Noninvasive enrichment of circulating tumor biomarkers in a mouse model of diffuse midline glioma using focused ultrasound

Background Diagnosing diffuse midline glioma (DMG) through invasive tissue biopsies is challenging due to the tumor's eloquent location at the pons. Liquid biopsies offer a promising non-invasive alternative; however, their limited detection sensitivity and lack of information on the source of biomarkers pose great challenges. This study aimed to evaluate the feasibility and safety of using focused ultrasound (FUS) with microbubbles to enrich circulating DMG tumor biomarkers in blood and cerebrospinal fluid (CSF) using a mouse model. Methods Murine DMG cells, transfected with enhanced green fluorescent protein (EGFP) and firefly luciferase (Fluc) genes, were orthotopically injected into the mouse brain. Magnetic resonance imaging was used to guide FUS targeting of the DMG tumor. Droplet digital PCR assays were developed to detect circulating tumor DNA (ctDNA) and RNA (ctRNA) of EGFP and Fluc in blood and CSF samples collected after FUS. Results FUS enhanced the plasma levels of EGFP ctRNA by 5.4-fold (p = 0.0112), compared with liquid biopsy. EGFP ctDNA was increase by 2.5-fold (p = 0.0253) and Fluc ctDNA was increased by 2.6-fold (p = 0.0253) with FUS in CSF. No brain tissue damage was observed associated with FUS sonication. Conclusions This study demonstrated the feasibility and safety of FUS in enriching tumor biomarkers in blood and CSF in a mouse model of DMG. The enrichment ratio on circulating biomarkers is dependent on the sources (plasma vs. CSF), analytes (ctDNA vs. ctRNA), and individual markers (EGFP vs. Fluc). These findings support the potential future application of FUS to advance the diagnosis of DMG through liquid biopsy.