Mouse P-glycoprotein Research Articles

The effect of low- and high-dose levothyroxine on the expression, protein level, and function of P-glycoprotein in mice

The study was investigated the effect of different doses of levothyroxine on the mRNA expression, protein level and function of Pgp. Mice were divided into 6 groups as control, low dose levothyroxine, high dose levothyroxine, fexofenadine, low dose levothyroxine+fexofenadine and high dose levothyroxine+fexofenadine. Mice received levothyroxine at doses of 8 and 80 µg/kg daily for 21 days. Fexofenadine was administered at dose of 40 mg/kg at the 24 h following the last administration of levothyroxine. The mRNA levels and protein level of Pgp in liver and small intestine were determined by RT-PCR and western blot analysis, respectively. Plasma concentrations of fexofenadine were determined using HPLC. Levothyroxine at low and high doses caused an insignificant increase intestinal mRNA expression of mdr1a, while high dose levothyroxine+fexofenadine caused a significant increase. Levothyroxine caused a dose-dependent decrease in intestinal mRNA expression of mdr1b. In liver, levothyroxine caused a dose-dependent increase in the mRNA expression of mdr1a. Fexofenadine significantly reduced the effect of levothyroxine on mRNA expression of mdr1a in liver. Levothyroxine increased the protein level of Pgp in liver and decrease in intestines. Low dose levothyroxine significantly increased the plasma concentration of fexofenadine. The effects of levothyroxine on the mRNA expression of mdr1a and b in small intestine and liver and protein level of Pgp varied depending on the dose, tissue type, and fexofenadine administration.

Maternal and Fetal Exposure to (-)-Δ9-tetrahydrocannabinol and Its Major Metabolites in Pregnant Mice Is Differentially Impacted by P-glycoprotein and Breast Cancer Resistance Protein.

(-)-Δ9-tetrahydrocannabinol (THC) is the primary pharmacological active constituent of cannabis. 11-hydroxy-THC (11-OH-THC) and 11-nor-9-carboxy-THC (THC-COOH) are respectively the active and nonactive circulating metabolites of THC in humans. While previous animal studies reported that THC could be a substrate of mouse P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), we have shown, in vitro, that only THC-COOH is a weak substrate of human BCRP, but not of P-gp. To confirm these findings and to investigate the role of P-gp and/or Bcrp in the maternal-fetal disposition of THC and its metabolites, we administrated 3 mg/kg of THC retro-orbitally to FVB wild-type (WT), P-gp -/-, Bcrp -/-, or P-gp-/- /Bcrp-/- pregnant mice on gestation day 18 and estimated the area under the concentration-time curve (AUC) of the cannabinoids in the maternal plasma, maternal brain, placenta, and fetus, as well as the tissue/maternal plasma AUC geometric mean ratios (GMRs) using a pooled data bootstrap approach. We found that the dose-normalized maternal plasma AUCs of THC in P-gp-/- and P-gp-/- /Bcrp-/- mice, and the placenta-to-maternal plasma AUC GMR of THC in Bcrp-/- mice were 279%, 271%, and 167% of those in WT mice, respectively. Surprisingly, the tissue-to-maternal plasma AUC GMRs of THC and its major metabolites in the maternal brain, placenta, or fetus in P-gp -/-, Bcrp -/- or P-gp-/- /Bcrp-/- mice were 28-78% of those in WT mice. This study revealed that P-gp and Bcrp do not play a role in limiting maternal brain and fetal exposure to THC and its major metabolites in pregnant mice. SIGNIFICANCE STATEMENT: This study systematically investigated whether P-gp and/or Bcrp in pregnant mice can alter the disposition of THC, 11-OH-THC, and THC-COOH. Surprisingly, except for Bcrp, which limits placental (but not fetal) exposure to THC, we found that P-gp-/- , Bcrp-/- , and/or P-gp-/- /Bcrp-/- significantly decreased exposure to THC and/or its metabolites in maternal brain, placenta, or fetus. The mechanistic basis for this decrease is unclear and needs further investigation. If replicated in humans, P-gp- or BCRP-based drug-cannabinoid interactions are not of concern.

