Abstract 2991: Establishment of patient-derived cancer cell lines to elucidate the resistant mechanism of tyrosine kinase inhibitors
Authors: Manabe Tadashi , Yasuda Hiroyuki , Terai Hideki , Hamamoto Junko , Ebisudani Toshiki , Kobayashi Keigo , Masuzawa Keita , Ikemura Shinnosuke , Kawada Ichiro , Fukunaga Koichi , Soejima Kenzo 
Published: September 2020

Abstract
In non-small cell lung cancer (NSCLC), several somatic mutations such as EGFR and EML4-ALK have been identified in a significant subgroup of patients. Multiple clinical trials involving tyrosine kinase inhibitors (TKIs) have demonstrated significant improvement in the prognosis of lung cancer patients with these mutations. However, in clinic, lung cancer cells gradually acquire resistance to these inhibitors in a span of approximately 1 - 2 years. In TKI resistant lung cancer patients, next-generation sequencing of clinical samples from individual patients enables the detection of genetic alterations that contribute to drug resistance, such as EGFR T790M and EGFR C797S mutations. However, it does not always offer an appropriate treatment strategy for patients with acquired resistance. In contrast, the presence of living cancer cells allows researchers to biologically evaluate the roles of mutations or bypass pathways. For a thorough clarification of resistance mechanisms, living cancer cells, in addition to genomic information, are essential. In our report, we have established six patient-derived cancer cells (PDCs) from NSCLC patients who were treated with various TKIs and thereafter experienced disease progression. The success rate for PDCs was as high as 50% (6/12). Upon the established cell lines, 2 cases had EML4-ALK and the rest had EGFR mutation as an oncogene. After establishing the PDCs, TKI resistance was confirmed by MTS cell proliferation assay and 5 of 6 cases showed matched TKI resistance referring to the clinical background. To elucidate the adaptive resistant mechanisms in PDCs, Sanger sequence was performed and none of the gene mutations that have been previously reported to contribute to resistance to TKIs was detected. Next, to investigate the bypass pathway activation in these cell lines, we performed phospho-receptor tyrosine kinase (RTK) array screening. Interestingly, 4 of 5 cases showed activation of bypass RTK signaling and 3 of 4 cases obtained combined effectiveness with the additional RTK inhibitor. Furthermore, we have performed western blotting in 3 PDCs and detected that combination treatment attenuated the phosphorylation of the downstream molecules. In conclusion, by using PDCs, we have clarified the mechanism of acquired resistance and detected the treatment strategy to overcome these resistances. The findings suggest that PDCs may help develop precision medicine for TKI resistant patients.
Citation Format: Tadashi Manabe, Hiroyuki Yasuda, Hideki Terai, Junko Hamamoto, Toshiki Ebisudani, Keigo Kobayashi, Keita Masuzawa, Shinnosuke Ikemura, Ichiro Kawada, Koichi Fukunaga, Kenzo Soejima. Establishment of patient-derived cancer cell lines to elucidate the resistant mechanism of tyrosine kinase inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2991.