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Cancer Research

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Cancer Research

Whole-genome sequencing studies have recently identified a quarter of cases of the rare childhood brainstem tumor diffuse intrinsic pontine glioma to harbor somatic mutations in ACVR1. This gene encodes the type I bone morphogenic protein receptor ALK2, with the residues affected identical to those that, when mutated in the germline, give rise to the congenital malformation syndrome fibrodysplasia ossificans progressiva (FOP), resulting in the transformation of soft tissue into bone. This unexpected link points toward the importance of developmental biology processes in tumorigenesis and provides an extensive experience in mechanistic understanding and drug development hard-won by FOP researchers to pediatric neurooncology. Here, we review the literature in both fields and identify potential areas for collaboration and rapid advancement for patients of both diseases. Cancer Res; 74(17); 4565–70. ©2014 AACR.

Understanding epithelial–mesenchymal transitions (EMT) during cancer metastasis remains a major challenge in modern biology. Recent observations of cell behavior together with progress in mapping the underlying regulatory genetic networks led to new understandings of carcinoma metastasis. It is now established that the genetic network that regulates the EMT also enables an epithelial–mesenchymal hybrid phenotype. These hybrid cells possess mixed carcinoma epithelial and mesenchymal characteristics that enable specialized capabilities such as collective cell migration. On the gene network perspective, a four-component decision unit composed of two highly interconnected chimeric modules—the miR34/SNAIL and the miR200/ZEB mutual-inhibition feedback circuits—regulates the coexistence of and transitions between the different phenotypes. Here, we present a new tractable theoretical framework to model and decode the underlying principles governing the operation of the regulatory unit. Our approach connects the knowledge about intracellular pathways with observations of cellular behavior and advances toward understanding the logic of cancer decision-making. We found that the miR34/SNAIL module acts as an integrator while the miR200/ZEB module acts as a three-way switch. Consequently, the combined unit can give rise to three phenotypes (stable states): (i) a high miR200 and low ZEB, or (1, 0) state; (ii) a low miR200 and high ZEB, or (0, 1) state; and (iii) a medium miR200 and medium ZEB, or (½, ½) state. We associate these states with the epithelial, mesenchymal, and hybrid phenotypes, respectively. We reflect on the consistency between our theoretical predictions and recent observations in several types of carcinomas and suggest new testable predictions. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4574–87. ©2014 AACR.

The first step in the spread of cancer is invasion by malignant cells of the normal tissue surrounding a tumor. There is considerable evidence both in vitro and in vivo that mechanical interactions with the tissue, in particular with the biopolymer network that makes up the extracellular matrix (ECM), are important factors in invasion. The interactions take two forms: (i) contractile cells on the surface of the tumor act on the nearby ECM and remodel it; in some cases, they align the fibers of the biopolymers; (ii) the aligned fibers can enhance invasion via contact guidance, the tendency of motile cells to follow alignment. Here, we give evidence, mainly for in vitro systems, that both effects are important. We discuss how alignment occurs in biopolymers such as collagen-I (a major component of the ECM). We propose a modeling framework for computing alignment and propose phenomenologic models for contact guidance. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4588–96. ©2014 AACR.

Extracellular matrix (ECM) stiffness induces focal adhesion assembly to drive malignant transformation and tumor metastasis. Nevertheless, how force alters focal adhesions to promote tumor progression remains unclear. Here, we explored the role of the focal adhesion protein vinculin, a force-activated mechanotransducer, in mammary epithelial tissue transformation and invasion. We found that ECM stiffness stabilizes the assembly of a vinculin–talin–actin scaffolding complex that facilitates PI3K-mediated phosphatidylinositol (3,4,5)-triphosphate phosphorylation. Using defined two- and three-dimensional matrices, a mouse model of mammary tumorigenesis with vinculin mutants, and a novel super resolution imaging approach, we established that ECM stiffness, per se, promotes the malignant progression of a mammary epithelium by activating and stabilizing vinculin and enhancing Akt signaling at focal adhesions. Our studies also revealed that vinculin strongly colocalizes with activated Akt at the invasive border of human breast tumors, where the ECM is stiffest, and we detected elevated mechanosignaling. Thus, ECM stiffness could induce tumor progression by promoting the assembly of signaling scaffolds, a conclusion underscored by the significant association we observed between highly expressed focal adhesion plaque proteins and malignant transformation across multiple types of solid cancer. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4597–611. ©2014 AACR.

Accurate prognosis and prediction of response to therapy are essential for personalized treatment of cancer. Even though many prognostic gene lists and predictors have been proposed, especially for breast cancer, high-throughput “omic” methods have so far not revolutionized clinical practice, and their clinical utility has not been satisfactorily established. Different prognostic gene lists have very few shared genes, the biological meaning of most signatures is unclear, and the published success rates are considered to be overoptimistic. This review examines critically the manner in which prognostic classifiers are derived using machine-learning methods and suggests reasons for the shortcomings and problems listed above. Two approaches that may hold hope for obtaining improved prognosis are presented. Both are based on using existing prior knowledge; one proposes combining molecular “omic” predictors with established clinical ones, and the second infers biologically relevant pathway deregulation scores for each tumor from expression data, and uses this representation to study and stratify individual tumors. Approaches such as the second one are referred to in the physics literature as “phenomenology”; they will, hopefully, play a significant role in future studies of cancer. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4612–21. ©2014 AACR.

