Mechanisms of transport and structure-permeability relationship of sulfasalazine and its analogs in Caco-2 cell monolayers

Mesalazine-PAMAM Nanoparticles for Transporter-Independent Intracellular Drug Delivery: Cellular Uptake and Anti-Inflammatory Activity

Background

Mesalazine is one of the main drugs used to treat inflammatory bowel diseases. However, its applicability is limited by its rapid inactivation and removal from the organism, as well as the need for its membrane transporter-dependent cellular uptake to exert therapeutic effect. The present study involved the development of an innovative nanocarrier, based on poly(amidoamine) (PAMAM) dendrimer of the 4th generation, to obtain higher concentrations of the drug in the intestinal epithelial cells, thus increasing its anti-inflammatory potential. The work involved synthesis and in vitro characterization of covalent PAMAM-mesalazine conjugate with succinic linker.

Results

PAMAM-mesalazine conjugate was synthesized and characterized by ¹H NMR, ¹³C NMR, FTIR and MALDI-TOF MS. This allowed to confirm the purity of the obtained compound and intermediates. Based on the analyses, it was found that ~45 drug molecules were successfully attached to one molecule of PAMAM dendrimer. The conjugate was then characterized in terms of hydrodynamic diameter, zeta potential, spectral properties, drug release from the carrier, as well as cellular uptake and cytotoxicity in two in vitro models of gastrointestinal epithelium (CaCo-2 and HT-29 human cell lines). Analyzing cellular parameters related to the specific mechanism of action of mesalazine (inhibition of NF-κB signaling, decrease in interleukin and prostaglandin synthesis, and ROS scavenging), we showed that such a dendrimer-based carrier may enhance cellular uptake of the drug, which translated into its improved anti-inflammatory efficacy.

Conclusion

The use of PAMAM macromolecule as a carrier for mesalazine increases the bioavailability of the drug, ensuring enhanced cellular uptake and bypassing the need to utilize mesalazine-specific membrane transporters. All these characteristics translate into an improved anti-inflammatory activity of mesalazine in vitro. In conjunction with appropriately designed in vivo studies, such a compound may prove to be a promising alternative to the therapeutics currently used in inflammatory bowel diseases.

Development and validation of HPLC-DAD and LC-(ESI)/MS methods for the determination of sulfasalazine, mesalazine and hydrocortisone 21-acetate in tablets and rectal suppositories: In vitro and ex vivo permeability studies

Controlled-release tablets and rectal suppositories of sulfasalazine (SLF) and hydrocortisone 21-acetate (HA) were prepared as recommended dosage forms for the treatment of acute episodes of ulcerative colitis, in patients who do not respond to monotherapy. A High-Performance Liquid Chromatography (HPLC) Diode-array method with a gradient elution mobile phase was developed to evaluate the production quality of both formulations (assay and dissolution profiles in gastric and intestinal fluids). Method's validation was carried out providing good linearity (r ≥ 0.9995), precision (RSD < 1.53%), recovery (96.9% - 103.7%) and limits of detection (LOD_SLF = 12 ng/mL, LOD_HA = 15 ng/mL). Experimental design and Plackett-Burman methodology was constructed to study the robustness of the analysis. In all composite substrates, a freezing lipid precipitation approach was used as purification step. The method was optimized by applying Central Composite design mode. The in-vitro/ex-vivo permeability studies of both formulations were evaluated by a Liquid Chromatography-Electron Spray Ionization Mass Spectrometry (LC-ESI/MS) +/- mode. The analysis of sulfamethazine (internal standard, SLM, m/z 279), HA (m/z 449, [M + HCOO]^-), SLF (m/z 399) and its active metabolite mesalazine (MSL, m/z 154) was performed using a C₁₈ column and gradient elution. The validation of the method met the requirements of the International Council for Harmonization (ICH) (r ≥ 0.9997, RSD ≤ 4.62%, Recovery > 95%, LOD_SLF = 1.28 ng/mL, LOD_HA = 1.07 ng/mL, LOD_MSL = 3.16 ng/mL). Based on the results, important conclusions were drawn concerning the role of excipients and SLF metabolism.

What dominates the changeable pharmacokinetics of natural sesquiterpene lactones and diterpene lactones: a review focusing on absorption and metabolism

Sesquiterpene lactones (STLs) and diterpene lactones (DTLs) are two groups of common phytochemicals with similar structures. It's frequently reported that both exhibit changeable pharmacokinetics (PK) in vivo, especially the unstable absorption and extensive metabolism. However, the recognition of their PK characteristics is still scattered. In this review, representative STLs (atractylenolides, alantolactone, costunolide, artemisinin, etc.) and DTLs (ginkgolides, andrographolide, diosbulbins, triptolide, etc.) as typical cases are discussed in detail. We show how the differences of treatment regimens and subjects alter the PK of STLs and DTLs, with emphasis on the effects from absorption and metabolism. These compounds tend to be quite permeable in intestinal epithelium, but gastrointestinal pH and efflux transporters (represented by P-glycoprotein) have great impact and result in the unstable absorption. As the only characteristic functional moiety, the metabolic behavior of lactone ring is not dominant. The α, β-unsaturated lactone moiety has the strongest metabolic activity. While with the increase of low-activity saturated lactone moieties, the metabolism is led by other groups more easily. The phase I (oxidation, reduction and hydrolysis reaction) and II metabolism (conjugation reaction) are both extensive. CYP450s, mainly CYP3A4, are largely involved in biotransformation. However, only UGTs (UGT1A3, UGT1A4, UGT2B4 and UGT2B7) has been mentioned in studies about phase II metabolic enzymes. Our work offers a beneficial reference for promoting the safety evaluation and maximizing the utilization of STLs and DTLs.

Establishment of modified biopharmaceutics classification system absorption model for oral Traditional Chinese Medicine (Sanye Tablet)

ETHNOPHARMACOLOGICAL RELEVANCE

As one of the new drugs of traditional Chinese medicine, Sanye Tablet is employed as a hypolipidemic in the traditional medicine, but the biopharmaceutical properties of the drug is still unclear.

AIM OF THE STUDY

Through the study of biopharmaceutical properties, the classical biopharmaceutics classification system (BCS) can be used to classify and predict the in vivo absorption properties. On this basis, the biopharmaceutical properties closely related to traditional Chinese medicine preparations are added and a modified BCS model is established to predict and judge the absorption degree of traditional Chinese medicine compound.

