Edmund S. Kostewicz

Predicting the precipitation of poorly soluble weak bases upon entry in the small intestine

Solubility and dissolution relationships in the gastrointestinal tract can be critical for the oral bioavailability of poorly soluble drugs. In the case of poorly soluble weak bases, the possibility of drug precipitation upon entry into the small intestine may also affect the amount of drug available for uptake through the intestinal mucosa. To simulate the transfer out of the stomach into the intestine, a transfer model was devised, in which a solution of the drug in simulated gastric fluid is continuously pumped into a simulated intestinal fluid, and drug precipitation in the acceptor medium is examined via concentration–time measurements. The in‐vitro precipitation of three poorly soluble weakly basic drugs, dipyridamole, BIBU 104 XX and BIMT 17 BS, was investigated. For all three, extensive supersaturation was achieved in the acceptor medium. Under simulated fasted‐state conditions, precipitation occurred for all three compounds whereas under simulated fed‐state conditions, the higher concentrations of bile components and the lower pH value in the acceptor medium inhibited precipitation at concentrations corresponding to usual doses in all cases. Comparison with pharmacokinetic data indicated that a combination of transfer model data with solubility and dissolution profiles should lead to better predictions of in‐vivo behaviour of poorly soluble weak bases.

Dissolution media simulating the intralumenal composition of the small intestine: physiological issues and practical aspects

The objective of this study was to test various aspects of dissolution media simulating the intralumenal composition of the small intestine, including the suitability of the osmolality‐adjusting agents and of the buffers, the substitution of crude sodium taurocholate (from ox bile) for pure sodium taurocholate and the substitution of partially hydrolysed soybean phosphatidylcholine for egg phosphatidylcholine. It was concluded that biorelevant media should contain sodium as the major cation species to better reflect the physiology. However, the use of non‐physiologically relevant buffers is inevitable, especially for simulation of the fed state in the small intestine. The buffers used may affect the solubility product of weakly basic compounds with pKa(s) higher than about 5, the solubility of extremely highly lipophilic compounds due to salting in/out properties of the anion of the buffer and the stability of the dissolving compound. It is prudent in relevant situations to run an additional dissolution test in a modified fed state simulated intestinal fluid (FeSSIF) (or fasted state simulated intestinal fluid (FaSSIF), where applicable) containing alternative buffer species. Although a mixture of bile salts is physiologically more relevant than pure sodium taurocholate, this issue seems to be of practical importance in only a few cases. Adequate simulations in these cases will probably require the use of a number of pure substances and could substantially increase the cost of the test. Finally, unless the drug is extremely lipophilic (ca. logP > 5), egg phosphatidylcholine can be substituted by partially hydrolysed soybean phosphatidylcholine.

In vitro models for the prediction of in vivo performance of oral dosage forms.

Accurate prediction of the in vivo biopharmaceutical performance of oral drug formulations is critical to efficient drug development. Traditionally, in vitro evaluation of oral drug formulations has focused on disintegration and dissolution testing for quality control (QC) purposes. The connection with in vivo biopharmaceutical performance has often been ignored. More recently, the switch to assessing drug products in a more biorelevant and mechanistic manner has advanced the understanding of drug formulation behavior. Notwithstanding this evolution, predicting the in vivo biopharmaceutical performance of formulations that rely on complex intraluminal processes (e.g. solubilization, supersaturation, precipitation…) remains extremely challenging. Concomitantly, the increasing demand for complex formulations to overcome low drug solubility or to control drug release rates urges the development of new in vitro tools. Development and optimizing innovative, predictive Oral Biopharmaceutical Tools is the main target of the OrBiTo project within the Innovative Medicines Initiative (IMI) framework. A combination of physico-chemical measurements, in vitro tests, in vivo methods, and physiology-based pharmacokinetic modeling is expected to create a unique knowledge platform, enabling the bottlenecks in drug development to be removed and the whole process of drug development to become more efficient. As part of the basis for the OrBiTo project, this review summarizes the current status of predictive in vitro assessment tools for formulation behavior. Both pharmacopoeia-listed apparatus and more advanced tools are discussed. Special attention is paid to major issues limiting the predictive power of traditional tools, including the simulation of dynamic changes in gastrointestinal conditions, the adequate reproduction of gastrointestinal motility, the simulation of supersaturation and precipitation, and the implementation of the solubility-permeability interplay. It is anticipated that the innovative in vitro biopharmaceutical tools arising from the OrBiTo project will lead to improved predictions for in vivo behavior of drug formulations in the GI tract.

Forecasting the oral absorption behavior of poorly soluble weak bases using solubility and dissolution studies in biorelevant media.

