About the possible origin and mechanism of circulating DNA apoptosis and active DNA release.

BACKGROUND: In addition to cell lysis, apoptosis has been advanced as the origin of circulating DNA on the basis of several observations. Plasma or serum DNA often presents a ladder pattern reminiscent of that displayed by apoptotic cells when subjected to electrophoresis. However, the phenomenon of active release of DNA from cells might also be expected to result in a ladder pattern on electrophoresis. Non-dividing cells, such as lymphocytes, frog auricles and cultured cell lines including HL-60, spontaneously release a nucleoprotein complex within a homeostatic system in which newly synthesized DNA is preferentially released. CONCLUSION: In relation to DNA synthesis, the phenomenon of extracellular DNA in different culture conditions favors apoptosis or spontaneous active DNA release.

Circulating nucleic acids in plasma or serum.

BACKGROUND: Nucleic acids can be found in small amounts in healthy and diseased human plasma/serum. Higher concentrations of DNA are present in the plasma of cancer patients sharing some characteristics with DNA of tumor cells. Together with decreased strand stability, the presence of specific oncogene or tumor-suppressor gene mutations, microsatellite alterations, Ig rearrangements and hypermethylation of several genes may be detected. Moreover, tumor-related mRNA has been found circulating in the plasma/serum. CONCLUSIONS: The results obtained in many different cancers have opened a new research area indicating that circulating nucleic acids might eventually be used for the development of noninvasive diagnostic, prognostic and follow-up tests for cancer.

Alu repeat sequences are present in increased proportions compared to a unique gene in plasma/serum DNA: evidence for a preferential release from viable cells?

Small amounts of DNA circulate freely in plasma or serum, but the mechanism of release is not known. To determine if DNA is actively excreted from viable cells, we utilized real-time PCR to measure the proportion of Alu repeat sequences compared to the beta-globin gene in serum and lymphocyte DNA in 27 cancer patients and 22 healthy controls. The proportion of Alu compared to beta-globin was significantly greater in serum DNA than in lymphocyte DNA both in control subjects (p = 0.003) and in cancer patients (p < 0.001). Overall, the proportion was similar in cancer and control patients (p = 0.79). Further experiments showed that the beta-globin gene was not more vulnerable to degradation by nuclease action than Alu sequences. Our results lead us to conclude that active DNA release is likely to play a significant role in the origin of circulating DNA.

Telomerase RNA as a detection marker in the serum of breast cancer patients.

Tumor-derived circulating DNA has been found in the plasma of cancer patients. Alterations include decreased strand stability, mutations of oncogenes or of tumor suppressor genes, microsatellite alterations, and hypermethylation of several genes. RNA has also been found circulating in the plasma of normal subjects and cancer patients. Tyrosinase mRNA has been extracted from the serum of melanoma patients and subjected to RT-PCR. Moreover, the presence of cell-free EBV-associated RNA has been reported in the plasma of patients with nasopharyngeal carcinoma. Human telomerase comprises two RNA subunits, telomerase RNA template (hTR) and its catalytic component, telomerase reverse transcriptase protein (hTERT). Expression of these subunits correlates with telomerase activity. Using RT-PCR, we investigated whether these RNA subunits were present in the serum of 18 patients with breast cancer, 2 patients with benign breast disease, and 21 normal subjects. The presence of amplifiable RNA was confirmed in all tissue and serum samples using RT-PCR of glyceraldehyde-3-phosphate dehydrogenase RNA. hTR was found in 17 of 18 tumors (94%) and 5 of 18 serum samples (28%). hTERT was also detected in 17 of 18 tumors (94%) and in 4 of 16 available serum samples (25%). hTR and hTERT were undetectable in tissues and sera taken from 2 patients with benign disease and in the sera of 21 normal subjects. We conclude that RNA is detectable in the serum of breast cancer patients and that tumor-derived mRNA can be extracted and amplified using RT-PCR, even in patients with localized disease. This may have implications for cancer diagnosis and follow-up in the future.

