Table 6.

Effects of Group 1 and Group 2 Compound 29 Variants on ATP Hydrolysis by Normal Human MDR1 P-glycoprotein^a

compound	stimulated ATPase (% DMSO, significance)		effect on stimulated ATPase	basal ATPase (% DMSO, significance)		effect on basal ATPase
DMSO	100 ± 6			100 ± 5
SMU29	62 ± 3	**	inhibitor	88 ± 9	NS	none
Group 1: ChemGen and docking selected
SMU29–216	64 ± 6	**	inhibitor	69 ± 8	**	inhibitor
SMU29–227	62 ± 5	**	inhibitor	83 ± 7	NS	none
SMU29–231	40 ± 3	****	inhibitor	70 ± 4	***	inhibitor
SMU29–541	66 ± 6	**	inhibitor	87 ± 9	NS	none
SMU29–551	27 ± 1	***	inhibitor	72 ± 9	*	inhibitor
Group 2: rationally designed/no docking selection
SMU29–238	61 ± 7	**	inhibitor	89 ± 7	NS	none
SMU29–255	59 ± 6	**	inhibitor	84 ± 9	NS	none
SMU29–278	63 ± 6	**	inhibitor	74 ± 6	**	inhibitor
SMU29–280	54 ± 7	***	inhibitor	76 ± 8	*	inhibitor
SMU29–286	59 ± 4	***	inhibitor	95 ± 3	NS	none

^aATP hydrolysis assays using purified human P-glycoprotein were performed (see Experimental Section) without added transport substrate (“basal ATPase”) or in the presence of verapamil (“stimulated ATPase”). Results are presented compared to DMSO control ± standard deviation (three independent experiments with duplicate samples). The specific basal activity of normal human MDR1 P-gp was between 123 and 193 nmol min⁻¹ g⁻¹, and transport substrate (verapamil)-stimulated activity was between 193 and 263 nmol min⁻¹ mg⁻¹. Effects on stimulated P-gp ATPase activity indicated whether a compound directly interfered with ATP usage by the protein (***, p < 0.001; **, p < 0.01; *, p < 0.1; NS, not significant).