GENE-40. CIRCULATING TUMOR DNA ANALYSIS IN PATIENT-DERIVED XENOGRAFT MODELS OF GLIOBLASTOMA

Abstract

Extracellular tumor-derived DNA in body fluids (also known as circulating tumor DNA or ctDNA) is being widely studied for noninvasive tumor genotyping, tracking clonal evolution, monitoring treatment response and early detection of cancer. In patients with glioblastoma (GBM), ctDNA is more readily detectable in cerebrospinal fluid as compared to blood plasma. In literature, sensitivity for mutation detection in DNA from CSF is ~60% compared to ~10% in plasma DNA. However, CSF is difficult to sample and other body fluids need to be studied carefully. To develop new strategies for plasma ctDNA detection and increase tumor DNA shedding into plasma in patients with GBM, we sought to utilize body fluid samples form patient derived xenograft (PDX) models. In this context, any human DNA detectable in mouse plasma is derived from the tumor xenograft. Hence, we developed a human-specific multiplexed droplet digital PCR assay to detect and accurately quantify plasma ctDNA in PDX models derived from patients with GBM. This assay is composed of 8 paired primer/probe sets, fluorescently labeled, with careful design accounting for unique diploid amplification, variable regions, cross amplification between species, and most common genomic aberrations in GBM. We will share results demonstrating the analytical validity of the assay as well as utility in testing approaches for increasing ctDNA yield and shedding from GBM tumors.