In vivo evaluation of thiolated poly(acrylic acid) as a drug absorption modulator for MRP2 efflux pump substrates

Oral meropenem for superbugs: challenges and opportunities

An increase in the number of multidrug-resistant microbial strains is the biggest threat to global health and is projected to cause >10 million deaths by 2055. The carbapenem family of antibacterial drugs are an important class of last-resort treatment of infections caused by drug-resistant bacteria and are only available as an injectable formulation. Given their instability within the gut and poor permeability across the gut wall, oral carbapenem formulations show poor bioavailability. Meropenem (MER), a carbapenem antibiotic, has broad-spectrum antibacterial activity, but suffers from the above-mentioned issues. In this review, we discuss strategies for improving the oral bioavailability of MER, such as inhibiting tubular secretion, prodrug formulations, and use of nanomedicine. We also highlight challenges and emerging approaches for the development of oral MER.

Increasing the stability of Lumbricus terrestris erythrocruorin via poly(acrylic acid) conjugation

Since donated red blood cells must be constantly refrigerated, they are often unavailable in remote areas and battlefields. The goal of this study was to synthesize a highly stable blood substitute that does not require refrigeration. Specifically, the extracellular haemoglobin (a.k.a. erythrocruorin, Ec) of the earthworm Lumbricus terrestris erythrocruororin (LtEc) was cross-linked with poly(acrylic acid) (PAA) and ethylene diamine (EDA). PAGE analysis of the LtEc nanoparticles reveals cross-linking between subunits, while dynamic light scattering and scanning electron microscopy show that cross-linking significantly increases the size of the LtEc nanoparticles (164 ± 13.9 nm). Cross-linking also significantly increased the thermal stability of the LtEc nanoparticles by 10 °C (Tm = 72 ± 0.84 °C) relative to native LtEc (Tm = 62 ± 0.6 °C). In addition, while native LtEc rapidly dissociates at pH 9, the LtEc nanoparticles resist subunit dissociation up to pH 10. The oxygen affinity of the LtEc nanoparticles (P50 = 6.85 ± 0.13 mm Hg) is much higher than native LtEc (P50 = 26.67 ± 0.4 mm Hg), but the cooperativity (n = 2.43 ± 0.12) is not affected. Altogether, these results show that cross-linking LtEc with PAA and EDA provides a potential blood substitute with increased stability and oxygen affinity.

Chemoresistance and chemosensitization in cholangiocarcinoma

One of the main difficulties in the management of patients with advanced cholangiocarcinoma (CCA) is their poor response to available chemotherapy. This is the result of powerful mechanisms of chemoresistance (MOC) of quite diverse nature that usually act synergistically. The problem is often worsened by altered MOC gene expression in response to pharmacological treatment. Since CCA includes a heterogeneous group of cancers their genetic signature coding for MOC genes is also diverse; however, several shared traits have been defined. Some of these characteristics are shared with other types of liver cancer, namely hepatocellular carcinoma and hepatoblastoma. An important goal in modern oncologic pharmacology is to develop novel strategies to overcome CCA chemoresistance either by increasing drug specificity, such as in targeted therapies aimed to inhibit receptors with tyrosine kinase activity, or to increase the amounts of active agents inside CCA cells by enhancing drug uptake or reducing efflux through export pumps. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Gene/cell therapy approaches for Immune Dysregulation Polyendocrinopathy Enteropathy X-linked syndrome

Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) syndrome is a rare autoimmune disease due to mutations in the gene encoding for Forkhead box P3 (FOXP3), a transcription factor fundamental for the function of thymus-derived (t) regulatory T (Treg) cells. The dysfunction of Treg cells results in the development of devastating autoimmune manifestations affecting multiple organs, eventually leading to premature death in infants, if not promptly treated by hematopoietic stem cell transplantation (HSCT). Novel gene therapy strategies can be developed for IPEX syndrome as more definitive cure than allogeneic HSCT. Here we describe the therapeutic approaches, alternative to HSCT, currently under development. We described that effector T cells can be converted in regulatory T cells by LV-mediated FOXP3-gene transfer in differentiated T lymphocytes. Despite FOXP3 mutations mainly affect a highly specific T cell subset, manipulation of stem cells could be required for long-term remission of the disease. Therefore, we believe that a more comprehensive strategy should aim at correcting FOXP3-mutated stem cells. Potentials and hurdles of both strategies will be highlighted here.

