Edmund Wilkes

Large-scale models of signal propagation in human cells derived from discovery phosphoproteomic data

Mass spectrometry is widely used to probe the proteome and its modifications in an untargeted manner, with unrivalled coverage. Applied to phosphoproteomics, it has tremendous potential to interrogate phospho-signalling and its therapeutic implications. However, this task is complicated by issues of undersampling of the phosphoproteome and challenges stemming from its high-content but low-sample-throughput nature. Hence, methods using such data to reconstruct signalling networks have been limited to restricted data sets and insights (for example, groups of kinases likely to be active in a sample). We propose a new method to handle high-content discovery phosphoproteomics data on perturbation by putting it in the context of kinase/phosphatase-substrate knowledge, from which we derive and train logic models. We show, on a data set obtained through perturbations of cancer cells with small-molecule inhibitors, that this method can study the targets and effects of kinase inhibitors, and reconcile insights obtained from multiple data sets, a common issue with these data.

Empirical inference of circuitry and plasticity in a kinase signaling network.

Significance Signaling pathways form complex networks of biochemical reactions, but inferring the topology of such networks and measuring how they are remodeled in disease is still challenging. Using MS, our study defined the circuitry and plasticity of a kinase signaling network de novo, with unprecedented depth and without prior assumptions of its topology. In addition, we observed a degree of stochasticity in how the network was remodeled upon chronic inhibition of phosphoinositide 3-kinase (PI3K) or mammalian target of rapamycin complexes 1/2 (mTORC1/2), suggesting that the initial condition of the system was not the only determinant of how cells become resistant to targeted therapies. These observations may have implications for our ability to predict the evolution of signaling networks during therapy to prevent the acquisition of resistance. Our understanding of physiology and disease is hampered by the difficulty of measuring the circuitry and plasticity of signaling networks that regulate cell biology, and how these relate to phenotypes. Here, using mass spectrometry-based phosphoproteomics, we systematically characterized the topology of a network comprising the PI3K/Akt/mTOR and MEK/ERK signaling axes and confirmed its biological relevance by assessing its dynamics upon EGF and IGF1 stimulation. Measuring the activity of this network in models of acquired drug resistance revealed that cells chronically treated with PI3K or mTORC1/2 inhibitors differed in the way their networks were remodeled. Unexpectedly, we also observed a degree of heterogeneity in the network state between cells resistant to the same inhibitor, indicating that even identical and carefully controlled experimental conditions can give rise to the evolution of distinct kinase network statuses. These data suggest that the initial conditions of the system do not necessarily determine the mechanism by which cancer cells become resistant to PI3K/mTOR targeted therapies. The patterns of signaling network activity observed in the resistant cells mirrored the patterns of response to several drug combination treatments, suggesting that the activity of the defined signaling network truly reflected the evolved phenotypic diversity.

Cross-species Proteomics Reveals Specific Modulation of Signaling in Cancer and Stromal Cells by Phosphoinositide 3-kinase (PI3K) Inhibitors

The tumor microenvironment plays key roles in cancer biology, but its impact on the regulation of signaling pathway activity in cancer cells has not been systemically investigated. We designed an analytical strategy that allows differential analysis of signaling between cancer and stromal cells present in tumor xenografts. We used this approach to investigate how in vivo growth conditions and PI3K inhibitors regulate pathway activities in both cancer and stromal cell populations. We found that, despite inducing more modest changes in protein expression, in vivo growing conditions extensively rewired protein kinase networks in cancer cells. As a result, different sets of phosphorylation sites were modulated by PI3K inhibitors in cancer cells growing in tumors relative to when these cells were in culture. The p110δ PI3K-selective compound CAL-101 (Idelalisib) did not inhibit markers of PI3K activity in cancer or stromal cells; however, unexpectedly, it induced phosphorylation on SQ motifs in both subpopulations of tumor cells in vivo but not in vitro. Thus, the interaction between cancer cells and the stroma modulated the ability of PI3K inhibitors to induce the activation of apoptosis in solid tumors. Our study provides proof-of-principle of a proteomics workflow for measuring signaling specifically in cancer and stromal cells and for investigating how cancer biochemistry is modulated in vivo.

