Based on Principles and Insights of COVID-19 Epidemiology, Genome Sequencing, and Pathogenesis: Retrospective Analysis of Sinigrin and ProlixinRX (Fluphenazine) Provides Off-Label Drug Candidates.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative pathogen of pandemic coronavirus disease 2019 (COVID-19). So far, no approved therapy has been developed to halt the spread of the pathogen, and unfortunately, the strategies for developing a new therapy will require a long time and very extensive resources. Therefore, drug repurposing has emerged as an ideal strategy toward a smart, versatile, quick way to confine the lethal disease. In this endeavor, natural products have been an untapped source for new drugs. This review represents the confederated experience of multidisciplinary researchers of 99 articles using several databases: Google Scholar, Science Direct, MEDLINE, Web of Science, Scopus, and PubMed. To establish the hypothesis, a Bayesian perspective of a systematic review was used to outline evidence synthesis. Our docking documentation of 69 compounds and future research agenda assumptions were directed toward finding an effective and economic anti-COVID-19 treatment from natural products. Glucosinolate, flavones, and sulfated nitrogenous compounds demonstrate direct anti-SARS-CoV-2 activity through inhibition protease enzymes and may be considered potential candidates against coronavirus. These findings could be a starting point to initiate an integrative study that may encompass interested scientists and research institutes to test the hypothesis in vitro, in vivo, and in clinics after satisfying all ethical requirements.

Binding of fluphenazine with human serum albumin in the presence of rutin and quercetin: An evaluation of food-drug interaction by spectroscopic techniques.

The interactions between human serum albumin (HSA) and fluphenazine (FPZ) in the presence or absence of rutin or quercetin were studied by fluorescence, absorption and circular dichroism (CD) spectroscopy and molecular modeling. The results showed that the fluorescence quenching mechanism was static quenching by the formation of an HSA-FPZ complex. Entropy change (ΔS0 ) and enthalpy change (ΔH0 ) values were 68.42 J/(mol⋅K) and -4.637 kJ/mol, respectively, which indicated that hydrophobic interactions and hydrogen bonds played major roles in the acting forces. The interaction process was spontaneous because the Gibbs free energy change (ΔG0 ) values were negative. The results of competitive experiments demonstrated that FPZ was mainly located within HSA site I (sub-domain IIA). Molecular docking results were in agreement with the experimental conclusions of the thermodynamic parameters and competition experiments. Competitive binding to HSA between flavonoids and FPZ decreased the association constants and increased the binding distances of FPZ binding to HSA. The results of absorption, synchronous fluorescence, three-dimensional fluorescence, and CD spectra showed that the binding of FPZ to HSA caused conformational changes in HSA and simultaneous effects of FPZ and flavonoids induced further HSA conformational changes.

Electrocatalysis of NADH oxidation using electrochemically activated fluphenazine on carbon nanotube electrode.

Electrocatalytic determination of NADH using a hybrid surface-modified electrode with multi-wall carbon nanotubes (MWCNTs) and a novel electrogenerated redox mediator is described. The redox mediator precursor - fluphenazine (Flu) was adsorbed on MWCNT-modified glassy carbon (GC) electrode which was then subjected to electrochemical activation in 0.1 M H2SO4 using cyclic voltammetry (CV) over a range of potentials -0.2 to 1.5 V vs. Ag/AgCl (6 scans at 100 mV s(-1)). Cyclic voltammograms of Flu indicated the formation of a stable electroactive material presenting one reversible redox couple at the formal potential of -0.115 vs. Ag/AgCl in a phosphate buffer (pH7.0) as a supporting electrolyte. The peaks increased linearly with increasing scan rate indicating electroactive molecules anchored to the electrode surface. The GC/MWCNT/Flu electrode efficiently catalyzed the oxidation of NADH with a decrease in the overpotential of about 600 mV and 150 mV compared to the bare GC and GC/MWCNT electrode, respectively. This modified electrode was successfully used as the working electrode in the chronoamperometric analysis. The peak current response to NADH was linear over its concentration range from 15 µM to 84 µM, and correlation coefficient 0.998. The limits of detection (5 µM) and quantitation (15 µM) were evaluated.

