1.The Inhibitor Ko143 Is Not Specific for ABCG2.
Weidner LD1, Zoghbi SS2, Lu S2, Shukla S2, Ambudkar SV2, Pike VW2, Mulder J2, Gottesman MM2, Innis RB2, Hall MD2. J Pharmacol Exp Ther. 2015 Sep;354(3):384-93. doi: 10.1124/jpet.115.225482. Epub 2015 Jul 6.
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-dioxopyrazino[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 μM) Ko143 also has an effect on the transport activity of both ABCB1 and ABCC1.
2.The antiepileptic drug lamotrigine is a substrate of mouse and human breast cancer resistance protein (ABCG2).
Römermann K1, Helmer R2, Löscher W3. Neuropharmacology. 2015 Jun;93:7-14. doi: 10.1016/j.neuropharm.2015.01.015. Epub 2015 Jan 31.
Resistance to antiepileptic drugs (AEDs) is the major problem in the treatment of epilepsy. One hypothesis to explain AED resistance suggests that seizure-induced overexpression of efflux transporters at the blood-brain barrier (BBB) restricts AEDs to reach their brain targets. Various studies examined whether AEDs are substrates of P-glycoprotein (Pgp; MDR1; ABCB1), whereas information about the potential role of breast cancer resistance protein (BCRP; ABCG2) is scanty. We used a highly sensitive in vitro assay (concentration equilibrium transport assay; CETA) with MDCKII cells transduced with murine Bcrp1 or human BCRP to evaluate whether AEDs are substrates of this major efflux transporter. Six of 7 AEDs examined, namely phenytoin, phenobarbital, carbamazepine, levetiracetam, topiramate, and valproate, were not transported by Bcrp at therapeutic concentrations, whereas lamotrigine exhibited a marked asymmetric, Bcrp-mediated transport in the CETA, which could be almost completely inhibited with the Bcrp inhibitor Ko143.
3.Efflux transport of chrysin and apigenin sulfates in HEK293 cells overexpressing SULT1A3: The role of multidrug resistance-associated protein 4 (MRP4/ABCC4).
Li W1, Sun H1, Zhang X1, Wang H1, Wu B2. Biochem Pharmacol. 2015 Nov 1;98(1):203-14. doi: 10.1016/j.bcp.2015.08.090. Epub 2015 Aug 17.
Efflux transport is a critical determinant to the pharmacokinetics of sulfate conjugates. Here we aimed to establish SULT1A3 stably transfected HEK293 cells, and to determine the contributions of BCRP and MRP transporters to excretion of chrysin and apigenin sulfates. The cDNA of SULT1A3 was stably introduced into HEK293 cells using a lentiviral vector, generating a sulfonation active cell line (i.e., SULT293 cells). Identification of sulfate transporters was achieved through chemical inhibition (using chemical inhibitors) and biological inhibition (using short-hairpin RNAs (shRNAs)) methods. Sulfated metabolites were rapidly generated and excreted upon incubation of SULT293 cells with chrysin and apigenin. Ko143 (a selective BCRP inhibitor) did not show inhibitory effects on sulfate disposition, whereas the pan-MRP inhibitor MK-571 caused significant reductions (38.5-64.3%, p<0.001) in sulfate excretion and marked elevations (160-243%, p<0.
4.P-Glycoprotein (ABCB1) limits the brain distribution of YQA-14, a novel dopamine D3 receptor antagonist.
Liu F1, Wang X, Li Z, Li J, Zhuang X, Zhang Z. Chem Pharm Bull (Tokyo). 2015;63(7):512-8. doi: 10.1248/cpb.c15-00089.
YQA-14 is a promising agent for treating addiction to cocaine and opioids. However, previous studies have showed there is marked contrast between the relatively small differences in pharmacological action in vivo and the large differences in their respective receptor binding properties in vitro. We hypothesized that the conflict between the in vivo and in vitro outcomes was attributable to poor brain exposure to YQA-14 caused by drug efflux transporters. To address this issue, we investigated the directional flux of YQA-14 across Caco-2 cells at 37°C or 4°C and the bidirectional transport in the presence and absence of transporter chemical inhibitors. These phenomena were further investigated by an in vivo determination of the brain and blood pharmacokinetics (PK) profile of YQA-14 following intraperitoneal administration with and without inhibitor. The efflux ratio of YQA-14 on Caco-2 cell monolayers was 2.39 and the efflux was temperature-dependent.