Figure 3.

Example 48 h EC₅₀ determination experiment in L3.6pl cells. The Control was set to 100% relative viability and was determined via the MTS reagent after 48 h growth period at 37°C. The DFMO-only cells were exposed to the 48 h DFMO IC₅₀ dose (and gave the expected 50% viability); the DFMO+Spd cells were exposed to the 48 h IC₅₀ DFMO dose and Spd (1 µM) (and shows increased viability due to Spd rescue); the remaining samples received a fixed DFMO IC₅₀ dose, a fixed Spd rescuing dose (1 µM), and increasing concentrations of the PTI agent 5a. As the PTI concentration is increased from 1 to 10 µM 5a, less Spd enters the cells and lower relative viability is observed. The PTI 5a was found to be non-toxic to L3.6pl cells at 2.5 µM during 48 h exposure. As seen in the graph above, the non-toxic PTI was able to block the rescuing effect of the added Spd. Note: PTI 5b gave a similar result.The EC₅₀ is shown graphically as the midpoint (in % viability) between the green and red lines, i.e. the DFMO+Spd and DFMO only controls.