Isabel González-Álvarez

Biowaiver monographs for immediate release solid oral dosage forms: Aciclovir

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing (biowaiver) for the approval of immediate release (IR) solid oral dosage forms containing aciclovir are reviewed. Aciclovir therapeutic use and therapeutic index, pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) studies were also taken into consideration in order to ascertain whether a biowaiver can be recommended. According to the Biopharmaceutics Classification System (BCS) and considering tablet strengths up to 400 mg, aciclovir would be BCS Class III. However, in some countries also 800 mg tablets are available which fall just within BCS Class IV. Aciclovir seems not to be critical with respect to a risk for bioinequivalence, as no examples of bioinequivalence have been identified. It has a wide therapeutic index and is not used for critical indications. Hence, if: (a) the test product contains only excipients present in aciclovir solid oral IR drug products approved in ICH or associated countries, for instance as presented in this article; and (b) the comparator and the test product both are very rapidly dissolving, a biowaiver for IR aciclovir solid oral drug products is considered justified for all tablet strengths.

Provisional Classification and in Silico Study of Biopharmaceutical System Based on Caco-2 Cell Permeability and Dose Number

Today, early characterization of drug properties by the Biopharmaceutics Classification System (BCS) has attracted significant attention in pharmaceutical discovery and development. In this direction, the present report provides a systematic study of the development of a BCS-based provisional classification (PBC) for a set of 322 oral drugs. This classification, based on the revised aqueous solubility and the apparent permeability across Caco-2 cell monolayers, displays a high correlation (overall 76%) with the provisional BCS classification published by World Health Organization (WHO). Current database contains 91 (28.3%) PBC class I drugs, 76 (23.6%) class II drugs, 97 (31.1%) class III drugs, and 58 (18.0%) class IV drugs. Other approaches for provisional classification of drugs have been surveyed. The use of a calculated polar surface area with a labetalol value as a high permeable cutoff limit and aqueous solubility higher than 0.1 mg/mL could be used as alternative criteria for provisionally classifying BCS permeability and solubility in early drug discovery. To develop QSPR models that allow screening PBC and BCS classes of new molecular entities (NMEs), 18 statistical linear and nonlinear models have been constructed based on 803 0-2D Dragon and 126 Volsurf+ molecular descriptors to classify the PBC solubility and permeability. The voting consensus model of solubility (VoteS) showed a high accuracy of 88.7% in training and 92.3% in the test set. Likewise, for the permeability model (VoteP), accuracy was 85.3% in training and 96.9% in the test set. A combination of VoteS and VoteP appropriately predicts the PBC class of drugs (overall 73% with class I precision of 77.2%). This consensus system predicts an external set of 57 WHO BCS classified drugs with 87.5% of accuracy. Interestingly, computational assignments of the PBC class reasonably correspond to the Biopharmaceutics Drug Disposition Classification System (BDDCS) allocations of drugs (accuracy of 63.3-69.8%). A screening assay has been simulated using a large data set of compounds in different drug development phases (1, 2, 3, and launched) and NMEs. Distributions of PBC forecasts illustrate the current status in drug discovery and development. It is anticipated that a combination of the QSPR approach and well-validated in vitro experimentations could offer the best estimation of BCS for NMEs in the early stages of drug discovery.

In Silico Prediction of Caco-2 Cell Permeability by a Classification QSAR Approach.

In the present study, 21 validated QSAR models that discriminate compounds with high Caco‐2 permeability (Papp≥8×10−6 cm/s) from those with moderate‐poor permeability (Papp<8×10−6 cm/s) were developed on a novel large dataset of 674 compounds. 20 DRAGON descriptor families were used. The global accuracies of obtained models were ranking between 78–82 %. A general model combining all types of molecular descriptors was developed and it classified correctly 81.56 % and 83.94 % for training and test sets, respectively. An external set of 10 compounds was predicted and 80 % was correctly assessed by in vitro Caco‐2 assays. The potential use of the final model was evaluated by a virtual screening of a human intestinal absorption database of 269 compounds. The model predicted 121 compounds with high Caco‐2 permeability and the 90 % of them had high values of human intestinal absorption (HIA≥80). This study provides the most comprehensive database of Caco‐2 permeability and evidenced the utility of the combined methodology (in silico+in vitro) in the prediction of Caco‐2 permeability. It suggests that the present methodology can be used in the design of large libraries of compounds with appropriate values of permeability and to perform virtual screening in the early stages of drug development.

Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM

The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time, <10 or >10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this work it was possible to demonstrate, from a functional point of view, the higher efflux capacity of the TC7 clone and to identify the apical membrane as the main resistance for the xenobiotic transport. This methodology can be extremely useful as a complementary tool for molecular biology approaches in order to establish meaningful hypotheses about transport mechanisms.

In-situ intestinal rat perfusions for human Fabs prediction and BCS permeability class determination: Investigation of the single-pass vs. the Doluisio experimental approaches

Intestinal drug permeability has been recognized as a critical determinant of the fraction dose absorbed, with direct influence on bioavailability, bioequivalence and biowaiver. The purpose of this research was to compare intestinal permeability values obtained by two different intestinal rat perfusion methods: the single-pass intestinal perfusion (SPIP) model and the Doluisio (closed-loop) rat perfusion method. A list of 15 model drugs with different permeability characteristics (low, moderate, and high, as well as passively and actively absorbed) was constructed. We assessed the rat intestinal permeability of these 15 model drugs in both SPIP and the Doluisio methods, and evaluated the correlation between them. We then evaluated the ability of each of these methods to predict the fraction dose absorbed (Fabs) in humans, and to assign the correct BCS permeability class membership. Excellent correlation was obtained between the two experimental methods (r(2)=0.93). An excellent correlation was also shown between literature Fabs values and the predictions made by both rat perfusion techniques. Similar BCS permeability class membership was designated by literature data and by both SPIP and Doluisio methods for all compounds. In conclusion, the SPIP model and the Doluisio (closed-loop) rat perfusion method are both equally useful for obtaining intestinal permeability values that can be used for Fabs prediction and BCS classification.

In Situ Perfusion Model in Rat Colon for Drug Absorption Studies: Comparison with Small Intestine and Caco-2 Cell Model.

Our aim is to develop and to validate the in situ closed loop perfusion method in rat colon and to compare with small intestine and Caco-2 cell models. Correlations with human oral fraction absorbed (Fa) and human colon fraction absorbed (Fa_colon) were developed to check the applicability of the rat colon model for controlled release (CR) drug screening. Sixteen model drugs were selected and their permeabilities assessed in rat small intestine and colon, and in Caco-2 monolayers. Correlations between colon/intestine/Caco-2 permeabilities versus human Fa and human Fa_colon have been explored to check model predictability and to apply a BCS approach in order to propose a cut off value for CR screening. Rat intestine perfusion with Doluisios method and single-pass technique provided a similar range of permeabilities demonstrating the possibility of combining data from different laboratories. Rat colon permeability was well correlated with Caco-2 cell-4 days model reflecting a higher paracellular permeability. Rat colon permeabilities were also higher than human colon ones. In spite of the magnitude differences, a good sigmoidal relationship has been shown between rat colon permeabilities and human colon fractions absorbed, indicating that rat colon perfusion can be used for compound classification and screening of CR candidates.

Influence of polyunsaturated fatty acids on Cortisol transport through MDCK and MDCK-MDR1 cells as blood-brain barrier in vitro model.

Transport across the blood-brain barrier is a relevant factor in the pharmacological action of many drugs and endogenous substances whose action site is located in brain. An overactive P-gp has been suggested to be of relevance for the resistance of the HPA system to be suppressed by glucocorticoids, which is one of the best described biological abnormalities in certain types of depression. PUFA acids have shown clinical efficacy in depressed patients and the hypothesis is that these compounds are able to reduce HPA axis activity as this effect has been shown in animal models of depression. The objective of the present work was (1) to characterize Cortisol transport through MDCK and MDCK-MDR1 cell lines (as in vitro models of the BBB) to confirm its transport mechanism as substrate of P-gp and (2) to evaluate the effect of PUFA acids as enhancers of Cortisol transport in the BBB model and explore the enhancement mechanism. Transport studies of Cortisol were performed in both directions, from apical-to-basolateral and from basolateral-to-apical sides. The in vitro experiments showed that Cortisol transport is concentration dependent and it is affected by several transporters (absorption and secretion processes). The results indicate that PUFA acids increase Cortisol transport in the BBB models but not through the inhibition of P-gp efflux but thanks to membrane fluidification and some effect on tight junction integrity.