The most common malignant primary brain tumor, glioblastoma multiforme (GBM) is a devastating disease with a grim prognosis. Patient survival is typically less than two years and fewer than 10% of patients survive more than five years. Magnetic resonance imaging (MRI) can have great utility in the diagnosis, grading, and management of patients with GBM as many of the physical manifestations of the pathologic processes in GBM can be visualized and quantified using MRI. Newer MRI techniques such as dynamic contrast enhanced and dynamic susceptibility contrast MRI provide functional information about the tumor hemodynamic status. Diffusion MRI can shed light on tumor cellularity and the disruption of white matter tracts in the proximity of tumors. MR spectroscopy can be used to study new tumor tissue markers such as IDH mutations. MRI is helping to noninvasively explore the link between the molecular basis of gliomas and the imaging characteristics of their physical processes. We, here, review several approaches to MR-based imaging and discuss the potential for these techniques to quantify the physical processes in glioblastoma, including tumor cellularity and vascularity, metabolite expression, and patterns of tumor growth and recurrence. We conclude with challenges and opportunities for further research in applying physical principles to better understand the biologic process in this deadly disease. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4622–37. ©2014 AACR.

Diffusion-weighted imaging (DWI) has been at the forefront of cancer imaging since the early 2000s. Before its application in clinical oncology, this powerful technique had already achieved widespread recognition due to its utility in the diagnosis of cerebral infarction. Following this initial success, the ability of DWI to detect inherent tissue contrast began to be exploited in the field of oncology. Although the initial oncologic applications for tumor detection and characterization, assessing treatment response, and predicting survival were primarily in the field of neurooncology, the scope of DWI has since broadened to include oncologic imaging of the prostate gland, breast, and liver. Despite its growing success and application, misconceptions about the underlying physical basis of the DWI signal exist among researchers and clinicians alike. In this review, we provide a detailed explanation of the biophysical basis of diffusion contrast, emphasizing the difference between hindered and restricted diffusion, and elucidating how diffusion parameters in tissue are derived from the measurements via the diffusion model. We describe one advanced DWI modeling technique, called restriction spectrum imaging (RSI). This technique offers a more direct in vivo measure of tumor cells, due to its ability to distinguish separable pools of water within tissue based on their intrinsic diffusion characteristics. Using RSI as an example, we then highlight the ability of advanced DWI techniques to address key clinical challenges in neurooncology, including improved tumor conspicuity, distinguishing actual response to therapy from pseudoresponse, and delineation of white matter tracts in regions of peritumoral edema. We also discuss how RSI, combined with new methods for correction of spatial distortions inherent in diffusion MRI scans, may enable more precise spatial targeting of lesions, with implications for radiation oncology and surgical planning. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4638–52. ©2014 AACR.

Successful cancer treatments are generally defined as those that decrease tumor quantity. In many cases, this decrease occurs exponentially, with deviations from a strict exponential being attributed to a growing fraction of drug-resistant cells. Deviations from an exponential decrease in tumor quantity can also be expected if drugs have a nonuniform spatial distribution inside the tumor, for example, because of interstitial pressure inside the tumor. Here, we examine theoretically different models of cell killing and analyze data from clinical trials based on these models. We show that the best description of clinical outcomes is by first-order kinetics with exponential decrease of tumor quantity. We analyzed the total tumor quantity in a diverse group of clinical trials with various cancers during the administration of different classes of anticancer agents and in all cases observed that the models that best fit the data describe the decrease of the sensitive tumor fraction exponentially. The exponential decrease suggests that all drug-sensitive cancer cells have a single rate-limiting step on the path to cell death. If there are intermediate steps in the path to cell death, they are not rate limiting in the observational time scale utilized in clinical trials—tumor restaging at 6- to 8-week intervals. On shorter time scales, there might be intermediate steps, but the rate-limiting step is the same. Our analysis, thus, points to a common pathway to cell death for cancer cells in patients. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4653–62. ©2014 AACR.

The issue of resistance to targeted drug therapy is of pressing concern, as it constitutes a major barrier to progress in managing cancer. One important aspect is the role of stochasticity in determining the nature of the patient response. We examine two particular experiments. The first measured the maximal response of melanoma to targeted therapy before the resistance causes the tumor to progress. We analyze the data in the context of a Delbruck–Luria type scheme, wherein the continued growth of preexistent resistant cells are responsible for progression. We show that, aside from a finite fraction of resistant cell-free patients, the maximal response in such a scenario would be quite uniform. To achieve the measured variability, one is necessarily led to assume a wide variation from patient to patient of the sensitive cells' response to the therapy. The second experiment is an in vitro system of multiple myeloma cells. When subject to a spatial gradient of a chemotherapeutic agent, the cells in the middle of the system acquire resistance on a rapid (two-week) timescale. This finding points to the potential important role of cell-to-cell differences, due to differing local environments, in addition to the patient-to-patient differences encountered in the first part. See all articles in this Cancer Research section, “Physics in Cancer Research.” Cancer Res; 74(17); 4663–70. ©2014 AACR.

