Abstract 3535: Whole genome sequencing of single circulating tumor cells from localized high-risk prostate cancer patients: Laser microdissection and 3Dtelomere profile
Authors: Pozzo Aline Rangel 
Published: September 2020

Abstract
Advances in the development of precision medicine for prostate cancer patients rely on accurate identification of the genomic features underlying a patient's tumor. Genomic analysis of circulating tumor cells (CTCs) could provide a unique and accessible representation of tumor diversity, however for the use of CTCs as a less-invasive sampling of prostate cancer and as biomarkers for patient stratification and selection of targeted therapy, complex platforms are necessary to ensure an efficient enrichment (isolation), detection (identification-imaging) and characterization strategies (molecular profiles). In this study, we combined a filtration-based CTC isolation technology with prostate cancer cell-specific antibodies to identify the prostate cancer CTCs. After identification, we performed the 3D telomere profiling prior to laser microdissection for whole genome sequencing of singles CTCs from 11 localized high-risk prostate cancer patient samples (36 CTCs in total). We identified unique and common somatic single nucleotide variants (SSNVs) and copy number alterations (CNAs) that can be used to predict high-risk lethal prostate cancer and treatment response in patients with clinically localized high- risk prostate cancers. The distribution of telomeres intensities show a range between 0 to 190.000 (a.u) and telomeres parameters were similar as described previously for high risk patients by our group. We analyzed 36 CTCs from 11 different patient samples and compared with normal lymphocytes from the same patient using whole genome sequencing (WGS). We identified 184 common mutated genes in all CTCs and two mutated genes with the same base pair (bp) mutation (PMS2 and EIF2AK4). We also identified 503 consensus mutations found in all patient but not in all CTCs and 1728 unique mutations found in all or any CTCs of only one patient, showing the heterogeneity that arises in single cells. The list of genes affected are all involved in potential pathways for tumor development such as immune system, signal transduction, homeostasis, gene expression, chromatin organization, DNA repair, cell cycle, programmed cell death, cell-cell communication and others. MCPH1, also known as BRIT1, is a key regulatory gene of the DNA damage response pathway and was mutated in all CTCs from prostate patients. MCPH1 deficiency promotes genomic instability and increases cancer susceptibility. The PMS2 gene is a member of a set of genes known as the mismatch repair (MMR) genes which promotes also genomic Instability. Those mutations can be closely linked with the genomic instability we found assessing the telomere profiles. The CDH17 gene is a member of the cadherin superfamily and in contrast to classic cadherins, such as E- and N-cadherin, LI-cadherin possess biological functions distinct from classic cadherins and reduced expression of LI-cadherin is closely associated with tumor progression and lymph node metastasis of human colorectal carcinoma. These mutations were also found in all CTCs. All this information is needed for individualized therapy and predict drug resistance, phenotypic transition which is heterogeneous from cell to cell from patient to patient.
Citation Format: Aline Rangel Pozzo. Whole genome sequencing of single circulating tumor cells from localized high-risk prostate cancer patients: Laser microdissection and 3Dtelomere profile [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3535.