Transporter effects on cell permeability in drug delivery

Role of Polymeric Micelles in Ocular Drug Delivery: An Overview of Decades of Research

Local drug delivery to the eye through conventional means has faced many challenges due to three essential barriers: (a) the complex structure of the cornea limiting drug absorption, (b) the capacity of ocular absorptive cells in drug metabolism, and (c) the washing effect of eye tears. Polymeric micelles (PMs) have been the focus of much interest for ocular drug delivery due to several advantages they provide for this application, including the capacity for the solubilization of hydrophobic drugs, nonirritability, nanoscopic diameter, and the clarity of their aqueous solution not interfering with vision. The potential to increase the release and residence time of incorporated medication at the site of absorption is also a bonus advantage for these delivery systems. This Review covers research conducted on single or mixed micelles prepared from small amphiphilic molecules, copolymers (diblock, triblock, and graft), and gel systems containing micelles. The purpose of this review is to provide an update on the status of micellar ocular delivery systems for different indications, with a focus on preclinical and clinical drug development. In this context, we are discussing the anatomy of the eye, various ocular barriers, different micellar formulations, and their benefits in ocular drug delivery, as well as the role of PMs in the management of ocular diseases both in preclinical models and in clinic. The encouraging preclinical effectiveness findings from experiments conducted in both laboratory settings and live animals have paved the way for the advancement of micellar systems in clinical trials for ocular administration and the first nanomicallar formulation approved for clinical use by the United States Food and Drug Administration (marketed as Cequa by Sun Pharmaceuticals).

Modulation of redox homeostasis: A strategy to overcome cancer drug resistance

Cancer treatment is hampered by resistance to conventional therapeutic strategies, including chemotherapy, immunotherapy, and targeted therapy. Redox homeostasis manipulation is one of the most effective innovative treatment techniques for overcoming drug resistance. Reactive oxygen species (ROS), previously considered intracellular byproducts of aerobic metabolism, are now known to regulate multiple signaling pathways as second messengers. Cancer cells cope with elevated amounts of ROS during therapy by upregulating the antioxidant system, enabling tumor therapeutic resistance via a variety of mechanisms. In this review, we aim to shed light on redox modification and signaling pathways that may contribute to therapeutic resistance. We summarized the molecular mechanisms by which redox signaling-regulated drug resistance, including altered drug efflux, action targets and metabolism, enhanced DNA damage repair, maintained stemness, and reshaped tumor microenvironment. A comprehensive understanding of these interrelationships should improve treatment efficacy from a fundamental and clinical research point of view.

DrugMAP: molecular atlas and pharma-information of all drugs

The efficacy and safety of drugs are widely known to be determined by their interactions with multiple molecules of pharmacological importance, and it is therefore essential to systematically depict the molecular atlas and pharma-information of studied drugs. However, our understanding of such information is neither comprehensive nor precise, which necessitates the construction of a new database providing a network containing a large number of drugs and their interacting molecules. Here, a new database describing the molecular atlas and pharma-information of drugs (DrugMAP) was therefore constructed. It provides a comprehensive list of interacting molecules for >30 000 drugs/drug candidates, gives the differential expression patterns for >5000 interacting molecules among different disease sites, ADME (absorption, distribution, metabolism and excretion)-relevant organs and physiological tissues, and weaves a comprehensive and precise network containing >200 000 interactions among drugs and molecules. With the great efforts made to clarify the complex mechanism underlying drug pharmacokinetics and pharmacodynamics and rapidly emerging interests in artificial intelligence (AI)-based network analyses, DrugMAP is expected to become an indispensable supplement to existing databases to facilitate drug discovery. It is now fully and freely accessible at: https://idrblab.org/drugmap/.

Current Advances in CETSA

Knowing that the drug candidate binds to its intended target is a vital part of drug discovery. Thus, several labeled and label-free methods have been developed to study target engagement. In recent years, the cellular thermal shift assay (CETSA) with its variations has been widely adapted to drug discovery workflows. Western blot–based CETSA is used primarily to validate the target binding of a molecule to its target protein whereas CETSA based on bead chemistry detection methods (CETSA HT) has been used to screen molecular libraries to find novel molecules binding to a pre-determined target. Mass spectrometry–based CETSA also known as thermal proteome profiling (TPP) has emerged as a powerful tool for target deconvolution and finding novel binding partners for old and novel molecules. With this technology, it is possible to probe thermal shifts among over 7,000 proteins from one sample and to identify the wanted target binding but also binding to unwanted off-targets known to cause adverse effects. In addition, this proteome-wide method can provide information on the biological process initiated by the ligand binding. The continued development of mass spectrometry labeling reagents, such as isobaric tandem mass tag technology (TMT) continues to increase the throughput of CETSA MS, allowing its use for structure–activity relationship (SAR) studies with a limited number of molecules. In this review, we discussed the differences between different label-free methods to study target engagement, but our focus was on CETSA and recent advances in the CETSA method.

