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Cancer Research

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Cancer Research

Microsatellites are simple tandem repeats that are present at millions of loci in the human genome. Microsatellite instability (MSI) refers to DNA slippage events on microsatellites that occur frequently in cancer genomes when there is a defect in the DNA-mismatch repair system. These somatic mutations can result in inactivation of tumor-suppressor genes or disrupt other noncoding regulatory sequences, thereby playing a role in carcinogenesis. Here, we will discuss the ways in which high-throughput sequencing data can facilitate genome- or exome-wide discovery and more detailed investigation of MSI events in microsatellite-unstable cancer genomes. We will address the methodologic aspects of this approach and highlight insights from recent analyses of colorectal and endometrial cancer genomes from The Cancer Genome Atlas project. These include identification of novel MSI targets within and across tumor types and the relationship between the likelihood of MSI events to chromatin structure. Given the increasing popularity of exome and genome sequencing of cancer genomes, a comprehensive characterization of MSI may serve as a valuable marker of cancer evolution and aid in a search for therapeutic targets. Cancer Res; 74(22); 6377–82. ©2014 AACR.

Several decades of humoral immunotherapy using monoclonal antibodies and cellular immunotherapy using hematopoietic cell transplantation have recently culminated in a successful merger: the development and clinical application of genetically engineered antibody–T cell chimeras. Also known as chimeric antigen receptor T cells (CAR T cells), these entities combine the exquisite antigen specificity of antibodies with the polyfunctionality and potency of cellular immunity and are a prime example of the potential for synthetic biology to treat disease. CAR T cells overcome several of the biologic obstacles that have historically hampered immunotherapy while providing fundamental mechanistic insights into cellular immunology and revealing new challenges in genetic engineering and target selection. Results from early-phase CAR T-cell–based clinical trials demonstrate the significant potential for this approach to affect dramatic and complete clinical responses while revealing novel toxicities associated with activation of potent and specific antitumor immunity. Cancer Res; 74(22); 6383–9. ©2014 AACR.

Cancer genome sequencing is being used at an increasing rate to identify actionable driver mutations that can inform therapeutic intervention strategies. A comparison of two of the most prominent cancer genome sequencing databases from different institutes (Cancer Cell Line Encyclopedia and Catalogue of Somatic Mutations in Cancer) revealed marked discrepancies in the detection of missense mutations in identical cell lines (57.38% conformity). The main reason for this discrepancy is inadequate sequencing of GC-rich areas of the exome. We have therefore mapped over 400 regions of consistent inadequate sequencing (cold-spots) in known cancer-causing genes and kinases, in 368 of which neither institute finds mutations. We demonstrate, using a newly identified PAK4 mutation as proof of principle, that specific targeting and sequencing of these GC-rich cold-spot regions can lead to the identification of novel driver mutations in known tumor suppressors and oncogenes. We highlight that cross-referencing between genomic databases is required to comprehensively assess genomic alterations in commonly used cell lines and that there are still significant opportunities to identify novel drivers of tumorigenesis in poorly sequenced areas of the exome. Finally, we assess other reasons for the observed discrepancy, such as variations in dbSNP filtering and the acquisition/loss of mutations, to give explanations as to why there is a discrepancy in pharmacogenomic studies, given recent concerns with poor reproducibility of data. Cancer Res; 74(22); 6390–6. ©2014 AACR.

Defining tumor stage at diagnosis is a pivotal point for clinical decisions about patient treatment strategies. In this respect, early detection of occult metastasis invisible to current imaging methods would have a major impact on best care and long-term survival. Mathematical models that describe metastatic spreading might estimate the risk of metastasis when no clinical evidence is available. In this study, we adapted a top-down model to make such estimates. The model was constituted by a transport equation describing metastatic growth and endowed with a boundary condition for metastatic emission. Model predictions were compared with experimental results from orthotopic breast tumor xenograft experiments conducted in Nod/Scidγ mice. Primary tumor growth, metastatic spread and growth were monitored by 3D bioluminescence tomography. A tailored computational approach allowed the use of Monolix software for mixed-effects modeling with a partial differential equation model. Primary tumor growth was described best by Bertalanffy, West, and Gompertz models, which involve an initial exponential growth phase. All other tested models were rejected. The best metastatic model involved two parameters describing metastatic spreading and growth, respectively. Visual predictive check, analysis of residuals, and a bootstrap study validated the model. Coefficients of determination were $R^2 = 0.94$ for primary tumor growth and $R^2 = 0.57$ for metastatic growth. The data-based model development revealed several biologically significant findings. First, information on both growth and spreading can be obtained from measures of total metastatic burden. Second, the postulated link between primary tumor size and emission rate is validated. Finally, fast growing peritoneal metastases can only be described by such a complex partial differential equation model and not by ordinary differential equation models. This work advances efforts to predict metastatic spreading during the earliest stages of cancer. Cancer Res; 74(22); 6397–407. ©2014 AACR.

