Compounds, I and II, induce extreme cytoplasmic vacuolization in U251 glioblastoma cells. Cells were seeded at 500,000 cells in 60 mm dishes. The day after plating, cells were treated with either 1 μM or 10 μM of the indicated compounds. Phase-contrast images were taken 4 h and 24 h after addition of the drugs. The scale bar is 10 microns and applies to all of the panels. The appearance of the cells treated with compounds III and IV was identical to control cultures treated with an equivalent volume of DMSO (not shown). Compound II was selected for further study and was designated MIPP.