A membrane vesicle-based assay to enable prediction of human biliary excretion

Abstract

1. Prediction of biliary excretion is a challenge due to the lack of in vitro assays. Our laboratory previously demonstrated a highly significant correlation between in vitro IC₅₀ values against mrp2 using rat canalicular liver plasma membrane vesicles and in vivo biliary excretion (Colombo et al., 2012). This study explores the possibility of predicting in vivo biliary excretion in human using membrane vesicles prepared from MDCKII cells transfected with human ABCC2.

2. In vitro MRP2 activity was determined by measuring the ATP-dependent uptake of 5(6)-carboxy-2′,7′-dichlorofluorescein (CDCF) in inside-out membrane vesicles isolated from MDCK-ABCC2 cells. CDCF uptake was time- and concentration-dependent (K_m of 4.0?±?1.2?µM and a V_max of 7.8?±?0.9?pmol/mg/min) and inhibited by benzbromarone and MK-571 with IC₅₀ values of 1.2 and 7.6?µM, respectively.

3. A significant linear correlation (r^2?=?0.790) between the in vitro IC₅₀ values from the described MRP2 assay and in vivo biliary excretion in humans was observed using 11 well-documented drugs covering low to high biliary excretions.

4. This study demonstrates, for the first time, that inhibition of CDCF uptake in MDCKII-ABCC2 vesicles not only provides a screening assay to assess MRP2 drug–drug interaction potential, but is also predictive of human MRP2-mediated biliary excretion.     

Interaction of sirolimus and everolimus with hepatic and intestinal organic anion-transporting polypeptide transporters

1. The goal of this study was to assess the interaction of the mTOR inhibitors (ImTORs) sirolimus and everolimus with the human organic anion-transporting polypeptides (OATPs) expressed in hepatocytes and enterocytes by conducting uptake experiments using (i) transfected HEK293T cells, (ii) the hepatocyte-like HepaRG cell line and (iii) the enterocyte-like Caco-2 cell line.

2. Sirolimus and everolimus inhibited in a dose-dependent manner the uptake of [³H]-estrone sulphate by OATP1A2 and OATP1B1 and that of mycophenolic acid 7-O-glucuronide (MPAG) by OATP1B3. ImTOR apparent 50% inhibitory concentrations (IC₅₀) for OATPs were 11.9 µM (OATP1A2), 9.8 µM (OATP1B1) and 1.3 µM (OATP1B3) for sirolimus and 4.2 µM (OATP1A2), 4.1 µM (OATP1B1) and 4.3 µM (OATP1B3) for everolimus.

3. No transport of sirolimus or everolimus by OATP1A2, OATP1B1 or OATP1B3 was observed in HEK-transfected cells and the OAT/OATP/MRP chemical inhibitor probenecid did not significantly decrease the uptake of sirolimus and everolimus in HepaRG and Caco-2 cells, but tended to increase their intracellular accumulation presumably through efflux inhibition.

4. In conclusion, our data suggest that the major OATP transporters expressed in the liver and the intestine do not contribute to the pharmacokinetics of sirolimus and everolimus. However, ImTORs are inhibitors of these transporters.

     

Baicalin,an emerging multi-therapeutic agent: pharmacodynamics,pharmacokinetics, and considerations from drug development perspectives

1. Baicalin was extensively researched for utility in a number of therapeutic areas owing to its anti-inflammatory, anti-oxidant, anti-bacterial, and anti-cancer properties.

2. A number of preclinical studies, in vitro work, and mechanistic studies were performed to understand the absorption, distribution, metabolism, and excretion profiles of baicalin.

3. The absorption of baicalin involved several complexities: the restriction to two distant sites; the conversion of baicalin to baicalein; the possible role of transporter(s); and enhanced absorption due to breakdown of conjugates by beta-glucuronidase.

4. Limited distribution data suggest that baicalin reached several sites such as the brain, eye lens, thymus, etc. Hepatobiliary recycling also served as a distribution phase for sustained delivery of baicalin.