Controlled Release of 18-β-Glycyrrhetinic Acid from Core-Shell Nanoparticles: Effects on Cytotoxicity and Intracellular Concentration in HepG2 Cell Line

18β-glycyrrhetinic acid (GA) is a pentacyclic triterpene with promising hepatoprotective and anti-Hepatocellular carcinoma effects. GA low water solubility however reduces its biodistribution and bioavailability, limiting its applications in biomedicine. In this work we used core-shell NPs made of PolyD-L-lactide-co-glycolide (PLGA) coated with chitosan (CS), prepared through an osmosis-based methodology, to efficiently entrap GA. NPs morphology was investigated with SEM and TEM and their GA payload was evaluated with a spectrophotometric method. GA-loaded NPs were administered to HepG2 cells and their efficiency in reducing cell viability was compared with that induced by the free drug in in vitro tests. Cell viability was evaluated by the MTT assay, as well as with Electric Cells-Substrate Impedance Sensing (ECIS), that provided a real-time continuous monitoring. It was possible to correlate the toxic effect of the different forms of GA with the bioavailability of the drug, evidencing the importance of real-time tests for studying the effects of bioactive substances on cell cultures.

Sampling efficiency of the counting method for permeability calculations estimated with the inhomogeneous solubility-diffusion model

Permeability is a key property in various fields such as membrane technology for chemical separation and transport of substances through cell membranes. At the molecular scale, the counting method uses the number of membrane crossings in a conventional unbiased molecular dynamics simulation to predict the permeability. This contribution investigates under which conditions the counting method has insufficient statistics. An equation is derived for a compartmental model based on the inhomogeneous solubility-diffusion (Smoluchowski) model, giving insight into how the flux correlates with the solubility of permeants. This equation shows that a membrane crossing is a rare event not only when the membrane forms a large free energy barrier but also when the membrane forms a deep free energy well that traps permeants. Such a permeant trap has a high permeability; yet, the counting method suffers from poor statistics. To illustrate this, coarse-grained MD was run for 16 systems of dipalmitoylphosphatidylcholine bilayer membranes with different permeant types. The composition rule for permeability is shown to also hold for fluxes, and it is highlighted that the considered thickness of the membrane causes uncertainty in the permeability calculation of highly permeable membranes. In conclusion, a high permeability in itself is not an effective indicator of the sampling efficiency of the counting method, and caution should be taken for permeants whose solubility varies greatly over the simulation box. A practical consequence relevant in, e.g., drug design is that a drug with high membrane permeability might get trapped by membranes thus reducing its efficacy.

Nanotechnology: revolutionizing the delivery of drugs to treat age-related macular degeneration

Introduction: Age-related macular degeneration (AMD) is a progressive retinal disease that degrades the eye's ability to grasp visual acuity. The antivascular endothelial growth factor (VEGF) therapies have made significant strides in improving the quality of life, and there is a continued opportunity to improve delivery, outcomes, and patient convenience and compliance. The treatments available could gain better clinical outcome from novel therapeutics through nanotechnology application.Areas covered: This review summarizes AMD biology and the pathophysiology of the disease along with the successes and limitations of available therapies. It further discusses the promising nanotechnology modalities that could become the cornerstone of future AMD research for improving delivery and reducing frequency of administration thus, enabling development of novel therapeutics.Expert opinion: The robust translation from preclinical work to clinical outcome for AMD remains an unmet need. Continuing to investigate in deeper understanding of biology and advancing high-quality targets into the clinic in combination with the application of advanced nanotechnology to design patient-centric offerings for both dry and wet AMD is needed. Because of the lack of regulatory precedence, and challenging manufacturing and supply chain need, the future of nano-enabled technologies is challenging but presents exciting treatment options for AMD.

Prodrugs and nanomicelles to overcome ocular barriers for drug penetration

INTRODUCTION

Ocular barriers hinder drug delivery and reduce drug bioavailability. This article focuses on enhancing drug absorption across the corneal and conjunctival epithelium. Both, transporter targeted prodrug formulations and nanomicellar strategy is proven to enhance the drug permeation of therapeutic agents across various ocular barriers. These strategies can increase aqueous drug solubility and stability of many hydrophobic drugs for topical ophthalmic formulations.

