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Electrical remodelling as a result of homeodomain transcription factor 2 (Pitx2)-dependent gene regulation was linked to atrial fibrillation (AF) and AF patients with single nucleotide polymorphisms at chromosome 4q25 responded favorably to class I antiarrhythmic drugs (AADs). The possible reasons behind this remain elusive. The purpose of this study was to assess the efficacy of the AADs disopyramide, quinidine, and propafenone on human atrial arrhythmias mediated by Pitx2-induced remodelling, from a single cell to the tissue level, using drug binding models with multi-channel pharmacology. Experimentally calibrated populations of human atrial action po-tential (AP) models in both sinus rhythm (SR) and Pitx2-induced AF conditions were constructed by using two distinct models to represent morphological subtypes of AP. Multi-channel pharmaco-logical effects of disopyramide, quinidine, and propafenone on ionic currents were considered. Simulated results showed that Pitx2-induced remodelling increased maximum upstroke velocity (dVdtmax), and decreased AP duration (APD), conduction velocity (CV), and wavelength (WL). At the concentrations tested in this study, these AADs decreased dVdtmax and CV and prolonged APD in the setting of Pitx2-induced AF. Our findings of alterations in WL indicated that disopyramide may be more effective against Pitx2-induced AF than propafenone and quinidine by prolonging WL., Competing Interests: The authors declare no conflict of interest.

P-glycoprotein (P-gp) is an ATP-dependent efflux pump that has a marked impact on the absorption, distribution, and excretion of therapeutic drugs. As P-gp inhibition can result in drug-drug interactions and altered drug bioavailability, identifying molecular properties that are linked to inhibition is of great interest in drug development. In this study, we combined chemical synthesis, in vitro testing, quantitative structure-activity relationship analysis, and docking studies to investigate the role of hydrogen bond (H-bond) donor/acceptor properties in transporter-ligand interaction. In a previous work, it has been shown that propafenone analogs with a 4-hydroxy-4-piperidine moiety exhibit a generally 10-fold higher P-gp inhibitory activity than expected based on their lipophilicity. Here, we specifically expanded the data set by introducing substituents at position 4 of the 4-phenylpiperidine moiety to assess the importance of H-bond donor/acceptor features in this region. The results suggest that indeed an H-bond acceptor, such as hydroxy and methoxy, increases the affinity by forming a H-bond with Tyr310., (© 2020 The Authors. Archiv der Pharmazie published by Wiley-VCH Verlag GmbH & Co. KGaA on behalf of Deutsche Pharmazeutische Gesellschaft.)

1. Propafenone, an antiarrhythmic drug, is a typical human cytochrome P450 (P450) 2D6 substrate used in preclinical studies. Here, propafenone oxidation by mammalian liver microsomes was investigated in vitro . 2. Liver microsomes from humans and marmosets preferentially mediated propafenone 5-hydroxylation, minipig, rat and mouse livers primarily mediated 4'-hydroxylation, but cynomolgus monkey and dog liver microsomes differently mediated N -despropylation. 3. Quinine, ketoconazole or anti-P450 2D antibodies suppressed propafenone 4'/5-hydroxylation in human and rat liver microsomes. Pretreatments with β-naphthoflavone or dexamethasone increased N -despropylation in rat livers. 4. Recombinant rat P450 2D2 efficiently catalysed propafenone 4'-hydroxylation in a substrate inhibition manner, comparable to rat liver microsomes, while human P450 2D6 displayed propafenone 5-hydroxylation. Human and rat P450 1A, 2C and 3A enzymes mediated propafenone N -despropylation with high capacities. 5. Carbon-4' of propafenone docked favourably into the active site of P450 2D2 based on an in silico model; in contrast, carbon-5 of propafenone docked into human P450 2D6. 6. These results suggest that the major roles of individual P450 2D enzymes in regioselective hydroxylations of propafenone differ between human and rat livers, while the minor roles of P450 1A, 2C and 3A enzymes for propafenone N -despropylation are similar in livers of both species.

A simple and rapid high-performance liquid chromatography tandem mass spectrometry method for the determination of propafenone (PPF) and its active metabolite 5-hydroxypropafenone (5-OHP) in human plasma was developed and validated. This new method was linear and allowed simultaneous quantification of PPF and 5-OHP at a lower level of 0.5 ng/mL. The aliquot of 200 μL plasma sample was simply treated with 4-fold methanol to deproteinize the plasma. The chromatographic separation was achieved on a Hedera ODS-2C18 analytical column with the mobile phase of methanol and 5 mM ammonium acetate solution containing 0.2% formic acid (pH 3.2) (68:32, v/v) at a flow rate of 0.4 mL/min. Quantitation of the analytes was achieved by multiple reaction monitoring under positive ionization mode. The method was successfully applied to a pharmacokinetic study of PPF and 5-OHP in healthy Chinese volunteers. After oral administration of a single dose of 425 mg PPF hydrochloride sustained-release capsule, the maximum peak plasma concentration (Cmax) of PPF was 210.9 ± 141.9 ng/mL with a Tmax of 6 ± 1 h, the Cmax of 5-OHP was 129.6 ± 65.4 ng/mL with a Tmax of 7 ± 2 h. The area under plasma concentration-time curve (AUC0-36) of PPF was 1610 ± 1309 ng·h/mL with a t1/2 of 4.6 ± 1.1 h, the AUC0-36 of 5-OHP was 1446 ± 754 ng·h/mL with a t1/2 of 7.6 ± 1.6 h., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Propafenone is a potent antiarrhythmic agent; clinically propafenone has been used for a number of cardiac arrhythmias because it possesses multiple modes of action, via beta adrenergic receptor blockade and calcium antagonistic activity. Propafenone (PPF) exhibits extensive saturable presystemic biotransformation (first-pass effect) resulting in two active metabolites: 5-hydroxypropafenone (5-OH PPF) formed by CYP2D6 and N-depropylpropafenone (NDP) formed by both CYP3A4 and CYP1A2 enzymes. A specific and sensitive LC-MS/MS method was developed and validated for quantitation of PPF, 5-OH PPF and NDP using turboion spray in a positive ion mode. A solid-phase extraction was employed for the extraction from human plasma. Chromatographic separation of analytes was achieved using an ACE-5 C 8 (50 × 4.6 mm) column with a gradient mobile phase comprising ammonium acetate containing 0.01% TFA in purified water and acetonitrile. The retention times achieved were 1.36, 1.23, 1.24 min and 1.34 min for PPF, 5-OH PPF, NDP and IS (carbamazepine), respectively. Quantitation was performed by monitoring multiple reaction monitoring transition pairs of m/z 342.30 to m/z 116.20, m/z 358.30 to m/z 116.20, m/z 300.30 to m/z 74.20 and m/z 237.20 to m/z 194.10, respectively. The developed method was validated for various parameters. The calibration curves of PPF and 5-OH PPF showed linearity from 1 to 500 ng/mL, with a lower limit of quantitation of 1.0 ng/mL and for NDP linearity from 0.1 to 25 ng/mL with a lower limit of quantitation of 0.1 ng/mL. The bias and precision for intra- and-inter batch assays were <10 and 5%, respectively. The developed assay was used to evaluate pharmacokinetic properties of propafenone and its major metabolites in healthy human subjects., (Copyright © 2017 John Wiley & Sons, Ltd.)

