Salmonella has a natural ability to target a wide range of tumors in animal models. However, strains used for cancer therapy have generally been selected only for their avirulence rather than tumor-targeting ability. To select Salmonella strains that are avirulent and yet efficient in tumor-targeting, a necessary criteria for clinical applications, we measured the relative fitness of 41,000 Salmonella transposon insertion mutants growing in mouse models of human prostate cancer and melanoma. Two classes of potentially safe mutants were identified. Class 1 mutants showed reduced fitness in normal tissues and unchanged fitness in tumors (e.g., mutants in htrA, SPI-2, and STM3120). Class 2 mutants showed reduced fitness in tumors and normal tissues (e.g., mutants in aroA and aroD). In a competitive fitness assay in human PC3 tumors growing in mice, class 1 mutant STM3120 had a fitness advantage over class 2 mutants aroA and aroD, validating the findings of the initial screening of a large pool of transposon mutants and indicating a potential advantage of class 1 mutants for delivery of cancer therapeutics. In addition, an STM3120 mutant successfully targeted tumors after intragastric delivery, opening up the oral route as an option for therapy administration.
Oncomirs are microRNAs (miRNA) that acts as oncogenes or tumor suppressor genes. Efficient identification of oncomirs remains a challenge. Here we report a novel, clinically guided genetic screening approach for the identification of oncomirs, identifying mir-30d through this strategy. mir-30d regulates tumor cell proliferation, apoptosis, senescence, and migration. The chromosomal locus harboring mir-30d was amplified in more than 30% of multiple types of human solid tumors (n = 1,283). Importantly, higher levels of mir-30d expression were associated significantly with poor clinical outcomes in ovarian cancer patients (n = 330, P = 0.0016). Mechanistic investigations suggested that mir-30d regulates a large number of cancer-associated genes, including the apoptotic caspase CASP3. The guided genetic screening approach validated by this study offers a powerful tool to identify oncomirs that may have utility as biomarkers or targets for drug development.
Multiple endocrine neoplasia type 1 (MEN1) is an inherited tumor syndrome that includes susceptibility to pancreatic islet tumors. This syndrome results from mutations in the MEN1 gene, encoding menin. Menin acts as an oncogenic co-factor for MLL-fusion protein-mediated histone H3 lysine 4 methylation, but the precise basis for how menin suppresses gene expression and proliferation of pancreatic beta cells remains poorly understood. Here we show that menin ablation enhances Hedgehog (Hh) signaling, a pro-proliferative and oncogenic pathway, in murine pancreatic islets. Menin directly interacts with protein arginine methyltransferase 5 (PRMT5), a negative regulator of gene transcription. Menin recruits PRMT5 to the promoter of the Gas1 gene, a crucial factor for binding of Sonic hedgehog (Shh) ligand to its receptor PTCH1 and subsequent activation of the Hh signaling pathway, increases repressive histone arginine dimethylation (H4R3m2s) and suppresses Gas1 expression. Notably, MEN1 disease-related menin mutants have reduced binding to PRMT5, and fail to impart the repressive H4R3m2s mark at the Gas1 promoter, resulting in its elevated expression. Pharmacological inhibition of Hh signaling significantly reduces proliferation of insulinoma cells, and expression of Hh signaling targets including Ptch1, in MEN1 tumors of mice. These findings uncover a novel link between menin and Hh signaling whereby menin/PRMT5 epigenetically suppress Hh signaling, revealing it as a target for treating MEN1 tumors.