AREAS COVERED

The article discusses various ocular barriers, ocular influx, and efflux transporters. It elaborates various prodrug strategies used for enhancing drug absorption. Along with this, the article also describes nanomicellar formulation, its characteristic and advantages, and applications in for anterior and posterior segment drug delivery.

EXPERT OPINION

Prodrugs and nanomicellar formulations provide an effective strategy for improving drug absorption and drug bioavailability across various ocular barriers. It will be exciting to see the efficacy of nanomicelles for treating back of the eye disorders after their topical application. This is considered as a holy grail of ocular drug delivery due to the dynamic and static ocular barriers, restricting posterior entry of topically applied drug formulations.

Improving Membrane Permeation in the Beyond Rule-of-Five Space by Using Prodrugs to Mask Hydrogen Bond Donors

A wide range of drug targets can be effectively modulated by peptides and macrocycles. Unfortunately, the size and polarity of these compounds prevents them from crossing the cell membrane to reach target sites in the cell cytosol. As such, these compounds do not conform to standard measures of drug-likeness and exist in beyond the rule-of-five space. In this work, we investigate whether prodrug moieties that mask hydrogen bond donors can be applied in the beyond rule-of-five domain to improve the permeation of macrocyclic compounds. Using a cyclic peptide model, we show that masking hydrogen bond donors in the natural polar amino acid residues (His, Ser, Gln, Asn, Glu, Asp, Lys, and Arg) imparts membrane permeability to the otherwise impermeable parent molecules, even though the addition of the masking group increases the overall compound molecular weight and the number of hydrogen bond acceptors. We demonstrate this strategy in PAMPA and Caco2 membrane permeability assays and show that masking with groups that reduce the number of hydrogen-bond donors at the cost of additional mass and hydrogen bond acceptors, a donor-acceptor swap, is effective.

Phase 0 of the Xenobiotic Response: Nuclear Receptors and Other Transcription Factors as a First Step in Protection from Xenobiotics

This mini-review examines the crucial importance of transcription factors as a first line of defense in the detoxication of xenobiotics. Key transcription factors that recognize xenobiotics or xenobiotic-induced stress such as reactive oxygen species (ROS), include AhR, PXR, CAR, MTF, Nrf2, NF-κB, and AP-1. These transcription factors constitute a significant portion of the pathways induced by toxicants as they regulate phase I-III detoxication enzymes and transporters as well as other protective proteins such as heat shock proteins, chaperones, and anti-oxidants. Because they are often the first line of defense and induce phase I-III metabolism, could these transcription factors be considered the phase 0 of xenobiotic response?

Determinants of drug entry into the developing brain

Background: A major concern for clinicians in prescribing medications to pregnant women and neonates is the possibility that drugs might have damaging effects, particularly on long-term brain development. Current understanding of drug permeability at placental and blood-brain barriers during development is poor. In adults, ABC transporters limit many drugs from entering the brain; however, little is known about their function during development. Methods: The transfer of clinically relevant doses of paracetamol (acetaminophen), digoxin and cimetidine into the brain and cerebrospinal fluid (CSF) was estimated using radiolabelled drugs in Sprague Dawley rats at three developmental stages: E19, P4 and adult. Drugs were applied intraperitoneally either acutely or following chronic exposure (for five days). Entry into brain, CSF and transfer across the placenta was measured and compared to three markers (L-glucose, sucrose, glycerol) that cross barriers by "passive diffusion". The expression of ABC transporters in the brain, choroid plexus and placenta was estimated using RT-qPCR. Results: All three drugs entered the developing brain and CSF in higher amounts than the adult brain and CSF. Comparisons with "passive" permeability markers suggested that this might be due to age-related differences in the functional capacity of ABC-efflux mechanisms. In adult animals, chronic treatment reduced digoxin (12% to 5%, p<0.01) and paracetamol (30% to 21%, p<0.05) entry compared to acute treatment, with the decrease in digoxin entry correlating with up-regulation of efflux transporter abcb1a (PGP). In fetal and newborn animals, no gene up-regulation or transfer decreases were observed. Instead, chronic paracetamol treatment resulted in increased transfer into the fetal brain (66% to 104%, p<0.001). Conclusions: These results suggest that the developing brain may be more at risk from acute drug exposure than the adult brain due to reduced efflux capacity and at greater risk from chronic treatment due to a lack of efflux mechanism regulatory capacity.