5. Metabolism data suggest the rapid conversion of baicalin to baicalein, which was extensively subjected to Phase 2 metabolism, conjugates baicalein glucuronide/sulfate have been identified.

6. Limited excretion data suggest involvement of renal and faecal routes—glucuronide and sulfate conjugates were excreted in urine and faeces (via biliary excretion).

7. The published data on baicalin suggest imminent challenges for developing baicalin and/or during co-administration with other agents. These challenges are absorption related (transporter or changes in the microenvironment), metabolism related (CYP2B6 induction and/or CYP2E1 inhibition), and excretion/efflux related (competitive biliary pathway and/or OATP1B1 transport).

     

Assessment of the in vitro cytochrome P450 (CYP) inhibition potential of ZYTP1, a novel poly (ADP-ribose) polymerase inhibitor

Abstract

1. ZYTP1 is a novel Poly (ADP-ribose) polymerase protein inhibitor being developed for cancer indications.

2. The focus of the work was to determine if ZYTP1 had a perpetrator role in the in vitro inhibition of cytochrome P450 (CYP) enzymes to aid dosing decisions during the clinical development of ZYTP1.

3. ZYTP1 IC₅₀ for CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4/5 was determined using human liver microsomes and LC-MS/MS detection. CYP3A4/5 IC₅₀ of depropylated metabolite of ZYTP1 was also determined. Time dependent inhibition of CYP3A4/5 by ZYTP1 was also assessed using substrates, testosterone and midazolam.

4. The mean IC₅₀ values of ZYTP1 were >100 µM for CYP1A2, 2B6 and 2D6, while 56.1, 24.5, 39.5 and 23.3–58.7 µM for CYP2C8, 2C9, 2C19 and 3A4/5, respectively. The CYP3A4/5 IC₅₀ of depropylated metabolite was 11.95–24.51 µM. Time dependent CYP3A4/5 inhibition was noted for testosterone and midazolam with IC₅₀ shift of 10.9- and 39.9-fold, respectively. With midazolam, the kinact and KI values of ZYTP1 were 0.075?min^?1 and 4.47 µM for the CYP3A4/5 time dependent inhibition, respectively.

5. Because of potent inhibition of CYP3A4/5, drugs that undergo metabolism via CYP3A4/5 pathway should be avoided during ZYTP1 therapy.

     

Validation of membrane vesicle-based breast cancer resistance protein and multidrug resistance protein 2 assays to assess drug transport and the potential for drug–drug interaction to support regulatory submissions

1. Breast cancer resistance protein (BCRP) and multidrug resistance protein 2 (MRP2) can play a role in the absorption, distribution, metabolism, and excretion of drugs, impacting on the potential for drug–drug interactions. This study has characterized insect cell– and mammalian cell–derived ABC-transporter–expressing membrane vesicle test systems and validated methodologies for evaluation of candidate drugs as substrates or inhibitors of BCRP or MRP2.

2. Concentration-dependent uptake of BCRP ([³H]oestrone 3-sulfate, [³H]methotrexate, [³H]rosuvastatin) and MRP2 ([³H]oestradiol 17β-glucuronide, [³H]pravastatin, carboxydichlorofluorescein) substrates, and inhibitory potencies (IC₅₀) of BCRP (sulfasalazine, novobiocin, fumitremorgin C) and MRP2 (benzbromarone, MK-571, terfenadine) inhibitors were determined.

3. The apparent K_m for probes [³H]oestrone 3-sulfate and [³H]oestradiol 17β-glucuronide was determined in insect cell vesicles to be 7.4?±?1.7 and 105?±?8.3?µM, respectively. All other substrates exhibited significant uptake ratios. Positive control inhibitors sulfasalazine and benzbromarone gave IC₅₀ values of 0.74?±?0.18 and 36?±?6.1 µM, respectively. All other inhibitors exhibited concentration-dependent inhibition. There was no significant difference in parameters generated between test systems.

