Showing papers on "Carcinogenesis published in 2007"

MicroRNA signatures in human cancers

Abstract: MicroRNA (miRNA) alterations are involved in the initiation and progression of human cancer. The causes of the widespread differential expression of miRNA genes in malignant compared with normal cells can be explained by the location of these genes in cancer-associated genomic regions, by epigenetic mechanisms and by alterations in the miRNA processing machinery. MiRNA-expression profiling of human tumours has identified signatures associated with diagnosis, staging, progression, prognosis and response to treatment. In addition, profiling has been exploited to identify miRNA genes that might represent downstream targets of activated oncogenic pathways, or that target protein- coding genes involved in cancer.

A human colon cancer cell capable of initiating tumour growth in immunodeficient mice

Abstract: Colon cancer is one of the best-understood neoplasms from a genetic perspective, yet it remains the second most common cause of cancer-related death, indicating that some of its cancer cells are not eradicated by current therapies. What has yet to be established is whether every colon cancer cell possesses the potential to initiate and sustain tumour growth, or whether the tumour is hierarchically organized so that only a subset of cells--cancer stem cells--possess such potential. Here we use renal capsule transplantation in immunodeficient NOD/SCID mice to identify a human colon cancer-initiating cell (CC-IC). Purification experiments established that all CC-ICs were CD133+; the CD133- cells that comprised the majority of the tumour were unable to initiate tumour growth. We calculated by limiting dilution analysis that there was one CC-IC in 5.7 x 10(4) unfractionated tumour cells, whereas there was one CC-IC in 262 CD133+ cells, representing >200-fold enrichment. CC-ICs within the CD133+ population were able to maintain themselves as well as differentiate and re-establish tumour heterogeneity upon serial transplantation. The identification of colon cancer stem cells that are distinct from the bulk tumour cells provides strong support for the hierarchical organization of human colon cancer, and their existence suggests that for therapeutic strategies to be effective, they must target the cancer stem cells.

Identification and expansion of human colon-cancer-initiating cells

Abstract: Colon carcinoma is the second most common cause of death from cancer. The isolation and characterization of tumorigenic colon cancer cells may help to devise novel diagnostic and therapeutic procedures. Although there is increasing evidence that a rare population of undifferentiated cells is responsible for tumour formation and maintenance, this has not been explored for colorectal cancer. Here, we show that tumorigenic cells in colon cancer are included in the high-density CD133+ population, which accounts for about 2.5% of the tumour cells. Subcutaneous injection of colon cancer CD133+ cells readily reproduced the original tumour in immunodeficient mice, whereas CD133- cells did not form tumours. Such tumours were serially transplanted for several generations, in each of which we observed progressively faster tumour growth without significant phenotypic alterations. Unlike CD133- cells, CD133+ colon cancer cells grew exponentially for more than one year in vitro as undifferentiated tumour spheres in serum-free medium, maintaining the ability to engraft and reproduce the same morphological and antigenic pattern of the original tumour. We conclude that colorectal cancer is created and propagated by a small number of undifferentiated tumorigenic CD133+ cells, which should therefore be the target of future therapies.

Patterns of Somatic Mutation in Human Cancer Genomes

Abstract: AACR Centennial Conference: Translational Cancer Medicine-- Nov 4-8, 2007; Singapore PL02-05 All cancers are due to abnormalities in DNA. The availability of the human genome sequence has led to the proposal that resequencing of cancer genomes will reveal the full complement of somatic mutations and hence all the cancer genes. To explore the nature of the information that will be derived from cancer genome sequencing we have sequenced the coding exons of the family of 518 protein kinases, ~1.3Mb DNA per cancer sample, in 210 cancers of diverse histological types. Despite the screen being directed toward the coding regions of a gene family that has previously been strongly implicated in oncogenesis, the results indicate that the majority of somatic mutations detected are “passengers”. There is considerable variation in the number and pattern of these mutations between individual cancers, indicating substantial diversity of processes of molecular evolution between cancers. The imprints of exogenous mutagenic exposures, mutagenic treatment regimes and DNA repair defects can all be seen in the distinctive mutational signatures of individual cancers. This systematic mutation screen and others have previously yielded a number of cancer genes that are frequently mutated in one or more cancer types and which are now anticancer drug targets (for example BRAF , PIK3CA , and EGFR ). However, detailed analyses of the data from our screen additionally suggest that there exist a large number of additional “driver” mutations which are distributed across a substantial number of genes. It therefore appears that cells may be able to utilise mutations in a large repertoire of potential cancer genes to acquire the neoplastic phenotype. However, many of these genes are employed only infrequently. These findings may have implications for future anticancer drug development.

