Abstract 4580: Changes in the efficacy of anti-EGFR antibody drugs by exosomes derived from colorectal cancer patients

Abstract

Abstract Background: One of the biggest hurdles in cancer treatment is drug resistance. Exosomes are small membrane vesicles of endocytic origin, which contain mRNAs, DNA fragments, and proteins, and are released by many different cell types, including cancer cells. Several studies have shown exosome-mediated drug resistance mechanisms: drug export via the exosome pathway, neutralization of antibody-based drugs and exosome-mediated transfer of miRNAs. Here, we demonstrated the effect of exosomes derived from colorectal cancer (CRC) patients on the efficacy of anti-EGFR agent by in vitro cell-based assay. Method: Exosomes were purified by ultracentrifugation from culture media of HCT116 cell line and the sera of CRC patients with stage IV pre- and post-treatment with cetuximab (Cmab). As a control, sera from healthy volunteers were used. The number of exosomes and amount of protein were determined by NanoSight and Qubit fluorometer, respectively. The isolated exosomes and 0.01 mg/mL and 0.1 mg/mL of Cmab were added to HT29 and NCI-H508, which stained with PKH dye previously. NCI-H508 is a Cmab super sensitive cell line. After culturing for 3 days, the cells were collected, stained with trypan blue, and the number of the remaining viable cancer cells was calculated with a cell counter. Cmab in the exosome fraction was quantified by ELISA. Result: HT29 became drug ineffective depending on the number of exosomes produced by Cmab-insensitive HCT-116 harboring KRAS G13D mutation. In addition, exosomes in 9 of 18 cases of colorectal cancer patients changed NCI-H508 into a drug-ineffective state and also correlated with clinical information. In contrast, NCI-H508 was not converted into a drug-ineffective state by exosomes of healthy volunteers and Cmab responder patients. However, on the other hand, quantitative results by ELISA showed that Cmab in sera of some patients remained in the exosome fraction and inhibited the growth of NCI-H508. As a remarkable point, exosomes derived from healthy volunteers significantly promoted the efficacy of Cmab. Conclusion: In this feasibility study, Cmab resistance in CRC patients may be reproducible by cell-based assay using exosomes. We believe that understanding this mechanism of action will contribute to drug discovery and personalized medicine in the future. Now, we are searching for biomarkers in these exosomes that change the efficacy of Cmab. Citation Format: Rii Morimura, Kei Tsukamoto, Shinji Irie, Shiro Kitano, Eiji Shinozaki, Kensei Yamaguchi. Changes in the efficacy of anti-EGFR antibody drugs by exosomes derived from colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4580.