In vitro-in vivo correlation of the effect of supersaturation on the intestinal absorption of BCS Class 2 drugs

Recent Progress in the Oral Delivery of Therapeutic Peptides and Proteins: Overview of Pharmaceutical Strategies to Overcome Absorption Hurdles

Purpose

Proteins and peptides have secured a place as excellent therapeutic moieties on account of their high selectivity and efficacy. However due to oral absorption limitations, current formulations are mostly delivered parenterally. Oral delivery of peptides and proteins (PPs) can be considered the need of the hour due to the immense benefits of this route. This review aims to critically examine and summarize the innovations and mechanisms involved in oral delivery of peptide and protein drugs.

Methods

Comprehensive literature search was undertaken, spanning the early development to the current state of the art, using online search tools (PubMed, Google Scholar, ScienceDirect and Scopus).

Results

Research in oral delivery of proteins and peptides has a rich history and the development of biologics has encouraged additional research effort in recent decades. Enzyme hydrolysis and inadequate permeation into intestinal mucosa are the major causes that result in limited oral absorption of biologics. Pharmaceutical and technological strategies including use of absorption enhancers, enzyme inhibition, chemical modification (PEGylation, pro-drug approach, peptidomimetics, glycosylation), particulate delivery (polymeric nanoparticles, liposomes, micelles, microspheres), site-specific delivery in the gastrointestinal tract (GIT), membrane transporters, novel approaches (self-nanoemulsifying drug delivery systems, Eligen technology, Peptelligence, self-assembling bubble carrier approach, luminal unfolding microneedle injector, microneedles) and lymphatic targeting, are discussed. Limitations of these strategies and possible innovations for improving oral bioavailability of protein and peptide drugs are discussed.

Conclusion

This review underlines the application of oral route for peptide and protein delivery, which can direct the formulation scientist for better exploitation of this route.

Quabodepistat (OPC-167832), a Novel Antituberculosis Drug Candidate: Enhancing Oral Bioavailability via Cocrystallization and Mechanistic Analysis of Bioavailability in Two Cocrystals

Quabodepistat (code name OPC-167832) is a novel antituberculosis drug candidate. This study aimed to discover cocrystals that improve oral bioavailability and to elucidate the mechanistic differences underlying the bioavailability of different cocrystals. Screening yielded two cocrystals containing 2,5-dihydroxybenzoic acid (2,5DHBA) or 2-hydroxybenzoic acid (2HBA). In bioavailability studies in beagle dogs, both cocrystals exhibited better bioavailability than the free form; however, the extent of bioavailability of cocrystals with 2HBA (quabodepistat-2HBA) was 1.4-fold greater than that of cocrystals with 2,5DHBA (quabodepistat-2,5DHBA). Dissolution studies at pH 1.2 yielded similar profiles for both cocrystals, although the percent dissolution differed: quabodepistat-2HBA dissolved more slowly than quabodepistat-2,5DHBA. The poor solubility of quabodepistat-2HBA is likely the primary factor limiting dissolution at pH 1.2. To identify a dissolution method that maintains the bioavailability in beagle dogs, we performed pH-shift dissolution studies that mimic the dynamic pH change from the stomach to the small intestine. Quabodepistat-2HBA demonstrated supersaturation after the pH was increased to 6.8, while quabodepistat-2,5DHBA did not demonstrate supersaturation. This result was consistent with the results of bioavailability studies in beagle dogs. We conclude that a larger quantity of orally administered quabodepistat-2HBA remained in its cocrystal form while being transferred to the small intestine compared with quabodepistat-2,5DHBA.

Small is Powerful: Demonstration of the Impact of Nanoformed Piroxicam in a Controlled Clinical Study

PURPOSE

New solutions are needed to enable the efficient use of poorly water-soluble drugs. Therefore, we aimed to demonstrate that decreasing particle size with a solution-to-particle method known as nanoforming can improve dissolution and thus bioavailability.

METHODS

Piroxicam, a poorly water-soluble non-steroidal anti-inflammatory drug (NSAID), was used as a model compound. A Quality-by-Design (QbD) approach was used to nanoform piroxicam and a design space was established. The pharmacokinetics of piroxicam nanoparticles were compared to two marketed products in a clinical trial.

RESULTS

Nanoformed tablets showed a 33% increase in exposure during the first hour after dosing (AUC0-1 h) compared with an immediate release tablet and was similar to a fast absorbing tablet incorporating complexation of piroxicam with β-cyclodextrin.

CONCLUSIONS

The results show that nanoforming enabled more rapid absorption in comparison to a typical marketed tablet and indicate that nanoforming is an alternative to complex formulation such as cyclodextrins based products. The study outcomes support the potential of nanoforming for producing fast-acting dosage forms of poorly soluble drugs.

