Head-To-Head Comparison of Different Solubility-Enabling Formulations of Etoposide and Their Consequent Solubility-Permeability Interplay

Application of the Box-Behnken Design in the Development of Amorphous PVP K30-Phosphatidylcholine Dispersions for the Co-Delivery of Curcumin and Hesperetin Prepared by Hot-Melt Extrusion

Background: Curcumin and hesperetin are plant polyphenols known for their poor solubility. To address this limitation, we prepared amorphous PVP K30-phosphatidylcholine dispersions via hot-melt extrusion. Methods: This study aimed to evaluate the effects of the amounts of active ingredients and phosphatidylcholine, as well as the process temperature, on the performance of the dispersions. A Box-Behnken design was employed to assess these factors. Solid-state characterization and biopharmaceutical studies were then conducted. X-ray powder diffraction (XRPD) was used to confirm the amorphous nature of the dispersions, while differential scanning calorimetry (DSC) provided insight into the miscibility of the systems. Fourier-transform infrared spectroscopy (FTIR) was employed to assess the intermolecular interactions. The apparent solubility and dissolution profiles of the systems were studied in phosphate buffer at pH 6.8. In vitro permeability across the gastrointestinal tract and blood-brain barrier was evaluated using the parallel artificial membrane permeability assay. Results: The quantities of polyphenols and phospholipids were identified as significant factors influencing the biopharmaceutical performance of the systems. Solid-state analysis confirmed the formation of amorphous dispersions and the development of interactions among components. Notably, a significant improvement in solubility was observed, with formulations exhibiting distinct release patterns for the active compounds. Furthermore, the in vitro permeability through the gastrointestinal tract and blood-brain barrier was enhanced. Conclusions: The findings suggest that amorphous PVP K30-phosphatidylcholine dispersions have the potential to improve the biopharmaceutical properties of curcumin and hesperetin.

Benefits of combining supersaturating and solubilizing formulations - Is two better than one?

A variety of enabling formulations has been developed to address poor oral drug absorption caused by insufficient dissolution in the gastrointestinal tract. As the in vivo performance of these formulations is a result of a complex interplay between dissolution, digestion and permeation, development of suitable in vitro assays that captures these phenomena are called for. The enabling-absorption (ENA) device, consisting of a donor and receiver chamber separated by a semipermeable membrane, has successfully been used to study the performance of lipid-based formulations. In this work, the ENA device was prepared with two different setups (a Caco-2 cell monolayer and an artificial lipid membrane) to study the performance of a lipid-based formulation (LBF), an amorphous solid dispersion (ASD) and the potential benefit of combining the two formulation strategies. An in vivo pharmacokinetic study in rats was performed to evaluate the in vitro-in vivo correlation. In the ENA, high drug concentrations in the donor chamber did not translate to a high mass transfer, which was particularly evident for the ASD as compared to the LBF. The solubility of the polymer used in the ASD was strongly affected by pH-shifts in vitro, and the ph_dependence resulted in poor in vivo performance of the formulation. The dissolution was however increased in vitro when the ASD was combined with a blank lipid-based formulation. This beneficial effect was also observed in vivo, where the drug exposure of the ASD increased significantly when the ASD was co-administered with the blank LBF. To conclude, the in vitro model managed to capture solubility limitations and strategies to overcome these for one of the formulations studied. The correlation between the in vivo exposure of the drug exposure and AUC in the ENA was good for the non pH-sensitive formulations. The deconvoluted pharmacokinetic data indicated that the receiver chamber was a better predictor for the in vivo performance of the drug, however both chambers provided valuable insights to the observed outcome in vivo. This shows that the advanced in vitro setting used herein successfully could explain absorption differences of highly complex formulations.

Amorphous Polymer-Phospholipid Solid Dispersions for the Co-Delivery of Curcumin and Piperine Prepared via Hot-Melt Extrusion

Curcumin and piperine are plant compounds known for their health-promoting properties, but their use in the prevention or treatment of various diseases is limited by their poor solubility. To overcome this drawback, the curcumin-piperine amorphous polymer-phospholipid dispersions were prepared by hot melt extrusion technology. X-ray powder diffraction indicated the formation of amorphous systems. Differential scanning calorimetry confirmed amorphization and provided information on the good miscibility of the active compound-polymer-phospholipid dispersions. Owing to Fourier-transform infrared spectroscopy, the intermolecular interactions in systems were investigated. In the biopharmaceutical properties assessment, the improvement in solubility as well as the maintenance of the supersaturation state were confirmed. Moreover, PAMPA models simulating the gastrointestinal tract and blood-brain barrier showed enhanced permeability of active compounds presented in dispersions compared to the crystalline form of individual compounds. The presented paper suggests that polymer-phospholipid dispersions advantageously impact the bioaccessibility of poorly soluble active compounds.

Ethanol-based solubility-enabling oral drug formulation development: Accounting for the solubility-permeability interplay

The aim of the current work was to investigate the key factors that govern the success/failure of an ethanol-based solubility-enabling oral drug formulation, including the effects of the ethanol on the solubility of the drug, the permeability across the intestinal membrane, the drug's dissolution in the aqueous milieu of the gastrointestinal tract (GIT), and the resulting solubility-permeability interplay. The concentration-dependent effects of ethanol-based vehicles on the solubility, the in-vitro Caco-2 permeability, the in-vivo rat permeability, and the biorelevant dissolution of the BCS class II antiepileptic drug carbamazepine were studied, and a predictive model describing the solubility-permeability relationship was developed. Significant concentration-dependent solubility increase of CBZ was obtained with increasing ethanol levels, that was accompanied by permeability decrease, both in Caco-2 and in rat perfusion studies, demonstrating a tradeoff between the increased solubility afforded by the ethanol and a concomitant permeability decrease. When ethanol absorption was accounted for, an excellent agreement was achieved between the predicted permeability and the experimental data. Biorelevant dissolution studies revealed that minimal ethanol levels of 30 % and 50 % were needed to fully dissolve 1 and 5 mg CBZ dose respectively, with no drug precipitation.In conclusion, key factors to be accounted for when developing ethanol-based formulation include the drug's solubility, permeability, the solubility-permeability interplay, and the drug dose intended to be delivered. Only the minimal amount of ethanol sufficient to solubilize the drug dose throughout the GIT should be used, and not more than that, to avoid unnecessarily permeability loss, and to maximize overall drug absorption.