Stage III/IV melanoma remains incurable in most cases due to chemotherapeutic resistance. Thus, predicting and monitoring chemotherapeutic responses in this setting offer great interest. To overcome limitations of existing assays in evaluating the chemosensitivity of dissociated tumor cells, we developed a label-free monitoring system to directly analyze the chemosensitivity of undissociated tumor tissue. Using a preparation of tumor micro-fragments (TMF) established from melanoma biopsies, we characterized the tissue organization and biomarker expression by immunocytochemistry. Robust generation of TMF was established successfully and demonstrated on a broad range of primary melanoma tumors and tumor metastases. Organization and biomarker expression within the TMF were highly comparable with tumor tissue, in contrast to dissociated, cultivated tumor cells. Using isolated TMF, sensitivity to six clinically relevant chemotherapeutic drugs (dacarbazine, doxorubicin, paclitaxel, cisplatin, gemcitabine, and treosulfan) was determined by impedance spectroscopy in combination with a unique microcavity array technology we developed. In parallel, comparative analyses were performed on monolayer tumor cell cultures. Lastly, we determined the efficacy of chemotherapeutic agents on TMF by impedance spectroscopy to obtain individual chemosensitivity patterns. Our results demonstrated nonpredictable differences in the reaction of tumor cells to chemotherapy in TMF by comparison with dissociated, cultivated tumor cells. Our direct impedimetric analysis of melanoma biopsies offers a direct ex vivo system to more reliably predict patient-specific chemosensitivity patterns and to monitor antitumor efficacy. Cancer Res; 74(22); 6408–18. ©2014 AACR.

The majority of causative variants in familial breast cancer remain unknown. Of the known risk variants, most are tumor cell autonomous, and little attention has been paid yet to germline variants that may affect the tumor microenvironment. In this study, we developed a system called the Consomic Xenograft Model (CXM) to map germline variants that affect only the tumor microenvironment. In CXM, human breast cancer cells are orthotopically implanted into immunodeficient consomic strains and tumor metrics are quantified (e.g., growth, vasculogenesis, and metastasis). Because the strain backgrounds vary, whereas the malignant tumor cells do not, any observed changes in tumor progression are due to genetic differences in the nonmalignant microenvironment. Using CXM, we defined genetic variants on rat chromosome 3 that reduced relative tumor growth and hematogenous metastasis in the SS.BN3IL2Rγ consomic model compared with the SSIL2Rγ parental strain. Paradoxically, these effects occurred despite an increase in the density of tumor-associated blood vessels. In contrast, lymphatic vasculature and lymphogenous metastasis were unaffected by the SS.BN3IL2Rγ background. Through comparative mapping and whole-genome sequence analysis, we narrowed candidate variants on rat chromosome 3 to six genes with a priority for future analysis. Collectively, our results establish the utility of CXM to localize genetic variants affecting the tumor microenvironment that underlie differences in breast cancer risk. Cancer Res; 74(22); 6419–29. ©2014 AACR.

Plasmacytoid dendritic cells (pDC) rapidly and massively produce type I IFN and other inflammatory cytokines in response to foreign nucleic acids, thereby indirectly influencing T-cell responses. Moreover, antigen (Ag)-presenting pDCs directly regulate T-cell differentiation. Depending on the immune environment, pDCs exhibit either tolerogenic or immunogenic properties. Here, we show that CpG-activated pDCs promote efficient Th17 differentiation. Indeed, Th17 responses are defective in mice selectively lacking MHCII on pDCs upon antigenic challenge. Importantly, in those mice, the frequency of Th17 cells infiltrating solid tumors is impaired. As a result, the recruitment of infiltrating leukocytes in tumors, including tumor-specific cytotoxic T lymphocytes (CTL), is altered and results in increased tumor growth. Importantly, following immunization with tumor Ag and CpG-B, MHCII-restricted Ag presentation by pDCs promotes the differentiation of antitumor Th17 cells that induce intratumor CTL recruitment and subsequent regression of established tumors. Our results highlight a new role for Ag presenting activated pDCs in promoting the development of Th17 cells and impacting on antitumor immunity. Cancer Res; 74(22); 6430–40. ©2014 AACR.

Vaccines based on tumor-associated antigens (TAA) have limited therapeutic efficacy due to their weak immunogenic nature and the various immune evasion mechanisms active in advanced tumors. In an effort to overcome these limitations, we evaluated a combination of the T-cell costimulatory molecule SA-4-1BBL with the TLR4 agonist monophosphoryl lipid A (MPL) as a novel vaccine adjuvant system. In the TC-1 mouse allograft model of human papilloma virus (HPV)-induced cancer, a single administration of this combination adjuvant with HPV E7 protein caused tumor rejection in all tumor-bearing mice. On its own, SA-4-1BBL outperformed MPL in this setting. Against established tumors, two vaccinations were sufficient to elicit rejection in the majority of mice. In the metastatic model of Lewis lung carcinoma, vaccination of the TAA survivin with SA-4-1BBL/MPL yielded superior efficacy against pulmonary metastases. Therapeutic efficacy of SA-4-1BBL/MPL was achieved in the absence of detectable toxicity, correlating with enhanced dendritic cell activation, CD8+ T-cell function, and an increased intratumoral ratio of CD8+ T effector cells to CD4+FoxP3+ T regulatory cells. Unexpectedly, use of MPL on its own was associated with unfavorable intratumoral ratios of these T-cell populations, resulting in suboptimal efficacy. The efficacy of MPL monotherapy was restored by depletion of T regulatory cells, whereas eliminating CD8+ T cells abolished the efficacy of its combination with SA-4-1BBL. Mechanistic investigations showed that IFNγ played a critical role in supporting the therapeutic effect of SA-4-1BBL/MPL. Taken together, our results offer a preclinical proof of concept for the use of a powerful new adjuvant system for TAA-based cancer vaccines. Cancer Res; 74(22); 6441–51. ©2014 AACR.

