Computer-Aided Recognition of ABC Transporters Substrates and Its Application to the Development of New Drugs for Refractory Epilepsy.

Despite the introduction of more than 15 third generation antiepileptic drugs to the market from 1990 to the moment, about one third of the epileptic patients still suffer from refractory to intractable epilepsy. Several hypotheses seek to explain the failure of drug treatments to control epilepsy symptoms in such patients. The most studied one proposes that drug resistance might be related with regional overactivity of efflux transporters from the ATP-Binding Cassette (ABC) superfamily at the blood-brain barrier and/or the epileptic foci in the brain. Different strategies have been conceived to address the transporter hypothesis, among them inhibiting or down-regulating the efflux transporters or bypassing them through a diversity of artifices. Here, we review scientific evidence supporting the transporter hypothesis along with its limitations, as well as computer-assisted early recognition of ABC transporter substrates as an interesting strategy to develop novel antiepileptic drugs capable of treating refractory epilepsy linked to ABC transporters overactivity.

Transepithelial transport of biperiden hydrochloride in Caco-2 cell monolayers.

The aim of this research has been to determine the biperiden hydrochloride permeability in Caco-2 model, in order to classify it based on the Biopharmaceutics Classification System (BCS). The World Health Organization (WHO) as well as many other authors have provisionally assigned the drug as BCS class I (high solubility-high permeability) or III (high solubility-low permeability), based on different methods. We determined biperiden BCS class by comparing its permeability to 5 pre-defined compounds: atenolol and ranitidine hydrochloride (low permeability group) and metoprolol tartrate, sodium naproxen and theophylline (high permeability group). Since biperiden permeability was higher than those obtained for high permeability drugs, we classified it as a BCS class I compound. On the other hand, as no differences were obtained for permeability values when apical to basolateral and basolateral to apical fluxes were studied, this drug cannot act as a substrate of efflux transporters. As a consequence of our results, we suggest that the widely used antiparkinsonian drug, biperiden, should be candidate for a waiver of in vivo bioequivalence studies.

Prediction of drug intestinal absorption by new linear and non-linear QSPR.

In order to minimize the high attrition rate that usually characterizes drug research and development projects, current medicinal chemists aim to characterize both pharmacological and ADME profiles at the beginning of drug R&D initiatives. Thus, the development of ADME High-Throughput Screening in vitro and in silico ADME models has become an important growing research area. Here we present new linear and non-linear predictive QSPR models to predict the human intestinal absorption rate, which are derived from a medium sized, balanced and diverse training set of organic compounds. The structure-property relationships so obtained involve only 4 molecular descriptors, and display an excellent ratio of number of cases to number of descriptors. Their adjustment of the training set data together with the performance achieved during the internal and external validation procedures are comparable to previously reported modeling efforts.

Characterization of 5-HT receptor subtypes mediating contraction in human umbilical vein. 1. Evidence of involvement of 5-HT2A receptors using functional and radioligand binding assays.

This study attempted to characterize pharmacologically the involvement of 5-HT(2A) receptors in 5-HT-induced contractile responses in human umbilical vein (HUV) rings employing functional and radioligand binding assays. In HUV rings, prazosin 1 micro M did not affect contractile responses elicited by 5-HT, ruling out the involvement of alpha(1)-adrenoceptors in contractile responses to 5-HT. 5-HT-induced contractions were competitively blocked by ketanserin, a 5-HT(2A)-selective antagonist. The apparent pA(2) value was 9.8 and the Schild slope significantly less than unity, suggesting that 5-HT-induced responses are mediated by a heterogeneous receptor population. Alpha-methyl-5-HT, a selective 5-HT(2) receptor agonist, induced contractions that were antagonized in a competitive manner by ketanserin. The slope regression was not significantly different from unity and the pA(2) value was 8.8. The selective 5-HT(2A) ligand spiperone produced a parallel rightward shift on 5-HT CRCs in HUV rings. The calculated pA(2) was 9.0, which is in accord for an interaction with the 5-HT(2A) receptor subtype. Alpha-methyl-5-HT CRCs were competitively blocked by spiperone treatment. The Schild analysis yielded a pA(2) of 9.1 with a slope not significantly different from unity. The 5-HT(2C/2A) antagonist mesulergine 10 nM did not affect 5-HT CRCs, suggesting that 5-HT(2C) receptors are not involved in 5-HT-elicited contractions. Higher concentrations of mesulergine showed a parallel rightward shift on 5-HT responses. The calculated pA(2) was 7.44, which suggests an interaction with the 5-HT(2A) receptor subtype. In addition, mesulergine competitively blocked alpha-methyl-5-HT CRCs. The Schild slope was not significantly different from unity and the p A(2) value was 7.98. The binding of [(3)H]ketanserin to HUV membranes was saturable and of high affinity. Ketanserin displayed a monophasic curve which was best fit with a single component of binding. Nonlinear least squares analysis of the binding curves revealed a high affinity K(d) of 0.30 nM and a B(max) of 134 fmol/mg protein. These findings provide strong pharmacological evidence of the involvement of 5-HT(2A) receptors in 5-HT-induced vasoconstriction in HUV. In addition, the contribution of another receptor population cannot be excluded. The results also suggest that this receptor population is neither an alpha(1)-adrenoceptor nor a 5-HT(2C) receptor subtype.