Abstract 2771: Neutrophil specific mitochondrial DNA copy number as a biomarker for breast cancer
Authors: Barcelo Helene , Brady Nicholas J. , Schwertfeger Kathryn L. , Gross Myron , Thyagarajan Bharat 
Published: August 2015

Background: We previously identified that mitochondrial DNA (mtDNA) copy number in pre-diagnostic peripheral blood samples collected up to 3 years prior to breast cancer diagnosis was associated with breast cancer risk. However, the biological mechanisms underlying this association remain poorly understood. To get a better understanding of the mtDNA copy number-breast cancer association we (a) evaluated the contribution of different cell subsets to whole blood mtDNA copy number and (b) developed a mouse model of early stage breast cancer that replicated the mtDNA copy number-breast cancer association observed in human populations.

Methods: Since cell subsets in peripheral blood have different amounts of mtDNA copy number, we evaluated the contribution of five different cell subsets to mtDNA copy number in peripheral blood from 10 healthy volunteers that were sorted into the following cell subtypes using magnetic beads separation: neutrophils (CD15+), lymphocytes (CD3+), B-cells (CD19+), natural killer (NK) cells (CD56+) and monocytes (CD14+). We utilized a transgenic mouse model that relies on an inducible mouse mammary tumor virus (MMTV) promoter-driven inducible FGFR1 (iFGFR1) construct that represents a model of early stage mammary tumorigenesis to evaluate changes in peripheral blood mtDNA copy number.

Results: The mtDNA copy number in the myeloid cell fractions (monocytes and neutrophils) were positively correlated with whole blood mtDNA copy number while the mtDNA copy number in the lymphocyte fractions (T and B lymphocytes and NK cells) were negatively correlated with whole blood mtDNA copy number. Specifically, the neutrophil mtDNA copy number was strongly correlated to the whole blood mtDNA copy number (r = 0.67), while the monocyte mtDNA copy number was weakly correlated with whole blood mtDNA copy number (r = 0.24). The lymphocyte cell subtypes (T lymphocytes, B lymphocytes and NK cells) showed weak negative correlations with whole blood mtDNA copy number (r = -0.16, r = -0.01 and r = -0.25 respectively). In the transgenic mouse model, we showed significant increase in mtDNA copy number in whole blood in treated mice (n = 4) versus control mice (n = 5) (2.87 vs. 1.53, p = 0.04), replicating our findings in human populations. Mitochondrial DNA copy number in sorted neutrophils from the transgenic mice also showed a similar trend.

Conclusion: These data along with other studies that show altered neutrophil function in cancer patients, suggests that altered neutrophil phenotype may explain the mtDNA copy number-breast cancer association and neutrophil specific mtDNA copy number may be useful as an early detection tool in breast cancer diagnosis. The early stage breast tumorigenesis mouse model that replicates the mtDNA copy number-breast cancer association in human populations can be used to understand the biological mechanisms underlying the increase in mtDNA copy number observed in the peripheral blood of breast cancer patients.

Citation Format: Helene Barcelo, Nicholas J. Brady, Kathryn L. Schwertfeger, Myron Gross, Bharat Thyagarajan. Neutrophil specific mitochondrial DNA copy number as a biomarker for breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2771. doi:10.1158/1538-7445.AM2015-2771