# Simulating cell-free chromatin using preclinical cancer models for liquid biopsy applications

## TL;DR

Researchers developed a method to simulate cell-free chromatin from cancer cells, enabling better study of cancer biomarkers in liquid biopsies.

## Contribution

A scalable preclinical framework to simulate tumor-derived cell-free chromatin for liquid biopsy research.

## Key findings

- Simulated cfChromatin reflects cell-type-specific gene expression and chromatin accessibility.
- Simulated cfChromatin shows stronger tumor-specific profiles than patient plasma due to less dilution.
- cfChIP-seq using simulated cfChromatin identified chromatin domains predictive of gene expression.

## Abstract

Cell-free DNA circulates in blood bound to nucleosomes, forming cell-free chromatin (cfChromatin) that retains epigenetic features, including nucleosome positioning and histone modifications. cfChromatin provides a rich source of cancer biomarkers; however, low abundance of tumor-derived cfChromatin and limited availability of clinical samples pose challenges for liquid biopsy research. To address this, we developed a framework to simulate cfChromatin nucleosomal distributions using nuclease-treated conditioned media from tissue cultures. Whole-genome sequencing confirmed that inferred nucleosome positioning reflected cell-type-specific gene expression and chromatin accessibility patterns, and comparisons with plasma cfChromatin from xenografted mice revealed concordant nucleosome profiles. Notably, simulated cfChromatin displayed stronger tumor-specific nucleosome profiles than patient plasma, where hematopoietic-derived cfChromatin dilutes signal. We further leveraged simulated cfChromatin to advance cell-free chromatin immunoprecipitation and sequencing methods, identifying repressive and bivalent chromatin domains predictive of transcriptional activity. Altogether, our results demonstrate the utility of simulated cfChromatin as a scalable preclinical tool for liquid biopsy research.

•Nuclease treatment of media simulates cfChromatin nucleosomal distributions•Simulated cfChromatin retains undiluted cancer-associated chromatin configurations•This platform advanced methods for cfChIP-seq targeting both H3K4me3 and H3K27me3•cfChIP-seq of both marks revealed bivalency and improved gene expression prediction

Nuclease treatment of media simulates cfChromatin nucleosomal distributions

Simulated cfChromatin retains undiluted cancer-associated chromatin configurations

This platform advanced methods for cfChIP-seq targeting both H3K4me3 and H3K27me3

cfChIP-seq of both marks revealed bivalency and improved gene expression prediction

Medical biotechnology; Genomics; Chromosome organization