo is limited, but it is likely that off-target effects within the same kinase families will affect efficacy and toxicity profiles. In addition, it is becoming clear that interplay between polo-like kinases and aurora kinases is much more extensive than initially anticipated, and that both kinase families are important factors in the response to classical chemotherapeutics that damage the genome or the mitotic spindle. In this Review we discuss the implications of these novel insights on the clinical applicability of polo-like kinase and aurora kinase inhibitors.

Bioactive tanshinones in Salvia miltiorrhiza inhibit the growth of prostate cancer cells in vitro and in mice

Searching for efficacious and safe agents for the chemoprevention and therapy of prostate cancer has become the top priority of research. The objective of this study was to determine the effects of a group of tanshinones from a Chinese herb Salvia Miltiorrhiza, cryptotanshinone (CT), tanshinone IIA (T2A) and tanshinone I (T1) on prostate cancer. The in vitro studies showed that these tanshinones inhibited the growth of human prostate cancer cell lines in a dose-dependent manner via cell cycle arrest and apoptosis induction. Among three compounds, T1 had the most potent activity with IC(50) s around 3-6 μM. On the other hand, tanshinones had much less adverse effects on the growth of normal prostate epithelial cells. The epigenetic pathway focused array assay identified Aurora A kinase as a possible target of tanshinone actions. The expression of Aurora A was overexpressed in prostate cancer cell lines. Moreover, knockdown of Aurora A in prostate cancer cells significantly decreased cell growth. Tanshinones significantly downregulated the Aurora A expression, suggesting Aurora A may be a functional target of tanshinones. Tanshinones, especially T1, also showed potent anti-angiogenesis activity in vitro and in vivo. Furthermore, T1 inhibited the growth of DU145 prostate tumor in mice associated with induction of apoptosis, decrease of proliferation, inhibition of angiogenesis and downregulation of Aurora A, whereas it did not alter food intake or body weight. Our results support that T1 may be an efficacious and safe chemopreventive or therapeutic agent against prostate cancer progression.

Chemotherapy and signaling: How can targeted therapies supercharge cytotoxic agents?

In recent years, oncologists have begun to conclude that chemotherapy has reached a plateau of efficacy as a primary treatment modality, even if toxicity can be effectively controlled. Emerging specific inhibitors of signaling and metabolic pathways (i.e., targeted agents) contrast with traditional chemotherapy drugs in that the latter primarily interfere with the DNA biosynthesis and the cell replication machinery. In an attempt to improve on the efficacy, combination of targeted drugs with conventional chemotherapeutics has become a routine way of testing multiple new agents in early phase clinical trials. This review discusses the recent advances including integrative systematic biology and RNAi approaches to counteract the chemotherapy resistance and to buttress the selectivity, efficacy and personalization of anti-cancer drug therapy.

Drug-resistant aurora A mutants for cellular target validation of the small molecule kinase inhibitors MLN8054 and MLN8237

The Aurora kinases regulate multiple aspects of mitotic progression, and their overexpression in diverse tumor types makes them appealing oncology targets. An intensive research effort over the past decade has led to the discovery of chemically distinct families of small molecule Aurora kinase inhibitors, many of which have demonstrated therapeutic potential in model systems. These agents are also important tools to help dissect signaling pathways that are orchestrated by Aurora kinases, and the antiproliferative target of pan-Aurora inhibitors such as VX-680 has been validated using chemical genetic techniques. In many cases the nonspecific nature of Aurora inhibitors toward unrelated kinases is well established, potentially broadening the spectrum of cancers to which these compounds might be applied. However, unambiguously demonstrating the molecular target(s) for clinical kinase inhibitors is an important challenge, one that is absolutely critical for deciphering the molecular basis of compound specificity, resistance, and efficacy. In this paper, we have investigated amino acid requirements for Aurora A sensitivity to the benzazepine-based Aurora inhibitor MLN8054 and the close analogue MLN8237, a second-generation compound that is in phase II clinical trials. A crystallographic analysis facilitated the design and biochemical investigation of a panel of resistant Aurora A mutants, a subset of which were then selected as candidate drug-resistance targets for further evaluation. Using inducible human cell lines, we show that cells expressing near-physiological levels of a functional but partially drug-resistant Aurora A T217D mutant survive in the presence of MLN8054 or MLN8237, authenticating Aurora A as a critical antiproliferative target of these compounds.

Conditional ablation of Ikkb inhibits melanoma tumor development in mice

Several lines of evidence suggest that tumor cells show elevated activity of the NF-kappaB transcription factor, a phenomenon often resulting from constitutive activity of IkappaB kinase beta (IKKbeta). However, others have found that loss of NF-kappaB activity or IKKbeta is tumor promoting. The role of NF-kappaB in tumor progression is therefore controversial and varies with tumor type. We sought to more extensively investigate the role IKKbeta in melanoma tumor development by specifically disrupting Ikkb in melanocytes in an established mouse model of spontaneous melanoma, whereby HRasV12 is expressed in a melanocyte-specific, doxycycline-inducible manner in mice null for the gene encoding the tumor suppressor inhibitor cyclin-dependent kinase 4/alternative reading frame (Ink4a/Arf). Our results show that Ink4a/Arf-/- mice with melanocyte-specific deletion of Ikkb were protected from HRasV12-initiated melanoma only when p53 was expressed. This protection was accompanied by cell cycle arrest, with reduced cyclin-dependent kinase 2 (Cdk2), Cdk4, Aurora kinase A, and Aurora kinase B expression. Increased p53-mediated apoptosis was also observed, with decreased expression of the antiapoptotic proteins Bcl2 and survivin. Enhanced stabilization of p53 involved increased phosphorylation at Ser15 and reduced phosphorylation of double minute 2 (Mdm2) at Ser166. Together, our findings provide genetic and mechanistic evidence that mutant HRas initiation of tumorigenesis requires Ikkbeta-mediated NF-kappaB activity.