Inhibition of the met receptor in mesothelioma.

BACKGROUND: Expression of the Met receptor and its ligand, hepatocyte growth factor (HGF), has been observed in 74% to 100% and 40% to 85% of malignant pleural mesothelioma (MPM) specimens, respectively. HGF stimulation has been shown to enhance MPM cell proliferation, migration, cell scattering, and invasiveness. EXPERIMENTAL DESIGN: To investigate a potential therapeutic role for the Met receptor in MPM, we examined the effects of PHA-665752, a specific small-molecule inhibitor of the Met receptor tyrosine kinase, in a panel of 10 MPM cell lines. RESULTS: Two of the cell lines, H2461 and JMN-1B, exhibited autocrine HGF production as measured by ELISA (3.9 and 10.5 ng/mL, respectively, versus <0.05 ng/mL in other cell lines). Evaluation of PHA-665752 across the 10 MPM cell lines indicated that despite Met expression in all cell lines, only in cell lines that exhibited a Met/HGF autocrine loop, H2461 and JMN-1B, did PHA-665752 inhibit growth with an IC(50) of 1 and 2 micromol/L, respectively. No activating mutations in Met were detected in any of the cell lines. Consistent with observed growth inhibition, PHA-665752 caused cell cycle arrest at G(1)-S boundary accompanied by a dose-dependent decrease in phosphorylation of Met, p70S6K, Akt, and extracellular signal-regulated kinase 1/2. Growth of H2461 cells was also inhibited by neutralizing antibodies to HGF and by RNA interference knockdown of the Met receptor, confirming that growth inhibition observed was through a Met-dependent mechanism. PHA-665752 also reduced MPM in vitro cell migration and invasion. CONCLUSIONS: Taken together, these findings suggest that inhibition of the Met receptor may be an effective therapeutic strategy for patients with MPM and provides a mechanism, the presence of a HGF/Met autocrine loop, by which to select patients for PHA-665752 treatment.     

A selective small molecule c-MET Inhibitor, PHA665752, cooperates with rapamycin.

PURPOSE: c-MET is believed to be an attractive receptor target for molecular therapeutic inhibition. TPR-MET, a constitutively active oncogenic variant of MET, serves as excellent model for testing c-MET inhibitors. Here, we characterized a small molecule c-MET inhibitor, PHA665752, and tested its cooperation with the mammalian target of rapamycin inhibitor as potential targeted therapy. EXPERIMENTAL DESIGN: The effect of PHA665752 treatment was determined on cell growth, motility and migration, apoptosis, and cell-cycle arrest of TPR-MET-transformed cells. Moreover, the effect of PHA665752 on the phosphorylation on MET, as well as its downstream effectors, p-AKT and p-S6K, was also determined. Finally, growth of TPR-MET-transformed cells was tested in the presence of PHA665752 and rapamycin. H441 non-small cell lung cancer (NSCLC) cells (with activated c-Met) were also tested against both PHA665752 and rapamycin. RESULTS: PHA665752 specifically inhibited cell growth in BaF3. TPR-MET cells (IC(50) < 0.06 micromol/L), induced apoptosis and cell cycle arrest. Constitutive cell motility and migration of the BaF3. TPR-MET cells was also inhibited. PHA665752 inhibited specific phosphorylation of TPR-MET as well as phosphorylation of downstream targets of the mammalian target of rapamycin pathway. When combined with PHA665752, rapamycin showed cooperative inhibition to reduce growth of BaF3. TPR-MET- and c-MET-expressing H441 NSCLC cells. CONCLUSIONS: PHA665752 is a potent small molecule-selective c-MET inhibitor and is highly active against TPR-MET-transformed cells both biologically and biochemically. PHA665752 is also active against H441 NSCLC cells. The c-MET inhibitor can cooperate with rapamycin in therapeutic inhibition of NSCLC, and in vivo studies of this combination against c-MET expressing cancers would be merited.     

A selective c-met inhibitor blocks an autocrine hepatocyte growth factor growth loop in ANBL-6 cells and prevents migration and adhesion of myeloma cells.