The Helmholtz Alliance Preclinical Comprehensive Cancer Center (PCCC; www.helmholtz-pccc.de) hosted the “1st International Kloster Seeon Meeting on Mouse Models of Human Cancer” in the Seeon monastery (Germany) from March 8 to 11, 2014. The meeting focused on the development and application of novel mouse models in tumor research and high-throughput technologies to overcome one of the most critical bottlenecks in translational bench-to-bedside tumor biology research. Moreover, the participants discussed basic molecular mechanisms underlying tumor initiation, progression, metastasis, and therapy resistance, which are the prerequisite for the development of novel treatment strategies and clinical applications in cancer therapy. Cancer Res; 74(17); 4671–5. ©2014 AACR.

Somatic mutations in FGFR2 are present in 4% to 5% of patients diagnosed with non–small cell lung cancer (NSCLC). Amplification and mutations in FGFR genes have been identified in patients with NSCLCs, and clinical trials are testing the efficacy of anti-FGFR therapies. FGFR2 and other FGFR kinase family gene alterations have been found in both lung squamous cell carcinoma and lung adenocarcinoma, although mouse models of FGFR-driven lung cancers have not been reported. Here, we generated a genetically engineered mouse model (GEMM) of NSCLC driven by a kinase domain mutation in FGFR2. Combined with p53 ablation, primary grade 3/4 adenocarcinoma was induced in the lung epithelial compartment exhibiting locally invasive and pleiotropic tendencies largely made up of multinucleated cells. Tumors were acutely sensitive to pan-FGFR inhibition. This is the first FGFR2-driven lung cancer GEMM, which can be applied across different cancer indications in a preclinical setting. Cancer Res; 74(17); 4676–84. ©2014 AACR.

Intraoperative delineation of breast cancer is a significant problem in surgical oncology. A reliable method for demarcation of malignant breast tissue during surgery would reduce the re-excision rate due to positive margins. We present a novel method of identifying breast cancer margins using combined dye-enhanced wide-field fluorescence polarization imaging for en face cancer margins and polarization-sensitive (PS) optical coherence tomography (OCT) for cross-sectional evaluation. Tumor specimens were collected following breast surgery, stained with methylene blue, and imaged. Wide-field fluorescence polarization images were excited at 640 nm and registered between 660 and 750 nm. Standard and PS OCT images were acquired using a commercial 1,310-nm swept-source system. The imaging results were validated against histopathology. Statistically significant higher fluorescence polarization of cancer as compared with both normal and fibrocystic tumor tissue was measured in all the samples. Fluorescence polarization delineated lateral breast cancer margins with contrast superior to that provided by OCT. However, OCT complemented fluorescence polarization imaging by facilitating cross-sectional inspection of tissue. PS OCT yielded higher contrast between cancer and connective tissue, as compared with standard OCT. Combined PS OCT and fluorescence polarization imaging shows promise for intraoperative delineation of breast cancer. Cancer Res; 74(17); 4685–93. ©2014 AACR.

Cancer/testis (CT) antigens are potential immunotherapeutic targets in cancer. However, the expression of particular antigens is limited to a subset of tumors of a given type. Thus, there is a need to identify antigens with complementary expression patterns for effective therapeutic intervention. In this study, we searched for genes that were distinctly expressed at a higher level in lung tumor tissue and the testes compared with other nontumor tissues and identified members of the VCX/Y gene family as novel CT antigens. VCX3A, a member of the VCX/Y gene family, was expressed at the protein level in approximately 20% of lung adenocarcinomas and 35% of squamous cell carcinomas, but not expressed in normal lung tissues. Among CT antigens with concordant mRNA and protein expression levels, four CT antigens, XAGE1, VCX, IL13RA2, and SYCE1, were expressed, alone or in combination, in about 80% of lung adenocarcinoma tumors. The CT antigen VCX/Y gene family broadens the spectrum of CT antigens expressed in lung adenocarcinomas for clinical applications. Cancer Res; 74(17); 4694–705. ©2014 AACR.

The matricellular protein osteopontin (OPN, Spp-1) is widely associated with cancer aggressiveness when produced by tumor cells, but its impact is uncertain when produced by leukocytes in the context of the tumor stroma. In a broad study using Spp1−/− mice along with gene silencing in tumor cells, we obtained evidence of distinct and common activities of OPN when produced by tumor or host cells in a spontaneously metastatic model of breast cancer. Different cellular localization of OPN is associated with its distinct activities, being mainly secreted in tumor cells while intracellular in myeloid cells. OPN produced by tumor cells supported their survival in the blood stream, whereas both tumor- and host-derived OPN, particularly from myeloid cells, rendered the metastatic site more immunosuppressive. Myeloid-derived suppressor cells (MDSC) expanded with tumor progression at both primary and lung metastatic sites. Of the expanded monocytic and granulocytic cell populations of MDSCs, the monocytic subset was the predominant source of OPN. In Spp1−/− mice, the inhibition of lung metastases correlated with the expansion of granulocyte-oriented MDSCs. Notably, monocytic MDSCs in Spp1−/− mice were less suppressive than their wild-type counterparts due to lower expression of arginase-1, IL6, and phospho-Stat3. Moreover, fewer regulatory T cells accumulated at the metastatic site in Spp1−/− mice. Our data find correlation with lung metastases of human mammary carcinomas that are associated with myeloid cells expressing OPN. Overall, our results unveiled novel functions for OPN in shaping local immunosuppression in the lung metastatic niche. Cancer Res; 74(17); 4706–19. ©2014 AACR.