Control of Dissolution and Supersaturation/Precipitation of Poorly Water-Soluble Drugs from Cocrystals Based on Solubility Products: A Case Study with a Ketoconazole Cocrystal

This study demonstrates in vitro and in vivo control of cocrystal dissolution with drug supersaturation/precipitation based on the solubility product of a cocrystal. As a cocrystal model, KTZ-4ABA (ketoconazole, KTZ, a poorly water-soluble drug cocrystal, with 4-aminobenzoic acid, 4ABA, a coformer) was used. The presence of 4ABA in the dissolution media dramatically reduced the dissolution rate of KTZ-4ABA and regulated the supersaturation/precipitation of KTZ, supported by the solubility product of KTZ-4ABA. In the in vitro dissolution study, the combined solid form of KTZ-4ABA and a ten-fold amount of 4ABA significantly lowered the degree of KTZ supersaturation without precipitation and further cocrystal dissolution. To confirm cocrystal dissolution control in the gastrointestinal tract with the same composition as the in vitro study, an in vivo oral administration study with rats was conducted. When KTZ was coadministered to rats in the cocrystal form, an excess of 4ABA coadministered with KTZ-4ABA in the solid form reduced the maximum plasma KTZ concentration (Cmax), prolonged the time to reach the Cmax, but did not influence the area under the plasma concentration-time curve. These results demonstrate that both in vitro and in vivo cocrystal dissolution can be regulated by adding an appropriate amount of coformer based on the solubility product, which can be one of the promising strategies for the oral use of cocrystal formulations.

The Effects of Degree and Duration of Supersaturation on In Vivo Absorption Profiles for Highly Permeable Drugs, Dipyridamole and Ketoconazole

The prediction of oral absorption from a supersaturating drug delivery system (SDDS) remains a significant challenge. Here we evaluated the effects of the degree and duration of supersaturation on in vivoabsorption for dipyridamole and ketoconazole. Various dose concentrations of supersaturated suspensions were prepared by a pH shift method, and in vitro dissolution and in vivo absorption profiles were determined. For dipyridamole, the duration of supersaturation decreased with the increase of the dose concentration owing to rapid precipitation. For ketoconazole, the initially constant dissolved concentrations due probably to the liquid-liquid phase separation (LLPS) as a reservoir were observed at high dose concentrations. However, the LLPS did not delay the peak plasma concentration of ketoconazole in rats, indicating that drug molecules were immediately released from the oil phase to the bulk aqueous phase. For both model drugs, the degree of supersaturation, but not the duration of supersaturation, correlated with systemic exposure, indicating quick drug absorption before precipitation. Therefore, the degree of supersaturation is an important parameter compared with the duration of supersaturation for enhancing the in vivo absorption of highly permeable drugs. These findings would help develop a promising SDDS.

In vitro, in-vivo, and in-silico investigation of physicochemical interactions between pioglitazone and rifampicin

There is a possibility of in-situ physicochemical interactions between concomitantly administered drugs. This study aimed to investigate such physicochemical interactions between pioglitazone and rifampicin. Pioglitazone exhibited significantly higher dissolution in the presence of rifampicin, while the dissolution of rifampicin remained unaffected. The solid-state characterization of precipitates recovered after pH-shift dissolution experiments revealed the conversion of pioglitazone into an amorphous form in the presence of rifampicin. The Density Function Theory (DFT) calculations showed the intermolecular hydrogen bonding between rifampicin and pioglitazone. In-situ conversion of pioglitazone in amorphous form and subsequent supersaturation of GIT milieu translated into significantly higher in-vivo exposure of pioglitazone and its metabolites (M-III and M-IV) in Wistar rats. Therefore, it is advisable to consider the possibility of physicochemical interactions between concomitantly administered drugs. Our findings may be beneficial in tailoring the dose of concomitantly administered drugs, particularly for chronic conditions that entail polypharmacy.

Amorphous System of Hesperetin and Piperine-Improvement of Apparent Solubility, Permeability, and Biological Activities

The low bioaccessibility of hesperetin and piperine hampers their application as therapeutic agents. Piperine has the ability to improve the bioavailability of many compounds when co-administered. The aim of this paper was to prepare and characterize the amorphous dispersions of hesperetin and piperine, which could help to improve solubility and boost the bioavailability of both plant-origin active compounds. The amorphous systems were successfully obtained by means of ball milling, as confirmed by XRPD and DSC studies. What's more, the FT-IR-ATR study was used to investigate the presence of intermolecular interactions between the systems' components. Amorphization enhanced the dissolution rate as a supersaturation state was reached, as well as improving the apparent solubility of both compounds by 245-fold and 183-fold, respectively, for hesperetin and piperine. In the in vitro permeability studies simulating gastrointestinal tract and blood-brain barrier permeabilities, these increased by 775-fold and 257-fold for hesperetin, whereas they were 68-fold and 66-fold for piperine in the GIT and BBB PAMPA models, respectively. Enhanced solubility had an advantageous impact on antioxidant as well as anti-butyrylcholinesterase activities-the best system inhibited 90.62 ± 0.58% of DPPH radicals and 87.57 ± 1.02% butyrylcholinesterase activity. To sum up, amorphization considerably improved the dissolution rate, apparent solubility, permeability, and biological activities of hesperetin and piperine.