Background: ATP-binding cassette (ABC) transporters, P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP/ABCG2) are major determinants of pharmacokinetic, safety and efficacy profiles of drugs thereby effluxing a broad range of endogenous substances across the plasma membrane. Overexpression of these transporters in various tumors is also implicated in the development of multidrug resistance (MDR) and thus, hampers the success of cancer chemotherapy. Modulators of these efflux transporters in combination with chemotherapeutics could be a promising concept to increase the effective intracellular concentration of anticancer drugs. However, broad and overlapped specificity for substrates and modulators of ABCB1 and ABCG2, merely induce toxicity and unwanted drug-drug interactions and thus, lead to late-stage failure of drugs., Objective: In present investigation, we aim to identify specific 3D structural requirements for selective inhibition of ABCB1 and ABCG2 transport function., Method: GRID Independent Molecular Descriptor (GRIND) models of selective inhibitors of both transporters have been developed, using their most probable binding conformations obtained from molecular docking protocol., Results: Our results demonstrated a dominant role of molecular shape and different H-bonding patterns in drug-ABCB1/ABCG2 selective interactions. Moreover, distinct distances of different pharmacophoric features from steric hot spots of the molecules provided a strong basis of selectivity for both transporters. Additionally, our results suggested the presence of two H-bond donors at a distance of 8.4-8.8 Å in selective modulators of ABCG2., Conclusion: Our findings concluded that molecular shape along with three dimensional pattern of Hbonding in MDR modulators play a critical role in determining the selectivity between the two targets., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Aims: We hypothesize that some drugs, besides flecainide, increase the inward rectifier current (IK1) generated by Kir2.1 homotetramers (IKir2.1) and thus, exhibit pro- and/or antiarrhythmic effects particularly at the ventricular level. To test this hypothesis, we analysed the effects of propafenone, atenolol, dronedarone, and timolol on Kir2.x channels., Methods and Results: Currents were recorded with the patch-clamp technique using whole-cell, inside-out, and cell-attached configurations. Propafenone (0.1 nM-1 µM) did not modify either IK1 recorded in human right atrial myocytes or the current generated by homo- or heterotetramers of Kir2.2 and 2.3 channels recorded in transiently transfected Chinese hamster ovary cells. On the other hand, propafenone increased IKir2.1 (EC50 = 12.0 ± 3.0 nM) as a consequence of its interaction with Cys311, an effect which decreased inward rectification of the current. Propafenone significantly increased mean open time and opening frequency at all the voltages tested, resulting in a significant increase of the mean open probability of the channel. Timolol, which interacted with Cys311, was also able to increase IKir2.1. On the contrary, neither atenolol nor dronedarone modified IKir2.1. Molecular modelling of the Kir2.1-drugs interaction allowed identification of the pharmacophore of drugs that increase IKir2.1., Conclusions: Kir2.1 channels exhibit a binding site determined by Cys311 that is responsible for drug-induced IKir2.1 increase. Drug binding decreases channel affinity for polyamines and current rectification, and can be a mechanism of drug-induced pro- and antiarrhythmic effects not considered until now., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

In this study, an extrusion-spheronization method was applied successfully to fabricate propafenone hydrochloride (PPF) sustained-release pellets. Using scanning electron microscopy, it was shown that the PPF pellets had a mean size of approximately 950 µm with a spherical shape. The in vitro release profiles indicated that the release of PPF from the pellets exhibited a sustained release behavior. The relatively high correlation coefficient (r) values obtained from the analysis of the amount of the drug released versus the square root of time indicated that the release followed a zero order kinetic model. A similar phenomenon was also observed in a pharmacokinetic study in dogs, in which the area under the curve (AUC) of the pellet formulation was 1.2-fold higher than that of PPF tablets. The present work demonstrated the feasibility of controlled delivery of PPF utilizing microcrystalline cellulose (MCC)-based pellets.

1. The efflux pump p-glycoprotein (P-gp/ABCB1) has received enormous attention in drug (xenobiotic) disposition due to its role in modulation of the drug availability and in protection of sensitive organs. 2. P-gp mediated efflux is one of main mechanisms for multidrug resistance in cancer cells. A main approach to reverse the resistance and restore the drug efficacy is to use specific inhibitors of P-gp that suppress the efflux activity. 3. This review summarizes the binding capabilities of known chemical inhibitors based on the analyses of structure-activity relationships, and computational modeling of the inhibitors as well as the binding site of P-gp protein. 4. The molecular models will facilitate the design of lead inhibitors as drug candidates. Also, it helps scientists in early drug discovery phase to synthesize chemical series with better understanding of their P-gp binding liabilities.