Menin; PRMT5; Hh signaling; Epigenetics; GDC-0449
Elevated oxidative stress is observed more frequently in cancer cells than in normal cells. It is therefore expected that additional exposure to a low level of reactive oxygen species (ROS) will push cancer cells toward death, whereas normal cells might maintain redox homeostasis through adaptive antioxidant responses. We previously demonstrated that parthenolide enhances ROS production in prostate cancer cells through activation of NADPH oxidase. The present study identifies KEAP1 as the downstream redox target that contributes to parthenolide’s radiosensitization effect in prostate cancer cells. In vivo, parthenolide increases radiosensitivity of mouse xenograft tumors but protects normal prostate and bladder tissues against radiation-induced injury. Mechanistically, parthenolide increases the level of cellular ROS and causes oxidation of thioredoxin (TrX) in prostate cancer cells, leading to a TrX-dependent increase in a reduced state of KEAP1, which in turn leads to KEAP1-mediated PGAM5 and Bcl-xL (BCL2L1) degradation. In contrast, parthenolide increases oxidation of KEAP1 in normal prostate epithelial cells, leading to increased Nrf2 (NFE2L2) levels and subsequent Nrf2-dependent expression of antioxidant enzymes. These results reveal a novel redox-mediated modification of KEAP1 in controlling the differential effect of parthenolide on tumor and normal cell radiosensitivity. Further, they show it is possible to develop a tumor-specific radiosensitizing agent with radioprotective properties in normal cells.
Keap1; Nrf2; PGAM5; Bcl-xL; parthenolide; radiotherapy; prostate cancer; reactive oxygen species (ROS); redox modification; antioxidant proteins; mitochondrial function
Tamoxifen is widely used to treat estrogen receptor (ER)-positive breast cancer. Recent findings that tamoxifen and its derivative 4-dehydroxy-tamoxifen (OHT) can exert ER-independent cytotoxic effects have prompted the initiation of clinical trials to evaluate its use in ER-negative malignancies. For example, tamoxifen and OHT exert cytotoxic effects in malignant peripheral nerve sheath tumors (MPNSTs) where estrogen is not involved. In this study, we gained insights into the ER-independent cytotoxic effects of OHT by studying how it kills MPNST cells. Although caspases were activated following OHT treatment, caspase inhibition provided no protection from OHT-induced death. Rather, OHT-induced death in MPNST cells was associated with autophagic induction and attenuated by genetic inhibition of autophagic vacuole formation. Mechanistic investigations revealed that OHT stimulated K-Ras degradation through autophagy induction, which is critical for survival of MPNST cells. Similarly, we found that OHT induced K-Ras degradation in breast, colon, glioma and pancreatic cancer cells. Our findings describe a novel mechanism of autophagic death triggered by tamoxifen and OHT in tumor cells that may be more broadly useful clinically in cancer treatment.
autophagy; K-Ras; MPNST; tamoxifen; PKC
The non-histone chromatin binding protein HMGA2 is expressed predominantly in the mesenchyme prior to its differentiation, but it is also expressed in tumors of epithelial origin. Ectopic expression of HMGA2 in epithelial cells induces epithelial-mesenchymal transition (EMT), which has been implicated in the acquisition of metastatic characters in tumor cells. However, little is known regarding in vivo modulation of HMGA2 and its effector functions in tumor metastasis. Here we report that HMGA2 loss-of-function in a mouse model of cancer reduces tumor multiplicity. HMGA2-positive cells were identified at the invasive front of human and mouse tumors. Additionally, in a mouse allograft model, HMGA2 overexpression converted non-metastatic 4TO7 breast cancer cells to metastatic cells that homed specifically to liver. Interestingly, expression of HMGA2 enhanced TGFβ signaling by activating expression of the TGFβ type II receptor (TGFβRII), which also localized to the invasive front of tumors. Together our results argued that HMGA2 plays a critical role in EMT by activating the TGFβ signaling pathway, thereby inducing invasion and metastasis of human epithelial cancers.