Inflammatory stimuli clearly contribute to lung cancer development and progression, but the underlying pathogenic mechanisms are not fully understood. We found that the proinflammatory cytokine IL-1β is dramatically elevated in the serum of patients with non–small cell lung cancer (NSCLC). In vitro studies showed that IL-1β promoted the proliferation and migration of NSCLC cells. Mechanistically, IL-1β acted through the COX2–HIF1α pathway to repress the expression of microRNA-101 (miR-101), a microRNA with an established role in tumor suppression. Lin28B was identified as critical effector target of miR-101 with its repression of Lin28B, a critical aspect of tumor suppression. Overall, IL-1β upregulated Lin28B by downregulating miR-101. Interestingly, cyclooxygenase-2 inhibition by aspirin or celecoxib abrogated IL-1β-mediated repression of miR-101 and IL-1β-mediated activation of Lin28B along with their stimulatory effects on NSCLC cell proliferation and migration. Together, our findings defined an IL-1β–miR-101–Lin28B pathway as a novel regulatory axis of pathogenic inflammatory signaling in NSCLC. Cancer Res; 74(17); 4720–30. ©2014 AACR.

Bag3, a nucleotide exchange factor of the heat shock protein Hsp70, has been implicated in cell signaling. Here, we report that Bag3 interacts with the SH3 domain of Src, thereby mediating the effects of Hsp70 on Src signaling. Using several complementary approaches, we established that the Hsp70–Bag3 module is a broad-acting regulator of cancer cell signaling by modulating the activity of the transcription factors NF-κB, FoxM1, Hif1α, the translation regulator HuR, and the cell-cycle regulators p21 and survivin. We also identified a small-molecule inhibitor, YM-1, that disrupts the Hsp70–Bag3 interaction. YM-1 mirrored the effects of Hsp70 depletion on these signaling pathways, and in vivo administration of this drug was sufficient to suppress tumor growth in mice. Overall, our results defined Bag3 as a critical factor in Hsp70-modulated signaling and offered a preclinical proof-of-concept that the Hsp70–Bag3 complex may offer an appealing anticancer target. Cancer Res; 74(17); 4731–40. ©2014 AACR.

The Notch signaling pathway governs many distinct cellular processes by regulating transcriptional programs. The transcriptional response initiated by Notch is highly cell context dependent, indicating that multiple factors influence Notch target gene selection and activity. However, the mechanism by which Notch drives target gene transcription is not well understood. Herein, we identify and characterize a novel Notch-interacting protein, Notch activation complex kinase (NACK), which acts as a Notch transcriptional coactivator. We show that NACK associates with the Notch transcriptional activation complex on DNA, mediates Notch transcriptional activity, and is required for Notch-mediated tumorigenesis. We demonstrate that Notch1 and NACK are coexpressed during mouse development and that homozygous loss of NACK is embryonic lethal. Finally, we show that NACK is also a Notch target gene, establishing a feed-forward loop. Thus, our data indicate that NACK is a key component of the Notch transcriptional complex and is an essential regulator of Notch-mediated tumorigenesis and development. Cancer Res; 74(17); 4741–51. ©2014 AACR.

Histone deacetylase 2 (HDAC2) is a chromatin modifier involved in epigenetic regulation of cell cycle, apoptosis, and differentiation that is upregulated commonly in human hepatocellular carcinoma (HCC). In this study, we show that specific targeting of this HDAC isoform is sufficient to inhibit HCC progression. siRNA-mediated silencing of HDAC inhibited HCC cell growth by blocking cell-cycle progression and inducing apoptosis. These effects were associated with deregulation of HDAC-regulated genes that control cell cycle, apoptosis, and lipid metabolism, specifically, by upregulation of p27 and acetylated p53 and by downregulation of CDK6 and BCL2. We found that HDAC2 silencing in HCC cells also strongly inhibited PPARγ signaling and other regulators of glycolysis (ChREBPα and GLUT4) and lipogenesis (SREBP1C and FAS), eliciting a marked decrease in fat accumulation. Notably, systemic delivery of HDAC2 siRNA encapsulated in lipid nanoparticles was sufficient to blunt the growth of human HCC in a murine xenograft model. Our findings offer preclinical proof-of-concept for HDAC2 blockade as a systemic therapy for liver cancer. Cancer Res; 74(17); 4752–61. ©2014 AACR.