MATERIALS AND METHODS

Representative components of Sanye Tablet were selected and subjected to different in vitro tests. The experimental results were compared with the results of the BCS to evaluate the accuracy and applicability to Sanye Tablet. We take parameters of dissolution and stability based on product characteristics into account. A "modified-BCS" was developed and the results of the improved method and the classic method were compared. Also the ability of each classification system to predict and determine the extent of absorption of the Chinese herbal compound was investigated based on the absolute bioavailability of representative components.

RESULTS

For classic BCS, the five representative components (except for nuciferine) are all class III, nuciferine is class I/II obtained by Caco-2 cell assay and class III/IV obtained by everted gut sac assay. For modified BCS, paeoniflorin is class III, rutin, hyperoside and salvianolic acid B are class III/IV, and nuciferine is class I/II based on Caco-2 cell assay, class III/IV based on everted gut sac assay. Nuciferine is the best of the five components, with absolute bioavailability reaching 61.91% based on in vivo bioavailability test.

CONCLUSIONS

The five representative components (except for nuciferine) are all class III/IV, which correlates well with the absolute bioavailability results and demonstrates that they are poorly absorbed substances. The correlation between the classification results obtained using the "modified-BCS" and absorption in the body is better than the correlation obtained using the classic method, suggesting that the improved BCS is more suitable for the characterization of Sanye Tablet. These results indicate that the oral formulation of Sanye Tablet is a BCS III/IV drug.

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Treatment of Inflammatory Bowel Disease

According to recent clinical consensus, pharmacotherapy of inflammatory bowel disease (IBD) is, or should be, personalized medicine. IBD treatment is complex, with highly different treatment classes and relatively few data on treatment strategy. Although thorough evidence-based international IBD guidelines currently exist, appropriate drug and dose choice remains challenging as many disease (disease type, location of disease, disease activity and course, extraintestinal manifestations, complications) and patient characteristics [(pharmaco-)genetic predisposition, response to previous medications, side-effect profile, necessary onset of response, convenience, concurrent therapy, adherence to (maintenance) therapy] are involved. Detailed pharmacological knowledge of the IBD drug arsenal is essential for choosing the right drug, in the right dose, in the right administration form, at the right time, for each individual patient. In this in-depth review, clinical pharmacodynamic and pharmacokinetic considerations are provided for tailoring treatment with the most common IBD drugs. Development (with consequent prospective validation) of easy-to-use treatment algorithms based on these considerations and new pharmacological data may facilitate optimal and effective IBD treatment, preferably corroborated by effectiveness and safety registries.

Application of Intestinal Epithelial Cells Differentiated from Human Induced Pluripotent Stem Cells for Studies of Prodrug Hydrolysis and Drug Absorption in the Small Intestine

Cell models to investigate intestinal absorption functions, such as those of transporters and metabolic enzymes, are essential for oral drug discovery and development. The purpose of this study was to generate intestinal epithelial cells from human induced pluripotent stem cells (hiPSC-IECs) and then clarify whether the functions of hydrolase and transporters in them reflect oral drug absorption in the small intestine. The hiPSC-IECs showed the transport activities of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and peptide transporter 1 (PEPT1), revealed by using their probe substrates ([³H]digoxin, sulfasalazine, and [¹⁴C]glycylsarcosine), and the metabolic activities of CYP3A4, CES2, and CES1, which were clarified using their probe substrates (midazolam, irinotecan, and temocapril). The intrinsic clearance by hydrolysis of six ester prodrugs into the active form in hiPSC-IECs was correlated with the plasma exposure (C_max , AUC, and bioavailability) of the active form after oral administration of these prodrugs to rats. Also, the permeability coefficients of 14 drugs, containing two substrates of P-gp (doxorubicin and [³H]digoxin), one substrate of BCRP (sulfasalazine), and 11 nonsubstrates of transporters (ganciclovir, [¹⁴C]mannitol, famotidine, sulpiride, atenolol, furosemide, ranitidine, hydrochlorothiazide, acetaminophen, propranolol, and antipyrine) in hiPSC-IECs were correlated with their values of the fraction of intestinal absorption (Fa) in human clinical studies. These findings suggest that hiPSC-IECs would be a useful cell model to investigate the hydrolysis of ester prodrugs and to predict drug absorption in the small intestine.

A novel biosensor based on intestinal 3D organoids for detecting the function of BCRP

Breast cancer resistance protein (BCRP), a key drug efflux transporter, significantly affects the therapeutic efficacy of many drugs. Thus, screening specific BCRP inhibitors and distinguishing between substrates and non-substrates of BCRP are valuable in drug discovery and development. This study presents a novel BCRP biosensor based on intestinal 3D organoids for rapid and sensitive detection of BCRP function. First, the crypts were isolated from mouse small intestine, and cultured in advanced DMEM/F12 medium to develop intestinal 3D organoids. Second, immunohistochemical studies demonstrated that BCRP protein in the organoids presented a similar expression and physiologic position to the small intestinal epithelium. Finally, the cultured organoids were treated in BCRP fluorogenic probe substrate Hoechst 33342 with or without BCRP inhibitor Ko143 and YHO-13177. The fluorescence intensity of Hoechst 33342 released from inner of the organoids was detected by microplate reader and the concentrations were calculated. Ko143 and YHO-13177 significantly inhibited the BCRP-mediated Hoechst 33342 transport in the 3D organoids. Consequently, a rapid and efficient biosensor has been successfully established to study BCRP, especially screening BCRP inhibitors in a high-throughput way.

Real-time imaging and quantitative analysis of doxorubicin transport in a perfusable microvessel platform

Here we report on real-time imaging and quantitative analysis of solute transport in perfusable cylindrical microvessels formed from Madin-Darby canine kidney (MDCK) cells embedded in a collagen matrix. Fluorescence microscopy was used to image the kinetics of doxorubicin transport following injection. To assess the role of efflux pumps on transport, experiments were performed in microvessels formed from MDCK.2, MDCKII-w/t, and MDCKII-MDR1 cells. MDCKII-w/t and MDCKII-MDR1 showed significant doxorubicin accumulation in the cells, characteristic of the pharmacokinetics of doxorubicin. We present a model for doxorubicin transport that takes into account transport across the cell layer. These results demonstrate how real-time imaging of cell microvessels can be used to analyze the mechanisms of transport and distribution following systemic delivery.

Prediction of the permeability of neutral drugs inferred from their solvation properties

Motivation: Determination of drug absorption is an important component of the drug discovery and development process in that it plays a key role in the decision to promote drug candidates to clinical trials. We have developed a method that, on the basis of an analysis of the dynamic distribution of water molecules around a compound obtained by molecular dynamics simulations, can compute a parameter-free value that correlates very well with the compound permeability measured using the human colon adenocarcinoma (Caco-2) cell line assay.