High-mobility group A2 (HMGA2); TGFβ type II receptor (TGFβRII); epithelial-mesenchymal transition (EMT); invasive front; metastasis
The emergence of antiestrogen resistance in breast cancer is an important clinical phenomenon affecting long-term survival in this disease. Identifying factors that convey cell survival in this setting may guide improvements in treatment. Estrogen (E2) can induce apoptosis in breast cancer cells that have been selected for survival after E2 deprivation for long periods (MCF-7:5C cells), but the mechanisms underlying E2-induced stress in this setting have not been elucidated. Here, we report that the c-Src kinase functions as a key adapter protein for the estrogen receptor (ER, ESR1) in its activation of stress responses induced by E2 in MCF-7:5C cells. E2 elevated phosphorylation of c-Src which was blocked by 4-hydroxytamoxifen (4-OHT), suggesting that E2 activated c-Src through the ER. We found that E2 activated the sensors of the unfolded protein response (UPR), IRE1α (ERN1) and PERK kinase (EIF2AK3), the latter of which phosphorylates eukaryotic translation initiation factor-2α (eIF2α). E2 also dramatically increased reactive oxygen species (ROS) production and up-regulated expression of heme oxygenase HO-1 (HMOX1), an indicator of oxidative stress, along with the central energy sensor kinase AMPK (PRKAA2). Pharmacological or RNAi-mediated inhibition of c-Src abolished the phosphorylation of eIF2α and AMPK, blocked E2-induced ROS production, and inhibited E2-induced apoptosis. Together, our results establish that c-Src kinase mediates stresses generated by E2 in long-term E2-deprived cells that trigger apoptosis. This work offers a mechanistic rationale for a new approach in the treatment of endocrine-resistant breast cancer.
c-Src; endoplasmic reticulum stress; oxidative stress; apoptosis; estrogen receptor
Both genetic mutations and ultraviolet (UV) irradiation can predispose individuals to melanoma. Although BRAFV600E is the most prevalent oncogene in melanoma, the BRAFV600E mutant is not sufficient to induce tumors in vivo. Mutation at the CDKN2A locus is another melanoma-predisposing event that can disrupt the function of both p16INK4a and ARF. Numerous studies have focused on the role of p16INK4a in melanoma, but the involvement of ARF, a well-known p53 activator, is still controversial. Using a transgenic BRAFV600E mouse model previously generated in our laboratory, we report that loss of ARF is able to enhance spontaneous melanoma formation and cause profound sensitivity to neonatal UVB exposure. Mechanistically, BRAFV600E and ARF deletion synergize to inhibit nucleotide excision repair by epigenetically repressing XPC and inhibiting the E2F4/DP1 complex. We suggest that the deletion of ARF promotes melanomagenesis not by abrogating p53 activation but by acting in concert with BRAFV600E to increase the load of DNA damage caused by UV irradiation.
BRAFV600E; ARF; UV melanomas; XPC; promoter methylation
Cisplatin is a widely used anticancer drug that acts by binding DNA and causing the formation of intrastrand and interstrand (ICL) cross-links, but the precise downstream effects of the latter damage are not well understood. In this study, we investigated the influence of cisplatin ICLs on synthetic nucleosomes that were platinated in a site-specific manner in vitro and on gene transcription in live mammalian cells. Nucleosome core particles (NCPs) that we constructed contained site-specific cisplatin 5′-d(G*pC)/5′-d(G*pC) ICLs, where the asterisk denotes the platinated nucleoside, to examine the influence of platinum lesions on the dynamic behavior of nucleosomes in solution. A cisplatin ICL, but not a 1,2-d(GpG) cross-link, significantly inhibited ATP-independent histone octamer-DNA sliding. We also used a novel linearization-recircularization strategy described here to synthesize mammalian expression vectors containing site-specific cisplatin ICLs. Plasmid vectors were tested in live mammalian cellsto study the transcription inhibition effects of cisplatin ICLs in the context of two different repair backgrounds. Cisplatin ICLs inhibit transcription as effectively as 1,2-d(GpG) cross-links. We determined that nucleotide excision repair plays a key role in the removal of cisplatin ICLs, acting in a replication-independent fashion. We also found that loss of mismatch repair function dramatically attenuatesthe transcription inhibition effects by cisplatin ICLs but not 1,2-d(GpG) intrastrand cross-links. Our results revealed the unique properties of cisplatin ICLs on nucleosome mobility and on transcription, and they defined how these adducts act in a manner completely different from that used for cisplatin 1,2-d(GpG) cross-links. These new findings provide direct support for a role of ICLs in the pharmacological activities of cisplatin, despite the lower frequency of their formation.