Resistance to receptor tyrosine kinase (RTK) blockade in breast cancer is often mediated by activation of bypass pathways that sustain growth. Src and mammalian target of rapamycin (mTOR) are two intrinsic targets that are downstream of most RTKs. To date, limited clinical efficacy has been observed with either Src or mTOR inhibitors when used as single agents. Resistance to mTOR inhibitors is associated with loss of negative feedback regulation, resulting in phosphorylation and activation of AKT. Herein, we describe a novel role for Src in contributing to rapalog-induced AKT activation. We found that dual activation of Src and the mTOR pathway occurs in nearly half of all breast cancers, suggesting potential cross-talk. As expected, rapamycin inhibition of mTOR results in feedback activation of AKT in breast cancer cell lines. Addition of the Src/c-Abl inhibitor, dasatinib, completely blocks this feedback activation, confirming convergence between Src and the mTOR pathway. Analysis in vivo revealed that dual Src and mTOR inhibition is highly effective in two mouse models of breast cancer. In a luminal disease model, combined dasatinib and rapamycin is more effective at inducing regression than either single agent. Furthermore, the combination of dasatinib and rapamycin delays tumor recurrence following the cessation of treatment. In a model of human EGFR-2–positive (HER2+) disease, dasatinib alone is ineffective, but potentiates the efficacy of rapamycin. These data suggest that combining mTOR and Src inhibitors may provide a new approach for treating multiple breast cancer subtypes that may circumvent resistance to targeted RTK therapies. Cancer Res; 74(17); 4762–71. ©2014 AACR.

New therapies are urgently needed for hematologic malignancies, especially in patients with relapsed acute myelogenous leukemia (AML) and multiple myeloma. We and others have previously shown that FDA-approved statins, which are used to control hypercholesterolemia and target the mevalonate pathway (MVA), can trigger tumor-selective apoptosis. Our goal was to identify other FDA-approved drugs that synergize with statins to further enhance the anticancer activity of statins in vivo. Using a screen composed of other FDA approved drugs, we identified dipyridamole, used for the prevention of cerebral ischemia, as a potentiator of statin anticancer activity. The statin–dipyridamole combination was synergistic and induced apoptosis in multiple myeloma and AML cell lines and primary patient samples, whereas normal peripheral blood mononuclear cells were not affected. This novel combination also decreased tumor growth in vivo. Statins block HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the MVA pathway. Dipyridamole blunted the feedback response, which upregulates HMGCR and HMG-CoA synthase 1 (HMGCS1) following statin treatment. We further show that dipyridamole inhibited the cleavage of the transcription factor required for this feedback regulation, sterol regulatory element–binding transcription factor 2 (SREBF2, SREBP2). Simultaneously targeting the MVA pathway and its restorative feedback loop is preclinically effective against hematologic malignancies. This work provides strong evidence for the immediate evaluation of this novel combination of FDA-approved drugs in clinical trials. Cancer Res; 74(17); 4772–82. ©2014 AACR.

In cancer cells, the epithelial–mesenchymal transition (EMT) confers the ability to invade basement membranes and metastasize to distant sites, establishing it as an appealing target for therapeutic intervention. Here, we report a novel function of the master metabolic kinase AMPK in suppressing EMT by modulating the Akt–MDM2–Foxo3 signaling axis. This mechanistic link was supported by the effects of siRNA-mediated knockdown and pharmacologic activation of AMPK on epithelial and mesenchymal markers in established breast and prostate cancer cells. Exposure of cells to OSU-53, a novel allosteric AMPK activator, as well as metformin and AICAR, was sufficient to reverse their mesenchymal phenotype. These effects were abrogated by AMPK silencing. Phenotypic changes were mediated by Foxo3a activation, insofar as silencing or overexpressing Foxo3a mimicked the effects of AMPK silencing or OSU-53 treatment on EMT, respectively. Mechanistically, Foxo3a activation led to the transactivation of the E-cadherin gene and repression of genes encoding EMT-inducing transcription factors. OSU-53 activated Foxo3a through two Akt-dependent pathways, one at the level of nuclear localization by blocking Akt- and IKKβ-mediated phosphorylation, and a second at the level of protein stabilization via cytoplasmic sequestration of MDM2, an E3 ligase responsible for Foxo3a degradation. The suppressive effects of OSU-53 on EMT had therapeutic implications illustrated by its ability to block invasive phenotypes in vitro and metastatic properties in vivo. Overall, our work illuminates a mechanism of EMT regulation in cancer cells mediated by AMPK, along with preclinical evidence supporting a tractable therapeutic strategy to reverse mesenchymal phenotypes associated with invasion and metastasis. Cancer Res; 74(17); 4783–95. ©2014 AACR.

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of kidney cancer and has the highest propensity to manifest as metastatic disease. Recent characterizations of the genetic signature of ccRCC have revealed several factors correlated with tumor cell migration and invasion; however, the specific events driving malignancy are not well defined. Furthermore, there remains a lack of targeted therapies that result in long-term, sustainable response in patients with metastatic disease. We show here that neuronal pentraxin 2 (NPTX2) is overexpressed specifically in ccRCC primary tumors and metastases, and that it contributes to tumor cell viability and promotes cell migration through its interaction with the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit GluR4. We propose NPTX2 as a novel molecular target for therapy for patients with ccRCC diagnosed with or at risk of developing metastatic disease. Cancer Res; 74(17); 4796–810. ©2014 AACR.

