Approximately 500 cells from each biopsy were seeded in each well of 1,536-well microtiter plates (PerkinElmer) and incubated overnight. Combinatorial drug library was pin-transferred to the seeded plates as previously described (8 (link)). Plates were incubated for 96 hours, fixed in 4% formaldehyde, washed in PBS containing 0.1% Triton (PBST), and incubated overnight with antibodies (1:200) to S100 (Dako). The plates were then washed twice, incubated with Alexa 488 secondary antibodies (1:1000, Life Technologies) and DAPI 2–16 hours, and washed with PBST. Plates were then imaged using the CellWorX high-throughput microscope (Applied Precision Inc.) and nuclei and cells with S100 staining were counted with the Multi-Wavelength Cell Scoring module of the MetaExpress image analysis software (Molecular Devices). Representative control well images from each sample were manually reviewed to confirm S100 staining corresponded to cells with melanoma morphology. Technical replicates were averaged. Where replicates were available, Z’ scores were calculated (19 (link)), varying from 0.15 for CBRC029 to 0.58 for CBRC056.