Efficacy assessment of sustained intraperitoneal paclitaxel therapy in a murine model of ovarian cancer using bioluminescent imaging.

We evaluated the pre-clinical efficacy of a novel intraperitoneal (i.p.) sustained-release paclitaxel formulation (PTX(ePC)) using bioluminescent imaging (BLI) in the treatment of ovarian cancer. Human ovarian carcinoma cells stably expressing the firefly luciferase gene (SKOV3(Luc)) were injected i.p. into SCID mice. Tumour growth was evaluated during sustained or intermittent courses of i.p. treatment with paclitaxel (PTX). In vitro bioluminescence strongly correlated with cell survival and cytotoxicity. Bioluminescent imaging detected tumours before their macroscopic appearance and strongly correlated with tumour weight and survival. As compared with intermittent therapy with Taxol, sustained PTX(ePC) therapy resulted in significant reduction of tumour proliferation, weight and BLI signal intensity, enhanced apoptosis and increased survival times. Our results demonstrate that BLI is a useful tool in the pre-clinical evaluation of therapeutic interventions for ovarian cancer. Moreover, these results provide evidence of enhanced therapeutic efficacy with the sustained PTX(ePC) implant system, which could potentially translate into successful clinical outcomes.

Breast cancer resistance protein: mediating the trans-placental transfer of glyburide across the human placenta.

Members of the ATP-binding cassette (ABC) efflux transporter family, including P-glycoprotein (PGP), the multidrug resistance-associated proteins (MRPs) and the breast cancer resistance protein (BCRP) have been shown to be highly expressed in the human placenta. Recent studies documented that the oral hypoglycemic glyburide does not cross the human placenta to an appreciable extent. Furthermore, the trans-placental transfer of glyburide has been shown not to be affected by either the presence of PGP inhibitor, verapamil or MRP inhibitor, indomethacin. Therefore, our objective was to identify other human placental ABC transporters potentially involved in limiting the trans-placental transfer of glyburide to the fetus. [(3)H]-glyburide transport was examined in brush border human placental vesicles in the presence or absence of specific inhibitors. Prepared vesicles were 70% oriented right-side-out and demonstrated 25-27 fold enrichment as compared to whole placenta. Functional studies demonstrated significant increases in the intra-vesicular accumulation of [(3)H]-glyburide in vesicles treated with the BCRP inhibitor, novobiocin. In contrast, PGP inhibition as well as MRP inhibition did not affect [(3)H]-glyburide accumulation. This is the first evidence to clearly indicate that glyburide is preferentially transported by BCRP, in the brush border of the human placenta. Our study also indicates that BCRP likely effluxes substrates in the fetal to maternal direction in the human placenta.

Hepatoprotective role of PXR activation and MRP3 in cholic acid-induced cholestasis.

BACKGROUND AND PURPOSE: Activation of the pregnane X receptor (PXR) has been shown to protect against cholestatic hepatotoxicity. As PXR alters the expression of numerous hepatic bile acid transporters, we sought to delineate their potential role in hepatoprotection. EXPERIMENTAL APPROACH: Wild-type (PXR+/+) and PXR-null (PXR-/-) mice were fed a 1% cholic acid (CA) diet with or without the PXR activator, PCN. Liver function was assessed along with the corresponding changes in hepatic gene expression. KEY RESULTS: CA administration caused significant hepatotoxicity in PXR+/+ mice and was associated with induction of several FXR and PXR regulated genes, which encode for bile acid transport and metabolizing proteins. Compared to CA alone, co-administration of PCN to CA-fed PXR+/+ mice significantly decreased hepatotoxicity and was associated with induction of MRP3 mRNA as well as CYP3A11 mRNA and functional activity. Unexpectedly, PXR-/- mice, which expressed significantly higher basal and CA-induced levels of MRP2, MRP3, OSTalpha, OSTbeta, OATP2 and CYP3A11, were dramatically less sensitive to CA hepatotoxicity than PXR+/+ mice. CONCLUSIONS: Protection of PXR+/+ mice against CA-induced hepatotoxicity by PCN is associated with the induction of MRP3 and CYP3A11 expression. Resistance against CA-induced hepatotoxicity in PXR-/- mice may result from higher basal and induced expression of bile acid transporters, particularly MRP3. These findings emphasize the importance of transport by MRP3 and metabolism as major protective pathways against cholestatic liver injury.

Within Our Skin.

