Circulating Tumor Cells and Circulating Tumor DNA Provide New Insights into Pancreatic Cancer.

Pancreatic cancer has a rather dismal prognosis mainly due to high malignance of tumor biology. Up to now, the relevant researches on pancreatic cancer lag behind seriously partly due to the obstacles for tissue biopsy, which handicaps the understanding of molecular and genetic features of pancreatic cancer. In the last two decades, liquid biopsy, including circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), is promising to provide new insights into the biological and clinical characteristics of malignant tumors. Both CTCs and ctDNA provide an opportunity for studying tumor heterogeneity, drug resistance, and metastatic mechanism for pancreatic cancer. Furthermore, they can also play important roles in detecting early-stage tumors, providing prognostic information, monitoring tumor progression and guiding treatment regimens. In this review, we will introduce the latest findings on biological features and clinical applications of both CTCs and ctDNA in pancreatic cancer. In a word, CTCs and ctDNA are promising to promote precision medicine in pancreatic cancer.

The multifaceted functions of sirtuins in cancer.

The sirtuins (SIRTs; of which there are seven in mammals) are NAD(+)-dependent enzymes that regulate a large number of cellular pathways and forestall the progression of ageing and age-associated diseases. In recent years, the role of sirtuins in cancer biology has become increasingly apparent, and growing evidence demonstrates that sirtuins regulate many processes that go awry in cancer cells, such as cellular metabolism, the regulation of chromatin structure and the maintenance of genomic stability. In this article, we review recent advances in our understanding of how sirtuins affect cancer metabolism, DNA repair and the tumour microenvironment and how activating or inhibiting sirtuins may be important in preventing or treating cancer.

Glutathione peroxidase 7 has potential tumour suppressor functions that are silenced by location-specific methylation in oesophageal adenocarcinoma.

OBJECTIVE: To investigate the potential tumour suppressor functions of glutathione peroxidase 7 (GPX7) and examine the interplay between epigenetic and genetic events in regulating its expression in oesophageal adenocarcinomas (OAC). DESIGN: In vitro and in vivo cell models were developed to investigate the biological and molecular functions of GPX7 in OAC. RESULTS: Reconstitution of GPX7 in OAC cell lines, OE33 and FLO-1, significantly suppressed growth as shown by the growth curve, colony formation and EdU proliferation assays. Meanwhile, GPX7-expressing cells displayed significant impairment in G1/S progression and an increase in cell senescence. Concordant with the above functions, Western blot analysis displayed higher levels of p73, p27, p21 and p16 with a decrease in phosphorylated retinoblastoma protein (RB), indicating its increased tumour suppressor activities. On the contrary, knockdown of GPX7 in HET1A cells (an immortalised normal oesophageal cell line) rendered the cells growth advantage as indicated with a higher EdU rate, lower levels of p73, p27, p21 and p16 and an increase in phosphorylated RB. We confirmed the tumour suppressor function in vivo using GPX7-expressing OE33 cells in a mouse xenograft model. Pyrosequencing of the GPX7 promoter region (-162 to +138) demonstrated location-specific hypermethylation between +13 and +64 in OAC (69%, 54/78). This was significantly associated with the downregulation of GPX7 (p<0.01). Neither mutations in the coding exons of GPX7 nor DNA copy number losses were frequently present in the OAC examined (<5%). CONCLUSIONS: Our data suggest that GPX7 possesses tumour suppressor functions in OAC and is silenced by location-specific promoter DNA methylation.

Global alterations of DNA methylation in cholangiocarcinoma target the Wnt signaling pathway.

UNLABELLED: The molecular mechanisms underlying the genesis of cholangiocarcinomas (CCs) are poorly understood. Epigenetic changes such as aberrant hypermethylation and subsequent atypical gene expression are characteristic features of most human cancers. In CC, data regarding global methylation changes are lacking so far. We performed a genome-wide analysis for aberrant promoter methylation in human CCs. We profiled 10 intrahepatic and 8 extrahepatic CCs in comparison to non-neoplastic biliary tissue specimens, using methyl-CpG immunoprecipitation (MCIp) combined with whole-genome CpG island arrays. DNA methylation was confirmed by quantitative mass spectrometric analysis and functional relevance of promoter hypermethylation was shown in demethylation experiments of two CC cell lines using 5-aza-2'deoxycytidine (DAC) treatment. Immunohistochemical staining of tissue microarrays (TMAs) from 223 biliary tract cancers (BTCs) was used to analyze candidate gene expression at the protein level. Differentially methylated, promoter-associated regions were nonrandomly distributed and enriched for genes involved in cancer-related pathways including Wnt, transforming growth factor beta (TGF-ß), and PI3K signaling pathways. In CC cell lines, silencing of genes involved in Wnt signaling, such as SOX17, WNT3A, DKK2, SFRP1, SFRP2, and SFRP4 was reversed after DAC administration. Candidate protein SFRP2 was substantially down-regulated in neoplastic tissues of all BTC subtypes as compared to normal tissues. A significant inverse correlation of SFRP2 protein expression and pT status was found in BTC patients. CONCLUSION: We provide a comprehensive analysis to define the genome-wide methylation landscape of human CC. Several candidate genes of cancer-relevant signaling pathways were identified, and closer analysis of selected Wnt pathway genes confirmed the relevance of this pathway in CC. The presented global methylation data are the basis for future studies on epigenetic changes in cholangiocarcinogenesis.