Host-guest inclusion complexes of cyclodextrins (CDs) with a potential cardiovascular drug propafenone hydrochloride (PFO), were prepared and characterized using absorption, fluorescence, time-resolved fluorescence, SEM, FT-IR, DSC, (1)H NMR, XRD and PM3 methods. The spectral studies suggested the phenyl ring along with carbonyl group is present inside of CD cavity. Solvent studies revealed that the normal Stokes shifted band originates from the locally excited state and the large Stokes shifted band occurs due to the emission from ICT. Nanosecond time-resolved studies indicated that PFO exhibits biexponential decay in water and triexponential decay in CD, indicating the formation of 1:1 inclusion complex. The results from solid state studies showed important modifications in the physicochemical properties of free PFO. The ΔH, ΔG and ΔS of the complexation process were determined and it was found that the complexation processes were spontaneous. Investigations of thermodynamic and electronic properties confirmed the stability of the inclusion complex., (Copyright © 2013 Elsevier B.V. All rights reserved.)

This paper extends the research of the utilization of borate coordination complexes in chiral separation by counter-current chromatography (CCC). Racemic propafenone was successfully enantioseparated by CCC with di-n-butyl l-tartrate combined with boric acid as the chiral selector. The two-phase solvent system was composed of chloroform/ 0.05 mol/L acetate buffer pH 3.4 containing 0.10 mol/L boric acid (1:1, v/v), in which 0.10 mol/L di-n-butyl l-tartrate was added in the organic phase. The influence of factors in the enantioseparation of propafenone were investigated and optimized. A total of 92 mg of racemic propafenone was completely enantioseparated using high-speed CCC in a single run, yielding 40-42 mg of (R)- and (S)-propafenone enantiomers with an HPLC purity over 90-95%. The recovery for propafenone enantiomers from fractions of CCC was in the range of 85-90%., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solid-liquid equilibrium (SLE) for binary mixture of Propafenone Hydrocloride (PP) with Metoprolol Tartrate (MT) was investigated using differential scanning calorimetry (DSC) and corresponding activity coefficients were calculated. Simple eutectic behavior for this system was observed. The excess thermodynamic functions: G(E) and S(E) for the pre-, post-, and eutectic composition have been obtained using the computed activity coefficients data of the eutectic phase with their excess chemical potentials μi(E) (i=1, 2). The experimental solid-liquid phase temperatures were compared with predictions obtained from available eutectic equilibrium models. The results indicate non-ideality in this mixture. Also, the compatibility of each component and their eutectic mixture with usual excipients was investigated, and the DSC experiments indicate possible weak interactions with α-lactose monohydrate and compatibility with corn starch. The results obtained were confirmed by FT-IR measurements., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Series of twelve chalcone and propafenone derivatives has been synthesized and evaluated for anticancer activities against HeLa, Fem-X, PC-3, MCF-7, LS174 and K562 cell lines. The 2D-QSAR and 3D-QSAR studies were performed for all compounds with cytotoxic activities against each cancer cell line. Partial least squares (PLS) regression has been applied for selection of the most relevant molecular descriptors and QSAR models building. Predictive potentials of the created 2D-QSAR and 3D-QSAR models for each cell line were compared, by use of leave-one-out cross-validation and external validation, and optimal QSAR models for each cancer cell line were selected. The QSAR studies have selected the most significant molecular descriptors and pharmacophores of the chalcone and propafenone derivatives and proposed structures of novel chalcone and propafenone derivatives with enhanced anticancer activity on the HeLa, Fem-X, PC-3, MCF-7, LS174 and K562 cells., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

The drug efflux pump P-glycoprotein (P-gp) has been shown to promote multidrug resistance (MDR) in tumors as well as to influence ADME properties of drug candidates. Here we synthesized and tested a series of benzophenone derivatives structurally analogous to propafenone-type inhibitors of P-gp. Some of the compounds showed ligand efficiency and lipophilic efficiency (LipE) values in the range of compounds which entered clinical trials as MDR modulators. Interestingly, although lipophilicity plays a dominant role for P-gp inhibitors, all compounds investigated showed LipE values below the threshold for promising drug candidates. Docking studies of selected analogues into a homology model of P-glycoprotein suggest that benzophenones show an interaction pattern similar to that previously identified for propafenone-type inhibitors., (© 2012 American Chemical Society)

CE coupled with dual electrochemical (EC) and electrochemiluminescence (ECL) detection was optimized for simultaneous analysis of six cardiovascular drugs (alprenolol, propafenone, acebutolol, verapamil, atenolol and metoprolol) via central composite design. Following this study, three critical electrophoretic factors governing the CE separation were investigated: Tris-H(3)PO(4) buffer concentration, buffer pH value and separation voltage. A modified chromatographic response was adopted for evaluating CE separation quality. Optimum conditions were achieved using Tris-H(3)PO(4) buffer 35.6 mM (pH 2.3) separated at 13.9 kV, which was employed experimentally and led to the successful simultaneous separation of the above six drugs. The good agreement of the chromatographic response was observed between predicted data and actual experimental results using these optimized conditions (RSD=3.75%). The proposed method was validated for linearity, repeatability and sensitivity, and subsequently successfully applied to determine six basic drugs in urine samples., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Overexpression of the xenotoxin transporter P-glycoprotein (P-gp) represents one major reason for the development of multidrug resistance (MDR), leading to the failure of antibiotic and cancer therapies. Inhibitors of P-gp have thus been advocated as promising candidates for overcoming the problem of MDR. However, due to lack of a high-resolution structure the concrete mode of interaction of both substrates and inhibitors is still not known. Therefore, structure-based design studies have to rely on protein homology models. In order to identify binding hypotheses for propafenone-type P-gp inhibitors, five different propafenone derivatives with known structure-activity relationship (SAR) pattern were docked into homology models of the apo and the nucleotide-bound conformation of the transporter. To circumvent the uncertainty of scoring functions, we exhaustively sampled the pose space and analyzed the poses by combining information retrieved from SAR studies with common scaffold clustering. The results suggest propafenone binding at the transmembrane helices 5, 6, 7 and 8 in both models, with the amino acid residue Y307 playing a crucial role. The identified binding site in the non-energized state is overlapping with, but not identical to, known binding areas of cyclic P-gp inhibitors and verapamil. These findings support the idea of several small binding sites forming one large binding cavity. Furthermore, the binding hypotheses for both catalytic states were analyzed and showed only small differences in their protein-ligand interaction fingerprints, which indicates only small movements of the ligand during the catalytic cycle.

