The Synthesis of L-Alanyl and β-Alanyl Derivatives of 2-Aminoacridone and Their Application in the Detection of Clinically-Important Microorganisms

In clinical microbiology the speed with which pathogenic microorganisms may be detected has a direct impact on patient health. One important strategy used in the laboratory is the growth of cultures in the presence of an enzymatic substrate which, once transformed by the appropriate microbial enzyme, generates a detectable colour or fluorescence output. Such substrates have previously been prepared by our group and others and are available as commercial diagnostic kits, however they all suffer from some degree of diffusion when used in a solid growth medium. This diffusion complicates the detection and differentiation of species in polymicrobial cultures and so we sought to improve on our previous work. In this work we have prepared and evaluated a series of novel fluorogenic enzyme substrates based on N-substituted-2-aminoacridones. All of the prepared substrates were found to be suitable for the detection and differentiation of certain microorganisms, however those based on the 2-amino-10-benzylacridone core in particular showed no apparent diffusion when incorporated into solid growth media. On transformation these substrates generated brightly fluorescent colonies that are clearly contrasted with the background medium due to the difference in emission wavelength (λ_em 445–450 nm for the substrate, λ_em 550 nm for the product). Here we have shown that our L-alanyl aminopeptidase substrate, 2-(N-L-alanylamino)-10-benzylacridone, is particularly suited to the detection of Gram-negative bacteria, and our β-alanyl aminopeptidase substrate, 2-(N- β-alanylamino)-10-benzylacridone, to the detection of Pseudomonas aeruginosa and Serratia marcescens when grown on solid media incorporating these substrates. The resulting fluorophore shows no apparent diffusion from the colonies of interest, and the enhanced sensitivity offered by fluorescent emission may allow for the detection of these organisms as microcolonies using automated fluorescence microscopy.

Copper transport and compartmentation in grape cells

Copper-based fungicides have been widely used against several grapevine (Vitis vinifera L.) diseases since the late 1800s when the Bordeaux mixture was developed, but their intensive use has raised phytotoxicity concerns. In this study, physiological, biochemical and molecular approaches were combined to investigate the impacts of copper in grape cells and how it is transported and compartmented intracellularly. Copper reduced the growth and viability of grape cells (CSB, Cabernet Sauvignon Berry) in a dose-dependent manner above 100 µM and was accumulated in specific metal ion sinks. The copper-sensitive probe Phen Green SK was used to characterize copper transport across the plasma membrane of CSB cells. The transport system (K(m) = 583 µM; V(max) = 177 × 10(-6) %ΔF min(-1) protoplast(-1)) was regulated by copper availability in the culture medium, stimulated by Ca(2+) and inhibited by Zn(2+). The pH-sensitive fluorescent probe ACMA (9-amino-6-chloro-2-methoxyacridine) was used to evaluate the involvement of proton-dependent copper transport across the tonoplast. Cu(2+) compartmentation in the vacuole was dependent on the transmembrane pH gradient generated by both V-H(+)-ATPase and V-H(+)-pyrophosphatase (PPase). High copper levels in the growth medium did not affect the activity of V-H(+)-PPase but decreased the magnitude of the H(+) gradient generated by V-H(+)-ATPase. Expression studies of VvCTr genes showed that VvCTr1 and VvCTr8 were distinctly affected by CuSO(4) availability in grape cell cultures and that both genes were highly expressed in the green stage of grape berries.

Diminished toxicity of C-1748, 4-methyl-9-hydroxyethylamino-1-nitroacridine, compared with its demethyl analog, C-857, corresponds to its resistance to metabolism in HepG2 cells

The narrow "therapeutic window" of anti-tumour therapy may be the result of drug metabolism leading to the activation or detoxification of antitumour agents. The aim of this work is to examine (i) whether the diminished toxicity of a potent antitumour drug, C-1748, 9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine, compared with its 4-demethyl analogue, C-857, results from the differences between the metabolic pathways for the two compounds and (ii) the impact of reducing and/or hypoxic conditions on studied metabolism. We investigated the metabolites of C-1748 and C-857 formed in rat and human liver microsomes, with human P450 reductase (POR) and in HepG2 cells under normoxia and hypoxia. The elimination rate of C-1748 from POR knockout mice (HRN) was also evaluated. Three products, 1-amino-9-hydroxyethylaminoacridine, 1-aminoacridinone and a compound with an additional 6-membered ring, were identified for C-1748 and C-857 in all studied metabolic systems. The new metabolite was found in HepG2 cells. We showed that metabolic rate and the reactivity of metabolites of C-1748 were considerably lower than those of C-857, in all investigated metabolic models. Compared with metabolism under normoxia, cellular metabolism under hypoxia led to higher levels of 1-aminoacridine and aza-acridine derivatives of both compounds and of the 6-membered ring metabolite of C-1748. In conclusion, the crucial role of hypoxic conditions and the direct involvement of POR in the metabolism of both compounds were demonstrated. Compared with C-857, the low reactivity of C-1748 and the stability of its metabolites are postulated to contribute significantly to the diminished toxicity of this compound observed in animals.