Solubility-permeability interplay of a supersaturated lutein delivery system constructed by glycosylated stevioside and hydroxypropyl-methylcellulose

This study investigated the solubilizing capacity of glycosylated stevioside/hydroxypropyl-methylcellulose (stevia-G-HPMC) complexes with varying mass ratios on lutein. The impact on the steady-state flux and permeability coefficient of intracellular lutein was also explored through the construction of a Caco-2 cellular transport model. The results indicated that the equilibrium solubility of lutein linearly increased with an increase in stevia-G amount. The stability constants of the ternary system surpassed those of the binary system. Molecular dynamics simulation revealed a tight and stable structure in lutein supersaturated complexes. Meanwhile, lutein-stevia-G-HPMC complexes demonstrated superior cumulative penetrations, with the peak Papp (AP → BL) value being (3.24 ± 0.89) × 10-5 cm·s-1. There was a slight decrease in Papp (BL → AP), which improved the forward transport of lutein. Highly soluble lutein in aqueous environments saturated the extracellular transport proteins on the AP side of cell membranes, thereby maintaining the high permeability transport. Notably, the permeability trend of lutein in Caco-2 cells negatively correlated with the equilibrium solubility and matched the single exponential growth model. When the mass ratio of lutein, stevia-G and HPMC was 1:21:5, the solubility-permeability trade-off of lutein was effectively maintained.

Solubility-enabling formulations for oral delivery of lipophilic drugs: considering the solubility-permeability interplay for accelerated formulation development

INTRODUCTION

Tackling low water solubility of drug candidates is a major challenge in today's pharmaceutics/biopharmaceutics, especially by means of modern solubility-enabling formulations. However, drug absorption from these formulations oftentimes remains unchanged or even decreases, despite substantial solubility enhancement.

AREAS COVERED

In this article, we overview the simultaneous effects of the formulation on the solubility and the apparent permeability of the drug, and analyze the contribution of this solubility-permeability interplay to the success/failure of the formulation to increase the overall absorption and bioavailability. Three different patterns of interplay were identified: (1) solubility-permeability tradeoff in which every solubility gain comes with a price of concomitant permeability loss; (2) an advantageous interplay pattern in which the permeability remains unchanged alongside the solubility gain; and (3) an optimal interplay pattern in which the formulation increases both the solubility and the permeability. Passive vs. active intestinal permeability considerations in the context of the solubility-permeability interplay are also thoroughly discussed.

EXPERT OPINION

The solubility-permeability interplay pattern of a given formulation has a critical effect on its overall success/failure, and hence, taking into account both parameters in solubility-enabling formulation development is prudent and highly recommended.

An Overview of Nanoemulgels for Bioavailability Enhancement in Inflammatory Conditions via Topical Delivery

The anti-inflammatory drugs that are generally available possess the disadvantage of hydrophobicity, which leads to poor permeability and erratic bioavailability. Nanoemulgels (NEGs) are novel drug delivery systems that aim to improve the solubility and permeability of drugs across the biological membrane. The nano-sized droplets in the nanoemulsion enhance the permeation of the formulation, along with surfactants and co-surfactants that act as permeation enhancers and can further improve permeability. The hydrogel component of NEG helps to increase the viscosity and spreadability of the formulation, making it ideal for topical application. Moreover, oils that have anti-inflammatory properties, such as eucalyptus oil, emu oil and clove oil, are used as oil phases in the preparation of the nanoemulsion, which shows a synergistic effect with active moiety and enhances its overall therapeutic profile. This leads to the creation of hydrophobic drugs that possess enhanced pharmacokinetic and pharmacodynamic properties, and simultaneously avoid systemic side effects in individuals with external inflammatory disorders. The nanoemulsion's effective spreadability, ease of application, non-invasive administration, and subsequent ability to achieve patient compliance make it more suitable for topical application in the combat of many inflammatory disorders, such as dermatitis, psoriasis, rheumatoid arthritis, osteoarthritis and so on. Although the large-scale practical application of NEG is limited due to problems regarding its scalability and thermodynamic instability, which arise from the use of high-energy approaches during the production of the nanoemulsion, these can be resolved by the advancement of an alternative nanoemulsification technique. Considering the potential advantages and long-term benefits of NEGs, the authors of this paper have compiled a review that elaborates the potential significance of utilizing nanoemulgels in a topical delivery system for anti-inflammatory drugs.

Formulation and Physicochemical and Biological Characterization of Etoposide-Loaded Submicron Emulsions with Biosurfactant of Sophorolipids

Etoposide (ETO), a traditional anticancer chemotherapeutic agent, is commercialized in oral soft gelatin capsules and non-aqueous parenteral solutions form. Novel formulation application and new excipients exploration are needed to improve the water-solubility and comfort of the drug administration. In the present study, novel etoposide-loaded submicron emulsions (ESE) with the biosurfactants of acidic sophorolipid (ASL) and lactonic sophorolipid (LSL) instead of the chemical surfactant of Tween-80 were prepared and characterized. Firstly, parameters of medium-chain triglyceride: long-chain triglyceride (MCT:LCT), lecithin concentration, homogenization pressure and cycle, and type and concentration of surfactants were investigated to optimize the formation of ESEs. Then the physicochemical properties, antitumor activity, stability, and security of ESEs were compared. The results showed that ASL performed the best properties and activities than Tween-80 and LSL in ESE formation. ASL-ESE showed higher drug loading capacity, slower release rate, and significantly increased antitumor activity against ovarian cancer cell line A2780 via apoptosis than Tween-ESE and commercial ETO injection. Besides, both ASL-ESE and Tween-ESE caused no hemolysis, and the safe dose of ASL was 2.14-fold that of Tween-80 in the hemolysis test, making ASL more reliable for drug delivery applications. Furthermore, ASL-ESE exhibited equivalent long-term and autoclaving stability to Tween-ESE. These results thus suggested the excellent competences of ASL in ESE formation, efficacy enhancement, and safety improvement.

