In the intricate landscape of cancer biology, the fragmentation and displacement of DNA within malignant cells pose profound challenges and opportunities for therapeutic innovation. Recent research conducted at the Sanford Burnham Prebys Medical Discovery Institute, alongside collaborators from multiple prestigious institutions, sheds new light on the behavior of extracellular circular DNA fragments, known as extrachromosomal DNA (ecDNA), and their preservation within patient-derived xenograft (PDX) models. These PDX models, which involve the transplantation of human tumor cells into immunodeficient mice, are widely regarded as crucial preclinical platforms for cancer research. This study rigorously validates their use specifically for tumors harboring ecDNA, offering a pivotal leap in understanding how these circular DNA elements influence tumor progression and treatment resistance in pediatric cancers.
ecDNA elements have been recognized for over half a century, first described in the mid-1960s through cytogenetic analyses that revealed chromosomal fragments forming circular DNA structures independent of the main chromosomal genome. The clinical significance of ecDNA came into sharper focus in the late 1970s when mouse models demonstrated their role in mediating resistance to chemotherapeutic agents. Since then, mounting evidence highlights that ecDNA are disproportionately abundant in aggressive cancers, where they frequently amplify oncogenes—genes that can transform a normal cell into a tumor cell when overexpressed or mutated. The spatial dislocation from chromosomes endows ecDNA with unique regulatory freedoms, enabling dynamic gene expression that fuels cancer cell adaptability and malignancy.
Dr. Lukas Chavez, a leading scientist specializing in the cancer genome and epigenetics at Sanford Burnham Prebys, underscores the clinical gravity of ecDNA presence in tumors. “The presence of these extrachromosomal DNA loops correlates strongly with worsened patient outcomes, underscoring their potential as both biomarkers and therapeutic targets,” Chavez explains. However, a pressing gap persisted in the field regarding the fidelity of PDX models to faithfully replicate the ecDNA landscape observed in original human tumors. Addressing this gap is critical because the utility of PDX models hinges on their ability to mirror human tumor biology as closely as possible.
To investigate this, the research team undertook a comprehensive analysis of nearly 300 pediatric tumor samples representing over 30 cancer types alongside their corresponding PDX models. Using high-resolution genomic sequencing techniques, they meticulously cataloged ecDNA elements, focusing on copy number variations of oncogenes carried extrachromosomally. The findings were striking—ecDNA were detected in approximately one-third of the tumor samples, reflecting a significant burden in pediatric oncology. Importantly, the oncogene amplification profiles on ecDNA matched those documented in large-scale cancer genomics datasets, reaffirming the clinical relevance of their observations.
A particularly compelling aspect of the study involved comparative genome sequencing of paired human tumors and their PDX counterparts. In over 80% of pairs, ecDNA presence was directly concordant, and the ecDNA sequences themselves were substantially preserved. This genomic fidelity implies that PDX models not only retain the structural features of ecDNA but also maintain the oncogenic potential encoded therein. These data provide robust evidence that PDX models are valid surrogates for studying ecDNA-driven biology in pediatric brain and other cancers.
Beyond bulk genomic analyses, the team harnessed single-cell sequencing technologies to dissect ecDNA distribution at the cellular level within tumors and PDX models. In one tumor-PDX pair, an overwhelming majority of cells contained ecDNA, suggesting a dominant clone driving tumorigenesis. Remarkably, another pair exhibited ecDNA only in a small fraction of tumor cells, yet the derived PDX model showed ecDNA presence in nearly all cells. This finding implies that ecDNA-positive cells possess a selective growth advantage during PDX development, potentially mirroring clonal expansion patterns in vivo.
These observations offer critical insights into tumor heterogeneity and clonal evolution, highlighting ecDNA as a molecular driver that shapes tumor architecture and treatment resistance. Given that ecDNA can dynamically modulate oncogene dosage and gene expression, their selective proliferation in PDX models reinforces the validity of these systems for therapeutic testing. Moreover, the research supports the notion that targeting ecDNA mechanisms, such as their replication or segregation during cell division, could open new avenues for combating aggressive, treatment-resistant cancers.
Looking ahead, the research consortium plans to employ PDX models to longitudinally track ecDNA evolution in response to conventional therapies, including chemotherapy and radiation. By elucidating how ecDNA facilitates cellular adaptation and survival under therapeutic pressure, scientists aim to identify vulnerabilities that can be exploited for more effective interventions. Such efforts could pave the way for precision medicine strategies tailored to the unique ecDNA landscape of individual tumors.
“Our primary goal is to deepen our understanding of ecDNA-mediated treatment resistance and uncover novel therapeutic targets that can improve outcomes for children battling these devastating cancers,” says Dr. Chavez. The study’s insights into the molecular fidelity of PDX models mark a crucial step toward this goal, providing researchers with robust tools to interrogate the complexities of cancer genome plasticity.
This research was made possible through the collaborative efforts of scientists from Sanford Burnham Prebys, Nagoya City University, the University of California San Diego, Rady Children’s Hospital, and Columbia University Irving Medical Center. Supported by prominent funding bodies, including the National Institutes of Health, National Cancer Institute, National Science Foundation, and several foundations dedicated to cancer research, the study epitomizes the power of interdisciplinary collaboration in advancing pediatric oncology.
In sum, this landmark study not only validates the use of PDX models for studying extrachromosomal DNA in childhood cancers but also heralds a new era of targeted therapeutic exploration. As the field evolves, leveraging such models to decode the role of ecDNA in treatment resistance and tumor evolution promises to transform pediatric cancer management, offering hope for more durable remissions and cures.
Subject of Research: Animals
Article Title: Preservation and clonal behavior of extrachromosomal DNA in patient-derived xenograft models of childhood cancers
News Publication Date: 28-May-2026
Web References:
- https://doi.org/10.1186/s13073-026-01676-0
- https://link.springer.com/article/10.1186/s13073-026-01676-0
Image Credits: Sanford Burnham Prebys
Keywords: Cancer, Brain cancer, Oncogenes, Cancer research, Cancer genomics, Genomics, Cancer genome sequencing, Cancer proliferation genes, Tumor suppressors, Single cell sequencing
