Hartmut Koeppen

Genentech, San Francisco, California, United States

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Publications (91)951.26 Total impact

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    ABSTRACT: The development of human cancer is a multistep process characterized by the accumulation of genetic and epigenetic alterations that drive or reflect tumour progression. These changes distinguish cancer cells from their normal counterparts, allowing tumours to be recognized as foreign by the immune system. However, tumours are rarely rejected spontaneously, reflecting their ability to maintain an immunosuppressive microenvironment. Programmed death-ligand 1 (PD-L1; also called B7-H1 or CD274), which is expressed on many cancer and immune cells, plays an important part in blocking the 'cancer immunity cycle' by binding programmed death-1 (PD-1) and B7.1 (CD80), both of which are negative regulators of T-lymphocyte activation. Binding of PD-L1 to its receptors suppresses T-cell migration, proliferation and secretion of cytotoxic mediators, and restricts tumour cell killing. The PD-L1-PD-1 axis protects the host from overactive T-effector cells not only in cancer but also during microbial infections. Blocking PD-L1 should therefore enhance anticancer immunity, but little is known about predictive factors of efficacy. This study was designed to evaluate the safety, activity and biomarkers of PD-L1 inhibition using the engineered humanized antibody MPDL3280A. Here we show that across multiple cancer types, responses (as evaluated by Response Evaluation Criteria in Solid Tumours, version 1.1) were observed in patients with tumours expressing high levels of PD-L1, especially when PD-L1 was expressed by tumour-infiltrating immune cells. Furthermore, responses were associated with T-helper type 1 (TH1) gene expression, CTLA4 expression and the absence of fractalkine (CX3CL1) in baseline tumour specimens. Together, these data suggest that MPDL3280A is most effective in patients in which pre-existing immunity is suppressed by PD-L1, and is re-invigorated on antibody treatment.
    Nature 11/2014; 515(7528):563-7. · 42.35 Impact Factor
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    ABSTRACT: Breast cancers are categorized into three subtypes based on protein expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2/ERBB2). Patients enroll onto experimental clinical trials based on ER, PR, and HER2 status and, as receptor status is prognostic and defines treatment regimens, central receptor confirmation is critical for interpreting results from these trials. Patients enrolling onto experimental clinical trials in the metastatic setting often have limited available archival tissue that might better be used for comprehensive molecular profiling rather than slide-intensive reconfirmation of receptor status. We developed a Random Forests-based algorithm using a training set of 158 samples with centrally confirmed IHC status, and subsequently validated this algorithm on multiple test sets with known, locally determined IHC status. We observed a strong correlation between target mRNA expression and IHC assays for HER2 and ER, achieving an overall accuracy of 97 and 96 %, respectively. For determining PR status, which had the highest discordance between central and local IHC, incorporation of expression of co-regulated genes in a multivariate approach added predictive value, outperforming the single, target gene approach by a 10 % margin in overall accuracy. Our results suggest that multiplexed qRT-PCR profiling of ESR1, PGR, and ERBB2 mRNA, along with several other subtype associated genes, can effectively confirm breast cancer subtype, thereby conserving tumor sections and enabling additional biomarker data to be obtained from patients enrolled onto experimental clinical trials.
    Breast Cancer Research and Treatment 10/2014; · 4.47 Impact Factor
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    ABSTRACT: Mesothelin (MSLN) is an attractive target for antibody-drug conjugate therapy because it is highly expressed in various epithelial cancers, with normal expression limited to non-dividing mesothelia. We generated novel anti-mesothelin antibodies and conjugated an internalizing one (7D9) to the microtubule-disrupting drugs monomethyl auristatin E (MMAE) and MMAF, finding the most effective to be MMAE with a lysosomal protease-cleavable valine-citrulline linker. The humanized (h7D9.v3) version, alphaMSLN-MMAE, specifically targeted mesothelin-expressing cells and inhibited their proliferation with an IC50 of 0.3nM. Because the anti-tumor activity of an anti-mesothelin immunotoxin (SS1P) in transfected mesothelin models did not translate to the clinic, we carefully selected in vivo efficacy models endogenously expressing clinically relevant levels of mesothelin, after scoring mesothelin levels in ovarian, pancreatic and mesothelioma tumors by immunohistochemistry. We found that endogenous mesothelin in cancer cells is upregulated in vivo and identified two suitable xenograft models for each of these three indications. A single dose of alphaMSLN-MMAE profoundly inhibited or regressed tumor growth in a dose-dependent manner in all six models, including two patient-derived tumor xenografts. The robust and durable efficacy of alphaMSLN-MMAE in preclinical models of ovarian, mesothelioma and pancreatic cancers justifies the ongoing phase I clinical trial.