Fluphenazine: from an isolated molecule to its interaction with lipid bilayers.

Fluphenazine (FPh) belongs to the phenothiazine family of compounds and exhibits a wide variety of biological effects, including antimutagenic, proapoptotic, antiproliferative and anti-multidrug resistance (MDR) activities. The ability of FPh to interact with lipid membranes can have a significant impact on its biological activities. However, the mechanisms involved in the interaction of FPh with lipid membranes are poorly understood. FTIR-ATR spectroscopy has been used in this study to visualize the interactions between FPh and a model lipid bilayer composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Subsequent interpretation of the temperature-dependent FTIR spectra obtained for FPh:DPPC systems containing different concentrations of FPh was efficiently supported by principal component analysis.

Phase separation in phosphatidylcholine membrane caused by the presence of a pyrimidine analogue of fluphenazine with high anti-multidrug-resistance activity.

Phenothiazine compounds are known as effective inhibitors of a multidrug resistance (MDR) of tumor cells to chemotherapeutic agents. This group consists of many important substances used in human medicine such as antipsychotic drugs in the case of fluphenazine (FPh) or chlorpromazine (CPZ). Fluphenazine was on the World Health Organization (WHO) list of Essential Medicines of 2009, and its new pyrimidine analog (FPh-prm) presented in this work has been documented to have a high anti-MDR activity. In order to discover the character of alterations of the lipid bilayer structure caused by the presence of FPh-prm inside the lipid membrane, which is responsible for the essential increase of an anti-MDR activity of FPh-prm, microcalorimetric (differential scanning calorimetry), Laurdan fluorescence, (31)P nuclear magnetic resonance spectroscopy (NMR), and attenuated total reflectance Fourier transfer infrared spectroscopy (FTIR-ATR) were used for dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes mixed with a different concentration of amine analogue. It was stated that the formation of domains with different content of FPh-prm/DPPC can be a reason for the membrane-related mechanism of chemoprevention associated with the inhibition of the outward transport of anticancer drugs by the glycoprotein P (Pgp) in cancer cells by the pyrimidine analog of FPh. To our best knowledge, this report is the first to show the bilayer structure of domains formed by incomplete miscibility of fluphenazine-related compounds and phospholipid molecules. Our results provide a sound basis for the design of future modifications of anti-MDR drugs by providing very effective inhibitors of the pump activity of Pgp.

UV-light effects on cytochrome c modulated by the aggregation state of phenothiazines.

The present study shows the factors that modulate the photodamage promoted by phenothiazines. Cytochrome c was irradiated with UV light for 120 min, over a pH range from 4.0 to 8.0, in the absence and in the presence of different concentrations of thioridazine (TR) and fluphenazine (FP). In the absence of phenothiazines, the maximal rate of a Soret band blue shift (nm/min) from 409 to 406 nm was obtained at pH 4.0 (0.028 nm/min). The presence of phenothiazines at the concentration range 10-25 µmol/L amplified and accelerated a cytochrome c blue shift (409 to 405 nm, at a rate = 0.041 nm/min). Above 25 µmol/L, crescent concentrations of phenothiazines contributed to cytochrome c protection with (maximal at 2500 µmol/L). Scanning electronic microscopy revealed the formation of nanostructures. The pH also influenced the effect of low phenothiazine concentrations on cytochrome c. Thus, the predominance of phenothiazine-promoted cytochrome c damage or protection depends on a balance of the following factors: the yield of photo-generated drug cation radicals, which is favored by acidic pH; the stability of the cation radicals, which is favored by the drug aggregation; and the cytochrome c structure, modulated by the pH.

Comparison of cytochrome p450 mediated metabolism of three central nervous system acting drugs.