Caveolin-2 (Cav-2), a member of caveolin protein family, is largely different from better known caveolin-1 (Cav-1) and thus might play distinct functions. Here, we provide the first genetic evidence suggesting that host-expressed Cav-2 promotes subcutaneous tumor growth and tumor-induced neovascularization using two independent syngeneic mouse models. Host deficiency in Cav-2 resulted in defective and reduced growth of subcutaneously implanted Lewis lung carcinoma (LLC) and B16-F10 melanoma tumors, respectively. Consistent with the defective growth, LLC and B16-F10 melanoma tumors implanted into Cav-2 KO mice displayed reduced microvascular density (MVD) determined by IHC with anti-CD31 antibodies, suggesting impaired pathologic angiogenesis. Additional studies involving LLC tumors extracted from Cav-2 KO mice just 10 days after implantation determined reduced cell proliferation, massive necrotic cell death, and fibrosis. In contrast with day 10, only MVD but not cell proliferation and survival was reduced in the earliest palpable LLC tumors extracted 6 days after implantation into Cav-2 KO mice, suggesting that impaired angiogenesis is the causative factor. Mechanistically, impaired LLC tumor growth and angiogenesis in Cav-2 KO mice was associated with increased expression levels of antiangiogenic thrombospondin-1 and inhibited S1177 phosphorylation of endothelial nitric oxide synthase. Taken together, our data suggest that host deficiency in Cav-2 impairs tumor-induced angiogenesis, leading to compromised tumor cell survival/proliferation manifested by the defective tumor growth. In conclusion, host-expressed Cav-2 may promote tumor growth via supporting tumor-induced angiogenesis. Thus, Cav-2 expressed in tumor microenvironment may potentially become a novel target for cancer therapy. Cancer Res; 74(22); 6452–62. ©2014 AACR.

Ovarian cancer is a deadly gynecologic malignancy for which novel biomarkers and therapeutic targets are imperative for improving survival. Previous studies have suggested the expression pattern of linker histone variants as potential biomarkers for ovarian cancer. To investigate the role of histone H1 in ovarian cancer cells, we characterize individual H1 variants and overexpress one of the major somatic H1 variants, H1.3, in the OVCAR-3 epithelial ovarian cancer cell line. We find that overexpression of H1.3 decreases the growth rate and colony formation of OVCAR-3 cells. We identify histone H1.3 as a specific repressor for the noncoding oncogene H19. Overexpression of H1.3 suppresses H19 expression, and knockdown of H1.3 increases its expression in multiple ovarian epithelial cancer cell lines. Furthermore, we demonstrate that histone H1.3 overexpression leads to increased occupancy of H1.3 at the H19 regulator region encompassing the imprinting control region (ICR), concomitant with increased DNA methylation and reduced occupancy of the insulator protein CTCF at the ICR. Finally, we demonstrate that H1.3 overexpression and H19 knockdown synergistically decrease the growth rate of ovarian cancer cells. Our findings suggest that H1.3 dramatically inhibits H19 expression, which contributes to the suppression of epithelial ovarian carcinogenesis. Cancer Res; 74(22); 6463–73. ©2014 AACR.

The kinase Fer and its spermatogenic meiotic variant, FerT, are coexpressed in normal testes and cancerous tumors, but whether they exert related roles in spermatogenic or malignant cells has not been known. Here, we show that Fer and FerT reside in the mitochondria of spermatogenic cells and are harnessed to the reprogrammed mitochondria of colon carcinoma cells. Both kinases bound complex I of the mitochondrial electron transport chain (ETC) in spermatogenic and in colon carcinoma cells, and silencing of either Fer or FerT was sufficient to impair the activity of this complex. Directed mitochondrial accumulation of FerT in nonmalignant NIH3T3 cells increased their ETC complex I activity, ATP production, and survival, contingent upon stress conditions caused by nutrient and oxygen deprivation. Strikingly, directed mitochondrial accumulation of FerT endowed nonmalignant cells with tumor-forming ability. Thus, recruitment of a meiotic mitochondrial component to cancer cell mitochondria highlights a pivotal role for reprogrammed mitochondria in tumorigenesis. Cancer Res; 74(22); 6474–85. ©2014 AACR.

SWI/SNF chromatin remodeling complexes regulate critical cellular processes, including cell-cycle control, programmed cell death, differentiation, genomic instability, and DNA repair. Inactivation of this class of chromatin remodeling complex has been associated with a variety of malignancies, including lung, ovarian, renal, liver, and pediatric cancers. In particular, approximately 10% of primary human lung non–small cell lung cancers (NSCLC) display attenuations in the BRG1 ATPase, a core factor in SWI/SNF complexes. To evaluate the role of BRG1 attenuation in NSCLC development, we examined the effect of BRG1 silencing in primary and established human NSCLC cells. BRG1 loss altered cellular morphology and increased tumorigenic potential. Gene expression analyses showed reduced expression of genes known to be associated with progression of human NSCLC. We demonstrated that BRG1 losses in NSCLC cells were associated with variations in chromatin structure, including differences in nucleosome positioning and occupancy surrounding transcriptional start sites of disease-relevant genes. Our results offer direct evidence that BRG1 attenuation contributes to NSCLC aggressiveness by altering nucleosome positioning at a wide range of genes, including key cancer-associated genes. Cancer Res; 74(22); 6486–98. ©2014 AACR.