PURPOSE: We wanted to examine the role of the hepatocyte growth factor (HGF) receptor c-Met in multiple myeloma by applying a novel selective small molecule tyrosine kinase inhibitor, PHA-665752, directed against the receptor. EXPERIMENTAL DESIGN: Four biological sequels of HGF related to multiple myeloma were studied: (1) proliferation of myeloma cells, (2) secretion of interleukin-11 from osteogenic cells, (3) migration of myeloma cells, and (4) adhesion of myeloma cells to fibronectin. We also examined effects of the c-Met inhibitor on intracellular signaling pathways in myeloma cells. RESULTS: PHA-665752 effectively blocked the biological responses to HGF in all assays, with 50% inhibition at 5 to 15 nmol/L concentration and complete inhibition at around 100 nmol/L. PHA-665752 inhibited phosphorylation of several tyrosine residues in c-Met (Tyr(1003), Tyr(1230/1234/1235), and Tyr(1349)), blocked HGF-mediated activation of Akt and p44/42 mitogen-activated protein kinase, and prevented the adaptor molecule Gab1 from complexing with c-Met. In the HGF-producing myeloma cell line ANBL-6, PHA-665752 revealed an autocrine HGF-c-Met-mediated growth loop. The inhibitor also blocked proliferation of purified primary myeloma cells, suggesting that autocrine HGF-c-Met-driven growth loops are important for progression of multiple myeloma. CONCLUSIONS: Collectively, these findings support the role of c-Met and HGF in the proliferation, migration, and adhesion of myeloma cells and identify c-Met kinase as a therapeutic target for treatment of patients with multiple myeloma.     

Loss of the exon encoding the juxtamembrane domain is essential for the oncogenic activation of TPR-MET.

TPR-MET, a transforming counterpart of the c-MET proto-oncogene detected in experimental and human cancer, results from fusion of the MET kinase domain with a dimerization motif encoded by TPR. In this rearrangement the exons encoding the Met extracellular, transmembrane and juxtamembrane domains are lost. The juxtamembrane domain has been suggested to be a regulatory region endowed with negative feedback control. To understand whether its absence is critical for the generation of the Tpr-Met transforming potential, we produced a chimeric molecule (Tpr-juxtaMet) with a conserved juxtamembrane domain. The presence of the domain (aa 962-1009) strongly inhibited Tpr-Met dependent cell transformation. Cell proliferation, anchorage-independent growth, motility and invasion were also impaired. The enzymatic behavior of Tpr-Met and Tpr-juxtaMet was the same, while Tpr-juxtaMet ability to associate cytoplasmic signal transducers and to elicit downstream signaling was severely impaired. These data indicate that the presence of the juxtamembrane domain counterbalances the Tpr-Met transforming potential and therefore the loss of the exon encoding the juxtamembrane domain is crucial in the generation of the active TPR-MET oncogene.     

A selective small molecule inhibitor of c-Met, PHA665752, inhibits tumorigenicity and angiogenesis in mouse lung cancer xenografts

The c-Met receptor tyrosine kinase is emerging as a novel target in many solid tumors, including lung cancer. PHA-665752 was identified as a small molecule, ATP competitive inhibitor of the catalytic activity of the c-Met kinase. Here, we show that treatment with PHA665752 reduced NCI-H69 (small cell lung cancer) and NCI-H441 (non-small cell lung cancer) tumorigenicity in mouse xenografts by 99% and 75%, respectively. Reduction in tumor size was also observed by magnetic resonance imaging of tumors in mice. PHA665752 inhibited c-Met phosphorylation at the autophosphorylation and c-Cbl binding sites in mouse xenografts derived from non-small cell lung cancer cell lines (NCI-H441 and A549) and small cell lung cancer cell line (NCI-H69). PHA665752 also inhibited angiogenesis by >85% in all the abovementioned cell lines and caused an angiogenic switch which resulted in a decreased production of vascular endothelial growth factor and an increase in the production of the angiogenesis inhibitor thrombospondin-1. These studies show the feasibility of selectively targeting c-Met with ATP competitive small molecule inhibitors and suggest that PHA665752 may provide a novel therapeutic approach to lung cancer.     