The rate at which a drug goes into solution is an important determinant of drug absorption from the gastrointestinal tract. Factors that are important to the kinetics of drug dissolution, as identified by the Nernst-Brunner and Levich modifications of the Noyes-Whitney model (1–3), are the physicochemical properties of the compound itself such as pKa, solubility, crystalline energy and specific surface area, and certain aspects of the prevailing conditions in the gastrointestinal (GI) tract. The physiological parameters that can play an important role include pH, surface tension, solubilization, buffer capacity, and the volume of the lumenal contents. These parameters not only change following the ingestion of food, but also can vary widely with position in the GI tract. Amphiphilic bile components including bile salts and lecithin, the concentration of which increase following a meal (4), have been shown to increase the in vitro dissolution rate for numerous poorly soluble compounds (5,6) either by an increase in solubility via micellar solubilization (at concentrations above the critical micelle concentration) and/or by the enhancement of the wettability of the compound. Dipyridamole, BIMT 17 BS and BIBU 104 XX (Fig. 1), were chosen as structurally diverse examples of poorly soluble weak bases each displaying a dissolution-rate limited component to their absorption behavior, with intrinsic solubilities of 0.008, 0.0075, and 0.0028 mg/ml, respectively (Table I). The pKa values of the compounds, 6.4 (dipyridamole), 6.03 (BIMT 17 BS), and 5.8 (BIBU 104 XX) suggest that the dissolution characteristics could vary considerably during transit through the GI tract. Furthermore, the relatively high log D values for both dipyridamole (3.95 at pH 7.0) and BIMT 17 BS (3.3 at pH 7.4) indicate that the dissolution of these compounds may be influenced by the solubilizing effects of bile salts and lecithin. The lower log D value for BIBU 104 XX (2.3 at pH 7.4) suggests a lesser solubilization effect. In the present study the aim was to assess the potential of in vitro solubility and dissolution studies using physiological relevant GI media to predict the in vivo absorption behavior of the aforementioned three poorly soluble weak bases.

Early pharmaceutical profiling to predict oral drug absorption: current status and unmet needs.

Preformulation measurements are used to estimate the fraction absorbed in vivo for orally administered compounds and thereby allow an early evaluation of the need for enabling formulations. As part of the Oral Biopharmaceutical Tools (OrBiTo) project, this review provides a summary of the pharmaceutical profiling methods available, with focus on in silico and in vitro models typically used to forecast active pharmaceutical ingredients (APIs) in vivo performance after oral administration. An overview of the composition of human, animal and simulated gastrointestinal (GI) fluids is provided and state-of-the art methodologies to study API properties impacting on oral absorption are reviewed. Assays performed during early development, i.e. physicochemical characterization, dissolution profiles under physiological conditions, permeability assays and the impact of excipients on these properties are discussed in detail and future demands on pharmaceutical profiling are identified. It is expected that innovative computational and experimental methods that better describe molecular processes involved in vivo during dissolution and absorption of APIs will be developed in the OrBiTo. These methods will provide early insights into successful pathways (medicinal chemistry or formulation strategy) and are anticipated to increase the number of new APIs with good oral absorption being discovered.

Discovery of 7-Hydroxy-6-methoxy-2-methyl-3-(3,4,5- trimethoxybenzoyl)benzo[b]furan (BNC105), a Tubulin Polymerization Inhibitor with Potent Antiproliferative and Tumor Vascular Disrupting Properties

A structure-activity relationship (SAR) guided design of novel tubulin polymerization inhibitors has resulted in a series of benzo[b]furans with exceptional potency toward cancer cells and activated endothelial cells. The potency of early lead compounds has been substantially improved through the synergistic effect of introducing a conformational bias and additional hydrogen bond donor to the pharmacophore. Screening of a focused library of potent tubulin polymerization inhibitors for selectivity against cancer cells and activated endothelial cells over quiescent endothelial cells has afforded 7-hydroxy-6-methoxy-2-methyl-3-(3,4,5-trimethoxybenzoyl)benzo[b]furan (BNC105, 8) as a potent and selective antiproliferative. Because of poor solubility, 8 is administered as its disodium phosphate ester prodrug 9 (BNC105P), which is rapidly cleaved in vivo to return the active 8. 9 exhibits both superior vascular disrupting and tumor growth inhibitory properties compared with the benchmark agent combretastatin A-4 disodium phosphate 5 (CA4P).

