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  • Extrachromosomal DNA (ecDNA)-Associated Transcription–Replication Conflicts in Cancer: Mechanisms, Synthetic Lethal Vulnerabilities, and Emerging Personalized Therapeutic Strategies

  • Fatemeh Pirani,1 Dr. Maryam Eslami,2,* Kimia Kalhori,3
    1. Department of Genetics, TeMS.C., Islamic Azad University, Tehran, Iran
    2. Department of Genetics, TeMS.C., Islamic Azad University, Tehran, Iran
    3. Department of Genetics, TeMS.C., Islamic Azad University, Tehran, Iran


  • Introduction: Unlike chromosomal amplifications, ecDNA molecules cluster within the nucleus, exhibit highly accessible chromatin, and drive extreme transcriptional output. This hypertranscription generates persistent collisions between RNA polymerase II and DNA replication forks — transcription–replication conflicts (TRCs) — that promote R-loop accumulation, single-stranded DNA exposure, fork stalling, and replication stress, ultimately increasing genomic instability. ecDNA-positive tumors rely heavily on the ATR–CHK1 checkpoint to tolerate this chronic stress, creating a tumor-selective vulnerability. This review summarizes mechanistic links between ecDNA biology, TRCs, and ATR–CHK1 dependency, and outlines synthetic lethal and combinatorial therapeutic strategies. Integrating ecDNA profiling into molecular diagnostics may enable biomarker-guided patient stratification and personalized therapies for ecDNA-driven cancers.
  • Methods: We reviewed recent studies employing genomic assays (KAS-seq, scCircle-seq, scATAC-seq), imaging (DNA-FISH, Comet-FISH, live-cell ecDNA imaging), genetic perturbations (siRNA, CRISPR), pharmacologic screens (transcription, CHK1/ATR, FGFR, MDM2 inhibitors), and computational models (individual-based simulations, Approximate Bayesian Computation). Public clinical datasets (TCGA) were analyzed to assess ecDNA prevalence and co-alterations. Results were organized around stages from hypertranscription to therapeutic vulnerability.
  • Results: ecDNA-bearing cancer cells display ≈4-fold higher transcriptional output than genetically matched ecDNA-negative cells, including coding, antisense, and intergenic transcripts. KAS-seq shows preferential ssDNA enrichment over actively transcribed ecDNA regions, and increased R-loop accumulation localizes to ecDNA loci. DNA fiber assays reveal significantly slower replication fork progression on ecDNA, with elevated pRPA2 phosphorylation indicating chronic replication stress that scales with ecDNA copy number. Transcription inhibition (triptolide) reduces replication-stress signatures, linking hypertranscription to fork instability. ecDNA-positive cells exhibit markedly increased DNA damage (γH2AX, 53BP1 foci; Comet-FISH–localized breaks), which activates ATR–CHK1 signaling (elevated pCHK1-S345). CRISPR-mediated CHK1 loss selectively impairs ecDNA-positive proliferation. CHK1 inhibitors (CHIR-124, GDC-0575, SRA737, and the oral agent BBI-2779, IC50 ≈ 0.3 nM) induce replication catastrophe and apoptosis preferentially in ecDNA-positive cells, with roughly tenfold greater sensitivity versus ecDNA-negative counterparts. Combining BBI-2779 with the FGFR inhibitor infigratinib yields superior tumor regression compared to monotherapy, supporting combinatorial strategies guided by ecDNA-associated features. Complementary studies identify CDK12 as a synthetic lethal dependency in MYC-driven contexts; CDK12 loss exacerbates TRCs and double-strand breaks at early-replicating, co-directionally transcribed regions. Multiple ecDNA species can co-segregate non-randomly during mitosis through transcription-dependent mechanisms, enabling co-selection of cooperating oncogenic ecDNAs, including enhancer-only ecDNAs that amplify neighboring oncogenes; therapeutic targeting can induce coordinated co-depletion of such cooperating species.
  • Conclusion: ecDNA amplification establishes a hypertranscriptional chromatin state that chronically generates transcription–replication conflicts, replication stress, and DNA damage, rendering ecDNA-positive cancer cells uniquely dependent on ATR–CHK1 checkpoint signaling for survival. This dependency constitutes a clinically actionable synthetic lethal vulnerability, distinct from conventional oncogene-directed therapy, that can be selectively exploited using CHK1 inhibitors such as BBI-2779, particularly in combination with oncogene-pathway inhibitors. Parallel insights into CDK12-mediated transcriptional suppression and the evolutionary dynamics of multi-species ecDNA co-inheritance further refine this therapeutic landscape, supporting transcription–replication conflict as a unifying, druggable hallmark of ecDNA-driven malignancy.
  • Keywords: Extrachromosomal DNA; Transcription Replication Conflict; Synthetic Lethality; Personalized Medicine

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