Role of P-glycoprotein in distribution of nelfinavir across the blood-mammary tissue barrier and blood-brain barrier

Optimizing rosemary oil nanoemulsion loaded with nelfinavir and epigallocatechin gallate: A Design Expert® endorsed approach for enhanced neuroAIDS management

This study focuses on optimizing the delivery of Nelfinavir (NFV), a vital protease inhibitor in antiretroviral therapy, and Epigallocatechin gallate (EGCG), a potent adjunctive anti- human immunodeficiency virus (anti-HIV) agent found in green tea. The challenge lies in NFV's low intrinsic dissolution rate, significant p-gp efflux, and high hepatic metabolism, necessitating frequent and high-dose administration. Our objective was to develop a nanoemulsion loaded with NFV and EGCG to enhance oral delivery, expediting antiretroviral effects for NeuroAIDS treatment. After meticulous excipient screening, we selected Tween 40 as the surfactant and polyethylene glycol 400 (PEG 400) as the co-surfactant. Employing a Quality by Design (QbD) approach with statistical multivariate methods, we optimized the nanoemulsion that exhibited a droplet size of 83.21 nm, polydispersity index (PDI) of 2.289, transmittance of 95.20 %, zeta potential of 1.495 mV, pH of 6.95, refractive index of 1.40, viscosity of 24.00 ± 0.42 mPas, and conductivity of 0.162 μS/cm. Pharmacokinetic studies demonstrated superior in vivo absorption of the optimized nanoemulsion compared to NFV and EGCG suspension. The optimized nanoemulsion showcased higher Cmax of NFV (9.75 ± 1.23 μg/mL) and EGCG (27.7 ± 1.22 μg/mL) in the brain, along with NFV (26.44 ± 1.44 μg/mL) and EGCG (313.20 ± 5.53 μg/mL) in the plasma. This study advocates for the potential of NFV and EGCG-loaded nanoemulsion in combination antiretroviral therapy (cART) for effective NeuroAIDS management.

Select drug-drug interactions with colchicine and cardiovascular medications: A review

Several randomized clinical trials have demonstrated the clinical utility of colchicine in the prevention and management of various cardiovascular conditions, including secondary prevention of atherosclerotic cardiovascular disease, acute and chronic pericarditis, and atrial fibrillation. As a result, it is reasonable to anticipate increased use of colchicine within the cardiovascular specialty. However, colchicine is metabolized by cytochrome P450 3A4 (CYP3A4) and a substrate of the efflux transporter, P-glycoprotein (P-gp), creating the potential for clinically significant drug-drug interactions (DDIs). Therefore, when colchicine is administered concomitantly with other cardiovascular agents that inhibit CYP3A4 or P-gp, there is an increased risk of significant DDIs, potentially leading to negative sequelae. This article summarizes the evidence supporting the use of colchicine for cardiovascular disease, describes the mechanisms behind DDIs with select cardiovascular medications, and provides suggestions regarding colchicine dosing and management of DDIs to minimize the risk of poor tolerability and colchicine toxicity.

Exploring Natural Product Activity and Species Source Candidates for Hunting ABCB1 Transporter Inhibitors: An In Silico Drug Discovery Study

The P-glycoprotein (P-gp/ABCB1) is responsible for a xenobiotic efflux pump that shackles intracellular drug accumulation. Additionally, it is included in the dud of considerable antiviral and anticancer chemotherapies because of the multidrug resistance (MDR) phenomenon. In the search for prospective anticancer drugs that inhibit the ABCB1 transporter, the Natural Product Activity and Species Source (NPASS) database, containing >35,000 molecules, was explored for identifying ABCB1 inhibitors. The performance of AutoDock4.2.6 software to anticipate ABCB1 docking score and pose was first assessed according to available experimental data. The docking scores of the NPASS molecules were predicted against the ABCB1 transporter. Molecular dynamics (MD) simulations were conducted for molecules with docking scores lower than taxol, a reference inhibitor, pursued by molecular mechanics-generalized Born surface area (MM-GBSA) binding energy estimations. On the basis of MM-GBSA calculations, five compounds revealed promising binding affinities as ABCB1 inhibitors with ΔGbinding < −105.0 kcal/mol. The binding affinity and stability of the identified inhibitors were compared to the chemotherapeutic agent. Structural and energetical analyses unveiled great steadiness of the investigated inhibitors within the ABCB1 active site throughout 100 ns MD simulations. Conclusively, these findings point out that NPC104372, NPC475164, NPC2313, NPC197736, and NPC477344 hold guarantees as potential ABCB1 drug candidates and warrant further in vitro/in vivo tests.

