To date, the Caco-2 model is considered as the gold standard to predict intestinal drug absorption. Often, aqueous phosphate buffers are used as apical medium. The purpose of this study was to use fasted state human intestinal fluid (FaHIF) as apical solvent system to generate biorelevant permeability values for a series of 16 model drugs that can be used as reference data to critically evaluate fasted state simulated intestinal fluid (FaSSIF) as possible substitute medium. Caco-2 compatibility with FaHIF was achieved when 50 mg/ml mucus was applied on top of the cells before adding the apical medium. The use of FaHIF as solvent system generated a broad range of apparent permeability values (Papp) for the series of model compounds. When Papp values obtained with FaHIF were compared to those obtained with FaSSIF, a strong correlation was observed (R = 0.951). The use of FaSSIF in the absence of mucus did not significantly alter this correlation. For FaHIF, FaSSIF and reference phosphate buffer blank FaSSIF, a strong sigmoidal relationship was found between Papp and fahuman, illustrated by correlation coefficients of 0.961, 0.893 and 0.868, respectively. In terms of inter-subject variability, the use of FaHIF from different volunteers originating from two distinct age groups (18–25 years; 65–72 years) exhibited an average coefficient of variance (CV) of 30%. However, no age dependency in permeability could be observed. In conclusion, the data generated in this article justify the use of FaSSIF as biorelevant apical medium in the Caco-2 assay to accurately predict in vivo drug absorption. Also, the optimized mucus-containing Caco-2 model can be used in combination with intestinal fluid samples aspirated after drug administration to further investigate intraluminal drug and formulation behavior.

Compound libraries that are screened for biological activity commonly contain heterocycles. Besides potency, drug-like properties need to be evaluated to ensure in vivo efficacy of test compounds. In this context, we determined hepatic and intestinal disposition profiles for 17 heterocyclic compounds. All studied compounds showed rapid uptake in suspended rat hepatocytes, whereas metabolism was poor and the rate-limiting step in hepatic elimination. In vitro assays demonstrated a relatively low solubility and high intestinal permeability. Based on these in vitro data, heterocycles were categorized in the biopharmaceutics classification system (BCS) and the biopharmaceutics drug disposition classification system (BDDCS) to predict disposition characteristics before clinical data are available. Our findings emphasized the importance to use hepatocytes in addition to microsomes to study metabolism, since the latter lack non-microsomal enzymes and cellular context. Moreover, intracellular exposure should be considered to gain insight in the relevant fraction of the compound available at the enzymatic site. Finally, the study reveals discrepancies associated with the classification of heterocycles in BCS versus BDDCS. These probably originate from the binary character of both systems.

The purpose of this paper is to collate all recently published solubility data of orally administered drugs in human intestinal fluids (HIF) that were aspirated from the upper small intestine (duodenum and jejunum). The data set comprises in total 102 solubility values in fasted state HIF and 37 solubility values in fed state HIF, covering 59 different drugs. Despite differences in the protocol for HIF sampling and subsequent handling, this summary of HIF solubilities provides a critical reference data set to judge the value of simulated media for intestinal solubility estimation. In this regard, the review includes correlations between the reported solubilizing capacity of HIF and fasted or fed state simulated intestinal fluid (FaSSIF/FeSSIF). Correlating with HIF solubilities enables the optimal use of solubility measurements in simulated biorelevant media to obtain accurate estimates of intestinal solubility during drug development. Considering the fraction of poorly soluble new molecular entities in contemporary drug discovery, adequate prediction of intestinal solubility is critical for efficient lead optimization, early candidate profiling, and further development.

A straightforward synthesis of pyrido[2,3-d]pyrimidine-2,4(1H,3H)-diones was developed starting from 2-chloropyridine-3-carboxylic acid by esterification, nucleophilic aromatic substitution and amide formation in one step, and ring closure allowing their synthesis with two identical or two different group attached to nitrogen. The structural diversity of these [2,3-d]pyrimidine-2,4(1H,3H)-diones resulted in significant variation in the biopharmaceutical properties. This was reflected by the broad range in fasted state simulated intestinal fluid solubility values (12.6μM to 13.8mM), Caco-2 permeability coefficients (1.2×10−6cm/s to 90.7×10−6cm/s) and in vitro-predicted human in vivo intrinsic clearance values (0 to 159ml/min/kg).

Five symmetric epibatidine analogues were evaluated for bioactivity, two selectively bind the α4β2 nAChR.

The synthesis and preliminary ADME evaluation of novel 4-(trifluoromethyl)-5,7,8,9-tetrahydro-6H-pyrido[3,2-b]azepin-6-ones is presented. The key step is a ring expansion of 4-(trifluoromethyl)-7,8-dihydroquinolin-5(6H)-ones via a Beckmann rearrangement. The rearrangement opens up possibilities to access novel unexplored scaffolds for medicinal chemistry. The biopharmaceutical profiling revealed a strong structural dependency of the druglike properties.

