Single Cell RNA Profiling of Circulating Tumor Cells in Patients With Prostate Cancer

148 Background: Molecular characterization of metastatic castration resistant prostate cancer (mCRPC) is limited by tumor tissue availability. The analysis of circulating tumor cells (CTC) offers an attractive noninvasive surrogate option to analyze molecular alterations. We report whole exome sequencing (WES) of CTCs at the single cell level in mCRPC patients. Methods: Blood samples were drawn from 11 enzalutamide or abiraterone pre-treated mCRPC patients enrolled in the clinical program MOSCATO (NCT02613962). CTC enrichment, immunofluorescent detection and single cell isolation were performed using three methods (ISET filtration, CellSearch and the VyCap puncher system and RosetteSep enrichment) to obtain pools of 1-10 CTCs with distinct epithelial or mesenchymal phenotypes. After Whole Genome Amplification (WGA), WES was performed on the Illumina HiSeq 2000 platform. GATK Haplotype Caller enabled identification of germline polymorphisms from each patient in normal DNA, metastatic sample and CTCs in order to consider WGA induced bias. The detection of sSNV in tumor biopsies and CTCs was assessed with Mutect and IndelGenotyper respectively. Results: 189 WGA of CTC pools were performed. 34 pools of phenotypically different CTCs from 7 patients were selected and sequenced. Mean coverage of 51% was obtained at a sequencing depth of 10X. Allelic drop out was lower for CTC pools containing 5-10 cells. 17/34 (50%) CTC samples had shared sSNV with the paired tumor sample (range 0.35%-68%) Epithelial CTCs had more shared sSNV with metastatic biopsies than CTCs of other phenotypes but shared sSNV were also detected in large non epithelial CTC pointing out a high level of genetic heterogeneity between CTC. Overall, 89 deleterious protein-coding mutations were found only in pools of CTC, including mutations affecting oncogenic drivers such as MAPK1, HSP90AB1 or KDM5B. Conclusions: We present single cell WES of CTCs harboring distinct phenotypes. The detection of shared sSNV between CTC pools and corresponding biopsy could validate the use of CTCs as a liquid biopsy. The finding of sSNV specific to CTCs could offer additional data on tumor heterogeneity.

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Prevalence and tissue concordance of BRCA2 copy number loss evaluated by single-cell, shallow whole genome sequencing of circulating tumor cells (CTCs) in castration-resistant prostate cancer (CRPC).

Journal of Clinical Oncology ◽

10.1200/jco.2020.38.15_suppl.5531 ◽

2020 ◽

Vol 38 (15_suppl) ◽

pp. 5531-5531

Author(s):

Ethan Barnett ◽

Joseph Schonhoft ◽

Nikolaus D. Schultz ◽

Jerry Lee ◽

Samir Zaidi ◽

...

Keyword(s):

Prostate Cancer ◽

Whole Genome Sequencing ◽

Single Cell ◽

Tumor Cells ◽

Circulating Tumor Cells ◽

Genome Sequencing ◽

Copy Number ◽

Cellular Heterogeneity ◽

Cancer Tissue ◽

Whole Genome

5531 Background: Genomic studies have shown that up to 25% of prostate cancer tissue specimens harbor alterations in DNA Damage Repair (DDR) genes, which may sensitize the tumor to poly ADP-ribose polymerase inhibitors (PARPi). Trials evaluating PARPi in patients with DDR deficiencies have shown varied response rates and differences regarding which genomic alterations predict for sensitivity to these agents, with the majority of objective responses seen in BRCA2-altered tumors. These results highlight the need to develop biomarker assays which can predict benefit from PARPi therapy. Tissue and cell-free DNA (cfDNA) have been the most utilized sources of tumor material for analysis in this setting, but success rates of obtaining sufficient tumor for analysis from bone are low and detecting tumor-derived copy number variants (CNVs) in cfDNA is challenging. Circulating tumor cells (CTCs) represent an alternate source of genetic information, for which assays are available to isolate and sequence individual cells in a manner that eliminates background noise from stroma and healthy cells, while capturing inter-cellular heterogeneity. Methods: Blood samples, collected from 138 progressing metastatic CRPC patients within 30 days of a pre-treatment biopsy intended for sequencing using MSK-IMPACT, were sent to EPIC Sciences for CTC analysis. Detected CTCs underwent single cell, low pass whole genome sequencing. Prevalence and concordance of BRCA2 copy-loss, regardless of whether single copy or homozygous, was compared in matched tissue and CTC samples. Results: BRCA2 copy-loss was identified in 21% (23/108) and 50% (58/115) of successfully sequenced tissue and CTC samples, respectively. In the 58 patients with CTC-detected BRCA2 loss, BRCA2 loss was detected in 36% (220/565) of the sequenced CTCs, representing a median of 46% (range 4-100%) of CTCs found in each individual sample. When both sequencing assays were successful, BRCA2 loss was detected in CTCs in 84% (16/19) of the tissue-positive cases, whereas tissue sequencing detected BRCA2 loss in 35% (16/46) of CTC-positive cases. Conclusions: Data from this study supports the notion that single-cell CTC sequencing can detect BRCA2 copy-loss at a high frequency, including cases that were negative in tissue, while also characterizing inter-cellular heterogeneity. Further studies will investigate whether CTC BRCA2 copy-loss can predict the likelihood of response to PARPi.

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