    Molecular Cancer Therapeutics 09/2014; · 5.60 Impact Factor
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    ABSTRACT: Molecularly-targeted drug therapies have revolutionized cancer treatment, however, resistance remains a major limitation to their overall efficacy. Epithelial to mesenchymal transition (EMT) has been linked to acquired resistance to tyrosine kinase inhibitors (TKIs), independent of mutational resistance mechanisms. AXL is a receptor tyrosine kinase (RTK) associated with EMT that has been implicated in drug resistance, and has emerged as a candidate therapeutic target. Across 643 human cancer cell lines that were analyzed, elevated AXL was strongly associated with a mesenchymal phenotype, particularly in triple negative breast cancer and non-small cell lung cancer. In an unbiased screen of small molecule inhibitors of cancer-relevant processes, we discovered that AXL inhibition was specifically synergistic with anti-mitotic agents in killing cancer cells that had undergone EMT and demonstrated associated TKI resistance. However, we did not find that AXL inhibition alone could overcome acquired resistance to EGFR TKIs in the EMT setting, as previously reported. These findings reveal a novel co-treatment strategy for tumors displaying mesenchymal features that otherwise render them treatment-refractory.
    Cancer Research 08/2014; · 9.28 Impact Factor
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    ABSTRACT: Pancreatic adenocarcinoma (PDAC) is a major unmet medical need and a deeper understanding of molecular drivers is needed to advance therapeutic options for patients. We report here that p21-activated kinase 1 (PAK1) is a central node in PDAC cells downstream of multiple growth factor signaling pathways, including hepatocyte growth factor (HGF) and MET receptor tyrosine kinase. PAK1 inhibition blocks signaling to cytoskeletal effectors and tumor cell motility driven by HGF/MET. MET antagonists, such as onartuzumab and crizotinib, are currently in clinical development. Given that even highly effective therapies have resistance mechanisms, we show that combination with PAK1 inhibition overcomes potential resistance mechanisms mediated either by activation of parallel growth factor pathways or direct amplification of PAK1. Inhibition of PAK1 attenuated in vivo tumor growth and metastasis in a model of pancreatic adenocarcinoma. In human tissues, PAK1 is highly expressed in a proportion of PDAC (33% IHC score 2 or 3; n = 304) and its expression is significantly associated with MET positivity (p < 0.0001) and linked to a widespread metastatic pattern in patients (p = 0.067). Taken together, our results provide evidence for a functional role of MET/PAK1 signaling in pancreatic adenocarcinoma and support further characterization of therapeutic inhibitors in this indication.
    The Journal of Pathology 07/2014; · 7.33 Impact Factor
  • Stephen P Hack, Jean-Marie Bruey, Hartmut Koeppen
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    ABSTRACT: Aberrant activation of the HGF/MET signaling axis has been strongly implicated in the malignant transformation and progression of gastroesophageal cancer (GEC). MET receptor overexpression in tumor samples from GEC patients has been consistently correlated with an aggressive metastatic phenotype and poor prognosis. In preclinical GEC models, abrogation of HGF/MET signaling has been shown to induce tumor regression as well as inhibition of metastatic dissemination. Promising clinical results in patient subsets in which MET is overexpressed have spurned several randomized studies of HGF/MET-directed agents, including two pivotal global Phase III trials. Available data highlight the need for predictive biomarkers in order to select patients most likely to benefit from HGF/MET inhibition. In this review, we discuss the current knowledge of mechanisms of MET activation in GEC, the current status of the clinical evaluation of MET-targeted therapies in GEC, characteristics of ongoing randomized GEC trials and the associated efforts to identify and validate biomarkers. We also discuss the considerations and challenges for HGF/MET inhibitor drug development in the GEC setting.
