Leukocyte DNA as Surrogate for the Evaluation of Imprinted Loci Methylation in Mammary Tissue DNA

There is growing interest in identifying surrogate tissues to identify epimutations in cancer patients since primary target tissues are often difficult to obtain. Methylation patterns at imprinted loci are established during gametogenesis and post fertilization and their alterations have been associated with elevated risk of cancer. Methylation at several imprinted differentially methylated regions (GRB10 ICR, H19 ICR, KvDMR, SNRPN/SNURF ICR, IGF2 DMR0, and IGF2 DMR2) were analyzed in DNA from leukocytes and mammary tissue (normal, benign diseases, or malignant tumors) from 87 women with and without breast cancer (average age of cancer patients: 53; range: 31–77). Correlations between genomic variants and DNA methylation at the studied loci could not be assessed, making it impossible to exclude such effects. Methylation levels observed in leukocyte and mammary tissue DNA were close to the 50% expected for monoallellic methylation. While no correlation was observed between leukocyte and mammary tissue DNA methylation for most of the analyzed imprinted genes, Spearman's correlations were statistically significant for IGF2 DMR0 and IGF2 DMR2, although absolute methylation levels differed. Leukocyte DNA methylation levels of selected imprinted genes may therefore serve as surrogate markers of DNA methylation in cancer tissue

Circulating methylated DNA to monitor the dynamics of RAS mutation clearance in plasma from metastatic colorectal cancer patients

The clearance of RAS mutations in plasma circulating tumor DNA (ctDNA) from originally RAS-mutant metastatic colorectal cancer (mCRC) has been recently demonstrated. Clinical trials investigating whether RAS mutant mCRC who “convert” to wild-type in plasma might benefit from EGFR blockade are ongoing. Detection of tumor-specific DNA methylation alterations in ctDNA has been suggested as a specific tool to confirm the tumoral origin of cell-free DNA. We monitored RAS clearance in plasma from patients with RAS-mutant mCRC at baseline (pre-treatment) (T0); after 4 months of first-line therapy (T1); at the time of first (T2) and second (T3) progression. A five-gene methylation panel was used to confirm the presence of ctDNA in samples in which RAS mutation clearance was detected. At T1 ctDNA analysis revealed wild-type RAS status in 83% of samples, all not methylated, suggesting at this time point the lack of ctDNA shedding. At T2 ctDNA analysis revealed wild-type RAS status in 83% of samples, of which 62.5% were found methylated. At T3 50% of wild-type-RAS samples were found methylated. Non-methylated samples were found in patients with lung or brain metastases. This five-gene methylation test might be useful to confirm the presence of ctDNA in RAS wild-type plasma samples

Birthweight, Maternal Weight Trajectories and Global DNA Methylation of LINE-1 Repetitive Elements

Low birthweight, premature birth, intrauterine growth retardation, and maternal malnutrition have been related to an increased risk of cardiovascular disease, type 2 diabetes mellitus, obesity, and neuropsychiatric disorders later in life. Conversely, high birthweight has been linked to future risk of cancer. Global DNA methylation estimated by the methylation of repetitive sequences in the genome is an indicator of susceptibility to chronic diseases. We used data and biospecimens from an epigenetic birth cohort to explore the association between trajectories of fetal and maternal weight and LINE-1 methylation in 319 mother-child dyads. Newborns with low or high birthweight had significantly lower LINE-1 methylation levels in their cord blood compared to normal weight infants after adjusting for gestational age, sex of the child, maternal age at delivery, and maternal smoking during pregnancy (p = 0.007 and p = 0.036, respectively), but the magnitude of the difference was small. Infants born prematurely also had lower LINE-1 methylation levels in cord blood compared to term infants, and this difference, though small, was statistically significant (p = 0.004). We did not find important associations between maternal prepregnancy BMI or gestational weight gain and global methylation of the cord blood or fetal placental tissue. In conclusion, we found significant differences in cord blood LINE-1 methylation among newborns with low and high birthweight as well as among prematurely born infants. Future studies may elucidate whether chromosomal instabilities or other functional consequences of these changes contribute to the increased risk of chronic diseases among individuals with these characteristics

Altérations génétiques et épigénétiques dans le cancer colique sporadique

Les cancers sont le plus souvent la conséquence d un défaut des voies de régulations impliquées dans la survie ou la mort cellulaire. Nous avons pu démontrer sur une base de population de 586 adénocarcinomes coliques, suivis par le registre bourguignon des cancers digestifs que la mutation activatrice d au moins un des trois gènes de la voie des MAP Kinases (KRAS, BRAF, PI3KCA) était associée a une moins bonne survie chez les patients porteurs d une tumeur sans instabilité des microsatellites. Nous avons également analysé sur cette base de population la méthylation de l ADN (caractérisation du phénotype CpG Island Methylator Phenotype CIMP). Trois groupes de méthylation ont été définis (No-CIMP, CIMP-Low, CIMP-High). Les cancers MSS/No-CIMP et MSS/CIMP-Low montraient des caractéristiques cliniques et génétiques similaires mais influençaient la survie de façon différente. Plus le niveau de méthylation était élevé, moins bonne était la survie des patients. Cette étude souligne l effet pronostique péjoratif de la méthylation chez les patients MSS et la nécessité d identifier les 3 groupes de méthylation. Ces travaux tirent leur importance de l utilisation récente, dans le traitement du cancer, de thérapeutiques dites ciblées dirigées des protéines impliquées dans la transduction du signal du milieu extracellulaire vers le milieu intracellulaire. L identification des mécanismes d activation des voies de signalisation et la caractérisation des altérations épigénétiques impliquées dans le cancer colique représentent donc des étapes fondamentales dans la connaissance des facteurs moléculaires pouvant moduler la prise en charge thérapeutique des patients.Cancer cells are often the result of alterations in signalling pathways implicated in cell survival or apoptosis. We successfully demonstrated in a population base of 586 colon adenocarcinomas, followed by the cancer registry of Burgundy, that activating mutation of at least one of the three genes from the MAPK signalling pathway (KRAS, BRAF, PI3KCA) was associated with a lower survival in patients bearing a tumour without microsatellite instability. In a second study, DNA Methylation, an epigenetic alteration, was evaluated in the population base (characterization of the CpG Island Methylator Phenotype). Three subgroups of methylation phenotype were identified (No-CIMP, CIMP-Low, and CIMP-High). The clinico-pathological features of cancers with MSS/No-CIMP and MSS/CIMP-Low were quite similar, but they affected survival to different degrees. The higher the level of methylation, the poorer the survival. Our work clearly showed the prognostic effect of methylation in MSS patients and the need to distinguish between the 3 groups of CIMP. These studies are all the more important since the recent use of targeted therapies against proteins from the signal transduction system have recently been used in cancer treatment. The identification of activating mechanisms of signalling pathways and the characterisation of epigenetic alterations involved in colon cancer are fundamental to the understanding of the molecular factors involved in colorectal cancer. Knowledge of these will have an impact on patient response and follow-up.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF