Exosomes are small vesicles, ranging from 30 to 100 nm in size, secreted from most types of cells. They contain proteins, lipids, and nucleic acids (e.g. DNA, mRNA, and microRNA) and are thought to play an important role in cell proliferation, invasion, and metastasis in human malignancies. Recently, circulating exosomes have also been of interest as a source for liquid biopsies. In this study, we examined the usefulness of exosomal RNA as a biomarker and attempted to detect the tumor-specific gene mutations from exosomal RNA derived from human oral squamous cell carcinoma (OSCC) cells. We used 3 human OSCC cells (HSC2, KT-T, KT-N). KT-T and KT-N cells were established from the lower gingival tumor and lymph node metastasis, respectively. First, we detected the somatic mutations in genomic DNA extracted from these cells by next-generation sequencing (NGS) with the use of HaloPlex Cancer Research Panel (Agilent Technologies). PIK3CA H1047R mutation was identified in all OSCC cells, and KT-N cells had the additional HRAS Q61R mutation. We confirmed these mutations of PIK3CA and HRAS in OSCC cells by TaqMan® SNP Genotyping Assays (Thermo Fisher Scientific). Subsequently, we evaluated the gene mutations in exosomal RNA from these OSCC cells. Exosomal RNA was isolated from the conditioned medium using exoRNeasy Serum/Plasma Maxi Kit (Qiagen) according to the manufacture’s protocol. In exosomal RNA, we found the PIK3CA H1047R mutation from all OSCC cells and HRAS Q61R mutation from KT-N cells by genotyping assays. Furthermore, we assessed the detection of these mutations in tumor xenograft mouse models. KT-T and KT-N cells (5 x 106) complexed with Matrigel® (BD) in 100-µl aliquots were injected subcutaneously space in the flank of male athymic nude mice. Exosomal RNA was isolated from the serum of tumor-bearing nude mice using exoRNeasy Serum/Plasma Midi Kit (Qiagen). By genotyping assays using serum exosomal RNA, PIK3CA H1047R mutation was observed in both types of xenograft mice and HRAS Q61R mutation was positive in KT-N xenograft mice. Cancer cell-derived exosomal RNA had the same gene mutations in those cells, and could be detected in the serum of tumor-bearing nude mice. These results suggest that exosomal RNA is useful for detecting somatic mutations in OSCC cells.

Citation Format: Norihiko Tokuzen, Koh-ichi Nakashiro, Hiroyuki Hamakawa. Detection of somatic mutations in exosomal RNA from human oral squamous cell carcinoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4461. doi:10.1158/1538-7445.AM2017-4461