Patterns of somatic mutation in human cancer genomes

Abstract: Cancers arise owing to mutations in a subset of genes that confer growth advantage. The availability of the human genome sequence led us to propose that systematic resequencing of cancer genomes for mutations would lead to the discovery of many additional cancer genes. Here we report more than 1,000 somatic mutations found in 274 megabases (Mb) of DNA corresponding to the coding exons of 518 protein kinase genes in 210 diverse human cancers. There was substantial variation in the number and pattern of mutations in individual cancers reflecting different exposures, DNA repair defects and cellular origins. Most somatic mutations are likely to be 'passengers' that do not contribute to oncogenesis. However, there was evidence for 'driver' mutations contributing to the development of the cancers studied in approximately 120 genes. Systematic sequencing of cancer genomes therefore reveals the evolutionary diversity of cancers and implicates a larger repertoire of cancer genes than previously anticipated.

MAP kinase signalling pathways in cancer.

Abstract: Cancer can be perceived as a disease of communication between and within cells. The aberrations are pleiotropic, but mitogen-activated protein kinase (MAPK) pathways feature prominently. Here, we discuss recent findings and hypotheses on the role of MAPK pathways in cancer. Cancerous mutations in MAPK pathways are frequently mostly affecting Ras and B-Raf in the extracellular signal-regulated kinase pathway. Stress-activated pathways, such as Jun N-terminal kinase and p38, largely seem to counteract malignant transformation. The balance and integration between these signals may widely vary in different tumours, but are important for the outcome and the sensitivity to drug therapy.

Identification of a subpopulation of cells with cancer stem cell properties in head and neck squamous cell carcinoma

Abstract: Like many epithelial tumors, head and neck squamous cell carcinoma (HNSCC) contains a heterogeneous population of cancer cells. We developed an immunodeficient mouse model to test the tumorigenic potential of different populations of cancer cells derived from primary, unmanipulated human HNSCC samples. We show that a minority population of CD44(+) cancer cells, which typically comprise <10% of the cells in a HNSCC tumor, but not the CD44(-) cancer cells, gave rise to new tumors in vivo. Immunohistochemistry revealed that the CD44(+) cancer cells have a primitive cellular morphology and costain with the basal cell marker Cytokeratin 5/14, whereas the CD44(-) cancer cells resemble differentiated squamous epithelium and express the differentiation marker Involucrin. The tumors that arose from purified CD44(+) cells reproduced the original tumor heterogeneity and could be serially passaged, thus demonstrating the two defining properties of stem cells: ability to self-renew and to differentiate. Furthermore, the tumorigenic CD44(+) cells differentially express the BMI1 gene, at both the RNA and protein levels. By immunohistochemical analysis, the CD44(+) cells in the tumor express high levels of nuclear BMI1, and are arrayed in characteristic tumor microdomains. BMI1 has been demonstrated to play a role in self-renewal in other stem cell types and to be involved in tumorigenesis. Taken together, these data demonstrate that cells within the CD44(+) population of human HNSCC possess the unique properties of cancer stem cells in functional assays for cancer stem cell self-renewal and differentiation and form unique histological microdomains that may aid in cancer diagnosis.