Effects of Src inhibitors on cell growth and epidermal growth factor receptor and MET signaling in gefitinib-resistant non-small cell lung cancer cells with acquired MET amplification

The efficacy of epidermal growth factor receptor (EGFR)–tyrosine kinase inhibitors such as gefitinib and erlotinib in non-small cell lung cancer (NSCLC) is often limited by the emergence of drug resistance conferred either by a secondary T790M mutation of EGFR or by acquired amplification of the MET gene. We now show that the extent of activation of the tyrosine kinase Src is markedly increased in gefitinib-resistant NSCLC (HCC827 GR) cells with MET amplification compared with that in the gefitinib-sensitive parental (HCC827) cells. In contrast, the extent of Src activation did not differ between gefitinib-resistant NSCLC (PC9/ZD) cells harboring the T790M mutation of EGFR and the corresponding gefitinib-sensitive parental (PC9) cells. This activation of Src in HCC827 GR cells was largely abolished by the MET-TKI PHA-665752 but was only partially inhibited by gefitinib, suggesting that Src activation is more dependent on MET signaling than on EGFR signaling in gefitinib-resistant NSCLC cells with MET amplification. Src inhibitors blocked Akt and Erk signaling pathways, resulting in both suppression of cell growth and induction of apoptosis, in HCC827 GR cells as effectively as did the combination of gefitinib and PHA-665752. Furthermore, Src inhibitor dasatinib inhibited tumor growth in HCC827 GR xenografts to a significantly greater extent than did treatment with gefitinib alone. These results provide a rationale for clinical targeting of Src in gefitinib-resistant NSCLC with MET amplification. ( Cancer Sci 2009)     

Ron kinase transphosphorylation sustains MET oncogene addiction

Receptors for the scatter factors HGF and MSP that are encoded by the MET and RON oncogenes are key players in invasive growth. Receptor cross-talk between Met and Ron occurs. Amplification of the MET oncogene results in kinase activation, deregulated expression of an invasive growth phenotype, and addiction to MET oncogene signaling (i.e., dependency on sustained Met signaling for survival and proliferation). Here we show that cancer cells addicted to MET also display constitutive activation of the Ron kinase. In human cancer cell lines coexpressing the 2 oncogenes, Ron is specifically transphosphorylated by activated Met. In contrast, Ron phosphorylation is not triggered in cells harboring constitutively active kinase receptors other than Met, including Egfr or Her2. Furthermore, Ron phosphorylation is suppressed by Met-specific kinase inhibitors (PHA-665752 or JNJ-38877605). Last, Ron phosphorylation is quenched by reducing cell surface expression of Met proteins by antibody-induced shedding. In MET-addicted cancer cells, short hairpin RNA-mediated silencing of RON expression resulted in decreased proliferation and clonogenic activity in vitro and tumorigenicity in vivo. Our findings establish that oncogene addiction to MET involves Ron transactivation, pointing to Ron kinase as a target for combinatorial cancer therapy.     

Single-agent and combination therapeutic strategies to inhibit hepatocyte growth factor/MET signaling in cancer

Receptor tyrosine kinases are often aberrantly activated in human malignancies and contribute to cancer development and progression. Specific receptor tyrosine kinase inhibitors have been shown to be clinically effective therapies in subsets of cancer patients with either hematologic or solid tumors. Activation of the hepatocyte growth factor (HGF)/MET signaling pathway has been found to play a critical role in oncogenesis, cancer metastasis, and drug resistance. These observations have led to the development of agents that can effectively inhibit HGF/MET signaling through direct inhibition of the receptor (anti-MET antibodies), through inactivation of its ligand HGF (AMG102, L2G7), by interfering with HGF binding to MET (NK4), or by inhibiting MET kinase activity (PHA-665752 and SU11274). Moreover, the combination of anti-MET therapeutic agents with either signal transduction inhibitors (ERBB family or mTOR inhibitors) or with cytotoxic chemotherapy has been evaluated in preclinical models. These studies provide insight into the rational development of combination therapeutic strategies that can be evaluated in clinical trials. This review will discuss different strategies of MET inhibition with a specific focus on combination therapeutic approaches.     