Ataxia-telangiectasia (A-T) is a genetic disorder associated with high incidence of B cell lymphoma. Using an A-T mouse model, we compared lymphoma incidence in several isogenic mouse colonies harboring different bacterial communities, finding that intestinal microbiota are a major contributor to disease penetrance and latency, lifespan, molecular oxidative stress and systemic leucocyte genotoxicity. High throughput sequence analysis of rRNA genes identified mucosa-associated bacterial phylotypes that were colony-specific. Lactobacillus johnsonii, which was deficient in the more cancer-prone mouse colony, was causally tested for its capacity to confer reduced genotoxicity when restored by short-term oral transfer. This intervention decreased systemic genotoxicity, a response associated with reduced basal leucocytes and the cytokine-mediated inflammatory state, and mechanistically linked to the host cell biology of systemic genotoxicity. Our results suggest that intestinal microbiota are a potentially modifiable trait for translational intervention in individuals at risk for B cell lymphoma, or for other diseases that are driven by genotoxicity or the molecular response to oxidative stress.
Ataxia telangiectasia; genotoxicity; Lactobacillus johnsonii; lymphoma; oxidative stress
DNA double-strand breaks (DSBs) occur frequently during replication in sister chromatids, and are dramatically increased when cells are exposed to chemotherapeutic agents including camptothecin. Such DSBs are efficiently repaired specifically by homologous recombination (HR) with the intact sister chromatid. HR hence plays pivotal roles in cellular proliferation and cellular tolerance to camptothecin. Mammalian cells carry several structure-specific endonucleases, such as Xpf-Ercc1 and Mus81-Eme1, in which Xpf and Mus81 are the essential subunits for enzymatic activity. Here we show the functional overlap between Xpf and Mus81 by conditionally inactivating Xpf in the chicken DT40 cell line, which has no Mus81 ortholog. Although mammalian cells deficient in either Xpf or Mus81 are viable, Xpf inactivation in DT40 cells was lethal, resulting in a marked increase in the number of spontaneous chromosome breaks. Similarly, inactivation of both Xpf and Mus81 in human HeLa cells and murine embryonic stem cells caused numerous spontaneous chromosome breaks. Furthermore, the phenotype of Xpf-deficient DT40 cells was reversed by ectopic expression of human Mus81-Eme1 or human Xpf-Ercc1 heterodimers. These observations indicate the functional overlap of Xpf-Ercc1 and Mus81-Eme1 in the maintenance of genomic DNA. Both Mus81-Eme1 and Xpf-Ercc1 contribute to the completion of HR as evidenced by the following data that the expression of Mus81-Eme1 or Xpf-Ercc1 diminished the number of camptothecin-induced chromosome breaks in Xpf-deficient DT40 cells, and preventing early steps in HR by deleting XRCC3 suppressed the inviability of Xpf-deficient DT40 cells. In summary, Xpf and Mus81 have a substantially overlapping function in completion of HR.
homologous recombination; Xpf; Mus81; nuclease; chemotherapeutic agents
Adaptive responses can be induced in cells by very low doses of ionizing radiation resulting in an enhanced resistance to much larger exposures. The inhibitor of apoptosis (IAP) protein, survivin, has been implicated in many adaptive responses to cellular stress. Computerized axial tomography (CAT) used in image guided radiotherapy to position and monitor tumor response utilizes very low radiation doses ranging from 0.5 to 100 mGy. We investigated the ability of these very low radiation doses administered along with two 2 Gy doses separated by 24 h, a standard conventional radiotherapy dosing schedule, to initiate adaptive responses resulting in the elevation of radiation resistance in exposed cells. Human colon carcinoma (RKO36), mouse sarcoma (SA-NH), along with transformed mouse embryo fibroblasts (MEF), wild type (WT) or cells lacking functional tumor necrosis factor receptors 1 and 2 (TNFR1−R2−) were used to assess their relative ability to express an adaptive response when grown either to confluence in vitro or as tumors in the flank of C57BL/6 mice. The survival of each of these cells was elevated from 5 to 20% (P ≤ 0.05) as compared to cells not receiving a 100 mGy or lesser dose. Additionally, the cells exposed to 100 mGy exhibited elevations in survivin levels, reductions in apoptosis frequencies, and loss of an adaptive response if transfected with survivin siRNA. This survivin-mediated adaptive response has the potential for affecting outcomes if regularly induced throughout a course of image guided radiation therapy.