    Oncotarget 05/2014; 5(10):2866-80. · 6.63 Impact Factor
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    ABSTRACT: Aberrant activation of the HGF/MET signaling axis has been strongly implicated in the malignant transformation and progression of gastroesophageal cancer (GEC). MET receptor overexpression in tumor samples from GEC patients has been consistently correlated with an aggressive metastatic phenotype and poor prognosis. In preclinical GEC models, abrogation of HGF/MET signaling has been shown to induce tumor regression as well as inhibition of metastatic dissemination. Promising clinical results in patient subsets in which MET is overexpressed have spurned several randomized studies of HGF/MET-directed agents, including two pivotal global Phase III trials. Available data highlight the need for predictive biomarkers in order to select patients most likely to benefit from HGF/MET inhibition. In this review, we discuss the current knowledge of mechanisms of MET activation in GEC, the current status of the clinical evaluation of MET-targeted therapies in GEC, characteristics of ongoing randomized GEC trials and the associated efforts to identify and validate biomarkers. We also discuss the considerations and challenges for HGF/MET inhibitor drug development in the GEC setting.
    Oncotarget 05/2014; · 6.63 Impact Factor
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    ABSTRACT: In a recent Phase II study of onartuzumab (MetMAb), patients whose non-small-cell lung cancer (NSCLC) tissue scored as positive for MET protein by immunohistochemistry (IHC) experienced a significant benefit with onartuzumab plus erlotinib (O+E) versus erlotinib. We describe development and validation of a standardized MET IHC assay and retrospectively evaluate multiple biomarkers as predictors of patient benefit. Biomarkers related to MET and/or epidermal growth factor receptor (EGFR) signaling were measured by IHC, FISH, quantitative reverse transcription PCR, mutation detection techniques and ELISA. A positive correlation between IHC, Western blotting, and MET mRNA expression was observed in NSCLC cell lines/tissues. An IHC scoring system of MET expression taking proportional and intensity-based thresholds into consideration was applied in an analysis of the Phase II study and resulted in the best differentiation of outcomes. Further analyses revealed a non-significant overall survival (OS) improvement with O+E in patients with high MET copy number (mean ≥5 copies/cell by FISH), however benefit was maintained in "MET IHC-positive"/MET FISH-negative patients (HR 0.37; P = 0.01). MET, EGFR, amphiregulin, epiregulin, or HGF mRNA expression did not predict a significant benefit with onartuzumab; a non-significant OS improvement was observed in patients with high tumor MET mRNA levels (HR 0.59; P = 0.23). Patients with low baseline plasma hepatocyte growth factor (HGF) exhibited a HR for OS of 0.519 (P = 0.09) in favor of onartuzumab treatment. MET IHC remains the most robust predictor of OS and PFS benefit from O+E relative to all examined exploratory markers.
    Clinical Cancer Research 03/2014; · 8.19 Impact Factor
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    ABSTRACT: The success of precision oncology relies on accurate and sensitive molecular profiling. The Ion AmpliSeq Cancer Panel, a targeted enrichment method for next-generation sequencing (NGS) using the Ion Torrent platform, provides a fast, easy, and cost-effective sequencing workflow for detecting genomic "hotspot" regions that are frequently mutated in human cancer genes. Most recently, the U.K. has launched the AmpliSeq sequencing test in its National Health Service. This study aimed to evaluate the clinical application of the AmpliSeq methodology.Methods.We used 10 ng of genomic DNA from formalin-fixed, paraffin-embedded human colorectal cancer (CRC) tumor specimens to sequence 46 cancer genes using the AmpliSeq platform. In a validation study, we developed an orthogonal NGS-based resequencing approach (SimpliSeq) to assess the AmpliSeq variant calls.Results.Validated mutational analyses revealed that AmpliSeq was effective in profiling gene mutations, and that the method correctly pinpointed "true-positive" gene mutations with variant frequency >5% and demonstrated high-level molecular heterogeneity in CRC. However, AmpliSeq enrichment and NGS also produced several recurrent "false-positive" calls in clinically druggable oncogenes such as PIK3CA.Conclusion.AmpliSeq provided highly sensitive and quantitative mutation detection for most of the genes on its cancer panel using limited DNA quantities from formalin-fixed, paraffin-embedded samples. For those genes with recurrent "false-positive" variant calls, caution should be used in data interpretation, and orthogonal verification of mutations is recommended for clinical decision making.