Non-ionic Surfactants as a P-Glycoprotein(P-gp) Efflux Inhibitor for Optimal Drug Delivery-A Concise Outlook

Significant research efforts have been devoted to unraveling the mystery of P-glycoprotein(P-gp) in drug delivery applications. The efflux membrane transporter P-gp is widely distributed in the body and accountable for restricting drug absorption and bioavailability. For these reasons, it is the primary cause of developing multidrug resistance (MDR) in most drug delivery applications. Therefore, P-gp inhibitors must be explored to address MDR and the low bioavailability of therapeutic substrates. Several experimental models in kinetics and dynamic studies identified the sensitivity of drug molecules and excipients as a P-gp inhibitor. In this review, we aimed to emphasize nonionic surface-active agents for effective reversal of P-gp inhibition. As it is inert, non-toxic, noncharged, and quickly reaching the cytosolic lipid membrane (the point of contact with P-gp efflux protein) enables it to be more efficient as P-gp inhibitors. Moreover, nonionic surfactant improves drug absorption and bioavailability through the various mechanism, involving (i) association of drug with surfactant improves solubilization, facilitating its cell penetration and absorption; (ii) weakening the lateral membrane packing density, facilitating the passive drug influx; and (iii) inhibition of the ATP binding cassette of transporter P-glycoprotein. The application of nonionic surfactant as P-gp inhibitors is well established and supported by various experiments. Altogether, herein, we have primarily focused on various nonionic surfactants and their development strategies to conquer the MDR-causing effects of P-gp efflux protein in drug delivery. Graphical Abstract.

Chemical synthesis, molecular docking and MepA efflux pump inhibitory effect by 1,8-naphthyridines sulfonamides

This study aimed to evaluate the antibacterial activity and to verify, in silico and in vitro, the inhibition of efflux mechanisms using a series of synthesized 1,8-naphthyridines sulfonamides against Staphylococcus aureus strains carrying MepA efflux pumps. The chemical synthesis occurred through the thermolysis of the Meldrum's acid adduct. The sulfonamide derivatives were obtained by the sulfonylation of 2-amino-5‑chloro-1,8-naphthyridine with commercial benzenesulfonyl chloride. Antibacterial activity was assessed by the broth microdilution test. Efflux pump inhibitory capacity was evaluated in silico by molecular docking and in vitro by analyzing synergistic effects on ciprofloxacin and ethidium bromide (EtBr) and by EtBr fluorescence emission assays. The following 1,8-naphthyridines were synthesized: 4-methyl-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10a); 2,5-dichloro-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10b); 4-fluoro-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10c); 2,3,4-trifluoro-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10d); 3-trifluoromethyl-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10e); 4‑bromo-2,5-difluoro-N-(5‑chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide (Compound 10f). The 1,8-naphthyridines derivatives associated with sulfonamides did not show antibacterial activity. However, they showed a favorable pharmacokinetic profile with possible MepA efflux pump inhibitory action, demonstrated in molecular docking. In addition to the promising results in reducing the concentration of intracellular EtBr. 1,8-naphthyridines act as putative agents in the inhibitory action of the MepA efflux pump.

The 1,8-naphthyridines sulfonamides are NorA efflux pump inhibitors

OBJECTIVE

Efflux pumps are transmembrane proteins associated with bacterial resistance mechanisms. Bacteria use these proteins to actively transport antibiotics to the extracellular medium, preventing the pharmacological action of these drugs. This study aimed to evaluate in vitro the antibacterial activity of 1,8-naphthyridines sulfonamides, as well as their ability to inhibit efflux systems of Staphylococcus aureus strains expressing different levels of the NorA efflux pump.

