The Inhibitor Ko143 Is Not Specific for ABCG2

Abstract

Imaging ATP-binding cassette (ABC) transporter activity in vivo with positron emission tomography requires both a substrate and a transporter inhibitor. However, for ABCG2, there is no inhibitor proven to be specific to that transporter alone at the blood-brain barrier. Ko143 [[(3S,6S,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino [19,29:1,6]pyrido [3,4-b]indole-3-propanoic acid 1,1-dimethylethyl ester], a nontoxic analog of fungal toxin fumitremorgin C, is a potent inhibitor of ABCG2, although its specificity in mouse and human systems is unclear. This study examined the selectivity of Ko143 using human embryonic kidney cell lines transfected with ABCG2, ABCB1, or ABCC1 in several in vitro assays. The stability of Ko143 in rat plasma was measured using high performance liquid chromatography. Our results show that, in addition to being a potent inhibitor of ABCG2, at higher concentrations ($1 mM) Ko143 also has an effect on the transport activity of both ABCB1 and ABCC1. Furthermore, Ko143 was found to be unstable in rat plasma. These findings indicate that Ko143 lacks specificity for ABCG2 and this should be taken into consideration when using Ko143 for both in vitro and in vivo experiments.

Tariquidar Is an Inhibitor and Not a Substrate of Human and Mouse P-glycoprotein

“…We believe this is related to high levels of cold TQR that block binding sites on plastic and elevate the free (non-plastic-bound) fraction of [ 3 H]TQR, although other possibilities exist, such as competition for lysosomal degradation. Consistent with our findings, displaceable specific binding has been observed before with the BCRP inhibitor [ 3 H]Ko143 (Weidner et al, 2015), and with the P-gp inhibitor [ 3 H]BIBW22 BS (4-(N-(2-hydroxy-2-methylpropyl)ethanolamino)-2,7-bis(cis-2,6-dimethylmorpholino)-6-phenylpteridine) (Liu et al, 1996).…”

“…Flow cytometry was used to measure the activity of P-gp in the presence of TQR, as well as the fluorescence of TQR itself, and confirm cell surface expression of BCRP on the newly generated LLC-BCRP cell line. The experiments were conducted as previously described (Weidner et al, 2015) with the following modifications. The efflux of the fluorescent P-gp substrate Rh123 was measured to determine the extent to which TQR increased cellular accumulation.…”

Marine Natural Products as Models to Circumvent Multidrug Resistance

“…Two derivatives, Ko132 (75) and Ko134 (76), were found to be potent inhibitors of the BCRP-mediated drug efflux in T6400 mouse and T8 human cell lines with low cytotoxicity at an effective concentration of 1 µM [163,169]. In addition, 77 was the most effective inhibitor of BCRP, with very low activity against P-gp or other known drug transporters [168,170]. In addition, the stereospecificity was shown to be very critical in the Ko family, for example, compounds having the 3S,6S,12αS configuration were 18 times more potent than those with 3S,6R,12αS configuration in inhibiting BCRP; however, this stereoselective effect was not observed in P-gp and MRP-1 [171].…”

Application of JC1 for non-toxic isolation of cells with MDR transporter activity by flow cytometry

“…These results demonstrate that in the 293T cells the generation of a JC1-SP occurs primarily or solely as a result of the activity of the ABCB1 transporter. The residual effect of Ko143 may in fact be due to a weak inhibitory effect of Ko143 on ABCB1 [24], a feature shared by FTC [25]. Consistent with this hypothesis, the 293T cells lacked a Hoechst–SP (Fig 3J), whereas the same cell type generated a large exclusion cohort when transduced with the ABCG2 gene (Fig 3K).…”