Fig. 5: Synergic anti-cancer effect of ER stress inducer and ATF6 inhibitor combination treatment on GIST growth, and the prognostic significance of ATF6 nuclear expression in patients with GIST.

A, B Cell viability after 72 h of treatment with PF429242 alone (PF, 30 µM and 50 µM) and PF with ER stress-inducing drugs (0.5 µM 17AAG and 1 nM bortezomib) was analyzed in imatinib-sensitive GIST430 and GIST882 cells, and imatinib-resistant GIST48 and GIST430-V654A cells. Imatinib (IM, 0.1 uM) was used as a control drug and the combined effect with PF was evaluated. C The expression of KIT and cATF6 was measured by western blotting after treatment of PF (30 µM). D The anti-tumor effect was measured in a GIST430 xenograft mouse model and GIST430-V654A model. Relative tumor volume was measured at indicated days in vehicle, IM (50 mg/kg), PF (30 mg/kg), bortezomib (Bor, 1 mg/kg), and PF with bortezomib treatment groups. Each group consisted of 5 mice. E, F Immunohistochemistry (IHC) analysis of KIT, Ki67, and cleaved caspase-3 was performed using tumor tissues obtained from xenograft mouse models. G Nuclear expression of ATF6 was evaluated by IHC analysis in 42 GIST tissues. Patients were divided into nuclear ATF6 expression negative and positive groups. H Relapse-free and overall survival curves were plotted by Kaplan–Meier analysis and assessed by log-rank test, according to nuclear ATF6 expression. Error bars represent the SD of the mean of three independent experiments. One-way ANOVA with a post-hoc test was performed to compare multiple means (*p < 0.05, **p < 0.01, ***p < 0.001).