Met and c-Src cooperate to compensate for loss of epidermal growth factor receptor kinase activity in breast cancer cells

Breast cancers are not responsive to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI), although 30% of breast cancers overexpress EGFR. The mechanism of intrinsic resistance to EGFR TKIs in breast cancer is the focus of current studies. Here, we observed that EGFR remains tyrosine phosphorylated in breast cancer cells that proliferate in the presence of EGFR TKIs. In one such cell line, SUM229, inhibiting c-Src kinase activity with either a dominant-negative c-Src or a c-Src TKI decreased EGFR phosphorylation on Tyr(845), Tyr(992), and Tyr(1086) in the presence of EGFR TKIs. Conversely, overexpressing wild-type (wt) c-Src in the EGFR TKI-sensitive breast cancer cell line SUM149 increased EGFR kinase-independent EGFR tyrosine phosphorylation. In addition, in the presence of EGFR TKIs, inhibiting c-Src kinase activity decreased cell growth in SUM229 cells, and overexpressing wt-c-Src increased cell growth in SUM149 cells. We identified the receptor tyrosine kinase Met to be responsible for activating c-Src in SUM229 cells. Inhibiting Met kinase activity with a small molecule inhibitor decreased c-Src phosphorylation and kinase activation. In addition, inhibiting Met kinase activity in SUM229 cells decreased EGFR tyrosine phosphorylation and growth in the presence of EGFR TKIs. Stimulating Met kinase activity in SUM149 cells with hepatocyte growth factor increased EGFR tyrosine phosphorylation and cell growth in the presence of EGFR TKIs. These data suggest a Met/c-Src-mediated signaling pathway as a mediator of EGFR tyrosine phosphorylation and cell growth in the presence of EGFR TKIs.     

Oncogenic Met receptor induces ectopic structures in Xenopus embryos

When aberrantly expressed or activated, the Met receptor tyrosine kinase is involved in tumor invasiveness and metastasis. In this study, we have used the Xenopus embryonic system to define the role of various Met proximal-binding partners and downstream signaling pathways in regulating an induced morphogenetic event. We show that expression of an oncogenic derivative of the Met receptor (Tpr-Met) induces ectopic morphogenetic structures during Xenopus embryogenesis. Using variant forms of Tpr-Met that are engineered to recruit a specific signaling molecule of choice, we demonstrate that the sole recruitment of either the Grb2 or the Shc adaptor protein is sufficient to induce ectopic structures and anterior reduction, while the recruitment of PI-3Kinase (PI-3K) is necessary but not sufficient for this effect. In contrast, the recruitment of PLCgamma can initiate the induction, but fails to maintain or elongate supernumerary structures. Finally, evidence indicates that the Ras/Raf/MAPK pathway is necessary, but not sufficient to induce these structures. This study also emphasizes the importance of examining signaling molecules in the regulatory context that is provided by receptor/effector interactions when assessing a role in cell growth and differentiation.     

Oncogenic activation of the Met receptor tyrosine kinase fusion protein, Tpr-Met, involves exclusion from the endocytic degradative pathway

Multiple mechanisms of dysregulation of receptor tyrosine kinases (RTKs) are observed in human cancers. In addition to gain-of-function, loss of negative regulation also contributes to oncogenic activation of RTKs. Negative regulation of many RTKs involves their internalization and degradation in the lysosome, a process regulated through ubiquitination. RTK oncoproteins activated following chromosomal translocation, are no longer transmembrane proteins, and are predicted to escape lysosomal degradation. To test this, we used the Tpr-Met oncogene, generated following chromosomal translocation of the hepatocyte growth factor receptor (Met). Unlike Met, Tpr-Met is localized in the cytoplasm and also lacks the binding site for Cbl ubiquitin ligases. We determined whether subcellular localization of Tpr-Met, and/or loss of its Cbl-binding site, is important for oncogenic activity. Presence of a Cbl-binding site and ubiquitination of cytosolic Tpr-Met oncoproteins does not alter their transforming activity. In contrast, plasma membrane targeting allows Tpr-Met to enter the endocytic pathway, and Tpr-Met transforming activity as well as protein stability are decreased in a Cbl-dependent manner. We show that transformation by Tpr-Met is in part dependent on its ability to escape normal downregulatory mechanisms. This provides a paradigm for many RTK oncoproteins activated following chromosomal translocation.     

From Tpr-Met to Met, tumorigenesis and tubes

The receptor for hepatocyte growth factor (HGF)/scatter factor (SF), Met, controls a program of invasive epithelial growth through the coordination of cell proliferation and survival, cell migration and epithelial morphogenesis. This process is important during embryogenesis and for organ regeneration in the adult. However, when deregulated the HGF/SF-Met signaling axis contributes to tumorigenesis and metastasis. Studies on the oncogenic activation of the Met receptor have shed light on the molecular mechanisms underlying the oncogenic activation of receptor tyrosine kinase (RTKs). More than a decade ago, work on the Met related oncogene, Tpr-Met, revealed the mechanism for activation of RTK-derived oncogenes generated following chromosomal translocation. More recently, studies on the mechanisms of downregulation of the Met RTK highlight a role for loss of downregulation in RTK oncogenic activation.     

