Fig. 10.

Pgp inhibition with tariquidar (TQ) leads to cell death after doxorubicin (DOXO) treatment. hCMEC/D3 and RBE4 cells expressing Pgp-EGFP (green) show a confluent monolayer 24 h after treatment with 10 µM DOXO (red) (A, C) as assessed after fixation of the cells and image acquisition using a Zeiss Axio Observer. Inhibition of Pgp by the addition of TQ (0.5 µM) to the cultures leads to cell death (B, D) as visible by defragmentation of cell nuclei and break down of the monolayer. All images are taken 24 h after DOXO treatment. In the absence of tariquidar (A, C), yellow aciniform vesicle aggregates (arrowheads in A and C) were observed in both cell lines that—as indicated by the yellow color—contained both Pgp-EGFP and DOXO. Such drug-sequestering vesicular (lysosomal) aggregates were recently described and characterized by us in more detail and termed “barrier bodies” [13] (see text). Note that the photomicrographs shown in Fig. 8 were taken immediately after 30 min exposure to DOXO, whereas the photomicrographs shown here were taken 24 h after 30 min DOXO exposure, which explains that more cytoplasmic Pgp was seen in the latter experiment shown here