Figure 5|. Setup and analysis of BKM120 and dabrafenib permeability by MALDI-MSI.

a) Setup of the cryostat for sectioning of BBB organoids. Organoids were collected at the bottom of a PCR tube and snap frozen in a dry ice/ethanol bath. The cap of the tube was then mounted onto the sample disc. b) Conductivity was measured on both sides of an indium tin oxide (ITO) coated glass slide with a voltage-meter to determine the correct ITO coated side for mounting of tissue sections. ITO coating resulted in a measurable electrical resistance on the surface of the slide, while the uncoated side was non-conductive. For MSI, cryo-sectioned tissues must be mounted onto the ITO-coated side. c) H&E stained images of the cryo-sections from each group confirmed the presence of BBB organoid tissues (n_organoid = 150). Serial sections were used for MSI. ‘Scan’ images were used to identify the position of organoid sections on the ITO slide. ‘Pixel’ images show the pixel distribution within the selected scanned region (spatial resolution of 30 μm). MALDI MSI ion images reveal the distribution/level of both drugs in the organoid sections, showing a high level of BKM120 accumulation within the organoids (in green m/z 411.1751 ± 0.001). Dabrafenib was not detected within the organoids (m/z 520.1083 ± 0.001). Scale bars for BKM image: 100 μm, Scale bar for Dabrafenib image: 200 μm. Images from panel (c) are adapted from Cho et al., Nature Communications (2017).⁶