Cyclometalated Iminophosphorane Gold(III) and Platinum(II) Complexes. A Highly Permeable Cationic Platinum(II) Compound with Promising Anticancer Properties.

New organometallic gold(III) and platinum(II) complexes containing iminophosphorane ligands are described. Most of them are more cytotoxic to a number of human cancer cell lines than cisplatin. Cationic Pt(II) derivatives 4 and 5, which differ only in the anion, Hg2Cl62– or PF6– respectively, display almost identical IC50 values in the sub-micromolar range (25–335-fold more active than cisplatin on these cell lines). The gold compounds induced mainly caspase-independent cell death, as previously reported for related cycloaurated compounds containing IM ligands. Cycloplatinated compounds 3, 4, and 5 can also activate alternative caspase-independent mechanisms of death. However, at short incubation times cell death seems to be mainly caspase dependent, suggesting that the main mechanism of cell death for these compounds is apoptosis. Mercury-free compound 5 does not interact with plasmid (pBR322) DNA or with calf thymus DNA. Permeability studies of 5 by two different assays, in vitro Caco-2 monolayers and a rat perfusion model, have revealed a high permeability profile for this compound (comparable to that of metoprolol or caffeine) and an estimated oral fraction absorbed of 100%, which potentially makes it a good candidate for oral administration.

The Use of Rule-Based and QSPR Approaches in ADME Profiling: A Case Study on Caco-2 Permeability

During the early ADME profiling the development of simple, interpretable and reliable in silico tools is very important. In this study, rule‐based and QSPR approaches were investigated using a large Caco‐2 permeability database. Three permeability classes were determined: high (H), moderate (M) and low (L). The main physicochemical properties related with permeability were ranked as follows: Polar Surface Area (PSA)>Lipophilicity (logP/logD)>Molecular Weight (MW)>number of Hydrogen Bond donors and acceptors>Ionization State>number of Rotatable Bonds>number of Rings. The best rule, based on the combination of PSA‐MW‐logD (3PRule), was able to identify the H, M and L classes with accuracy of 72.2, 72.9 and 70.6 %, respectively. Subsequently, a consensus system based on three voting binary classification trees was constructed. It accurately predicted 78.4/76.1/79.1 % of H/M/L compounds on training and 78.6/71.1/77.6 % on test set. Finally, the 3PRule and multiclassifier were validated with 23 drugs in a Caco‐2 assay. The rule is very useful to improve assay design and prioritize the high absorption candidates. Meanwhile the QSPR model exhibits appropriate classification performance. Due to the simplicity, easy interpretation and accuracy, the 3PRule and consensus model developed here can be used in early ADME profiling.

Kinetic modelling of the intestinal transport of sarafloxacin. Studies in situ in rat and in vitro in Caco-2 cells

The absorption kinetics of sarafloxacin, as a model of fluoroquinolone structure, were studied in the rat small intestine and in Caco-2 cells. The objective of the study was to investigate the mechanistic basis of the drugs intestinal transport in comparison with other members of the fluoroquinolone family and to apply a mathematical modelling approach to the transport process. In the rat small intestine, sarafloxacin showed dual mechanisms of intestinal absorption with a passive diffusional component and an absorptive carrier-mediated component. The characteristics of the animal study design made it suitable for population analysis, thus allowing the accurate estimation of transport parameters and their inter and intra-individual variances. The transport system in the rat model was ATP-dependent, as sodium azide was able to decrease the absorption rate constant in a concentration-dependent fashion. The inhibition mechanism of sodium azide was modelled based on its ATP depletion capacity. The rationale of this approach was to consider the inhibitor-carrier interaction as a concentration- dependent response. This interaction was accurately described by a non-competitive mechanism. In Caco-2 cells, sarafloxacin showed a concentration dependent permeability in both directions apical to basal, and basal to apical. The permeability values and ratios of permeability values at different concentrations suggested the presence of two carriers (absorption and efflux carriers). The passive diffusion component in both systems was compared to that predicted by the absorption–partition correlation, previously established for two series of fluoroquinolones. The discrepancy between the experimental and predicted value suggested the presence of an efflux mechanism similar to that already described for other fluoroquinolones. The differences and similarities of the in situ and the in vitro results are discussed as well as the usefulness of the modelling approach.