Treatment of human pre-B acute lymphoblastic leukemia with the Aurora kinase inhibitor PHA-739358 (Danusertib)

ABSTRACT: BACKGROUND: Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemias (Ph-positive ALL) with clinically approved inhibitors of the Bcr/Abl tyrosine kinase frequently results in the emergence of a leukemic clone carrying the T315I mutation in Bcr/Abl, which confers resistance to these drugs. PHA-739358, an Aurora kinase inhibitor, was reported to inhibit the Bcr/Abl T315I mutant in CML cells but no preclinical studies have examined this in detail in human ALL. RESULTS: We compared the sensitivity of human Bcr/Abl T315I, Bcr/Abl wild type and non-Bcr/Abl ALL cells to this drug. PHA-739358 inhibited proliferation and induced apoptosis independently of Bcr/Abl, the T315I mutation, or presence of the tumor suppressor p53, but the degree of effectiveness varied between different ALL samples. Since short-term treatment with a single dose of drug only transiently inhibited proliferation, we tested combination treatments of PHA-739358 with the farnesyltransferase inhibitor Lonafarnib, with vincristine and with dasatinib. All combinations reduced viability and cell numbers compared to treatment with a single drug. Clonogenic assays showed that 25 nM PHA-739358 significantly reduced the colony growth potential of Ph-positive ALL cells, and combined treatment with a second drug abrogated colony growth in this assay. PHA-739358 further effectively blocked Bcr/Abl tyrosine kinase activity and Aurora kinase B in vivo, and mice transplanted with human Bcr/Abl T315I ALL cells treated with a 3x 7-day cycle of PHA-739358 as mono-treatment had significantly longer survival. CONCLUSIONS: PHA-739358 represents an alternative drug for the treatment of both Ph-positive and negative ALL, although combined treatment with a second drug may be needed to eradicate the leukemic cells.     

Targeting MET by Tyrosine Kinase Inhibitor Suppresses Growth and Invasion of Nasopharyngeal Carcinoma Cell Lines

Nasopharyngeal carcinoma (NPC) represents a common cancer in endemic areas with high invasive and metastatic potential. It is now known that the HGF-MET signaling pathway plays an important role in mediating the invasive growth of many different types of cancer, including head and neck squamous cell carcinoma. HGF has been shown to stimulate NPC cell growth and invasion in cell line model. The current study aims at demonstrating the effect of MET inhibition by small molecule tyrosine kinase inhibitor PHA665752 on the growth and invasive potential of NPC cell lines. NPC cell lines were used for immunohistochemistry for the MET protein, as well as western blot analysis on MET together with its downstream cascade signaling proteins after treatment with PHA665752. The effect on cell growth, migration and invasion after PHA665752 treatment was also studied. MET inhibition by PHA665752 resulted in highly significant inhibition on NPC cell growth, migration and invasion in vitro. Down-regulation of phospho-MET, phospho-Akt, phospho-MAPK, phospho-STAT3, cyclin D1, β-catenin and PCNA was detected in NPC cells after PHA665752 treatment. MET inhibition with tyrosine kinase inhibitor resulted in suppression of NPC cell growth and invasive potential via down-regulation of a variety of signaling onco-proteins. MET is an important therapeutic target for NPC that warrants further studies and clinical trials.     

晚期非小细胞肺癌靶向治疗进展与展望:聚焦小分子酪氨酸激酶抑制剂

目前晚期非小细胞肺癌的治疗已经迈入靶向时代并且发展迅速,药物不断推陈出新.小分子酪氨酸激酶抑制剂占据了其中最大的一块版图,它们往往有明确的分子靶标作为疗效预测因素,在特定分子分型的患者中表现出卓越的疗效,因此成为靶向治疗的典型代表.表皮生长因子酪氨酸激酶抑制剂厄洛替尼、吉非替尼、埃克替尼和间变性淋巴瘤激酶酪氨酸激酶抑制剂克唑替尼带来了里程碑式的进步.而近年来新一代酪氨酸激酶抑制剂在上述两类药物获得性耐药患者中又取得了巨大的成功,同时新的治疗靶点也不断涌现.本文就此对重要的药物和临床研究进行了梳理和总结,并对未来的发展做出展望.     