    The Oncologist 03/2014; · 4.54 Impact Factor
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    ABSTRACT: Tailoring cancer treatment to tumor molecular characteristics promises to make personalized medicine a reality. However, reliable genetic profiling of archived clinical specimens has been hindered by limited sensitivity and high false positive rates. Here, we describe a novel methodology, MMP-seq, which enables sensitive and specific high-throughput, high content genetic profiling in archived clinical samples. We first validated MMP-seq's technical performance in 66 cancer cell lines and a Latin square cross-dilution of known somatic mutations. We next characterized the performance of MMP-seq in 17 formalin-fixed paraffin embedded (FFPE) clinical samples using matched fresh frozen (FF) tissue from the same tumors as benchmarks. To demonstrate the potential clinical utility of our methodology, we profiled FFPE tumor samples from 73 endometrial cancer patients. We demonstrated that MMP-seq enabled rapid and simultaneous profiling of a panel of 88 cancer genes in 48 samples, and detected variants at frequencies as low as 0.4%. We identified DNA degradation and deamination as the main error sources and developed practical and robust strategies for mitigating these issues, and dramatically reduced the false positive rate. Applying MMP-seq to a cohort of endometrial tumor samples identified extensive, potentially actionable alterations in the PI3K and RAS pathways, including novel PIK3R1 hotspot mutations that may disrupt negative regulation of PIK3CA. MMP-seq provides a robust solution for comprehensive, reliable and high-throughput genetic profiling of clinical tumor samples, paving the way for the incorporation of genomic-based testing into clinical investigation and practice.
    Clinical Cancer Research 02/2014; · 8.19 Impact Factor
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    ABSTRACT: Patients with newly diagnosed, early stage estrogen receptor positive (ER+) breast cancer often show disease free survival in excess of five years following surgery and systemic adjuvant therapy. An important question is whether diagnostic tumor tissue from the primary lesion offers an accurate molecular portrait of the cancer post recurrence and thus may be used for predictive diagnostic purposes for patients with relapsed, metastatic disease. As the class I phosphatidylinositol 3' kinase (PI3K) pathway is frequently activated in ER+ breast cancer and has been linked to acquired resistance to hormonal therapy, we hypothesized pathway status could evolve over time and treatment. Biomarker analyses were conducted on matched, asynchronous primary and metastatic tumors from 77 patients with ER+ breast cancer. We examined whether PIK3CA and AKT1 alterations or PTEN and Ki67 levels showed differences between primary and metastatic samples. We also sought to look more broadly at gene expression markers reflective of proliferation, molecular subtype, and key receptors and signaling pathways using an mRNA analysis platform developed on the Fluidigm BioMark™ microfluidics system to measure the relative expression of 90 breast cancer related genes in formalin-fixed paraffin-embedded (FFPE) tissue. Application of this panel of biomarker assays to matched tumor pairs showed a high concordance between primary and metastatic tissue, with generally few changes in mutation status, proliferative markers, or gene expression between matched samples. The collection of assays described here has been optimized for FFPE tissue and may have utility in exploratory analyses to identify patient subsets responsive to targeted therapies.
    PLoS ONE 02/2014; 9(2):e88401. · 3.53 Impact Factor
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    ABSTRACT: Structure based methods were used to design a potent and highly selective group-II PAK inhibitor with a novel binding mode, compound 17. Hydrophobic interactions within a lipophilic pocket past the methionine gatekeeper of group-II PAKs approached by these type 1½ binders was found to be important for improving potency. A structure-based hypothesis and strategy for achieving selectivity over group-I-PAKs, and the broad kinome, based on unique flexibility of this lipophilic pocket, is presented. A concentration dependent decrease in tumor cell migration and invasion in two triple-negative breast cancer cell lines was observed with compound 17.
