Fig. 4.

Disorazole C₁ resistance is reversible with verapamil treatment. HeLa (circles) or HeLa/DZR (squares) cells were incubated in the presence (open symbols) or in the absence (closed symbols) of 5 μM verapamil and with various concentrations of compounds for 72 h, and the total number of cells was determined by Hoechst staining nuclei using an ArrayScan reader as described under Materials and Methods. Each value was the mean of four determinations. Bars equal S.E.M. unless the value was less than the size of the symbol. A, disorazole C₁. B, disorazole A₁. C, vinblastine.