Results: The method has been tested on twenty-three neutral drugs for which a consistent set of experimental data is available. We show here that our method reproduces the experimental data better than other existing tools. Furthermore it provides a detailed view of the relationship between the hydration and the permeability properties of molecules.

Contact:anna.tramontano@uniroma1.it

Supplementary information:Supplementary data are available at Bioinformatics online.

Review article: The pharmacokinetics and pharmacodynamics of drugs used in inflammatory bowel disease treatment

BACKGROUND

The following review is a compilation of the recent advances and knowledge on the behaviour of the most frequently used compounds to treat inflammatory bowel disease in an organism.

RESULTS

It considers clinical aspects of each entity and the pharmacokinetic/pharmacodynamic relationship supported by the use of plasma monitoring, tissue concentrations, and certain aspects derived from pharmacogenetics.

Evaluation of fasted and fed state simulated and human intestinal fluids as solvent system in the Ussing chambers model to explore food effects on intestinal permeability

The Ussing chambers model is almost exclusively used in the presence of plain aqueous phosphate buffers as solvent system. In an attempt to further elucidate the effect of luminal ingredients and postprandial conditions on intestinal permeability, pooled fasted and fed state human intestinal fluids (FaHIFpool, FeHIFpool) were used. In addition, simulated intestinal fluids of both nutritional states (FaSSIF, FeSSIF) were evaluated as possible surrogate media for HIF. The use of FaHIFpool generated a broad range of Papp values for a series of 16 model drugs, ranging from 0.03×10(-6)cm/s (carvedilol) to 33.8×10(-6)cm/s (naproxen). A linear correlation was observed between Papp values using FaSSIF and FaHIFpool as solvent system (R=0.990), justifying the use of FaSSIF as surrogate medium for FaHIF in the Ussing chambers. In exclusion of the outlier carvedilol, a strong sigmoidal relationship was found between Papp and fahuman of 15 model drugs, illustrated by correlation coefficients of 0.961 and 0.936 for FaHIFpool and FaSSIF, respectively. When addressing food effects on intestinal permeability, the use of FeHIFpool resulted in a significantly lower Papp value for nine out of sixteen compounds compared to fasting conditions. FeSSIF as solvent system significantly overestimated Papp values in FeHIFpool. To conclude, the optimized Ussing chambers model using biorelevant media as apical solvent system holds great potential to investigate food effects in a more integrative approach, taking into account drug solubilisation, supersaturation and formulation effects.

Evaluation of fasted state human intestinal fluid as apical solvent system in the Caco-2 absorption model and comparison with FaSSIF

To date, the Caco-2 model is considered as the gold standard to predict intestinal drug absorption. Often, aqueous phosphate buffers are used as apical medium. The purpose of this study was to use fasted state human intestinal fluid (FaHIF) as apical solvent system to generate biorelevant permeability values for a series of 16 model drugs that can be used as reference data to critically evaluate fasted state simulated intestinal fluid (FaSSIF) as possible substitute medium. Caco-2 compatibility with FaHIF was achieved when 50mg/ml mucus was applied on top of the cells before adding the apical medium. The use of FaHIF as solvent system generated a broad range of apparent permeability values (Papp) for the series of model compounds. When Papp values obtained with FaHIF were compared to those obtained with FaSSIF, a strong correlation was observed (R=0.951). The use of FaSSIF in the absence of mucus did not significantly alter this correlation. For FaHIF, FaSSIF and reference phosphate buffer blank FaSSIF, a strong sigmoidal relationship was found between Papp and fahuman, illustrated by correlation coefficients of 0.961, 0.893 and 0.868, respectively. In terms of inter-subject variability, the use of FaHIF from different volunteers originating from two distinct age groups (18-25 years; 65-72 years) exhibited an average coefficient of variance (CV) of 30%. However, no age dependency in permeability could be observed. In conclusion, the data generated in this article justify the use of FaSSIF as biorelevant apical medium in the Caco-2 assay to accurately predict in vivo drug absorption. Also, the optimized mucus-containing Caco-2 model can be used in combination with intestinal fluid samples aspirated after drug administration to further investigate intraluminal drug and formulation behavior.

Study on the mechanism of intestinal absorption of epimedins a, B and C in the Caco-2 cell model

Epimedium spp. is commonly used in Traditional Chinese Medicine. Epimedins A, B, and C are three major bioactive flavonoids found in Epimedium spp. that share similar chemical structures. In this study, the intestinal absorption mechanism of these three compounds was investigated using the Caco-2 cell monolayer model in both the apical-to-basolateral (A-B) and the basolateral-to-apical (B-A) direction. The absorption permeability (P_AB) of epimedins A, B, and C were extremely low and increased as the concentration of the epimedins increased from 5 to 20 μM, but, at 40 μM, the P_AB values were reduced. Meanwhile, the amount of transported compounds increased in a time-dependent manner. The P_AB of epimedins A and C were significantly increased and efflux ratios decreased in the presence of verapamil (an inhibitor of P-glycoprotein) and dipyridamole (an inhibitor of breast cancer resistance protein) while, in the presence of MK571 (an inhibitor of multidrug resistance proteins), the absorption of epimedins A and C did not change significantly, indicating that P-gp and BCRP might be involved in the transport of epimedins A and C. The P_AB of epimedin B significantly increased while its secretory permeability (P_BA) significantly decreased in the presence of dipyridamole, indicating that BCRP might be involved in the transport of epimedin B. No obvious changes in the transport of epimedin B were observed in the presence of verapamil and MK571. In summary, our results clearly demonstrate, for the first time, that poor bioavailability of these three prenylated flavonoids is the result of poor intrinsic permeability and efflux by apical efflux transporters.

Keeping a critical eye on the science and the regulation of oral drug absorption: a review

This review starts with an introduction on the theoretical aspects of biopharmaceutics and developments in this field from mid-1950s to late 1970s. It critically addresses issues related to fundamental processes in oral drug absorption such as the complex interplay between drugs and the gastrointestinal system. Special emphasis is placed on drug dissolution and permeability phenomena as well as on the mathematical modeling of oral drug absorption. The review ends with regulatory aspects of oral drug absorption focusing on bioequivalence studies and the US Food and Drug Administration and European Medicines Agency guidelines dealing with Biopharmaceutics Classification System and Biopharmaceutic Drug Disposition Classification System.

Effect of the ATP-binding cassette transporter ABCG2 on pharmacokinetics: experimental findings and clinical implications

INTRODUCTION

The ATP-binding cassette transporter ABCG2 can actively extrude a broad range of endogenous and exogenous substrates across biological membranes. Thereby, ABCG2 limits oral drug bioavailability, mediates hepatobiliary and renal excretion and participates functionally in the blood-brain barrier.