The investigation of cytochrome P450 (CYP) mediated metabolism reactions by determination of enzyme kinetic parameters, Michaelis constant (K(m)), maximum reaction velocity (V(max)), and intrinsic clearance (CL(int)) is important aspects in discovery and development of drugs. The kinetic parameters can be used to predict the clearance prior to human administration and for better understanding the mechanism of clearance in vivo. In this study, the metabolic activities of three major hepatic CYP isoforms (2C19, 2D6, and 3A4) were investigated on structurally different central nervous system (CNS) acting drugs, amitriptyline, fluphenazine, and dothiepin. By using our novel in vitro evaluation system, we could compare the kinetic parameters for the metabolism of fluphenazine and dothiepin for the first time. Comparing CL(int) values thus obtained, we concluded that 2C19 could be predominant for metabolic activity on tricyclic antidepressants as expected, but not on phenothiazine-related antipsychotic drugs. Since the metabolism of CNS drugs is susceptible to single nucleotide polymorphisms of human gene, our results suggest that phenothiazine could be an alternative to clinical application of CNS drugs.

Calmodulin inhibition contributes to sensitize TRAIL-induced apoptosis in human lung cancer H1299 cells.

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) preferentially triggers apoptosis in tumor cells versus normal cells. However, TRAIL alone is not effective in treating TRAIL-resistant tumors. We evaluated the effect of 180 enzyme inhibitors on TRAIL-induced apoptosis in human lung cancer H1299 cells, and found fluphenazine-N-2-chloroethane (a calmodulin (CaM) antagonist) sensitized TRAIL-induced apoptosis. Interestingly, in the presence of TRAIL, it increased caspase-8 binding to the Fas-associated death domain (FADD), but decreased binding of FADD-like interleukin-1beta-converting enzyme inhibitory proteins (FLIPs). Additionally, its combination with TRAIL inhibited Akt phosphorylation. These results were consistently observed in cells treated with CaM siRNA. We suggested the blockade of CaM could sensitize lung cancer cells to TRAIL-induced apoptosis in at least 2 ways: (i) it can activate death-inducing signaling complex mediated apoptosis by inhibiting TRAIL-induced binding of FLIP and TRAIL-enhanced binding of caspase-8 to FADD; (ii) it can inhibit Akt phosphorylation, consequently leading to decreased expression of anti-apoptotic molecules such as FLIP and members of the inhibitor of apoptosis protein family. This study suggests the combination of CaM antagonists with TRAIL may have the therapeutic potential to overcome the resistance of lung cancers to apoptosis.

Interactions of dihydrochloride fluphenazine with DPPC liposomes: ATR-IR and 31P NMR studies.

The influence of dihydrochloride fluphenazine (FPh) on the dipalmitoylphosphatidylcholine (DPPC) bilayer structure was investigated using ATR-IR and (31)P NMR methods. The ATR-IR results indicate an increase in conformational disorder in the hydrophobic part compared with pure DPPC liposomes and a decrease in temperature of the chain-melting phase transition in FPh/DPPC liposomes. These effects depended on the concentration of the drug in the DPPC bilayer. The dihydrochloride fluphenazine molecules form H-bonds with the proton-acceptor carbonyl groups of DPPC molecules. At a higher concentration of the drug, the lipid bilayer structure is destroyed, and an isotropic phase is observed using (31)P NMR spectroscopy. The interactions between FPh and the lipid bilayer have a crucial role in MDR (multidrug-resistant) activity of this drug. These results improve one possible strategy of cancer chemoprevention with FPh accompanied by fluidization and destabilization of the model lipid bilayer structure.

Fluphenazine release from biodegradable microparticles: characterization and modelling of release.