Nature and uses of fluorescent dyes for drug transporter studies

INTRODUCTION

Drug transporters are now recognized as major players involved in pharmacokinetics and toxicology. Methods for assessing their activity are important to consider, particularly owing to regulatory requirements with respect to inhibition of drug transporter activity and prediction of drug-drug interactions. In this context, the use of fluorescent-dye-based transport assays is likely to deserve attention.

AREAS COVERED

This review provides an overview of the nature of fluorescent dye substrates for ATP-binding cassette and solute carrier drug transporters. Their use for investigating drug transporter activity in cultured cells and clinical hematological samples, drug transporter inhibition, drug transporter imaging and drug transport at the organ level are summarized.

EXPERT OPINION

A wide range of fluorescent dyes is now available for use in various aspects of drug transporter studies. The use of these dyes for transporter analyses may, however, be hampered by classic pitfalls of fluorescence technology, such as quenching. Transporter-independent processes such as passive diffusion of dyes through plasma membrane or dye sequestration into subcellular compartments must also be considered, as well as the redundant handling by various distinct transporters of some fluorescent probes. Finally, standardization of dye-based transport assays remains an important on-going issue.

The P-glycoprotein inhibitory effect and related mechanisms of thiolated chitosan and its S-protected derivative

P-gp inhibitory mechanisms mediated by CS-TGA and CS-TGA-6MNA lie in the decreasing membrane fluidity and inhibiting P-gp ATPase activity, while not influencing the expression of P-gp and decreasing ATP level at the investigation concentration.

Polymers influencing transportability profile of drug

Drug release from various polymers is generally governed by the type of polymer/s incorporated in the formulation and mechanism of drug release from polymer/s. A single polymer may show one or more mechanisms of drug release out of which one mechanism is majorly followed for drug release. Some of the common mechanisms of drug release from polymers were, diffusion, swelling, matrix release, leaching of drug, etc. Mechanism or rate of drug release from a polymer or a combination of polymers can be predicted by using different computational methods or models. These models were capable of predicting drug release from its dosage form in advance without actual formulation and testing of drug release from dosage form. Quantitative structure-property relationship (QSPR) is an important tool used in the prediction of various physicochemical properties of actives as well as inactives. Since last several decades QSPR has been applied in new drug development for reducing the total number of drugs to be synthesized, as it involves a selection of the most desirable compound of interest. This technique was also applied in predicting in vivo performance of drug/s for various parameters. QSPR serves as a predictive tool to correlate structural descriptors of molecules with biological as well as physicochemical properties. Several researchers have contributed at different extents in this area to modify various properties of pharmaceuticals. The present review is focused on a study of different polymers that influence the transportability profiles of drugs along with the application of QSPR either to study different properties of polymers that regulate drug release or in predicting drug transportability from different polymer systems used in formulations.

Reversal of multidrug resistance by the inhibition of ATP-binding cassette pumps employing "Generally Recognized As Safe" (GRAS) nanopharmaceuticals: A review