AREAS COVERED

The paper provides a review of the clinical evidence of the role of ABCG2 in the bioavailability and brain disposition of drugs. It also sheds light on the value of experimental/preclinical data in predicting the role of ABCG2 in pharmacokinetics in humans.

EXPERT OPINION

Experimental studies indicate that ABCG2 may limit the oral bioavailability and brain penetration of many drugs. ABCG2 has also been recognized as an important determinant of the disposition of some drugs in humans. For example, loss-of-function variants of ABCG2 affect the pharmacokinetics and pharmacodynamics of rosuvastatin in a clinically significant manner. Moreover, clinically relevant pharmacokinetic drug-drug interactions have been attributed to ABCG2 inhibition. However, examples from human studies are still rare compared with the overwhelming evidence from experimental studies. The large degree of functional redundancy of ABCG2 with other transporters such as P-glycoprotein may explain the rare occurrence of ABCG2-dependent drug-drug interactions in humans. Providing clinicians with consolidated information on the clinically relevant interactions of drugs with ABCG2 remains a matter of future exploration.

The influence of probiotic treatment on sulfasalazine metabolism in rat

Probiotics are live microorganisms claimed to exert beneficial effects on the host. This study investigated their effect on the metabolism and pharmacokinetics of sulfasalazine (SSZ), a drug whose efficacy depends on metabolism by azoreductase (AR) in the gut microbiota to sulfapyridine (SP) and 5-acetylsalicylic acid (5-ASA). The probiotic strains Lactobacillus acidophilus L10, Bifidobacterium lactis B94 and Streptococcus salivarius K12 possessed AR activity and a corresponding ability to metabolize SSZ. Treatment of male Wistar rats (n = 5) with oral 2 g doses of a mixture of the three probiotics (total dose 1.8 × 10⁹ cfu) every 12 h for 3 days resulted in a significant increase (p < 0.05) in AR activity in ex vivo colon contents with a corresponding increase in SSZ metabolism. Similar probiotic treatment of male Wistar rats (n = 8) followed by an oral 100 mg/kg dose of SSZ produced high plasma levels of SP, but pharmacokinetic parameters of SSZ and SP were not significantly different from control rats given SSZ. These results indicate that probiotic strains possess AR activity and can metabolize SSZ. Treatment with probiotics increases AR activity in the gut microbiota but has no effect on plasma levels of SSZ and SP following a subsequent oral dose of SSZ.

Drug transport by breast cancer resistance protein

IMPORTANCE OF THE FIELD

The ATP-binding cassette transporter ABCG2 is a well-known major mediator of multi-drug resistance in cancers. Beyond multi-drug resistance, experimental and recent clinical studies demonstrate a role for ABCG2 as a determinant of drug pharmacokinetic, safety and efficacy profiles.

AREAS COVERED IN THIS REVIEW

The clinical evidence of the role of ABCG2 in pharmacokinetics and pharmacodynamics is reviewed. Key questions that arise from the perspective of preclinical drug evaluation are addressed, including the structure of ABCG2 and mechanisms of drug-transporter interactions, mechanisms responsible for the polyspecificity of ABCG2, methods suitable for studying drug-ABCG2 interactions in vitro and in silico prediction of ABCG2 substrates and inhibitors.

WHAT THE READER WILL GAIN

An update on current knowledge of the importance of ABCG2 in drug disposition with special emphasis on drug development.

TAKE HOME MESSAGE

The field of drug-ABCG2 interaction is rapidly advancing and beginning to expand into clinical practice. However, the structural understanding of drug binding and transport by ABCG2 is still incomplete. Incorporation of novel concepts of drug-transporter interactions such as electrostatic funneling might help explain the multispecificity of ABCG2 and enable in silico predictions.

Evaluation and suggested improvements of the Biopharmaceutics Classification System (BCS)

This review has evaluated the Biopharmaceutics Classification System (BCS) and improvements have been proposed. The BCS has a very strict solubility/dissolution limit, a generous Pe-limit (≥ 14-times higher rate constant limit for dissolution than for permeation), and is stricter for drugs with a long half-life (t1/2). Available human in-vivo, in-vitro, and in-silico Pe-methods cannot classify Pe for moderately to highly permeable substances sufficiently well, and in-vitro data often underpredict the in-vivo dissolution potential and rate. Good in-vivo dissolution and absorption can be expected for most high Pe drug products. It has not been possible to find a highly permeable product with a Dose number (Do) &lt; 385 (&lt; 2400 in the fed state) that is clearly incompletely absorbed, and near complete uptake has been shown for a drug product with a Do of 660000. The potential implication of these findings is that many true BCS Class I drug products are incorrectly classified. This could be a reason for the limited use of this system. On this basis, it has been suggested that: the limit for high for solubility/dissolution is decreased (to &gt;40 and &gt;95% dissolved within 30min and 3 h, respectively); the limit for high Pe is increased (to &gt;Pe of metoprolol); accurate Pe-models or in-vivo fraction absorbed data are used; solubility/dissolution tests are performed using real or validated simulated gastrointestinal fluids; in-vitro/in-vivo dissolution relationships are established; the t½ is considered; and the rate-limiting step for in-vivo absorption is determined. A major change could be to reduce the BCS into two classes: permeation-rate (Class I) or dissolution-rate (Class II) limited absorption. It is believed that this could give a better balance and increase the number of biowaivers.

Sulfasalazine transport in in-vitro, ex-vivo and in-vivo absorption models: contribution of efflux carriers and their modulation by co-administration of synthetic nature-identical fruit extracts

Sulfasalazine is characterised by low oral bioavailability. In this study, its intestinal transport characteristics were studied in an in-vitro, ex-vivo and in-situ system. The absorptive transport of sulfasalazine across Caco-2 monolayers appeared to be lower than the secretory transport (Papp-abs = 0.21 ± 0.02 times 10−6 cm s−1 and Papp-secr = 2.97 ± 0.30 times 10−6 cm s−1, respectively). This polarity in transport of sulfasalazine was not mediated by P-glycoprotein (P-gp), as inclusion of verapamil (100 μm) did not have any effect on the transport polarity of sulfasalazine. However, inclusion of the multidrug resistance-associated protein (MRP) inhibitors benzbromarone (50 μm) and sulfinpyrazone (1 mm), and the glutathione-depleting agent chlorodinitrobenzene (100 μm), resulted in an increased absorptive transport of sulfasalazine in the Caco-2 system (Papp-abs = 0.64 ± 0.02, 0.51 ± 0.04 and 0.60 ± 0.03 times 10−6 cm s−1, respectively). The interference of carriers implies that, during absorption, interactions with food components may occur at the level of this carrier. Therefore, the effect of food extracts was studied in a parallel set of experiments. For two standardized nature-identical fruit extracts (pineapple and apricot extract) a concentration-dependent absorption-enhancing effect could be observed in the Caco-2 system. The functional expression of similar carriers was also demonstrated in rat ileum in the Ussing chamber system. Interaction studies with fruit extracts in the Ussing chamber system, as well as in the in-situ intestinal perfusion study, revealed a 2- to 4-fold increase in the absorptive transport of sulfasalazine. These results indicate that food components in the intestinal lumen can have a significant impact on the intestinal absorption characteristics of sulfasalazine by modulating the biochemical barrier function of the intestinal mucosa.