4. On the basis of the validation results, acceptance criteria to identify substrates/inhibitors of BCRP and MRP2 were determined for insect cell vesicles. The approach builds on earlier validations to support drug registration and extends from those cell-based systems to encompass assay formats using membrane vesicles.

     

Sitagliptin attenuates metformin-mediated AMPK phosphorylation through inhibition of organic cation transporters

1. To assess potential interactions between sitagliptin and metformin, we sought to characterize the in vitro inhibitory potency of sitagliptin on the uptake of MPP⁺ and metformin, representative substrates for OCTs, and to evaluate the pharmacological pathways that may be affected by the combination of metformin and sitagliptin.

2. Among the OATs and OCTs screened, OAT3-mediated salicylate uptake and OCT1- and OCT2-mediated MPP⁺ uptake were inhibited by sitagliptin. The K_i values of sitagliptin for OCT1- and OCT2-mediated metformin uptake were 34.9 and 40.8?μM, respectively.

3. As OCT1 is the gate protein for metformin action in the liver, we investigated whether sitagliptin-mediated OCT1 inhibition affected metformin-induced activation of AMPK signalling. Treatment with sitagliptin in MDCK-OCT1 and HepG2 cells resulted in a reduced level of phosphorylated AMPK, with K_i values of 38.8 and 43.3?μM, respectively.

4. These results suggest that the inhibitory potential of sitagliptin on OCT1 may attenuate the first step of metformin action, that is, the phosphorylation of AMPK. Nevertheless, the likelihood of a drug–drug interaction between sitagliptin and metformin is believed to be remote in usual clinical setting.

     

In vitro inhibition and induction of human cytochrome P450 enzymes by mirabegron,a potent and selective β3-adrenoceptor agonist

1. The potential for mirabegron, a β₃-adrenoceptor agonist for the treatment of overactive bladder, to cause drug–drug interactions via inhibition or induction of cytochrome P450 (CYP) enzymes was investigated in vitro.

2. Mirabegron was shown to be a time-dependent inhibitor of CYP2D6 in the presence of NADPH as the IC₅₀ value in human liver microsomes decreased from 13 to 4.3 μM after 30-min pre-incubation. Further evaluation indicated that mirabegron may act partly as an irreversible or quasi-irreversible metabolism-dependent inhibitor of CYP2D6. Therefore, the potential of mirabegron to inhibit the metabolism of CYP2D6 substrates in vivo cannot be excluded. Mirabegron was predicted not to cause clinically significant metabolic drug–drug interactions via inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2E1, or CYP3A4/5 because the IC₅₀ values for these enzymes both with and without pre-incubation were >100 μM (370 times maximum human plasma concentration [C_max]).

3. Whereas positive controls (100 µM omeprazole and 10 µM rifampin) caused the anticipated CYP induction, the highest concentration of mirabegron (10 µM; 37 times plasma C_max) had minimal effect on CYP1A2 and CYP3A4/5 activity, and CYP1A2 and CYP3A4 mRNA levels in freshly isolated human hepatocytes, suggesting that mirabegron is not an inducer of these enzymes.

     

Naturally occurring flavonoids as inhibitors of purified cytosolic glutathione S-transferase

1. Flavonoids are known to modulate catalytic activity and expression of various enzymes. Glutathione S-transferases (GSTs) are the important biotransformation enzymes defending cells against potentially toxic xenobiotics. Therefore, the modulation of GST activity may influence detoxification of xenobiotics. The aim of this study was to evaluate the in vitro inhibitory activity of several dietary flavonoids towards purified equine liver cytosolic GST.