A strong B cell response is part of the immune landscape in human high-grade serous ovarian metastases.

Purpose: In high-grade serous ovarian cancer (HGSOC), higher densities of both B cells and the CD8+ T-cell infiltrate were associated with a better prognosis. However, the precise role of B cells in the antitumor response remains unknown. As peritoneal metastases are often responsible for relapse, our aim was to characterize the role of B cells in the antitumor immune response in HGSOC metastases. Experimental Design: Unmatched pre and post-chemotherapy HGSOC metastases were studied. B-cell localization was assessed by immunostaining. Their cytokines and chemokines were measured by a multiplex assay, and their phenotype was assessed by flow cytometry. Further in vitro and in vivo assays highlighted the role of B cells and plasma cell IgGs in the development of cytotoxic responses and dendritic cell activation. Results: B cells mainly infiltrated lymphoid structures in the stroma of HGSOC metastases. There was a strong B-cell memory response directed at a restricted repertoire of antigens and production of tumor-specific IgGs by plasma cells. These responses were enhanced by chemotherapy. Interestingly, transcript levels of CD20 correlated with markers of immune cytolytic responses and immune complexes with tumor-derived IgGs stimulated the expression of the costimulatory molecule CD86 on antigen-presenting cells. A positive role for B cells in the antitumor response was also supported by B-cell depletion in a syngeneic mouse model of peritoneal metastasis. Conclusions: Our data showed that B cells infiltrating HGSOC omental metastases support the development of an antitumor response. Clin Cancer Res; 23(1); 250–62. ©2016 AACR.

NCK Associated Protein 1 Modulated by miRNA-214 Determines Vascular Smooth Muscle Cell Migration, Proliferation, and Neointima Hyperplasia.

Background MicroRNA miR‐214 has been implicated in many biological cellular functions, but the impact of miR‐214 and its target genes on vascular smooth muscle cell (VSMC) proliferation, migration, and neointima smooth muscle cell hyperplasia is unknown. Methods and Results Expression of miR‐214 was closely regulated by different pathogenic stimuli in VSMCs through a transcriptional mechanism and decreased in response to vascular injury. Overexpression of miR‐214 in serum‐starved VSMCs significantly decreased VSMC proliferation and migration, whereas knockdown of miR‐214 dramatically increased VSMC proliferation and migration. Gene and protein biochemical assays, including proteomic analyses, showed that NCK associated protein 1 (NCKAP1)—a major component of the WAVE complex that regulates lamellipodia formation and cell motility—was negatively regulated by miR‐214 in VSMCs. Luciferase assays showed that miR‐214 substantially repressed wild‐type but not the miR‐214 binding site mutated version of NCKAP1 3′ untranslated region luciferase activity in VSMCs. This result confirmed that NCKAP1 is the functional target of miR‐214 in VSMCs. NCKAP1 knockdown in VSMCs recapitulates the inhibitory effects of miR‐214 overexpression on actin polymerization, cell migration, and proliferation. Data from cotransfection experiments also revealed that inhibition of NCKAP1 is required for miR‐214–mediated lamellipodia formation, cell motility, and growth. Importantly, locally enforced expression of miR‐214 in the injured vessels significantly reduced NCKAP1 expression levels, inhibited VSMC proliferation, and prevented neointima smooth muscle cell hyperplasia after injury. Conclusions We uncovered an important role of miR‐214 and its target gene NCKAP1 in modulating VSMC functions and neointima hyperplasia. Our findings suggest that miR‐214 represents a potential therapeutic target for vascular diseases.

Approaches for measuring signalling plasticity in the context of resistance to targeted cancer therapies.