Characterization of the Lipidome and Biophysical Properties of Membranes from High Five Insect Cells Expressing Mouse P-Glycoprotein.

The lipid composition of biomembranes influences the properties of the lipid bilayer and that of the proteins. In this study, the lipidome and the lipid/protein ratio of membranes from High Five™ insect cells overexpressing mouse P-glycoprotein was characterized. This provides a better understanding of the lipid environment in which P-glycoprotein is embedded, and thus of its functional and structural properties. The relative abundance of the distinct phospholipid classes and their acyl chain composition was characterized. A mass ratio of 0.57 ± 0.11 phospholipids to protein was obtained. Phosphatidylethanolamines are the most abundant phospholipids, followed by phosphatidylcholines. Membranes are also enriched in negatively charged lipids (phosphatidylserines, phosphatidylinositols and phosphatidylglycerols), and contain small amounts of sphingomyelins, ceramides and monoglycosilatedceramides. The most abundant acyl chains are monounsaturated, with significant amounts of saturated chains. The characterization of the phospholipids by HPLC-MS allowed identification of the combination of acyl chains, with palmitoyl-oleoyl being the most representative for all major phospholipid classes except for phosphatidylserines, which are mostly saturated. A mixture of POPE:POPC:POPS in the ratio 45:35:20 is proposed for the preparation of simple representative model membranes. The adequacy of the model membranes was further evaluated by characterizing their surface potential and fluidity.

The effects of anthracycline drugs on the conformational distribution of mouse P-glycoprotein explains their transport rate differences

P-glycoprotein (Pgp) is an ATP-dependent efflux transporter and plays a major role in anti-cancer drug resistance by pumping a chemically diverse range of cytotoxic drugs from cancerous tumors. Despite numerous studies with the transporter, the molecular features that drive anti-cancer drug efflux are not well understood. Even subtle differences in the anti-cancer drug molecular structure can lead to dramatic differences in their transport rates. To unmask these structural differences, this study focused on two closely-related anthracycline drugs, daunorubicin (DNR), and doxorubicin (DOX), with mouse Pgp. While only differing by a single hydroxyl functional group, DNR has a 4 to 5-fold higher transport rate than DOX. They both non-competitively inhibited Pgp-mediated ATP hydrolysis below basal levels. The Km of Pgp-mediated ATP hydrolysis extracted from the kinetics curves was lower for DOX than DNR. However, the dissociation constants (KDs) for these drugs determined by fluorescence quenching were virtually identical. Acrylamide quenching of Pgp tryptophan fluorescence to probe the tertiary structure of Pgp suggested that DNR shifts Pgp to a “closed” conformation, while DOX shifts Pgp to an “intermediate” conformation. The effects of these drugs on the Pgp conformational distributions in a lipid bilayer were also examined by atomic force microscopy (AFM). Analysis of AFM images revealed that DNR and DOX cause distinct and significant shifts in the conformational distribution of Pgp. The results were combined to build a conformational distribution model for anthracycline transport by Pgp.

Allosteric Modulation of ATP Hydrolysis of the Mouse P-Glycoprotein by Substrates and Inhibitors

Allosteric Modulation of ATP Hydrolysis of the Mouse P-Glycoprotein by Substrates and Inhibitors

Interspecies comparison of putative ligand binding sites of human, rat and mouse P-glycoprotein