The Hedgehog (HH) signaling pathway represents an important class of emerging developmental signaling pathways that play critical roles in the genesis of a large number of human cancers. The pharmaceutical industry is currently focused on developing small molecules targeting Smoothened (Smo), a key signaling effector of the HH pathway that regulates the levels and activity of the Gli family of transcription factors. Although one of these compounds, vismodegib, is now FDA-approved for patients with advanced basal cell carcinoma, acquired mutations in Smo can result in rapid relapse. Furthermore, many cancers also exhibit a Smo-independent activation of Gli proteins, an observation that may underlie the limited efficacy of Smo inhibitors in clinical trials against other types of cancer. Thus, there remains a critical need for HH inhibitors with different mechanisms of action, particularly those that act downstream of Smo. Recently, we identified the FDA-approved anti-pinworm compound pyrvinium as a novel, potent (IC50, 10 nmol/L) casein kinase-1α (CK1α) agonist. We show here that pyrvinium is a potent inhibitor of HH signaling, which acts by reducing the stability of the Gli family of transcription factors. Consistent with CK1α agonists acting on these most distal components of the HH signaling pathway, pyrvinium is able to inhibit the activity of a clinically relevant, vismodegib -resistant Smo mutant, as well as the Gli activity resulting from loss of the negative regulator suppressor of fused. We go on to demonstrate the utility of this small molecule in vivo, against the HH-dependent cancer medulloblastoma, attenuating its growth and reducing the expression of HH biomarkers. Cancer Res; 74(17); 4811–21. ©2014 AACR.

Triple-negative breast cancer (TNBC) is a highly heterogeneous and recurrent subtype of breast cancer that lacks an effective targeted therapy. To identify candidate therapeutic targets, we profiled global gene expression in TNBC and breast tumor-initiating cells with a patient survival dataset. Eight TNBC-related kinases were found to be overexpressed in TNBC cells with stem-like properties. Among them, expression of PKC-α, MET, and CDK6 correlated with poorer survival outcomes. In cases coexpressing two of these three kinases, survival rates were lower than in cases where only one of these kinases was expressed. In functional tests, two-drug combinations targeting these three kinases inhibited TNBC cell proliferation and tumorigenic potential in a cooperative manner. A combination of PKC-α-MET inhibitors also attenuated tumor growth in a cooperative manner in vivo. Our findings define three kinases critical for TNBC growth and offer a preclinical rationale for their candidacy as effective therapeutic targets in treating TNBC. Cancer Res; 74(17); 4822–35. ©2014 AACR.

Isocitrate dehydrogenase 1 (IDH1) mutations occur in most lower grade glioma and not only drive gliomagenesis but are also associated with longer patient survival and improved response to temozolomide. To investigate the possible causative relationship between these events, we introduced wild-type (WT) or mutant IDH1 into immortalized, untransformed human astrocytes, then monitored transformation status and temozolomide response. Temozolomide-sensitive parental cells exhibited DNA damage (γ-H2AX foci) and a prolonged G2 cell-cycle arrest beginning three days after temozolomide (100 μmol/L, 3 hours) exposure and persisting for more than four days. The same cells transformed by expression of mutant IDH1 exhibited a comparable degree of DNA damage and cell-cycle arrest, but both events resolved significantly faster in association with increased, rather than decreased, clonogenic survival. The increases in DNA damage processing, cell-cycle progression, and clonogenicity were unique to cells transformed by mutant IDH1, and were not noted in cells transformed by WT IDH1 or an oncogenic form (V12H) of Ras. Similarly, these effects were not noted following introduction of mutant IDH1 into Ras-transformed cells or established glioma cells. They were, however, associated with increased homologous recombination (HR) and could be reversed by the genetic or pharmacologic suppression of the HR DNA repair protein RAD51. These results show that mutant IDH1 drives a unique set of transformative events that indirectly enhance HR and facilitate repair of temozolomide-induced DNA damage and temozolomide resistance. The results also suggest that inhibitors of HR may be a viable means to enhance temozolomide response in IDH1-mutant glioma. Cancer Res; 74(17); 4836–44. ©2014 AACR.

Following mutations in BRAF and NRAS, the RAC1 c.85C>T single-nucleotide variant (SNV) encoding P29S amino acid change represents the next most frequently observed protein-coding hotspot mutation in melanoma. However, the biologic and clinical significance of the RAC1 P29S somatic mutation in approximately 4% to 9% of patients remains unclear. Here, we demonstrate that melanoma cell lines possessing the RAC1 hotspot variant are resistant to RAF inhibitors (vemurafenib and dabrafenib). Enforced expression of RAC1 P29S in sensitive BRAF-mutant melanoma cell lines confers resistance manifested by increased viability, decreased apoptosis, and enhanced tumor growth in vivo upon treatment with RAF inhibitors. Conversely, RNAi-mediated silencing of endogenous RAC1 P29S in a melanoma cell line with a co-occurring BRAF V600 mutation increased sensitivity to vemurafenib and dabrafenib. Our results suggest RAC1 P29S status may offer a predictive biomarker for RAF inhibitor resistance in melanoma patients, where it should be evaluated clinically. Cancer Res; 74(17); 4845–52. ©2014 AACR.

