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Weerts MJA, Timmermans EC, van de Stolpe A, Vossen RHAM, Anvar SY, Foekens JA, Sleijfer S, Martens JWM. Tumor-Specific Mitochondrial DNA Variants Are Rarely Detected in Cell-Free DNA. Neoplasia 2018; 20:687-696. [PMID: 29842994 PMCID: PMC6030393 DOI: 10.1016/j.neo.2018.05.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 05/07/2018] [Accepted: 05/08/2018] [Indexed: 12/14/2022] Open
Abstract
The use of blood-circulating cell-free DNA (cfDNA) as a “liquid biopsy” in oncology is being explored for its potential as a cancer biomarker. Mitochondria contain their own circular genomic entity (mitochondrial DNA, mtDNA), up to even thousands of copies per cell. The mutation rate of mtDNA is several orders of magnitude higher than that of the nuclear DNA. Tumor-specific variants have been identified in tumors along the entire mtDNA, and their number varies among and within tumors. The high mtDNA copy number per cell and the high mtDNA mutation rate make it worthwhile to explore the potential of tumor-specific cf-mtDNA variants as cancer marker in the blood of cancer patients. We used single-molecule real-time (SMRT) sequencing to profile the entire mtDNA of 19 tissue specimens (primary tumor and/or metastatic sites, and tumor-adjacent normal tissue) and 9 cfDNA samples, originating from 8 cancer patients (5 breast, 3 colon). For each patient, tumor-specific mtDNA variants were detected and traced in cfDNA by SMRT sequencing and/or digital PCR to explore their feasibility as cancer biomarker. As a reference, we measured other blood-circulating biomarkers for these patients, including driver mutations in nuclear-encoded cfDNA and cancer-antigen levels or circulating tumor cells. Four of the 24 (17%) tumor-specific mtDNA variants were detected in cfDNA, however at much lower allele frequencies compared to mutations in nuclear-encoded driver genes in the same samples. Also, extensive heterogeneity was observed among the heteroplasmic mtDNA variants present in an individual. We conclude that there is limited value in tracing tumor-specific mtDNA variants in blood-circulating cfDNA with the current methods available.
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Affiliation(s)
- M J A Weerts
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands.
| | - E C Timmermans
- Philips Research Laboratories, High Tech Campus 11, Eindhoven, The Netherlands
| | - A van de Stolpe
- Philips Research Laboratories, High Tech Campus 11, Eindhoven, The Netherlands
| | - R H A M Vossen
- Leiden Genome Technology Center (LGTC), Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - S Y Anvar
- Leiden Genome Technology Center (LGTC), Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands; Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands; Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, The Netherlands
| | - J A Foekens
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - S Sleijfer
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - J W M Martens
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands
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Weerts MJA, Timmermans EC, Vossen RHAM, van Strijp D, Van den Hout-van Vroonhoven MCGN, van IJcken WFJ, van der Zaag PJ, Anvar SY, Sleijfer S, Martens JWM. Sensitive detection of mitochondrial DNA variants for analysis of mitochondrial DNA-enriched extracts from frozen tumor tissue. Sci Rep 2018; 8:2261. [PMID: 29396409 PMCID: PMC5797170 DOI: 10.1038/s41598-018-20623-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 01/22/2018] [Indexed: 11/25/2022] Open
Abstract
Large variation exists in mitochondrial DNA (mtDNA) not only between but also within individuals. Also in human cancer, tumor-specific mtDNA variation exists. In this work, we describe the comparison of four methods to extract mtDNA as pure as possible from frozen tumor tissue. Also, three state-of-the-art methods for sensitive detection of mtDNA variants were evaluated. The main aim was to develop a procedure to detect low-frequent single-nucleotide mtDNA-specific variants in frozen tumor tissue. We show that of the methods evaluated, DNA extracted from cytosol fractions following exonuclease treatment results in highest mtDNA yield and purity from frozen tumor tissue (270-fold mtDNA enrichment). Next, we demonstrate the sensitivity of detection of low-frequent single-nucleotide mtDNA variants (≤1% allele frequency) in breast cancer cell lines MDA-MB-231 and MCF-7 by single-molecule real-time (SMRT) sequencing, UltraSEEK chemistry based mass spectrometry, and digital PCR. We also show de novo detection and allelic phasing of variants by SMRT sequencing. We conclude that our sensitive procedure to detect low-frequent single-nucleotide mtDNA variants from frozen tumor tissue is based on extraction of DNA from cytosol fractions followed by exonuclease treatment to obtain high mtDNA purity, and subsequent SMRT sequencing for (de novo) detection and allelic phasing of variants.
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Affiliation(s)
- M J A Weerts
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Rotterdam, The Netherlands.
| | - E C Timmermans
- Philips Research Laboratories, High Tech Campus 11, 5656 AE, Eindhoven, The Netherlands
| | - R H A M Vossen
- Leiden Genome Technology Center (LGTC), Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - D van Strijp
- Philips Research Laboratories, High Tech Campus 11, 5656 AE, Eindhoven, The Netherlands
| | | | | | - P J van der Zaag
- Philips Research Laboratories, High Tech Campus 11, 5656 AE, Eindhoven, The Netherlands
| | - S Y Anvar
- Leiden Genome Technology Center (LGTC), Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.,Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.,Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, The Netherlands
| | - S Sleijfer
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Rotterdam, The Netherlands
| | - J W M Martens
- Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Rotterdam, The Netherlands
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