From "beauty is only skin deep" to "it takes a thick skin," there are a countless number of skin-related aphorisms that serve as social commentaries on the beauty and resilience of skin. The skin as an interface to society may have diverse psychological implications, but its physiological importance to health is undeniable. As the largest organ in the body, the skin presents a formidable barrier that serves to protect our internal physiology from potentially harmful stimuli of the external environment.

Transport of glyburide by placental ABC transporters: implications in fetal drug exposure.

Much evidence has demonstrated that a number of ATP-binding cassette (ABC) efflux transporters including P-glycoprotein (PGP), the multidrug resistance-associated proteins (MRPs) and the breast cancer resistance protein (BCRP) are highly expressed in placental tissues and are believed to profoundly limit the passage of therapeutic or toxic xenobiotics to the fetus. Recent studies indicate that the oral hypoglycemic glyburide does not cross the human placenta to an appreciable extent. Our objective was to identify placental transporters potentially involved in limiting the transplacental transfer of glyburide to the fetus. Thus, [(3)H]-glyburide transport was examined in BCRP, PGP, MRP1, MRP2 and MRP3 over-expressing cell lines in the presence or absence of specific inhibitors. Our results demonstrated significant increases in the intracellular accumulation of [(3)H]-glyburide in BCRP and MRP3 over-expressing cells in the presence of the inhibitors novobiocin and indomethacin, respectively. PGP inhibition with verapamil or MRP inhibition with indomethacin did not affect [(3)H]-glyburide accumulation in the PGP or MRP2 over-expressing cell lines and only limited changes were seen in the MRP1 over-expressing cell line. On the other hand, glyburide was found to significantly inhibit MRP1-, MRP2- and MRP3-mediated efflux of 5-carboxyfluorescein diacetate and PGP-mediated transport of rhodamine 123. Our evidence is the first to clearly indicate that glyburide is preferentially transported by BCRP and MRP3.

The Bugs Within Our Body: The Human Microbiota.

The human microbiota is the ecological community of microorganisms that live within our bodies. Emerging evidence has revealed that dysregulation of the host-microbe symbiotic relationship contributes to the pathogenesis of a vast number of human diseases and impacts the efficacy and toxicity of therapeutic drugs. Therefore, a deeper understanding of the human microbiota is crucial to the development of therapeutic interventions that target the microbiota and also provides fundamental insights towards understanding intersubject variability in therapeutic outcomes.

Hybrid films from blends of chitosan and egg phosphatidylcholine for localized delivery of paclitaxel.

Chitosan and egg phosphatidylcholine (ePC) were used as a unique combination to prepare composite films for localized drug delivery. In comparison to other phospholipids analyzed, ePC was found to produce chitosan-based films with minimal swelling and a high degree of stability. The properties of the chitosan-ePC films were characterized and found to be dependent on the ratio of chitosan:ePC present. FTIR analysis of chitosan-ePC films revealed that their high stability may be attributed to interactions present between these two biomaterials. In vitro evaluation of the cytotoxicity and protein adsorption properties of the films were used to provide a preliminary indication of their biocompatibility. The chitosan-ePC film was also evaluated as a matrix for the localized delivery of the anti-cancer agent, paclitaxel. Nanoparticles containing paclitaxel were dispersed throughout the chitosan-ePC film to result in a drug:material ratio of 1:8 (wt/wt). The film was found to provide a sustained release of paclitaxel over a 4-month period in biologically relevant media. The biological activity of paclitaxel loaded in the chitosan-ePC film was confirmed in SKOV-3 human ovarian cancer cells.

Blood-brain barrier: an impediment to neuropharmaceuticals.

The blood-brain barrier (BBB) serves as a highly selective barrier separating the central nervous system from the systemic circulation. Although contributing to neurological health, the BBB restricts the ability of drugs to reach their site of action and thus presents a major challenge to the treatment of neurological disorders. Advances in our understanding of the complexity of the BBB have fostered development of novel pharmacometric models and drug delivery strategies to better predict and improve therapeutic access.

Effect of aging on the pharmacokinetics of acebutolol enantiomers.

