Abstract 4916: Development of a NGS-based method for EGFRvIII detection: sequence analysis of the junction

Abstract

Abstract Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary tumor in humans. One of the most common mutations in GBMs is an interstitial deletion in the epidermal growth factor receptor (EGFR), EGFRvIII, which occurs at a frequency of ∼30%. EGFR is a transmembrane tyrosine kinase receptor and the EGFRvIII mutant is characterized by a deletion of 267 amino acids in the extracellular domain leading to ligand independent constitutive activation. The deletion of exons 2-7 leads to an in-frame deletion in EGFR with a novel glycine residue at the junction. The amino acid at the junction of exons 1 and 2 is a valine, making the novel transcript an attractive target for immunotherapy. A custom next generation sequencing (NGS) based assay and bioinformatic pipeline have been developed in our laboratory to detect EGFRvIII from RNA extracted from formalin fixed paraffin embedded tissue. The targets include the exon 1-2 boundary (wild type), the exon 1-8 boundary (EGFRvIII), amplification of various sized RNA fragments to determine RNA degradation and bioavailability, and expression levels of three housekeeping genes. Following cDNA synthesis multiplex PCR of all targets are captured simultaneously for the sequencing library with NGS performed on the Illumina MiSeq. The output from the bioinformatics pipeline includes the sequence and number of reads from the wild-type and mutant, ratio of EGFRvIII reads with respect to total EGFR sequenced, expression of three housekeeping genes and relative amount of bioavailable EGFR RNA. This assay was validated through comparison of NGS sequence results with an established qRT-PCR to detect normal and mutant EGFR. Negative controls from normal brain (temporal lobe excisions from epilepsy patients) and adipose tissue (a tissue with high expression of EGFR) were used to determine whether low-level exon 1-8 fusions from mis-splicing were detectable in normal tissue (Figure 1). Twenty five GBM specimens were sequenced, with 8/25 positive for EGFRvIII (Figure 2), and confirmed by RT-PCR. In addition to detection of the EGFRvIII mutant, relative expression of EGFR is detected in this assay, and when taken together with EGFR amplifications detected by routine NGS panels, we can determine whether the EGFRvIII is present on the amplified or unamplified allele and whether additional mutations are detectable. Detection of EGFRvIII utilizing NGS improves the precision of mutant detection to better serve CART-EGFRvIII clinical trial to ensure the target is present. The NGS assay provides the EGFRvIII/wild-type ratio, relative expression levels for EGFR and EGFRvIII and evaluation of RNA degradation in a single assay. Figure 1A. Baseline in normal samples. EGFRvIII ratio in 18 “normal” brain and 11 adipose tissue samples, plotted without (top panel) and with (bottom panel) a EGFRvIII positive sample. Figure 2. EGFRvIII ratio in 25 GBM samples. Cutoff for EGFRvIII positive is EGFRvIII ratio of 0.3 (30%). Citation Format: Jianhua Zhao, Shrey Sukhadia, Alan Fox, David Lieberman, Barnett Li, Robert D. Daber, Matthew C. Hiemenz, David B. Roth, Maria Martinez-Large, Arati Desai, Donald M. O'Rourke, Marcela V. Maus, Jennifer JD Morrissette. Development of a NGS-based method for EGFRvIII detection: sequence analysis of the junction. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4916. doi:10.1158/1538-7445.AM2015-4916