Prior to the clinical phases of testing, safety, efficacy and pharmacokinetic profiles of lead compounds are evaluated in animal studies. These tests are primarily performed in rodents, such as mouse and rats. In order to reduce the number of animal experiments, computational models that predict the outcome of these studies and thus aid in prioritization of preclinical candidates are heavily needed. However, although computational models for human off-target interactions with decent quality are available, they cannot easily be transferred to rodents due to lack of respective data. In this study, we assess the transferability of human P-glycoprotein activity data for development of in silico models to predict in vivo effects in rats and mouse using a structure-based approach. P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that transports xenobiotic compounds such as toxins and drugs out of cells and has a broad substrate and inhibitor specificity. Being mostly expressed at barriers, it influences the bioavailability of drugs and thus contributes also to toxicity. Comparison of the binding site interaction profiles of human, rat and mouse P-gp derived from docking studies with a set of common inhibitors suggests that the inhibitors share potentially similar binding modes. These findings encourage the use of in vitro human P-gp data for predicting in vivo effects in rodents and thus contributes to the 3Rs (Replace, Reduce and Refine) of animal experiments.

Ketamine Pharmacokinetics and Pharmacodynamics Are Altered by P-Glycoprotein and Breast Cancer Resistance Protein Efflux Transporters in Mice.

To understand the systemic impact of breast cancer resistance protein (Bcrp) and P-glycoprotein (Pgp) deletion, untargeted metabolomics was performed on cerebral spinal fluid (CSF) and plasma of wild-type (WT) and Pgp and Bcrp double-knockout (dKO) rats anesthetized with ketamine-xylazine. We unexpectedly found elevated ketamine levels in both CSF and plasma of dKO versus WT rats. Therefore, the effect of these transporters was investigated on the 1) oral and intraperitoneal serum pharmacokinetics (PK) of ketamine, using a liquid chromatography method (high-performance liquid chromatography with ultraviolet detection), and 2) the anesthetic effect of ketamine using a duration of loss-of-righting reflex (dLORR) test in WT, Bcrp knockout (KO), Pgp KO, and Pgp/Bcrp dKO mice. The PK data demonstrated a significantly increased oral bioavailability and serum exposure of ketamine in dKO > Pgp KO > Bcrp KO mice compared with WT mice. Intraperitoneal ketamine-induced dLORR was significantly longer in dKO > Pgp KO > Bcrp KO > WT mice compared with WT mice. Inhibition of Bcrp and Pgp in WT mice using the dual Pgp/Bcrp inhibitor elacridar increased the ketamine-induced dLORR compared with vehicle-treated mice. The ketamine intracellular concentration was significantly decreased in Madin-Darby canine kidney II BCRP/PGP cells compared with the parental cells. In total, these results demonstrate that ketamine appears to be a dual Pgp/Bcrp substrate whose PK and pharmacodynamics are affected by Pgp and Bcrp-mediated efflux.

Circadian control of P-glycoprotein in Hepa1-6 hepatocarcinoma tumor cells and Hepa1-6 tumor-bearing mice

Circadian control of P-glycoprotein in Hepa1-6 hepatocarcinoma tumor cells and Hepa1-6 tumor-bearing mice

A Computational Approach From Gene to Structure Analysis of the Human ABCA4 Transporter Involved in Genetic Retinal Diseases.

The aim of this article is to report the investigation of the structural features of ABCA4, a protein associated with a genetic retinal disease. A new database collecting knowledge of ABCA4 structure may facilitate predictions about the possible functional consequences of gene mutations observed in clinical practice. In order to correlate structural and functional effects of the observed mutations, the structure of mouse P-glycoprotein was used as a template for homology modeling. The obtained structural information and genetic data are the basis of our relational database (ABCA4Database). Sequence variability among all ABCA4-deposited entries was calculated and reported as Shannon entropy score at the residue level. The three-dimensional model of ABCA4 structure was used to locate the spatial distribution of the observed variable regions. Our predictions from structural in silico tools were able to accurately link the functional effects of mutations to phenotype. The development of the ABCA4Database gathers all the available genetic and structural information, yielding a global view of the molecular basis of some retinal diseases. ABCA4 modeled structure provides a molecular basis on which to analyze protein sequence mutations related to genetic retinal disease in order to predict the risk of retinal disease across all possible ABCA4 mutations. Additionally, our ABCA4 predicted structure is a good starting point for the creation of a new data analysis model, appropriate for precision medicine, in order to develop a deeper knowledge network of the disease and to improve the management of patients.