METHODS

The broth microdilution test was performed to assess antibacterial activity. Efflux pump inhibition was evaluated in silico by molecular docking and in vitro by fluorometric tests, and the minimum inhibitory concentration (MIC) was determined. The MIC was determined in the association between 1,8-naphthyridine and norfloxacin or ethidium bromide.

RESULTS

The 1,8-naphthyridines did not show direct antibacterial activity. However, they effectively reduced the MIC of multidrug-resistant bacteria by associating with norfloxacin and ethidium bromide, in addition to increasing the fluorescence emission. In silico analysis addressing the binding between NorA and 1,8-naphthyridines suggests that hydrogen bonds and hydrophilic interactions represent the interactions with the most favourable binding energy, corroborating the experimental data.

CONCLUSION

Our data suggest that 1,8-naphthyridines sulfonamides inhibit bacterial resistance through molecular mechanisms associated with inhibition of the NorA efflux pump in S. aureus strains.

Effects of verapamil on the pharmacokinetics of ivermectin in rabbits

This study was aimed to investigate the influence of verapamil-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetics of ivermectin (IVM) given orally and subcutaneously (SC) to rabbits. Twenty New Zealand rabbits were allotted to 4 groups (n = 5) and received IVM either orally or SC (0.4 mg/kg) alone or co-administered with verapamil (2 mg/kg SC, 3 times at a 12-hr interval). Plasma, fecal, and urine samples were collected over 30 days after medication to assess IVM concentrations in these samples. No significant differences were observed in the pharmacokinetic parameters of IVM between oral and SC administrations. The area under the plasma concentration-time curve was higher (p < .05) after IVM (oral)/verapamil treatment, compared with oral IVM alone. Moreover, the time to the C_max of IVM was shorter (p < .05), whereas the elimination half-life and the mean residence time were longer (p < .05) in the presence of verapamil. The IVM/verapamil combination administered orally or SC reduced fecal IVM concentrations, compared with IVM alone. In conclusion, the significant changes by verapamil on the pharmacokinetics of IVM, likely due to the inhibition of a P-gp-mediated intestinal secretion, may change IVM's antinematodal activity.

Tuning Properties for Blood-Brain Barrier Permeation: A Statistics-Based Analysis

In the effort to define a set of rules useful in tuning the properties for a successful blood-brain barrier (BBB) permeation, we statistically analyzed a set of 328 compounds and correlated their experimental in vivo logBB with a series of computed descriptors. Contingency tables were constructed, observed and expected distributions were calculated, and chi-square (χ²) distributions were evaluated. This allowed to point out a significant dependence of certain physicochemical properties in influencing the BBB permeation. Of over 15 computed descriptors, 9 resulted to be particularly important showing highly significant χ² distribution: polar surface area (χ² = 66.79; p = 1.08 × 10^-13), nitrogen and oxygen count (χ² = 51.17; p = 2.06 × 10^-10), logP (χ² = 47.38; p = 1.27 × 10^-9), nitrogen count (χ² = 38.29; p = 9.77 × 10^-8), logD (χ² = 36.80; p = 36.80), oxygen count (χ² = 35.83; p = 3.13 × 10^-7), ionization state (χ² = 33.02, p = 3.19 × 10^-7), hydrogen bond acceptors (χ² = 30.80; p = 3.36 × 10^-6), and hydrogen bond donors (χ² = 29.29; p = 6.81 × 10^-6). Other parameters describing the mass and size of the molecules (molecular weight: 11.18; p = 2.46 × 10^-2) resulted in being not significant since the population within the observed and expected distribution was similar. Depending on the combination of the significant descriptors, we set a three cases probabilistic scenario (BBB⁺, BBB^-, BBB⁺/BBB^-) that would prospectively be used to tune properties for BBB permeation.

Pharmacological role of efflux transporters: Clinical implications for medication use during breastfeeding

The World Health Organisation recommends exclusive breastfeeding for the first six months of an infant’s life and in combination with solid food thereafter. This recommendation was introduced based on research showing numerous health benefits of breastfeeding for both the mother and the infant. However, there is always concern regarding the transfer of medications from mother to their breastfed baby via milk. Pharmacokinetic properties of a drug are usually used to predict its transferability into breast milk. Although most drugs are compatible with breastfeeding, cases of toxic drug exposure have been reported. This is thought to be due to active transport mechanisms whereby efflux transporter proteins expressed in the epithelial cells of the mammary gland actively secrete drugs into milk. An example of such efflux transporters including the breast cancer resistance protein which is strongly induced during lactation and this could result in contamination of milk with the substrates of this transporter which may place the suckling infant at risk of toxicity. Furthermore, there is little known about the substrate specificity of most efflux transporters as we have highlighted in this review. There also exists some degree of contradiction between in vivo and in vitro studies which makes it difficult to conclusively predict outcomes and drug-drug interactions.