Influence of Hydrodynamics and Particle Size on the Absorption of Felodipine in Labradors

AbstractPurpose. To study the influence of GI hydrodynamics and drug particle size on felodipine absorption in the dog. Methods. Labradors fistulated at midjejunum were used to selectively study the influence of hydrodynamics and particle size on the in vivodissolution and absorption of the poorly soluble, lipophilic drug felodipine. A combination of infusion and oral administration of either normal saline or a 5% glucose solution was used to maintain “fasted” and establish “fed” state motility patterns, respectively. The absorption characteristics of both a micronized (8 μm) and a coarse fraction (125 μm) of felodipine were subsequently studied under these two motility patterns. Results. A reduction in particle size led up to an approximate 22-fold increase in maximum plasma concentration and up to an approximate 14-fold increase in area under the curve, with a commensurate decrease in the time at which the maximum plasma concentration occurred. Although the absorption of felodipine from the solution and micronized suspension was not influenced by a change in the hydrodynamics, felodipine was absorbed from the coarse suspension almost twice as well in the “fed” state as under “fasted” conditions. Conclusions. Absorption from coarse suspensions of felodipine was sensitive to luminal hydrodynamics, whereas micronized suspensions were not. However, the particle size seems to have a much more important influence on the bioavailability of felodipine than the hydrodynamics per se.

Synthesis and biological evaluation of polysulfated oligosaccharide glycosides as inhibitors of angiogenesis and tumor growth

A series of polysulfated penta- and tetrasaccharide glycosides containing alpha(1-->3)/alpha(1-->2)-linked mannose residues were synthesized as heparan sulfate (HS) mimetics and evaluated for their ability to inhibit angiogenesis. The compounds bound tightly to angiogenic growth factors (FGF-1, FGF-2, and VEGF) and strongly inhibited heparanase activity. In addition, the compounds exhibited potent activity in cell-based and ex vivo assays indicative of angiogenesis, with tetrasaccharides exhibiting activity comparable to that of pentasaccharides. Selected compounds also showed good antitumor activity in vivo in a mouse melanoma (solid tumor) model resistant to the phase III HS mimetic 1 (muparfostat, formerly known as PI-88). The lipophilic modifications also resulted in reduced anticoagulant activity, a common side effect of HS mimetics, and conferred a reasonable pharmacokinetic profile in the rat, as exemplified by the sulfated octyl tetrasaccharide 5. The data support the further investigation of this class of compounds as potential antiangiogenic, anticancer therapeutics.

Comparison of in vitro tests at various levels of complexity for the prediction of in vivo performance of lipid-based formulations: Case studies with fenofibrate

The objectives of this study were to characterise three prototype fenofibrate lipid-based formulations using a range of in vitro tests with differing levels of complexity and to assess the extent to which these methods provide additional insight into in vivo findings. Three self-emulsifying drug delivery systems (SEDDS) were prepared: a long chain (LC) Type IIIA SEDDS, a medium chain (MC) Type IIIA SEDDS, and a Type IIIB/IV SEDDS containing surfactants only (SO). Dilution, dispersion and digestion tests were performed to assess solubilisation and precipitation behaviour in vitro. Focussed beam reflectance measurements and solid state characterisation of the precipitate was conducted. Oral bioavailability was evaluated in landrace pigs. Dilution and dispersion testing revealed that all three formulations were similar in terms of maintaining fenofibrate in a solubilised state on dispersion in biorelevant media. During in vitro digestion, the Type IIIA formulations displayed limited drug precipitation (<5%), whereas the Type IIIB/IV formulation displayed extensive drug precipitation (~70% dose). Solid state analysis confirmed that precipitated fenofibrate was crystalline. The oral bioavailability was similar for the three lipid formulations (65-72%). In summary, the use of LC versus MC triglycerides in Type IIIA SEDDS had no impact on the bioavailability of fenofibrate. The extensive precipitation observed with the Type IIIB/IV formulation during in vitro digestion did not adversely impact fenofibrate bioavailability in vivo, relative to the Type IIIA formulations. These results were predicted suitably using in vitro dilution and dispersion testing, whereas the in vitro digestion method failed to predict the outcome of the in vivo study.

Trypanothione Reductase High-Throughput Screening Campaign Identifies Novel Classes of Inhibitors with Antiparasitic Activity

ABSTRACT High-throughput screening of 100,000 lead-like compounds led to the identification of nine novel chemical classes of trypanothione reductase (TR) inhibitors worthy of further investigation. Hits from five of these chemical classes have been developed further through different combinations of preliminary structure-activity relationship rate probing and assessment of antiparasitic activity, cytotoxicity, and chemical and in vitro metabolic properties. This has led to the identification of novel TR inhibitor chemotypes that are drug-like and display antiparasitic activity. For one class, a series of analogues have displayed a correlation between TR inhibition and antiparasitic activity. This paper explores the process of identifying, investigating, and evaluating a series of hits from a high-throughput screening campaign.