In Vitro-In Vivo Correlation in Cocrystal Dissolution: Consideration of Drug Release Profiles Based on Coformer Dissolution and Absorption Behavior

This study assessed the in vitro-in vivo correlation in cocrystal dissolution based on the coformer behavior. 4-Aminobenzoic acid (4ABA) was used as a coformer. Cocrystals of poorly water-soluble drugs with 4ABA, ketoconazole cocrystal (KTZ-4ABA), posaconazole cocrystal (PSZ-4ABA), and itraconazole cocrystal (ITZ-4ABA) were used. These three cocrystals generated supersaturated solutions in fasted state simulated intestinal fluid (FaSSIF) in a small-scale, 8 mL dissolution vessel. The time profile of the dissolved amount of 4ABA, an indicator of cocrystal dissolution, was significantly different among the three cocrystals. Under the conditions utilized, half of the KTZ-4ABA cocrystal solid rapidly dissolved within 5 min and the dissolved amount (% of applied amount) of KTZ and 4ABA was the same. Then, even though the residual solid cocrystal gradually dissolved, KTZ precipitated with time. The PSZ-4ABA cocrystal dissolved in a linear fashion with time but the dissolved concentration of PSZ reached a plateau in the supersaturated state and was maintained for at least 2 h. The dissolution rate of ITZ-4ABA was very slow compared to those of the other cocrystals, but a similar tendency was observed between cocrystal dissolution and the dissolved amount of ITZ. The rank order of the cocrystal dissolution rate based on the conformer concentration was KTZ-4ABA > PSZ-4ABA > ITZ-4ABA. Furthermore, cocrystallization of the three drugs with 4ABA significantly enhanced the oral drug absorption in rats. The rank order of the in vivo cocrystal dissolution rate by a deconvolution analysis with the plasma concentration-time profile of 4ABA was KTZ-4ABA > PSZ-4ABA > ITZ-4ABA, which corresponded well with the in vitro dissolution profiles of the cocrystals. These results indicate that analysis of cocrystal dissolution based on the coformer behavior may be useful to evaluate the in vitro and in vivo cocrystal dissolution.

Maximizing the Oral Bioavailability of Poorly Water-Soluble Drugs Using Novel Oil-Like Materials in Lipid-Based Formulations

Lipid-based formulations, such as self-microemulsifying drug-delivery systems (SMEDDSs), are promising tools for the oral delivery of poorly water-soluble drugs. However, failure to maintain adequate aqueous solubility after coming into contact with gastrointestinal fluids is a major drawback. In this study, we examined the use of a novel cinnamic acid-derived oil-like material (CAOM) that binds drugs with a high affinity through π-π stacking and hydrophobic interactions, as an oil core in a SMEDDS for the oral delivery of fenofibrate in rats. The use of the CAOM in the SMEDDS resulted in an unprecedented enhancement in fenofibrate bioavailability, which exceeded the bioavailability values obtained using SMEDDSs based on corn oil, a conventional triglyceride oil, or Labrasol, an enhancer of intestinal permeation. Further characterization revealed that the CAOM SMEDDS does not alter the intestinal permeability and has no inhibitory activity on P-glycoprotein-mediated drug efflux. The results reported herein demonstrate the strong potential of CAOM formulations as new solubilizers for the efficient and safe oral delivery of drugs that have limited water solubility.

Hydrophilic nanofibers as a supersaturating delivery system for carvedilol

Polymer nanofibers represent a promising delivery system for poorly water-soluble drugs; however, their supersaturating potential has not been explored yet. Here, carvedilol-loaded nanofibers based on poly(ethyleneoxide) and on amphiphilic block copolymer poloxamer 407 were produced by electrospinning. These nanofibers provided high carvedilol loading and improved dissolution of carvedilol. Their dissolution resulted in a supersaturated system that was not stable, and thus to avoid carvedilol precipitation, hydroxypropyl methylcelluloses or polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus) were additionally incorporated into the nanofibers. The morphology of the electrospun product was not affected by incorporation of carvedilol and the polymer precipitation inhibitors, as shown by scanning electron microscopy. The hydroxypropyl methylcelluloses were not effective polymer precipitation inhibitors for carvedilol. Incorporation of Soluplus significantly extended the duration of carvedilol supersaturation (>24 h) compared to the dissolution of nanofibers without Soluplus. Moreover, after 1 h of dissolution, incorporation of Soluplus into the nanofibers provided significantly higher carvedilol concentration (94.4 ± 2.5 μg/mL) compared to the nanofibers without Soluplus (32.7 ± 5.8 μg/mL), the polymer film (24.0 ± 2.2 μg/mL), and the physical mixture (3.3 ± 0.4 μg/mL). Thus, this study shows the great potential for hydrophilic nanofibers as a delivery system for sustained carvedilol supersaturation.