Recent advance of nanoparticle-based topical drug delivery to the posterior segment of the eye

INTRODUCTION

Considering that the number of patients afflicted by posterior eye diseases is increasing, effective drug delivery is currently in high clinical demand. Topical administration has been identified as the preferred option, while sufferingfrom multiple barriers. The development of nanoparticle-based drug delivery system provides an option, which would enhance the drug permeability across the barriers and achieve the desired drug level in the targeted tissue.

AREAS COVERED

This review highlights the barrier to the posterior segment of the eye via topical administration. The up-to-date development of lipid nanoparticles, liposomes, emulsions, spanlastics, micelles, polymeric nanoparticles, layered double hydroxides (LDH), dendrimers, cyclodextrins(CDs), and prodrugs are summarized. Moreover, nanocarriers currently in clinical trials for posterior segment diseases have been discussed.

EXPERT OPINION

Topical nanoparticle-based drug delivery systems have demonstrated significant progress. An ideal formulation should prolong retention time on the surface, enhance drug permeability through the ocular tissues, and efficiently deliver drugs to the targeted site. To design the rational targeting nanoparticle-based drug delivery system, a better understanding of the distribution of transporters and receptors on the eye is required. Ultimately, there is an urgent need to develop targeting hybrid drug delivery systems with the combination of the advantages of several nanocarriers.

Functional intercalated nanocomposites with chitosan-glutathione-glycylsarcosine and layered double hydroxides for topical ocular drug delivery

Background

To enhance ocular bioavailability, the traditional strategies have focused on prolonging precorneal retention and improving corneal permeability by nano-carriers with positive charge, thiolated polymer, absorption enhancer and so on. Glycylsarcosine (GS) as an active target ligand of the peptide tranpsporter-1 (PepT-1), could specific interact with the PepT-1 on the cornea and guide the nanoparticles to the treating site.

Purpose

The objective of the study was to explore the active targeting intercalated nanocomposites based on chitosan-glutathione-glycylsarcosine (CG-GS) and layered double hydroxides (LDH) as novel carriers for the treatment of mid-posterior diseases.

Materials and methods

CG-GS-LDH intercalated nanocomposites were prepared by the coprecipitation hydrothermal method. In vivo precorneal retention study, ex vivo fluorescence images, in vivo experiment for distribution and irritation were studied in rabbits. The cytotoxicity and cellular uptake were studied in human corneal epithelial primary cells (HCEpiC).

Results

CG-GS-LDH nanocomposites were prepared successfully and characterized by FTIR and XRD. Experiments with rabbits showed longer precorneal retention and higher distribution of fluorescence probe/model drug. In vitro cytological study, CG-GS-LDH nanocomposites exhibited enhanced cellular uptake compared to pure drug solution. Furthermore, the investigation of cellular uptake mechanisms demonstrated that both the active transport by PepT-1 and clathrin-mediated endocytosis were involved in the internalization of CG-GS-LDH intercalated nanocomposites. An ocular irritation study and a cytotoxicity test indicated that these nanocomposites produced no significant irritant effects.

Conclusions

The active targeting intercalated nanocomposites could have great potential for topical ocular drug delivery due to the capacity for prolonging the retention on the ocular surface, enhancing the drug permeability through the cornea, and efficiently delivering the drug to the targeted site.

A comprehensive insight on ocular pharmacokinetics

The eye is a distinctive organ with protective anatomy and physiology. Several pharmacokinetics compartment models of ocular drug delivery have been developed for describing the absorption, distribution, and elimination of ocular drugs in the eye. Determining pharmacokinetics parameters in ocular tissues is a major challenge because of the complex anatomy and dynamic physiological barrier of the eye. In this review, pharmacokinetics of these compartments exploring different drugs, delivery systems, and routes of administration is discussed including factors affecting intraocular bioavailability. Factors such as precorneal fluid drainage, drug binding to tear proteins, systemic drug absorption, corneal factors, melanin binding, and drug metabolism render ocular delivery challenging and are elaborated in this manuscript. Several compartment models are discussed; these are developed in ocular drug delivery to study the pharmacokinetics parameters. There are several transporters present in both anterior and posterior segments of the eye which play a significant role in ocular pharmacokinetics and are summarized briefly. Moreover, several ocular pharmacokinetics animal models and relevant studies are reviewed and discussed in addition to the pharmacokinetics of various ocular formulations.