2. Pure GST was incubated in the presence or absence of flavonoids (10 nM–100 µM), its activity was assayed using 1-chloro-2,4-dinitrobenzene (CDNB) as a substrate, and half maximal inhibitory concentrations (IC₅₀) were determined. The obtained results were confirmed by GST activity staining of native polyacrylamide gel electrophoresis (PAGE) gels. For the most potent inhibitor, the inhibition kinetics study was performed.

3. From 24 flavonoids tested, the most potent GST inhibitor was gallocatechin gallate (IC₅₀ = 1.26 µM). The inhibition kinetics of this compound followed noncompetitive mechanism versus both glutathione (K_i = 35.9 µM) and CDNB (K_i = 34.1 µM).

4. The inhibitory potency of different flavonoids for GST activity depended mainly on the pattern of hydroxylation and number of hydroxyl groups in the ring B. Especially, pyrogallol-type catechins with 3-OH group esterified with gallic acid showed strong potential to inhibit GST in vitro.

     

The evolution of the OATP hepatic uptake transport protein family in DMPK sciences: from obscure liver transporters to key determinants of hepatobiliary clearance

1. Over the last two decades the impact on drug pharmacokinetics of the organic anion transporting polypeptides (OATPs: OATP-1B1, 1B3 and 2B1), expressed on the sinusoidal membrane of the hepatocyte, has been increasingly recognized.

2. OATP-mediated uptake into the hepatocyte coupled with subsequent excretion into bile via efflux proteins, such as MRP2, is often referred to as hepatobiliary excretion.

3. OATP transporter proteins can impact some drugs in several ways including pharmacokinetic variability, pharmacodynamic response and drug-drug interactions (DDIs).

4. The impact of transporter mediated hepatic clearance is illustrated with case examples, from the literature and also from the Pfizer portfolio.

5. The currently available in vitro techniques to study the hepatic transporter proteins involved in the hepatobiliary clearance of drugs are reviewed herein along with recent advances in using these in vitro data to predict the human clearance of compounds recognized by hepatic uptake transporters.

     

Renal elimination of a novel and potent αvβ3 integrin antagonist in animals

1. Compound A (3-{2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]napthyridin-2-yl)propyl]-imidazolidin-1-yl}-3(S)-(6-methoxy-pyridin-3-yl)propionic acid), a hydrophilic zwitterion, is a potent and selective α_vβ₃ integrin antagonist currently under clinical development for the treatment of osteoporosis. The mechanism of renal excretion of compound A was investigated using a combination of in vivo and in vitro approaches.

2. In rats, renal excretion of compound A involved tubular secretion; ratios between renal clearance, corrected for unbound fraction in plasma (CL_r,u) and glomerular filtration rate (GFR) were greater than unity (2–5). The tubular secretion of compound A was saturable at high plasma levels (>?26?μM), and was inhibited significantly, although modestly (about twofold) by relatively high plasma concentrations of the organic anion PAH (160?µM) and the cation cimetidine (about 400?μM), but not by the P-gp inhibitor quinidine (about 50?μM). However, compound A (about 100?μM) had a minimal effect on CL_r/GFRs for cimetidine and PAH.

3. In rhesus monkeys, renal elimination of compound A also involved tubular secretion, with a CL_r,u/GFR ratio of about 30. The renal secretion of compound A was not affected by either cimetidine (about 120?μM) or PAH (about 80?μM). Similarly, compound A (about 40?μM) had a minimal effect on the renal tubular secretion of both cimetidine and PAH.

4. At the doses studied, neither rat nor monkey plasma protein binding of compound A, cimetidine or PAH was affected in the presence of each other.

5. In vitro transport studies showed that compound A was not a substrate for P-gp in the Caco-2, human MDR1 and mouse mdr1a transfected LLC-PK1 cell lines. In an uptake study using rOAT1 and rOAT3 transfected HEK cell lines, compound A was shown to be a substrate for rat OAT3 (K_m?=?15?μM), but not rat OAT1.