Restoration of p53 function leads to tumour regression in vivo

Abstract: The p53 tumour suppressor is either mutated or inactivated by other alterations in most human cancers. Two papers in this issue show that even brief reactivation of the endogenous p53 genes in established tumours can cause cancer regression in some animal models. In some tumours, p53 reactivation causes cellular senescence associated with an innate immune response that contributes to tumour clearance. These experiments used gene manipulation to alter p53 levels, but they lend further support to the idea that p53-boosting drugs could be a useful form of cancer treatment. One of two papers showing that reactivation of the endogenous p53 tumour suppressor genes in established tumours causes cancer regression. In some tumours, p53 reactivation causes cellular senescence associated with an innate immune response that contributes to tumour clearance. Tumorigenesis is a multi-step process that requires activation of oncogenes and inactivation of tumour suppressor genes1. Mouse models of human cancers have recently demonstrated that continuous expression of a dominantly acting oncogene (for example, Hras, Kras and Myc) is often required for tumour maintenance2,3,4,5; this phenotype is referred to as oncogene addiction6. This concept has received clinical validation by the development of active anticancer drugs that specifically inhibit the function of oncoproteins such as BCR-ABL, c-KIT and EGFR7,8,9,10. Identifying additional gene mutations that are required for tumour maintenance may therefore yield clinically useful targets for new cancer therapies. Although loss of p53 function is a common feature of human cancers11, it is not known whether sustained inactivation of this or other tumour suppressor pathways is required for tumour maintenance. To explore this issue, we developed a Cre-loxP-based strategy to temporally control tumour suppressor gene expression in vivo. Here we show that restoring endogenous p53 expression leads to regression of autochthonous lymphomas and sarcomas in mice without affecting normal tissues. The mechanism responsible for tumour regression is dependent on the tumour type, with the main consequence of p53 restoration being apoptosis in lymphomas and suppression of cell growth with features of cellular senescence in sarcomas. These results support efforts to treat human cancers by way of pharmacological reactivation of p53.

Genome-wide analysis of genetic alterations in acute lymphoblastic leukaemia

Abstract: Chromosomal aberrations are a hallmark of acute lymphoblastic leukaemia (ALL) but alone fail to induce leukaemia. To identify cooperating oncogenic lesions, we performed a genome-wide analysis of leukaemic cells from 242 paediatric ALL patients using high-resolution, single-nucleotide polymorphism arrays and genomic DNA sequencing. Our analyses revealed deletion, amplification, point mutation and structural rearrangement in genes encoding principal regulators of B lymphocyte development and differentiation in 40% of B-progenitor ALL cases. The PAX5 gene was the most frequent target of somatic mutation, being altered in 31.7% of cases. The identified PAX5 mutations resulted in reduced levels of PAX5 protein or the generation of hypomorphic alleles. Deletions were also detected in TCF3 (also known as E2A), EBF1, LEF1, IKZF1 (IKAROS) and IKZF3 (AIOLOS). These findings suggest that direct disruption of pathways controlling B-cell development and differentiation contributes to B-progenitor ALL pathogenesis. Moreover, these data demonstrate the power of high-resolution, genome-wide approaches to identify new molecular lesions in cancer.

MicroRNA-29 family reverts aberrant methylation in lung cancer by targeting DNA methyltransferases 3A and 3B.

Abstract: MicroRNAs (miRNAs) are small, noncoding RNAs that regulate expression of many genes. Recent studies suggest roles of miRNAs in carcinogenesis. We and others have shown that expression profiles of miRNAs are different in lung cancer vs. normal lung, although the significance of this aberrant expression is poorly understood. Among the reported down-regulated miRNAs in lung cancer, the miRNA (miR)-29 family (29a, 29b, and 29c) has intriguing complementarities to the 3′-UTRs of DNA methyltransferase (DNMT)3A and -3B (de novo methyltransferases), two key enzymes involved in DNA methylation, that are frequently up-regulated in lung cancer and associated with poor prognosis. We investigated whether miR-29s could target DNMT3A and -B and whether restoration of miR-29s could normalize aberrant patterns of methylation in non-small-cell lung cancer. Here we show that expression of miR-29s is inversely correlated to DNMT3A and -3B in lung cancer tissues, and that miR-29s directly target both DNMT3A and -3B. The enforced expression of miR-29s in lung cancer cell lines restores normal patterns of DNA methylation, induces reexpression of methylation-silenced tumor suppressor genes, such as FHIT and WWOX, and inhibits tumorigenicity in vitro and in vivo. These findings support a role of miR-29s in epigenetic normalization of NSCLC, providing a rationale for the development of miRNA-based strategies for the treatment of lung cancer.