Experimental modelling of drug membrane permeability by capillary electrophoresis using liposomes, micelles and microemulsions

Capillary electrophoresis (CE) was evaluated as an in-vitro format for experimental modelling of membrane permeability using only nanogram quantities of drug compounds. The rationale for the CE technique emanates from emulation of a lipid-like pseudo-stationary phase that governs separations mainly as a result of differences in molecular size, lipophilicity, hydrogen bonding and charge, all of which also have a strong influence on in-vivo drug absorption. By means of micellar, microemulsion and liposome electrolytes, the migration behaviour was studied at 37°C for 22 model drug compounds. The generated CE retention factor data were then compared with membrane permeability reference data. Both simple log D and more common Caco-2 cell parameters were evaluated. In addition, permeation through intestinal segments of rat ileum and rat colon was included. An improved correlation was obtained in the order: micellar&lt;microemulsion&lt;liposome systems. Although the correlation for the best liposome CE system was only R2 = 0.77, the evaluation results for all emphasized the strength and flexibility of CE for assessing specific drug-membrane interaction through tailor-made lipophilic media.

Small intestinal efflux mediated by MRP2 and BCRP shifts sulfasalazine intestinal permeability from high to low, enabling its colonic targeting

Sulfasalazine is characterized by low intestinal absorption, which essentially enables its colonic targeting and therapeutic action. The mechanisms behind this low absorption have not yet been elucidated. The purpose of this study was to investigate the role of efflux transporters in the intestinal absorption of sulfasalazine as a potential mechanism for its low small-intestinal absorption and colonic targeting following oral administration. The effects of P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP) inhibitors on sulfasalazine bidirectional permeability were studied across Caco-2 cell monolayers, including dose-response analysis. Sulfasalazine in vivo permeability was then investigated in the rat jejunum by single-pass perfusion, in the presence vs. absence of inhibitors. Sulfasalazine exhibited 19-fold higher basolateral-to-apical (BL-AP) than apical-to-basolateral (AP-BL) Caco-2 permeability, indicative of net mucosal secretion. MRP2 inhibitors (MK-571 and indomethacin) and BCRP inhibitors [fumitremorgin C (FTC) and pantoprazole] significantly increased AP-BL and decreased BL-AP sulfasalazine Caco-2 transport in a concentration-dependent manner. No effect was observed with the P-gp inhibitors verapamil and quinidine. The IC50 values of the specific MRP2 and BCRP inhibitors MK-571 and FTC on sulfasalazine secretion were 21.5 and 2.0 microM, respectively. Simultaneous inhibition of MRP2 and BCRP completely abolished sulfasalazine Caco-2 efflux. Without inhibitors, sulfasalazine displayed low (vs. metoprolol) in vivo intestinal permeability in the rat model. MK-571 or FTC significantly increased sulfasalazine permeability, bringing it to the low-high permeability boundary. With both MK-571 and FTC present, sulfasalazine displayed high permeability. In conclusion, efflux transport mediated by MRP2 and BCRP, but not P-gp, shifts sulfasalazine permeability from high to low, thereby enabling its colonic targeting and therapeutic action. To our knowledge, this is the first demonstration of intestinal efflux acting in favor of oral drug delivery.

Molecular and functional characteristics of proton-coupled folate transporter

Proton-coupled folate transporter (PCFT) has recently been identified as the molecular entity of the carrier-mediated intestinal folate transport system. PCFT has been demonstrated to be most abundantly expressed in the upper small intestine, localizing at the brush border membrane of epithelial cells, transport folate and its analogs more efficiently at lower (acidic) pH by a H(+)-coupled cotransport mechanism, and have a high affinity for folate with a Michaelis constant (K(m)) of a few microM at pH 5.5 and somewhat lower affinities for reduced folates and methotrexate (MTX). A loss of PCFT function due to a homozygous mutation in its gene has been indicated to be responsible for hereditary folate malabsorption. Thus, PCFT has all the characteristics of the brush border H(+)-coupled cotransporter for folate and analogs, which has long been suggested to be present in the intestine. Furthermore, sulfasalazine was found to be a potent inhibitor of PCFT, suggesting that it is a risk factor that would cause malabsorption of folate and also MTX, when coadministered in the treatment of rheumatoid arthritis. Understanding the molecular and functional characteristics of PCFT should be important and helpful in exploring therapeutic strategies for folate malabsorption and in optimizing therapies using antifolate drugs.

Ins and outs of the ABCG2 multidrug transporter: an update on in vitro functional assays

The major aim of this chapter is to provide a critical overview of the in vitro methods available for studying the function of the ABCG2 multidrug transporter protein. When describing the most applicable assay systems, in each case we present a short overview relevant to ABC multidrug transporters in general, and then we concentrate on the tools applicable to analysis of substrate-drug interactions, the effects of potential activators and inhibitors, and the role of polymorphisms of the ABCG2 transporter. Throughout this chapter we focus on recently developed assay systems, which may provide new possibilities for analyzing the pharmacological aspects of this medically important protein.