MTHFR C677T polymorphism and differential methylation status in gastric cancer: an association with Helicobacter pylori infection.

MTHFR C677T and Helicobacter pylori infection are believed to play critical roles in the DNA methylation process, an epigenetic feature frequently found in gastric cancer. The aim of this study was to verify the associations between the MTHFR C677T polymorphism and the methylation status of three gastric cancer-related genes. The influence of H. pylori strains was also assessed. DNA extracted from 71 gastric tumor samples was available for MTHFR C677T genotyping by PCR-RFLP, promoter methylation identification by MS-PCR and H. pylori detection and posterior subtyping (cagA and vacA genes) by PCR. In the distal tumors, a positive correlation was found between the methylation of CDKN2A and the allele T carriers (r=0.357; p=0.009). Considering the eldest patients (age ≥60 years old), this correlation was even higher (r=0,417; p=0.014). H. pylori infection by highly pathogenic strains (cagA+/vacAs1m1) was also found correlated to promoter methylation of CDKN2A and the allele T carriers in distal tumors (r=0.484; p=0.026). No significant correlation was verified between MTHFR C677T genotype and promoter methylation status when we analyzed the general sample. DNA methylation in CDKN2A associated to the MTHFR 677T carrier is suggested to be a distal tumor characteristic, especially in those 60 years old or older, and it seems to depend on the infection by H. pylori cagA/vacAs1m1 strains.

Differential expressions and DNA methylation patterns of lysophosphatidic acid receptor genes in human colon cancer cells.

Lysophosphatidic acid (LPA), which is a bioactive phospholipid, interacts with specific G protein-coupled transmembrane receptors. Recently, alterations of LPA receptor genes have been reported in some tumor cells. In this study, we examined the expression profiles and DNA methylation status of LPA receptor 1-5 (LPA1-5) genes in human colon cancer cells and also looked for the mutations. Reverse transcription-polymerase chain reaction (PCR) and bisulfite sequencing analyses were carried out. While LPA1, LPA2, and LPA4 genes were expressed in DLD1, SW480, HCT116, CaCo-2, SW48, and LoVo cells, the expressions of LPA3 and LPA5 genes were various. These expression levels were correlated with DNA methylation status in the 5' upstream regions of the LPA receptor genes. Mutation analysis was also performed using a PCR-single-strand conformation polymorphism method. Although no mutations in LPA1, LPA3 and LPA5 genes were found in all types of cells, LPA2 mutations in DLD1 and SW48 cells, and LPA4 mutation were found in DLD1 cells. On the basis of the present results, we demonstrate that these colon cancer cells will be available to understanding the molecular pathway through LPA receptors in the development of tumor cells, and that LPA receptors may be new molecular targets for therapeutic approaches and chemoprevention.

Reversible regulation of metastasis by ROS-generating mtDNA mutations.

It has been controversial whether mtDNA mutations are responsible for oncogenic transformation (normal cells to develop tumors), and for malignant progression (tumor cells to develop metastases). To clarify this issue, we created trans-mitochondrial cybrids with mtDNA exchanged between mouse tumor cells that express different metastatic phenotypes. The G13997A mutation in the ND6 gene of mtDNA from high metastatic tumor cells reversibly controlled development of metastases by overproduction of reactive oxygen species (ROS), but did not control development of tumors. The mtDNA-mediated reversible control of metastasis reveals a novel function of mtDNA, and suggests that ROS scavengers may be therapeutically effective in suppressing metastasis.

Microvessel damage may play an important role in tumoricidal effect for murine h(22) hepatoma cells with hyperthermia in vivo.