The ability of cells in multicellular organisms to respond to signals in their environment is critical for their survival, development and differentiation. Once differentiated and occupying their functional niche, cells need to maintain phenotypic stability while responding to diverse extracellular perturbations and environmental signals (such as nutrients, temperature, cytokines and hormones) in a co-ordinated manner. To achieve these requirements, cells have evolved numerous intracellular signalling mechanisms that confer on them the ability to resist, respond and adapt to external changes. Although fundamental to normal biological processes, as is evident from their evolutionary conservation, such mechanisms also allow cancer cells to evade targeted therapies, a problem of immediate clinical importance. In the present article, we discuss the role of signalling plasticity in the context of the mechanisms underlying both intrinsic and acquired resistance to targeted cancer therapies. We then examine the emerging analytical techniques and theoretical paradigms that are contributing to a greater understanding of signalling on a global and untargeted scale. We conclude with a discussion on how integrative approaches to the study of cell signalling have been used, and could be used in the future, to advance our understanding of resistance mechanisms to therapies that target the kinase signalling network.

Oxidative stress downstream of mTORC1 but not AKT causes a proliferative defect in cancer cells resistant to PI3K inhibition

Compounds targeting phosphatidylinositol-3-kinase/mammalian target of rapamycin (PI3K/mTOR) signaling are being investigated in multiple clinical settings, but drug resistance may reduce their benefit. Compound rechallenge after drug holidays can overcome such resistance, yet little is known about the impact of drug holidays on cell biochemistry. We found that PI3K inhibitor (PI3Ki)-resistant cells cultured in the absence of PI3Ki developed a proliferative defect, increased oxygen consumption and accumulated reactive oxygen species (ROS), leading to lactate production through hypoxia-inducible factor-1α. This metabolic imbalance was reversed by mammalian target of rapamycin complex 1 (mTORC1) inhibitors. Interestingly, neither AKT nor c-MYC was involved in mediating the metabolic phenotype, despite the latter contributing to resistant cells’ proliferation. These data suggest that an AKT-independent PI3K/mTORC1 axis operates in these cells. The excessive ROS hampered cell division, and the metabolic phenotype made resistant cells more sensitive to hydrogen peroxide and nutrient starvation. Thus, the proliferative defect of PI3Ki-resistant cells during drug holidays is caused by defective metabolic adaptation to chronic PI3K/mTOR pathway inhibition. This metabolic imbalance may open the therapeutic window for challenge with metabolic drugs during drug holidays.

Abstract P3-06-02: Characterization of resistance to the selective CDK4/6 inhibitor palbociclib in ER positive breast cancer

Background: Dysregulation of the cyclin D-CDK4/6-Rb axis occurs in a substantial proportion of ER-positive (ER+) breast cancers and has been linked with endocrine resistance. Adding the CDK4/6 inhibitor palbociclib to endocrine treatment has led to a substantial improvement of the outcome of patients with ER+ metastatic breast cancer. However, with the increasing clinical use, acquired resistance to palbociclib is merging as a new major clinical challenge. Methods: The ER+ cell lines T47D and MCF7 have been shown to be highly sensitive to treatment with palbociclib. Using long-term co-culture with increasing doses of Palbociclib, we generated MCF7 and T47D cell line clones with acquired resistance to Palbociclib. Three distinct resistant clones were selected for each cell line showing an IC50 shift from sensitive to resistant of approximately 300nM to 3uM for MCF7 and 400nM to 3.5uM for T47D, respectively. Resistant cell lines were characterized using RNA sequencing and mass spectrometry-based phosphoproteomics. Effects on selected target proteins (eg pAKT, pS6, pRB, RB or Cyclin D1) were confirmed using Western Blots. To modify resistance to palbociclib, a targeted in vitro drug-screen was performed using a range of inhibitors of the PI3K/AKT/mTOR and MEK pathways. Results: Western blot analysis of resistant cell lines demonstrated sustained down-regulation of Rb and phospho-Rb in response to palbociclib, which was reversible after discontinuation of palbociclib. Mass spectrometry identified >6,000 peptides across parental and resistant cells corresponding to 4,757 phospho-peptides and 5,337 phosphorylation sites. Pathway analysis suggested increased activity in the P3IK/AKT/mTOR pathway in resistant clones (including Akt1, p90S6K and mTOR), as well as changes in p53 and apoptotic regulation (e.g. phosphorylation of BAD). In addition, resistant clones showed multiple phosphorylation changes in the Rho/Rac pathway, suggesting changes in cytoskeletal organisation and a more invasive phenotype. Targeted drug screening showed a variable pattern across resistant clones with increased sensitivity to co-treatment of palbociclib with AKT inhibitors, PI3K alpha/delta inhibitors and/or MEK inhibitors in selected resistant clones, whereas pan-PI3K or PI3K beta/delta inhibitors showed limited efficacy in the selected clones. Conclusions: Phosphoproteomic analysis of palbociclib-resistant ER+ breast cancer cell lines demonstrated up-regulation of PI3K/AKT/mTOR and anti-apoptotic pathways. Resistant cell lines were sensitive to inhibition of PI3K/AKT/mTOR and/or MEK pathways with distinct patterns of activity across resistant clones suggesting that co-treatment of CDK4/6 inhibitors and PI3K/AKT and/or MEK inhibitors warrants further investigation as potential new therapeutic strategies in palbociclib resistance. Citation Format: Lenihan C, Bouchekioua-Bouzaghou K, Shia A, Wilkes E, Casado-Izquierdo1 P, Cutillas P, Schmid P. Characterization of resistance to the selective CDK4/6 inhibitor palbociclib in ER positive breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-06-02.

