title: Origin and quantification of circulating DNA in mice with human colorectal cancer xenografts.
abstract: Although circulating DNA (ctDNA) could be an attractive tool for early cancer detection, diagnosis, prognosis, monitoring or prediction of response to therapies, knowledge on its origin, form and rate of release is poor and often contradictory. Here, we describe an experimental system to systematically examine these aspects. Nude mice were xenografted with human HT29 or SW620 colorectal carcinoma (CRC) cells and ctDNA was analyzed by Q-PCR with highly specific and sensitive primer sets at different times post-graft. We could discriminate ctDNA from normal (murine) cells and from mutated and non-mutated tumor (human) cells by using species-specific KRAS or PSAT1 primers and by assessing the presence of the BRAF V600E mutation. The concentration of human (mutated and non-mutated) ctDNA increased significantly with tumor growth. Conversely, and differently from previous studies, low, constant level of mouse ctDNA was observed, thus facilitating the study of mutated and non-mutated tumor derived ctDNA. Finally, analysis of ctDNA fragmentation confirmed the predominance of low-size fragments among tumor ctDNA from mice with bigger tumors. Higher ctDNA fragmentation was also observed in plasma samples from three metastatic CRC patients in comparison to healthy individuals. Our data confirm the predominance of mononucleosome-derived fragments in plasma from xenografted animals and, as a consequence, of apoptosis as a source of ctDNA, in particular for tumor-derived ctDNA. Altogether, our results suggest that ctDNA features vary during CRC tumor development and our experimental system might be a useful tool to follow such variations.
authors.affiliation: Sysdiag UMR3145 - CNRS/BIO-RAD, CAP DELTA 1682 Rue de la Valsière, 34184 Montpellier CEDEX 4, France. alain.thierry@sysdiag.cnrs.fr
authors.forename: Alain R
authors.initials: AR
authors.lastname: Thierry
authors.forename: Florent
authors.initials: F
authors.lastname: Mouliere
authors.forename: Celine
authors.initials: C
authors.lastname: Gongora
authors.forename: Jeremy
authors.initials: J
authors.lastname: Ollier
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
authors.forename: Marc
authors.initials: M
authors.lastname: Ychou
authors.forename: Maguy
authors.initials: M
authors.lastname: Del Rio
authors.forename: Franck
authors.initials: F
authors.lastname: Molina
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000097:blood* / Q000235:genetics / Q000473:pathology; D053938:DNA Fragmentation; D017931:DNA Primers / Q000592:standards; D004273:DNA, Neoplasm / Q000097:blood* / Q000737:chemistry; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D009368:Neoplasm Transplantation; D010949:Plasma / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000592:standards; D044967:Serum / Q000378:metabolism; D013045:Species Specificity; D014183:Transplantation, Heterologous
chemical_list: D017931:DNA Primers; D004273:DNA, Neoplasm