Therapeutic potential of nanocarrier for overcoming to P-glycoprotein

Enhancement of targeted therapeutic effect in the body and achievement of high bioavailability are major concern for the researchers due to the complex physiology of human body. There are so many barriers that hinder the absorption and permeation of drugs from the body, thus influencing the bioavailability of therapeutics. P-glycoprotein (P-gp) is one of such barrier present on the apical membranes of various organs such as small intestine, brain, kidney and liver. This protein interacts with vast variety of therapeutics and efflux out them preventing their entrance to the desired site, thus modulating their pharmacokinetic properties. To address this, a concerned number of approaches have been used such as the use of chemo sensitizers along with the therapeutics and various novel techniques. In this review, we are going to discuss the basic introduction to this protein and overview of various strategies used earlier to tackle the problem of P-gp efflux as well as the role of nanocarriers in confronting this issue. Nanocarriers have played great role in the enhancement of the bioavailability of many antineoplastic agents as well as other P-gp substrates. Encapsulation of P-gp inhibitors in the nanocarrier system prevents toxicity and gives site-specific action.

Tacrolimus placental transfer at delivery and neonatal exposure through breast milk

AIM(S)

The current investigation aims to provide new insights into fetal exposure to tacrolimus in utero by evaluating maternal and umbilical cord blood (venous and arterial), plasma and unbound concentrations at delivery. This study also presents a case report of tacrolimus excretion via breast milk.

METHODS

Maternal and umbilical cord (venous and arterial) samples were obtained at delivery from eight solid organ allograft recipients to measure tacrolimus and metabolite bound and unbound concentrations in blood and plasma. Tacrolimus pharmacokinetics in breast milk were assessed in one subject.

RESULTS

Mean (±SD) tacrolimus concentrations at the time of delivery in umbilical cord venous blood (6.6 ± 1.8 ng ml(-1)) were 71 ± 18% (range 45-99%) of maternal concentrations (9.0 ± 3.4 ng ml(-1)). The mean umbilical cord venous plasma (0.09 ± 0.04 ng ml(-1)) and unbound drug concentrations (0.003 ± 0.001 ng ml(-1)) were approximately one fifth of the respective maternal concentrations. Arterial umbilical cord blood concentrations of tacrolimus were 100 ± 12% of umbilical venous concentrations. In addition, infant exposure to tacrolimus through the breast milk was less than 0.3% of the mother's weight-adjusted dose.

CONCLUSIONS

Differences between maternal and umbilical cord tacrolimus concentrations may be explained in part by placental P-gp function, greater red blood cell partitioning and higher haematocrit levels in venous cord blood. The neonatal drug exposure to tacrolimus via breast milk is very low and likely does not represent a health risk to the breastfeeding infant.

Coadministration of lapatinib increases exposure to docetaxel but not doxorubicin in the small intestine of mice

Combination therapy is increasingly being utilized for the treatment of metastatic breast cancer. However, coadministration of drugs, particularly agents that are substrates for or inhibitors of p-glycoprotein, can result in increased tissue toxicity. Unfortunately, determination of levels of chemotherapeutics in human tissues is challenging, and plasma drug concentrations are not always indicative of tissue toxicokinetics or toxicodynamics, especially when tissue penetration is altered. The aim of the present work was to determine whether concomitant administration of compounds currently being combined in clinical trials for metastatic breast cancer treatment alters plasma and tissue pharmacokinetics in mice if both agents are p-glycoprotein substrates and/or inhibitors. Accordingly, we investigated the pharmacokinetic interactions of the classic cytotoxics and p-glycoprotein substrates docetaxel and doxorubicin when administered concurrently with the targeted agent and p-glycoprotein inhibitor lapatinib. Our time-course plasma and tissue distribution studies showed that coadministration of lapatinib with doxorubicin did not appreciably alter the pharmacokinetics of this anthracycline in the plasma or six tissues evaluated in mice, presumably because, at doses relevant to human exposure, lapatinib inhibition of p-glycoprotein did not significantly alter doxorubicin transport out of these tissue compartments. However, combining lapatinib with docetaxel significantly increased intestinal exposure to this chemotherapeutic, which has clinical implications for enhancing gastrointestinal toxicity. The significant lapatinib-docetaxel interaction is likely CYP3A4-mediated, suggesting that caution should be exercised when this combination is administered, particularly to patients with compromised CYP3A activity, and recipients should be monitored closely for enhanced toxicity, particularly for adverse effects on the intestine.

