*4.3. Cell lines and Culture Conditions*

SK-LMS-1 leiomyosarcoma, RD rhabdomyosarcoma, HT-1080 fibrosarcoma and U2-OS osteosarcoma cell lines were purchased from American Type Culture Collection (ATCC). GIST T-1 cell line was generated from a metastatic pleural tumor from stomach GIST. This cell line exhibited the heterozygous 57-base pair deletion (V570-Y578) in *KIT* exon 11 [40]. IM-resistant GIST T-1R subline was generated in our laboratory. For this purpose, GIST T-1 cell line was continuously cultured with IM with a gradually increased concentration of the drug from 0.4 nM to 1000 Nm [41]. The IM-resistant GIST 430 cell line was generated from human GIST after developing resistance to IM therapy. This cell line has a heterozygous primary *KIT* exon 11 deletion (V560\_L576del) and a secondary *KIT* exon 13-point mutation (V654A) [1]. GIST cell lines were cultured in a humidified atmosphere of 5% CO<sup>2</sup> at 37 ◦C (LamSystems, Myass, Russia).
