Abstract 2198: Allelic phasing of genomic alterations through linked read whole genome sequencing in human prostate cancer cell lines
Authors: Pham Minh-Tam , Gupta Harshath , Gupta Anuj , Vaghasia Ajay , Skaist Alyza M. , Garrison McKinzie A. , Chikamarne Roshan , Wheelan Sarah J. , Nelson William G. , Yegnasubramanian Srinivasan 
Published: July 2021

Abstract
Prostate cancer research has relied on a limited number of prostate cancer cell lines despite decades of effort in establishing them from human prostate cancers. These cell lines thus represent precious resources for in vitro and in vivo preclinical studies of prostate cancer and have fueled many advances in the field. While there has been tremendous effort in characterizing their molecular profiles and genomic features, comprehensive whole genome sequencing with allelic phasing of genomic alterations has not been undertaken to date. Here, we utilized powerful whole genome linked-read sequencing of high molecular weight DNA (&gt;60Kbp) from eight common prostate cancer cell lines as well as four castrate resistant (CR) subclones derived from three of those cell lines. Long range information enabled assembly of mutations (single nucleotide variants-SNVs and small indels) and structural variants (SVs) across the genome into large phased blocks. This allowed accounting of multiple mutations within a given gene to assess whether they were present on a single allele, or on opposite alleles, to assess the “allelic status” of phased mutations. Using this phased mutational analysis, we found that in cell lines with microsatellite instability (MSI; LNCaP, LAPC4, DU145, CWR22Rv1), 10-20% of a priori defined driver genes are inactivated by at least two heterozygous mutations on opposite alleles. Overall, MSI cell lines had higher levels of mutations and fewer SVs than those that were microsatellite stable (MSS; PC3, VCaP). The phased SV analysis allowed identification of complex rearrangement chains consistent with chromothripsis (PC3, DU145) and chromoplexy (VCAP, LnCAP-C42b), including reconstruction of the complex chained TMPRSS2-ERG rearrangement in VCaP. Additionally, comparison of parental and CR subclones revealed previously known as well as several novel genomic alterations that were associated with the CR subclones, including chromosome 8 amplification (in LNCaP-Abl and LAPC4-CR), further androgen receptor amplification amongst a host of increased complex SVs (in VCAP-CR), SWI/SNF mutations and increased complex SVs (in LNCAP-C42b), CDK12 biallelic loss and numerous tandem duplications (in LAPC4-CR). This study therefore comprehensively characterizes allelically phased genomic alterations in the commonly used prostate cancer cell lines and provides a useful resource for future cancer research.
Citation Format: Minh-Tam Pham, Harshath Gupta, Anuj Gupta, Ajay Vaghasia, Alyza M. Skaist, McKinzie A. Garrison, Roshan Chikamarne, Sarah J. Wheelan, William G. Nelson, Srinivasan Yegnasubramanian. Allelic phasing of genomic alterations through linked read whole genome sequencing in human prostate cancer cell lines [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 2198.