    Journal of Medicinal Chemistry 01/2014; · 5.48 Impact Factor
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    ABSTRACT: We sought to identify predictive biomarkers for a novel nicotinamide phosphoribosyltransferase (NAMPT) inhibitor. We use a NAMPT inhibitor, GNE-617, to evaluate nicotinic acid (NA) rescue status in a panel of over 400 cancer cell lines. Using correlative analysis and RNAi, we identify a specific biomarker for NA rescue status. We next determine the mechanism of regulation of expression of the biomarker. Finally, we develop IHC and DNA methylation assays and evaluate cancer tissue for prevalence of the biomarker across indications. Nicotinate phosphoribosyltransferase (NAPRT1) is necessary for NA rescue and its expression is the major determinant of rescue status. We demonstrate that NAPRT1 promoter methylation accounts for NAPRT1 deficiency in cancer cells, and NAPRT1 methylation is predictive of rescue status in cancer cell lines. Bisulfite NGS mapping of the NAPRT1 promoter identified tumor specific sites of NAPRT1 DNA methylation and enabled development of a quantitative methylation specific PCR (QMSP) assay suitable for use on archival formalin fixed paraffin embedded tumor tissue. Tumor-specific promoter hyper-methylation of NAPRT1 inactivates one of two NAD salvage pathways, resulting in synthetic lethality with the co-administration of a NAMPT inhibitor. NAPRT1 expression is lost due to promoter hyper-methylation in most cancer types evaluated at frequencies ranging from 5 to 65%. NAPRT1-specific IHC or DNA methylation assays can be used on archival formalin paraffin embedded cancer tissue to identify patients likely to benefit from co-administration of a Nampt inhibitor and NA.
    Clinical Cancer Research 10/2013; · 8.19 Impact Factor
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    Adrian M Jubb, Hartmut Koeppen, Jorge S Reis-Filho
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    ABSTRACT: The rapid pace of drug discovery and drug development in oncology, immunology and ophthalmology brings new challenges; the efficient and effective development of new targeted drugs will require more detailed molecular classifications of histologically homogeneous diseases that show heterogeneous clinical outcomes. To this end single companion diagnostics for specific drugs will be replaced by multiplex diagnostics for entire therapeutic areas, preserving tissue and enabling rapid molecular taxonomy. The field will move away from the development of new molecular entities as single agents, to which resistance is common. Instead a detailed understanding of the pathological mechanisms of resistance, in patients and in preclinical models, will be key to the validation of scientifically rational and clinically effective drug combinations. To remain at the heart of disease diagnosis and appropriate management, pathologists must evolve into translational biologists and biomarker scientists. Herein, we provide examples of where this metamorphosis has already taken place, in lung cancer and melanoma, where the transformation has yet to begin, in the use of immunotherapies for ophthalmology and oncology, and where there is fertile soil for a revolution in treatment, in efforts to classify glioblastoma and personalize treatment. The challenges of disease heterogeneity, the regulatory environment and adequate tissue are ever present, but these too are being overcome in dedicated academic centers. In summary, the tools necessary to overcome the "whens" and "ifs" of the molecular revolution are in the hands of pathologists today, it is a matter of standardization, training and leadership to bring these into routine practice and translate science into patient benefit. This Annual Review Issue of the Journal of Pathology highlights the central role for pathology in modern drug discovery and development.
    The Journal of Pathology 10/2013; · 7.33 Impact Factor
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    Hartmut Koeppen, Sandra Rost, Robert L Yauch
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    ABSTRACT: Activation of the MET signaling pathway is critical in regulating multiple cellular processes underlying tumourigenic growth and has represented an attractive target for therapeutic intervention in cancer. Early stage clinical studies of multiple agents targeting this pathway have been undertaken, frequently in unselected patient cohorts with variable results. Promising data in patient subgroups in these studies indicate the need for predictive biomarkers to identify the patients most likely to benefit from these therapies. In this review, we discuss the current knowledge of mechanisms of MET activation, the status of the clinical evaluation of MET-targeted therapies, the associated efforts to identify and validate biomarkers and the considerations and challenges for potential development of companion diagnostics.
    The Journal of Pathology 09/2013; · 7.33 Impact Factor
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    ABSTRACT: The phosphatidylinositol 3-kinase (PI3K) pathway is a central mediator of vascular endothelial growth factor (VEGF)-driven angiogenesis. The discovery of small molecule inhibitors that selectively target PI3K or PI3K and mammalian target of rapamycin (mTOR) provides an opportunity to pharmacologically determine the contribution of these key signaling nodes in VEGF-A-driven tumor angiogenesis in vivo. This study used an array of micro-vascular imaging techniques to monitor the antivascular effects of selective class I PI3K, mTOR, or dual PI3K/mTOR inhibitors in colorectal and prostate cancer xenograft models. Micro-computed tomography (micro-CT) angiography, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), vessel size index (VSI) MRI, and DCE ultrasound (DCE-U/S) were employed to quantitatively evaluate the vascular (structural and physiological) response to these inhibitors. GDC-0980, a dual PI3K/mTOR inhibitor, was found to reduce micro-CT angiography vascular density, while VSI MRI demonstrated a significant reduction in vessel density and an increase in mean vessel size, consistent with a loss of small functional vessels and a substantial antivascular response. DCE-MRI showed that GDC-0980 produces a strong functional response by decreasing the vascular permeability/perfusion-related parameter, K (trans). Interestingly, comparable antivascular effects were observed for both GDC-980 and GNE-490 (a selective class I PI3K inhibitor). In addition, mTOR-selective inhibitors did not affect vascular density, suggesting that PI3K inhibition is sufficient to generate structural changes, characteristic of a robust antivascular response. This study supports the use of noninvasive microvascular imaging techniques (DCE-MRI, VSI MRI, DCE-U/S) as pharmacodynamic assays to quantitatively measure the activity of PI3K and dual PI3K/mTOR inhibitors in vivo.
    Neoplasia (New York, N.Y.) 07/2013; 15(7):694-711. · 5.40 Impact Factor
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    ABSTRACT: PURPOSE: The aim of this study was to identify conserved pharmacodynamic and potential predictive biomarkers of response to anti-VEGF therapy using gene expression profiling in preclinical tumor models and in patients. EXPERIMENTAL DESIGN: Surrogate markers of VEGF inhibition (VEGF dependent genes or VDV) were identified by profiling gene expression changes induced in response to VEGF blockade in preclinical tumor models and in human biopsies from patients treated with anti-VEGF monoclonal antibodies. The potential value of VDV genes as candidate predictive biomarkers was tested by correlating high or low VDV gene expression levels in pre-treatment clinical samples with the subsequent clinical efficacy of bevacizumab (anti-VEGF) containing therapy. RESULTS: We show that VEGF-dependent vasculature (VDV) genes, including direct and more distal VEGF downstream endothelial targets, enable detection of VEGF signaling inhibition in mouse tumor models and human tumor biopsies. Retrospective analyses of clinical trial data indicates that patients with higher VDV expression in pre-treatment tumor samples exhibited improved clinical outcome when treated with bevacizumab containing therapies. CONCLUSIONS: In this work we identified surrogate markers (VDV genes) for in vivo VEGF signaling in tumors and showed clinical data supporting a correlation between pre-treatment VEGF bioactivity and the subsequent efficacy of anti-VEGF therapy. We propose that VDV genes are candidate biomarkers with the potential to aid the selection of novel indications as well as patients likely to respond to anti-VEGF therapy. The data presented here define a diagnostic biomarker hypothesis based on translational research that warrants further evaluation in additional retrospective and prospective trials.
    Clinical Cancer Research 05/2013; · 8.19 Impact Factor
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    ABSTRACT: Preclinical data suggest that signalling through the HGF-MET pathway may confer resistance to BRAF inhibition in BRAF(V) (600E/K) melanoma. Therefore, blockade of HGF-MET signalling might be a valid therapeutic strategy, in combination with BRAF inhibition, in BRAF(V) (600E/K) melanoma. The aim of this study was to investigate the clinical relevance of these observations by evaluating the survival impact of MET expression in patients with BRAF(V) (600E/K) advanced melanoma treated with vemurafenib. Formalin-fixed tissue blocks were obtained of tumours from patients enrolled in the BRIM2 (n = 59) and BRIM3 (n = 150) trials of vemurafenib in advanced BRAF(V) (600E/K) melanoma. Immunohistochemistry for MET (SP44 rabbit monoclonal antibody) was performed with a highly validated assay and clinically validated scoring system. Pretreatment MET expression was frequent at the ≥1 + cutoff (BRIM3, 31%; BRIM2, 49%), but relatively infrequent at the ≥2 + cutoff (BRIM3, 9%; BRIM2, 19%). Retrospective subset analyses showed that, irrespective of the cutoff used or the treatment arm, MET expression did not show prognostic significance, in terms of objective response rate, progression-free survival, or overall survival. MET is expressed in a proportion of BRAF(V) (600E/K) advanced melanomas. Further analyses on appropriately powered subsets are needed to determine the prognostic and predictive significance of MET in vemurafenib-treated melanoma.