BACKGROUND: In the present study, murine H(22) hepatoma cells were provided hyperthermia with different thermal dose in vitro and in vivo, thereafter we investigated the apoptosis, necrosis rates, and intratumoral microvessel density (MVD) to determine that microvessel damage plays an important role in the tumoricidal effect of hyperthermia. METHODS: H(22) hepatoma cells were inoculated in the right hind legs of mice with immunosuppression. Local hyperthermia was administered to these mice for 15, 30, and 45 min, respectively. After hyperthermia, some mice with heat treatment of 30 min were killed at 3, 6, 12, 24, 48, 72, and 96 h after operation and others were immediately sacrificed. All tumor tissues were removed. They were analyzed for the death rate of tumor cells by flow cytometer (FCM) and observed MVD by immunohistochemistry. H(22) hepatoma cells in vitro were also given hyperthermia for 15, 30, and 45 min, respectively, and analyzed for the death rate by FCM. RESULTS: Most of the dead cells were apoptotic cells in the initiation phase of hyperthermia, then the necrosis rates rose gradually. The difference of death rates between in vivo and in vitro was significant for hyperthermia for 15 min, 30 min, and 45 min (P < 0.05). A strong positive linear correlation (r = -0.879) was observed between the death rate of tumor cells and MVD. CONCLUSION: Our study has shown that microvessel damage may play an important role in tumoricidal effect of hyperthermia.

The role of pre-replicative complex (pre-RC) components in oncogenesis.

Normal DNA replication is stringently regulated to ensure a timely occurrence no more than once per cell cycle. Abrogation of the exquisite control mechanisms that maintain this process results in detrimental gains and losses of genomic DNA commonly seen in cancer and developmental defects. Replication initiation proteins, known as prereplicative complex (pre-RC) proteins, serve as a primary level of regulation, controlling when DNA replication can begin. Unsurprisingly, several pre-RC proteins are overexpressed in cancer and serve as good tumor markers. However, their direct correlation with increasing tumor grade and poor prognosis has posed a long-standing question: Are pre-RC proteins oncogenic? Recently, a growing body of data indicates that deregulation of individual pre-RC proteins, either by overexpression or functional deficiency in several organismal models, results in significant and consistently perturbed cell cycle regulation, genomic instability, and, potentially, tumorigenesis. In this review, we examine this broad range of evidence suggesting that pre-RC proteins play roles during oncogenesis that are more than simply indicative of proliferation, supporting the notion that pre-RC proteins may potentially have significant diagnostic and therapeutic value.

Chromatin assembly factor-1 (CAF-1)-mediated regulation of cell proliferation and DNA repair: a link with the biological behaviour of squamous cell carcinoma of the tongue?

AIMS: Squamous cell carcinoma (SCC) of the tongue shows aggressive behaviour and a poor prognosis. Clinicopathological parameters fail to provide reliable prognostic information, so the search continues for new molecular markers for this tumour. Chromatin assembly factor-1 (CAF-1) plays a major role in chromatin assembly during cell replication and DNA repair and has been proposed as a new proliferation marker. The aim of this study was to investigate its expression in SCC of the tongue. METHODS AND RESULTS: The immunohistochemical expression of the p60 and p150 subunits of CAF-1 were evaluated in a series of SCCs of the tongue. The findings were correlated with the expression of proliferation cell nuclear antigen (PCNA) and patients' clinicopathological and follow-up data. CAF-1/p60 was expressed in all the tumours, whereas CAF-1/p150 was down-regulated in a number of cases. Overexpression of CAF-1/p60 and down-regulation of CAF-1/p150 identified SCCs with poor outcome, in addition to the classical prognostic parameters. CONCLUSIONS: Simultaneous CAF-1-mediated deregulation of cell proliferation and DNA repair takes place in aggressive SCC of the tongue. Therefore, the evaluation of CAF-1 expression may be a valuable tool for evaluation of the biological behaviour of these tumours. This may be relevant to the introduction of improved follow-up protocols and/or alternative therapeutic regimens.

Concise review: Telomere biology in normal and leukemic hematopoietic stem cells.