Scaffold-Hopping Strategy on a Series of Proteasome Inhibitors Led to a Preclinical Candidate for the Treatment of Visceral Leishmaniasis

There is an urgent need for new treatments for visceral leishmaniasis (VL), a parasitic infection which impacts heavily large areas of East Africa, Asia, and South America. We previously reported on the discovery of GSK3494245/DDD01305143 (1) as a preclinical candidate for VL and, herein, we report on the medicinal chemistry program that led to its identification. A hit from a phenotypic screen was optimized to give a compound with in vivo efficacy, which was hampered by poor solubility and genotoxicity. The work on the original scaffold failed to lead to developable compounds, so an extensive scaffold-hopping exercise involving medicinal chemistry design, in silico profiling, and subsequent synthesis was utilized, leading to the preclinical candidate. The compound was shown to act via proteasome inhibition, and we report on the modeling of different scaffolds into a cryo-EM structure and the impact this has on our understanding of the series’ structure–activity relationships.

Nasr F, Noman O, Alharbi A, Alqahtani MS, Alanazi FK. Development, Characterization Optimization, and Assessment of Curcumin-Loaded Bioactive Self-Nanoemulsifying Formulations and Their Inhibitory Effects on Human Breast Cancer MCF-7 Cells

Curcumin (CUR) is an attractive polyphenol for its anti-inflammatory, antibacterial, antioxidant, and anticancer properties. Poor solubility in water and sensitivity against sunlight are the most challenging characteristics in the development of CUR for clinical use. The aim is to develop oral lipid-based bioactive self-nanoemulsifying drug delivery systems (Bio-SNEDDSs) for curcumin as a candidate for cancer therapy. Bio-SNEDDSs containing black seed oil, medium-chain mono- and diglycerides, and surfactants were prepared as CUR delivery vehicles. The morphology, droplet size, physical stability, encapsulation efficiency, risk of precipitation, lipid digestion, antioxidant activity, and antimicrobial activity were evaluated for the representative formulations. Finally, an MTT assay was performed on MCF-7 cells to determine the cytotoxic effect of the different formulations. The results showed lower droplet size (28.53 nm) and higher drug-loading (CUR 20 mg, thymoquinone 1.2 mg) for the representative Bio-SNEDDS (black seed oil/Imwitor 988/KolliphorEL (35/15/50) % w/w), along with a transparent appearance upon aqueous dilution. The dynamic dispersion and in-vitro lipolysis data proved that the Bio-SNEDDS was able to keep the CUR in a solubilized form in the gastrointestinal tract. From the antioxidant and antimicrobial studies, it was suggested that the Bio-SNEDDS had the highest activity for disease control. The MTT assay showed that the representative Bio-SNEDDS treatment led to a reduction of cell viability of MCF-7 cells compared to pure CUR and conventional SNEDDSs. A Bio-SNEDDS with elevated entrapment efficiency, antioxidant/antimicrobial activities, and an antiproliferative effect could be the best anticancer drug candidate for potential oral delivery.

Bottom-Up Physiologically Based Oral Absorption Modeling of Free Weak Base Drugs

In this study, we systematically evaluated "bottom-up" physiologically based oral absorption modeling, focusing on free weak base drugs. The gastrointestinal unified theoretical framework (the GUT framework) was employed as a simple and transparent model. The oral absorption of poorly soluble free weak base drugs is affected by gastric pH. Alternation of bulk and solid surface pH by dissolving drug substances was considered in the model. Simple physicochemical properties such as pKa, the intrinsic solubility, and the bile micelle partition coefficient were used as input parameters. The fraction of a dose absorbed (Fa) in vivo was obtained by reanalyzing the pharmacokinetic data in the literature (15 drugs, a total of 85 Fa data). The AUC ratio with/without a gastric acid-reducing agent (AUCr) was collected from the literature (22 data). When gastric dissolution was neglected, Fa was underestimated (absolute average fold error (AAFE) = 1.85, average fold error (AFE) = 0.64). By considering gastric dissolution, predictability was improved (AAFE = 1.40, AFE = 1.04). AUCr was also appropriately predicted (AAFE = 1.54, AFE = 1.04). The Fa values of several drugs were slightly overestimated (less than 1.7-fold), probably due to neglecting particle growth in the small intestine. This modeling strategy will be of great importance for drug discovery and development.

Discovery and Characterization of Clinical Candidate LXE408 as a Kinetoplastid-Selective Proteasome Inhibitor for the Treatment of Leishmaniases

Visceral leishmaniasis is responsible for up to 30,000 deaths every year. Current treatments have shortcomings that include toxicity and variable efficacy across endemic regions. Previously, we reported the discovery of GNF6702, a selective inhibitor of the kinetoplastid proteasome, which cleared parasites in murine models of leishmaniasis, Chagas disease, and human African trypanosomiasis. Here, we describe the discovery and characterization of LXE408, a structurally related kinetoplastid-selective proteasome inhibitor currently in Phase 1 human clinical trials. Furthermore, we present high-resolution cryo-EM structures of the Leishmania tarentolae proteasome in complex with LXE408, which provides a compelling explanation for the noncompetitive mode of binding of this novel class of inhibitors of the kinetoplastid proteasome.