Background and Purpose: Human ether-a-go-go related gene (HERG) channel inhibitors may be subdivided into compounds that are trapped in the closed channel conformation and others that dissociate at rest. The structural peculiarities promoting resting state dissociation from HERG channels are currently unknown. A small molecule-like propafenone is efficiently trapped in the closed HERG channel conformation. The aim of this study was to identify structural moieties that would promote dissociation of propafenone derivatives., Experimental Approach: Human ether-a-go-go related gene channels were heterologously expressed in Xenopus oocytes and potassium currents were recorded using the two-microelectrode voltage clamp technique. Recovery from block by 10 propafenone derivatives with variable side chains, but a conserved putative pharmacophore, was analysed., Key Results: We have identified structural determinants of propafenone derivatives that enable drug dissociation from the closed channel state. Propafenone and four derivatives with 'short' side chains were trapped in the closed channel. Five out of six bulky derivatives efficiently dissociated from the channel at rest. One propafenone derivative with a similar bulk but lacking an H-bond acceptor in this region was trapped. Correlations were observed between molecular weight and onset of channel block as well as between pK(a) and recovery at rest., Conclusion and Implications: The data show that extending the size of a trapped HERG blocker-like propafenone by adding a bulky side chain may impede channel closure and thereby facilitate drug dissociation at rest. The presence of an H-bond acceptor in the bulky side chain is, however, essential., (© 2011 The Authors. British Journal of Pharmacology © 2011 The British Pharmacological Society.)

In this paper the pH-equilibrium solubility profiles of ionizable drugs are presented. The aim of the present work was to study the validity of the Henderson-Hasselbalch (HH) relationship in the case of structurally diverse weak bases. In the case of monoprotic bases, namely papaverine, promethazine and propafenone the experimental equilibrium solubility data precisely follow the theoretical HH curve until the limit of salt solubility. The common ion effect on salt solubility was found to be significant at low pHs. Deviation from the HH equation in the case of dibasic quetiapine hydrogen fumarate can be easily interpreted with the formation of different salt compositions. The significance of pH control and the effect of the salt form (e.g., fumarate) was also investigated. It is critical that the pKa value and the intrinsic solubility are accurately determined when the HH relationship is used to predict the pH-dependent aqueous solubility of drugs.

Melanogenesis is a physiological process that results in the synthesis of melanin pigments, which play a crucial protective role against skin photocarcinogenesis. The present study was conducted to determine the inhibitory effects of propafenone on melanogenesis and to elucidate the molecular events involved in the inhibition of melanogenesis by propafenone. To accomplish this, several experiments were conducted using human epidermal melanocyte cells. The melanin content and cAMP production were evaluated, and western blots for proteins involved in melanogenesis were conducted. The melanin content was significantly inhibited by propafenone in a concentration-dependent manner. To clarify the mechanism of the depigmenting property of propafenone, we examined the involvement of propafenone in cAMP signaling. In the cAMP production assay, the intracellular cAMP level was reduced by propafenone. The level of microphthalmia-associated transcription factor (MITF) protein, the upstream transcription factor of tyrosinase, was also reduced by propafenone. In addition, propafenone inhibited the expression of tyrosinase, TRP-1, and TRP-2. Taken together, the results of our study show that propafenone inhibits melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins and suggests that propafenone may be an effective inhibitor of hyperpigmentation.

Stereoselective glucuronidation of propafenone and its beta-blocker analogues by human recombinant UGT1A3 and UGT1A9 from the recombinant baculovirus in insect sf9 cells was studied. The glucuronides produced in incubation mixtures were assayed by HPLC equipped with UV detector, and identified by beta-glucuronidase. The stereoselective glucuronidation was measured by pre-column 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocynate (GITC) derivatization HPLC method for propafenone and esomolol. In all of ten beta-blocker drugs studied, six showed the glucuronidation activity with UGT1A9, while four with UGT1A3. From roughly quantitative stereoselective glucuronidation study of racemic beta-blocker analogues by UGT1A9, propranolol had a high ratio of the ratios of S- to R-isomer glucuronide (S-G/R-G), about 4.3, the ratios of terbutaline, atenolol and esomolol were 3.3, 3.1 and 2.8 respectively, sotalol and propafenone were 2.3 and 2.0. In a word, S-isomers of these drugs were glucuronidated by human UGT1A9 much faster than their antipodes.

The inner cavity of the hERG potassium ion channel can accommodate large, structurally diverse compounds that can be trapped in the channel by closure of the activation gate. A small set of propafenone derivatives was synthesized, and both use-dependency and recovery from block were tested in order to gain insight into the behavior of these compounds with respect to trapping and non-trapping. Ligand-protein docking into homology models of the closed and open state of the hERG channel provides the first evidence for the molecular basis of drug trapping.

Two HPLC methods are described for the enantioselective analysis of R- and S-propafenone in plasma. In a column switching approach, centrifuged plasma was injected onto a silica-based strong acid cation-exchanger and the fraction containing propafenone was switched on-line onto an enantioselective Chiralcel column for separation of the enantiomers. In another approach, propafenone was extracted from plasma by liquid-liquid extraction at pH 11.4. The extracted components were transferred into aqueous medium and separated on a Chiralcel ODR. Both methods were validated and showed comparable performance. Within-day and between-day precision was better than 5% for both methods. Linear calibration functions were obtained (r(2)>0.999), and the limit of detection for each enantiomer was 0.2 microg/mL for column switching and 0.55 microg/mL for liquid-liquid extraction. The analysis methods were applied for the determination of the effect of physical exercise on the enantiomeric ratio of R- and S-propafenone in plasma of healthy volunteers. During exercise, the concentration of both enantiomers reached a maximum, followed by a significant decrease during recovery.