Adaptive-response; Survivin; Computed Tomography; TNF receptors
The peroxisome proliferator-activated receptor-δ (PPARδ) regulates a multitude of physiological processes associated with glucose and lipid metabolism, inflammation and proliferation. One or more of these processes are potential risk factors for the ability of PPARδ agonists to promote tumorigenesis in the mammary gland. In the present study, we describe a new transgenic mouse model in which activation of PPARδ in the mammary epithelium by endogenous or synthetic ligands resulted in progressive histopathological changes that culminated in the appearance of estrogen receptor- and progesterone receptor-positive and ErbB2-negative infiltrating ductal carcinomas. Multiparous mice presented with mammary carcinomas after a latency of 12 months, and administration of the PPARδ ligand GW501516 reduced tumor latency to five months. Histopathological changes occurred concurrently with an increase in an inflammatory, invasive, metabolic and proliferative gene signature, including expression of the trophoblast gene, Plac1, beginning one week after GW501516 treatment, and remained elevated throughout tumorigenesis. The appearance of malignant changes correlated with a pronounced increase in phosphatidylcholine and lysophosphatidic acid metabolites, which coincided with activation of Akt and mTor signaling that were attenuated by treatment with the mTor inhibitor everolimus. Our findings are the first to demonstrate a direct role of PPARδ in the pathogenesis of mammary tumorigenesis, and suggest a rationale for therapeutic approaches to prevent and treat this disease.
PPARδ; transgenic; tumorigenesis; mTor; Plac1
Fanconi anemia (FA) is a genome-instability syndrome that has been associated with both cancer predisposition and bone-marrow failure. FA proteins are involved in cellular response to replication stress in which they coordinate DNA repair with DNA replication and cell cycle progression. One regulator of the replication stress response is the ATP-dependent DNA translocase FANCM which we have shown to be hyperphosphorylated in response to various genotoxic agents. However, the significance of this phosphorylation remained unclear. Here we show that genotoxic stress-induced FANCM phosphorylation is ATR dependent and that this modification is highly significant for the cellular response to replication stress. We identified serine (S1045) residue of FANCM that is phosphorylated in response to genotoxic stress and this effect is ATR dependent. We show that S1045 is required for FANCM functions including its role in FA pathway integrity, recruiting FANCM to the site of interstrand cross links, preventing the cells from entering mitosis prematurely, and efficient activation of the CHK1 and G2/M checkpoints. Overall, our data suggest that an ATR-FANCM feedback loop is present in the FA and replication-stress-response pathways, and that it is required for both efficient ATR/CHK1-checkpoint activation and FANCM function.
DNA Repair; Phosphorylation; FANCM; Fanconi anemia; ATR
Hyperpolarized 13C magnetic resonance spectroscopy (MRS) provides a unique opportunity to detect real-time metabolic fluxes as a means to measure metabolic treatment responses in vivo. Here we show that pharmacological inhibition of lactate dehydrogenase A suppressed the conversion of hyperpolarized 13C-pyruvate to lactate in murine xenografts of P493 human lymphoma. In contrast, a glutaminase inhibitor reduced conversion of 13C-pyruvate to alanine without affecting conversion of pyruvate to lactate. These results illustrate the ability to monitor biomarkers for responses to anti-metabolic therapy in real time, paving the way for clinical development of imaging biomarkers to monitor metabolic pharmacodynamics.
Degradation of signaling proteins is one of the most powerful tumor suppressive mechanisms by which a cell can control its own growth. Here, we identify RHOA as the molecular target by which autophagy maintains genomic stability. Specifically, inhibition of autophagosome degradation by the loss of the v-ATPase a3 (TCIRG1) subunit is sufficient to induce aneuploidy. Underlying this phenotype, active RHOA is sequestered via p62 (SQSTM1) within autolysosomes, and fails to localize to the plasma membrane or to the spindle midbody. Conversely, inhibition of autophagosome formation by ATG5 shRNA dramatically increases localization of active RHOA at the midbody, followed by diffusion to the flanking zones. As a result, all of the approaches we examined that compromise autophagy (irrespective of the defect: autophagosome formation, sequestration or degradation) drive cytokinesis failure, multinucleation, and aneuploidy, processes that directly have an impact upon cancer progression. Consistently, we report a positive correlation between autophagy defects and the higher expression of RHOA in human lung carcinoma. We therefore propose that autophagy may act in part as a safeguard mechanism that degrades and thereby maintains the appropriate level of active RHOA at the midbody for faithful completion of cytokinesis and genome inheritance.