A multiple functional supramolecular system for synergetic treatments of hepatocellular carcinoma

In the current times, achieving specific targeted and controllable drug delivery remains one of the major challenges in the treatment of hepatocellular carcinoma (HCC). The present study reported the development of a multiple functional indocyanine green (ICG)-cyclodextrin (CD) system, wherein loaded etoposide (EPS) was used as the model chemotherapeutic drug. In the developed system, ICG segment served as a photosensitizer for photothermal therapy (PTT) and the targeting moiety, which was primarily attributed to the specific retention properties in HCC tissues. The Ex vivo evaluation showed that ICG-CD@EPS exhibited a laser-triggered release profile with the photothermal efficiency and cytotoxicity towards HepG2 cells. In vivo evaluation suggested that ICG could navigate the systems to HCC tissues and retained at the site for 48 h, producing a drug accumulation in HCC. Further, laser irradiation boosted EPS release and local hyperthermia effects in HCC. Thus, the present study explored a novel and specific HCC targeting mechanism, and provided a feasible and controllable strategy for synergistic PTT and chemotherapy treatments for HCC.

Stiripentol Enteric Solid Dispersion-Loaded Effervescent Tablets: Enhanced Dissolution, Stability, and Absorption

Due to poor solubility and stability in acid conditions, the gastrointestinal administration of stiripentol (STP) is still a significant challenge. This study aimed to explore the applicability of effervescent tablets compressed from STP-loaded enteric solid dispersions to improve the solubility and stability of the insoluble and acid-labile drug. STP-loaded solid dispersions (STP-SDs) and the effervescent tablets (STP-SD-ETs) were prepared using solvent evaporation and dry granulation technology, respectively, and their formulations were optimized. Then, STP-SDs were characterized regarding solid state, in vitro release, stability, etc. Results showed that enteric amorphous STP-SDs were successfully prepared and significantly improved the solubility and stability of STP. Moreover, compared with STP suspensions, the bioavailability of STP-SD-ETs was as high as 138.71%. Concomitantly, STP-SD-ETs significantly increased the intestinal absorption rate of STP. Overall, the oral preparation encompassing enteric solid dispersion combined with effervescent tablet technology possesses excellent performance in enhancing dissolution, anti-acid hydrolysis stability, and absorption of STP. Our work provides a promising method to improve the delivery of drugs with poor solubility and acid-labile stability.

Recent Advances in Enhancement of Dissolution and Supersaturation of Poorly Water-Soluble Drug in Amorphous Pharmaceutical Solids: A Review

Amorphization is one of the most effective pharmaceutical approaches to enhance the dissolution and oral bioavailability of poorly water-soluble drugs. In recent years, amorphous formulations have been experiencing rapid development both in theoretical and practical application. Based on using different types of stabilizing agents, amorphous formulations can be mainly classified as polymer-based amorphous solid dispersion, coamorphous formulation, mesoporous silica-based amorphous formulation, etc. This paper summarizes recent advances in the dissolution and supersaturation of these amorphous formulations. Moreover, we also highlight the roles of stabilizing agents such as polymers, low molecular weight co-formers, and mesoporous silica. Maintaining supersaturation in solution is a key factor for the enhancement of dissolution profile and oral bioavailability, and thus, the strategies and challenges for maintaining supersaturation are also discussed. With an in-depth understanding of the inherent mechanisms of dissolution behaviors, the design of amorphous pharmaceutical formulations will become more scientific and reasonable, leading to vigorous development of commercial amorphous drug products.

Photochemical Internalization of Etoposide Using Dendrimer Nanospheres Loaded with Etoposide and Protoporphyrin IX on a Glioblastoma Cell Line

Glioblastoma multiforme (GBM) is the most common malignant primary neoplasm of the adult central nervous system originating from glial cells. The prognosis of those affected by GBM has remained poor despite advances in surgery, chemotherapy, and radiotherapy. Photochemical internalization (PCI) is a release mechanism of endocytosed therapeutics into the cytoplasm, which relies on the membrane disruptive effect of light-activated photosensitizers. In this study, phototherapy by PCI was performed on a human GBM cell-line using the topoisomerase II inhibitor etoposide (Etop) and the photosensitizer protoporphyrin IX (PpIX) loaded in nanospheres (Ns) made from generation-5 polyamidoamine dendrimers (PAMAM(G5)). The resultant formulation, Etop/PpIX-PAMAM(G5) Ns, measured 217.4 ± 2.9 nm in diameter and 40.5 ± 1.3 mV in charge. Confocal microscopy demonstrated PpIX fluorescence within the endo-lysosomal compartment, and an almost twofold increase in cellular uptake compared to free PpIX by flow cytometry. Phototherapy with 3 min and 5 min light illumination resulted in a greater extent of synergism than with co-administered Etop and PpIX; notably, antagonism was observed without light illumination. Mechanistically, significant increases in oxidative stress and apoptosis were observed with Etop/PpIX-PAMAM(G5) Ns upon 5 min of light illumination in comparison to treatment with either of the agents alone. In conclusion, simultaneous delivery and endo-lysosomal co-localization of Etop and PpIX by PAMAM(G5) Ns leads to a synergistic effect by phototherapy; in addition, the finding of antagonism without light illumination can be advantageous in lowering the dark toxicity and improving photo-selectivity.