miR-21-mediated tumor growth

Abstract: MicroRNAs (miRNAs) are ∼22 nucleotide non-coding RNA molecules that regulate gene expression post-transcriptionally. Although aberrant expression of miRNAs in various human cancers suggests a role for miRNAs in tumorigenesis, it remains largely unclear as to whether knockdown of a specific miRNA affects tumor growth. In this study, we profiled miRNA expression in matched normal breast tissue and breast tumor tissues by TaqMan real-time polymerase chain reaction miRNA array methods. Consistent with previous findings, we found that miR-21 was highly overexpressed in breast tumors compared to the matched normal breast tissues among 157 human miRNAs analysed. To better evaluate the role of miR-21 in tumorigenesis, we transfected breast cancer MCF-7 cells with anti-miR-21 oligonucleotides and found that anti-miR-21 suppressed both cell growth in vitro and tumor growth in the xenograft mouse model. Furthermore, this anti-miR-21-mediated cell growth inhibition was associated with increased apoptosis and decreased cell proliferation, which could be in part owing to downregulation of the antiapoptotic Bcl-2 in anti-miR-21-treated tumor cells. Together, these results suggest that miR-21 functions as an oncogene and modulates tumorigenesis through regulation of genes such as bcl-2 and thus, it may serve as a novel therapeutic target.

Crosstalk between cancer and immune cells: role of STAT3 in the tumour microenvironment.

Abstract: Immune cells in the tumour microenvironment not only fail to mount an effective anti-tumour immune response, but also interact intimately with the transformed cells to promote oncogenesis actively. Signal transducer and activator of transcription 3 (STAT3), which is a point of convergence for numerous oncogenic signalling pathways, is constitutively activated both in tumour cells and in immune cells in the tumour microenvironment. Constitutively activated STAT3 inhibits the expression of mediators necessary for immune activation against tumour cells. Furthermore, STAT3 activity promotes the production of immunosuppressive factors that activate STAT3 in diverse immune-cell subsets, altering gene-expression programmes and, thereby, restraining anti-tumour immune responses. As such, STAT3 propagates several levels of crosstalk between tumour cells and their immunological microenvironment, leading to tumour-induced immunosuppression. Consequently, STAT3 has emerged as a promising target for cancer immunotherapy.

Impaired microRNA processing enhances cellular transformation and tumorigenesis.

Abstract: MicroRNAs (miRNAs) are a new class of small noncoding RNAs that post-transcriptionally regulate the expression of target mRNA transcripts. Many of these target mRNA transcripts are involved in proliferation, differentiation and apoptosis, processes commonly altered during tumorigenesis. Recent work has shown a global decrease of mature miRNA expression in human cancers. However, it is unclear whether this global repression of miRNAs reflects the undifferentiated state of tumors or causally contributes to the transformed phenotype. Here we show that global repression of miRNA maturation promotes cellular transformation and tumorigenesis. Cancer cells expressing short hairpin RNAs (shRNAs) targeting three different components of the miRNA processing machinery showed a substantial decrease in steady-state miRNA levels and a more pronounced transformed phenotype. In animals, miRNA processing-impaired cells formed tumors with accelerated kinetics. These tumors were more invasive than control tumors, suggesting that global miRNA loss enhances tumorigenesis. Furthermore, conditional deletion of Dicer1 enhanced tumor development in a K-Ras-induced mouse model of lung cancer. Overall, these studies indicate that abrogation of global miRNA processing promotes tumorigenesis.