Microtubule nucleation requires the γ-tubulin ring complex, and during the M-phase (mitosis) this complex accumulates at the centrosome to support mitotic spindle formation. The posttranslational modification of γ-tubulin through ubiquitination is vital for regulating microtubule nucleation and centrosome duplication. Blocking the BRCA1/BARD1-dependent ubiquitination of γ-tubulin causes centrosome amplification. In the current study, we identified BRCA1-associated protein-1 (BAP1) as a deubiquitination enzyme for γ-tubulin. BAP1 was downregulated in metastatic adenocarcinoma breast cell lines compared with noncancerous human breast epithelial cells. Furthermore, low expression of BAP1 was associated with reduced overall survival of patients with breast cancer. Reduced expression of BAP1 in breast cancer cell lines was associated with mitotic abnormalities. Importantly, rescue experiments including expression of full length but not the catalytic mutant of BAP1 reduced ubiquitination of γ-tubulin and prevented mitotic defects. Our study uncovers a new mechanism for BAP1 involved in deubiquitination of γ-tubulin, which is required to prevent abnormal mitotic spindle formation and genome instability. Cancer Res; 74(22); 6499–508. ©2014 AACR.

Acquired resistance to TGFβ is a key step in the early stages of tumorigenesis. Mutations in TGFβ signaling components are rare, and little is known about the development of resistance in breast cancer. On the other hand, an activated Notch pathway is known to play a substantial role in promoting breast cancer development. Here, we present evidence of crosstalk between these two pathways through HEYL. HEYL, a basic helix–loop–helix transcription factor and a direct target of Notch signaling, is specifically overexpressed in breast cancer. HEYL represses TGFβ activity by binding to TGFβ-activated Smads. HeyL−/− mice have defective mammary gland development with fewer terminal end buds. On the other hand, HeyL transgenic mice show accelerated mammary gland epithelial proliferation and 24% of multiparous mice develop mammary gland cancer. Therefore, repression of TGFβ signaling by Notch acting through HEYL may promote initiation of breast cancer. Cancer Res; 74(22); 6509–18. ©2014 AACR.

Recent studies of the interferon-induced transcription factor STAT1 have associated its dysregulation with poor prognosis in some cancers, but its mechanistic contributions are not well defined. In this study, we report that the STAT1 pathway is constitutively upregulated in type II endometrial cancers. STAT1 pathway alteration was especially prominent in serous papillary endometrial cancers (SPEC) that are refractive to therapy. Our results defined a “SPEC signature” as a molecular definition of its malignant features and poor prognosis. Specifically, we found that STAT1 regulated MYC as well as ICAM1, PD-L1, and SMAD7, as well as the capacity for proliferation, adhesion, migration, invasion, and in vivo tumorigenecity in cells with a high SPEC signature. Together, our results define STAT1 as a driver oncogene in SPEC that modulates disease progression. We propose that STAT1 functions as a prosurvival gene in SPEC, in a manner important to tumor progression, and that STAT1 may be a novel target for molecular therapy in this disease. Cancer Res; 74(22); 6519–30. ©2014 AACR.

Osteosarcoma is a malignant bone tumor in children and adolescents characterized by intrinsic therapeutic resistance. The IGF2 is expressed at elevated levels in osteosarcoma after treatment with chemotherapy, prompting an examination of its functional contributions to resistance. We found that continuous exposure to IGF2 or insulin in the absence of serum created a dormant growth state in osteosarcoma cells that conferred resistance to various chemotherapeutic drugs in vitro. Mechanistic investigations revealed that this dormant state correlated with downregulation of downstream signaling by the IGF1 receptor, heightened cell survival, enhanced autophagy, and the presence of extracellular glutamine. Notably, inhibiting autophagy or depleting glutamine was sufficient to increase chemotherapeutic sensitivity in osteosarcoma xenografts in mice. Clinically, we confirmed that IGF expression levels were elevated in human osteosarcoma specimens from patients who received chemotherapy. Together, our results suggest that activation of IGF or insulin signaling preserves the survival of osteosarcoma cells under chemotherapeutic stress, providing a drug-resistant population that may engender minimal residual disease. Attenuating this survival mechanism may help overcome therapeutic resistance in osteosarcoma. Cancer Res; 74(22); 6531–41. ©2014 AACR.

The androgen receptor (AR) is the key driver of both early and advanced prostate cancer, making a complete understanding of its regulation important. Here, we report the identification of multiple AR-binding sites in the gene encoding the transcription factor CtBP2 (carboxyl terminal–binding protein), genetic variations of which have been associated with prostate cancer susceptibility. Notably, we found that SNPs in the human CTBP2 gene that were associated with prostate cancer development were correlated with AR-enhancer activity. High CtBP2 expression levels correlated with poor prognosis in patients, whereas CtBP2 silencing reduced tumor growth in a mouse xenograft model of human prostate cancer. Consistent with its function as a transcriptional corepressor, CtBP2 repressed tumor-suppressor genes and AR corepressors in prostate cancer cells, such as NCOR and RIP140, by binding with AR to the promoter enhancers of these genes. Global gene-expression analyses revealed a positive effect on androgen-mediated gene expression, and CtBP2 silencing was found to increase AR interactions with corepressors that limit histone modification. Overall, our results show how CtBP2 contributes to prostate cancer progression by modulating AR and oncogenic signaling. Cancer Res; 74(22); 6542–53. ©2014 AACR.