SIMDOT-AbMe: microphysiologically based simulation tool for quantitative prediction of systemic and local bioavailability of targeted oral delivery formulations

The purpose of this study was to develop a physiologically based simulation tool that is able to predict local as well as systemic bioavailability of 5-aminosalicylic acid (5-ASA)-targeted delivery formulations using the existing understanding of the transport and metabolism mechanisms of 5-ASA. The model accounts for active and passive transcellular transport (absorptive and efflux), passive paracellular transport, intestinal biotransformation, and systemic metabolism and clearance. The intestinal physiology was represented by transverse segments for ileum and proximal colon and longitudinal compartments for the microphysiology of the intestinal tissue. The tool, equipped with an optimization routine that enables tuning model parameters, was developed in Matlab and uses a user-friendly graphical interface for data input and output. Physiologic and kinetic model parameters were estimated either from literature monolayer transport studies using nonlinear curve fitting or obtained directly from the literature. 5-ASA clinical pharmacokinetic profiles of a once-daily (one 4-g/day dose) and twice-daily (two 2-g/day doses) dosing regimen were used to partially calibrate and validate the model, respectively. Simulation results showed that drug C(max) in the gut mucosal layers reached a higher level and was achieved sooner than in the systemic blood level. The computed relative local bioavailability with respect to the systemic bioavailability was 0.063. With use of the model, the relative local bioavailability of different formulations can be established for fast performance verification of new preparations based on measured systemic bioavailability. These types of models play a critical role in designing such preparations and rapidly assessing their effectiveness and will foster efficient experimental designs, saving time and resources.

A modified fast (4 day) 96-well plate Caco-2 permeability assay

INTRODUCTION

The Caco-2 permeability assay is widely used for lead optimization in drug discovery. A 3 to 5-day system using a 24-well plate and a 10 to 21-day system using a 96-well plate have been established. Here, we modified the assay system to provide a ready-to-use Caco-2 cell monolayer using a 96-well plate in just 4 days.

METHODS AND RESULTS

In our system, collagen-coated inserts and the prolongation of the culture period after seeding leads to greater Caco-2 cell proliferation and sufficient contact-inhibition. The differentiation of Caco-2 cells was enhanced, when the contact-inhibited Caco-2 cells were exposed to the differentiation-inducing agent butyric acid. The permeability to nine well-known compounds showed a statistical correlation between our 4-day system using a 96-well plate and the conventional 21-day system using a 24-well plate.

DISCUSSION

We conclude that our system is more useful for evaluating many compounds for lead optimization in drug discovery.

Estimation of ADME Properties in Drug Discovery: Predicting Caco-2 Cell Permeability Using Atom-Based Stochastic and Non-stochastic Linear Indices

The in vitro determination of the permeability through cultured Caco-2 cells is the most often-used in vitro model for drug absorption. In this report, we use the largest data set of measured P(Caco-2), consisting of 157 structurally diverse compounds. Linear discriminant analysis (LDA) was used to obtain quantitative models that discriminate higher absorption compounds from those with moderate-poorer absorption. The best LDA model has an accuracy of 90.58% and 84.21% for training and test set. The percentage of good correlation, in the virtual screening of 241 drugs with the reported values of the percentage of human intestinal absorption (HIA), was greater than 81%. In addition, multiple linear regression models were developed to predict Caco-2 permeability with determination coefficients of 0.71 and 0.72. Our method compares favorably with other approaches implemented in the Dragon software, as well as other methods from the international literature. These results suggest that the proposed method is a good tool for studying the oral absorption of drug candidates.

Functional characterization of PCFT/HCP1 as the molecular entity of the carrier-mediated intestinal folate transport system in the rat model

Proton-coupled folate transporter/heme carrier protein 1 (PCFT/HCP1) has recently been identified as a transporter that mediates the translocation of folates across the cellular membrane by a proton-coupled mechanism and suggested to be the possible molecular entity of the carrier-mediated intestinal folate transport system. To further clarify its role in intestinal folate transport, we examined the functional characteristics of rat PCFT/HCP1 (rPCFT/HCP1) expressed in Xenopus laevis oocytes and compared with those of the carrier-mediated folate transport system in the rat small intestine evaluated by using the everted tissue sacs. rPCFT/HCP1 was demonstrated to transport folate and methotrexate more efficiently at lower acidic pH and, as evaluated at pH 5.5, with smaller Michaelis constant (K(m)) for the former (2.4 microM) than for the latter (5.7 microM), indicating its characteristic as a proton-coupled folate transporter that favors folate than methotrexate as substrate. rPCFT/HCP1-mediated folate transport was found to be inhibited by several but limited anionic compounds, such as sulfobromophthalein and sulfasalazine. All these characteristics of rPCFT/HCP1 were in agreement with those of carrier-mediated intestinal folate transport system, of which the K(m) values were 1.2 and 5.8 microM for folate and methotrexate, respectively, in the rat small intestine. Furthermore, the distribution profile of the folate transport system activity along the intestinal tract was in agreement with that of rPCFT/HCP1 mRNA. This study is the first to clone rPCFT/HCP1, and we successfully provided several lines of evidence that indicate its role as the molecular entity of the intestinal folate transport system.

Application and limitation of inhibitors in drug-transporter interactions studies

The objective of the present study was to investigate the reliability of transporter inhibitors in the elucidation of drug-transporter interactions when multiple transporters are present in a test system. The bidirectional permeabilities of digoxin, estrone-3-sulfate (E3S), and sulfasalazine, substrates of P-gp, BCRP/MRP2 and unspecified efflux transporters, respectively, were examined in Caco-2 and MDR-MDCK cells in the absence and presence of transporter inhibitors: CsA (P-gp), FTC (BCRP) and MK571 (MRP). Digoxin showed significant efflux ratios (ER) in both Caco-2 (ER=17) and MDR-MDCK (ER=120), whereas E3S and sulfasalazine only showed significant efflux in Caco-2 (ER=15 and 88, respectively) but not in MDR-MDCK cells (ER=1.1 and 1.3, respectively). CsA at 10 microM showed complete inhibition of digoxin efflux, partial inhibition of E3S efflux and no effect on sulfasalazine efflux. FTC and MK571 had different inhibitory effects on the efflux of these compounds. The present study shows evidence of the functional expression of multiple efflux transporter systems in Caco-2 cells. Although the use of Caco-2 cells and selected inhibitors of efflux transporters can provide useful mechanistic information on drug-drug interactions involving efflux transporters, the potential cross-reaction of inhibitors with multiple transporters makes it difficult to discern the role of individual transporters in drug transport or drug-drug interactions.

Computational models to assign biopharmaceutics drug disposition classification from molecular structure

PURPOSE

We applied in silico methods to automatically classify drugs according to the Biopharmaceutics Drug Disposition Classification System (BDDCS).

MATERIALS AND METHODS

Models were developed using machine learning methods including recursive partitioning (RP), random forest (RF) and support vector machine (SVM) algorithms with ChemDraw, clogP, polar surface area, VolSurf and MolConnZ descriptors. The dataset consisted of 165 training and 56 test set molecules.

