Τομέας Ι [Θεωρητική Χημεία – Φυσικοχημεία – Ανόργανη Ανάλυση – Ενόργανη Ανάλυση – Οργανολογία – Χημική Μηχανική (Εφαρμ. Φυσικοχημεία)]
Library of the School of Science

2014-07-15

2014

Χειμωνίδου Μαρία

Ευρύκλεια Λιανίδου, Καθηγήτρια Αναλυτικής Χημείας ΕΚΠΑ (επιβλεπούσα), Βασίλειος Γεωργούλιας Καθηγητής Ιατρικής Σχολής Κρητής, Γεωργία Σωτηροπούλου Αν. Καθηγήτρια Φαρμακευτικής Πανεπιστήμιο Πατρών

Μελέτη και κλινική αξιολόγηση δεικτών μεθυλίωσης DNA στον καρκίνο του μαστού

Greek

Study and clinical evaluation of DNA methylation biomarkers in breast cancer

Epidemiological studies have shown that breast cancer is the second cause of
death from malignancy and the first in women between 40-49 years of age. The
emerging field of epigenetics revealed that DNA methylation is an important
regulator of gene transcription and a large body of evidence has demonstrated
that genes with high levels of 5-methylcytosine in their promoter region are
transcriptionally silent, and that DNA methylation gradually accumulates upon
long-term gene silencing.. Aberrant DNA methylation patterns –compared to
normal tissue – have been associated with a large number of human malignancies
while methylation may give selective advantage to tumor cells increasing
genetic instability and allowing them to metastasize. Abnormal methylation is
detectable in early precancerous lesions, suggesting that directly contributes
to the malignant transformation of cells and is a late event caused by genetic
alterations
In recent years, the need to identify molecular markers characterized by high
sensitivity and specificity in detecting and monitoring early breast cancer has
increased. Tumor heterogeneity is one of the major problems limiting the
efficacy of targeted therapies and compromising treatment outcomes. Therefore,
blood may be a reservoir for collecting DNA from different sources, including
CTCs, cfDNA, and occult micrometastatic deposits in secondary organs. As the
scope of breast cancer intratumour genetic heterogeneity unravels, analysis of
Circulating tumour cells and cell-free plasma DNA contribute for the completion
of tumor molecular characterization.
Circulating tumor cells (CTCs) are cells that have shed into the vasculature
from a primary tumor and circulate in the bloodstream. CTCs thus constitute
seeds for subsequent growth of additional tumors (metastasis) in vital distant
organs, triggering a mechanism that is responsible for the vast majority of
cancer-related deaths. On the other hand, the presence of extractable amounts
of DNA in serum of cancer patients was early identified, suggesting that
circulating DNA maybe shed from tumours.
In the present phD thesis, we studied DNA methylation of suppressor and
metastasis suppressor genes, CST6, SOX17 and BRMS1 developing and applying MSP
(Methylation Specific PCR) in primary tumors, cell-free DNA and circulating
tumor cells and correlation with clinicopathological features of patients.
Firstly, we evaluated the presence of CST6 promoter methylation in cell-free
DNA (cfDNA) circulating in plasma of breast cancer patients. CST6 promoter was
found highly methylated in cfDNA of breast cancer patients, but not in healthy
individuals. CST6 promoter methylation in cfDNA, should be prospectively
validated as a novel plasma tumor biomarker for breast cancer in a large cohort
of breast cancer patients.
We examined for the first time the relationship between epigenetic silencing of
BRMS1 and clinical outcome in operable breast cancers and evaluated the
expression of BRMS1 protein and BRMS1 methylation status in CTCs using a highly
sensitive and specific MSP assay for BRMS1 promoter methylation. Our data show
that BRMS1 promoter methylation results in the transcriptional repression of
this gene and highlight the potential clinical relevance of this methylation
event in operable breast cancer. We show that BRMS1 promoter is methylated in
primary tumors of patients with early breast cancer and in corresponding CTC
samples but not in noncancerous breast tissues. Additionally, CTCs were highly
heterogeneous in respect to BRMS1 expression even in the same patient.
Finally we investigated for the first time whether there is a direct connection
between the presence of DNA methylation of these three genes in primary tumors
and corresponding CTCs and cfDNA in patients with operable breast cancer and
verified metastasis. To address this question we have studied DNA methylation
of these genes by the same methodology in well characterized matched clinical
samples of breast cancer patients. Our results suggest that there is a direct
connection between the presence of CTCs and cfDNA in patients with operable
breast cancer, after surgical removal of the primary tumor and prove the tumor
origin of circulating tumor DNA. The epigenetic characterization of ctDNA has
been shown to be a complementary tool with molecular characterization of CTCs
for diagnosis, prognosis and management of cancer patients.

CTC (circulating tumor cells), cfDNA (cell free DNA), DNA methylation, MSP (Methylation specific PCR), Tumor Suppressor Genes

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https://pergamos.lib.uoa.gr/uoa/dl/object/1309033