    Histopathology 04/2013; · 3.30 Impact Factor
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    ABSTRACT: Although K-Ras, Cdc42 and PAK4 signaling are commonly deregulated in cancer, only a few studies have sought to comprehensively examine the spectrum of phosphorylation-mediated signaling downstream of each of these key signaling nodes. In this study we completed a label-free quantitative analysis of oncogenic K-Ras, activated Cdc42 and PAK4-mediated phosphorylation signaling, and report relative quantitation of 2152 phosphorylated peptides on 1062 proteins. We define the overlap in phosphopeptides regulated by K-Ras, Cdc42, and PAK4, and find that perturbation of these signaling components affects phosphoproteins associated with microtubule depolymerization, cytoskeletal organization, and the cell cycle. These findings provide a resource for future studies to characterize novel targets of oncogenic K-Ras signaling and validate biomarkers of PAK4 inhibition.
    Molecular &amp Cellular Proteomics 04/2013; · 7.25 Impact Factor
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    ABSTRACT: Background Although remarkable clinical response rates in melanoma have been observed using vemurafenib or dabrafenib in patients with tumors carrying oncogenic mutations in BRAF, a substantial unmet medical need remains for the subset of patients with wild-type BRAF tumors.Methods To investigate the role of p21-activated kinases (PAKs) in melanoma, we determined PAK1 genomic copy number and protein expression for a panel of human melanoma tissues. PAK1 was inhibited in vitro and in vivo using RNA interference or PF-3758309 inhibitor treatment in a panel of melanoma cell lines with known BRAF and RAS (rat sarcoma) genotype to better understand its role in melanoma cell proliferation and migration. Tumorigenesis was assessed in vivo in female NCR nude mice and analyzed with cubic spline regression and area under the curve analyses. All statistical tests were two-sided.ResultsStrong cytoplasmic PAK1 protein expression was prevalent in melanomas (27%) and negatively associated with activating mutation of the BRAF oncogene (P < .001). Focal copy number gain of PAK1 at 11q13 was also observed in 9% of melanomas (n = 87; copy number ≥ 2.5) and was mutually exclusive with BRAF mutation (P < .005). Selective PAK1 inhibition attenuated signaling through mitogen-activated protein kinase (MAPK) as well as cytoskeleton-regulating pathways to modulate the proliferation and migration of BRAF wild-type melanoma cells. Treatment of BRAF wild-type melanomas with PF-3758309 PAK inhibitor decreased tumor growth for SK-MEL23 and 537MEL xenografts (91% and 63% inhibition, respectively; P < .001) and MAPK pathway activation in vivo.Conclusions Taken together, our results provide evidence for a functional role of PAK1 in BRAF wild-type melanoma and therapeutic use of PAK inhibitors in this indication.
    CancerSpectrum Knowledge Environment 03/2013; · 14.07 Impact Factor

Publication Stats

5k Citations
951.26 Total Impact Points


  • 2012–2014
    • Genentech
      • • Department of Discovery Oncology
      • • Department of Pathology
      San Francisco, California, United States
  • 2010–2011
    • University of Oxford
      • • Nuffield Division of Clinical Laboratory Sciences
      • • Weatherall Institute of Molecular Medicine
      Oxford, ENG, United Kingdom
    • University of Texas MD Anderson Cancer Center
      • Department of Hematopathology
      Houston, TX, United States
  • 2009
    • University of Texas Southwestern Medical Center
      • Department of Pathology
      Dallas, TX, United States
  • 2006
    • University of Leeds
      • Leeds Institute of Molecular Medicine (LIMM)
      Leeds, ENG, United Kingdom