Evaluating supersaturation in vitro and predicting its performance in vivo with Biphasic gastrointestinal Simulator: A case study of a BCS IIB drug

This study aimed to develop an evaluation approach for supersaturation by employing an in vitro bio-mimicking apparatus designed to predict in vivo performance. The Biphasic Gastrointestinal Simulator (BGIS) is composed of three chambers with absorption phases that represent the stomach, duodenum, and jejunum, respectively. The concentration of apatinib in each chamber was detected by fiber optical probes in situ. The dissolution data and the pharmacokinetic data were correlated by Gastroplus^TM. The precipitates were characterized by polarizing microscope, Scanning Electron Microscopy, Powder X-ray diffraction and Differential scanning calorimetry. According to the results, Vinylpyrrolidone-vinyl acetate copolymer (CoPVP) prolonged supersaturation by improving solubility and inhibiting crystallization, while Hydroxypropyl methylcellulose (HPMC) prolonged supersaturation by inhibiting crystallization alone. Furthermore, a predictive in vitro-in vivo correlation was established, which confirmed the anti-precipitation effect of CoPVP and HPMC on in vitro performance and in vivo behavior. In conclusion, CoPVP and HPMC increased and prolonged the supersaturation of apatinib, and then improved its bioavailability. Moreover, BGIS was demonstrated to be a significant approach for simulating in vivo conditions for in vitro-in vivo correlation in a supersaturation study. This study presents a promising approach for evaluating supersaturation, screening precipitation inhibitors in vitro, and predicting their performances in vivo.

The Significance of Utilizing In Vitro Transfer Model and Media Selection to Study the Dissolution Performance of Weak Ionizable Bases: Investigation Using Saquinavir as a Model Drug

This study investigated the dissolution behavior of BCS class II ionizable weak base Saquinavir and its mesylate salt in the multi-compartment transfer setup employing different composition of dissolution media. The dissolution behavior of Saquinavir was studied by using a two-compartment transfer model representing the transfer of drug from the stomach (donor compartment) to the upper intestine (acceptor compartment). Various buffers like phosphate, bicarbonate, FaSSIF, and FeSSIF were employed. The dissolution was also studied in the concomitant presence of the additional solute, i.e., Quercetin. Further, the dissolution profiles of Saquinavir and its mesylate salt were simulated by GastroPlus^TM, and the simulated dissolution profiles were compared against the experimental ones. The formation of in situ HCl salt and water-soluble amorphous phosphate aggregates was confirmed in the donor and acceptor compartments of the transfer setup, respectively. As the consequence of the lower solubility product of HCl salt of Saquinavir, the solubility advantage of mesylate salt was vanished leading to the lower than the predicted dissolution in the acceptor compartment. However, the formation of water-soluble aggregates in the presence of the phosphate salts was observed leading to the higher than the predicted dissolution of the free base in the transfer setup. Interestingly, the formation of such water-soluble aggregates was found to be hindered in the concomitant presence of an ionic solute resulting in the lower dissolution rates. The in situ generation of salts and aggregates in the transfer model lead to the inconsistent prediction of dissolution profiles by GastroPlus^TM.

Evaluating side-by-side diffusion models for studying drug supersaturation in an absorptive environment: a case example of fenofibrate and felodipine

OBJECTIVE

To test whether a side-by-side diffusion model is suitable for studying drug supersaturation in an absorptive environment.

METHODS

The µD/P model and the µFLUX model, using a Caco-2 cell monolayer/PAMPA membrane as the permeation barrier, respectively, were compared in terms of robustness and ease of handling, while studying the drug supersaturation-precipitation-permeation interplay. Continuing with the best model, the impact of the acceptor media and the importance of studying drug supersaturation in a combined dissolution-permeation model, as compared to a simple dissolution model, were evaluated.

KEY FINDINGS

The two models produced similar results in terms of supersaturation, precipitation and permeation. The µFLUX model was considered more robust and easier to handle based on its cell-free permeation system. Using the µFLUX model, it was found that an acceptor medium with a high surfactant concentration increased the amount of permeated drug. The effect of absorption on drug supersaturation was found to be dependent on the drug, and the tested level of supersaturation.

CONCLUSION

The tested models were comparable; however, Caco-2 cell monolayers were considered too sensitive to be used to study drug supersaturation. Further studies are needed to evaluate the observed drug-dependent effects of absorption on drug supersaturation.