Detecting tumor-related alterations in plasma or serum DNA of patients diagnosed with breast cancer.

Chromosomal abnormalities are associated with the development of breast cancer, and widespread allelic loss or imbalance is frequently found in tumor tissues taken from patients with this disease. Using different markers, we studied a total of 61 patients (divided into three groups) for the presence of microsatellite instability and loss of heterozygosity (LOH) in plasma or serum DNA. Of the initial 27 patients, 35% of the tumor samples displayed LOH, whereas 15% had identical alterations in the corresponding plasma samples. In addition, the adjacent normal breast tissue of two patients also displayed LOH. In a second group of 11 patients, 45% of the tumors displayed LOH, and 27% displayed identical plasma DNA alterations; one case displayed an identical LOH in adjacent nontumor tissue. In a third series of 23 patients also studied with tetranucleotide repeats, 81% of the tumor samples displayed LOH, whereas 48% had LOH in the corresponding serum samples. The fact that small tumors (T1) of histoprognostic grade 1 or in situ carcinomas could present DNA alterations in the plasma/serum at an early stage, allied to the widely increased range of available microsatellite markers, suggests that plasma or serum DNA may become a useful diagnostic tool for early and potentially curable breast cancer.

A prospective study of K-ras mutations in the plasma of pancreatic cancer patients.

K-ras mutations are frequently found in primary pancreatic adenocarcinomas. In this prospective study, we looked for K-ras mutations in the plasma of patients with pancreatic cancer. We isolated plasma DNA from 21 pancreatic cancer patients using a simple and rapid extraction technique and detected K-ras alterations with a PCR assay and subsequent product sequencing. Patients were followed up to determine their clinical outcome. We found K-ras mutations in the plasma of 17 patients (81%). In cases in which both plasma and pancreatic tissue were available, DNA mutations were similar in corresponding plasma and tissue samples. Plasma DNA alterations were found 5-14 months before clinical diagnosis in four patients. Mutant DNA was not found in the plasma of two patients with chronic pancreatitis or in five healthy controls. Our results indicate that K-ras mutations are often found in DNA isolated from the plasma of pancreatic cancer patients and that a noninvasive plasma-based assay may provide qualitative diagnostic information to clinicians in the future. Larger studies are required to further assess the relevance of our findings to clinical practice.

K-ras mutations are found in DNA extracted from the plasma of patients with colorectal cancer.

BACKGROUND & AIMS: Circulating DNA can be isolated from the plasma of healthy subjects and from patients with cancer. The aim of this study was to detect K-ras mutations in DNA extracted from the plasma of patients with colorectal cancer. METHODS: Tumor and plasma DNA were extracted from 14 patients with colorectal cancer (stages A-D), and K-ras alterations were detected using a polymerase chain reaction assay that uses sequence-specific primers to amplify mutant DNA. These results were confirmed with another polymerase chain reaction assay that creates an enzyme restriction site in the absence of a K-ras mutation followed by direct sequencing and additional cloning techniques. RESULTS: Seven patients (50%) had a codon 12 K-ras mutation within their primary tumor, and identical mutations were found in the plasma DNA of 6 patients (86%). Mutant DNA was not detected in the plasma specimens of 7 patients whose tumors tested negative for K-ras alterations or in healthy control subjects. Similar results were obtained using all three molecular biological techniques. CONCLUSIONS: K-ras abnormalities can be detected in circulating DNA extracted from the plasma specimens of patients with colorectal cancer. If these results are confirmed in larger studies, genetic analysis of plasma DNA may have clinical applications in the future.

Microsatellite alterations in plasma DNA of small cell lung cancer patients.