A Mechanistic Study of Drug Mass Transport from Supersaturated Solutions Across PAMPA Membranes

There is an increasing shift from dissolution testing to dissolution-permeation testing of formulations during formulation development and this has led increasing application of permeability measurements using parallel artificial membrane permeability assay (PAMPA) membranes. However, there is a lack of thorough analysis of the impact of variabilities in the PAMPA setup on the mass flow rate outcomes, particularly for complex solubility-enabling formulations. In this study, we investigated the impact of amorphous drug-rich nanodroplets, formed in supersaturated solutions by liquid-liquid phase separation, on membrane transport by measuring mass flow rate across PAMPA membranes. In addition, we explored the impact of PAMPA variants such as lipid composition, hydrophobicity and pore size of the filter support, as well as receiver sink properties on membrane mass flow rates of solutions containing amorphous nanodroplets. Filter properties and lipid composition did not show a notable influence on the mass flow rates for lipophilic molecules, while a marked impact was observed for hydrophilic molecules. High sink conditions in the receiver compartment, arising from addition of micellar surfactant, altered the membrane integrity for lipid-impregnated hydrophilic membranes. In contrast, no such effect was observed for a hydrophobic filter support. Membrane integrity tests also suggested that monitoring water transport may be an improved approach over using Lucifer yellow. Furthermore, high sink conditions in the receiver compartment resulted in an increase in the overall mass flow rate. This was due to the effect of asymmetric conditions, generated across the membrane, on mass transport kinetics. Linearity between mass flow rate and donor concentration was observed until the donor concentration reached the amorphous solubility. Above the amorphous solubility, a gradual increase in mass flow rate was observed i.e., with an increasing number of nanodroplets in the solution. This was attributed to decrease in the permeability barrier across unstirred water layer due to reduction of the concentration gradient as nanodroplets dissolved to replenish absorbed drug. Observations made in this study provide insights into the mechanisms associated with mass transport of supersaturated solutions across PAMPA membranes, which are critical for improved evaluation of enabling formulations.

Drug-Rich Phases Induced by Amorphous Solid Dispersion: Arbitrary or Intentional Goal in Oral Drug Delivery?

Among many methods to mitigate the solubility limitations of drug compounds, amorphous solid dispersion (ASD) is considered to be one of the most promising strategies to enhance the dissolution and bioavailability of poorly water-soluble drugs. The enhancement of ASD in the oral absorption of drugs has been mainly attributed to the high apparent drug solubility during the dissolution. In the last decade, with the implementations of new knowledge and advanced analytical techniques, a drug-rich transient metastable phase was frequently highlighted within the supersaturation stage of the ASD dissolution. The extended drug absorption and bioavailability enhancement may be attributed to the metastability of such drug-rich phases. In this paper, we have reviewed (i) the possible theory behind the formation and stabilization of such metastable drug-rich phases, with a focus on non-classical nucleation; (ii) the additional benefits of the ASD-induced drug-rich phases for bioavailability enhancements. It is envisaged that a greater understanding of the non-classical nucleation theory and its application on the ASD design might accelerate the drug product development process in the future.

Prediction of in vivo supersaturation and precipitation of poorly water-soluble drugs: Achievements and aspirations

This review focuses on options available to a pharmaceutical scientist to predict in vivo supersaturation and precipitation of poorly water-soluble drugs. As no single device or system can simulate the complex gastrointestinal environment, a combination of appropriate in vitro tools may be utilized to get optimal predictive information. To address the empirical issues encountered during small-scale and full-scale in vitro predictive testing, theoretical background and relevant case studies are discussed. The practical considerations for selection of appropriate tools at various stages of drug development are recommended. Upcoming technologies that have potential to further reduce in vivo studies and expedite the drug development process are also discussed.

Orally Administered Drug Solubility-Enhancing Formulations: Lesson Learnt from Optimum Solubility-Permeability Balance

Although oral drug delivery is considered as most acceptable route for administering the active pharmaceutical ingredients to patients of all age-groups with the exceptions of bed-ridden patients and infants, the extent and rate of drug reaching the systemic circulation (in other word, drug bioavailability) always depends on many factors such as drug solubility in gastrointestinal fluids and drug permeation into intraluminal epithelial membrane structure, absence (fasting state) and presence (fed state) of food materials in the gastrointestinal tract, and individual variations in gastric emptying time. Taking the most influential factors like drug solubility and its permeability into consideration, these two factors play a pivotal role and even act as the litmus test for the formulation scientists who involve in oral dosage form development. It is very clear that there should be an optimum solubility and permeability balance to be reachable for getting the desired drug bioavailability to exert the intended therapeutic activity. The objectives of current review are (1) to provide an overview of two-different categories of poorly water soluble API molecules, (2) to describe briefly three-different case studies taken from drug solubility-enhancing formulations dealing with interplay between solubility and permeability, and (3) to showcase selected examples of solubility-permeability interplay phenomena arising out from the various orally administrable dosage forms. The lessons learnt from the past and current literatures are certainly encouraging to go ahead for oral dosage form development but with the prior knowledge about the possible existence of solubility-permeability interplay/tradeoff phenomenon.