RESULTS

RF model 3, RP model 1, and SVM model 1 can correctly predict 73.1, 63.6 and 78.6% test compounds in classes 1, 2 and 3, respectively. Both RP and SVM models can be used for class 4 prediction. The inclusion of consensus analysis resulted in improved test set predictions for class 2 and 4 drugs.

CONCLUSIONS

The models can be used to predict BDDCS class for new compounds from molecular structure using readily available molecular descriptors and software, representing an area where in silico approaches could aid the pharmaceutical industry in speeding drugs to the patient and reducing costs. This could have significant applications in drug discovery to identify molecules that may have future developability issues.

Predicting effect of food on extent of drug absorption based on physicochemical properties

PURPOSE

To develop a statistical model for predicting effect of food on the extent of absorption (area under the curve of time-plasma concentration profile, AUC) of drugs based on physicochemical properties.

MATERIALS AND METHODS

Logistic regression was applied to establish the relationship between the effect of food (positive, negative or no effect) on AUC of 92 entries and physicochemical parameters, including clinical doses used in the food effect study, solubility (pH 7), dose number (dose/solubility at pH 7), calculated Log D (pH 7), polar surface area, total surface area, percent polar surface area, number of hydrogen bond donor, number of hydrogen bond acceptors, and maximum absorbable dose (MAD).

RESULTS

For compounds with MAD >or= clinical dose, the food effect can be predicted from the dose number category and Log D category, while for compounds with MAD < clinical dose, the food effect can be predicted from the dose number category alone. With cross validation, 74 out of 92 entries (80%) were predicted into the correct category. The correct predictions were 97, 79 and 68% for compounds with positive, negative and no food effect, respectively.

CONCLUSIONS

A logistic regression model based on dose, solubility, and permeability of compounds is developed to predict the food effect on AUC. Statistically, solubilization effect of food primarily accounted for the positive food effect on absorption while interference of food with absorption caused negative effect on absorption of compounds that are highly hydrophilic and probably with narrow window of absorption.

Sulfasalazine-induced reduction of glutathione levels in breast cancer cells: enhancement of growth-inhibitory activity of Doxorubicin

BACKGROUND

We previously showed that the anti-inflammatory drug, sulfasalazine (salicylazosulfapyridine, SASP), can arrest proliferation of MCF-7 and MDA-MB-231 mammary cancer cells by inhibiting uptake of cystine via the x(c-) cystine/glutamate antiporter. Here we examined SASP with regard to reduction of cellular glutathione (GSH) levels and drug efficacy-enhancing ability.

METHODS

GSH levels were measured spectrophotometrically. Cellular drug retention was determined with 3H-labeled methotrexate, and drug efficacy with a colony formation assay.

RESULTS

Incubation of the mammary cancer cells with SASP (0.3-0.5 mM) led to reduction of their GSH content in a time- and concentration-dependent manner. Similar to MK-571, a multidrug resistance-associated protein inhibitor, SASP increased intracellular accumulation of methotrexate. Preincubation of cells with SASP (0.3 mM) significantly enhanced the potency of the anticancer agent doxorubicin (2.5 nM).

CONCLUSIONS

SASP-induced reduction of cellular GSH levels can lead to growth arrest of mammary cancer cells and enhancement of anticancer drug efficacy.

Efflux transporters in ulcerative colitis: decreased expression of BCRP (ABCG2) and Pgp (ABCB1)

BACKGROUND

Efflux transport proteins are important components of the intestinal barrier against bacterial toxins, carcinogens, and drugs. This investigation was conducted to determine the expression of Breast Cancer Resistance Protein (BCRP/ABCG2), P-glycoprotein (Pgp/MDR1/ABCB1), and Multidrug Resistance Protein 2 (MRP2/ABCC2) in the gut mucosa of patients with ulcerative colitis (UC).

METHODS

Patients were thoroughly diagnosed according to well-established clinical, endoscopic, and histologic criteria to be included in the group of patients with active UC (n = 16) or UC in remission (n = 17). Colonic and rectal mucosa from patients with UC were compared with tissues from control subjects (n = 15). The mRNA expression (TaqMan) of the efflux transporters and the proinflammatory cytokines interleukin (IL)-1beta and IL-6 was determined. Western blot was used in the analysis of protein expression and the tissue localization of BCRP was determined with confocal microscopy.

RESULTS

BCRP and Pgp expression was strongly reduced in individuals with active inflammation compared with controls and was negatively correlated with the levels of IL-6 mRNA. The BCRP staining of colonic epithelium seen in healthy mucosa was diminished in inflamed tissues, with concurrent disruption of epithelial F-actin structure.

CONCLUSIONS

Two of the efflux transporters of importance for the barrier function of the gut mucosa, Pgp and BCRP, are expressed at strongly reduced levels during active inflammation in patients with UC. Investigations are warranted to determine whether the low levels of efflux transporters during active UC contribute to altered transport and tissue exposure of carcinogens, bacterial toxins, and drugs.

Use of a pH-sensitive fluorescent probe for measuring intracellular pH of Caco-2 cells

This paper describes the application of a pH-sensitive fluorescent probe [2',7'-bis(2-carboxylethyl)-5(6)-carboxyfluorescein or BCECF] to measure intracellular pH (pH(i)) changes in Caco-2 cells. As a function of BCECF's ionization, the fluorescence was monitored at lambda(ex)=440 and 503nm, and lambda(em)=535nm. Time course studies were conducted with the addition of two weak acid delivery agents, one weak base delivery agent, oleic acid, or tetradecylamine. When applicable, 10microM bovine serum albumin or 10mM ammonium chloride was added into the cell suspension to hinder the pH gradient effect. Adding a weak acid at 2, 10, or 50mM to the cell suspension, the pH(i) dropped substantially from 7.4 to 7.1, 6.9, or 6.7, respectively. The pH(i) then increased gradually over a 10-min period but did not return to its initial value. Conversely, the pH(i) increased instantaneously after the addition of a weak base. When Caco-2 cells were placed in solutions with different bulk pH (7.0, 7.5, and 8.0), the lower the pH in which the cells were exposed, the larger the pH(i) drop occurred with the addition of an acid. The results suggest that these weak acids or bases are transported transcellularly across Caco-2 cells.

Mechanisms responsible for poor oral bioavailability of paeoniflorin: Role of intestinal disposition and interactions with sinomenine

PURPOSE

To determine the intestinal disposition mechanisms of paeoniflorin, a bioactive glucoside, and to investigate the mechanisms by which sinomenine increases paeoniflorin bioavailability.

MATERIALS AND METHODS

A single-pass "four-site" rat intestinal perfusion model and a cultured Caco-2 cell model were employed.

