Duaa H. Al-Rawi

High-level copy-number (CN) amplification (HLAMP) is a major mechanism of oncogene activation in human cancer. Despite progress in therapeutically targeting HLAMPs, the processes underlying HLAMP evolution are incompletely understood, leaving critical knowledge gaps in their etiology and mechanisms of therapeutic response. To address this, we analyzed using novel computational approaches, the evolutionary trajectories of HLAMP in single-cell whole-genome sequencing of 86,239 cancer cells from 94 patients and 8 experimental systems. We found that two common etiologies of oncogene amplification - intrachromosomal amplification (ICamp) and extrachromosomal circular DNA (ecDNA) - lead to distinct CN distributions across cells in amplitude, variance and clone specificity. Notably, ICamp events exhibited widespread subclonal specificity, indicating their dynamic evolution through numeric or structural modulation associated with clonal expansions. In contrast, ecDNAs exhibited higher cell-to-cell CN variation linked to structural rearrangements, whereby complex ecDNA architectures were resolved at single-nucleotide resolution in individual cell genomes. Through joint analysis of ecDNA structure and their cellular abundance, we observed both divergent and convergent modes of ecDNA evolution shaped by DNA damage, selection, and chromosomal re-integration. Finally, modeling single-cell distributions of ecDNAs substantially improved bulk genome-graph based predictions, revealing that ecDNA prevalence is tissue-type specific, rather than broadly shared across cancer types, with implications for ecDNA-directed therapy.

Emergence of drug resistance is the main cause of therapeutic failure in patients with high-grade serous ovarian cancer (HGSOC)¹. To study drug resistance in patients, we developed CloneSeq-SV, which combines single-cell whole-genome sequencing² with targeted deep sequencing of clone-specific genomic structural variants in time-series cell-free DNA. CloneSeq-SV exploits tumour clone-specific structural variants as highly sensitive endogenous cell-free DNA markers, enabling the relative abundance measurements and evolutionary analysis of co-existing clonal populations over the therapeutic time course. Here, using this approach, we studied 18 patients with HGSOC over a multi-year period from diagnosis to recurrence and showed that drug resistance typically arose from selective expansion of a single or small subset of clones present at diagnosis. Drug-resistant clones frequently showed interpretable and distinctive genomic features, including chromothripsis, whole-genome doubling, and high-level amplifications of oncogenes such as CCNE1, RAB25, MYC and NOTCH3. Phenotypic analysis of matched single-cell RNA sequencing data³ indicated pre-existing and clone-specific transcriptional states such as upregulation of epithelial-to-mesenchymal transition and VEGF pathways, linked to drug resistance. In one notable case, clone-specific ERBB2 amplification affected the efficacy of a secondary targeted therapy with a positive patient outcome. Together, our findings indicate that drug-resistant states in HGSOC pre-exist at diagnosis, leading to positive selection and reduced clonal complexity at relapse. We suggest these findings motivate investigation of evolution-informed adaptive treatment regimens to ablate drug resistance in future HGSOC studies.

Whole-genome doubling (WGD) is a common feature of human cancers and is linked to tumour progression, drug resistance, and metastasis^1,2,3,4,5,6. Here we examine the impact of WGD on somatic evolution and immune evasion at single-cell resolution in patient tumours. Using single-cell whole-genome sequencing, we analysed 70 high-grade serous ovarian cancer samples from 41 patients (30,260 tumour genomes) and observed near-ubiquitous evidence that WGD is an ongoing mutational process. WGD was associated with increased cell–cell diversity and higher rates of chromosomal missegregation and consequent micronucleation. We developed a mutation-based WGD timing method called doubleTime to delineate specific modes by which WGD can drive tumour evolution, including early fixation followed by considerable diversification, multiple parallel WGD events on a pre-existing background of copy-number diversity, and evolutionarily late WGD in small clones and individual cells. Furthermore, using matched single-cell RNA sequencing and high-resolution immunofluorescence microscopy, we found that inflammatory signalling and cGAS-STING pathway activation result from ongoing chromosomal instability, but this is restricted to predominantly diploid tumours (WGD-low). By contrast, predominantly WGD tumours (WGD-high), despite increased missegregation, exhibited cell-cycle dysregulation, STING1 repression, and immunosuppressive phenotypic states. Together, these findings establish WGD as an ongoing mutational process that promotes evolvability and dysregulated immunity in high-grade serous ovarian cancer.

Supplementary tables and figures

Supplementary tables and figures

Purpose:Targeted therapies have improved outcomes for patients with metastatic colorectal cancer, but their impact is limited by rapid emergence of resistance. We hypothesized that an understanding of the underlying genetic mechanisms and intrinsic tumor features that mediate resistance to therapy will guide new therapeutic strategies and ultimately allow the prevention of resistance.Experimental Design:We assembled a series of 52 patients with paired pretreatment and progression samples who received therapy targeting EGFR (n = 17), BRAF V600E (n = 17), KRAS G12C (n = 15), or amplified HER2 (n = 3) to identify molecular and clinical factors associated with time on treatment (TOT).Results:All patients stopped treatment for progression and TOT did not vary by oncogenic driver (P = 0.5). Baseline disease burden (≥3 vs. <3 sites, P = 0.02), the presence of hepatic metastases (P = 0.02), and gene amplification on baseline tissue (P = 0.03) were each associated with shorter TOT. We found evidence of chromosomal instability (CIN) at progression in patients with baseline MAPK pathway amplifications and those with acquired gene amplifications. At resistance, copy-number changes (P = 0.008) and high number (≥5) of acquired alterations (P = 0.04) were associated with shorter TOT. Patients with hepatic metastases demonstrated both higher number of emergent alterations at resistance and enrichment of mutations involving receptor tyrosine kinases.Conclusions:Our genomic analysis suggests that high baseline CIN or effective induction of enhanced mutagenesis on targeted therapy underlies rapid progression. Longer response appears to result from a progressive acquisition of genomic or chromosomal instability in the underlying cancer or from the chance event of a new resistance alteration.