Adequate formulation approach for oral chemotherapy: Etoposide solubility, permeability, and overall bioavailability from cosolvent- vs. vitamin E TPGS-based delivery systems

Injectable-to-oral conversions for anticancer drugs represent an important trend. The goal of this research was to investigate the suitability of formulation approaches for anticancer oral drug delivery, aiming to reveal mechanistic insights that may guide oral chemotherapy development. TPGS vs. PEG-400 were studied as oral formulations for the anticancer drug etoposide, accounting for drug solubility, biorelevant dissolution, permeability, solubility-permeability interplay, and overall bioavailability. Increased etoposide solubility was demonstrated with both excipients. Biorelevant dissolution revealed that TPGS or PEG-400, but not aqueous suspension, allowed complete dissolution of the entire drug dose. Both TPGS and PEG-400 resulted in decreased in-vitro etoposide permeability across artificial membrane, i.e. solubility-permeability tradeoff. While PEG-400 resulted in the same solubility-permeability tradeoff also in-vivo, TPGS showed the opposite trend: the in-vivo permeability of etoposide was markedly increased in the presence of TPGS. This increased permeability was similar to the drug permeability under P-gp inhibition. Rat PK study demonstrated significantly higher etoposide bioavailability from TPGS vs. PEG-400 or suspension (AUC of 72, 41, and 26 µg·min/mL, respectively). All in all, TPGS-based delivery system allows overcoming the solubility-permeability tradeoff, increasing systemic etoposide exposure. Since poor solubility and strong efflux are common to many anticancer agents, this work can aid in the development of better oral delivery approach for chemotherapeutic drugs.

Improvements in the Oral Absorption and Anticancer Efficacy of an Oxaliplatin-Loaded Solid Formulation: Pharmacokinetic Properties in Rats and Nonhuman Primates and the Effects of Oral Metronomic Dosing on Colorectal Cancer

Objective

The anticancer efficacy of orally administered chemotherapeutics is often constrained by low intestinal membrane permeability and oral bioavailability. In this context, we designed a solid oral formulation of oxaliplatin (OP), a third-generation cisplatin analog, to improve oral bioavailability and investigate its application in metronomic chemotherapy.

Methods

An ion-pairing complex of OP with a permeation enhancer, N^α-deoxycholyl-l-lysyl-methylester (DLM), was successfully prepared and then mixed with dispersing agents (including poloxamer 188 and Labrasol) to form the solid, amorphous oral formulation OP/DLM (OP/DLM-SF; hereafter, ODSF).

Results

The optimized powder formulation was sized in the nanoscale range (133±1.47 nm). The effective permeability of OP increased by 12.4-fold after ionic complex formation with DLM and was further increased by 24.0-fold after incorporation into ODSF. ODSF exhibited respective increases of 128% and 1010% in apparent permeability across a Caco-2 monolayer, compared to OP/DLM and OP. Furthermore, inhibition of bile acid transporters by actinomycin D and caveola-mediated uptake by brefeldin in Caco-2 cell monolayers reduced the apparent permeability values of ODSF by 58.4% and 51.1%, respectively, suggesting predominant roles for bile acid transporters and caveola-mediated transport in intestinal absorption of ODSF. In addition, macropinocytosis and paracellular and transcellular passive transport significantly influenced the intestinal permeation of ODSF. The oral bioavailabilities of ODSF in rats and monkeys were 68.2% and 277% higher, respectively, than the oral bioavailability of free OP. In vivo analyses of anticancer efficacy in CT26 and HCT116 cell-bearing mice treated with ODSF demonstrated significant suppression of tumor growth, with respective maximal tumor volume reductions of 7.77-fold and 4.07-fold, compared to controls.

Conclusion

ODSF exhibits therapeutic potential, constituting an effective delivery system that increases oral bioavailability, with applications to metronomic chemotherapy.

Prodrugs for Improved Drug Delivery: Lessons Learned from Recently Developed and Marketed Products

Prodrugs are bioreversible, inactive drug derivatives, which have the ability to convert into a parent drug in the body. In the past, prodrugs were used as a last option; however, nowadays, prodrugs are considered already in the early stages of drug development. Optimal prodrug needs to have effective absorption, distribution, metabolism, and elimination (ADME) features to be chemically stable, to be selective towards the particular site in the body, and to have appropriate safety. Traditional prodrug approach aims to improve physicochemical/biopharmaceutical drug properties; modern prodrugs also include cellular and molecular parameters to accomplish desired drug effect and site-specificity. Here, we present recently investigated prodrugs, their pharmaceutical and clinical advantages, and challenges facing the overall prodrug development. Given examples illustrate that prodrugs can accomplish appropriate solubility, increase permeability, provide site-specific targeting (i.e., to organs, tissues, enzymes, or transporters), overcome rapid drug metabolism, decrease toxicity, or provide better patient compliance, all with the aim to provide optimal drug therapy and outcome. Overall, the prodrug approach is a powerful tool to decrease the time/costs of developing new drug entities and improve overall drug therapy.

Enhanced oral bioavailability of an etoposide multiple nanoemulsion incorporating a deoxycholic acid derivative-lipid complex

In this study, a system for oral delivery of etoposide (ETP) was designed to avoid the problems associated with low and variable bioavailability of a commercially available ETP emulsion comprised of polyethylene glycol, glycerol, and citric acid anhydrous. ETP was complexed with low-molecular-weight methylcellulose (ETP/LMC) and loaded into a water-in-oil-in-water multiple nanoemulsion to formulate an ETP/LMC-nanoemulsion (ELNE). To further enhance the oral bioavailability, an ionic complex formed by anionic lipid 1,2-didecanoyl-sn-glycero-3-phosphate (sodium salt) and cationic N^α-deoxycholyl-l-lysyl-methylester was incorporated into ELNE, yielding ELNE#7. As expected, ELNE#7 showed 4.07- and 2.25-fold increases in artificial membrane and Caco-2/HT29-MTX-E12 permeability (P_app), respectively, resulting in 224% greater oral bioavailability compared with the commercially available ETP emulsion. In contrast, inhibition of clathrin- and caveola-mediated endocytosis, macropinocytosis, and bile acid transporters by chlorpromazine, genistein, amiloride, and actinomycin D in Caco-2/HT-29-MTX-E12 monolayers reduced the P_app by 45.0%, 20.5%, 28.8%, and 31.1%, respectively. These findings suggest that these routes play important roles in enhancing the oral absorption of ELNE#7. In addition, our mechanistic study suggested that P-glycoprotein did not have an inhibitory effect on the permeation of ELNE#7. Notably, ELNE#7 showed significantly enhanced toxicity in LLC and A549 cells compared with ETP-E. These observations support the improved oral absorption of ETP in ELNE#7, suggesting that it is a better alternative than ETP emulsion.

