Genetic and epigenetic alterations in pancreatic carcinogenesis

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers worldwide. Despite significant progresses in the last decades, the origin of this cancer remains unclear and no efficient therapy exists. PDAC does not arise de novo: three remarkable different types of pancreatic lesions can evolve towards pancreatic cancer. These precursor lesions include: Pancreatic intraepithelial neoplasia (PanIN) that are microscopic lesions of the pancreas, Intraductal Papillary Mucinous Neoplasms (IPMN) and Mucinous Cystic Neoplasms (MCN) that are both macroscopic lesions. However, the cellular origin of these lesions is still a matter of debate. Classically, neoplasm initiation or progression is driven by several genetic and epigenetic alterations. The aim of this review is to assemble the current information on genetic mutations and epigenetic disorders that affect genes during pancreatic carcinogenesis. We will further discuss the interest of the genetic and epigenetic alterations for the diagnosis and prognosis of PDAC. Large genetic alterations (chromosomal deletion/amplification) and single point mutations are well described for carcinogenesis inducers. Mutations classically occur within key regions of the genome. Consequences are various and include activation of mitogenic pathways or silencing of apoptotic processes. Alterations of K-RAS, P16 and DPC4 genes are frequently observed in PDAC samples and have been described to arise gradually during carcinogenesis. DNA methylation is an epigenetic process involved in imprinting and X chromosome inactivation. Alteration of DNA methylation patterns leads to deregulation of gene expression, in the absence of mutation. Both genetic and epigenetic events influence genes and non-coding RNA expression, with dramatic effects on proliferation, survival and invasion. Besides improvement in our fundamental understanding of PDAC development, highlighting the molecular alterations that occur in pancreatic carcinogenesis could provide new clinical tools for early diagnosis of PDAC and the molecular basis for the development of new effective therapies.     

Sixty years of follow-up of Hiroshima and Nagasaki survivors: current progress in molecular epidemiology studies

This article provides an overview of the on-going molecular epidemiology studies among atomic-bomb survivors conducted at the Radiation Effects Research Foundation in Japan. The focus is on: (a) inter-individual variations in sensitivity to radiation-induced somatic mutations (glycophorin A (GPA) mutations) and their potential relevance to differences in susceptibility to radiation-related cancers and (b) the role of specific mutations/rearrangements in radiation-induced thyroid and colorectal cancers. The glycophorin A mutant fractions showed large differences between the survivors at each of the estimated bone marrow doses. Of note is the finding at doses>or=1 Gy; that the slope of the mutant fraction was significantly higher in the 'cancer group' than in the 'non-cancer group'. This study provided the basis for validating the use of gammaH2AX and reticulocyte micronucleus assays for evaluating radiosensitivity differences and genetic instability, respectively, in our studies in the coming years. Preliminary results from our molecular oncology studies on adult-onset papillary thyroid cancer provide evidence for the induction of RET/PTC rearrangements and BRAF point mutation (both known to be early stage events in adult-onset papillary thyroid cancer) but with a difference: cases associated with the rearrangements were more frequent at high doses, and developed sooner than those with BRAF mutation. In the case of colorectal cancer, the results suggest that radiation exposure might influence microsatellite instability (MSI) status through MSI-related epigenetic and genetic alterations-processes that might occur in the early stage of colorectal carcinogenesis.     

The new pig on the block: modelling cancer in pigs

The molecular mechanisms underlying many human cancers are now reasonably well understood. The challenge now is to bridge the gap between laboratory and clinical oncology, so these accomplishments can be translated into practical benefits for human patients. While genetically modified mice have played a prominent role in basic research, they are less suitable for many preclinical studies. Other animals can provide important complementary resources to aid the development, validation and application of new medicines and procedures. Powerful methods of genetic engineering have now been extended to physiologically more relevant species, particularly the pig, opening the prospect of more representative, genetically defined, cancer models at human scale. We briefly review the field and outline our program to generate gene-targeted pigs carrying mutations in tumour suppressor genes and proto-oncogenes that replicate key lesions responsible for a variety of human cancers. We also highlight some important issues for the future development and usefulness of porcine cancer models.     