Microsatellite instability is an important characteristic of many tumor types especially those associated with hereditary non-polyposis colorectal carcinoma (HNPCC) syndrome. Microsatellite alterations in 50% of primary small cell lung carcinoma (SCLC) have been found. These alterations were also found in the sputum. Because neoplastic characteristics such as decreased strand stability9 and ras mutations have been found in the plasma DNA of cancer patients, we looked for microsatellite alterations in the plasma of SCLC patients. A microsatellite alteration was present in 16 out of 21 (76%) SCLC tumors and in 15 out of 21 (71%) plasma samples. In one case, the alteration was present only in the plasma DNA. If confirmed in larger studies, microsatellite analysis of plasma DNA might constitute a new tool for tumor staging, management and, possibly, detection.

[Transformation of NIH/3T3 cells and SW 480 cells displaying K-ras mutation]. / Transformation de cellules NIH/3T3 et cellules SW 480 porteuses d'une mutation K-ras.

The spontaneous release of a glyconucleoprotein complex in the supernatant of eukaryote cell cultures is a general phenomenon independent of cell lysis. The DNA recovered from this glyconucleoprotein material contains most part of the genome. The SW 480 cell line, originating from a human colon carcinoma, presents a point mutation of the K-ras gene on both alleles. These cells in culture release the mutated K-ras gene. When crude SW 480 cell supernatant is given, without any other adjonction, to NIH/3T3 mouse cells, transformed foci appear as numerous as those occurring after a transfection provoked by a cloned E.J. ras gene administered as a calcium precipitate. The presence of a mutated ras gene in the transfected foci of the 3T3 cells has been checked by hybridization, after PCR, with an oligonucleotide probe specific to the mutation. This result was confirmed by sequencing the PCR product.

Point mutations of the N-ras gene in the blood plasma DNA of patients with myelodysplastic syndrome or acute myelogenous leukaemia.

Oncogene mutations are frequently found in several tumour types and, among these, point mutations of the ras gene are particularly significant. A predominance of N-ras mutations has been found in the bone marrow DNA of patients with myelodysplastic syndrome (MDS) or acute myelogenous leukaemia (AML). On the other hand, increased levels of plasma DNA have previously been observed in patients suffering from various malignant diseases. In the present work we have investigated, by polymerase chain reaction (PCR), point mutations of the N-ras gene in the DNA of plasma, blood cells and bone marrow of 10 patients suffering from AML or MDS. The different ras mutations detected in five cases were always present in the plasma DNA while sometimes absent in the DNA of peripheral blood cells or bone marrow. This indicates that a bone marrow biopsy or aspiration does not necessarily contain all the malignant clones involved in the disease. Plasma could thus prove to be an easily accessible and useful material for detection and monitoring of myeloid disorders.

Neoplastic characteristics of the DNA found in the plasma of cancer patients.

About one third of patients with various malignant diseases were found to have extractable amounts of DNA in their plasma whereas no DNA could be detected in normal controls. Using the test established by one of us (M.B.), which is based on decreased strand stability of cancer cell DNA, we have found that several plasma DNA originate from cancer cells.

Isolation and characterization of DNA from the plasma of cancer patients.

UNLABELLED: Ten out of 37 patients with advanced malignant diseases were found to have extractable amounts of DNA in their plasma whereas no DNA could be detected in 50 normal controls. After its purification from the original nucleoprotein complex, DNA plasma levels ranging from 0.15 to 12 micrograms/ml were measured, the lowest concentration detectable with our method being 0.1 microgram/ml. Knowing from recovery experiments performed with 32P-DNA that the loss of DNA during the extraction procedure is about 65%, the real concentration of DNA in the plasma corresponds to about 3 times the given figures. The purified DNA was shown to be double-stranded and composed of fractions ranging from 21 kb to less than 0.5 kb, as determined by agarose gel electrophoresis. All these fractions hybridized with a 32P-labelled human DNA probe indicating the human origin of the bulk of the circulating DNA. IN CONCLUSION: the finding of extractable amounts of DNA in the plasma of 27% of the investigated cancer patients, and its absence from the controls, suggests some correlation with malignancy.