High-Throughput Dissolution/Permeation Screening -A 96-Well Two-Compartment Microplate Approach

Early formulation screening can alleviate development of advanced oral drug formulations, such as amorphous solid dispersions (ASDs). Traditionally, dissolution is used to predict ASD performance. Here, a high-throughput approach is described that simultaneously screens drug dissolution and permeation employing a two-compartment 96-well plate. Freeze-drying from hydro-alcoholic solutions was used to prepare amorphous formulations. The screening approach was tested on amorphous and crystalline tadalafil formulations with and without Soluplus^®. The workflow consisted of: 1) dispersion of the formulations; 2) incubation within the two-compartment plate, where a dialysis membrane separated donor (dispersed formulation) and acceptor; 3) sampling (donor and acceptor), where donor samples were centrifuged to remove non-dissolved material; and 4) quantification by UHPLC-UV. To identify optimal screening conditions, the following parameters were varied: dispersion medium (buffer / biomimetic media), acceptor medium (buffer / surfactant solutions), and incubation time (1, 3, and 6 h). Surfactants (acceptor) increased tadalafil permeation. Biomimetic medium (donor) enhanced dissolution, but not permeation, except for freeze-dried tadalafil, for which the permeated amount increased. The predictiveness was evaluated by comparing dissolution-/permeation-results with in vivo bioavailability. In general, both dissolution and permeation reflected bioavailability, whereof the latter was a better predictor. High-throughput dissolution/permeation is regarded promising for formulation screening.

Molybdenum disulfide-based hyaluronic acid-guided multifunctional theranostic nanoplatform for magnetic resonance imaging and synergetic chemo-photothermal therapy

The construction of multifunctional theranostic nanoplatforms to integrate accurate imaging and enhanced therapy to treat tumors is highly attractive but remains a challenge. Here, we developed a molybdenum disulfide (MoS₂)-based hyaluronic acid (HA)-functionalized nanoplatform capable of achieving the targeted co-delivery of the gadolinium (Gd)-based contrast agents (CAs) and the anticancer drug gefitinib (Gef) for magnetic resonance imaging (MRI) and synergetic chemo-photothermal therapy of tumors. Gd³⁺ ions were coupled to HA-grafted MoS₂ nanosheets with diethylenetriaminepentaacetic acid (DTPA) as a linker, followed by the incorporation of Gef. The resulting MoS₂-HA-DTPA-Gd/Gef exhibited enhanced relaxivity, 3.3 times greater than that of the commercial CA DTPA-Gd, which facilitated the MRI in vivo. Moreover, the nanoplatform effectively converted the absorbed near-infrared (NIR) light into heat, which not only induced the photothermal ablation of cancer cells but also triggered the release of Gef from MoS₂-HA-DTPA-Gd/Gef, enabling the synergetic chemo-photothermal therapy. The results of in vitro and in vivo experiments revealed that MoS₂-HA-DTPA-Gd/Gef upon NIR irradiation effectively blocked the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) signaling pathway and activated apoptosis-related proteins to induce cell apoptosis and suppress cell proliferation, thus inhibiting the tumor growth in lung cancer cell-bearing mice. Taken together, this multifunctional theranostic nanoplatform has significant promise for the diagnosis and treatment of cancer.

Analysis of the Complicated Nonlinear Pharmacokinetics of Orally Administered Telmisartan in Rats Using a Stable Isotope-IV Method

This study aimed to kinetically analyze the nonlinear absorption and systemic exposure of telmisartan (TEL) after oral administration to rats by using a stable isotope-IV method. Rats were orally administered different dose of TEL, followed by the intravenous injection of 0.005 mg/kg of deuterium-labeled TEL (TEL-d3). Assuming that TEL-d3 shows same pharmacokinetic properties with TEL, systemic clearance (CL_tot), oral bioavailability (F_oral), and intestinal and hepatic availability (F_a*F_g, F_h) of TEL were calculated in each individual rat. AUC_po of TEL increased disproportionately with dose and showed a sigmoid-type relation, indicating the involvement of multi-nonlinear processes in oral absorption of TEL. F_a*F_g of TEL increased with dose at the low-dose range while decreased at the high-dose range. In contrast, F_h increased and CL_tot decreased significantly in the middle range (2 to 6 mg/kg). As main factors of nonlinearity, saturations of solubility, efflux transport in the intestine, and the hepatic uptake of TEL were indicated. In conclusion, this study demonstrated a high possibility of a stable isotope-IV method to characterize complicated pharmacokinetic properties of oral drugs in animals, which can help to consider the future risks in their clinical use.

In Vitro Assessment of Supersaturation/Precipitation and Biological Membrane Permeation of Poorly Water-Soluble Drugs: A Case Study With Albendazole and Ketoconazole

This study aimed to elucidate the relationship between supersaturation and precipitation and the effect of a supersaturated state on drug membrane permeation. Stock solutions of albendazole (ALB) and ketoconazole (KTZ) dissolved in dimethyl sulfoxide (0.1-50 mg/mL) were diluted 100-fold with buffer solution (pH 6.8, 37°C). In the case of ALB, a supersaturated state and immediate precipitation were observed at 10 μg/mL or less and 20 μg/mL or higher, respectively. When KTZ was used, at an initial concentration of 200 μg/mL or higher, precipitation was observed, although the dissolved concentration remained at approximately 120 μg/mL for at least 30 min. These dissolved concentrations of ALB and KTZ related to approximately 10-fold and 14-fold over the saturated solubility from respective bulk powder. An in vitro permeation study implied that the rate of drug permeation across a biological membrane increased with increasing supersaturation. These results suggested favorable strategies for development of a supersaturable formulation could depend on the precipitation properties of the drug. Immediate- and controlled-release forms might be suitable for supersaturable formulations for KTZ and ALB, respectively.