6. The results suggest that the tubular secretion of compound A is not mediated by P-gp, but rather is mediated, at least in part, via the organic anion transporter OAT3, the renal transporter shown to be capable of transporting both the organic anion PAH and the organic cation cimetidine. Although there is a possibility for pharmacokinetic interactions between compound A and substrates or inhibitors of OAT3, at the renal excretion level, the magnitude of interaction would likely be modest in humans at clinically relevant doses.

     

In vitro metabolic interactions between black cohosh (Cimicifuga racemosa) and tamoxifen via inhibition of cytochromes P450 2D6 and 3A4

1. Women who experience hot flashes as a side effect of tamoxifen (TAM) therapy often try botanical remedies such as black cohosh to alleviate these symptoms. Since pharmacological activity of TAM is dependent on the metabolic conversion into active metabolites by the action of cytochromes P450 2D6 (CYP2D6) and 3A4, the objective of this study was to evaluate whether black cohosh extracts can inhibit formation of active TAM metabolites and possibly reduce its clinical efficacy.

2. At 50 μg/mL, a 75% ethanolic extract of black cohosh inhibited formation of 4-hydroxy- TAM by 66.3%, N-desmethyl TAM by 74.6% and α-hydroxy TAM by 80.3%. In addition, using midazolam and dextromethorphan as probe substrates, this extract inhibited CYP3A4 and CYP2D6 with IC₅₀ values of 16.5 and 50.1 μg/mL, respectively.

3. Eight triterpene glycosides were identified as competitive CYP3A4 inhibitors with IC₅₀ values ranging from 2.3–5.1 µM, while the alkaloids protopine and allocryptopine were identified as competitive CYP2D6 inhibitors with K_i values of 78 and 122?nM, respectively.

4. The results of this study suggests that co-administration of black cohosh with TAM might interfere with the clinical efficacy of this drug. However, additional clinical studies are needed to determine the clinical significance of these in vitro results.

     

The in vitro metabolism of bupropion revisited: concentration dependent involvement of cytochrome P450 2C19

1. The involvement of cytochrome P450 2B6 (CYP2B6) to the in vitro and in vivo metabolism of bupropion has been well studied. In these investigations we performed a detailed in vitro phenotyping study to characterize isoforms other than CYP2B6.

2. A total of nine metabolites were identified (M1–M9) in the incubations with cDNA-expressed P450s (rhCYP) and human liver microsomes (HLM).

3. Incubations in rhCYP identified CYP2B6 as the isoform responsible for the formation of hydroxybupropion (M3). CYP2C19 was involved in bupropion metabolism primarily through alternate hydroxylation pathways (M4–M6) with higher activity at lower substrate concentrations, near 1 µM.

4. The results from HLM inhibition studies using CYP2B6 and CYP2C19 inhibitory antibodies indicated that CYP2B6 contributed to approximately 90% of M3 formation, and CYP2C19 contributed to approximately 70–90% of M4, M5, and M6 formation.

5. Studies using single donor HLM with varying degrees of CYP2B6 and CYP2C19 activities showed a good relationship between M3 formation and CYP2B6 activity and M4/M5 formation and CYP2C19 activity.

6. These results confirmed the principle role of CYP2B6 in hydroxybupropion formation, as a selective CYP2B6 probe. In addition, the new findings revealed that CYP2C19 also contributes to bupropion metabolism through alternate hydroxylation pathways.

     

Interactions between the chemotherapeutic agent eribulin mesylate (E7389) and P-glycoprotein in CF-1 abcb1a-deficient mice and Caco-2 cells

1. Eribulin is a new anticancer agent currently in Phase III clinical trials for the treatment of metastatic breast cancer. In the current studies, we have investigated the effects of P-glycoprotein (P-gp) on the in vivo disposition of eribulin using CF-1 abcb1a-deficient mice, and the influence of eribulin on P-gp-mediated efflux of digoxin in Caco-2 cells.

