Measurement of sensitivity to etoposide. JN394t2-4 cells with either wild-type or mutant TOP2 were spread on plates containing stepwise concentrations of etoposide (A, C and E) or doxorubicin (B, D and F) and incubated at 35°C. (A and B) Examples of colony growth (wild-type and H759P). (C and D) Colony formation of the Pro mutants was plotted as a function of drug concentration. Filled circles, open circles, filled triangles, open triangles, filled squares, open squares and open diamonds are for wild-type, H759P, M762P, T767P, N770P, Q773P and N774P, respectively. (E and F) Colony formation with wild-type (filled circles), H759A (filled diamonds) and H759P (open circles), plotted as a function of drug concentration.