Intestinal absorption of pallidifloside D are limited by P-glycoprotein in mice

1. Pallidifloside D, a saponin glycoside constituent from the total saponins of Smilax riparia, had been proved to be very effective in hyperuricemic control. But it is poorly bioavailable after oral administration. Here, we determined the role of P-glycoprotein (P-gp) in the intestinal absorption of Pallidifloside D.2. We found that Pallidifloside D significantly stimulated P-gp ATPase activity in vitro ATPase assay with a small EC50 value of 0.46 μM.3. In the single-pass perfused mouse intestine model, the absorption of Pallidifloside D was not favored in the small intestine (duodenum, jejunum and ileum) with a P*w value of 0.35–0.78. By contrast, this compound was well-absorbed in the colon with a P*w value of 1.23. The P-gp inhibitors cyclosporine significantly enhanced Pallidifloside D absorption in all four intestinal segments (duodenum, jejunum, ileum and colon) and the fold change ranged from 5.5 to 15.3. Pharmacokinetic study revealed that cyclosporine increased the systemic exposure of Pallidifloside D by a 2.5-fold after oral administration.4. These results suggest that P-gp-mediated efflux is a limiting factor for intestinal absorption of Pallidifloside D in mice.

Structure based classification for bile salt export pump (BSEP) inhibitors using comparative structural modeling of human BSEP

The bile salt export pump (BSEP) actively transports conjugated monovalent bile acids from the hepatocytes into the bile. This facilitates the formation of micelles and promotes digestion and absorption of dietary fat. Inhibition of BSEP leads to decreased bile flow and accumulation of cytotoxic bile salts in the liver. A number of compounds have been identified to interact with BSEP, which results in drug-induced cholestasis or liver injury. Therefore, in silico approaches for flagging compounds as potential BSEP inhibitors would be of high value in the early stage of the drug discovery pipeline. Up to now, due to the lack of a high-resolution X-ray structure of BSEP, in silico based identification of BSEP inhibitors focused on ligand-based approaches. In this study, we provide a homology model for BSEP, developed using the corrected mouse P-glycoprotein structure (PDB ID: 4M1M). Subsequently, the model was used for docking-based classification of a set of 1212 compounds (405 BSEP inhibitors, 807 non-inhibitors). Using the scoring function ChemScore, a prediction accuracy of 81% on the training set and 73% on two external test sets could be obtained. In addition, the applicability domain of the models was assessed based on Euclidean distance. Further, analysis of the protein–ligand interaction fingerprints revealed certain functional group-amino acid residue interactions that could play a key role for ligand binding. Though ligand-based models, due to their high speed and accuracy, remain the method of choice for classification of BSEP inhibitors, structure-assisted docking models demonstrate reasonably good prediction accuracies while additionally providing information about putative protein–ligand interactions.

Insight into the molecular mechanism of P-glycoprotein mediated drug toxicity induced by bioflavonoids: an integrated computational approach

In this work, molecular docking, pharmacophore modeling and molecular dynamics (MD) simulation were rendered for the mouse P-glycoprotein (P-gp) (code: 4Q9H) and bioflavonoids; amorphigenin, chrysin, epigallocatechin, formononetin and rotenone including a positive control; verapamil to identify protein–ligand interaction features including binding affinities, interaction characteristics, hot-spot amino acid residues and complex stabilities. These flavonoids occupied the same binding site with high binding affinities and shared the same key residues for their binding interactions and the binding region of the flavonoids was revealed that overlapped the ATP binding region with hydrophobic and hydrophilic interactions suggesting a competitive inhibition mechanism of the compounds. Root mean square deviations (RMSDs) analysis of MD trajectories of the protein–ligand complexes and NBD2 residues, and ligands pointed out these residues were stable throughout the duration of MD simulations. Thus, the applied preliminary structure-based molecular modeling approach of interactions between NBD2 and flavonoids may be gainful to realize the intimate inhibition mechanism of P-gp at NBD2 level and on the basis of the obtained data, it can be concluded that these bioflavonoids have the potential to cause herb–drug interactions or be used as lead molecules for the inhibition of P-gp (as anti-multidrug resistance agents) via the NBD2 blocking mechanism in future.