The mixed micelles and vesicles present in the intraluminal environment of the postprandial state exhibit suitable solubilizing capacities for lipophilic drugs. This increase in solubility, however, is accompanied by a decrease in the free fraction caused by micellar entrapment of these lipophilic compounds. In this study, both simulated and aspirated human intestinal fluids of fasted and fed state conditions were used to evaluate the influence of food on the intestinal disposition of a series of structurally related β-blockers, with varying logP values. Using the in situ intestinal perfusion technique with mesenteric blood sampling in rats, it was demonstrated that fed state conditions significantly decreased the absorptive flux of the more lipophilic compounds metoprolol, propranolol and carvedilol, whereas the influence on the flux of the hydrophilic β-blocker atenolol was limited. The solubility of BCS class II compound carvedilol was found to increase significantly in simulated and aspirated media of the fed state. Intestinal perfusions using intestinal media saturated with carvedilol, revealed a higher flux in the fasted state compared to the fed state, despite the higher solubility in the fed state. This study underscores the importance of addressing the complex nature of the behavior of compounds in the intraluminal environment in fasted and fed state conditions. Moreover, our data point out the value of studying the effect of food on both solubility and permeability using biorelevant experimental conditions.

The highly potent natural alkaloid epibatidine remains a source of inspiration in the search for new analgesic drugs. In this paper, we describe an expansion of our previously reported synthesis of epibatidine analogues, and five synthetic alkaloids characterized by a symmetric, 1-substituted 7-azabicyclo[2.2.1]heptane skeleton, were evaluated for their biological activity. Two of these are binding selectively to the α4β2 subtype of the nicotinic acetylcholine receptor. Their Ki values were determined to be 40 and 290 nM. After a favourable evaluation of these compounds' cytotoxicity and metabolic stability, they were submitted to a rat tail flick test. The compounds did not show antinociceptive effects, which may be caused by a combination of insufficient potency and poor brain penetration.

The Ussing chambers model is almost exclusively used in the presence of plain aqueous phosphate buffers as solvent system. In an attempt to further elucidate the effect of luminal ingredients and postprandial conditions on intestinal permeability, pooled fasted and fed state human intestinal fluids (FaHIFpool, FeHIFpool) were used. In addition, simulated intestinal fluids of both nutritional states (FaSSIF, FeSSIF) were evaluated as possible surrogate media for HIF. The use of FaHIFpool generated a broad range of Papp values for a series of 16 model drugs, ranging from 0.03×10−6cm/s (carvedilol) to 33.8×10−6cm/s (naproxen). A linear correlation was observed between Papp values using FaSSIF and FaHIFpool as solvent system (R=0.990), justifying the use of FaSSIF as surrogate medium for FaHIF in the Ussing chambers. In exclusion of the outlier carvedilol, a strong sigmoidal relationship was found between Papp and fahuman of 15 model drugs, illustrated by correlation coefficients of 0.961 and 0.936 for FaHIFpool and FaSSIF, respectively. When addressing food effects on intestinal permeability, the use of FeHIFpool resulted in a significantly lower Papp value for nine out of sixteen compounds compared to fasting conditions. FeSSIF as solvent system significantly overestimated Papp values in FeHIFpool. To conclude, the optimized Ussing chambers model using biorelevant media as apical solvent system holds great potential to investigate food effects in a more integrative approach, taking into account drug solubilisation, supersaturation and formulation effects.

Free radicals are known to play a key role in the human body. When considering potential biomaterials, their interaction with free radicals needs to be considered at an early exploratory stage. In this contribution, we identify inorganic oxides that exhibit a free radical scavenging capacity. A convenient screening protocol was developed for identifying the anti-oxidant properties of highly dispersed inorganic materials. The method compares the degradation of an organic dye with radicals in the absence and presence of the material under investigation. The radicals are generated via Fenton chemistry over a heterogeneous goethite catalyst in a phosphate buffer. The procedure conveniently evaluates the anti-or pro-oxidant capacity of a large set of materials with routine laboratory equipment. Semi-quantitative EPR measurements of the radical concentration using a spin-trapping agent were used to validate the screening procedure. Besides the documented cerium oxide, four other materials were identified to exhibit comparable or even better anti-oxidant activity: aluminium titanate, antimony oxide, titanium silicalite-1 zeolite and titanium xonotlite; pro-oxidant activity was demonstrated for several zeolites.

The pyrido-pyrimidine structure is associated with different biological activities, including kinase inhibition and antibacterial activity. However, drug-like properties of this scaffold have not been explored thoroughly. Therefore, the biopharmaceutical profile of ten pyrido[4,3-d]pyrimidines with different substitution pattern was determined at the intestinal and hepatic level.The compounds' biopharmaceutical properties were significantly affected by the substitution pattern, resulting in a broad range in fasted state simulated intestinal fluid solubility values (1.9 mu M-4.2 mM) and Caco-2 permeability coefficients (0.17 x 10(-6) cm/s to 52 x 10(-6) cm/s). A phenylhydrazido group was responsible for the low FaSSIF solubility. Caco-2 permeability was impaired by a dimethoxyphenyl substituent. All analogs were metabolically stable in human intestinal microsomes. The hepatic metabolism, reflected by the extraction ratio, was intermediate to high (ER > 0.3). Aliphatic chains, methoxy groups on a phenyl substituent, ketone and amine substituents were predicted as most susceptible sites for hepatic metabolism. Correlations were found between polar surface area of the compound and Caco-2 permeability (R = 0.86) and metabolic stability (R = 0.76). No toxicity was seen for the pyrido[4,3-d]pyrimidines with Caco-2 cells and sandwich-cultured rat hepatocytes.In conclusion, the large diversity of substituents on the pyrido[4,3-d]pyrimidine core highly influenced the compounds' drug-like properties. (C) 2013 Elsevier B.V. All rights reserved.