The interaction of propafenone (PPF) enantiomers with human plasma, human serum albumin (HSA), alpha(1)-acid glycoprotein (AGP), as well as with plasma from rat, rabbit, and cow was investigated using indirect chiral high performance liquid chromatography (HPLC) and ultrafiltration techniques. The stronger binding of the S-PPF found in human plasma was due to AGP. Two classes of binding sites in AGP were identified: one with high-affinity and small binding capacity (K(1(S)) = 7.65 x 10(6) M(-1), n(1(S)) = 0.50; K(1(R)) = 2.81 x 10(6) M(-1), n(1(R)) = 0.46), which revealed stereoselectivity; the other with low-affinity and high-binding capacity (n(2(S)) K(2(S)) = 9.95 x 10(3) M(-1); n(2(R)) K(2(R)) = 9.74 x 10(3) M(-1)). The binding to HSA was found to be weak and not enantioselective (nK(S) = 2.08 x 10(3) M(-1), nK(R) = 2.05 x 10(3) M(-1)). The interaction between enantiomers observed in human plasma was confirmed as a competitive type interacting at the high-affinity site in AGP. The binding mode of both enantiomers with AGP was mainly hydrophobic bond. PPF enantiomers had higher-binding affinity for the F-S variant of human AGP. Drug-drug binding interaction studies showed that verapamil, diazepam, nifedipine, furosemide, nitrendipine, and nimodipine did not affect the binding of PPF enantiomers except quinidine and aprindine at the therapeutic concentration. Comparative studies indicated considerable species-dependent binding stereoselectivity between plasma of the four species investigated., (2008 Wiley-Liss, Inc.)

Background: Physicians have frequently encountered difficulties when prescribing drugs not available in doses suitable for pediatric age groups. Furthermore, children have difficulty swallowing tablets. This study aimed to determine the stability of an oral propafenone suspension made from commercial tablets with a syrup vehicle and to establish its reliable use with children., Methods: An extemporaneous suspension of propafenone 1.5 mg/ml was prepared with commercial tablets. Its physicochemical and microbiologic stability was established by constant monitoring during 90 days at room temperature (15 +/- 5 degrees C) and at refrigeration (3-5 degrees C). Plasma levels of propafenona were measured in two children with supraventricular tachycardia at steady state., Results: The suspension was stable, maintaining its original physicochemical and microbiologic properties. Moreover, no apparent changes in color or odor were observed. Plasma levels of propafenone in patients demonstrated therapeutic concentrations after they had taken the suspension, with no unwanted outcome., Conclusions: The conservation of both physicochemical and microbiologic stability of the suspension represents an option for the administration of propafenone to children.

Lipid microparticles, containing 30% and 50% (w/w) propafenone hydrochloride as the active molecule and cetearyl alcohol and Pluronic F68 as excipients, were prepared by Hot Air Coating (HAC). The aim of the work was to identify the kinetics and the mechanism of the drug release process from these microparticulate systems. The application of the Weibull model to the release data from each single fraction of microparticles suggests that a diffusive mechanism governs drug release from microparticles. Thus, we proposed and applied a release kinetic model to the experimental data that takes into account the diffusion as the predominantly mechanism of drug release. The model proposed is a modified version of the exponential equation in which the product of the apparent release rate constant K, specific for each drug/excipient mixture, and the area-to-volume ratio of particles was used. The K values of single fractions of HAC microparticles (coded K(fr)) are very similar to those of the mixtures of particles obtained from the process (coded K(pool)). Using the K(pool) constants, the release behaviour of ensembles of different size microparticles of well-known composition was predicted. The strength of the model was proved by the good fitting of the experimental release data versus those predicted (R(2)> or =0.997).

Nanostructure-initiator mass spectrometry (NIMS) is a new surface-based MS technique that uses a nanostructured surface to trap liquid ('initiator') compounds. Analyte materials adsorbed onto this 'clathrate' surface are subsequently released by laser irradiation for mass analysis. In this protocol, we describe the preparation of NIMS surfaces capable of producing low background and high-sensitivity mass spectrometric measurement using the initiator compound BisF17. Examples of analytes that adsorb to this surface are small molecules, drugs, lipids, carbohydrates and peptides. Typically, NIMS is used to analyze samples ranging from simple analytical standards and proteolytic digests to more complex samples such as tissues, cells and biofluids. Critical experimental considerations of NIMS are described. Specifically, NIMS sensitivity is examined as a function of pre-etch cleaning treatment, etching current density, etching time, initiator composition, sample concentration, sample deposition method and laser fluence. Typically, NIMS surface preparation can be completed in less than 2 h. Subsequent sample preparation requires 1-5 min, depending on sample deposition method. Mass spectrometric data acquisition typically takes 1-30 s per sample.

Self-organizing maps were trained to separate high- and low-active propafenone-type inhibitors of P-glycoprotein. The trained maps were subsequently used to identify highly active compounds in a virtual screen of the SPECS compound library.

The hybrid molecules have been designed on the basis of the structural features of pyrazole-based drugs and MDR modulator propafenone. A simple synthetic strategy and solvent-based regioselectivity have been used for the synthesis of newly designed molecules and they are evaluated for their interactions with P-glycoprotein (P-gp). Some of the molecules show considerable interactions with P-gp and compounds 15, 28 and 40 could be the potential candidates for their use as MDR modulators.

A spectrofluorimetric method was described for the determination of drugs containing active methylene groups adjacent to carbonyl groups. The method was applied successfully to the determination of three life saving cardiovascular drugs, with narrow therapeutic indices: pentoxifylline (I), propafenone hydrochloride (II) and acebutolol hydrochloride (III), in laboratory-prepared mixtures, in commercial tablets and in plasma samples. The method involved the reaction of each of the tested drugs with N1-methyl nicotinamide chloride (NMNCl) in the presence of alkali, followed by addition of formic acid, where highly fluorescent reaction products were produced. The produced fluorescence were measured quantitatively at 472 nm (lambdaex 352 nm), 409 nm (lambdaex 310 nm) and 451 nm (lambdaex 266 nm) for (I), (II), and (III) respectively. The method was linear over concentration ranges of 10-1000 microg/ml , 0.2-12 microg/ml and 0.08-10 microg/ml in standard solutions for (I), (II), and (III) respectively. In spiked human plasma samples, calibration graphs were linear over concentration ranges of 20-1000 microg/ml, 0.2-15 microg/ml and 0.08-10 microg/ml for (I), (II), and (III) respectively. The method showed good accuracy, specificity and precision in both laboratory-prepared mixtures and spiked human plasma samples. The proposed method is simple, with low instrumentation requirements, suitable for quality control application, bioavailability and bioequivalency studies.