2. Eribulin was administered intravenously and orally in both CF-1 wild-type and CF-1 abcb1a-deficient mice. P-gp-mediated efflux of digoxin in Caco-2 cell monolayers was measured in the presence of eribulin.

3. The plasma exposure to eribulin was higher in CF-1 abcb1a-deficient mice than that in CF-1 wild-type mice after intravenous (IV) and oral (PO) administrations. The oral bioavailability of eribulin was 62.3% in CF-1 abcb1a-deficient mice compared with 7.6% in wild-type mice. The brain penetration of eribulin in CF-1 abcb1a-deficient mice was 30-fold greater than that in wild-type mice. Eribulin decreased the efflux ratio of digoxin in a concentration-dependent manner, with the result of IC₅₀ greater than 10 µM. The [I]/IC₅₀ of eribulin was estimated to be <0.05.

4. P-gp is likely to limit the oral absorption and brain penetration of eribulin in CF-1 wild-type mice. Eribulin inhibited the efflux of digoxin with IC₅₀ greater than 10 µM in Caco-2 cells. These results suggest that eribulin, given intravenously at the clinically relevant concentrations, may not alter P-gp-mediated disposition of concurrently administered drugs.

     

In vitro assessment of metabolic drug–drug interaction potential of AZD2624, neurokinin-3 receptor antagonist,through cytochrome P450 enzyme identification,inhibition, and induction studies

1. AZD2624 was pharmacologically characterized as a NK3 receptor antagonist intended for treatment of schizophrenia. The metabolic drug–drug interaction potential of AZD2624 was evaluated in in vitro studies.

2. CYP3A4 and CYP3A5 appeared to be the primary enzymes mediating the formation of pharmacologically active ketone metabolite (M1), whereas CYP3A4, CYP3A5, and CYP2C9 appeared to be the enzymes responsible for the formation of the hydroxylated metabolite (M2). The apparent K_m values were 1.5 and 6.3 µM for the formation of M1 and M2 in human liver microsomes, respectively.

3. AZD2624 exhibited an inhibitory effect on microsomal CYP3A4/5 activities with apparent IC₅₀ values of 7.1 and 19.8 µM for midazolam and testosterone assays, respectively. No time-dependent inactivation of CYP3A4/5 activity (midazolam 1′-hydroxylation) by AZD2624 was observed. AZD2624 demonstrated weak to no inhibition of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP2D6.

4. AZD2624 was not an inducer of CYP1A2 or CYP2B6. Although AZD2624-induced CYP3A4 activity in hepatocytes, the potential of AZD2624 to cause inductive drug interactions of this enzyme was low at relevant exposure concentration.

5. Together with targeted low efficacious concentration, the results of this study demonstrated AZD2624 has a relatively low metabolic drug–drug interaction potential towards co-administered drugs. However, metabolism of AZD2624 might be inhibited when co-administrated with potent CYP3A4/5 inhibitors.

     

Use of primary rat hepatocytes in the gel entrapment culture to predict in vivo biliary excretion

1. In vitro models have been widely used in characterizing the hepatobiliary elimination of compounds. However, the application of in vitro models is often limited by their imperfect simulation of in vivo situations. The current paper aims to introduce the gel entrapment culture of rat hepatocytes as an alternative method for measuring hepatobiliary transport, with the sandwich culture of rat hepatocytes set as the control.

2. First, the culture conditions of the gel-entrapped hepatocytes were modified to enhance hepatic transport function. When cultured under optimal conditions, i.e. the collagen concentration was set to 0.6?mg/mL and the regular Williams’ E medium was supplemented with epidermal growth factor, the hepatocytes maintained much higher hepatic transporter gene expression levels and transport activities than that in regular gel entrapment and sandwich culture.

3. Compared with the actual values in rats, the predicted intrinsic biliary clearance (CL_{bile,int,predicted}) of the 10 model compounds in the optimized gel entrapment culture showed a high correlation coefficient squared (R²) of 0.94, with the majority falling within the two-fold error range of the in vivo values, which was much better than the comparable sandwich culture.