Chromosomal instability (CIN) is associated with poor outcome in epithelial malignancies, including breast carcinomas. Evidence suggests that prognostic signatures in estrogen receptor–positive (ER+) breast cancer define tumors with CIN and high proliferative potential. Intriguingly, CIN induction in lower eukaryotic cells and human cells is context dependent, typically resulting in a proliferation disadvantage but conferring a fitness benefit under strong selection pressures. We hypothesized that CIN permits accelerated genomic evolution through the generation of diverse DNA copy-number events that may be selected during disease development. In support of this hypothesis, we found evidence for selection of gene amplification of core regulators of proliferation in CIN-associated cancer genomes. Stable DNA copy-number amplifications of the core regulators TPX2 and UBE2C were associated with expression of a gene module involved in proliferation. The module genes were enriched within prognostic signature gene sets for ER+ breast cancer, providing a logical connection between CIN and prognostic signature expression. Our results provide a framework to decipher the impact of intratumor heterogeneity on key cancer phenotypes, and they suggest that CIN provides a permissive landscape for selection of copy-number alterations that drive cancer proliferation. Cancer Res; 74(17); 4853–63. ©2014 AACR.

A central confounding factor in the development of targeted therapies is tumor cell heterogeneity, particularly in tumor-initiating cells (TIC), within clinically identical tumors. Here, we show how activation of the Sonic Hedgehog (SHH) pathway in neural stem and progenitor cells creates a foundation for tumor cell evolution to heterogeneous states that are histologically indistinguishable but molecularly distinct. In spontaneous medulloblastomas that arise in Patched (Ptch)+/− mice, we identified three distinct tumor subtypes. Through cell type–specific activation of the SHH pathway in vivo, we determined that different cells of origin evolved in unique ways to generate these subtypes. Moreover, TICs in each subtype had distinct molecular and cellular phenotypes. At the bulk tumor level, the three tumor subtypes could be distinguished by a 465-gene signature and by differential activation levels of the ERK and AKT pathways. Notably, TICs from different subtypes were differentially sensitive to SHH or AKT pathway inhibitors, highlighting new mechanisms of resistance to targeted therapies. In summary, our results show how evolutionary processes act on distinct cells of origin to contribute to tumoral heterogeneity, at both bulk tumor and TIC levels. Cancer Res; 74(17); 4864–74. ©2014 AACR.

TRIM29 (ATDC) exhibits a contextual function in cancer, but seems to exert a tumor-suppressor role in breast cancer. Here, we show that TRIM29 is often silenced in primary breast tumors and cultured tumor cells as a result of aberrant gene hypermethylation. RNAi-mediated silencing of TRIM29 in breast tumor cells increased their motility, invasiveness, and proliferation in a manner associated with increased expression of mesenchymal markers (N-cadherin and vimentin), decreased expression of epithelial markers (E-cadherin and EpCAM), and increased expression and activity of the oncogenic transcription factor TWIST1, an important driver of the epithelial–mesenchymal transition (EMT). Functional investigations revealed an inverse relationship in the expression of TRIM29 and TWIST1, suggesting the existence of a negative regulatory feedback loop. In support of this relationship, we found that TWIST1 inhibited TRIM29 promoter activity through direct binding to a region containing a cluster of consensus E-box elements, arguing that TWIST1 transcriptionally represses TRIM29 expression. Analysis of a public breast cancer gene-expression database indicated that reduced TRIM29 expression was associated with reduced relapse-free survival, increased tumor size, grade, and metastatic characteristics. Taken together, our results suggest that TRIM29 acts as a tumor suppressor in breast cancer through its ability to inhibit TWIST1 and suppress EMT. Cancer Res; 74(17); 4875–87. ©2014 AACR.

Endocrine therapy is the standard treatment for advanced prostate cancer; however, relapse occurs in most patients with few treatment options available after recurrence. To overcome this therapeutic hurdle, the identification of new molecular targets is a critical issue. The capability to proliferate in three-dimensional (3D) conditions is a characteristic property of cancer cells. Therefore, factors that regulate 3D growth are considered rational targets for cancer therapy. Here, we applied a functional genomic approach to the 3D spheroid cell culture model and identified TRIB1, a member of the Trib family of serine/threonine kinase-like proteins, as an essential factor for prostate cancer cell growth and survival. RNAi-mediated silencing of TRIB1 suppressed prostate cancer cell growth selectively under the 3D conditions. This effect was rescued by ectopic expression of an RNAi-resistant TRIB1 exogene. Gene signature–based analysis revealed that TRIB1 was related to endoplasmic reticulum (ER) pathways in prostate cancer and was required for expression of the ER chaperone GRP78, which is critical for prostate tumorigenesis. Of note, GRP78 was expressed preferentially in a subpopulation of prostate cancer cells that possess tumor-propagating potential, and these tumor-propagating cells were highly sensitive to TRIB1 and GRP78 depletion. In a xenograft model of human prostate cancer, TRIB1 depletion strongly inhibited tumor formation. Supporting these observations, we documented frequent overexpression of TRIB1 in clinical specimens of prostate cancer. Overall, our results indicated that the TRIB1–ER chaperone axis drives prostate tumorigenesis and the survival of the tumor-propagating cells. Cancer Res; 74(17); 4888–97. ©2014 AACR.