The classic model of tumor suppression implies that malignant transformation requires full “two-hit” inactivation of a tumor-suppressor gene. However, more recent work in mice has led to the proposal of a “continuum” model that involves more fluid concepts such as gene dosage-sensitivity and tissue specificity. Mutations in the tumor-suppressor gene von Hippel-Lindau (VHL) are associated with a complex spectrum of conditions. Homozygotes or compound heterozygotes for the R200W germline mutation in VHL have Chuvash polycythemia, whereas heterozygous carriers are free of disease. Individuals with classic, heterozygous VHL mutations have VHL disease and are at high risk of multiple tumors (e.g., CNS hemangioblastomas, pheochromocytoma, and renal cell carcinoma). We report here an atypical family bearing two VHL gene mutations in cis (R200W and R161Q), together with phenotypic analysis, structural modeling, functional, and transcriptomic studies of these mutants in comparison with classical mutants involved in the different VHL phenotypes. We demonstrate that the complex pattern of disease manifestations observed in VHL syndrome is perfectly correlated with a gradient of VHL protein (pVHL) dysfunction in hypoxia signaling pathways. Thus, by studying naturally occurring familial mutations, our work validates in humans the “continuum” model of tumor suppression. Cancer Res; 74(22); 6554–64. ©2014 AACR.

Bladder cancer is a highly prevalent human disease in which retinoblastoma (Rb) pathway inactivation and epigenetic alterations are common events. However, the connection between these two processes is still poorly understood. Here, we show that the in vivo inactivation of all Rb family genes in the mouse urothelium is sufficient to initiate bladder cancer development. The characterization of the mouse tumors revealed multiple molecular features of human bladder cancer, including the activation of E2F transcription factor and subsequent Ezh2 expression and the activation of several signaling pathways previously identified as highly relevant in urothelial tumors. These mice represent a genetically defined model for human high-grade superficial bladder cancer. Whole transcriptional characterizations of mouse and human bladder tumors revealed a significant overlap and confirmed the predominant role for Ezh2 in the downregulation of gene expression programs. Importantly, the increased tumor recurrence and progression in human patients with superficial bladder cancer is associated with increased E2F and Ezh2 expression and Ezh2-mediated gene expression repression. Collectively, our studies provide a genetically defined model for human high-grade superficial bladder cancer and demonstrate the existence of an Rb–E2F–Ezh2 axis in bladder whose disruption can promote tumor development. Cancer Res; 74(22); 6565–77. ©2014 AACR.

The developmental receptor NOTCH plays an important role in various human cancers as a consequence of oncogenic mutations. Here we describe a novel mechanism of NOTCH-induced tumor suppression involving modulation of the deacetylase SIRT1, providing a rationale for the use of SIRT1 inhibitors to treat cancers where this mechanism is inactivated because of SIRT1 overexpression. In Ewing sarcoma cells, NOTCH signaling is abrogated by the driver oncogene EWS-FLI1. Restoration of NOTCH signaling caused growth arrest due to activation of the NOTCH effector HEY1, directly suppressing SIRT1 and thereby activating p53. This mechanism of tumor suppression was validated in Ewing sarcoma cells, B-cell tumors, and human keratinocytes where NOTCH dysregulation has been implicated pathogenically. Notably, the SIRT1/2 inhibitor Tenovin-6 killed Ewing sarcoma cells in vitro and prohibited tumor growth and spread in an established xenograft model in zebrafish. Using immunohistochemistry to analyze primary tissue specimens, we found that high SIRT1 expression was associated with Ewing sarcoma metastasis and poor prognosis. Our findings suggest a mechanistic rationale for the use of SIRT1 inhibitors being developed to treat metastatic disease in patients with Ewing sarcoma. Cancer Res; 74(22); 6578–88. ©2014 AACR.

Epidemiologic studies linking high serum iron with cancer risks are limited and inconclusive, despite evidence implicating body iron in human carcinogenesis. A cohort of 309,443 adults in Taiwan who had no history of cancer had serum iron levels tested at the time of recruitment (1997–2008). Initially measured iron levels were associated with subsequent cancer risk by linking individuals with the National Cancer Registry and National Death File. HRs were calculated by the Cox model. One third of males (35%) and one fifth of females (18%) had high serum iron (≥120 μg/dL), which was associated with a 25% increase in risk for incidence of all cancers [HR, 1.25; 95% confidence interval (CI), 1.16–1.35] and with a 39% increase in risk for mortality from all cancers (HR, 1.39; 95% CI, 1.23–1.57). The relationship between serum iron and cancer risk was a J-shaped one, with higher cancer risk at both ends, either at lower than 60 μg/dL or higher than 120 μg/dL. At the higher end, cancer risk increased by 4% for every 10 μg/dL increment above 80 μg/dL, showing a dose–response relationship, with 60 to 79 μg/dL as a reference level. In a sensitivity analysis, the increases in risk were still observed after the first 5 years of cancer cases were excluded. Liver cancer risk was increased in HBV (−) non-hepatitis B carrier (3-fold) and HBV (+) hepatitis B carrier (24-fold). Lifestyle risks such as smoking, drinking, or inactivity interacted synergistically with high serum iron and significantly increased the cancer risks. The liver (HR, 2.49; 95% CI, 1.97–3.16) and the breast (HR, 1.31; 95% CI, 1.01–1.70) were the two major cancer sites where significant cancer risks were observed for serum iron either ≥120 μg/dL or ≥140 μg/dL, respectively. This study reveals that high serum iron is both a common disorder and a marker of increased risk for several cancers. Cancer Res; 74(22); 6589–97. ©2014 AACR.