4. All of these results indicate that the optimized gel entrapment culture of hepatocytes is a suitable approach for estimating in vivo biliary excretion.

     

Saturable sinusoidal uptake is rate-determining process in hepatic elimination of docetaxel in rats

1. Identifying kinetic determinants of hepatic elimination of drugs would be crucial for better understanding its pharmacokinetics and predicting drug interactions. Present study investigated the kinetics of sinusoidal uptake of docetaxel and its impact on the overall hepatic elimination of docetaxel in rats.

2. The non-renal clearance (CL_NR; hepatic elimination) of docetaxel were significantly reduced by co-administration of intravenous rifampicin, a potent inhibitor of organic anion transporting peptides (OATPs; Oatps), at a dose of 20?mg/kg. Docetaxel uptake into isolated rat hepatocytes was found to be temperature/concentration/energy-dependent, saturable, and reduced by Oatps inhibitors (rifampicin and bromosulfophthalein). Moreover, docetaxel uptake into perfused rat liver was significantly reduced in the presence of 10-µM rifampicin. However, docetaxel metabolism in rat hepatic microsome was not affected by rifampicin at less than 50 µM.

3. Based on the comparison of intrinsic clearances related to hepatic clearance, it can be suggested that sinusoidal uptake could be the rate-determining process in the overall hepatic elimination of docetaxel in rats.

     

Pharmacokinetics of liquiritigenin and its two glucuronides,M1 and M2, in rats with acute hepatitis induced by d-galactosamine/lipopolysaccharide or CCl4

1. Cytoprotective effects of liquiritigenin (LQ) against liver injuries have been reported, but its pharmacokinetics has not been studied in acute hepatitis. Thus, pharmacokinetics of LQ and its two conjugated glucuronide metabolites: 4′-O-glucuronide (M1) and 7-O-glucuronide (M2), in rats with acute hepatitis induced by d-galactosamine/lipopolysaccharide (GalN/LPS) rats or carbon tetrachloride-treated (CCl₄-treated) rats were evaluated.

2. LQ was administered intravenously (20?mg kg^?1) and orally (50?mg kg^?1) to control GalN/LPS and CCl₄-treated rats. Expression of uridine 5′-diphospho-glucuronosyltransferases 1A (UGT1A) and in vitro metabolism of LQ in hepatic and intestinal microsomes were also measured.

3. After intravenous administration of LQ, area under the plasma concentration-time curve (AUC) of LQ in GalN/LPS rats was significantly smaller than that in controls due to faster non-renal clearance, as a result of its greater free fraction in plasma and faster hepatic blood flow rate than the controls. In CCl₄-treated rats, the AUC_{M1, 0?8 h}/AUC_LQ and AUC_{M2, 0?8 h}/AUC_LQ ratios were significantly greater than the controls due to decrease in biliary excretion of M1 and M2. However, no significant pharmacokinetic changes were observed in both acute hepatitis rats after oral administration due to comparable intestinal metabolism of LQ.

4. Modification of oral dosage regimen of LQ may not be necessary in patients with acute hepatitis; but human studies are required.

     

Reversal of P-glycoprotein-mediated multidrug resistance in human hepatoma cells by hedyotiscone A,a compound isolated from Hedyotis corymbosa

1. Multidrug resistance is a major problem in hepatocellular carcinoma. Hedyotiscone A, a compound isolated from Chinese herbal medicine Hedyotis corymbosa (HC, family Rubiaceae), was used as the chemical marker to distinguish between HC and an anticancer herb Hedyotis diffusa (HD) in our previous study.

2. The present study aimed to investigate whether HA exhibited antiproliferative activities in multidrug-resistant hepatocellular carcinoma cells R-HepG2 and the parental cells HepG2 using MTT assay and [³H]-thymidine incorporation assay.