Pumps of the ATP-binding cassette superfamily (ABCs) regulate the access of drugs to the intracellular space. In this context, the overexpression of ABCs is a well-known mechanism of multidrug resistance (MDR) in cancer and infectious diseases (e.g., viral hepatitis and the human immunodeficiency virus) and is associated with therapeutic failure. Since their discovery, ABCs have emerged as attractive therapeutic targets and the search of compounds that inhibit their genetic expression and/or their functional activity has gained growing interest. Different generations of pharmacological ABC inhibitors have been explored over the last four decades to address resistance in cancer, though clinical results have been somehow disappointing. "Generally Recognized As Safe" (GRAS) is a U.S. Food and Drug Administration designation for substances that are accepted as safe for addition in food. Far from being "inert", some amphiphilic excipients used in the production of pharmaceutical products have been shown to inhibit the activity of ABCs in MDR tumors, emerging as a clinically translatable approach to overcome resistance. The present article initially overviews the classification, structure and function of the different ABCs, with emphasis on those pumps related to drug resistance. Then, the different attempts to capitalize on the activity of GRAS nanopharmaceuticals as ABC inhibitors are discussed.

Development and in vivo evaluation of an oral vitamin B12 delivery system

Recently, poly(acrylic acid)-cysteine (PAA-cys) based formulations have shown to modulate vitamin B12 absorption across Caco-2 cells monolayers and rat intestinal mucosa. The aim of the present study was to provide a proof-of-principle for a delivery system based on PAA-cys in vivo by administering vitamin B12 to Sprague Dawley rats. In vitro, the permeation enhancing effect of unmodified and thiolated PAA was evaluated using rat intestinal mucosa mounted on Ussing type chambers and was compared to that of verapamil and reduced glutathione (GSH). Vitamin B12 transport in the presence of 0.5% (m/v) PAA-cys was 3.96-fold improved compared to buffer, while 91.5% and 56.5% increased compared to verapamil and GSH, respectively. In vivo, the oral administration of minitablets based on 0.5mg vitamin B12 with 4.5mg PAA or PAA-cys resulted in a significant improvement of vitamin B12 absolute bioavailability. The area under the serum concentration-time curve (AUC₀₋₈) of vitamin B12 after administration of PAA and PAA-cys minitablets was 1.74-fold and 2.92-fold higher in comparison with oral solution, respectively. Thiolated formulations provided an absolute bioavailability of 0.89%. According to the achieved results, PAA-cys can be considered a valuable tool for improving the oral bioavailability of vitamin B12.

Preactivated thiomers: permeation enhancing properties

The study was aimed to prepare a series of poly(acrylic acid)-cysteine-2-mercaptonicotinic acid conjugates (preactivated thiomers) and to evaluate the influence of molecular mass or degree of preactivation with 2-mercaptonicotinic acid (2MNA) on their permeation enhancing properties. Preactivated thiomers with different molecular mass and different degree of preactivation were synthesized and categorized on the basis of their molecular mass and degree of preactivation as PAA₁₀₀-Cys-2MNA (h), PAA₂₅₀-Cys-2MNA (h), PAA₄₅₀-Cys-2MNA (h), PAA₄₅₀-Cys-2MNA (m) and PAA₄₅₀-Cys-2MNA (l). In vitro permeation studies, the permeation enhancement ability for preactivated thiomers was ranked as PAA₄₅₀-Cys-2MNA (h) > PAA₂₅₀-Cys-2MNA (h) > PAA₁₀₀-Cys-2MNA (h) on both Caco-2 cell monolayers and rat intestinal mucosa. Comparing the influence of degree of preactivation with 2MNA on permeation enhancement, the following order PAA₄₅₀-Cys-2MNA (h) > PAA₄₅₀-Cys-2MNA (m) ≈ PAA₄₅₀-Cys-2MNA (l) on Caco-2 cell monolayers and PAA₄₅₀-Cys-2MNA (m) > PAA₄₅₀-Cys-2MNA (h) > PAA₄₅₀-Cys-2MNA (l) on intestinal mucosa was observed. The P_app of sodium fluorescein was 5.08-fold improved on Caco-2 cell monolayers for PAA₄₅₀-Cys-2MNA (h) and 2.46-fold improved on intestinal mucosa for PAA₄₅₀-Cys-2MNA (m), respectively, in comparison to sodium fluorescein in buffer only. These results indicated that preactivated thiomers could be considered as a promising macromolecular permeation enhancing polymer for non-invasive drug administration.