Many patients with glioma harbor specific mutations in the isocitrate dehydrogenase gene IDH1 that associate with a relatively better prognosis. IDH1-mutated tumors produce the oncometabolite 2-hydroxyglutarate. Because IDH1 also regulates several pathways leading to lipid synthesis, we hypothesized that IDH1-mutant tumors have an altered phospholipid metabolite profile that would impinge on tumor pathobiology. To investigate this hypothesis, we performed 31P-MRS imaging in mouse xenograft models of four human gliomas, one of which harbored the IDH1-R132H mutation. 31P-MR spectra from the IDH1-mutant tumor displayed a pattern distinct from that of the three IDH1 wild-type tumors, characterized by decreased levels of phosphoethanolamine and increased levels of glycerophosphocholine. This spectral profile was confirmed by ex vivo analysis of tumor extracts, and it was also observed in human surgical biopsies of IDH1-mutated tumors by 31P high-resolution magic angle spinning spectroscopy. The specificity of this profile for the IDH1-R132H mutation was established by in vitro 31P-NMR of extracts of cells overexpressing IDH1 or IDH1-R132H. Overall, our results provide evidence that the IDH1-R132H mutation alters phospholipid metabolism in gliomas involving phosphoethanolamine and glycerophosphocholine. These new noninvasive biomarkers can assist in the identification of the mutation and in research toward novel treatments that target aberrant metabolism in IDH1-mutant glioma. Cancer Res; 74(17); 4898–907. ©2014 AACR.

Despite its aggressive nature, triple-negative breast cancer (TNBC) often exhibits leucocyte infiltrations that correlate with favorable prognosis. In this study, we offer an explanation for this apparent conundrum by defining TNBC cell subsets that overexpress the IL15 immune receptor IL15RA. This receptor usually forms a heterotrimer with the IL2 receptors IL2RB and IL2RG, which regulates the proliferation and differentiation of cytotoxic T cells and NK cells. However, unlike IL15RA, the IL2RB and IL2RG receptors are not upregulated in basal-like TNBC breast cancer cells that express IL15RA. Mechanistic investigations indicated that IL15RA signaling activated JAK1, STAT1, STAT2, AKT, PRAS40, and ERK1/2 in the absence of IL2RB and IL2RG, whereas neither STAT5 nor JAK2 were activated. RNAi-mediated attenuation of IL15RA established its role in cell growth, apoptosis, and migration, whereas expression of the IL15 cytokine in IL15RA-expressing cells stimulated an autocrine signaling cascade that promoted cell proliferation and migration and blocked apoptosis. Notably, coexpression of IL15RA and IL15 was also sufficient to activate peripheral blood mononuclear cells upon coculture in a paracrine signaling manner. Overall, our findings offer a mechanistic explanation for the paradoxical association of some high-grade breast tumors with better survival outcomes, due to engagement of the immune stroma. Cancer Res; 74(17); 4908–21. ©2014 AACR.

Emerging results indicate that cancer stem–like cells contribute to chemoresistance and poor clinical outcomes in many cancers, including ovarian cancer. As epigenetic regulators play a major role in the control of normal stem cell differentiation, epigenetics may offer a useful arena to develop strategies to target cancer stem–like cells. Epigenetic aberrations, especially DNA methylation, silence tumor-suppressor and differentiation-associated genes that regulate the survival of ovarian cancer stem–like cells (OCSC). In this study, we tested the hypothesis that DNA-hypomethylating agents may be able to reset OCSC toward a differentiated phenotype by evaluating the effects of the new DNA methytransferase inhibitor SGI-110 on OCSC phenotype, as defined by expression of the cancer stem–like marker aldehyde dehydrogenase (ALDH). We demonstrated that ALDH+ ovarian cancer cells possess multiple stem cell characteristics, were highly chemoresistant, and were enriched in xenografts residual after platinum therapy. Low-dose SGI-110 reduced the stem-like properties of ALDH+ cells, including their tumor-initiating capacity, resensitized these OCSCs to platinum, and induced reexpression of differentiation-associated genes. Maintenance treatment with SGI-110 after carboplatin inhibited OCSC growth, causing global tumor hypomethylation and decreased tumor progression. Our work offers preclinical evidence that epigenome-targeting strategies have the potential to delay tumor progression by reprogramming residual cancer stem–like cells. Furthermore, the results suggest that SGI-110 might be administered in combination with platinum to prevent the development of recurrent and chemoresistant ovarian cancer. Cancer Res; 74(17); 4922–36. ©2014 AACR.

Methods to visualize metastasis exist, but additional tools to better define the biologic and physical processes underlying invasion and intravasation are still needed. One difficulty in studying metastasis stems from the complexity of the interface between the tumor microenvironment and the vascular system. Here, we report the development of an investigational platform that positions tumor cells next to an artificial vessel embedded in an extracellular matrix. On this platform, we used live-cell fluorescence microscopy to analyze the complex interplay between metastatic cancer cells and a functional artificial microvessel that was lined with endothelial cells. The platform recapitulated known interactions, and its use demonstrated the capabilities for a systematic study of novel physical and biologic parameters involved in invasion and intravasation. In summary, our work offers an important new tool to advance knowledge about metastasis and candidate antimetastatic therapies. Cancer Res; 74(17); 4937–45. ©2014 AACR.