Adaptive immunity maintains occult cancer in an equilibrium state

Abstract: The capacity of immunity to control and shape cancer, that is, cancer immunoediting, is the result of three processes that function either independently or in sequence: elimination (cancer immunosurveillance, in which immunity functions as an extrinsic tumour suppressor in naive hosts); equilibrium (expansion of transformed cells is held in check by immunity); and escape (tumour cell variants with dampened immunogenicity or the capacity to attenuate immune responses grow into clinically apparent cancers). Extensive experimental support now exists for the elimination and escape processes because immunodeficient mice develop more carcinogen-induced and spontaneous cancers than wild-type mice, and tumour cells from immunodeficient mice are more immunogenic than those from immunocompetent mice. In contrast, the equilibrium process was inferred largely from clinical observations, including reports of transplantation of undetected (occult) cancer from organ donor into immunosuppressed recipients. Herein we use a mouse model of primary chemical carcinogenesis and demonstrate that equilibrium occurs, is mechanistically distinguishable from elimination and escape, and that neoplastic cells in equilibrium are transformed but proliferate poorly in vivo. We also show that tumour cells in equilibrium are unedited but become edited when they spontaneously escape immune control and grow into clinically apparent tumours. These results reveal that, in addition to destroying tumour cells and sculpting tumour immunogenicity, the immune system of a naive mouse can also restrain cancer growth for extended time periods.

Histone deacetylases and cancer.

Abstract: Histone deacetylases (HDACs) regulate the expression and activity of numerous proteins involved in both cancer initiation and cancer progression. By removal of acetyl groups from histones, HDACs create a non-permissive chromatin conformation that prevents the transcription of genes that encode proteins involved in tumorigenesis. In addition to histones, HDACs bind to and deacetylate a variety of other protein targets including transcription factors and other abundant cellular proteins implicated in control of cell growth, differentiation and apoptosis. This review provides a comprehensive examination of the transcriptional and post-translational mechanisms by which HDACs alter the expression and function of cancer-associated proteins and examines the general impact of HDAC activity in cancer.

The Biology of Cancer Stem Cells

Abstract: Cancers originally develop from normal cells that gain the ability to proliferate aberrantly and eventually turn malignant. These cancerous cells then grow clonally into tumors and eventually have the potential to metastasize. A central question in cancer biology is, which cells can be transformed to form tumors? Recent studies elucidated the presence of cancer stem cells that have the exclusive ability to regenerate tumors. These cancer stem cells share many characteristics with normal stem cells, including self-renewal and differentiation. With the growing evidence that cancer stem cells exist in a wide array of tumors, it is becoming increasingly important to understand the molecular mechanisms that regulate self-renewal and differentiation because corruption of genes involved in these pathways likely participates in tumor growth. This new paradigm of oncogenesis has been validated in a growing list of tumors. Studies of normal and cancer stem cells from the same tissue have shed light on the ontogeny of tumors. That signaling pathways such as Bmi1 and Wnt have similar effects in normal and cancer stem cell self-renewal suggests that common molecular pathways regulate both populations. Understanding the biology of cancer stem cells will contribute to the identification of molecular targets important for future therapies.

Inflammation and cancer: an ancient link with novel potentials.

Abstract: Infection and chronic inflammation contribute to about 1 in 4 of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and post-translational modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer. Recent discovery of an interaction between microRNAs and innate immunity during inflammation has further strengthened the association between inflammation and cancer.

LKB1 modulates lung cancer differentiation and metastasis

Abstract: Germline mutation in serine/threonine kinase 11 (STK11, also called LKB1) results in Peutz-Jeghers syndrome, characterized by intestinal hamartomas and increased incidence of epithelial cancers. Although uncommon in most sporadic cancers, inactivating somatic mutations of LKB1 have been reported in primary human lung adenocarcinomas and derivative cell lines. Here we used a somatically activatable mutant Kras-driven model of mouse lung cancer to compare the role of Lkb1 to other tumour suppressors in lung cancer. Although Kras mutation cooperated with loss of p53 or Ink4a/Arf (also known as Cdkn2a) in this system, the strongest cooperation was seen with homozygous inactivation of Lkb1. Lkb1-deficient tumours demonstrated shorter latency, an expanded histological spectrum (adeno-, squamous and large-cell carcinoma) and more frequent metastasis compared to tumours lacking p53 or Ink4a/Arf. Pulmonary tumorigenesis was also accelerated by hemizygous inactivation of Lkb1. Consistent with these findings, inactivation of LKB1 was found in 34% and 19% of 144 analysed human lung adenocarcinomas and squamous cell carcinomas, respectively. Expression profiling in human lung cancer cell lines and mouse lung tumours identified a variety of metastasis-promoting genes, such as NEDD9, VEGFC and CD24, as targets of LKB1 repression in lung cancer. These studies establish LKB1 as a critical barrier to pulmonary tumorigenesis, controlling initiation, differentiation and metastasis.