Analysis of mitochondrial DNA mutations in D-loop region in thyroid lesions

Background

Mitochondrial defects have been associated with various human conditions including cancers.

Methods

We analyzed the mutations at the mitochondrial DNA (mtDNA) in patients with different thyroid lesions. In particular, in order to investigate if the accumulation of mtDNA mutations play a role in tumor progression, we studied the highly variable main control region of mtDNA, the displacement-loop (D-loop) in patients with non-tumor nodular goiters, with benign thyroid adenomas, and with malignant thyroid carcinomas. Total thyroid tumor or goiter samples were obtained from 101 patients, matched with nearby normal tissue and blood from the same subject.

Results

Noticeably, mitochondrial microsatellite instability (mtMSI) was detected in 2 of 19 nodular goiters (10.53%), and 8 of 77 (10.39%) malignant thyroid carcinomas. In addition, 6 patients, including 5 (6.49%) with malignant thyroid carcinomas and 1 (5.26%) with nodular goiter, were found to harbor point mutations. The majority of the mutations detected were heteroplasmic.

General significance

Our results indicate that mtDNA alterations in the D-loop region could happen before tumorigenesis in thyroid, and they might also accumulate during tumorigenesis.     

Germline polymorphism of cancer susceptibility genes in gynecologic cancer

The multifactorial process of carcinogenesis involves mutations in oncogenes, or tumor suppressor genes, as well as the influence of environmental etiological factors. Common DNA polymorphisms in low penetrance genes have emerged as genetic factors that seem to modulate an individual’s susceptibility to malignancy. Genetic studies, which lead to a true association, are expected to increase understanding of the pathogenesis of each malignancy and to be a powerful tool for prevention and prognosis in the future. Here, we review the findings of genetic association studies of gene polymorphisms in gynecologic cancer with special reference to glutathione-S-transferase, FAS/CD95 and p53 genes including our recent research results.     

Molecular changes in thyroid neoplasia

All authors integrating the known facts into a model of thyroid carcinogenesis concur that two main histotypes of thyroid cancer exhibit different routes of molecular development. RET rearrangements are an initiating event in papillary carcinoma, and simultaneously the most characteristic mutation for this type of cancer. They are followed by further, not well recognized, mutations. RAS mutations are regarded as a crucial event in the development of follicular tumors already at the adenoma step, while in papillary cancer they belong to the spectrum of secondary mutations, enabling tumor progression. Aberrant DNA methylation, causing loss of P16 tumor supressor gene, may be a common event in both types of cancer. Aneuploidy is seen much more frequently in follicular than in papillary cancer, which also exhibits a low rate for loss of heterozygosity and microsatellite instability. Mutations of the P53 tumor supressor gene are a common feature of undifferentiated thyroid cancers and could be responsible for their aggressive phenotype. RET rearrangements have been proposed as identifying fingerprints for irradiation induced thyroid cancer in children. Our own data speak against this hypothesis. We noted a high frequency of RET/PTC3 mutations in a group of Polish children with papillary thyroid carcinoma, regarded as sporadic cancer.     

Retinoblastoma regulatory pathway in lung cancer

Lung cancer is the leading cause of cancer related deaths accounting for more deaths than breast, colon and prostate cancers combined. The Rb-p16 regulatory pathway plays an essential role in tumor suppression in the lung epithelium. This is evidenced by the nearly universal alterations in Rb-p16 pathway components in lung cancer, and the increased incidence of pulmonary carcinomas in persons with germline Rb mutations. Interestingly, p16 loss and Rb mutations preferentially occur in phenotypically distinct lung cancer subtypes. Analysis of human tumors has identified progressive preneoplastic lesions that accumulate molecular alterations in an orderly sequence. Epigenetic p16 gene modifications represent an early event in lung cancer progression. This review summarizes the human studies that demonstrate a critical role for the Rb-p16 tumor suppressor pathway in lung carcinogenesis, and discusses how these findings in combination with genetically engineered mouse models have significantly contributed to our understanding of lung cancer pathogenesis.     