P-glycoprotein Inhibition for Optimal Drug Delivery

P-glycoprotein (P-gp), an efflux membrane transporter, is widely distributed throughout the body and is responsible for limiting cellular uptake and the distribution of xenobiotics and toxic substances. Hundreds of structurally diverse therapeutic agents are substrates to it and it impedes the absorption, permeability, and retention of the drugs, extruding them out of the cells. It is overexpressed in cancer cells and accountable for obstructing cell internalization of chemotherapeutic agents and for developing transporter mediated resistance by cancer cells during anti-tumor treatments. As it jeopardizes the success of drug delivery and cancer targeting, strategies are being developed to overcome P-gp mediated drug transport. This concise review represents a brief discussion on P-gp mediated drug transport and how it hinders the success of various therapies. Its main focus is on various strategies used to tackle this curb in the field of drug delivery and targeting.

Modeling bioavailability to organs protected by biological barriers

Computational pharmacokinetic (PK) modeling gives access to drug concentration vs. time profiles in target organs and allows better interpretation of clinical observations of therapeutic or toxic effects. Physiologically-based PK (PBPK) models in particular, based on mechanistic descriptions of the body anatomy and physiology, may also help to extrapolate in vitro or animal data to human.

Once in the systemic circulation, a chemical has access to the microvasculature of every organ or tissue. However, its penetration in the brain, retina, thymus, spinal cord, testis, placenta,… may be limited or even fully prevented by dynamic physiological blood-tissue barriers. Those barriers are both physical (involving tight junctions between adjacent cells) and biochemical (involving metabolizing enzymes and transporters).

On those cases, correct mechanistic characterization of the passage (or not) of molecules through the barrier can be crucial for improved PBPK modeling and prediction.

In parallel, attempts to understand and quantitatively characterize the processes involved in drug penetration of physiological barriers have led to the development of several in vitro experimental models. Data from such assays are very useful to calibrate PBPK models.

We review here those in vitro and computational models, highlighting the challenges and perspectives for in vitro and computational models to better assess drug availability to target tissues.

Pharmacogenetics of chronic pain and its treatment

This paper reviews the impact of genetic variability of drug metabolizing enzymes, transporters, receptors, and pathways involved in chronic pain perception on the efficacy and safety of analgesics and other drugs used for chronic pain treatment. Several candidate genes have been identified in the literature, while there is usually only limited clinical evidence substantiating for the penetration of the testing for these candidate biomarkers into the clinical practice. Further, the pain-perception regulation and modulation are still not fully understood, and thus more complex knowledge of genetic and epigenetic background for analgesia will be needed prior to the clinical use of the candidate genetic biomarkers.

Impact of ATP-binding cassette transporters on human immunodeficiency virus therapy

Even though potent antiretrovirals are available against human immunodeficiency virus (HIV)-1 infection, therapy fails in a significant fraction of patients. Among the most relevant reasons for treatment failure are drug toxicity and side effects, but also the development of viral resistance towards the drugs applied. Efflux by ATP-binding cassette (ABC-) transporters represents one major mechanism influencing the pharmacokinetics of antiretroviral drugs and particularly their distribution, thus modifiying the concentration within the infected cells, that is, at the site of action. Moreover, drug-drug interactions may occur at the level of these transporters and modulate their activity or expression thus influencing the efficacy and toxicity of the substrate drugs. This review summarizes current knowledge on the interaction of antiretrovirals used for HIV-1 therapy with ABC-transporters and highlights the impact of ABC-transporters for cellular resistance and therapeutic success. Moreover, the suitability of different cell models for studying the interaction of antiretrovirals with ABC-transporters is discussed.