The release of actives encapsulated in biodegradable poly-lactide-co-glycolide (PLGA)-based microparticles may be diffusion controlled, dependent on polymer degradation, or may occur by a combination of drug diffusion and polymer degradation. This report applies a model, describing combined diffusional and polymer degradation-assisted drug release, to quantify the release of fluphenazine HCl (F-HCl) from PLGA microspheres. Parameters for the release process showed that both the initial drug release phase and the polymer controlled drug release phase were dependent on the F-HCl loading of the microspheres. The percentage drug released in the burst phase and the length of the lag phase were dependent on F-HCl loading. In the degradation controlled release phase, drug release was faster the higher the loading, as shown by the decrease in t(max) from 27 to 10 days, as F-HCl loadings increased from 4.2 to 16.6%w/w. The presence of F-HCl was found to catalyse the degradation of PLGA polymer during particle manufacture and during dissolution. When compared to drug free microspheres, F-HCl accelerated PLGA degradation as shown by the approximately 5-fold increase in both PLGA degradation rate constant (k) and reduction in t(max).

Interaction of chlorpromazine, fluphenazine and trifluoperazine with ocular and synthetic melanin in vitro.

The aim of this study was to examine in vitro the binding capacity of three phenothiazine derivatives--chlorpromazine, fluphenazine and trifluoperazine--causing adverse effects in the eye structures, to natural melanin isolated from pig eyes as well as to synthetic DOPA-melanin used as a model polymer. The amount of drug bound to melanin was determined by UV spectrophotometry. The analysis of results for the kinetics of drug-melanin complex formation showed that the amount of drug bound to melanin increases with increasing initial drug concentration and longer incubation time, attaining an equilibrium state after about 24 h. Binding parameters, i.e. the number of binding sites (n) and association constants (K), were determined on the basis of Scatchard plots. For neuroleptic-ocular melanin and neuroleptic-DOPA-melanin complexes two classes of independent binding sites were found, with association constants K1 approximately 10(4) and K2 approximately 10(2) M (-1) for chlorpromazine and fluphenazine complexes, and K1 approximately 10(5) and K2 approximately 10(3) M(-1) for trifluoperazine complexes. The numbers of strong (n1) and weak (n2) binding sites indicate lower affinity of the drugs examined to ocular melanin compared with DOPA-melanin. The ability of chlorpromazine, fluphenazine and trifluoperazine to interact with melanin, especially the ocular melanin, in vitro is discussed in relation to the ocular toxicity of these drugs in vivo.

Photoaddition of fluphenazine to nucleophiles in peptides and proteins. Possible cause of immune side effects.

By the action of UVA light, fluphenazine reacted with nucleophiles through a mechanism involving defluorination of its trifluoromethyl group, giving rise to carboxylic acid derivatives that were easily detected by electrospray mass spectrometry. This photoreaction took place with alcohols, sulphydryls, and amines. When irradiation of fluphenazine was carried out in the presence of an amino acid at pH 7.4, the alpha-amino group was covalently bound to the drug. With amino acids possessing a further nucleophilic residue on the side chain, such as lysine, tyrosine, and cysteine--but not serine--both groups reacted, resulting in a fluphenazine-amino acid-fluphenazine diadduct. The same occurred with the physiological peptide glutathione (gamma-glutamylcysteinylglycine). By means of MALDI mass spectrometry, it was shown that fluphenazine also covalently bound to peptides and proteins such as calmodulin. This binding may result in the formation of antibodies, ultimately leading to the destruction of the granulocytes and thus suggesting that photoactivation of this drug may play a role in its clinical side effects, such as agranulocytosis.

The neuroleptic drug, fluphenazine, blocks neuronal voltage-gated sodium channels.