Application of a Refined Developability Classification System

In 2010, the Developability Classification System was proposed as an extension of the Biopharmaceutics Classification System to align the classification system with the need for early evaluation of drug candidates according to their developability as oral formulations. Recent work on the Developability Classification System has resulted in the refined developability classification system (rDCS), consisting of standard investigations to estimate drug candidate solubility and permeability and offering customized investigations that are triggered when there is a potential for supersaturation/precipitation (e.g., salts of acids, weak bases) or to investigate permeation versus dissolution-limited absorption. In the present study, the rDCS concept was successfully applied to 6 marketed compounds (aciclovir, albendazole, danazol, dantrolene, dipyridamole, and piroxicam), for which there is a rich database of information. Furthermore, the rDCS was applied to 20 pipeline compounds from past and current research projects at Bayer AG. The rDCS was able to predict the results in humans correctly in 80% of cases. Overall, the results suggest that the rDCS is a highly useful tool for estimating the in vivo behavior of new drug candidates.

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.

Development, current applications and future roles of biorelevant two-stage in vitro testing in drug development

Objectives

Various types of two stage in vitro testing have been used in a number of experimental settings. In addition to its application in quality control and for regulatory purposes, two-stage in vitro testing has also been shown to be a valuable technique to evaluate the supersaturation and precipitation behavior of poorly soluble drugs during drug development.

Key findings

The so-called ‘transfer model’, which is an example of two-stage testing, has provided valuable information about the in vivo performance of poorly soluble, weakly basic drugs by simulating the gastrointestinal drug transit from the stomach into the small intestine with a peristaltic pump. The evolution of the transfer model has resulted in various modifications of the experimental model set-up. Concomitantly, various research groups have developed simplified approaches to two-stage testing to investigate the supersaturation and precipitation behavior of weakly basic drugs without the necessity of using a transfer pump.

Summary

Given the diversity among the various two-stage test methods available today, a more harmonized approach needs to be taken to optimize the use of two stage testing at different stages of drug development.

Intestine-on-a-Chip Microfluidic Model for Efficient in Vitro Screening of Oral Chemotherapeutic Uptake

Many highly effective chemotherapeutic agents can only be administered intravenously as their oral delivery is compromised by low gastro-intestinal solubility and permeability. SN-38 (7-ethyl-10-hydroxycamptothecin) is one such drug; however, recently synthesized lipophilic prodrugs offer a potential solution to the low oral bioavailability issue. Here we introduce a microfluidic-based intestine-on-a-chip (IOAC) model, which has the potential to provide new insight into the structure-permeability relationship for lipophilic prodrugs. More specifically, the IOAC model utilizes external mechanical cues that induce specific differentiation of an epithelial cell monolayer to provide a barrier function that exhibits an undulating morphology with microvilli expression on the cell surface; this is more biologically relevant than conventional Caco-2 Transwell models. IOAC permeability data for SN38 modified with fatty acid esters of different chain lengths and at different molecular positions correlate excellently with water-lipid partitioning data and have the potential to significantly advance their preclinical development. In addition to advancing mechanistic insight into the permeability of many challenging drug candidates, we envisage the IOAC model to also be applicable to nanoparticle and biological entities.

Automated Supersaturation Stability Assay to Differentiate Poorly Soluble Compounds in Drug Discovery

Increasingly, in vitro assays evaluate a compound's tendency to maintain supersaturation toward improving oral absorption. Throughput remains a challenge and only small sets of compounds are evaluated in reported studies. The present work describes an automated workflow and data analysis approach to determine supersaturation stability after 16 min. Eight increasing concentrations were targeted and supernatant concentration was measured following solvent shift in fasted-state simulated intestinal fluid. The effect of dimethyl sulfoxide both on equilibrium solubility and on induced supersaturation was addressed, whereas the change in concentration was evaluated over time. Our sample set included 24 commercial compounds, along with comparison to literature results. To demonstrate in vivo relevance of in vitro supersaturation, classification of supersaturation stability was proposed based on the target concentration achieved and the percentage of area under the curve dose proportionality in 42 preclinical and clinical studies. Eighty-one percent of low supersaturation stability compounds (target concentrations ≤50 μM) had proportionality <0.8, whereas 100% of high supersaturation stability compounds (target concentrations ≥200 μM) demonstrated proportionality ≥0.8. The robust, automated assay and its impact on dose proportionality downstream make this approach applicable in drug discovery where low-soluble compounds with otherwise attractive properties may be differentiated on the basis of supersaturation stability.