Activating mutations in the Met receptor overcome the requirement for autophosphorylation of tyrosines crucial for wild type signaling.

Mutations in Met have been identified in human cancer, and we have previously shown that these mutations deregulate the enzymatic activity of this tyrosine kinase receptor, thereby unleashing its oncogenic potential. Signal transduction via wild type Met has been shown to require the autophosphorylation of two tyrosine doublets; Y8,9 which functions to enhance enzymatic activity, and Y14,15 which provides docking sites for signaling molecules, and in the present investigation we examine the importance of these residues for signaling via mutationally activated Met. We find that activating mutations introduced into a membrane-spanning Met receptor circumvent the normally stringent requirement for Y8,9 phosphorylation, and do so in a largely ligand-dependent fashion. Similarly, activating mutations introduced into a constitutively dimerized cytoplasmic form of Met (i.e. Tpr-Met) facilitate its autophosphorylation and oncogenic activity in the absence of Y8,9 phosphorylation. We also find that activating mutations allow a membrane-spanning Met receptor to overcome the requirement for the Y14,15 phosphorylation in a manner which is largely ligand-independent. These findings support a model whereby activating mutations stabilize an active conformation of the Met kinase via a mechanism which can function independently of Y8,9 autophosphorylation and suggest that signaling via wild type Met and mutationally activated Met may proceed through distinct pathways.     

Mice transgenic for NPM-ALK develop non-Hodgkin lymphomas

BACKGROUND: The t(2;5)(p23;q35) translocation is associated with a high percentage of anaplastic large-cell lymphomas (ALCL) of T- or null-cell phenotype. The translocation produces an 80 kDa hyperphosphorylated chimeric protein (p80) derived from the fusion of the anaplastic lymphoma kinase (ALK) with nucleophosmin (NPM). The NPM-ALK chimeric protein is an activated tyrosine kinase that has been shown to be a potent oncogene and presumably plays a causative role in lymphomagenesis. MATERIALS AND METHODS: A transgenic mouse line was generated, where the human NPM-ALK cDNA is driven by the lck promoter conferring transgene expression to early T-cells. RESULTS: Mice rapidly developed large cell lymphoblastic lymphomas with a median latency of 8 weeks, primarily involving the thymus, with lymph node as well as histologically evident extranodal organ infiltration by large tumor cells. CONCLUSION: The transgenic approach described provides direct evidence for the strong transforming potential of NPM-ALK in T-cells and furthermore represents a system for the analysis of the oncogenic events mediated by NPM-ALK in vivo, which might be instrumental in the development of tyrosine kinase inhibitor therapies of potential clinical use.     

PHA-680632, a novel Aurora kinase inhibitor with potent antitumoral activity.

PURPOSE: Aurora kinases play critical roles during mitosis in chromosome segregation and cell division. The aim of this study was to determine the preclinical profile of a novel, highly selective Aurora kinase inhibitor, PHA-680632, as a candidate for anticancer therapy. EXPERIMENTAL DESIGN: The activity of PHA-680632 was assayed in a biochemical ATP competitive kinase assay. A wide panel of cell lines was evaluated for antiproliferative activity. Cell cycle analysis. Immunohistochemistry, Western blotting, and Array Scan were used to follow mechanism of action and biomarker modulation. Specific knockdown of the targets by small interfering RNA was followed to validate the observed phenotypes. Efficacy was determined in different xenograft models and in a transgenic animal model of breast cancer. RESULTS: PHA-680632 is active on a wide range of cancer cell lines and shows significant tumor growth inhibition in different animal tumor models at well-tolerated doses. The mechanism of action of PHA-680632 is in agreement with inhibition of Aurora kinases. Histone H3 phosphorylation in Ser10 is mediated by Aurora B kinase, and our kinetic studies on its inhibition by PHA-680632 in vitro and in vivo show that phosphorylation of histone H3 is a good biomarker to follow activity of PHA-680632. CONCLUSIONS: PHA-680632 is the first representative of a new class of Aurora inhibitors with a high potential for further development as an anticancer therapeutic. On treatment, different cell lines respond differentially, suggesting the absence of critical cell cycle checkpoints that could be the basis for a favorable therapeutic window.