Apoptosis in HMC-1 cells assessed by TUNEL assay. HMC-1.1 cells (A) and HMC-1.2 cells (B) were incubated in control medium (i,v), PKC412, 1 μM (ii,vi), AMN107, 1 μM (iii,vii), or imatinib, 1 μM (iv,viii) at 37°C for 24 hours. Thereafter, cells were harvested and subjected to TUNEL assay. As visible, PKC412 produced apoptosis in most HMC-1.1 and HMC-1.2 cells, whereas AMN107 and imatinib showed potent apoptosis-inducing effects in HMC-1.1 cells (iii-iv), but not in HMC-1.2 cells exhibiting KIT D816V (vii-viii). Images were obtained using a Nikon Plan Apo 40 ×/1.0 numeric aperture oil objective. Images were acquired from FITC-labeled cells using a Hamamatsu high-resolution digital camera (model C4242-95; Hamamatsu, Japan) and HPD-CPX32 Microsoft Windows 95 software (Microsoft, Redmond, WA). Citifluor (Agar Science, Stansted, United Kingdom) was used as imaging solution.