Lactation stage-dependent expression of transporters in rat whole mammary gland and primary mammary epithelial organoids

Since solute carrier (SLC) and ATP-binding cassette (ABC) transporters play pivotal roles in the transport of both nutrients and drugs into breast milk, drug-nutrient transport interactions at the lactating mammary gland are possible. Our purpose was to characterize lactation stage-dependent changes in transporter expression in rat mammary gland and isolated mammary epithelial organoids (MEO) to provide additional insight for the safe use of maternal medications during breastfeeding. We used quantitative reverse transcription-polymerase chain reaction to assess the temporal expression patterns of SLC and ABC transporters in rat mammary gland and isolated MEO at different stages of lactation. In whole mammary gland five distinct patterns of expression emerged relative to late gestation: (i) decreasing throughout lactation (Mdr1a, Mdr1b, Mrp1, Octn2, Ent2, Ent3, Ncbt2, Mtx1); (ii) prominent increase in early lactation, which may remain elevated or decline with advancing lactation (Octn1, Cnt2, Cnt3, Ent1, Pept1, Pept2); (iii) constant but decreasing later in lactation (Octn3, Dmt1); (iv) increasing until mid-to-late lactation (Oct1, Cnt1); and (v) prominent increase late in lactation (Ncbt1). In isolated MEO (an enriched source of mammary epithelial cells) major differences in expression patterns were noted for Octn3, Ncbt1, and Mtx1, but otherwise were reasonably similar with the whole mammary gland. In conclusion our study augments existing data on transporter expression in the lactating mammary gland. These data should facilitate investigations into lactation-stage dependent changes in drug or nutrient milk-to-serum concentration ratios, the potential for drug- or disease-transporter interactions, and mechanistic studies of transporter function in the lactating mammary gland.

Short communication: Attempts to identify Clostridium botulinum toxin in milk from three experimentally intoxicated Holstein cows

Three adult lactating Holstein cows were injected in the subcutaneous abdominal vein with 175 ng/kg of body weight of Clostridium botulinum type C toxin (451 cow median toxic doses) to determine if this botulinum toxin crosses the blood-milk barrier. Whole blood (in sodium heparin) and clotted blood serum samples were taken at 0 min, 10 min, and 3, 6, 9, and 12 h postinoculation. Milk samples were taken at 0 min and at 3, 6, 9 and 12 h postinoculation. All samples were tested for the presence of the toxin using the mouse bioassay and immunostick ELISA test. The immunostick ELISA identified the toxin in whole blood and the mouse bioassay identified the toxin in serum at all times examined in all 3 animals. Toxin was not identified by either detection method in milk samples collected from the 3 animals. From these results, it appears that Clostridium botulinum type C toxin does not cross from the blood to the milk in detectable concentrations.

N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) as a chemical ATP-binding cassette transporter family G member 2 (Abcg2) knockout model to study nitrofurantoin transfer into milk

Genetic knockout mice studies suggested ATP-binding cassette transporter family G member 2 (ABCG2)/Abcg2 translocates nitrofurantoin at the mammary-blood barrier, resulting in drug accumulation in milk. The purpose of this study was to establish the role of Abcg2 in nitrofurantoin accumulation in rat milk using N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) as a "chemical knockout" equivalent. The inhibitory effect of GF120918 was verified in Madin-Darby canine kidney II cells stably expressing rat Abcg2 with Hoechst 33342 and nitrofurantoin flux in Transwells. Nitrofurantoin was infused (0.5 mg/h) in the absence and presence of GF120918 (10 mg/kg in dimethyl sulfoxide) to Sprague-Dawley lactating female rats using a balanced crossover design. Administration of GF120918 increased nitrofurantoin concentration in serum (from 443 +/- 51 to 650 +/- 120 ng/ml) and decreased concentration in milk (from 18.1 +/- 0.9 to 1.9 +/- 1.2 microg/ml), resulting in corresponding mean values for milk to serum concentration ratio (M/S) of 41.4 +/- 19.1 versus 3.04 +/- 2.27 in the absence and presence of GF120918 (p < 0.05), respectively. There was a decrease in systemic clearance with GF120918 (2.8 +/- 0.5 l/h/kg) compared with vehicle controls (4.1 +/- 0.5 l/h/kg; p < 0.05). Western blot analysis revealed good expression of Abcg2 and no P-glycoprotein (P-gp) expression in mammary gland, whereas immunohistochemistry confirmed the apical expression of Abcg2 in lactating mammary gland epithelia. Nitrofurantoin active transport into rat milk can be inhibited by GF120918 resulting in a 10-fold lower M/S. Although GF120918 inhibits both Abcg2 and P-gp, the high expression of Abcg2 and the absence of detectable P-gp expression in lactating mammary gland validate an important role for Abcg2 in nitrofurantoin accumulation in rat milk. GF120918 is particularly useful as a rat chemical knockout model to establish ABCG2's role in drug transfer into milk during breastfeeding.