3. Our results showed that HA could significantly inhibit cell proliferation in R-HepG2 and HepG2 (IC₅₀?=?43.7 and 56.3 µg/mL, respectively), but not in normal human liver cells WRL-68 (IC₅₀ > 100 µg/mL) cells, suggesting its selective cytotoxic effects. Besides, HA induced apoptosis in R-HepG2 cells, as confirmed by annexin-V & propidium iodide staining, and DNA fragmentation assay. The caspase cascade was activated as shown by a significant increase of cleaved caspases-3, -7 and -9 in HA-treated R-HepG2 cells. The activities and protein expression of P-glycoprotein as well as mRNA expression of MDR1 were also decreased in HA-treated R-HepG2 cells.

4. Our study demonstrated for the first time the antiproliferative activities of hedyotiscone A in multidrug-resistant R-HepG2 cells. The findings revealed the potential of this compound in treating multidrug-resistant tumor.

     

Chan-Yu-Bao-Yuan-Tang induces apoptosis in NSCLC and SCLC cell lines via a mitochondria-mediated pathway

1. Previous clinical studies have shown efficacy and safety of the traditional Chinese medicinal herb extract Chan-Yu-Bao-Yuan-Tang (CYBYT) in lung cancer patients.

2. The effects of CYBYT on proliferation and apoptosis in the non-small cell lung cancer cell line NCI-H460 and the small cell lung cancer cell line NCI-H446 were investigated in vitro.

3. CYBYT significantly induced antiproliferative effects of NCI-H460 and NCI-H446 cells in a concentration- and time-dependent manner. The IC₅₀ values in NCI-H460 cells were 94.37 µg/mL (24?h) and 20.89 µg/mL (48?h), whereas in NCI-H446 cells IC₅₀ values were 214.72 µg/mL (24?h) and 114.58 µg/mL (48?h). Annexin V–FITC/PI staining showed CYBYT could significantly induce apoptosis in NCI-H460 and NCI-H446 cells, and the total apoptosis rates were positively correlated with the concentration and time of CYBYT treatment. Furthermore, treatment with the broad-spectrum caspase inhibitor (z-VAD-fmk) effectively protected NCI-H460 and NCI-H446 cells against CYBYT-triggered apoptosis. The apoptotic processes involved were a marked decrease in antiapoptotic protein Bcl-2 and an increase in proapoptotic protein Bax. The release of mitochondrial cytochrome c into the cytosol was also observed, which, in turn, resulted in the activation of caspase-9 and caspase-3.

4. CYBYT exerts antiproliferative and growth inhibition effects on NCI-H460 and NCI-H446 cells through the mitochondrial caspase-dependent cell death pathway.

     

Decreased urinary secretion of belotecan in folic acid-induced acute renal failure rats due to down-regulation of Oat1 and Bcrp

1. The effects of folic acid-induced acute renal failure on the renal excretion of belotecan were investigated in rats after intravenous administration.

2. Both glomeruli and renal tubules were seriously damaged by folic acid-induced acute renal failure. The renal excretion clearance, CL_r, of belotecan was significantly decreased by folic acid-induced acute renal failure. Furthermore, glomerular filtration rate and secretion clearance of the drug were dramatically decreased by folic acid-induced acute renal failure.

3. In vivo renal uptake of belotecan was inhibited by p-aminohippurate, whereas renal excretion was inhibited by GF120918, but not by verapamil and bromosulphalein. This indicates that Oat1/3 and Bcrp are involved in the renal uptake and urinary excretion of belotecan, respectively.

4. Both mRNA and protein levels of Oat1, Oat3 and Bcrp were significantly decreased in folic acid-induced acute renal failure rats. Based on the finding that belotecan is a substrate of OAT1 but not of OAT3, the decrease in CL_r of belotecan in folic acid-induced acute renal failure could, therefore, mainly be attributed to the down-regulation of Oat1 and Bcrp, in addition to the decrease in glomerular filtration rate.