Ko 143

Ko 143 is a potent and selective breast cancer resistance protein multidrug transporter (BCRP) inhibitor with IC50 value of 26 nM [1].

BCRP is a member of ATP- binding cassette transport protein superfamily, which is a plasma membrane protein associated with multidrug resistance of cancer cells.It is found in the intestinal epithelium, liver canaliculi, the placental trophoblasts, mammary ducts and lobules, and endothelial cells of veins and capillaries. MDR is the principal reason for the failure of anticancer chemotherapy, where BCRP may act as a broad specificity drug efflux pump and confer multidrug resistance. When overexpressed, BCRP is able to confer the resistance of various cancer cell lines to drugs including topotecan, doxorubicin, daunorubicin and mitoxantrone.

BCRP is the first potent and specific BCRP inhibitor applicable in vivo. When a library of potent compounds was screened in mouse T6400 and human T8 cancer cell line, Ko 143 was identified as the inhibitor with the high inhibitory activity and low cytotoxicity. Additionally, Ko 143 was observed to have 200-fold selectivity over P-glycoprotein and multidrug resistance protein-1 [2]. The effect of Ko 143 in reversing Bcrp-1/BCRP-mediated drug resistance was also observed in mouse T6400 and human T8 cell line respectively. At EC90 concentration of Ko 143, it reversed the Bcrp-1/BCRP-mediated drug resistance in the drug selected T6400 and T8 cell line, resulting in 10-fold sensitization to topotecan and mitoxantrone [2].

In mouse model, oral administration of Ko 143 50 mg/day or higher showed no evidence of acute of delayed cellular toxicity [2]. In Mdr1a/1b-/- mice, oral administration of Ko 143 of 10 mg/kg resulted in increasing plasma topotecan level by 4-6 folds at 30 min and 60 min after oral administration of the drug. It suggested Ko 143 suppressed the multidrug resistance conferred by BCRP [2].

References:
[1] Loevezijn AV et al. , Inhibition of BCRP-mediated drug efflux by fumitremorgin-type indolyl diketopiperazines. Bioorg. Med. Chem. Lett. 2001, 11(1), 29-32.
[2] Allen J D et al. , Potent and Specific Inhibition of the Breast Cancer Resistance Protein Multidrug Transporter in Vitro and in Mouse Intestine by a Novel Analogue of Fumitremorgin C. Mol. Cancer Ther. 2002, 1, 417-425.

Synthesis of a new inhibitor of breast cancer resistance protein with significantly improved pharmacokinetic profiles.[Pubmed:26642765]

Bioorg Med Chem Lett. 2016 Jan 15;26(2):551-555.

The design, synthesis, in vitro inhibitory potency, and pharmacokinetic (PK) profiles of Ko143 analogs are described. Compared to commonly used Ko143, the new breast cancer resistance protein (BCRP) inhibitor (compound A) showed the same potency and a significantly improved PK profile in rats (lower clearance [1.54L/h/kg] and higher bioavailability [123%]). Ko143 on the other hand suffers from poor bioavailability. Compared to Ko143, compound A would be a useful probe for delineating the role of BCRP during in vivo studies in animals.

The linker region of breast cancer resistance protein ABCG2 is critical for coupling of ATP-dependent drug transport.[Pubmed:26708291]

Cell Mol Life Sci. 2016 May;73(9):1927-37.

The ATP-binding cassette (ABC) transporters of class G display a different domain organisation than P-glycoprotein/ABCB1 and bacterial homologues with a nucleotide-binding domain preceding the transmembrane domain. The linker region connecting these domains is unique and its function and structure cannot be predicted. Sequence analysis revealed that the human ABCG2 linker contains a LSGGE sequence, homologous to the canonical C-motif/ABC signature present in all ABC nucleotide-binding domains. Predictions of disorder and of secondary structures indicated that this C2-sequence was highly mobile and located between an alpha-helix and a loop similarly to the C-motif. Point mutations of the two first residues of the C2-sequence fully abolished the transport-coupled ATPase activity, and led to the complete loss of cell resistance to mitoxantrone. The interaction with potent, selective and non-competitive, ABCG2 inhibitors was also significantly altered upon mutation. These results suggest an important mechanistic role for the C2-sequence of the ABCG2 linker region in ATP binding and/or hydrolysis coupled to drug efflux.

Effect of quercetin on the uptake and efflux of aristolochic acid I from Caco-2 cell monolayers.[Pubmed:27166429]

J Pharm Pharmacol. 2016 Jul;68(7):883-9.