Fluphenazine (Prolixin(R)) is a potent phenothiazine-based dopamine receptor antagonist, first introduced into clinical practice in the late 1950s as a novel antipsychotic. The drug emerged as a 'hit' during a routine ion channel screening assay, the present studies describe our electrophysiological examination of fluphenazine at tetrodotoxin-sensitive (TTX-S) and resistant (TTX-R) voltage-gated sodium channel variants expressed in three different cell populations. Constitutively expressed TTX-S conductances were studied in ND7/23 cells (a dorsal root ganglion-derived clonal cell line) and rat primary cerebrocortical neurons. Recombinant rat Na(V)1.8 currents were studied using ND7/23 cells as a host line for heterologous expression. Sodium currents were examined using standard whole-cell voltage-clamp electrophysiology. Current-voltage relationships for either ND7/23 cell or Na(V)1.8 currents revealed a prominent fluphenazine block of sodium channel activity. Steady-state inactivation curves were shifted by approximately 10 mV in the hyperpolarizing direction by fluphenazine (3 microM for ND7/23 currents and 10 microM for Na(V)1.8), suggesting that the drug stabilizes the inactivated channel state. Fluphenazine's apparent potency for blocking either ND7/23 or Na(V)1.8 sodium channels was increased by membrane depolarization, corresponding IC(50) values for the ND7/23 cell conductances were 18 microM and 960 nM at holding potentials of -120 mV and -50 mV, respectively. Frequency-dependent channel block was evident for each of the cell/channel variants, again suggesting a preferential binding to inactivated channel state(s). These experiments show fluphenazine to be capable of blocking neuronal sodium channels. Several unusual pharmacokinetic features of this drug suggest that sodium channel block may contribute to the overall clinical profile of this classical neuroleptic agent.

In vitro phototoxicity of phenothiazines: involvement of stable UVA photolysis products formed in aqueous medium.

This paper reports the results of an in vitro evaluation of the phototoxic potential of stable photoproducts formed by UVA photolysis of three phenothiazines, perphenazine, fluphenazine, and thioridazine, in a water environment. Perphenazine gave a single product due to dechlorination. From thioridazine, the two major products formed; the endocyclic sulfoxide and the endocyclic N-oxide in which the 2-SCH3 substituent was replaced by a hydroxy group were tested. From fluphenazine, two products have been examined as follows: an exocyclic N-piperazine oxide and a carboxylic acid arising from hydrolysis of the 2-CF3 group. The phototoxicity of the isolated photoproducts has been studied in order to determine their possible involvement in the photosensitizing effects exhibited by the parent drugs, using hemolysis and 3T3 fibroblasts viability as in vitro assays. As fluphenazine, perphenazine, and thioridazine did, some photoproducts proved phototoxic. In particular, the perphenazine dechlorinated photoproduct and the thioridazine N-oxide were found to exert phototoxic properties similar to the parent compounds. Therefore, our data suggest that some phenothiazine photoproducts may play a role in the mechanism of photosensitivity of these drugs. Because some of these photoproducts correspond to metabolic products of phenothiazines found in humans, it cannot be ruled out that metabolites of phenothiazines can be phototoxic in vivo.

Anthrax toxin protective antigen: inhibition of channel function by chloroquine and related compounds and study of binding kinetics using the current noise analysis.

Protective antigen (PA) of the tripartite anthrax toxin binds to a cell surface receptor and mediates the transport of two enzymatic components, edema factor and lethal factor, into the cytosol of host cells. Here recombinant PA(63) from Bacillus anthracis was reconstituted into artificial lipid bilayer membranes and formed ion permeable channels. The heptameric PA(63)-channel contains a binding site for 4-aminoquinolones, which block ion transport through PA in vitro. This result allowed a detailed investigation of ligand binding and the stability constants for the binding of chloroquine, fluphenazine, and quinacrine to the binding site inside the PA(63)-channel were determined using titration experiments. Open PA(63)-channels exhibit 1/f noise in the frequency range between 1 and 100 Hz, whereas the spectral density of the ligand-induced current noise was of Lorentzian type. The analysis of the power density spectra allowed the evaluation of the on- and off-rate constants (k(1) and k(-1)) of ligand binding. The on-rate constants of ligand binding were between 10(6) and 10(8) M(-1) s(-1) and were dependent on the ionic strength of the aqueous phase, sidedness of ligand addition, as well as the orientation and intensity of the applied electric field. The off-rates varied between approximately 10 s(-1) and 2600 s(-1) and depended mainly on the structure of the ligand.

Comparison of the effect of the R2 phenothiazine ring substituent on fluphenazine and perphenazine interactions with cyclodextrins.