Acebutolol (AC) is a chiral beta-blocker that is metabolized to an equipotent chiral metabolite, diacetolol (DC). A stereoselective disposition of AC and DC enantiomers has recently been reported in young healthy subjects. As many physiologic properties affecting drug disposition are progressively altered with increasing age, the effect of aging on the pharmacokinetics of AC and DC enantiomers were investigated in nine subjects ranging from 60 to 75 years after administration of an oral 200-mg dose of racemic AC. Increasing age resulted in a significant prolongation of the elimination t1/2s of R- (r = 0.913) and S-DC (r = 0.811). Also, the S:R ratios of AC urinary excretion (sigma Xu) of enantiomers was significantly correlated with age (r = 0.677). Contribution of declining renal function to age-associated pharmacokinetics changes was subsequently examined. Renal clearance and cumulative urinary excretion of both AC and DC enantiomers were positively correlated with creatinine clearance. In addition, declining creatinine clearance was associated with a subsequent decline in the enantiomer S:R ratio of AC in plasma (AUC S:R, r = 0.807) and urine (sigma Xu S:R r = 0.807). Similarly, a progressive decline in the S:R ratio of DC collected in urine was evident (r = 0.689). Age-related changes in the enantiomers ratios may suggest that an active stereoselective pathway such as renal tubular secretion or nonrenal excretion may be affected in the elderly.

Regulation of the hepatic multidrug resistance gene expression by endotoxin and inflammatory cytokines in mice.

P-glycoprotein (PGP), an ATP-dependent membrane transporter is found in epithelial tissues of the liver, kidneys, intestine and blood-brain barrier. In tumor cells, PGP is often overexpressed and confers multidrug resistance toward cancer chemotherapeutics. It has been previously shown in rats that induction of an inflammatory response evokes a decrease in hepatic expression of PGP. In order to identify the inflammatory mediators involved in this phenomenon, we examined the influence of experimentally induced inflammation and pro-inflammatory cytokines (interleukin (IL)-6, IL-1beta and tumor necrosis factor (TNF)-alpha) on the hepatic expression of PGP in mice. A significant reduction in the hepatic expression of mdr1a, mdr1b, mdr2 and spgp genes were seen in endotoxin (lipopolysaccharide (LPS)) and turpentine-treated mice. Similarly, IL-6-treated mice displayed a 70% reduction in protein expression and a 40-70% reduction in the mRNA levels of all PGP mdr isoforms. Administration IL-1beta caused an increase in both mdr1b mRNA and protein expression, however, mRNA levels of mdr1a, mdr2 and spgp were significantly reduced. Administration of TNF-alpha also caused increases in mdr1b mRNA. These findings indicate that IL-6 plays a principal role in the downregulation of PGP that is observed in the livers of mice during an inflammatory response.

Pharmacokinetics of acebutolol enantiomers in humans.

The chiral beta-blocker acebutolol (AC) is marketed as a racemic mixture. Both AC and its major metabolite, diacetotol (DC), are chiral, the S-enantiomer possessing beta-blocking activity. The pharmacokinetics of AC and DC enantiomers was determined in 12 healthy subjects following oral administration of 200 mg of AC. Plasma and urine were collected over a 24-hr period and both AC and DC enantiomers were measured utilizing a stereospecific HPLC assay. Concentrations of S-AC were predominant in both plasma and urine [AUC S:R, 1.20 +/- 0.1; cumulative urinary excretion (sigma Xu) S:R, 1.17 +/- 0.05), which corresponded to a significantly greater oral clearance of R-AC (106 +/- 30 L/h) than S-AC (87 +/- 22 L/h). The Cmax of R-DC was significantly greater than for S-DC (S/R 0.7 +/- 0.1). The half-life (t1/2) of R-DC (6.4 +/- 1.6 h) was significantly shorter than that of S-DC (8.8 +/- 2.4 h). The observed AUC values for R- and S-DC were not significantly different. Renal clearance of R-DC (70 +/- 34 mL/min) was significantly greater than that of S-DC (53 +/- 29 mL/min). The data suggest that the first-pass metabolism of R-AC to R-DC is stereoselective. This metabolism, coupled with the stereoselective renal excretion of R-DC is likely a major contributor to the observed stereoselective disposition of AC and its major metabolite in humans.

Expression of human polyspecific renal organic cation transport activity in Xenopus laevis oocytes.