Interactions and cooperativity between P-glycoprotein structural domains determined by thermal unfolding provides insights into its solution structure and function

Structural changes in mouse P-glycoprotein (Pgp) induced by thermal unfolding were studied by differential scanning calorimetry (DSC), circular dichroism and fluorescence spectroscopy to gain insight into the solution conformation(s) of this ABC transporter that may not be apparent from current crystal structures. DSC of reconstituted Pgp showed two thermal unfolding transitions in the absence of MgATP, suggesting that each transition involved the cooperative unfolding of two or more interacting structural domains. A low calorimetric unfolding enthalpy and minimal structural changes were observed, which are hallmarks of the thermal unfolding of α-helical membrane proteins, because generally only the extramembranous regions undergo significant unfolding. Nucleotide binding increased the unfolding temperature of both transitions to the same extent, suggesting that one nucleotide binding domain (NBD) unfolds with each transition. Combined with the results from the two isolated NBDs, we propose that each DSC transition represents the cooperative unfolding of one NBD and the two contacting intracellular loops. Further, the presence of two transitions in both apo and MgATP bound wild-type Pgp suggests the NBD-dimeric conformation is transient, and that Pgp resides predominantly in the crystallographically observed inward-facing conformation with NBDs separated, even under conditions supporting continuous MgATP hydrolysis. In contrast, DSC of the vanadate-trapped MgADP·Pgp complex and the MgATP-bound catalytically inactive mutant, E552A/E1197A, show an additional transition at much higher temperature, corresponding to the unfolding of the nucleotide-trapped NBD-dimeric outward-facing conformation. The collective results indicate a strong preference for an NBD dissociated, inward-facing conformation of Pgp.

The effect of 17α-ethynylestradiol induced intrahepatic cholestasis of pregnancy on placental P-glycoprotein in mice: Implications in the individualized transplacental digoxin treatment for fetal heart failure

IntroductionPlacental P-glycoprotein (P-gp) plays a significant role in controlling transplacental digoxin transfer rate. Investigations on P-gp regulation in placenta of women with different pregnant pathological states are of great significance to individualized transplacental digoxin treatment for fetal heart failure (FHF). This study aimed to explore the effect of 17α-ethynylestradiol induced intrahepatic cholestasis of pregnancy (ICP) on placental P-gp in mice. MethodsICP model in mice was induced by subcutaneous injection of 17α-ethynylestradiol dissolved in propylene glycol once daily from E12.5 to E16.5. Maternal plasma ALT, AST, TB, DBIL, γ-GT, LDH, ALP and TBA concentrations were measured. HE staining was applied for observation of maternal liver cells degeneration, necrosis and intrahepatic cholestasis. Placental Abcb1a/Abcb1b/HIF-1α mRNA and P-gp/HIF-1α protein expression were determined by real-time quantitative PCR and western-blot. Maternal plasma and fetal-unit digoxin concentrations were detected by a commercial kit assay. ResultsThe ICP group showed higher levels of maternal plasma ALT, AST, TB, DBIL, γ-GT, LDH, ALP and TBA concentrations, reduction in fetal survival rates, lower placental and fetal weights, and typical liver cells degeneration, necrosis and intrahepatic cholestasis. The placental Abcb1a mRNA and P-gp expression of ICP group were significantly elevated, while transplacental digoxin transfer rates were significantly decreased. Both placental HIF-1α mRNA and protein expression was significantly elevated in the ICP group, and there was a positive correlation between Abcb1a mRNA and HIF-1α mRNA. Conclusions17α-ethynylestradiol induced ICP could up-regulate placental P-gp expression and reduce transplacental digoxin transfer rate in mice, which might be partly associated with higher expression of HIF-1α.