Overexpression of membrane bound, ATP-dependent transport proteins is one of the predominant mechanisms leading to multiple drug resistance in tumor therapy as well as in the treatment of bacterial and fungal infections. In tumor therapy, P-glycoprotein (P-gp, ABCB1) is responsible for transport of a wide variety of natural product toxins out of tumor cells leading to decreased accumulation of cytotoxic drugs within the cells. Inhibition of P-gp thus gives rise to a resensitization of multidrug resistant tumor cells and represents a versatile approach for modulation of multidrug resistance. Within this paper, a set of propafenone-type inhibitors of P-gp were analyzed using both interaction field based methods such as CoMFA and CoMSIA and Hologram QSAR. With both methods, highly predictive models with q2-values>0.65 were obtained. Models using logP as additional descriptor generally yielded higher predictive power. On basis of unfavorable steric and favorable electrostatic and hydrophobic interaction fields, these models were able to explain all outlayers identified in previous Hansch-analyses. For HQSAR analysis, models with q2-values up to 0.72 were obtained. Positive influences were found for electron donating groups on the aromatic systems. Highly negative influences were found for diphenylalkylamine substituents, which is a further hint for steric hindrance. The models with highest predictive power were used for screening of a small virtual library. Synthesis and pharmacological testing of a sub set of this library showed that the external predictivity of the HQSAR models generally is lower than the internal one.

P-glycoprotein (P-gp) is an energy-dependent multidrug efflux pump conferring resistance to cancer chemotherapy. Characterization of the mechanism of drug transport at a molecular level represents an important prerequisite for the design of pump inhibitors, which resensitize cancer cells to standard chemotherapy. In addition, P-glycoprotein plays an important role for early absorption, distribution, metabolism, excretion, and toxicity profiling in drug development. A set of propafenonetype substrate photoaffinity ligands has been used in this study in conjunction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to define the substrate binding domain(s) of P-gp in more detail. The highest labeling was observed in transmembrane segments 3, 5, 8, and 11. A homology model for P-gp was generated on the basis of the dimeric crystal structure of Vibrio cholerae MsbA, an essential lipid transporter. Thereafter, the labeling pattern was projected onto the 3D atomic-detail model of P-gp to allow a visualization of the binding domain(s). Labeling is predicted by the model to occur at the two transmembrane domain/transmembrane domain interfaces formed between the amino- and carboxyl-terminal half of P-gp. These interfaces are formed by transmembrane (TM) segments 3 and 11 on one hand and TM segments 5 and 8 on the other hand. Available data on LmrA and AcrB, two bacterial multidrug efflux pumps, suggest that binding at domain interfaces may be a general feature of polyspecific drug efflux pumps.

Considerable effort has been devoted to the characterization of P-glycoprotein - drug interaction in the past. Systematic quantitative structure-activity relationship (QSAR) studies identified both predictive physicochemical parameters and pharmacophoric substructures within homologous series of compounds. Comparative molecular field analysis (CoMFA) led to distinct 3D-QSAR models for propafenone and phenothiazine analogs. Recently, several pharmacophore models have been generated for diverse sets of ligands. Starting from a training set of 15 propafenone-type MDR-modulators, we established a chemical function-based pharmacophore model. The pharmacophoric features identified by this model were (i) one hydrogen bond acceptor, (ii) one hydrophobic area, (iii) two aromatic hydrophobic areas, and (iv) one positive ionizable group. In silico screening of the Derwent World Drug Index using the model led to identification of 28 compounds. Substances retrieved by database screening are diverse in structure and include dihydropyridines, chloroquine analogs, phenothiazines, and terfenadine. On the basis of its general applicability, the presented 3DQSAR model allows in silico screening of virtual compound libraries to identify new potential lead compounds.

Lipophilicity is one of the major determining physicochemical descriptors for P-glycoprotein (P-gp) inhibitory activity. Recently, Pajeva and Wiese showed that in case of P-gp interaction, lipophilicity may be regarded as space-directed property. In the present study, a series of propafenone-type P-gp inhibitors with systematically varying hydrophobicity distribution within the molecules were synthesised and pharmacologically tested. QSAR studies on the basis of multiple linear regression analysis showed that with increasing lipophilicity of the substituents on the amine moiety, the statistical significance of the indicator variables, denoting the substitution pattern on the central aromatic ring system, also increases. This indicates that the distribution of hydrophobicity within the molecules influences the mode of interaction with P-gp.

The enantioselective assay for S(+)- and R(-)-propafenone (PPF) in human urine that developed in this work involves extraction of propafenone from human urine and using S(+)-propafenone as internal standard, chiral derivatization with 2,3,4,6-tetra-O-beta-D-glucopranosyl isothiocyanate, and quantitation by an RP-HPLC system with UV detection (lambda=220 nm). A baseline separation of propafenone enantiomers was achieved on a 5-microm reverse phase ODS column, with a mixture of acetic acid (25:12:0.02,v/v) as mobile phase. There was good linear relationship from 24.9 ng/ml to 1875.0 ng/ml for both of enantiomers. The regression equations of the standard curves based on C(S-PPF) (or C(R-PPF)) versus ratio of A(S-PPF)/A(S) (or A(R-PPF)/A(S)) were y=0.0032x-0.081, (r=0.999) for S-PPF and y=0.0033x+0.0039, (r=0.998) for R-PPF, respectively. The method's limit of detection was 12.5 ng/ml for both enantiomers, and the method's limit of quantitation was 28.2+/-0.52 ng/ml for S-PPF, 30.4+/-methanol:water:glacial 0.53 ng/ml for R-PPF (RSD<8%, n=5). The analytical method yielded average recovery of 98.9% and 100.4% for S-PPF and R-PPF, respectively. The relative standard deviation was no more than 6.11% and 6.22% for S-PPF and R-PPF, respectively. The method enabled study of metabolism of S(+)- and R(-)-propafenone in human urine. The results from 7 volunteers administered 150 mg racemic propafenone indicated that propafenone enantiomers undergo stereoselective metabolism and that in the human body, S(+)-propafenone is metabolized more extensively than R(-)-propafenone.