Cell-based drug screenings indicate that tumors displaying c-MET gene amplification are “addicted” to MET signaling and therefore are very sensitive to MET-targeted agents. However, these screenings were conducted in the absence of the MET ligand, hepatocyte growth factor (HGF), which is abundant in the tumor microenvironment. Sensitivity of six MET-addicted human tumor cells to three MET kinase inhibitors (JNJ-38877605, PHA-665752, crizotinib) and one antagonistic anti-MET antibody (DN30 Fab) was analyzed in the absence or presence of HGF, in a stroma–tumor coculture system, and by combining anti-MET drugs with an HGF neutralizing antibody (ficlatuzumab) in human HGF knock-in mice bearing c-MET–amplified tumors. In all models examined, HGF promoted resistance to MET-targeted agents, affecting both their potency and efficacy. HGF-induced resistance was due to restoration of physiologic GAB1–mediated PI3K activation that compensated for loss of aberrant HER3-dependent PI3K signaling. Ficlatuzumab restored sensitivity to MET-targeted agents in coculture systems and overcame resistance to JNJ-38877605, crizotinib, and DN30 Fab in human HGF knock-in mice. These data suggest that c-MET–amplified tumor cells—which normally exhibit ligand-independent, constitutive MET activation—become dependent on HGF for survival upon pharmacologic MET inhibition. Because HGF is frequently overexpressed in human cancer, this mechanism may represent a major cause of resistance to anti-MET therapies. The ability of ficlatuzumab to overcome HGF-mediated resistance generates proof of principle that vertical inhibition of both a tyrosine kinase receptor and its ligand can be therapeutically beneficial and opens new perspectives for the treatment of MET-dependent tumors. Cancer Res; 74(22); 6598–609. ©2014 AACR.

Plasticity in cancer stem–like cells (CSC) may provide a key basis for cancer heterogeneity and therapeutic response. In this study, we assessed the effect of combining a drug that abrogates CSC properties with standard-of-care therapy in a Ewing sarcoma family tumor (ESFT). Emergence of CSC in this setting has been shown to arise from a defect in TARBP2-dependent microRNA maturation, which can be corrected by exposure to the fluoroquinolone enoxacin. In the present work, primary ESFT from four patients containing CD133+ CSC subpopulations ranging from 3% to 17% of total tumor cells were subjected to treatment with enoxacin, doxorubicin, or both drugs. Primary ESFT CSC and bulk tumor cells displayed divergent responses to standard-of-care chemotherapy and enoxacin. Doxorubicin, which targets the tumor bulk, displayed toxicity toward primary adherent ESFT cells in culture but not to CSC-enriched ESFT spheres. Conversely, enoxacin, which enhances miRNA maturation by stimulating TARBP2 function, induced apoptosis but only in ESFT spheres. In combination, the two drugs markedly depleted CSCs and strongly reduced primary ESFTs in xenograft assays. Our results identify a potentially attractive therapeutic strategy for ESFT that combines mechanism-based targeting of CSC using a low-toxicity antibiotic with a standard-of-care cytotoxic drug, offering immediate applications for clinical evaluation. Cancer Res; 74(22); 6610–22. ©2014 AACR.

MPHOSPH1 is a critical kinesin protein that functions in cytokinesis. Here, we show that MPHOSPH1 is overexpressed in hepatocellular carcinoma (HCC) cells, where it is essential for proliferation. Attenuating MPHOSPH1 expression with a tumor-selective shRNA-expressing adenovirus (Ad-shMPP1) was sufficient to arrest HCC cell proliferation in a manner associated with an accumulation of multinucleated polyploid cells, induction of postmitotic apoptosis, and increased sensitivity to taxol cytotoxicity. Mechanistic investigations showed that attenuation of MPHOSPH1 stabilized p53, blocked STAT3 phosphorylation, and prolonged mitotic arrest. In a mouse subcutaneous xenograft model of HCC, tumoral injection of Ad-shMPP1 inhibited MPHOSPH1 expression and tumor growth in a manner correlated with induction of apoptosis. Combining Ad-shMPP1 injection with taxol administration enhanced antitumor efficacy relative to taxol alone. Furthermore, Ad-shMPP1 tail vein injection suppressed formation of orthotopic liver nodules and prevented hepatic dysfunction. Taken together, our results identify MPHOSPH1 as an oncogenic driver and candidate therapeutic target in HCC. Cancer Res; 74(22); 6623–34. ©2014 AACR.