A novel colorimetric assay for CXCR4 and CCR5 tropic human immunodeficiency viruses

The majority of HIV isolated from infected patients uses CCR5 as a coreceptor (R5-HIV). Although R5-HIV fails to replicate efficiently in human transformed T-cell lines, HIV using CXCR4 (X4-HIV) can replicate well in such cell lines. Therefore, most of screening systems using the T-cell lines detect only X4-HIV replication. Here we report a new assay to monitor the replication of R5- as well as X4-HIV. An MTT assay using CD4-, CXCR4-, and CCR5-transduced human glioma NP-2 cells (NCK45 cells) was established and then compared with the representative assays including multinuclear activation of a galactosidase indicator assay (MAGI assay). The antiviral activities of not only an adsorption inhibitor and reverse transcriptase inhibitors but also a Tat antagonist in the NCK45 cells, were comparable to those obtained from the MTT assay using MT-4 cells or the MAGI assay. However, the activity of protease inhibitors (PIs) was underestimated, even though expressions of major multidrug resistant genes involved in efflux of PIs were comparable in MT-2, NP-2, and NCK45 cells. After cultivation of more than 6 months, NCK45 cells remained susceptible to HIV infection since NCK45 cells consistently expressed CD4, CXCR4, and CCR5. On the other hand, MAGI cells lost the CD4 expression during culture. Thus, this assay system can stably detect the replication of both X4- and R5-HIV, indicating that it should be useful for the evaluation of HIV replication and drug susceptibility.

Dependence of nelfinavir brain uptake on dose and tissue concentrations of the selective P-glycoprotein inhibitor zosuquidar in rats

Most reverse transcriptase and protease inhibitors used in highly active antiretroviral therapy for treating human immunodeficiency virus (HIV) infections exhibit poor penetration into the brain, raising the concern that the brain may be a sanctuary site for the development of resistant HIV variants. This study explores the relationship between the dose and plasma and brain concentrations of zosuquidar and the effect of this selective P-glycoprotein inhibitor on central nervous system penetration of the HIV protease inhibitor nelfinavir maintained at steady state by intravenous infusions in rats. Nelfinavir was infused (10 mg/kg/h) for up to 10 h with or without concurrent administration of an intravenous bolus dose of 2, 6, or 20 mg/kg zosuquidar given at 4 h. Brain tissue and plasma were analyzed for both drug concentrations. Brain tissue/plasma nelfinavir concentration ratios (uncorrected for the vascular contribution) increased nonlinearly with zosuquidar dose from 0.06 +/- 0.03 in the absence of zosuquidar and 0.09 +/- 0.02 between 2 and 6 h after 2 mg/kg zosuquidar to 0.85 +/- 0.19 after 6 mg/kg and 1.58 +/- 0.67 after 20 mg/kg zosuquidar. Zosuquidar brain tissue/plasma concentration ratios exhibited a similar abrupt increase from 2.8 +/- 0.3 after a 2 mg/kg dose to approximately 15 after the 6 and 20 mg/kg doses. The apparent threshold in the plasma concentration of zosuquidar necessary to produce significant enhancement in brain uptake of nelfinavir appears to be close to the plasma concentrations associated with the maximum tolerated dose reported in the literature after repeated dosing of zosuquidar in patients.