An extended set of multidrug-resistance modulators of the propafenone type were investigated using CoMFA and CoMSIA. A number of 3D-QSAR models were derived from steric, electrostatic, and hydrophobic fields and their combinations. The hydrophobic fields alone and in combination with the steric and both (steric and electrostatic) fields yielded the models with the highest cross-validated predictivity, in agreement with a previous analysis of a smaller data set of propafenone-type multidrug-resistance (MDR) modulators. Inclusion of lipophilicity did not lead to an improvement of the models. The results point to the importance of hydrophobicity as a space-directed molecular property for MDR-modulating activity. The influence of variable selection applying the GOLPE procedure was investigated with an external test set. Variable-selection procedure was repetitively applied, keeping at each stage variables with uncertain contribution to the models. For the CoMFA-based 3D-QSAR models, an increase in external prediction quality was found. In contrast, the CoMSIA-based 3D-QSAR models were not improved by the GOLPE variable-selection procedure.

In this study, we tested a series of 12 previously identified, highly effective propafenone-type multidrug resistance (MDR) modulators for their possible undesirable effects on cardiac tissue. We used rat papillary muscle preparations and quantitatively determined the potency of these substances to block action potential (AP) upstroke velocity (Vmax) and to prolong APD50. Simultaneously, the effects on isometric twitch parameters were evaluated. Concentration-response curves were obtained for all parameters. Within a subset of the compounds, we found a significant rank correlation (r' = 0.87; p < 0.05) between potencies to block Vmax (kiVmax) and to inhibit daunomycin efflux in MDR cells (IC50). Surprisingly, the most lipophilic compounds with additional aromatic side chains completely lacked effects on AP and mechanical twitch parameters, although they are the most effective MDR modulators. Additional structural modifications such as fluoride substitution of the aromatic ring, introduction of arylpiperazine or piperidine side chains, as well as modifying the hydrogen bond acceptor strength of the carbonyl group did not reestablish cardiac side effects. In contrast, when these substances were truncated at the phenylpropiophenone moiety of the propafenone core structure, cardiac effects reoccurred. We conclude that aromatic substituents in the vicinity of the nitrogen atom prevent interaction with ion channels, likely due to steric hindrance, and are thus a prerequisite for eliminating unwanted cardiac effects.

A database containing 130 propafenone type chemicals which have been tested for their multidrug resistance (MDR) reversal activity was compiled. Using the Multiple Computer-Automated Structure Evaluation (MCASE) program to analyze this database, an underlying relationship between MDR reversal activity and octanol/water partition coefficient was found. An MDR reversal model was created based on this database by the baseline activity identification algorithm (BAIA) of the MCASE program. The main phamacophores relevant to MDR reversal activity were identified.

A set of 9,10-dihydro-9,10-ethano and ethenoanthracene derivatives was tested with the aim to quantify the effect observed on drug efflux. Structure activity relationships and molecular modeling studies allowed to define topological display of pharmacophoric groups for these reversal agents.

Multidrug resistance (MDR) to antitumor agents represents a significant challenge to effective chemotherapy. The use of MDR modulators is a promising approach to overcome the undesired MDR phenotype. The more effective MDR modulators are urgently needed for clinical use. This review focuses on literatures published in 1998-2001.

Estimation of bioavailability and toxicity at the very beginning of the drug development process is one of the big challenges in drug discovery. Most of the processes involved in ADME are driven by rather unspecific interactions between drugs and biological macromolecules. Within the past decade, drug transport pumps such as P-glycoprotein (Pgp) have gained increasing interest in the early ADME profiling process. Due to the high structural diversity of ligands of Pgp, traditional QSAR methods were only successful within analogous series of compounds. We used an approach based on similarity calculations to predict Pgp-inhibitory activity of a series of propafenone analogues. This SIBAR approach is based on selection of a highly diverse reference compound set and calculation of similarity values to these reference compounds. The similarity values (denoted as SIBAR descriptors) are then used for PLS analysis. Our results show, that for a set of 131 propafenone type compounds, models with good predictivity were obtained both in cross validation procedures and with a 31-compound external test set. Thus, these new descriptors might be a versatile tool for generation of predictive ADME models.

Conformation analysis was performed in propaphenone and two potential antiarrhythmic agents of the carbamate type, employing the method of molecular mechanics for calculations. Energetically stable conformers were optimized by means of the quantumchemical method AM1 and the optimized structures were used to construct the pharmacophore. Using the programme Chem-X, four groups of stable conformations of these drug were found, and comparisons by means of the molecular graphic method were employed to graphically visualize the degree of their similarity and to determine the interatomic distances of the groups with free electron pairs and a lipophilic aromatic nucleus.

An enantioselective assay for S(+)- and R(-)-propafenone in transgenic Chinese hamster CHL cells expressing human cytochrome P450 was developed. The method involved extraction of propafenone from the S9s incubates, and formation of propafenone diastereomeric derivatives with the chiral reagent 2,3,4, 6-tetra-O-beta-D-glucopranosyl isothiocyanate. Separation and quantitation of diastereomeric propafenone derivatives were carried out in a reverse-phase-HPLC system with UV detection. The assay was linear from 2 to 200 microg/mL for each enantiomer. The analytical method gave average recoveries of 97.5% and 97.0% for S(+)- and R(-)-propafenone, respectively. The limits of detection and quantitation for the method are 0.1 and 2.0 microg/mL for both S(+)- and R(-)-propafenone, respectively. The reproducibility of the assay was good (RSD <10%). The method allowed study of the depletion of S(+)- and R(-)-propafenone in transgenic Chinese hamster CHL cells expressing human cytochrome P450. The stereoselectivity of propafenone phase I metabolism via cDNA-expressed CYP3A4 was observed., (Copyright 2000 John Wiley & Sons, Ltd.)