Etoposide and olaparib polymer-coated nanoparticles within a bioadhesive sprayable hydrogel for post-surgical localised delivery to brain tumours

Glioblastoma is a malignant brain tumour with a median survival of 14.6 months from diagnosis. Despite maximal surgical resection and concurrent chemoradiotherapy, reoccurrence is inevitable. To try combating the disease at a stage of low residual tumour burden immediately post-surgery, we propose a localised drug delivery system comprising of a spray device, bioadhesive hydrogel (pectin) and drug nanocrystals coated with polylactic acid-polyethylene glycol (NCPPs), to be administered directly into brain parenchyma adjacent to the surgical cavity. We have repurposed pectin for use within the brain, showing in vitro and in vivo biocompatibility, bio-adhesion to mammalian brain and gelling at physiological brain calcium concentrations. Etoposide and olaparib NCPPs with high drug loading have shown in vitro stability and drug release over 120 h. Pluronic F127 stabilised NCPPs to ensure successful spraying, as determined by dynamic light scattering and transmission electron microscopy. Successful delivery of Cy5-labelled NCPPs was demonstrated in a large ex vivo mammalian brain, with NCPP present in the tissue surrounding the resection cavity. Our data collectively demonstrates the pre-clinical development of a novel localised delivery device based on a sprayable hydrogel containing therapeutic NCPPs, amenable for translation to intracranial surgical resection models for the treatment of malignant brain tumours.

The Solubility-Permeability Interplay for Solubility-Enabling Oral Formulations

The Biopharmaceutical classification system (BCS) classifies the drugs based on their intrinsic solubility and intestinal permeability. The drugs with good solubility and intestinal permeability have good bioavailability. The drugs with poor solubility and poor permeability have solubility dependent and permeability dependent bioavailability, respectively. In the current pharmaceutical field, most of the drugs have poor solubility. To solve the problem of poor solubility, various solubility enhancement approaches have been successfully used. The effects of these solubility enhancing approaches on the intestinal permeability of the drugs are a matter of concern, and must not be overlooked. The current review article focuses on the effect of various solubility enhancing approaches viz. cyclodextrin, surfactant, cosolvent, hydrotropes, and amorphous solid dispersion, on the intestinal permeability of drugs. This article will help in the designing of the optimized formulations having balanced solubility enhancement without affecting the permeability of drugs.

Degrees of order: A comparison of nanocrystal and amorphous solids for poorly soluble drugs

Poor aqueous solubility is currently a prevalent issue in the development of small molecule pharmaceuticals. Several methods are possible for improving the solubility, dissolution rate and bioavailability of Biopharmaceutics Classification System (BCS) class II and class IV drugs. Two solid state approaches, which rely on reductions in order, and can theoretically be applied to all molecules without any specific chemical prerequisites (compared with e.g. ionizable or co-former groups, or sufficient lipophilicity), are the use of the amorphous form and nanocrystals. Research involving these two approaches is relatively extensive and commercial products are now available based on these technologies. Nevertheless, their formulation remains more challenging than with conventional dosage forms. This article describes these two technologies from both theoretical and practical perspectives by briefly discussing the physicochemical backgrounds behind these approaches, as well as the resulting practical implications, both positive and negative. Case studies demonstrating the benefits and challenges of these two techniques are presented.

The solubility, permeability and the dose as key factors in formulation development for oral lipophilic drugs: Maximizing the bioavailability of carbamazepine with a cosolvent-based formulation

The purpose of this research was to investigate drug dose, solubility, permeability, and their interplay, as key factors in oral formulation development for lipophilic drugs. A PEG400-based formulation was studied for five doses of the lipophilic drug carbamazepine, accounting for biorelevant dissolution of the dose in the GIT, and in-vivo bioavailability in rats. With the three lower doses (10, 25 and 50 mg/kg), complete in-vitro dissolution was achieved and maintained throughout the experiment with this formulation, while significant precipitation was obtained with higher doses (100 and 200 mg/kg). Likewise, the studied formulation allowed complete bioavailability in-vivo with the three lower doses, while the same formulation allowed only 76% and 42% bioavailability for the 100 and 200 mg/kg doses, respectively. There was good correlation between the in-vitro and in-vivo results. In conclusion, this work demonstrates that the dose is a crucial factor in formulation development; while a given formulation may be optimal for a certain drug dose, it may no longer be optimal for higher doses of the same drug. Hence, the solubility, the permeability, and their interplay, have to be considered in light of the drug dose intended to be administered in order to achieve successful oral formulation development.

Methacrylate-Copolymer Eudragit EPO as a Solubility-Enabling Excipient for Anionic Drugs: Investigation of Drug Solubility, Intestinal Permeability, and Their Interplay

The purpose of this work was to investigate the use of the dimethylaminoethyl methacrylate-copolymer Eudragit EPO (EPO) in oral solubility-enabling formulations for anionic lipophilic drugs, aiming to guide optional formulation design and maximize oral bioavailability. We have studied the solubility, the permeability, and their interplay, using the low-solubility nonsteroidal anti-inflammatory drug mefenamic acid as a model drug. Then, we studied the biorelevant solubility enhancement of mefenamic acid from EPO-based formulations throughout the gastrointestinal tract (GIT), using the pH-dilution dissolution method. EPO allowed a profound and linear solubility increase of mefenamic acid, from 10 μg/mL without EPO to 9.41 mg/mL in the presence of 7.5% EPO (∼940-fold; 37 °C); however, a concomitant decrease of the drug permeability was obtained, both in vitro and in vivo in rats, indicating a solubility-permeability trade-off. In the absence of an excipient, the unstirred water layer (UWL) adjacent to the GI membrane was found to hinder the permeability of the drug, accounting for this UWL effect and revealing that the true membrane permeability allowed good prediction of the solubility-permeability trade-off as a function of EPO level using a direct relationship between the increased solubility afforded by a given EPO level and the consequent decreased permeability. Biorelevant dissolution studies revealed that EPO levels of 0.05 and 0.1% were insufficient to dissolve mefenamic acid dose during the entire dissolution time course, whereas 0.5 and 1% EPO allowed complete solubility with no drug precipitation. In conclusion, EPO may serve as a potent solubility-enabling excipient for BCS class II/IV acidic drugs; however, it should be used carefully. It is prudent to use the minimal EPO amounts just sufficient to dissolve the drug dose throughout the GIT and not more than that. Excess amounts of EPO provide no solubility gain and cause further permeability loss, jeopardizing the overall success of the formulation. This work may help the formulator to hit the optimal solubility-permeability balance, maximizing the oral bioavailability afforded by the formulation.