Polyspecific organic cation transporters in the basolateral and brush border membrane of the kidney play a role in the elimination of many clinically important drugs and endogenous compounds. In this study we report the functional expression of organic cation transport activity in Xenopus laevis oocytes injected with poly(A)+RNA (mRNA) isolated from human kidney. Uptake of [14C]tetraethylammonium (TEA) was measured in mRNA-injected or water-injected oocytes, 4 days after injection. In oocytes injected with 50 ng of mRNA isolated from human renal cortex, the uptake of [14C]TEA was significantly increased in comparison with water-injected oocytes (7.2 +/- 0.6 and 3.5 +/- 0.3 pmol/oocyte/h, respectively). Injection of 20 ng of an enriched size-fraction (fraction C) of mRNA (mean size of 2.3 kb) resulted in further enhancement of [14C]TEA uptake: [14C]TEA uptake was enhanced six-to seven-fold in oocytes injected with fraction C (23.7 +/- 3.7 pmol/oocyte/h) in comparison with water-injected oocytes. The uptake of TEA in mRNA-injected oocytes was significantly inhibited by 5 mM of unlabeled TEA, cimetidine, and N1-methylnicotinamide. These data suggest that polyspecific organic cation transport activity can be successfully expressed in Xenopus laevis oocytes injected with mRNA isolated from human kidney.

Regulation of the multidrug resistance genes by stress signals.

Transporters in the body play a large role in the distribution and elimination of many clinically important therapeutic substances. Of these, perhaps the one that has been best studied is P-Glycoprotein (PGP), a 170 kDa membrane-bound protein which has been implicated as a primary cause of multidrug-resistance in tumors. An understanding of the physiological regulation of these transporters is key to designing strategies for the improvement of therapeutic efficacy of drugs which are their substrates. To that end, we examine herein the current state of understanding of the molecular regulation of PGP by a variety of endogenous and environmental stimuli which evoke stress responses including cytotoxic agents, heat shock, irradiation, genotoxic stress, inflammation, inflammatory mediators, cytokines and growth factors.

Inflammation: the dynamic force of health and disease.

Replacing "happiness" with "inflammation" in Thomas Merton's quotation holds true for the processes that govern our immune response and health. The balance between pro- and anti-inflammatory signals regulates inflammatory responses, leading to either restoration of health or the development and progression of disease, depending on whether it creates equilibrium or dysfunction. This issue of Clinical Pharmacology & Therapeutics highlights emerging research and concepts related to inflammation and its underlying role in chronic disease and variable drug response.

Network medicine: finding the links to personalized therapy.

Network medicine is a new approach that focuses on applying systems biology to pharmacology by "understanding the molecular system [and its perturbations] as a whole" so as to unravel the complex relationships among disease processes, genes, drugs, therapeutic indicators, and adverse effects.(1,2.)

Epigenetics: a new link toward understanding human disease and drug response.

Molecular medicine is moving beyond genomics to encompass the new scientific field of epigenetics. First described as a conceptual model of how genes might interact with their surroundings to produce a phenotype, epigenomic research currently investigates mechanisms of nongenetic modification contributing to gene regulation and examines the impact of these changes on human health and behavior.

Pharmacokinetic studies in pregnant women.

Prescription and over-the-counter drug use during pregnancy is necessary for many women today. A study of US and Canadian women found that, on average, 2.3 drugs were used during pregnancy; however, 28% reported using more than 4. For some women, this is because they become pregnant with preexisting conditions that require ongoing or intermittent pharmacotherapy. For others, this is because pregnancy itself can give rise to new medical conditions such as gestational diabetes and preeclampsia. The principal concern of prescribing physicians is whether or not agents will harm the fetus (i.e., have teratogenic effects). This concern rose to prominence primarily as a result of the thalidomide disaster. Marketed for use in morning sickness, thalidomide was found to be a potent teratogen capable of producing a variety of birth defects relating to development. Consequently, determining the teratogenicity of new drugs currently dominates the objectives of pregnancy-relevant experiments conducted throughout drug development. This often comes at the expense of valuable pharmacokinetic (PK) studies, which are seldom performed pre-market. Sex differences in PK parameters have been demonstrated in animals and humans since the 1930s. It is, therefore, not surprising that differences also arise in pregnancy. A wide array of physiological and hormonal changes occur during pregnancy; most begin early in the first trimester and increase linearly until parturition. Physicians lacking adequate PK information typically prescribe the standard adult dose in pregnancy, and this can be either inadequate or excessive depending on a variety of factors. The purpose of this report is to highlight this issue and illustrate how current methods used to obtain PK data in pregnancy are insufficient. The steps that are being taken to address this issue will also be discussed.