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

Since its development, tariquidar (TQR; XR9576; N-[2-[[4-[2-(6,7-Dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethyl]phenyl]carbamoyl]-4,5-dimethoxyphenyl]quinoline-3-carboxamide) has been widely regarded as one of the more potent inhibitors of P-glycoprotein (P-gp), an efflux transporter of the ATP-binding cassette (ABC) transporter family. A third-generation inhibitor, TQR exhibits high affinity for P-gp, although it is also a substrate of another ABC transporter, breast cancer resistance protein (BCRP). Recently, several studies have questioned the mechanism by which TQR interfaces with P-gp, suggesting that TQR is a substrate for P-gp instead of a noncompetitive inhibitor. We investigated TQR and its interaction with human and mouse P-gp to determine if TQR is a substrate of P-gp in vitro. To address these questions, we used multiple in vitro transporter assays, including cytotoxicity, flow cytometry, accumulation, ATPase, and transwell assays. A newly generated BCRP cell line was used as a positive control that demonstrates TQR-mediated transport. Based on our results, we conclude that TQR is a potent inhibitor of both human and mouse P-gp and shows no signs of being a substrate at the concentrations tested. These in vitro data further support our position that the in vivo uptake of [(11)C]TQR into the brain can be explained by its high-affinity binding to P-gp and by it being a substrate of BCRP, followed by amplification of the brain signal by ionic trapping in acidic lysosomes.

Identification of a Cryptic Bacterial Promoter in Mouse (mdr1a) P-Glycoprotein cDNA.

The efflux transporter P-glycoprotein (P-gp) is an important mediator of various pharmacokinetic parameters, being expressed at numerous physiological barriers and also in multidrug-resistant cancer cells. Molecular cloning of homologous cDNAs is an important tool for the characterization of functional differences in P-gp between species. However, plasmids containing mouse mdr1a cDNA display significant genetic instability during cloning in bacteria, indicating that mdr1a cDNA may be somehow toxic to bacteria, allowing only clones containing mutations that abrogate this toxicity to survive transformation. We demonstrate here the presence of a cryptic promoter in mouse mdr1a cDNA that causes mouse P-gp expression in bacteria. This expression may account for the observed toxicity of mdr1a DNA to bacteria. Sigma 70 binding site analysis and GFP reporter plasmids were used to identify sequences in the first 321 bps of mdr1a cDNA capable of initiating bacterial protein expression. An mdr1a M107L cDNA containing a single residue mutation at the proposed translational start site was shown to allow sub-cloning of mdr1a in E. coli while retaining transport properties similar to wild-type P-gp. This mutant mdr1a cDNA may prove useful for efficient cloning of mdr1a in E. coli.

Sodium tanshinone IIA sulfonate and sodium danshensu open the placental barrier through down-regulation of placental P-glycoprotein in mice: Implications in the transplacental digoxin treatment for fetal heart failure

Sodium tanshinone IIA sulfonate and sodium danshensu open the placental barrier through down-regulation of placental P-glycoprotein in mice: Implications in the transplacental digoxin treatment for fetal heart failure

3D Cryo-Electron Reconstruction of BmrA, a Bacterial Multidrug ABC Transporter in an Inward-Facing Conformation and in a Lipidic Environment