Autophagy; RHOA; tumor suppression; cytokinesis; aneuploidy
Intravasation, the active entry of primary tumor cells into the vasculature, remains the least studied step in the metastatic cascade. Protease-mediated escape and stromal invasion of tumor cells represent widely-accepted processes leading up to the intravasation step. However, molecular factors that contribute directly to tumor cell vascular penetration have not been identified. In this study, the in vivo role of the collagenolytic protease, MMP-1, in cancer cell intravasation and metastasis was analyzed by employing a highly-disseminating variant of human HEp3 epidermoid carcinoma, HEp3-hi/diss. Whereas naturally-acquired or experimentally-induced MMP-1 deficiency substantially suppressed HEp3-hi/diss intravasation, supplementation of recombinant MMP-1 to MMP-1-silenced primary tumors, restored their impaired vascular dissemination. Surprisingly, abrogation of MMP-1 production and activity did not affect significantly HEp3-hi/diss migration or matrix invasion, suggesting non-collagenolytic mechanisms underlying MMP-1-dependent cell intravasation. In support of such non-collagenolytic mechanisms, MMP-1 silencing in HEp3-hi/diss cells modulated the microarchitecture and integrity of the angiogenic vasculature in a novel microtumor model. Concomitantly, MMP-1 deficiency led to decreased levels of intratumoral vascular permeability, tumor cell intravasation and metastatic dissemination. Taking advantage of PAR1 deficiency of HEp3-hi/diss cells, we further demonstrate that endothelial PAR1 is a putative non-tumor-cell/non-matrix target, activation of which by carcinoma-produced MMP-1 regulates endothelial permeability and transendothelial migration. The inhibitory effects of specific PAR1 antagonists in live animals have also indicated that the mechanisms of MMP-1-dependent vascular permeability in tumors involve endothelial PAR1 activation. Together, our findings mechanistically underscore the contribution of a tumor MMP-1/endothelial PAR1 axis to actual intravasation events manifested by aggressive carcinoma cells.
Matrix metalloproteinase-1; PAR1; metastasis; squamous cell carcinoma
The Drosophila Eyes Absent Homologue 1 (EYA1) is a component of the retinal determination gene network (RDGN) and serves as an H2AX phosphatase. The cyclin D1 gene encodes the regulatory subunits of a holoenzyme that phosphorylates and inactivates the pRb protein. Herein, comparison with normal breast demonstrated EYA1 is overexpressed with cyclin D1 in luminal B breast cancer subtype. EYA1 enhanced breast tumor growth in mice in vivo requiring the phosphatase domain. EYA1 enhanced cellular proliferation, inhibited apoptosis, and induced contact-independent growth and cyclin D1 abundance. The induction of cellular proliferation and cyclin D1 abundance, but not apoptosis, was dependent upon the EYA1 phosphatase domain. The EYA1-mediated transcriptional induction of cyclin D1 occurred via the AP-1 binding site at −953 and required the EYA1 phosphatase function. The AP-1 mutation did not affect SIX1-dependent activation of cyclin D1. EYA1 was recruited in the context of local chromatin to the cyclin D1 AP-1 site. The EYA1 phosphatase function determined the recruitment of CBP, RNA polymerase II and acetylation of H3K9 at the cyclin D1 gene AP-1 site regulatory region in the context of local chromatin. The EYA1 phosphatase regulates cell cycle control via transcriptional complex formation at the cyclin D1 promoter.