The genetics of bladder cancer: a cytogeneticist's perspective

Cytogenetic studies of bladder cancer have helped to define two clinically distinct subtypes: benign tumors with few genetic mutations and a stable karyotype and aggressive cancers with chromosomal instability and many non-random cytogenetic aberrations. While the cytogenetic data does not provide complete information, these studies have been important for suggesting pathways for bladder carcinoma initiation and its progression. In addition, molecular cytogenetic studies have proven useful for diagnosing bladder cancer and for monitoring patients for cancer recurrence. More detailed molecular genetic studies and expression array analyses are needed to fully comprehend the biologic processes associated with urothelial cancers, but cytogenetics studies have laid the foundation for further investigation.     

Molecular mechanisms of medullary thyroid carcinoma: current approaches in diagnosis and treatment

Medullary thyroid carcinoma is the most common cause of death among patients with multiple endocrine neoplasia (MEN) 2. Dominant-activating mutations in the RET proto-oncogene have been shown to have a central role in the development of MEN 2 and sporadic medullary thyroid cancer (MTC): about half of sporadic MTCs are caused by somatic genetic changes of the RET oncogene. Inactivating mutations of the same gene lead to Hirschprung disease and other developmental defects. Thus, RET genetic changes lead to phenotypes that largely depend on their location in the gene and the function and timing of developmental expression of the RET protein. The reproducibility of the phenotype caused by each RET genotype led to MEN 2/MTC being among the first conditions in Medicine where a drastic measure is applied to prevent cancer, following genetic testing: thyroidectomy is currently routinely done in young children that are carriers of MTC-predisposing RET mutations. RET inhibitors have been also developed recently and are used in various types of thyroid and other cancers. This report reviews the RET involvement in the etiology of MEN 2 and MTC and updates the therapeutic approach in preclinical and clinical studies.     

Comparative studies of nuclear DNA content in benign and malignant thyroid lesions

Currently available data suggest that DNA aneuploidy is associated with aggressive behavior of and unfavorable prognosis in several malignant human tumors as compared with diploid malignancies. However, the diagnostic and prognostic importance of flow cytometric DNA measurements in the case of thyroid neoplasms remains controversial. Therefore, the aim of our study was to evaluate utility of DNA index (DI) and proliferative index (PI) in distinguishing benign from malignant thyroid lesions taking into account the possible influence of intra-tumor heterogeneity and tissue preparation mode on DNA flow-cytometry measurements. A retrospective study was performed on 71 paraffin-embedded specimens from 57 patients with benign and malignant thyroid pathologies: 13 colloid goitres, 12 parenchymatous goitres, 19 adenomas and 13 carcinomas. In 14 of 57 cases two separate specimens taken from different areas of the same lesion were analysed and DNA parameters were compared. Additionally, flow cytometry DNA analysis was parallelly performed on 3 adjacent but differently processed tissue sections (fresh, formalin-fixed and paraffin-embedded) taken from each of 26 surgically excised thyroid lesions. DNA content was also analysed in both fresh and formalin-fixed twin specimens of normal pig thyroid glands (N = 6). We demonstrated that all tumors diagnosed as thyroid carcinomas were associated with abnormal nuclear DNA content although aneuploidy was not found specific to malignant thyroid tumors. Aneuploid samples of benign thyroid lesions exhibited higher proliferative activity, expressed as mean PI values, than diploid ones. In carcinomas the mean PI values were significantly higher than in benign lesions, independently whether they concerned aneuploid or diploid tissues. Considering intra-tumor heterogeneity, the flow cytometric DNA parameters can be assumed as reproducible despite differences in the mode of tissue fixation and preparation for analysis.     

MEK1 mutations,but not ERK2 mutations,occur in melanomas and colon carcinomas,but none in thyroid carcinomas

Mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in the pathogenesis of melanoma, colon cancer and thyroid cancer, which commonly harbor RAS and BRAF mutations. However, mutations in exon 2 of MEK1 and exon 7 of ERK2 have not been investigated in these cancers although they are occasionally found in some other cancers or cell lines. In this study, we performed mutational analysis to search for these mutations in 185 samples, including 167 tumor samples and 18 cell lines of melanoma, colon cancer, and thyroid cancer. We found one MEK1 mutation in 1 of 37(3%) melanoma tumor samples and another MEK1 mutation in 1 of 45 (2.2%) colon cancer samples. We did not find any MEK1 mutation in 99 thyroid tumor samples and 12 thyroid cancer cell lines. We also did not find any ERK2 mutation in melanoma, colon cancer, and thyroid cancer. We thus report for the first time a low prevalence of MEK1 mutations in melanoma and colon cancer. Both of the two mutants have been demonstrated to be activating in the MAPK signaling pathway and may therefore provide potential target for effective therapy in cases of melanomas and colon cancer harboring these mutations.     