Prostate cancer is thought to be driven by oxidative stress, lipid metabolism, androgen receptor (AR) signaling, and activation of the PI3K–AKT–mTOR pathway, but it is uncertain how they may become coordinated during progression to castration-resistant disease that remains incurable. The mitotic kinase polo-like kinase 1 (Plk1) is elevated in prostate cancer, where its expression is linked to tumor grade. Notably, Plk1 signaling and lipid metabolism were identified recently as two of the top five most upregulated pathways in a mouse xenograft model of human prostate cancer. Herein, we show that oxidative stress activates both the PI3K–AKT–mTOR pathway and AR signaling in a Plk1-dependent manner in prostate cells. Inhibition of the PI3K–AKT–mTOR pathway prevented oxidative stress-induced activation of AR signaling. Plk1 modulation also affected cholesteryl ester accumulation in prostate cancer via the SREBP pathway. Finally, Plk1 inhibition enhanced cellular responses to androgen signaling inhibitors (ASI) and overcame ASI resistance in both cultured prostate cancer cells and patient-derived tumor xenografts. Given that activation of AR signaling and the PI3K–AKT–mTOR pathway is sufficient to elevate SREBP-dependent expression of key lipid biosynthesis enzymes in castration-resistant prostate cancer (CRPC), our findings argued that Plk1 activation was responsible for coordinating and driving these processes to promote and sustain the development of this advanced stage of disease. Overall, our results offer a strong mechanistic rationale to evaluate Plk1 inhibitors in combination drug trials to enhance the efficacy of ASIs in CRPC. Cancer Res; 74(22); 6635–47. ©2014 AACR.

miRNAs are essential for self-renewal and differentiation of normal and malignant stem cells by regulating the expression of key stem cell regulatory genes. Here, we report evidence implicating the miR100 in self-renewal of cancer stem–like cells (CSC). We found that miR100 expression levels relate to the cellular differentiation state, with lowest expression in cells displaying stem cell markers. Utilizing a tetracycline-inducible lentivirus to elevate expression of miR100 in human cells, we found that increasing miR100 levels decreased the production of breast CSCs. This effect was correlated with an inhibition of cancer cell proliferation in vitro and in mouse tumor xenografts due to attenuated expression of the CSC regulatory genes SMARCA5, SMARCD1, and BMPR2. Furthermore, miR100 induction in breast CSCs immediately upon their orthotopic implantation or intracardiac injection completely blocked tumor growth and metastasis formation. Clinically, we observed a significant association between miR100 expression in breast cancer specimens and patient survival. Our results suggest that miR100 is required to direct CSC self-renewal and differentiation. Cancer Res; 74(22); 6648–60. ©2014 AACR.

Mechanisms of neuroendocrine tumor (NET) proliferation are poorly understood, and therapies that effectively control NET progression and metastatic disease are limited. We found amplification of a putative oncogene, RABL6A, in primary human pancreatic NETs (PNET) that correlated with high-level RABL6A protein expression. Consistent with those results, stable silencing of RABL6A in cultured BON-1 PNET cells revealed that it is essential for their proliferation and survival. Cells lacking RABL6A predominantly arrested in G1 phase with a moderate mitotic block. Pathway analysis of microarray data suggested activation of the p53 and retinoblastoma (Rb1) tumor-suppressor pathways in the arrested cells. Loss of p53 had no effect on the RABL6A knockdown phenotype, indicating that RABL6A functions independent of p53 in this setting. By comparison, Rb1 inactivation partially restored G1 to S phase progression in RABL6A-knockdown cells, although it was insufficient to override the mitotic arrest and cell death caused by RABL6A loss. Thus, RABL6A promotes G1 progression in PNET cells by inactivating Rb1, an established suppressor of PNET proliferation and development. This work identifies RABL6A as a novel negative regulator of Rb1 that is essential for PNET proliferation and survival. We suggest RABL6A is a new potential biomarker and target for anticancer therapy in PNET patients. Cancer Res; 74(22); 6661–70. ©2014 AACR.

Deregulation of protein synthesis is a hallmark of cancer cell proliferation, survival, and metastatic progression. eIF5A1 and its highly related isoform eIF5A2 are translation initiation factors that have been implicated in a range of human malignancies, but how they control cancer development and disease progression is still poorly understood. Here, we investigated how eIF5A proteins regulate pancreatic ductal adenocarcinoma (PDAC) pathogenesis. eIF5A proteins are the only known proteins regulated by a distinct posttranslational modification termed hypusination, which is catalyzed by two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). The highly selective nature of the hypusine modification and its amenability to pharmacologic inhibition make eIF5A proteins attractive therapeutic targets. We found that the expression and hypusination of eIF5A proteins are upregulated in human PDAC tissues and in premalignant pancreatic intraepithelial neoplasia tissues isolated from Pdx-1-Cre: LSL-KRASG12D mice. Knockdown of eIF5A proteins in PDAC cells inhibited their growth in vitro and orthotopic tumor growth in vivo, whereas amplification of eIF5A proteins increased PDAC cell growth and tumor formation in mice. Small-molecule inhibitors of DHPS and DOHH both suppressed eIF5A hypusination, preventing PDAC cell growth. Interestingly, we found that eIF5A proteins regulate PDAC cell growth by modulating the expression of PEAK1, a nonreceptor tyrosine kinase essential for PDAC cell growth and therapy resistance. Our findings suggest that eIF5A proteins utilize PEAK1 as a downstream effector to drive PDAC pathogenesis and that pharmacologic inhibition of the eIF5A–hypusine–PEAK1 axis may provide a novel therapeutic strategy to combat this deadly disease. Cancer Res; 74(22); 6671–81. ©2014 AACR.

