Measurement of Plasma Cell-Free Mitochondrial Tumor DNA Improves Detection of Glioblastoma in Patient-Derived Orthotopic Xenograft Models.

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Mair, Richard 
Mouliere, Florent 
Smith, Christopher G 
Chandrananda, Dineika  ORCID logo
Gale, Davina 

The factors responsible for the low detection rate of cell-free tumor DNA (ctDNA) in the plasma of patients with glioblastoma (GBM) are currently unknown. In this study, we measured circulating nucleic acids in patient-derived orthotopically implanted xenograft (PDOX) models of GBM (n = 64) and show that tumor size and cell proliferation, but not the integrity of the blood-brain barrier or cell death, affect the release of ctDNA in treatment-naïve GBM PDOX. Analysis of fragment length profiles by shallow genome-wide sequencing (<0.2× coverage) of host (rat) and tumor (human) circulating DNA identified a peak at 145 bp in the human DNA fragments, indicating a difference in the origin or processing of the ctDNA. The concentration of ctDNA correlated with cell death only after treatment with temozolomide and radiotherapy. Digital PCR detection of plasma tumor mitochondrial DNA (tmtDNA), an alternative to detection of nuclear ctDNA, improved plasma DNA detection rate (82% vs. 24%) and allowed detection in cerebrospinal fluid and urine. Mitochondrial mutations are prevalent across all cancers and can be detected with high sensitivity, at low cost, and without prior knowledge of tumor mutations via capture-panel sequencing. Coupled with the observation that mitochondrial copy number increases in glioma, these data suggest analyzing tmtDNA as a more sensitive method to detect and monitor tumor burden in cancer, specifically in GBM, where current methods have largely failed. SIGNIFICANCE: These findings show that detection of tumor mitochondrial DNA is more sensitive than circulating tumor DNA analysis to detect and monitor tumor burden in patient-derived orthotopic xenografts of glioblastoma.

Animals, Biomarkers, Tumor, Body Fluids, Circulating Tumor DNA, DNA, Mitochondrial, DNA, Neoplasm, Female, Glioblastoma, High-Throughput Nucleotide Sequencing, Humans, Mitochondria, Rats, Rats, Nude, Tumor Cells, Cultured, Xenograft Model Antitumor Assays
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Cancer Res
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American Association for Cancer Research (AACR)
Cancer Research Uk (None)
Cancer Research UK (C48525/A18345)
Addenbrooke's Charitable Trust (ACT) (unknown)
Cancer Research UK (CB4100)
Cancer Research UK (C14303/A17197)
European Research Council (337905)
Cancer Research UK (unknown)
N. Rosenfeld and K. Brindle are supported by the University of Cambridge, Cancer Research UK (grant numbers A11906, A20240, 17242, 16465) and Hutchison Whampoa Limited. N. Rosenfeld has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 337905. C. Watts is supported by The Brain Tumour Charity grant 10/136.