Aims: To determine role of CYP2D6 activity in the pharmacokinetics of propafenone (PPF) enantiomers in native Chinese subjects., Methods: Sixteen extensive metabolizers (EMs) and one poor metabolizer (PM), whose phenotype had been previously assessed with dextromethorphan metabolic phenotyping, were enrolled. Blood samples (0 approximately 15 h) were taken after oral administration of a single dose (400 mg) of racemic-propafenone hydrochloride. A reverse-phase h.p.l.c. method with pre-column derivatization was employed to quantitate enantiomeric concentrations of propafenone in plasma., Results: For the EM subjects, S-PPF was less rapidly metabolized and had higher peak plasma concentrations than R-PPF (413+/-143 vs 291+/-109 ng ml-1, P<0.001). The AUC was markedly higher for S-PPF than for R-PPF (2214+/-776 vs 1639+/-630 microg h l-1, P<0.001), whereas the clearance of S-PPF was significantly lower than that of R-PPF (96.0+/-39.0 vs 138+/-78 l h-1, P<0.01). There were no differences in t1/2, and Cmax between the two isomers (P >0.05). In the one PM subject, not only did S-PPF appear to undergo less rapid metabolism than R-PPF, but the subject also showed 2 approximately 3 fold differences in Cmax, CL and AUC compared with EMs. The correlation coefficients (rs ) between dextromethorphan metabolic ratio (lg MR) and pharmacokinetic parameters (Cmax, CL and AUC) were 0.63, -0.87, 0.87 for S-PPF and 0. 57, -0.73, 0.86 for R-PPF, respectively., Conclusions: Our results suggest that CYP2D6 activity contributes to the pharmacokinetic variability of propafenone enantiomers in Chinese subjects.

The effects of pilsicainide on vagally induced atrial fibrillation and on electrophysiological parameters were compared with those of propafenone in alpha-chloralose-anesthetized dogs. Conduction velocity, effective refractory period, wavelength, averaged atrial fibrillation cycle length and activation sequence in the right atrial free wall were determined before and after drug administration. Pilsicainide (2 mg/kg/5 min and 3 mg/kg/h)(n=10) or propafenone (2 mg/kg/15 min and 4 mg/kg/h)(n=10) was intravenously infused during stable atrial fibrillation sustaining > 30 min. Pilsicainide terminated atrial fibrillation in nine dogs, while propafenone did so in three (p < 0.01). After the drug, conduction velocity was suppressed more in the pilsicainide than in the propafenone group(p < 0.01). There was no difference in effective refractory period after drug between the two groups. Mean wavelength was prolonged from 46.0 to 70.4 mm in the pilsicainide group and from 45.0 to 110.8 mm in the propafenone (p < 0.01 vs. pilsicainide). Activation mapping during atrial fibrillation showed Type II or III atrial fibrillation as previously defined [Konings, K.T.S., Kirchhof, C.J.H.J., Smeets, J.R.L.M., Wellens, H.J.J., Penn, O.C., Allessie, M.A., 1994. High-density mapping of electrically induced atrial fibrillation in humans. Circulation. Vol. 89, pp. 511-521.] before the drug, and changed to Type I before atrial fibrillation termination. Thus, pilsicainide was more effective to terminate vagally induced atrial fibrillation than was propafenone despite a greater effect of propafenone than of pilsicainide on wavelength. In this canine atrial fibrillation model, the suppression of conduction velocity may play an important role in changing the activation pattern of atrial fibrillation and thus, terminating atrial fibrillation.

A series of 48 propafenone-type modulators of multidrug resistance was synthesized and their P-glycoprotein inhibitory activity was measured using the daunomycin efflux assay. Both a Free-Wilson and a combined Hansch/Free-Wilson analysis were performed using log P, partial log P and molar refraction values as Hansch descriptors. The results of the Free-Wilson analysis show that modifications on the central aromatic ring generally influence pharmacological activity, whereby in almost all cases a decrease in MDR-modulating potency is observed (Q2cv = 0.66). The combined approach results in equations with remarkably higher predictive power (Q2cv = 0.83), specifically molar refractivity shows high significance in all equations derived. This indicates that polar interactions also contribute to protein binding.

We present a method for the enantioselective analysis of propafenone in human plasma for application in clinical pharmacokinetic studies. Propafenone enantiomers were resolved on a 10-microm Chiralcel OD-R column (250 x 4.6 mm I.D.) after solid-phase extraction using disposable solid-phase extraction tubes (RP-18). The mobile phase used for the resolution of propafenone enantiomers and the internal standard propranolol was 0.25 M sodium perchlorate (pH 4.0)-acetonitrile (60:40, v/v), at a flow-rate of 0.7 ml/min. The method showed a mean recovery of 99.9% for (S)-propafenone and 100.5% for (R)-propafenone, and the coefficients of variation obtained in the precision and accuracy study were below 10%. The proposed method presented quantitation limits of 25 ng/ml and was linear up to a concentration of 5000 ng/ml of each enantiomer.

All four stereoisomers of the propafenone-type MDR-modulator GP-88 (1) were synthesized using a combined approach with chiral pool building blocks and an acetalic protective group, which allows not only diastereoseparation but also assignment of absolute configuration via NMR spectroscopy. Those isomers with different configuration on the center of chirality in the propanolamine side chain showed statistically different PGP-inhibitory activity. Generally, the (R)-configured isomers were by a factor of nearby two higher active than the (S)-isomers. No differences in activity were observed for isomers with different configuration on the benzylic center of chirality.

A reversed phase HPLC method to stereoselectively determine enantiomers of propafenone in human plasma has been developed. After extraction of 1 ml plasma with 3 ml of n-C6H14:CH2Cl2:2-C3H7OH (100:50:5, v/v) and dried under N2, the enantiomers of propafenone were allowed to react with homochiral S(+)-1-(1-naphthyl) ethyl isocyanate (5.66 micrograms in 60 microliters CH2Cl2) at RT for 30 min, to give the diastereomeric derivatives. Their separation was achieved using HPLC with a C18-column and UV-detection (220 nm) and the enantiomeric ratios were measured. The concentration of each enantiomer were then calculated using the enantiomeric ratios and the racemic propafenone concentrations previously measured. This method after validation procedures has been applied to the multisample analyses of a human pharmacokinetic study with 10 healthy volunteers after an oral dose of 300 mg propafenone hydrochloride. The method was shown to be sensitive (7.5 ng.ml-1), convenient and reproducible.