OBJECTIVE: The purpose of this study was to determine whether quercetin decreases the uptake of aristolochic acid I (AAI) from the apical membranes of Caco-2 cells via H(+) -linked MCTs at neutral pH as well as to confirm the secretion of AAI through the Caco-2 cell monolayers via ABC transporters. METHODS: Caco-2 cells cultured on the dishes or permeable membranes were incubated with AAI in the absence or presence of quercetin or transporter inhibitors. KEY FINDINGS: Coincubation with quercetin decreased the uptake of AAI by Caco-2 cells cultured on the dishes at pH 7.4, and a similar decrease in AAI uptake was found when the cells were coincubated with acetic acid or benzoic acid. In contrast, the basolateral-to-apical transport of AAI was higher than the apical-to-basolateral transport of AAI at pH 7.4, and the former transport was decreased by quercetin and the BCRP inhibitors of Ko-143 and mitoxantrone, but not by P-gp or MRP2 inhibitors. CONCLUSIONS: AAI appears to be secreted from the apical membranes of Caco-2 cells via BCRP at neutral pH, although a small amount of AAI is taken up from the apical membranes via H(+) -linked MCTs, and quercetin may decrease both the BCRP-mediated efflux and the MCT-mediated influx of AAI.

Effect of Ursolic Acid on Breast Cancer Resistance Protein-mediated Transport of Rosuvastatin In Vivo and Vitro.[Pubmed:26960302]

Chin Med Sci J. 2015 Dec;30(4):218-25.

OBJECTIVE: To evaluate whether ursolic acid can inhibit breast cancer resistance protein (BCRP)-mediated transport of rosuvastatin in vivo and in vitro. METHODS: Firstly, we explored the pharmacokinetics of 5-fluorouracil (5-FU, a substrate of BCRP) in rats in the presence or absence of ursolic acid. Secondly, we studied the pharmacokinetics of rosuvastatin in rats in the presence or absence of ursolic acid or Ko143 (inhibitor of BCRP). Finially, the concentration-dependent transport of rosuvastatin and the inhibitory effects of ursolic acid and Ko143 were examined in Madin-Darby Canine Kidney (MDCK) 2-BCRP421CC (wild type) cells and MDCK2-BCRP421AA (mutant type) cells. RESULTS: As a result, significant changes in pharmacokinetics parameters of 5-FU were observed in rats following pretreatment with ursolic acid. Both ursolic acid and Ko143 could significantly affect the pharmacokinetics of rosuvastatin. The rosuvastatin transport in the BCRP overexpressing system was increased in a concentration-dependent manner. However, there was no statistical difference in BCRP-mediated transport of rosuvastatin betweent the wild type cells and mutant cells. The same as Ko143, ursolic acid inhibited BCRP-mediated transport of rosuvastatin in vitro. CONCLUSION: Ursolic acid appears to be a potent modulator of BCRP that affects the pharmacokinetic of rosuvastatin in vivo and inhibits the transport of rosuvastatin in vitro.

Sulfonation of raloxifene in HEK293 cells overexpressing SULT1A3: Involvement of breast cancer resistance protein (BCRP/ABCG2) and multidrug resistance-associated protein 4 (MRP4/ABCC4) in excretion of sulfate metabolites.[Pubmed:26611713]

Drug Metab Pharmacokinet. 2015 Dec;30(6):425-33.

Excretion of sulfate metabolites is an essential process in disposition of raloxifene via the sulfonation pathway. However, the transporters responsible for excretion of raloxifene sulfates remain undefined. Here, sulfonation of raloxifene and excretion of its sulfate metabolites were investigated using SULT1A3-overexpressing HEK293 cells (or SULT293 cells) with significant expression of BCRP and MRP4. SULT293 cell lysate catalyzed the sulfonation of raloxifene at both 6-OH and 4'-OH groups, generating raloxifene-6-sulfate (R-6-S) and raloxifene-4'-sulfate (R-4'-S), respectively. Sulfate formation followed the Michaelis-Menten kinetics (Km = 0.49 muM and Vmax = 5.79 pmol/min/mg for R-6-S; Km = 0.33 muM and Vmax = 1.25 pmol/min/mg for R-4'-S). As expected, the recombinant SULT1A3 enzyme showed a high similarity in raloxifene sulfonation profiles with the lysate preparation. Ko143, a selective inhibitor of BCRP, significantly decreased the excretion rates of raloxifene sulfates (maximal 66.1%) while increasing the intracellular sulfates (maximal 282%). As a result, the apparent efflux clearance (CLef,app, representing the efflux efficiency of raloxifene sulfates) was substantially reduced (maximal 85.6%). Likewise, the pan-MRP inhibitor MK-571 significantly deceased the excretion rates (maximal 69.6%) and CLef,app values (maximal 96.0%) of raloxifene sulfates while increasing the intracellular sulfates (maximal 667%). Further, the short-hairpin RNA (shRNA) targeting BCRP significantly reduced (maximal 35.0%) sulfate excretion. Use of BCRP shRNA also caused significant decreases (maximal 52.5%) in the CLef,app values. Silencing of MRP4 by shRNA led to a substantial alteration in sulfate disposition (i.e., 28.6-37.8% reductions in sulfate excretion, 30.5-59.3% elevations in intracellular sulfates, and 44.8-47.7% deceases in CLef,app values). In conclusion, two sulfate metabolites R-6-S and R-4'-S were generated from raloxifene in SULT293 cells. Cellular excretion of the raloxifene sulfates was mainly mediated by BCRP and MRP4.