Metastasis, the leading cause of cancer death, requires tumor cell intravasation, migration through the bloodstream, arrest within capillaries, and extravasation to invade distant tissues. Few mechanistic details have been reported thus far regarding the extravasation process or re-entry of circulating tumor cells at metastatic sites. Here, we demonstrate that neuropilin-2 (NRP-2), a multi-functional non-kinase receptor for semaphorins, vascular endothelial growth factor (VEGF), and other growth factors, expressed on cancer cells interacts with α5 integrin on endothelial cells to mediate vascular extravasation and metastasis in zebrafish and murine xenograft models of clear cell renal cell carcinoma (RCC) and pancreatic adenocarcinoma. In tissue from RCC patients, NRP-2 expression is positively correlated with tumor grade and highest in metastatic tumors. In a prospectively acquired cohort of patients with pancreatic cancer, high NRP-2 expression co-segregated with poor prognosis. Through biochemical approaches as well as Atomic Force Microscopy (AFM), we describe a unique mechanism through which NRP-2 expressed on cancer cells interacts with α5 integrin on endothelial cells to mediate vascular adhesion and extravasation. Taken together, our studies reveal a clinically significant role of NRP-2 in cancer cell extravasation and promotion of metastasis.
Neuropilin; metastasis; integrin; renal cell carcinoma; pancreatic cancer; endothelial cells; adhesion; extravasation
Aggressive metastasis is the chief cause of the high morbidity and mortality associated with pancreatic cancer, yet the basis for its aggressive behavior remains elusive. Extracellular DNA (exDNA) is a recently discovered component of inflammatory tissue states. Here we report that exDNA is present on the surface of pancreatic cancer cells where it is critical for driving metastatic behavior. ExDNA was abundant on the surface and vicinity of cultured pancreatic cancer cells, but absent from normal pancreas cells. Strikingly, treatment of cancer cell cultures with DNase I to degrade DNA non-specifically reduced metastatic characters associated with matrix attachment, migration and invasion. We further assessed the role of exDNA in pancreatic cancer metastasis in vivo using an orthotopic xenograft model established by implantation of pancreatic cancer cells expressing firefly luciferase. Non-invasive bioluminescent imaging confirmed that DNase I treatment was sufficient to suppress tumor metastasis. Mechanistic investigations suggested the existence of a positive feedback loop in which exDNA promotes expression of the inflammatory chemokine CXCL8 which leads to higher production of exDNA by pancreatic cancer cells, with a significant reduction in CXCL8 levels achieved by DNase I treatment. Taken together, our results strongly suggest that exDNA contributes to the highly invasive and metastatic character of pancreatic cancer.
extracellular DNA; DNase; CXCL8/IL-8; pancreatic cancer; metastasis; inflammation
The TWEAK (TNFSF12) receptor Fn14 (TNFRSF12A) is expressed at low levels in normal tissues but frequently highly expressed in a wide range of tumor types such as lung, melanoma, and breast and therefore it is a potentially unique therapeutic target for these diverse tumor types. We have generated a recombinant protein containing a humanized, dimeric single-chain anti-Fn14 antibody fused to recombinant gelonin toxin as a potential therapeutic agent (designated hSGZ). The hSGZ immunotoxin is a highly potent and selective agent that kills Fn14-positive tumor cells in vitro. Treatment of cells expressing the multidrug resistance protein MDR1 (ABCB1B) showed no cross-resistance to hSGZ. Induced overexpression of Fn14 levels in MCF7 cells through HER2 (ERBB2) signaling translated to an improved therapeutic index of hSGZ treatment. In combination with trastuzumab, hSGZ demonstrated an additive or synergistic cytotoxic effect on HER2+/Fn14+ breast cancer cell lines. Also, hSGZ treatment inhibited Erb3/Akt signaling in HER2-overexpressing breast cancer cells. Pharmacokinetic studies in mice revealed that hSGZ exhibited a bi-exponential clearance from plasma with a rapid initial clearance (t 1/2 α = 1.26 h) followed by a 7-fold longer plasma half life (t 1/2 β = 7.29 h). At 24, 48 and 72 h after injection, uptake of the hSGZ into tumors was 5.1, 4.8 and 4.7 %ID/g, with a tumor-to-muscle ratio of 5.6, 6.2 and 9.0, respectively. Therapeutic efficacy studies showed significant tumor inhibition effects using an MDA-MB-231/Luc breast cancer xenograft model. Our findings show that hSGZ is an effective anticancer agent and a potential candidate for clinical studies.
