Fig 1. D425MED cells, but not D283MED, are sensitive to topotecan in culture.

(A-B) D283 and clone 5 of D425 medulloblastoma cells, expressing firefly luciferase, were seeded at 2×10³ cells/well into 96-well plates, and methotrexate (MTX), cytosine arabinoside (ARA-C) or topotecan (TPT) were added for 72 h. Cells were analyzed for residual bioluminescence (Radiance) as a measurement of cells surviving following treatment. Data are averages of duplicate measurements of duplicate wells ±SEM. 72 h IC50 for TPT was 248 μM in D283 cells (A) and 35 nM in D425 cells (B). IC50 was not reached for MTX or ARA-C in either cell line. (C) D425 clones #4, #5 and #7 expressing firefly luciferase were seeded at 1×10⁴ cells/well into a 96-well plate and exposed to the indicated concentrations of topotecan for 96 h between days 2 and 6 after plating, with drug/medium replaced on day 2 and on day 4 after plating. Bioluminescence was assessed 6 days after plating. Data are mean measurements of quadruplicate wells ±SEM. The 96 h IC50s were 2.9 nM (clone #7), 1.8 nM (clone #5) and 3.6 nM (clone #4), with mean IC50 of 2.8 nM ± 0.52 (SEM). Error bars for most data points are smaller than the symbols and are not visible.