ABC (ATP-binding cassette) membrane exporters are efflux transporters of a wide diversity of molecule across the membrane at the expense of ATP. A key issue regarding their catalytic cycle is whether or not their nucleotide-binding domains (NBDs) are physically disengaged in the resting state. To settle this controversy, we obtained structural data on BmrA, a bacterial multidrug homodimeric ABC transporter, in a membrane-embedded state. BmrA in the apostate was reconstituted in lipid bilayers forming a mixture of ring-shaped structures of 24 or 39 homodimers. Three-dimensional models of the ring-shaped structures of 24 or 39 homodimers were calculated at 2.3nm and 2.5nm resolution from cryo-electron microscopy, respectively. In these structures, BmrA adopts an inward-facing open conformation similar to that found in mouse P-glycoprotein structure with the NBDs separated by 3nm. Both lipidic leaflets delimiting the transmembrane domains of BmrA were clearly resolved. In planar membrane sheets, the NBDs were even more separated. BmrA in an ATP-bound conformation was determined from two-dimensional crystals grown in the presence of ATP and vanadate. A projection map calculated at 1.6nm resolution shows an open outward-facing conformation. Overall, the data are consistent with a mechanism of drug transport involving large conformational changes of BmrA and show that a bacterial ABC exporter can adopt at least two open inward conformations in lipid membrane.

Refined Structures of Mouse P-Glycoprotein

Refined Structures of Mouse P-Glycoprotein

Suppression of the growth of subcutaneous transplanted human liver cancer and lung metastasis in nude mice treated by sorafenib combined with fluorouracil

The aim of this study was to explore the inhibitory effect of sorafenib and 5-Fu on transplanted human liver cancer in nude mice, and to investigate the synergistic effect and mechanism between sorafenib and 5-Fu. The nude mouse model of human liver cancer was made by transplantation of human highly metastatic liver cancer cell line HCCLM3 cells, and the tumor-bearing nude mice were treated with sorafenib, 5-Fu or both, respectively, and mock-treated tumor-bearing nude mice as negative control. To assess the anti-tumor effect of sorafenib and the synergistic effect of sorafenib combined with 5-Fu by measuring the tumor weight and number of lung metastases. Moreover, the expressions of phosphorylated extracellular signal-regulated kinase (p-ERK), P-glycoprotein (P-gp) and topoisomerase 2-alpha (Topo IIa) in the nude mice were assayed by immunocytochemistry and Western blot. The tumor weights and numbers of lung metastases were: (2.7 ± 0.825) g and 12.714 ± 6.317 in the negative control group, (0.933 ± 0.333) g and 4.333 ± 3.983 in the sorafenib group, (0.786 ± 0.212) g and 5.429 ± 4.315 in the Sorafenib + 5-Fu combination group, and (2.438 ± 0.793) g and 10.429 ± 6.241 in the 5-Fu group. Statistically, the tumor weights and numbers of lung metastases in the sorafenib group and combination group were significantly decreased, compared with that in the control group (P < 0.05). There was no significant difference in the tumor weight and number of lung metastases between the sorafenib group and the combination treatment group (P > 0.05). The expression levels of p-ERK, P-gp and Topo IIa proteins in the tumors after normalization were: negative control (0.017 ± 0.010, 0.085 ± 0.012, 0.103 ± 0.093), sorafenib group (0.010 ± 0.008, 0.044 ± 0.020, 0.020 ± 0.018), combination group (0.011 ± 0.007, 0.043 ± 0.023, 0.062 ± 0.026), and 5-Fu group (0.018 ± 0.009, 0.063 ± 0.032, 0.065 ± 0.034), respectively. Statistically, the expression of p-ERK, P-gp and Topo IIa in the Sorafenib group was significantly reduced compared with that of the control group (P < 0.05), and there was no significant difference in the expression of p-ERK, P-gp and Topo IIa between the sorafenib group and the combination treatment group (P > 0.05). Sorafenib can inhibit not only the tumor growth and lung metastsis in the nude mouse models, but also reduce the expression of multidrug resistance proteins P-gp and Topo IIa as well. There is no significant advantage for the sorafenib + 5-Fu combination treatment than Sorafenib alone in inhibiting the expression of p-ERK, P-gp and Topo IIa.