In vitro digestion models to evaluate lipid based drug delivery systems; present status and current trends

During the past two decades, a range of in vitro models simulating the digestion processes occurring in the stomach and small intestine have been developed to characterize lipid based drug delivery systems (LbDDSs). This review describes the presently existing range of in vitro digestion models and their use in the field of oral drug delivery. The models are evaluated in terms of their suitability to assess LbDDSs, and their ability to produce in vitro - in vivo correlations (IVIVCs). While the pH-stat lipolysis model is by far the most commonly utilized in vitro digestion model in relation to characterizing LbDDSs, a series of recent studies have shown a lack of IVIVCs limiting its future use. Presently, no single in vitro digestion model exists which is able to predict the in vivo performance of various LbDDSs. However, recent research has shown the potential of combined digestion-permeation models as well as species specific digestion models.

Investigating Permeation Behavior of Flufenamic Acid Cocrystals Using a Dissolution and Permeation System

The dissolution and permeation of the cocrystals, flufenamic acid-nicotinamide (FFA-NIC) and flufenamic acid-theophylline (FFA-TP), have been investigated in the presence of two polymers, polyvinylpyrrolidone (PVP) and copolymer of vinylpyrrolidone/vinyl acetate (PVP-VA), using a dissolution/permeation (D/P) system. It showed that the types and concentrations of the polymers and their interactions with the coformers had significant effects on the dissolution and permeation of the FFA cocrystals. The role of PVP as a stabilizing agent was not altered in spite of its interaction with the coformer of NIC or TP, which was supported by the proportional flux rate of FFA to the dissolution performance parameter (DPP). With an appropriate PVP concentration, the maximal flux rate of FFA could be obtained for a given FFA cocrystal. The situation was complicated in the presence of PVP-VA. The role of PVP-VA could change because of its association with the coformers, i.e., from a stabilizing agent to a solubilization agent. In addition, PVP-VA reduced the flux rate of FFA, in contrast to its DPP for FFA cocrystals. Finally, ¹H NMR provided evidence regarding the molecular interactions between FFA, coformers, and polymers at the atomic level and gave insight into the mechanism underlying the supersaturated solution and subsequent permeation behavior of the cocrystals.

Ranking Itraconazole Formulations Based on the Flux through Artificial Lipophilic Membrane

PURPOSE

The goal of the study was to evaluate a miniaturized dissolution-permeation apparatus (μFLUX™ apparatus) for its ability to benchmark several itraconazole (ITZ) formulations for which in vivo PK data was available in the literature.

METHOD

Untreated and micronized powders of ITZ and various enabling formulations of ITZ (commercial Sporanox® solid dispersion, a Soluplus®-based solid dispersion and a nanosuspension) were introduced to the donor compartment of μFLUX™ apparatus. Donor and acceptor chambers were divided from each other by a lipophilic membrane. In addition to the flux evaluations, changes in solid state as a function of time were investigated to gain further insight into the flux changes observed over time for the solid dispersion formulations.

RESULTS

Initial flux values from Sporanox®, the nanosuspension and the micronized ITZ showed ratios of 52/4/1 with a decreasing flux from nanosuspension and both solid dispersions after 2.5-3 h. Although the initial flux from the Soluplus® formulation was 2.2 times lower than the one observed for Sporanox®, the decrease in flux observed was milder and became ~ 2 times higher than Sporanox® after approximately 2.5 h. The total amounts of ITZ in the receiver compartment after 240 min showed the same rank order as the rodent AUCs of these formulations reported in literature.

CONCLUSIONS

It was demonstrated that in vitro flux measurements using lipophilic artificial membranes could correctly reproduce the rank order of PK results for ITZ formulations. The drop in flux over time for solid dispersions could be backed by experimental indications of crystallization.

Recent advances in improving oral drug bioavailability by cocrystals

Introduction: Oral drug delivery is the most favored route of drug administration. However, poor oral bioavailability is one of the leading reasons for insufficient clinical efficacy. Improving oral absorption of drugs with low water solubility and/or low intestinal membrane permeability is an active field of research. Cocrystallization of drugs with appropriate coformers is a promising approach for enhancing oral bioavailability.

Methods: In the present review, we have focused on recent advances that have been made in improving oral absorption through cocrystallization. The covered areas include supersaturation and its importance on oral absorption of cocrystals, permeability of cocrystals through membranes, drug-coformer pharmacokinetic (PK) interactions, conducting in vivo-in vitro correlations for cocrystals. Additionally, a discussion has been made on the integration of nanocrystal technology with supramolecular design. Marketed cocrystal products and PK studies in human subjects are also reported.

