Table 4. Inhibitory Potencies of Selected Indole Derivatives against the ABC Transporters ABCB1, ABCC1, and ABCG2 Obtained in Calcein AM (ABCB1),^2,52−59 Daunorubicin (ABCB1^52,60 and ABCC1^52,58−60), and Pheophorbide A (ABCG2)^2,52−60 Assays Using ABCB1-Expressing A2780/ADR (A), ABCC1-Expressing H69AR (B), and ABCG2-Expressing MDCK II BCRP (C) Cells, Respectively^a.

no.	ABCB1 calcein AMIC50 ± SEM [μM]	ABCB1 daunorubicinIC50 ± SEM [μM]	ABCC1 daunorubicinIC50 ± SEM [μM]	ABCG2 pheophorbide AIC50 ± SEM [μM]
22	24.3 ± 6.4b	n.t.	17.3 ± 2.2i	99.5 ± 24.5j
23	5.32 ± 1.67b	n.t.	19.1 ± 3.4i	43.5 ± 7.5j
24	0.983 ± 0.135c	1.49 ± 0.05f	n.t.	n.t.
30	1.51 ± 0.08d	2.77 ± 0.02g	n.t.	n.t.
31	1.40 ± 0.11e	1.19 ± 0.12h	n.t.	n.t.
34	0.960 ± 0.018	0.851 ± 0.003
35			0.215 ± 0.033
36				0.161 ± 0.011

^aMean ± SEM values of at least three independent experiments are shown.

^bConstrained to the reference ABCB1 inhibitor 34.

^cI_max = 66.8 ± 3.3%.

^dI_max = 61.1 ± 2.1%

^eI_max = 47.9 ± 4.9%.

^fI_max = 84.0 ± 2.5%.

^gI_max = 93.3 ± 2.6%.

^hI_max = 39.0 ± 2.8%.

ⁱConstrained to the reference ABCC1 inhibitor 35.^58,61

^jConstrained to the reference ABCG2 inhibitor 36; n.t., not tested due to lack of inhibitory activity in the initial screening.