Abstract 2404: Increased mitochondrial DNA copy number occurs during prostate cancer progression and in cancer precursor lesions across multiple organs
Authors: Chen Jiayu , Zheng Qizhi , Hicks Jessica L. , Trabzonlu Levent , Antonarakis Emmanuel S. , Markowski Mark C. , Denmeade Samuel R. , Ozbek Busra , Gupta Anuj , Larman Tatianna C. , Hruban Ralph H. , Wheelan Sarah , Yegnasubramanian Srinivasan , De Marzo Angelo M. 
Published: July 2021

Abstract
Accurately measuring mitochondrial DNA copy number (mtDNAcn) is important for improving our understanding of cancer biology. Prior studies have revealed differences in mtDNAcn between matched bulk tumor-normal pairs from a range of different organs. However, there is little consistency across tumor types; compared to their normal tissue counterparts, some cancers appear to have increased mtDNAcn, others appear to have decreased mtDNAcn, and in others, such as prostate cancer, studies have shown contradictory results. The lack of consistency of mtDNAcn changes in tumor-normal pairs may reflect a failure to address the marked heterogeneity in mtDNAcn across different cell types within normal tissues. In addition, tumor cell heterogeneity in mtDNAcn has also not been taken into account in most prior studies, which can further confound tumor-normal comparisons. Finally, little is known about mtDNAcn alterations in cancer precursor lesions. To address these technical limitations, we combined a recently introduced quantitative in situ hybridization method with immunohistochemistry in a multiplex assay. This enabled us to measure mtDNAcn using digital image analysis in specific cell populations of interest on formalin fixed paraffin embedded (FFPE) and frozen tissue samples. We determined that normal prostate basal cells have approximately 3-fold higher mtDNA levels than normal prostate luminal cells. Compared to the adjacent normal prostate glands, we found markedly increased levels of mtDNA in high-grade prostatic intraepithelial neoplasia (HGPIN), the presumptive precursor lesions to most prostate cancers. We also found increased levels as well as heterogeneity of mtDNAcn in invasive prostate cancer lesions, and more consistently elevated levels in castration-resistant metastatic prostate cancer (CRPC). Increased mtDNA copy number was also identified by whole genome sequencing and quantitative PCR from laser capture micro-dissected human prostate tumor-normal pairs. We also observed higher mtDNAcn in two other precancer lesion types, pancreatic intraepithelial neoplasia and colorectal adenomas. Our approach represents a technological advance as it facilitates mtDNAcn measurements in a manner that preserves morphology, allowing for the evaluation of specific cell populations of interest. These findings raise the hypothesis that increased mitochondrial mass and function may drive the development of precancerous lesions in the prostate, pancreas and colon, as well as invasive prostate cancer development and progression.
Citation Format: Jiayu Chen, Qizhi Zheng, Jessica L. Hicks, Levent Trabzonlu, Emmanuel S. Antonarakis, Mark C. Markowski, Samuel R. Denmeade, Busra Ozbek, Anuj Gupta, Tatianna C. Larman, Ralph H. Hruban, Sarah Wheelan, Srinivasan Yegnasubramanian, Angelo M. De Marzo. Increased mitochondrial DNA copy number occurs during prostate cancer progression and in cancer precursor lesions across multiple organs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2404.