Tumor-suppressive miR-34a induces senescence-like growth arrest through modulation of the E2F pathway in human colon cancer cells

Abstract: Accumulating evidence suggests a role for microRNAs in human carcinogenesis as novel types of tumor suppressors or oncogenes. However, their precise biological role remains largely elusive. In the present study, we aimed to identify microRNA species involved in the regulation of cell proliferation. Using quantitative RT-PCR analysis, we demonstrated that miR-34a was highly up-regulated in a human colon cancer cell line, HCT 116, treated with a DNA-damaging agent, adriamycin. Transient introduction of miR-34a into two human colon cancer cell lines, HCT 116 and RKO, caused complete suppression of cell proliferation and induced senescence-like phenotypes. Moreover, miR-34a also suppressed in vivo growth of HCT 116 and RKO cells in tumors in mice when complexed and administered with atelocollagen for drug delivery. Gene-expression microarray and immunoblot analyses revealed down-regulation of the E2F pathway by miR-34a introduction. Up-regulation of the p53 pathway was also observed. Furthermore, 9 of 25 human colon cancers (36%) showed decreased expression of miR-34a compared with counterpart normal tissues. Our results provide evidence that miR-34a functions as a potent suppressor of cell proliferation through modulation of the E2F signaling pathway. Abrogation of miR-34a function could contribute to aberrant cell proliferation, leading to colon cancer development.

The oncogene HER2; Its signaling and transforming functions and its role in human cancer pathogenesis

Abstract: The year 2007 marks exactly two decades since Human Epidermal Growth Factor Receptor-2 (HER2) was functionally implicated in the pathogenesis of human breast cancer. This finding established the HER2 oncogene hypothesis for the development of some human cancers. The subsequent two decades have brought about an explosion of information about the biology of HER2 and the HER family. An abundance of experimental evidence now solidly supports the HER2 oncogene hypothesis and etiologically links amplification of the HER2 gene locus with human cancer pathogenesis. The molecular mechanisms underlying HER2 tumorigenesis appear to be complex and a unified mechanistic model of HER2-induced transformation has not emerged. Numerous hypotheses implicating diverse transforming pathways have been proposed and are individually supported by experimental models and HER2 may indeed induce cell transformation through multiple mechanisms. Here I review the evidence supporting the oncogenic function of HER2, the mechanisms that are felt to mediate its oncogenic functions, and the evidence that links the experimental evidence with human cancer pathogenesis.

Distinct classes of chromosomal rearrangements create oncogenic ETS gene fusions in prostate cancer

Abstract: Recently, we identified recurrent gene fusions involving the 5' untranslated region of the androgen-regulated gene TMPRSS2 and the ETS (E26 transformation-specific) family genes ERG, ETV1 or ETV4 in most prostate cancers. Whereas TMPRSS2-ERG fusions are predominant, fewer TMPRSS2-ETV1 cases have been identified than expected on the basis of the frequency of high (outlier) expression of ETV1 (refs 3-13). Here we explore the mechanism of ETV1 outlier expression in human prostate tumours and prostate cancer cell lines. We identified previously unknown 5' fusion partners in prostate tumours with ETV1 outlier expression, including untranslated regions from a prostate-specific androgen-induced gene (SLC45A3) and an endogenous retroviral element (HERV-K_22q11.23), a prostate-specific androgen-repressed gene (C15orf21), and a strongly expressed housekeeping gene (HNRPA2B1). To study aberrant activation of ETV1, we identified two prostate cancer cell lines, LNCaP and MDA-PCa 2B, that had ETV1 outlier expression. Through distinct mechanisms, the entire ETV1 locus (7p21) is rearranged to a 1.5-megabase prostate-specific region at 14q13.3-14q21.1 in both LNCaP cells (cryptic insertion) and MDA-PCa 2B cells (balanced translocation). Because the common factor of these rearrangements is aberrant ETV1 overexpression, we recapitulated this event in vitro and in vivo, demonstrating that ETV1 overexpression in benign prostate cells and in the mouse prostate confers neoplastic phenotypes. Identification of distinct classes of ETS gene rearrangements demonstrates that dormant oncogenes can be activated in prostate cancer by juxtaposition to tissue-specific or ubiquitously active genomic loci. Subversion of active genomic regulatory elements may serve as a more generalized mechanism for carcinoma development. Furthermore, the identification of androgen-repressed and insensitive 5' fusion partners may have implications for the anti-androgen treatment of advanced prostate cancer.