The effect of -CF3 R2 fluphenazine (FLF) and -Cl R2 perphenazine (PF) substituents on interactions of these phenothiazine derivatives with cyclodextrins (CD) was compared. Inclusion complexes of protonated and basic forms of FLF and PF with CDs were obtained in HCl 0.01 mol/L (pH 1.9 or 2.1), in phosphate buffer (pH 5.8) and in Britton-Robinson's buffer (pH 10.2) solutions and studied using spectral method. It was established. that the uncharged forms of both phenothiazine derivatives interact with CDs stronger than protonated molecules and that the perphenazine-CD inclusion complexes characterize greater apparent stability constants in comparison to adequate fluphenazine complexes. The thermodynamic parameters, estimated from linear Van't Hoff plot, suggest that the van der Waals forces accompanied by hydrophobic effects were operating in the investigated FLF-CD and PF-CD systems. The effect of pH and presence of CD on photostability of FLF or PF was also compared. The photochemical decomposition of both phenothiazine derivatives, in the absence and in the presence of CDs, proceeds according to the first order reaction. It was also established that independent on the charge of molecule, perphenazine was more stabile than fluphenazine and that the inclusion complexation with CDs improved the photostability of both drugs. The data of 2D NMR analysis suggest, that the aromatic portion of FLF and PF molecules, without R2 substituent, tend to the interior of CD.

Flow and injection characteristics of pharmaceutical parenteral formulations using a micro-capillary rheometer.

A micro-capillary rheometer consisted of a fine needle with an internal diameter of 347 microm attached to a 1 ml removable-needle syringe within an Instron device that operated in compression mode to provide various crosshead speeds ranging from 150 to 950 mm min(-1) covering typical clinical injection rates, and that determined the resulting force on the plunger. The crosshead speed and the resulting force were used to calculate the shear rate and the shear stress respectively. These were used in standard capillary flow expressions together with an independent measurement of the wall frictional force and allowed the viscosity of parenteral Newtonian solutions and non-Newtonian suspensions to be measured quantitatively and their rheological behaviour in needles of clinical dimensions to be established. Commercial pharmaceutical parenteral formulations consisting of three oil-based solutions and three aqueous suspensions were chosen for this study. The net injection forces were also obtained and it was shown that both the oil-based solutions and the aqueous suspensions covered similar ranges. The viscosities for the parenteral solutions were determined from the slope of the linear regression (R(2)>0.97) between shear stress and shear rate and ranged between 0.029 and 0.060 Pas. For the aqueous suspensions examined, viscosities decreased from low shear rate to high shear rate, following a power-law model and indicating a pseudo plastic behaviour. Standardisation of the micro-capillary rheometer with Newtonian silicone oils calibrated with a Rheometrics Fluids Spectrometer showed viscosity values consistent between the rotational flow measurements and capillary flow measurements which were within 5% and showed very high degrees of reproducibility between replicate samples. This degree of reproducibility allowed differences in the contribution of the wall frictional force to the required plunger force for both the oil-based and aqueous parenteral formulations to be determined reliably. The wall frictional force values for all formulations were similar (0.6-1.6 N) but the frictional forces of aqueous systems were found to decline significantly with plunger speed. The micro-capillary rheometer has been used to evaluate the impact of concentration changes due to sedimentation on the injectability of one of the aqueous suspensions, where it was shown that not only the viscosity increased but the shear thinning behaviour ceased at higher shear rates. The micro-capillary rheometer which was able to operate in clinical shear rate ranges has been shown to detect deteriorations in the injectable rheology of suspensions, which in the case here was due to pre-injection sedimentation.

Antimutagenic activity of new analogues of fluphenazine.