Purpose:Targeted therapies have improved outcomes for patients with metastatic colorectal cancer, but their impact is limited by rapid emergence of resistance. We hypothesized that an understanding of the underlying genetic mechanisms and intrinsic tumor features that mediate resistance to therapy will guide new therapeutic strategies and ultimately allow the prevention of resistance.Experimental Design:We assembled a series of 52 patients with paired pretreatment and progression samples who received therapy targeting EGFR (n = 17), BRAF V600E (n = 17), KRAS G12C (n = 15), or amplified HER2 (n = 3) to identify molecular and clinical factors associated with time on treatment (TOT).Results:All patients stopped treatment for progression and TOT did not vary by oncogenic driver (P = 0.5). Baseline disease burden (≥3 vs. <3 sites, P = 0.02), the presence of hepatic metastases (P = 0.02), and gene amplification on baseline tissue (P = 0.03) were each associated with shorter TOT. We found evidence of chromosomal instability (CIN) at progression in patients with baseline MAPK pathway amplifications and those with acquired gene amplifications. At resistance, copy-number changes (P = 0.008) and high number (≥5) of acquired alterations (P = 0.04) were associated with shorter TOT. Patients with hepatic metastases demonstrated both higher number of emergent alterations at resistance and enrichment of mutations involving receptor tyrosine kinases.Conclusions:Our genomic analysis suggests that high baseline CIN or effective induction of enhanced mutagenesis on targeted therapy underlies rapid progression. Longer response appears to result from a progressive acquisition of genomic or chromosomal instability in the underlying cancer or from the chance event of a new resistance alteration.

Purpose: Targeted therapies have improved outcomes for patients with metastatic colorectal cancer, but their impact is limited by rapid emergence of resistance. We hypothesized that an understanding of the underlying genetic mechanisms and intrinsic tumor features that mediate resistance to therapy will guide new therapeutic strategies and ultimately allow the prevention of resistance. Experimental Design: We assembled a series of 52 patients with paired pretreatment and progression samples who received therapy targeting EGFR (n = 17), BRAF V600E (n = 17), KRAS G12C (n = 15), or amplified HER2 (n = 3) to identify molecular and clinical factors associated with time on treatment (TOT). Results: All patients stopped treatment for progression and TOT did not vary by oncogenic driver (P = 0.5). Baseline disease burden (≥3 vs. <3 sites, P = 0.02), the presence of hepatic metastases (P = 0.02), and gene amplification on baseline tissue (P = 0.03) were each associated with shorter TOT. We found evidence of chromosomal instability (CIN) at progression in patients with baseline MAPK pathway amplifications and those with acquired gene amplifications. At resistance, copy-number changes (P = 0.008) and high number (≥5) of acquired alterations (P = 0.04) were associated with shorter TOT. Patients with hepatic metastases demonstrated both higher number of emergent alterations at resistance and enrichment of mutations involving receptor tyrosine kinases. Conclusions: Our genomic analysis suggests that high baseline CIN or effective induction of enhanced mutagenesis on targeted therapy underlies rapid progression. Longer response appears to result from a progressive acquisition of genomic or chromosomal instability in the underlying cancer or from the chance event of a new resistance alteration.

Chromosomal instability (CIN) and epigenetic alterations are characteristics of advanced and metastatic cancers^1–4, but whether they are mechanistically linked is unknown. Here we show that missegregation of mitotic chromosomes, their sequestration in micronuclei^5,6and subsequent rupture of the micronuclear envelope⁷profoundly disrupt normal histone post-translational modifications (PTMs), a phenomenon conserved across humans and mice, as well as in cancer and non-transformed cells. Some of the changes in histone PTMs occur because of the rupture of the micronuclear envelope, whereas others are inherited from mitotic abnormalities before the micronucleus is formed. Using orthogonal approaches, we demonstrate that micronuclei exhibit extensive differences in chromatin accessibility, with a strong positional bias between promoters and distal or intergenic regions, in line with observed redistributions of histone PTMs. Inducing CIN causes widespread epigenetic dysregulation, and chromosomes that transit in micronuclei experience heritable abnormalities in their accessibility long after they have been reincorporated into the primary nucleus. Thus, as well as altering genomic copy number, CIN promotes epigenetic reprogramming and heterogeneity in cancer.

Summary: Immune checkpoint blockade has been ineffective in ovarian cancer, and there is an ongoing effort to identify biomarkers of therapeutic benefit. Despite promising preclinical data, a substudy of the IMagyn050 trial found that patients with homologous recombination deficient tumors did not have improved progression-free survival with the addition of the PD-L1 inhibitor atezolizumab. See related article by Landen et al., p. 1698