Chronic inflammation and oxidative stress in human carcinogenesis.

Abstract: A wide array of chronic inflammatory conditions predispose susceptible cells to neoplastic transformation. In general, the longer the inflammation persists, the higher the risk of cancer. A mutated cell is a sine qua non for carcinogenesis. Inflammatory processes may induce DNA mutations in cells via oxidative/nitrosative stress. This condition occurs when the generation of free radicals and active intermediates in a system exceeds the system's ability to neutralize and eliminate them. Inflammatory cells and cancer cells themselves produce free radicals and soluble mediators such as metabolites of arachidonic acid, cytokines and chemokines, which act by further producing reactive species. These, in turn, strongly recruit inflammatory cells in a vicious circle. Reactive intermediates of oxygen and nitrogen may directly oxidize DNA, or may interfere with mechanisms of DNA repair. These reactive substances may also rapidly react with proteins, carbohydrates and lipids, and the derivative products may induce a high perturbation in the intracellular and intercellular homeostasis, until DNA mutation. The main substances that link inflammation to cancer via oxidative/nitrosative stress are prostaglandins and cytokines. The effectors are represented by an imbalance between pro-oxidant and antioxidant enzyme activities (lipoxygenase, cyclooxygenase and phospholipid hydroperoxide glutathione-peroxidase), hydroperoxides and lipoperoxides, aldehydes and peroxinitrite. This review focalizes some of these intricate events by discussing the relationships occurring among oxidative/nitrosative/metabolic stress, inflammation and cancer.

Mutational loss of PTEN induces resistance to NOTCH1 inhibition in T-cell leukemia

Abstract: Gain-of-function mutations in NOTCH1 are common in T-cell lymphoblastic leukemias and lymphomas (T-ALL), making this receptor a promising target for drugs such as γ-secretase inhibitors, which block a proteolytic cleavage required for NOTCH1 activation. However, the enthusiasm for these therapies has been tempered by tumor resistance and the paucity of information on the oncogenic programs regulated by oncogenic NOTCH1. Here we show that NOTCH1 regulates the expression of PTEN (encoding phosphatase and tensin homolog) and the activity of the phosphoinositol-3 kinase (PI3K)-AKT signaling pathway in normal and leukemic T cells. Notch signaling and the PI3K-AKT pathway synergize in vivo in a Drosophila melanogaster model of Notch-induced tumorigenesis, and mutational loss of PTEN is associated with human T-ALL resistance to pharmacological inhibition of NOTCH1. Overall, these findings identify transcriptional control of PTEN and regulation of the PI3K-AKT pathway as key elements of the leukemogenic program activated by NOTCH1 and provide the basis for the design of new therapeutic strategies for T-ALL.

TP53 mutations in human cancers: functional selection and impact on cancer prognosis and outcomes

Abstract: A large amount of data is available on the functional impact of missense mutations in TP53 and on mutation patterns in many different cancers. New data on mutant p53 protein function, cancer phenotype and prognosis have recently been integrated in the International Agency for Research on Cancer TP53 database (http://www-p53.iarc.fr/). Based on these data, we summarize here current knowledge on the respective roles of mutagenesis and biological selection of mutations with specific functional characteristic in shaping the patterns and phenotypes of mutations observed in human cancers. The main conclusion is that intrinsic mutagenicity rates, loss of transactivation activities, and to a lesser extent, dominant-negative activities are the main driving forces that determine TP53 mutation patterns and influence tumor phenotype. In contrast, current experimental data on the acquisition of oncogenic activities (gain of function) by p53 mutants are too scarce and heterogenous to assess whether this property has an impact on tumor development and outcome. In the case of inherited TP53 mutations causing Li-Fraumeni and related syndromes, the age at onset of some tumor types is in direct relation with the degree of loss of transactivation capacity of missense mutations. Finally, studies on large case series demonstrate that TP53 mutations are independent markers of bad prognosis in breast and several other cancers, and that the exact type and position of the mutation influences disease outcome. Further studies are needed to determine how TP53 haplotypes or loss of alleles interact with mutations to modulate their impact on cancer development and prognosis.