The measurement of telomere length can give an insight into the replicative history of the cells in question. Much of the observed telomere loss occurs at the stem and progenitor cell level, even though these populations express the enzyme telomerase. Telomerase-transfected hematopoietic stem cells (HSC), although able to maintain telomere length, are still limited in terms of ability to undergo sequential transplantation, and other factors require to be addressed to achieve optimal levels of stem cell expansion. Unchecked telomere loss by HSC, meanwhile, would appear to play a significant role in the pathogenesis of bone marrow failure, as observed in the condition dyskeratosis congenita. This heterogeneous inherited condition appears to exhibit telomerase dysfunction as a common final pathogenic mechanism. Although less well-established for acquired marrow failure syndromes, mutations in key telomerase components have been described. The identification of the leukemic stem cell (LSC), along with the desire to target this population with anti-leukemia therapy, demands that telomerase biology be fully understood in this cell compartment. Future studies using primary selected LSC-rich samples are required. A better understanding of telomerase regulation in this population may allow effective targeting of the telomerase enzyme complex using small molecule inhibitors or additional novel approaches. Disclosure of potential conflicts of interest is found at the end of this article.

Newly identified c-KIT receptor tyrosine kinase ITD in childhood AML induces ligand-independent growth and is responsive to a synergistic effect of imatinib and rapamycin.

Activating mutations of c-KIT lead to ligand-independent growth. Internal tandem duplications (ITDs) of exon 11, which encodes the juxtamembrane domain (JMD), are constitutively activating mutations found in 7% of gastrointestinal stromal tumors (GISTs) but have not been described in childhood acute myeloid leukemia (AML). DNA and cDNA from 60 children with AML were screened by polymerase chain reaction (PCR) for mutations of the JMD. A complex ITD (kit cITD) involving exon 11 and exon 12 was identified with a relative frequency of 7% (4/60). The human kit cITDs were inserted into the murine c-Kit backbone and expressed in Ba/F3 cells. KIT cITD induced factorindependent growth and apoptosis resistance, and exhibited constitutive autophosphorylation. KIT cITD constitutively activated the PI3K/AKT pathway and phosphorylated STAT1, STAT3, STAT5, and SHP-2. Imatinib (IM) or rapamycin (Rap) led to complete inhibition of growth, with IC50 values at nanomolar levels. IM and Rap synergistically inhibited growth and surmounted KIT cITD-induced apoptosis resistance. IM but not LY294002 inhibited phosphorylation of STAT3 and STAT5, suggesting aberrant cross talk between PI3K- and STAT-activating pathways. The findings presented may have immediate therapeutic impact for a subgroup of childhood AML-expressing c-KIT mutations.

Mitochondrial DNA mutations in human disease.

Since their first association with human disease in 1988, more than 250 pathogenic point mutations and rearrangements of the 16.6 kb mitochondrial genome (mtDNA) have been reported in a spectrum of clinical disorders which exhibit prominent muscle and central nervous system involvement. With novel mutations and disease phenotypes still being described, mtDNA disorders are recognized collectively as common, inherited genetic diseases although relatively little is still known concerning the precise pathophysiological mechanisms that lead to cell dysfunction and pathology. This review considers the basic principles of mitochondrial genetics which govern both the behaviour and investigation of pathogenic mtDNA mutations summarizing recent advances in this area, and an assessment of the ongoing debate into the role of somatic mtDNA mutations in neurodegenerative disease, ageing and cancer.

Inter-relation of apoptosis and DNA double-strand breaks in patients with multiple primary cancers.

Since the development of multiple primary cancers in an individual is considered an unlikely event, it is suspected that a defect in DNA repair or apoptosis is the underlying cause for some of these patients. Therefore, this study was based on the hypothesis that such patients have increased remaining DNA double-strand breaks (DSBs) and reduced levels of apoptosis after in vitro irradiation. To investigate these mechanisms in cancer patients, 19 with multiple primary cancers were selected out of 25 121 cancer patients. For inclusion in this study, patients had to present with first malignancy at an early age, have a positive family history of cancer and no risk factors. The exclusion criteria were recurrence of cancer or metastasis, haematological tumours and tumours possibly connected to a patient risk factor such as smoking or drinking. Their peripheral blood lymphocytes were tested for proper repair of DNA DSBs and apoptosis after in vitro irradiation. DSBs were measured using constant field gel electrophoresis at 0, 8 and 24 h after irradiation. Apoptotic rates were determined at 24, 48 and 72 h after irradiation using the TUNEL assay. We found that patients' lymphocytes had significantly more initial DNA DSBs compared with controls, but there was no difference in the number of remaining DNA DSBs. Apoptotic rates of lymphocytes were only slightly lower in patients than in controls. These findings show that there are limited differences between patients with multiple cancers and healthy individuals. However, we found a trend towards an inverse correlation between remaining DNA DSBs and apoptotic rates in patients' lymphocytes. This is indicative of DNA DSBs persisting in patients' cells, presumably leading to a higher level of stable chromosomal aberrations that may contribute to tumour formation.

