Abstract 7497: Nanopore sequencing of single-cell derived sublines provides insights into melanoma heterogeneity and evolution

Abstract Melanoma is the most serious form of skin cancer, developed by the malignant evolution of melanocytes. Malignant melanoma incidence is increasing faster than most other cancers. While stage zero melanoma is highly treatable, survivability dramatically decreases in its advanced stages. Melanoma has shown to be one of the most heterogeneous cancers from RNA and exome analyses by The Cancer Genome Atlas and other groups. A better understanding of the key genomic and epigenomic events that characterize the diverse subclonal populations in melanoma may reveal key insights into what drives its progression and therapeutic resistance. In this study, we leveraged Nanopore long-read sequencing to study the evolution of the mouse B2905 melanoma cell line. Twenty-four distinct clonal sublines were derived in vitro from single cells of the cell line, and the genetically homogeneous population from each subline was sequenced using PromethION R10 flow cells. Enabled by long reads to perform haplotype phasing and accurate structural variation detection, our goal is to integrate small and structural variants to better our understanding of melanoma evolution, and build upon prior analyses of short-read sequenced sublines. We employed multiple SNV calling approaches, including DeepVariant and Clair, in order to provide highly accurate variants for phylogeny reconstruction using Trisicell. We performed structural variant calling with our cancer somatic structural variant (SV) caller Severus as well as copy-number alteration (CNA) analysis with our method Wakhan. Lastly, we placed SNVs, SVs, and CNAs on our reconstructed phylogeny to examine the progression of different types of variants during subline evolution. We identified approximately 560k unique SNVs and around 2, 400 unique SVs. The majority of SNVs (19%) are either clonal or private (73%); however, a meaningful fraction of subclonal variants were available for phylogenetic tree reconstruction. SVs are distributed across the phylogenetic tree branches similarly to SNVs. We identified loss of heterozygosity (LOH) events throughout the subline evolution as well as subclonal CNAs resulting from chromosomal translocations. We find clonal and subclonal evidence of densely clustered SNVs and SV, resembling kataegis; however, our analysis of mutational signatures did not reveal APOBEC-mediated mutations. By analyzing mutational signatures within individual branches of the phylogenetic tree, we observed relative timing of different mutational processes, such as early clonal signatures of UV damage. By incorporating structural variations, copy number changes, and small variant data in the phylogenetic reconstruction, our analysis offers a better characterization of the genetic landscape of subclonal evolution in melanoma. Citation Format: Anton Goretsky, Yuelin Liu, Ayse Keskus, Tanveer Ahmad, Salem Malikic, Glenn Merlino, Chi-Ping Day, Erin Molloy, S. Cenk Sahinalp, Mikhail Kolmogorov. Nanopore sequencing of single-cell derived sublines provides insights into melanoma heterogeneity and evolution [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7497.