TABLE 10

Example of experimental design and dose-effect relationships of paclitaxel, cisplatin, and topotecan and their two- and three-drug combinations on growth inhibition of 833K teratocarcinoma cells after 96 h of exposure (modified fromChou et al., 1994, J Natl Cancer Inst86:1517-1524) Experimental data were subjected to automated calculation of m, Dm, and r parameters as well as plots simulations using CompuSyn (Chou and Martin, 2005). For detailed CompuSyn analysis, see Supplemental Data Appendix IV (http://pharmrev.aspetjournals.org/cgi/content/full/pr.58.3.10/DC1).

Drug Fractional Inhibition, fa Parametera CIb
Paclitaxel Cisplatin Topotecan m Dmr
μM μM
(D)1
0.002 0.429
0.004 0.708
0.005 0.761
0.01 0.882
0.02 0.932 1.248 0.00217 0.990
(D)2
0.05 0.055
0.1 0.233
0.2 0.301
0.5 0.559
1.0 0.821
2.0 0.953 1.458 0.320 0.986
(D)3
0.01 0.069
0.02 0.213
0.05 0.373
0.1 0.785
0.2 0.940
0.5 0.991 1.855 0.0462 0.991
(D)1 + (D)2 (1:100)c
0.001 0.1 0.450 0.900
0.002 0.2 0.701 0.815
0.005 0.5 0.910 0.0001147 0.681d
0.01 1.0 0.968 1.572 + 0.11471 0.602
(D)2 + (D)3 (100:10)
0.05 0.005 0.304 0.445
0.1 0.01 0.413 0.658
0.2 0.02 0.675 0.669
0.5 0.05 0.924 0.1053 0.561
1.0 1.0 0.977 1.588 + 0.01053 0.989 0.522
(D)1 + (D)3 (1:10)
0.001 0.01 0.274 1.373
0.002 0.02 0.579 1.078
0.005 0.05 0.901 0.00166 0.719
0.01 0.1 0.965 1.891 + 0.01661 0.999 0.681
(D)1 + (D)2 + (D)3 (1:100:10)
0.001 0.1 0.01 0.456 1.121
0.002 0.2 0.02 0.806 0.001162 0.729
0.003 0.3 0.03 0.947 + 0.11616 0.403
0.005 0.5 0.05 0.995 3.363 + 0.011612 0.984 0.136
  • a The parameters m, Dm, and r are the slope, antilog of the x-intercept, and the linear correlation coefficient of the median-effect plot, which signifies the shape of the dose-effect curve, the potency (IC50), and the conformity of the data to the mass-action law, respectively. Dm and m values are used for calculating the CI values

  • b CI < 1, CI = 1, and CI > 1 indicate synergism, additive effect, and antagonism, respectively. As based on the classic isobologram equation, CI can be calculated by eq. 16: CI = [(D)1/(Dx)1] + [(D)2/(Dx)2], where Dx = Dm[fa/(1 — fa)]1/m (eq. 8)

  • c The drug mixture was serially diluted and added to incubation mixture at 0 h. The combination ratio was approximately equal to the Dm ratio of the component drugs (i.e., close to their equipotency ratio)

  • d Sample pocket calculator calculation of the CI value of 0.005 μM paclitaxel + 0.5 μM cisplatin that inhibited 833K cell growth by 91.0% (fa = 0.910). On the basis of eq. 8, for paclitaxel alone to inhibit cell growth by 91% would require [D0.91]paclitaxel = (Dm)paclitaxel [0.91/(1 — 0.91)]1/1.248 = 0.00217 μM × 6.385 = 0.01385 μM and for cisplatin alone to inhibit cell growth by 91% would require [D0.91]cisplatin = (Dm)cisplatin [0.91/(1 — 0.91)]1/1.458 = 0.320 μM × 4.888 = 1.564 μM. Therefore, CI = (0.005 μM/0.01385 μM) + (0.5 μM/1.564 μM) = 0.681 at 91% inhibition