Results: Considering supersaturation and consequent precipitation properties is necessary when evaluating dissolution and bioavailability of cocrystals. Appropriate excipients should be included to control precipitation kinetics and to capture solubility advantage of cocrystals. Beside to solubility, cocrystals may modify membrane permeability of drugs. Therefore, cocrystals can find applications in improving oral bioavailability of poorly permeable drugs. It has been shown that cocrystals may interrupt cellular integrity of cellular monolayers which can raise toxicity concerns. Some of coformers may interact with intestinal absorption of drugs through changing intestinal blood flow, metabolism and inhibiting efflux pumps. Therefore, caution should be taken into account when conducting bioavailability studies. Nanosized cocrystals have shown a high potential towards improving absorption of poorly soluble drugs.

Conclusions: Cocrystals have found their way from the proof-of-principle stage to the clinic. Up to now, at least two cocrystal products have gained approval from regulatory bodies. However, there are remaining challenges on safety, predicting in vivo behavior and revealing real potential of cocrystals in the human.

Drug permeability profiling using cell-free permeation tools: Overview and applications

Cell-free permeation systems are gaining interest in drug discovery and development as tools to obtain a reliable prediction of passive intestinal absorption without the disadvantages associated with cell- or tissue-based permeability profiling. Depending on the composition of the barrier, cell-free permeation systems are classified into two classes including (i) biomimetic barriers which are constructed from (phospho)lipids and (ii) non-biomimetic barriers containing dialysis membranes. This review provides an overview of the currently available cell-free permeation systems including Parallel Artificial Membrane Permeability Assay (PAMPA), Phospholipid Vesicle-based Permeation Assay (PVPA), Permeapad®, and artificial membrane based systems (e.g. the artificial membrane insert system (AMI-system)) in terms of their barrier composition as well as their predictive capacity in relation to well-characterized intestinal permeation systems. Given the potential loss of integrity of cell-based permeation barriers in the presence of food components or pharmaceutical excipients, the superior robustness of cell-free barriers makes them suitable for the combined dissolution/permeation evaluation of formulations. While cell-free permeation systems are mostly applied for exploring intestinal absorption, they can also be used to evaluate non-oral drug delivery by adjusting the composition of the membrane.

Advances in Polymer Design for Enhancing Oral Drug Solubility and Delivery

Synthetic polymers have enabled amorphous solid dispersions (ASDs) to emerge as an oral delivery strategy for overcoming poor drug solubility in aqueous environments. Modern ASD products noninvasively treat a range of chronic diseases (for example, hepatitis C, cystic fibrosis, and HIV). In such formulations, polymeric carriers generate and maintain drug supersaturation upon dissolution, increasing the apparent drug solubility to enhance gastrointestinal barrier absorption and oral bioavailability. In this Review, we outline several approaches in designing polymeric excipients to drive interactions with active pharmaceutical ingredients (APIs) in spray-dried ASDs, highlighting polymer-drug formulation guidelines from industrial and academic perspectives. Special attention is given to new commercial and specialized polymer design strategies that can solubilize highly hydrophobic APIs and suppress the propensity for rapid drug recrystallization. These molecularly customized excipients and hierarchical excipient assemblies are promising toward informing early-stage drug-discovery development and reformulating existing API candidates into potentially lifesaving oral medicines for our growing global population.

Active intestinal drug absorption and the solubility-permeability interplay

The solubility-permeability interplay deals with the question: what is the concomitant effect on the drug's apparent permeability when increasing the apparent solubility with a solubility-enabling formulation? The solubility and the permeability are closely related, exhibit certain interplay between them, and ongoing research throughout the past decade shows that treating the one irrespectively of the other may be insufficient. The aim of this article is to provide an overview of the current knowledge on the solubility-permeability interplay when using solubility-enabling formulations for oral lipophilic drugs, highlighting active permeability aspects. A solubility-enabling formulation may affect the permeability in opposite directions; the passive permeability may decrease as a result of the apparent solubility increase, according to the solubility-permeability tradeoff, but at the same time, certain components of the formulation may inhibit/saturate efflux transporters (when relevant), resulting in significant apparent permeability increase. In these cases, excipients with both solubilizing and e.g. P-gp inhibitory properties may lead to concomitant increase of both the solubility and the permeability. Intelligent development of such formulation will account for the simultaneous effects of the excipients' nature/concentrations on the two arms composing the overall permeability: the passive and the active arms. Overall, thorough mechanistic understanding of the various factors involved in the solubility-permeability interplay may allow developing better solubility-enabling formulations, thereby exploiting the advantages analyzed in this article, offering oral delivery solution even for BCS class IV drugs.

Amorphous Polymeric Drug Salts as Ionic Solid Dispersion Forms of Ciprofloxacin

Ciprofloxacin (CIP) is a poorly soluble drug that also displays poor permeability. Attempts to improve the solubility of this drug to date have largely focused on the formation of crystalline salts and metal complexes. The aim of this study was to prepare amorphous solid dispersions (ASDs) by ball milling CIP with various polymers. Following examination of their solid state characteristics and physical stability, the solubility advantage of these ASDs was studied, and their permeability was investigated via parallel artificial membrane permeability assay (PAMPA). Finally, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ASDs were compared to those of CIP. It was discovered that acidic polymers, such as Eudragit L100, Eudragit L100-55, Carbopol, and HPMCAS, were necessary for the amorphization of CIP. In each case, the positively charged secondary amine of CIP was found to interact with carboxylate groups in the polymers, forming amorphous polymeric drug salts. Although the ASDs began to crystallize within days under accelerated stability conditions, they remained fully X-ray amorphous following exposure to 90% RH at 25 °C, and demonstrated higher than predicted glass transition temperatures. The solubility of CIP in water and simulated intestinal fluid was also increased by all of the ASDs studied. Unlike a number of other solubility enhancing formulations, the ASDs did not decrease the permeability of the drug. Similarly, no decrease in antibiotic efficacy was observed, and significant improvements in the MIC and MBC of CIP were obtained with ASDs containing HPMCAS-LG and HPMCAS-MG. Therefore, ASDs may be a viable alternative for formulating CIP with improved solubility, bioavailability, and antimicrobial activity.