PHLDA1 Mediates Drug Resistance in Receptor Tyrosine Kinase-Driven Cancer

Summary Development of resistance causes failure of drugs targeting receptor tyrosine kinase (RTK) networks and represents a critical challenge for precision medicine. Here, we show that PHLDA1 downregulation is critical to acquisition and maintenance of drug resistance in RTK-driven cancer. Using fibroblast growth factor receptor (FGFR) inhibition in endometrial cancer cells, we identify an Akt-driven compensatory mechanism underpinned by downregulation of PHLDA1. We demonstrate broad clinical relevance of our findings, showing that PHLDA1 downregulation also occurs in response to RTK-targeted therapy in breast and renal cancer patients, as well as following trastuzumab treatment in HER2+ breast cancer cells. Crucially, knockdown of PHLDA1 alone was sufficient to confer de novo resistance to RTK inhibitors and induction of PHLDA1 expression re-sensitized drug-resistant cancer cells to targeted therapies, identifying PHLDA1 as a biomarker for drug response and highlighting the potential of PHLDA1 reactivation as a means of circumventing drug resistance.

Label-Free Phosphoproteomic Approach for Kinase Signaling Analysis

Phosphoproteomics is a powerful platform for the unbiased profiling of kinase-driven signaling pathways. Quantitation of phosphorylation can be performed by means of either labeling or label-free mass spectrometry (MS) methods. Because of their simplicity and universality, label-free methodology is gaining acceptance and popularity in molecular biology research. Analytical workflows for label-free quantification of phosphorylation, however, need to overcome several hurdles for the technique to be accurate and precise. These include the use of biochemical extraction procedures that efficiently and reproducibly isolate phosphopeptides from complex peptide matrices and an analytical strategy that can cope with missing MS/MS phosphopeptide spectra in a subset of the samples being compared. Testing the accuracy of the developed workflows is an essential prerequisite in the analysis of small molecules by MS, and this is achieved by constructing calibration curves to demonstrate linearity of quantification for each analyte. This level of analytical rigor is rarely shown in large-scale quantification of proteins using either label-based or label-free techniques. In this chapter we show an approach to test linearity of quantification of each phosphopeptide quantified by liquid chromatography (LC)-MS without the need to synthesize standards or label proteins. We further describe the appropriate sample handling techniques required for the reproducible recovery of phosphopeptides and explore the essential algorithmic features that enable the handling of missing MS/MS spectra and thus make label-free data suitable for such analyses. The combined technology described in this chapter expands the applicability of phosphoproteomics to questions not previously tractable with other methodologies.