Stabilizing Agents for Drug Nanocrystals: Effect on Bioavailability

Drug nanocrystals are a versatile option for drug delivery purposes, and while the number of poorly soluble drug materials is all the time increasing, more research in this area is performed. Drug nanocrystals have a simple structure-a solid drug core is surrounded by a layer of stabilizing agent. However, despite the considerably simple structure, the selection of an appropriate stabilizer for a certain drug can be challenging. Mostly, the stabilizer selection is based purely on the requirement of physical stability, e.g., maintaining the nanosized particle size as long as possible after the formation of drug nanocrystals. However, it is also worth taking into account that stabilizer can affect the bioavailability in the final formulation via interactions with cells and cell layers. In addition, formation of nanocrystals is only one process step, and for the final formulation, more excipients are often added to the composition. The role of the stabilizers in the final formulation can be more than only stabilizing the nanocrystal particle size. A good example is the stabilizer's role as cryoprotectant during freeze drying. In this review, the stabilizing effect, role of stabilizers in final nanocrystalline formulations, challenges in reaching in vitro-in vivo correlation with nanocrystalline products, and stabilizers' effect on higher bioavailability are discussed.

Effects of gastric pH on oral drug absorption: In vitro assessment using a dissolution/permeation system reflecting the gastric dissolution process

The aim of the present study was to evaluate the effects of gastric pH on the oral absorption of poorly water-soluble drugs using an in vitro system. A dissolution/permeation system (D/P system) equipped with a Caco-2 cell monolayer was used as the in vitro system to evaluate oral drug absorption, while a small vessel filled with simulated gastric fluid (SGF) was used to reflect the gastric dissolution phase. After applying drugs in their solid forms to SGF, SGF solution containing a 1/100 clinical dose of each drug was mixed with the apical solution of the D/P system, which was changed to fasted state-simulated intestinal fluid. Dissolved and permeated amounts on applied amount of drugs were then monitored for 2h. Similar experiments were performed using the same drugs, but without the gastric phase. Oral absorption with or without the gastric phase was predicted in humans based on the amount of the drug that permeated in the D/P system, assuming that the system without the gastric phase reflected human absorption with an elevated gastric pH. The dissolved amounts of basic drugs with poor water solubility, namely albendazole, dipyridamole, and ketoconazole, in the apical solution and their permeation across a Caco-2 cell monolayer were significantly enhanced when the gastric dissolution process was reflected due to the physicochemical properties of basic drugs. These amounts resulted in the prediction of higher oral absorption with normal gastric pH than with high gastric pH. On the other hand, when diclofenac sodium, the salt form of an acidic drug, was applied to the D/P system with the gastric phase, its dissolved and permeated amounts were significantly lower than those without the gastric phase. However, the oral absorption of diclofenac was predicted to be complete (96-98%) irrespective of gastric pH because the permeated amounts of diclofenac under both conditions were sufficiently high to achieve complete absorption. These estimations of the effects of gastric pH on the oral absorption of poorly water-soluble drugs were consistent with observations in humans. In conclusion, the D/P system with the gastric phase may be a useful tool for better predicting the oral absorption of poorly water-soluble basic drugs. In addition, the effects of gastric pH on the oral absorption of poorly water-soluble drugs may be evaluated by the D/P system with and without the gastric phase.

Nanonization of andrographolide by a wet milling method: the effects of vitamin E TPGS and oral bioavailability enhancement

Andrographolide (AND) has wide prospects in clinical use, but suffers from the restriction of poor oral bioavailability, due to its low solubility, rapid and extensive metabolism and efflux by P-glycoprotein (P-gp).

Deconstructing HPMCAS: Excipient Design to Tailor Polymer-Drug Interactions for Oral Drug Delivery

Spray-dried dispersions (SDDs) are fascinating polymer-drug mixtures that exploit the amorphous state of a drug to dramatically elevate its apparent aqueous solubility above equilibrium. For practical usage in oral delivery, understanding how polymers mechanistically provide physical stability during storage and prevent supersaturated drugs from succumbing to precipitation during dissolution remains a formidable challenge. To this end, we developed a versatile polymeric platform with functional groups analogous to hydroxypropyl methyl cellulose acetate succinate (HPMCAS, a heterogeneous leading excipient candidate for SDDs) and studied its interactions with Biopharmaceutical Classification System Class II drug models probucol, danazol, and phenytoin at various dosages. By conducting reversible addition-fragmentation chain transfer polymerizations with monomeric components chemically analogous to HPMCAS, we synthetically dismantled the highly polydisperse architecture of HPMCAS into well-defined polymer systems (i.e., targetable M_n, Đ < 1.3, tunable T_g). In the powdered SDD form, by wide-angle X-ray diffraction all HPMCAS analogs yielded amorphous danazol and phenytoin up to 50 wt % loading, whereas for probucol, hydrophobic methoxy functionality and high polymeric T_g were key to inhibit immediate partitioning into crystalline domains. Nonsink in vitro dissolution tests revealed distinct release profiles. The polymer containing only acetyl and succinoyl substituents spray-dried with probucol increased the area under the dissolution curve by a factor of 180, 112, and 26 over pure drug at 10, 25, and 50 wt % loading, respectively. For crystallization-prone danazol and phenytoin, we observed that the water-soluble polymer with hydroxyl groups inhibited crystal growth and enabled high burst release and supersaturation maintenance. Our findings provide fundamental insight into how excipient microstructures can complex with drugs for excipient formulation applications.