Fluphenazine (FPh) exhibited antimutagenic activity in lymphocyte cultures, markedly decreasing genotoxic effects of standard mutagenic agents present in cell cultures. However, the strong pharmacological activity of this neuroleptic drug, together with its serious side effects on the central nervous system, limits its use as an antimutagenic compound. In this paper we describe a route of chemical synthesis of FPh analogues that are more hydrophilic than the model compound, thus probably penetrate more weakly through the blood-brain barrier. These new analogues were tested for their antimutagenic and pro-apoptotic activities in human lymphocyte cultures, genotoxically damaged in vitro with benzo[a]pyrene [40 microM, 30 min] and subsequently cultured for 48 h in the presence of the tested compounds. The fluphenazine analogues enhanced apoptosis in genotoxically damaged lymphocytes more strongly than the model compound did. The increase of apoptotic cell frequency was the highest with compound 4a [2-(trifluoromethyl)-10-[3-(diethanolamino)-2-hydroxypropyl] phenothiazine]--a 35% higher effect than that of fluphenazine. The cytotoxicity of derivative 4a was the lowest among the tested compounds; it was 60% lower than that of fluphenazine. The antimutagenic effect of 4a was about 10% stronger than that of fluphenazine. Compound 4a also had the highest hydrophilicity of the new FPh analogues. Compound 4a was chosen for further study as a potentially usable antimutagen that would only weakly penetrate the central nervous system.

Mechanism of C2-toxin inhibition by fluphenazine and related compounds: investigation of their binding kinetics to the C2II-channel using the current noise analysis.

The binding component C2II of the binary actin ADP-ribosylating C2-toxin from Clostridium botulinum is essential for intoxication of target cells. Activation by a protease leads to channel formation and this is presumably required for the transport of the toxic C2I component into cells. The C2II-channel is cation selective and contains a binding site for fluphenazine and structurally related compounds. Ion transport through C2II and in vivo intoxication is blocked when the sites are occupied by the ligands. C2II was reconstituted into artificial lipid bilayer membranes and formed ion permeable channels. The binding constant of chloroquine, primaquine, quinacrine, chloropromazine and fluphenazine to the C2II-channel was determined using titration experiments, which resulted in its block. The ligand-induced current noise of the C2II-channels was investigated using fast Fourier transformation. The noise of the open channels had a rather small spectral density, which was a function of the inverse frequency up to about 100 Hz. Upon addition of ligands to the aqueous phase the current through C2II decreased in a dose-dependent manner. Simultaneously, the spectral density of the current noise increased drastically and its frequency dependence was of Lorentzian type, which was caused by the on and off-reactions of the ligand-mediated channel block. The ligand-induced current noise of C2II was used for the evaluation of the binding kinetics for different ligands to the channel. The on-rate constant of ligand binding was between 10(7) and 10(9) M(-1) s(-1) and was dependent on the ionic strength of the aqueous phase. The off-rate varied between about 10 s(-1) and 3900 s(-1) and depended on the structure of the ligand. The role of structural requirements for the effective block of C2II by the different ligands is discussed.

Photosensitization of DNA strand breaks by three phenothiazine derivatives.

The interaction and the photosensitizing activity of three phenothiazine derivatives, fluphenazine hydrochloride (FP), thioridazine hydrochloride (TR), and perphenazine (PP), toward DNA were studied. Evidences obtained from various spectroscopic studies such as fluorimetric and linear dichroism measurements indicate that these derivatives bind to the DNA at least in two ways: intercalation and external stacking on the DNA helix, depending on their relative concentrations. Irradiation of supercoiled plasmid DNA in the presence of these phenothiazines leads to single strand breaks. The DNA photocleavage appears to be due to externally bound molecules rather than to those intercalated. The highest photocleavage activity was observed with PP and TR whereas FP was less efficient. The efficiency of the photocleavage in aerated and deaerated solutions does not change thus indicating that an involvement of singlet oxygen can be excluded. Primer extension analysis of plasmid DNA irradiated in the presence of phenothiazines indicates that photocleavage of DNA occurs predominantly at Gua and Cyt residues. Laser flash experiments carried out in the presence of 2'-deoxyguanosine 5'-monophosphate reveal an efficient electron transfer between the nucleotide and the radical cations produced by photoionization of the phenothiazines. In the presence of DNA, an electron transfer process takes place within the laser pulse from the lowest singlet state of phenothiazines to the DNA bases; the time-resolved measurements showed that the back-electron transfer is a negligible decay pathway for the charged species.