Pc9 cell line

The HCC827 and H1975 cell lines (human NSCLC cell lines) were obtained from the American Type Culture Collection (ATCC), and the PC‐9 cell line (a human NSCLC cell line) was obtained from the European Collection of Authenticated Cell Cultures (ECACC). The PC9‐COR cell line was established from the PC‐9 cell line as previously reported.³¹ All cell lines were authenticated using the short tandem repeat method and were maintained in RPMI medium (FUJIFILM Wako Pure Chemical Corporation) supplemented with 10% fetal bovine serum (FBS; Cytiva, Marlborough, MA). The EGFR status of the cell lines is summarized in Table S2. All cell lines were used after they were confirmed to be negative for Mycoplasma contamination with a PCR Mycoplasma Detection Kit (TaKaRa Bio) according to the manufacturer's instructions. Erlotinib and osimertinib were obtained from Cayman Chemical Company. TAS‐121 and TAS‐116 were kindly provided by Taiho Pharmaceutical Co., Ltd.

DNA oligonucleotides including PCR primers and padlock probe DNA were chemically synthesized and purified by high performance liquid chromatography (Bionics, Korea). The padlock probe DNA that can hybridize to the sequence of EGFR exon 19-del site was modified with phosphate at the 5’-end to be ligated into a circular template for subsequent RCA. The sequences of the oligonucleotides are listed in Table S1. Ex Taq polymerase and dNTPs mixture (dATP, dGTP, dCTP, and dTTP) was purchased from Takara Korea Biomedical Inc. (Korea). Thioflavin T (ThT) was purchased from Sigma-Aldrich Korea (Korea). Phi29 DNA polymerase and Taq DNA ligase were purchased from New England Bio-labs (USA). Pooled normal human plasma was purchased from Innovative Research (Novi, MI, USA).
The A549 cell line was from the American Type Culture Collection (ATCC, CCL-185, USA) and PC9 cell line was from the European Collection of Authenticated Cell Cultures (ECACC, 90071810, UK). A549 cells possess the wild-type EGFR exon 19 gene, whereas PC9 cells contain EGFR exon 19 deletion mutation (E746-A750). All cells were cultured in DMEM high glucose (Hyclone, USA) supplemented with 10% fetal bocine serum (Hyclone) and 100 U/ml penicillin (WelGene, Korea) in a humidified incubator under 5% CO₂ at 37°C.