The Inhibitor Ko143 Is Not Specific for ABCG2.[Pubmed:26148857]

J Pharmacol Exp Ther. 2015 Sep;354(3):384-93.

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,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-diox opyrazino[1',2':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 muM) 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.

Mouse breast cancer resistance protein (Bcrp1/Abcg2) mediates etoposide resistance and transport, but etoposide oral availability is limited primarily by P-glycoprotein.[Pubmed:12649196]

Cancer Res. 2003 Mar 15;63(6):1339-44.

The breast cancer resistance protein [BCRP (BCRP/ABCG2)] has not previously been directly identified as a source of resistance to epipodophyllotoxins.However, when P-glycoprotein (P-gp)- and Mrp1-deficient mouse fibroblast and kidney cell lines were selected for resistance to etoposide, amplification and overexpression of Bcrp1 emerged as the dominant resistance mechanism in five of five cases. Resistance was accompanied by reduced intracellular etoposide accumulation. Bcrp1 sequence in all of the resistant lines was wild-type in the region spanning the R482 mutation hot spot known to alter the substrate specificity of mouse Bcrp1 (mouse cognate of BCRP) and human BCRP. Transduced wild-type Bcrp1 cDNA mediated resistance to etoposide and teniposide in fibroblast lines and trans-epithelial etoposide transport in polarized Madin-Darby canine kidney II cells. Bcrp1-mediated etoposide resistance was reversed by two structurally different BCRP/Bcrp1 inhibitors, GF120918 and Ko143. BCRP/Bcrp1 (inhibition) might thus impact on the antitumor activity and pharmacokinetics of epipodophyllotoxins. However, treatment of P-gp-deficient mice with GF120918 did not improve etoposide oral uptake, suggesting that Bcrp1 activity is not a major limiting factor in this process. In contrast, use of GF120918 to inhibit P-gp in wild-type mice increased the plasma levels of etoposide after oral administration 4-5-fold. It may thus be worthwhile to test inhibition of P-gp in humans to improve the oral availability of etoposide.

Potent and specific inhibition of the breast cancer resistance protein multidrug transporter in vitro and in mouse intestine by a novel analogue of fumitremorgin C.[Pubmed:12477054]

Mol Cancer Ther. 2002 Apr;1(6):417-25.

Inhibitors of the breast cancer resistance protein (BCRP/ABCG2) multidrug transporter are of interest as chemosensitizers for clinical drug resistance, for improving the pharmacokinetics of substrate chemotherapeutic drugs, and in functional assays of BCRP activity for tailoring chemotherapy. The fungal toxin fumitremorgin C (FTC) is a potent and specific inhibitor of BCRP, but its neurotoxic effects preclude use in vivo. We have therefore evaluated a new tetracyclic analogue of FTC, Ko143, as a practical inhibitor of BCRP, comparing it with two other analogues in the same class and with GF120918. All three FTC analogues are effective inhibitors of both mouse Bcrp1 and human BCRP, proving highly active for increasing the intracellular drug accumulation and reversing Bcrp1/BCRP-mediated multidrug resistance. Indeed, Ko143 appears to be the most potent BCRP inhibitor known thus far. In contrast, the compounds have only low activity against P-glycoprotein, the multidrug resistance-associated protein (MRP1), or other known drug transporters. They are nontoxic in vitro at useful concentrations and evinced no signs of toxicity in mice at high oral or i.p. doses. Administered p.o. to inhibit intestinal Bcrp1, Ko143 markedly increased the oral availability of topotecan in mice. It is thus the first highly potent and specific BCRP inhibitor applicable in vivo. As such, Ko143 and other FTC analogues of this type represent valuable reagents for analysis of drug resistance mechanisms and may be candidates for development as clinical BCRP inhibitors.

Ko 143 is a potent and selective ATP-binding cassette subfamily G member 2 (ABCG2/BCRP) inhibitor. Ko 143 displays >200-fold selectivity over P-gp and MRP-1 transporters.

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