A single bolus addition or sequential additions of 1,4-BQ can provide differential toxicities based on the endpoint measured.

<p><b>(A)</b> Clonogenic survival of MIA PaCa-2 cells was evaluated after a bolus addition of 600 fmol cell^-1 of 1,4-BQ or incremental additions of 1,4-BQ every 20 min over the 4-h exposure period (12 separate but equal additions) to yield a total dose of 600 fmol cell^-1. Controls represent additions of DMSO only to the culture media using protocols parallel to additions of 1,4-BQ. Clonogenic survival was the same for both exposure methods (<i>n</i> = 3, error bars are standard deviation of the mean). There is no statistical difference in the clonogenic survival between the two protocols. Each is different from the controls (<i>p</i> < 0.05). <b>(B)</b> Cell viability as indicated with trypan blue staining produced quite different results using a bolus dose of 1,4-BQ <i>vs</i>. sequential addition (<i>n</i> = 3, error bars are standard deviation of the mean). A single bolus addition produces a significant difference between control and sequential addition (<i>p</i> < 0.05). Whereas the sequential addition is the same as the control (<i>p</i> > 0.05).