Table 1. Values of growth inhibition 50% of reference cytotoxic drugs and diphyllin derivatives in Sk-mel-5 cells co-incubated with or without the MDR1/Pgp inhibitor verapamil (n = 3).

	+ vehicle	+ verapamil (2.3μM)
Vincristine	1.04±0.90 nM	0.15±0.02 nM (p <0.01)
Camptothecin	6.93±1.51 nM	7.22±2.15 nM
Diphyllin methyl ether	2.33±0.24 μM	2.49±0.51 μM
Justicidin B	1.15±0.26 μM	1.22±0.23 μM
Diphyllin apioside	0.050±0.016 μM	0.046±0.045 μM
Diphyllin acetylapioside	0.045±0.008 μM	0.040±0.015 μM