Cervical cancers, a malignancy associated with oncogenic papilloma viruses, remain a major disease burden in the absence of effective implementation of preventive strategies. CD66+ cells have previously been identified as a tumor-propagating subset in cervical cancers. We investigated the existence, differentiation state, and neoplastic potential of CD66+ cells in a precancer cell line harboring HPV31b episomes. The gene expression profile of CD66high cells overlaps with differentiated keratinocytes, neoplastic mesenchymal transition, cells of the squamocolumnar junction, and cervical cancer cell line–derived spheroids. There is elevated expression of DNMT1, Notch1, and the viral gene product E1⁁E4 in CD66high cells. Thus, CD66high cells, in the absence of differentiating signals, express higher levels of key regulators of keratinocytes stemness, differentiation, and the viral life cycle, respectively. We also find a striking association of neoplastic traits, including migration, invasion, and colony formation, in soft agar with CD66high cells. These properties and a distinct G2–M–enriched cell-cycle profile are conserved in cells from cervical cancers. Principally, using a precancerous cell line, we propose that CD66high cells have an intermediate differentiation state, with a cellular milieu connected with both viral replication and neoplastic potential, and validate some key features in precancer lesions. Such pathophysiologically relevant systems for defining cellular changes in the early phases of the disease process provide both mechanistic insight and potential therapeutic strategies. Collectively, our data provide a rationale for exploring novel therapeutic targets in CD66+ subsets during cancer progression. Cancer Res; 74(22); 6682–92. ©2014 AACR.

Human BRAF-driven tumors are aggressive malignancies with poor clinical outcome and lack of sensitivity to therapies. TRAP1 is a HSP90 molecular chaperone deregulated in human tumors and responsible for specific features of cancer cells, i.e., protection from apoptosis, drug resistance, metabolic regulation, and protein quality control/ubiquitination. The hypothesis that TRAP1 plays a regulatory function on the BRAF pathway, arising from the observation that BRAF levels are decreased upon TRAP1 interference, was tested in human breast and colorectal carcinoma in vitro and in vivo. This study shows that TRAP1 is involved in the regulation of BRAF synthesis/ubiquitination, without affecting its stability. Indeed, BRAF synthesis is facilitated in a TRAP1-rich background, whereas increased ubiquitination occurs upon disruption of the TRAP1 network that correlates with decreased protein levels. Remarkably, BRAF downstream pathway is modulated by TRAP1 regulatory activity: indeed, TRAP1 silencing induces (i) ERK phosphorylation attenuation, (ii) cell-cycle inhibition with cell accumulation in G0–G1 and G2–M transitions, and (iii) extensive reprogramming of gene expression. Interestingly, a genome-wide profiling of TRAP1-knockdown cells identified cell growth and cell-cycle regulation as the most significant biofunctions controlled by the TRAP1 network. It is worth noting that TRAP1 regulation on BRAF is conserved in human colorectal carcinomas, with the two proteins being frequently coexpressed. Finally, the dual HSP90/TRAP1 inhibitor HSP990 showed activity against the TRAP1 network and high cytostatic potential in BRAF-mutated colorectal carcinoma cells. Therefore, this novel TRAP1 function represents an attractive therapeutic window to target dependency of BRAF-driven tumors on TRAP1 translational/quality control machinery. Cancer Res; 74(22); 6693–704. ©2014 AACR.

Extramedullary myelopoiesis occurs commonly in tumor-bearing animals and is known to lead to accumulation of peripheral myeloid-derived suppressor cells (MDSC), which play an important role in immune escape. However, the cellular and molecular mechanisms by which tumors induce extramedullary myelopoiesis are poorly understood. In this study, we found that osteopontin expressed by tumor cells enhances extramedullary myelopoiesis in a CD44-dependent manner through the Erk1/2–MAPK pathway. Osteopontin-mediated extramedullary myelopoiesis was directly associated with increased MDSCs in tumor-bearing hosts. More importantly, osteopontin silencing in tumor cells delayed both tumor growth and extramedullary myelopoiesis, while the same treatment did not affect tumor growth in vitro. Finally, treatment with an antibody against osteopontin inhibited tumor growth and synergized with cell-based immunotherapeutic vaccines in mediating antitumor immunity. Our findings unveil a novel immunosuppressive role for tumor-derived osteopontin and offer a rationale for its therapeutic targeting in cancer treatment. Cancer Res; 74(22); 6705–16. ©2014 AACR.

Colorectal tumorigenesis is accompanied by the generation of oxidative stress, but how this controls tumor development is poorly understood. Here, we studied how the H2O2-reducing enzyme glutathione peroxidase 2 (GPx2) regulates H2O2 stress and differentiation in patient-derived “colonosphere” cultures. GPx2 silencing caused accumulation of radical oxygen species, sensitization to H2O2-induced apoptosis, and strongly reduced clone- and metastasis-forming capacity. Neutralization of radical oxygen species restored clonogenic capacity. Surprisingly, GPx2-suppressed cells also lacked differentiation potential and formed slow-growing undifferentiated tumors. GPx2 overexpression stimulated multilineage differentiation, proliferation, and tumor growth without reducing the tumor-initiating capacity. Finally, GPx2 expression was inversely correlated with H2O2-stress signatures in human colon tumor cohorts, but positively correlated with differentiation and proliferation. Moreover, high GPx2 expression was associated with early tumor recurrence, particularly in the recently identified aggressive subtype of human colon cancer. We conclude that H2O2 neutralization by GPx2 is essential for maintaining clonogenic and metastatic capacity, but also for the generation of differentiated proliferating tumor mass. The results reveal an unexpected redox-controlled link between tumor mass formation and metastatic capacity. Cancer Res; 74(22); 6717–30. ©2014 AACR.