Coordination of nuclear- and mitochondrial-DNA encoded proteins in cancer and normal colon tissues.

To support the rapid growth of tumors, the cell can respond by increasing the number of mitochondria, in a concerted biosynthesis of mitochondrial constituents (nuclear and mitochondria encoded). Increased transcription, availability and stability of oxidative phosphorylation mRNAs, without increasing mitochondria number could also lead to more rapid energy-yielding effects. Mitochondria biogenesis and de novo formation of respiratory chain components imply coordination of nuclear and mt gene transcription. The mitochondrial mass is regulated by a number of physiopathological conditions. In response to external stimuli, mitochondria biogenesis is dependent on an orchestrated crosstalk between the nuclear and the mitochondrial genomes. Based on the higher incidence of glycolysis over oxidative phosphorylation in cancer tissues, we studied by differential proteomics the energy metabolism pathway of matched samples of normal and cancer tissue. Our results indicated that oxidative phosphorylation in cancer cells seemed altered because there is an unbalanced coordination between nuclear- and mitochondria-encoded mitochondrial proteins.

The role of telomeres and telomerase in the pathology of human cancer and aging.

Cellular senescence, the state of permanent growth arrest, is the inevitable fate of replicating normal somatic cells. Postulated to underlie this finite replicative span is the physiology of telomeres, which constitute the ends of chromosomes. The repetitive sequences of these DNA-protein complexes progressively shorten with each mitosis. When the critical length is bridged, telomeres trigger DNA repair and cell cycle checkpoint mechanisms that result in chromosomal fusions, cell cycle arrest, senescence and/or apoptosis. Should senescence be bypassed at such time, continued cell divisions in the face of dysfunctional telomeres and activated DNA repair machinery can result in the genomic instability favourable for oncogenesis. The longevity and malignant progression of the thus transformed cell requires coincident telomerase expression or other means to negate the constitutional telomeric loss. Practically then, telomeres and telomerase may represent plausible prognostic and screening cancer markers. Furthermore, if the argument is extended, with assumptions that telomeric attrition is indeed the basis of cellular senescence and that accumulation of the latter equates to aging at the organismal level, then telomeres may well explain the increased incidence of cancer with human aging.

Induction of aberrant crypt foci in DNA mismatch repair-deficient mice by the food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP).

Disruption of the DNA mismatch repair (MMR) pathway results in elevated mutation rates, inappropriate survival of cells bearing DNA damage, and increased cancer risk. Relatively little is known about the impact of environmentally relevant carcinogens on cancer risk in individuals with MMR-deficiency. We evaluated the effect of MMR status (Mlh1(+/+) versus Mlh1(-/-)) on the carcinogenic potential of the cooked-meat mutagen, 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) in mice. PhIP exposure did not obviously increase lymphoma or small intestinal tumorigenesis in either Mlh1-deficient or -proficient mice. In contrast, the frequency of aberrant crypt foci (ACF), a preneoplastic biomarker for colon tumorigenesis, was increased by PhIP, and the increase due to PhIP was significantly greater in Mlh1(-/-) versus wild-type littermates. This apparent heightened susceptibility to induction of ACF parallels the previously reported hypermutability of Mlh1-deficient mice to PhIP and is consistent with the hypothesis that MMR-deficiency would increase the likelihood of PhIP-induced carcinogenic mutations. Further evaluation of the risk that consumption of heterocyclic amines may impart to MMR-deficient individuals therefore is warranted.

DNA demethylation and carcinogenesis.

DNA methylation plays an important role in the establishment and maintenance of the program of gene expression. Tumor cells are characterized by a paradoxical alteration of DNA methylation pattern: global DNA demethylation and local hypermethylation of certain genes. Hypermethylation and inactivation of tumor suppressor genes are well documented in tumors. The role of global genome demethylation in carcinogenesis is less studied. New data provide evidence for independence of DNA hypo- and hypermethylation processes in tumor cells. These processes alter expression of genes that have different functions in malignant transformation. Recent studies have demonstrated that global decrease in the level of DNA methylation is related to hypomethylation of repeated sequences, increase in genetic instability, hypomethylation and activation of certain genes that favor tumor growth, and increase in their metastatic and invasive potential. The recent data on the role of DNA demethylation in carcinogenesis are discussed in this review. The understanding of relationships between hypo- and hypermethylation in tumor cells is extremely important due to reversibility of DNA methylation and attempts to utilize for anti-tumor therapy the drugs that modify DNA methylation pattern.