MicroRNA-34a functions as a potential tumor suppressor by inducing apoptosis in neuroblastoma cells.

Abstract: Neuroblastoma (NB) is one of the most common forms of cancer in children, accounting for 15% of pediatric cancer deaths. The clinical course of these tumors is highly variable and is dependent on such factors as age at presentation, stage, ploidy and genomic abnormalities. Hemizygous deletion of chromosome 1p occurs in approximately 30% of advanced stage tumors, is associated with a poor prognosis, and likely leads to the loss of one or more tumor suppressor genes. We show here that microRNA (miRNA)-34a (1p36.23) is generally expressed at lower levels in unfavorable primary NB tumors and cell lines relative to normal adrenal tissue and that reintroduction of this miRNA into three different NB cell lines causes a dramatic reduction in cell proliferation through the induction of a caspase-dependent apoptotic pathway. As a potential mechanistic explanation for this observation, we demonstrate that miR-34a directly targets the messenger ribonucleic acid (mRNA) encoding E2F3 and significantly reduces the levels of E2F3 protein, a potent transcriptional inducer of cell-cycle progression. Furthermore, miR-34a expression increases during retinoic acid-induced differentiation of the SK-N-BE cell line, whereas E2F3 protein levels decrease. Thus, adding to the increasing role of miRNAs in cancer, miR-34a may act as a suppressor of NB tumorgenesis.

Dynamics of the Immune Reaction to Pancreatic Cancer from Inception to Invasion

Abstract: The dynamics of cancer immunosurveillance remain incompletely understood, hampering efforts to develop immunotherapy of cancer. We evaluated the evolving in vivo immune response to a spontaneous tumor in a genetically defined mouse model of pancreatic ductal adenocarcinoma from the inception of preinvasive disease to invasive cancer. We observed a prominent leukocytic infiltration even around the lowest grade preinvasive lesions, but immunosuppressive cells, including tumor-associated macrophages, myeloid-derived suppressor cells (MDSC), and regulatory T cells (Treg), dominated the early response and persisted through invasive cancer. Effector T cells, however, were scarce in preinvasive lesions, found in only a subset of advanced cancers, and showed no evidence of activation. The lack of tumor-infiltrating effector T cells strongly correlated with the presence of intratumoral MDSC with a near mutual exclusion. In vitro, we found that MDSC suppressed T-cell proliferation. Overall, our results show that suppressive cells of the host immune system appear early during pancreatic tumorigenesis, preceding and outweighing antitumor cellular immunity, and likely contribute to disease progression. Thus, in contrast to the hypothesis that an early "elimination phase" of cancer immunosurveillance is eventually overwhelmed by a growing invasive tumor, our findings suggest that productive tumor immunity may be undermined from the start. Efforts to test potent inhibitors of MDSC, tumor-associated macrophages, and Treg, particularly early in the disease represent important next steps for developing novel immunotherapy of cancer.

Engineering tumors with 3D scaffolds.

Abstract: Microenvironmental conditions control tumorigenesis and biomimetic culture systems that allow for in vitro and in vivo tumor modeling may greatly aid studies of cancer cells' dependency on these conditions. We engineered three-dimensional (3D) human tumor models using carcinoma cells in polymeric scaffolds that recreated microenvironmental characteristics representative of tumors in vivo. Strikingly, the angiogenic characteristics of tumor cells were dramatically altered upon 3D culture within this system, and corresponded much more closely to tumors formed in vivo. Cells in this model were also less sensitive to chemotherapy and yielded tumors with enhanced malignant potential. We assessed the broad relevance of these findings with 3D culture of other tumor cell lines in this same model, comparison with standard 3D Matrigel culture and in vivo experiments. This new biomimetic model may provide a broadly applicable 3D culture system to study the effect of microenvironmental conditions on tumor malignancy in vitro and in vivo.