Micronuclei frequency in peripheral blood lymphocytes of cancer patients: a meta-analysis

Micronuclei (MN) frequency is a biomarker of chromosomal damage, genome instability, and cancer risk that integrates acquired mutations and genetic susceptibility. To evaluate and summarize the evidence reporting association between cancer and MN formation, we performed a meta-analysis assessing the frequency of this biomarker in cancer patients. Findings from 37 publications were retrieved through an extensive search of the MedLine/PubMed database. Given the heterogeneity of the study design, all studies were re-classified into three groups: (i) baseline MN frequency of untreated cancer patients (25 studies), (ii) induced MN frequency in thyroid cancer patients undergoing radioiodine treatment (9 studies), and (iii) radiosensitivity of lymphocytes (12 studies) in untreated cancer patients. A meta-estimate of the frequency ratio (meta-FR) was computed in each group. A significant increase of MN frequency was found in untreated cancer patients (meta-FR=1.45; 95% Confidence Interval (95% CI): 1.28-1.64) and in thyroid cancer patients after radioiodine treatment (meta-FR=2.26; 95% CI: 1.90-2.68). The third meta-analysis showed a negative trend of meta-FR's when plotted vs. the dose used to study patients' radiosensitivity, possibly associated to a high rate of apoptosis. The results of this review substantiate the existing evidence about a role of MN in various steps of carcinogenesis. The relatively small numbers of papers suitable for the meta-analysis call for new and larger studies, possibly based on high-throughput techniques, to further understand the role of MN formation in the occurrence of genetic instability and cancer.     

Cancer prevention by bovine lactoferrin: from animal studies to human trial

Colorectal cancer (CRC) is one of the most frequently diagnosed cancers and, despite improved colonoscopic screening, CRC is a leading cause of death from cancer. Administration of bovine lactoferrin (bLF) suppresses carcinogenesis in the colon and other organs of test animals, and recently it was shown that ingestion of bLF inhibits the growth of adenomatous polyps in human patients. Here we review work which established bLF as an anti-carcinogenic agent in laboratory animals and the results of a clinical trial which demonstrated that bLF can reduce the risk of colon carcinogenesis in humans.     

Mutagenicity and repair of oxidative DNA damage: insights from studies using defined lesions

Oxidative DNA damage has been implicated in mutagenesis, carcinogenesis and aging. Endogenous cellular processes such as aerobic metabolism generate reactive oxygen species (ROS) that interact with DNA to form dozens of DNA lesions. If unrepaired, these lesions can exert a number of deleterious effects including the induction of mutations. In an effort to understand the genetic consequences of cellular oxidative damage, many laboratories have determined the patterns of mutations generated by the interaction of ROS with DNA. Compilation of these mutational spectra has revealed that GC → AT transitions and GC → TA transversions are the most commonly observed mutations resulting from oxidative damage to DNA. Since mutational spectra convey only the end result of a complex cascade of events, which includes formation of multiple adducts, repair processing, and polymerase errors, it is difficult if not impossible to asses the mutational specificity of individual DNA lesions directly from these spectra. This problem is especially complicated in the case of oxidative DNA damage owing to the multiplicity of lesions formed by a single damaging agent. The task of assigning specific features of mutational spectra to individual DNA lesions has been made possible with the advent of a technology to analyze the mutational properties of single defined adducts, in vitro and in vivo. At the same time, parallel progress in the discovery and cloning of repair enzymes has advanced understanding of the biochemical mechanisms by which cells excise DNA damage. This combination of tools has brought our understanding of DNA lesions to a new level of sophistication. In this review, we summarize the known properties of individual oxidative lesions in terms of their structure, mutagenicity and repairability.