Fn14; immunotoxin; hSGZ
Metformin inhibits cancer cell proliferation and epidemiology studies suggest an association with increased survival in cancer patients taking metformin, however, the mechanism by which metformin improves cancer outcomes remains controversial. To explore how metformin might directly affect cancer cells, we analyzed how metformin altered the metabolism of prostate cancer cells and tumors. We found that metformin decreased glucose oxidation and increased dependency on reductive glutamine metabolism in both cancer cell lines and in a mouse model of prostate cancer. Inhibition of glutamine anaplerosis in the presence of metformin further attenuated proliferation while increasing glutamine metabolism rescued the proliferative defect induced by metformin. These data suggest that interfering with glutamine may synergize with metformin to improve outcomes in patients with prostate cancer.
It is poorly understood how driver mutations in cancer genes work together to promote tumor development. Renal cell carcinoma (RCC) offers a unique opportunity to study complex relationships among cancer genes. The four most commonly mutated genes in RCC of clear-cell type (the most common type) are two-hit tumor suppressor genes and they cluster in a 43 Mb region on chromosome 3p that is deleted in ~90% of tumors: VHL (mutated in ~80%), PBRM1 (~50%), BAP1 (~15%) and SETD2 (~15%). Meta-analyses that we conducted show that mutations in PBRM1 and SETD2 co-occur in tumors at a frequency higher than expected by chance alone, indicating that these mutations may cooperate in tumorigenesis. In contrast, consistent with our previous results, mutations in PBRM1 and BAP1 tend to be mutually exclusive. Mutation exclusivity analyses (often confounded by lack of statistical power) raise the possibility of functional redundancy. However, mutation exclusivity may indicate negative genetic interactions, as proposed herein for PBRM1 and BAP1, and mutations in these genes define RCC with different pathologic features, gene expression profiles, and outcomes. Negative genetic interactions among cancer genes point toward broader context-dependencies of cancer gene action beyond tissue dependencies. Understanding cancer genes dependencies may unravel vulnerabilities that can be exploited therapeutically.
Radiotherapy is used to treat many types of cancer, but many treated patients relapse with local tumor recurrence. Tumor-infiltrating myeloid cells (TIMs), including CD11b (ITGAM)+F4/80 (EMR1)+ tumor-associated macrophages (TAMs) and CD11b+Gr-1 (LY6G)+ myeloid-derived suppressor cells (MDSCs), respond to cancer-related stresses and play critical roles in promoting tumor angiogenesis, tissue remodeling and immunosuppression. In this report, we employed a prostate cancer model to investigate the effects of irradiation on TAMs and MDSCs in tumor-bearing animals. Unexpectedly, when primary tumor sites were irradiated we observed a systemic increase of MDSCs in spleen, lung, lymph nodes and peripheral blood. Cytokine analysis showed that the macrophage colony-stimulating factor CSF1 increased by 2-fold in irradiated tumors. Enhanced macrophage migration induced by conditioned media from irradiated tumor cells was completely blocked by a selective inhibitor of CSF1R. These findings were confirmed in prostate cancer patients, where serum levels of CSF1 increased after radiotherapy. Mechanistic investigations revealed the recruitment of the DNA damage-induced kinase ABL1 into cell nuclei where it bound the CSF1 gene promoter and enhanced CSF1 gene transcription. When added to radiotherapy, a selective inhibitor of CSF1R suppressed tumor growth more effectively than radiation alone. Our results highlight the importance of CSF1/CSF1R signaling in the recruitment of TIMs which can limit the efficacy of radiotherapy. Further, they suggest that CSF1 inhibitors should be evaluated in clinical trials in combination with radiotherapy as a strategy to improve outcomes.
radiotherapy; myeloid cells; TAM; MDSC; CSF1; CSF1R; ABL1