RESULTS

In both model systems, paeoniflorin permeability was poor. In the perfusion model, maximal absorption and metabolism of paeoniflorin occurred in duodenum and jejunum, which were significantly decreased by a glucosidase inhibitor gluconolactone (20 mM). On the other hand, paeoniflorin absorption in terminal ileum increased significantly but its metabolism did not in the presence of sinomenine and cyclosporine A. In the Caco-2 cell model, paeoniflorin was transported 48-fold slower than its aglycone (paeoniflorigenin). Absorptive transport of paeoniflorin was significantly (p < 0.05) increased by sinomenine (38%), verapamil (27%), and cyclosporine A (41%), whereas its secretory transport was significantly (p < 0.01) decreased by sinomenine (50%), verapamil (35%) and cyclosporine A (37%). In contrast, MRP inhibitors MK-571 and leukotriene C4 did not affect transport of paeoniflorin. Lastly, sinomenine was also shown to significantly increase the absorptive transport of digoxin (a prototypical p-glycoprotein substrate) and to significantly decrease its secretory transport.

CONCLUSIONS

Poor permeation, p-gp-mediated efflux, and hydrolysis via a glucosidase contributed to the poor bioavailability of paeoniflorin. Sinomenine (an inhibitor of the p-gp-mediated digoxin efflux) increased paeoniflorin's bioavailability via the inhibition of p-gp-mediated paeoniflorin efflux in the intestine.

Review article: mode of action and delivery of 5-aminosalicylic acid - new evidence

The effectiveness of sulfasalazine depends on the splitting of the diazo bond in the molecule by the action of bacteria in the large bowel, releasing the pharmacologically active moiety, 5-aminosalicylic acid. The development of pH-dependent, delayed-release formulations of 5-aminosalicylic acid abolished the toxicity associated with the sulfapyridine part of sulfasalazine. 5-aminosalicylic acid is now believed to act by activating a class of nuclear receptors involved in the control of inflammation, cell proliferation, apoptosis and metabolic function, the gamma form of peroxisome proliferator-activated receptors. These receptors are expressed at particularly high levels in colon epithelial cells, where their expression appears to be at least in part stimulated by gut bacteria. Other drugs known to act via peroxisome proliferator-activated receptor-gamma, such as rosiglitazone and the selective peroxisome proliferator-activated receptor-gamma ligand GW1929, can be displaced from their binding sites on the peroxisome proliferator-activated receptor-gamma molecule by 5-aminosalicylic acid at concentrations of 5-aminosalicylic acid that correspond with the concentrations found in the lumen of ulcerative colitis patients taking oral mesalazine. Genetically engineered heterozygous knockout mice (peroxisome proliferator-activated receptor-gamma+/-) are particularly susceptible to colonic inflammation, and inflammation is more severe in these mice, in response to chemicals that induce experimental colonic ulcers. In these experimental models, 5-aminosalicylic acid is ineffective in peroxisome proliferator-activated receptor-gamma+/- mice. This new insight provides a mechanistic foundation for the possibility that long-term treatment with 5-aminosalicylic acid can reduce the risk of colorectal cancer in patients with ulcerative colitis.

Transport studies with 5-aminosalicylate

OBJECTIVE

It is generally accepted that 5-aminosalicylate (5-ASA; mesalamine), widely used in inflammatory bowel disease therapy, exerts its action from the intraluminal site of the intestine. In addition to local metabolism of 5-ASA, it has been assumed that therapeutic mucosal concentrations of 5-ASA depend on transporter-mediated secretion back to the lumen.

METHODS

We tested the hypothesis that 5-ASA represents a substrate of P-glycoprotein (P-gp) and/or multidrug resistance-associated protein 2 (MRP2), thereby possibly contributing to variable therapeutic effects. Polarized, basal-to-apical transport of [(3)H]5-ASA was studied in monolayers of Caco-2 and L-MDR cells, both of which express P-gp in their apical membrane, as well as in MDCK cells transfected with human MRP2. Moreover, we investigated the influence of 5-ASA on transport of digoxin in Caco-2 cells.

RESULTS

In Caco-2 cells a P-gp-mediated efflux of 5-ASA (5-500 muM) could be excluded. Likewise, in L-MDR1 and MRP2 cells no transport differences in either the basal-to-apical or apical-to-basal direction were measurable. 5-ASA (50 muM to 5 mM) had no effect on the transport of digoxin.

CONCLUSION

From these in-vitro experiments one can conclude that intestinal secretion of 5-ASA is apparently not mediated by P-gp or MRP2. Further studies are needed to identify the nature of the involved active carrier system(s).

Breast cancer resistance protein (Bcrp/abcg2) is a major determinant of sulfasalazine absorption and elimination in the mouse

Sulfasalazine is used in the treatment of ulcerative colitis, Crohn's disease, and rheumatoid arthritis. When administered orally, sulfasalazine is poorly absorbed with an estimated bioavailability of 3-12%. Recent studies using the T-cell line (CEM) have shown that sulfasalazine is a substrate for the ATP-binding cassette (ABC) efflux pump ABCG2. ABCG2 is known to efflux a number of xenobiotics and appears to be a key determinant of efficacy and toxicity of ABCG2 substrates. To date, there has not been any systematic study on the mechanisms involved in the transport of sulfasalazine in vivo. Accordingly, we investigated whether Bcrp (abcg2) is involved in the disposition of sulfasalazine. After oral administration of 20 mg/kg sulfasalazine, the area under the plasma concentration (AUC) time profile in Bcrp1 (abcg2)-/- knockout (KO) mice was approximately 111-fold higher than that in FVB wild-type (WT) mice. After intravenous administration of 5 mg/kg sulfasalazine, the AUC in Bcrp1 (abcg2)-/- KO mice was approximately 13-fold higher than that in WT mice. Moreover, treatment of WT mice with a single oral dose of gefitinib (Iressa; 50 mg/kg), a known inhibitor of Bcrp, given 2 h prior to administering a single oral dose of sulfasalazine (20 mg/kg), resulted in a 13-fold increase in the AUC of sulfasalazine compared to the AUC in vehicle-treated mice. Since gefitinib is also an inhibitor of P-glycoprotein (P-gp), the impact of P-gp on sulfasalazine absorption in vivo was also examined. The sulfasalazine AUC in mdr1a-/- KO versus WT mice did not differ significantly after either an oral (20 mg/kg) or an intravenous dose (5 mg/kg). We conclude that Bcrp (abcg2) is an important determinant for the oral bioavailability and the elimination of sulfasalazine in the mouse, and that sulfasalazine has the potential to be utilized as a specific in vivo probe of Bcrp (abcg2).