IM and MK-4440 combination induces cell cycle arrest and apoptosis. Immunoblot assays of WCEs from GIST-T1 treated with 40 nM IM, 120 nM MK-4440 or the combination; and GIST-T1/829 and GIST430 treated with 1 μM IM, 3 μM MK-4440, or the combination. All treatments were 20 h in duration. Equal quantities of WCE from each sample were subjected to immunoblotting with specific antibodies, as indicated. GAPDH served as loading control (A). Representative flow cytometry plots (B) and quantification (E) of BrdU incorporation in GIST-T1 treated with 40 nM IM, 120 nM MK-4440 and combination for 72 h; k = 1 × 103. For comparisons between the combination (IM/ MK-4440) treatment vs. all monotherapies (Vehicle, IM, MK-4440) statistically significant reduction in S-phase, an increase in cell death (**** p < 0.00007), G1 arrest for comparison between the combination (IM/ MK-4440) treatment vs. Vehicle (p < 0.02) and G2 arrest between the combination (IM/ MK-4440) treatment vs. IM, MK-4440 monotherapies (p = 0.01) were observed. Representative flow cytometry plots (C) and quantification (F) of BrdU incorporation in GIST430 treated with 1 μM IM, 3 μM MK-4440 and combination for 72 h. For comparisons between the combination (IM/ MK-4440) treatment vs. all monotherapies (Vehicle, IM, MK-4440) statistically significant reduction in S-phase, an increase in cell death (*** p < 0.0002), and G1 arrest for comparison between the combination (IM/ MK-4440) treatment vs. Vehicle and IM (p < 0.009), and G2 arrest between the combination (IM/ MK-4440) vs. IM treatment (p < 0.008) were observed. Representative flow cytometry plots (D) and quantification (G) of BrdU incorporation in GIST-T1/829 treated with 1 μM IM, 3 μM MK-4440 and combination for 72 h. For comparisons between the combination (IM/ MK-4440) treatment vs. Vehicle and IM treatments statistically significant reduction in S-phase (** p < 0.002), an increase in cell death (p < 0.02), and G1 arrest for comparison between the combination (IM/ MK-4440) treatment vs. all monotherapies (Vehicle, IM, MK-4440) (p < 0.0004) were observed. Data represent mean of three experiments + SD. Ns- no significance.