Table 1. OSU-03012 and sildenafil synergize to kill glioblastoma cells.

GBM6 and GBM12 cells (250–1500 cells/well) were plated in sextuplicate and allowed to attach for 12h. Cells were treated with OSU-03012 (OSU, 0.5–2.0 μM); sildenafil (SIL, 0.5–2.0 μM); or the drugs combined for 24h. Media was removed, plates washed, and cells cultured for the next 10–14 days in media lacking drugs. After ~10 days media was removed, plates washed, and cells fixed and stained. The number of colonies per plate (> 50 cells per colony) was counted, plating efficiencies determined, and the relative changes in colony formation entered into the Calcusyn for Windows program to determine synergy (n = 3). A CI (combination index) of less than 0.70 indicates a strong level of synergy.

GBM6			GBM12
OSU μM	SIL μM	CI	OSU μM	SIL μM	CI
0.50	0.50	0.63	0.50	0.50	0.69
1.00	1.00	0.58	1.00	1.00	0.63
1.50	1.50	0.49	1.50	1.50	0.56
2.00	2.00	0.44	2.00	2.00	0.49