Overcoming multidrug resistance via photodestruction of ABCG2-rich extracellular vesicles sequestering photosensitive chemotherapeutics

Multidrug resistance (MDR) remains a dominant impediment to curative cancer chemotherapy. Efflux transporters of the ATP-binding cassette (ABC) superfamily including ABCG2, ABCB1 and ABCC1 mediate MDR to multiple structurally and functionally distinct antitumor agents. Recently we identified a novel mechanism of MDR in which ABCG2-rich extracellular vesicles (EVs) form in between attached neighbor breast cancer cells and highly concentrate various chemotherapeutics in an ABCG2-dependent manner, thereby sequestering them away from their intracellular targets. Hence, development of novel strategies to overcome MDR modalities is a major goal of cancer research. Towards this end, we here developed a novel approach to selectively target and kill MDR cancer cells. We show that illumination of EVs that accumulated photosensitive cytotoxic drugs including imidazoacridinones (IAs) and topotecan resulted in intravesicular formation of reactive oxygen species (ROS) and severe damage to the EVs membrane that is shared by EVs-forming cells, thereby leading to tumor cell lysis and the overcoming of MDR. Furthermore, consistent with the weak base nature of IAs, MDR cells that are devoid of EVs but contained an increased number of lysosomes, highly accumulated IAs in lysosomes and upon photosensitization were efficiently killed via ROS-dependent lysosomal rupture. Combining targeted lysis of IAs-loaded EVs and lysosomes elicited a synergistic cytotoxic effect resulting in MDR reversal. In contrast, topotecan, a bona fide transport substrate of ABCG2, accumulated exclusively in EVs of MDR cells but was neither detected in lysosomes of normal breast epithelial cells nor in non-MDR breast cancer cells. This exclusive accumulation in EVs enhanced the selectivity of the cytotoxic effect exerted by photodynamic therapy to MDR cells without harming normal cells. Moreover, lysosomal alkalinization with bafilomycin A1 abrogated lysosomal accumulation of IAs, consequently preventing lysosomal photodestruction of normal breast epithelial cells. Thus, MDR modalities including ABCG2-dependent drug sequestration within EVs can be rationally converted to a pharmacologically lethal Trojan horse to selectively eradicate MDR cancer cells.

Altered mitochondrial membrane potential, mass, and morphology in the mononuclear cells of humans with type 2 diabetes

Mitochondrial membrane hyperpolarization and morphologic changes are important in inflammatory cell activation. Despite the pathophysiologic relevance, no valid and reproducible method for measuring mitochondrial homeostasis in human inflammatory cells is available currently. The purpose of this study was to define and validate reproducible methods for measuring relevant mitochondrial perturbations and to determine whether these methods could discern mitochondrial perturbations in type 2 diabetes mellitus (T2DM), which is a condition associated with altered mitochondrial homeostasis. We employed 5,5',6,6'-tetrachloro-1,1'3,3'-tetraethylbenzamidazol-carboncyanine (JC-1) to estimate mitochondrial membrane potential (Psi(m)) and acridine orange 10-nonyl bromide (NAO) to assess mitochondrial mass in human mononuclear cells isolated from blood. Both assays were reproducible. We validated our findings by electron microscopy and pharmacologic manipulation of Psi(m). We measured JC-1 and NAO fluorescence in the mononuclear cells of 27 T2DM patients and 32 controls. Mitochondria were more polarized (P = 0.02) and mitochondrial mass was lower in T2DM (P = 0.008). Electron microscopy demonstrated diabetic mitochondria were smaller, were more spherical, and occupied less cellular area in T2DM. Mitochondrial superoxide production was higher in T2DM (P = 0.01). Valid and reproducible measurements of mitochondrial homeostasis can be made in human mononuclear cells using these fluorophores. Furthermore, potentially clinically relevant perturbations in mitochondrial homeostasis in T2DM human mononuclear cells can be detected.

New development of 'sono-functional' molecule: binding to DNA by sonication

'Sono-functional' molecule 1 was prepared and its binding properties to DNA under ultrasonic irradiation were studied by UV spectra. As a result, it was shown that the binding of 1 to DNA was enhanced by ultrasound. Being compared with its precursor 2, it is clear that terminal thiol groups of 1 play an important role in specific binding to DNA.

A comparison of three flow cytometry methods for evaluating mitochondrial damage during staurosporine-induced apoptosis in Jurkat cells

Measuring cytochrome c release during apoptosis provides valuable information about the nature and extent of apoptosis. Several years ago a flow cytometric method (based on selective permeabilization of the plasma membrane with digitonin) was developed that has advantages over other techniques. These experiments describe a comprehensive evaluation of that method. Apoptosis was triggered in Jurkat cells with staurosporine and then flow cytometry was used to measure three aspects of mitochondrial damage: (1) cytochrome c release (with the digitonin assay and a commercially available kit based on the same principle), using a DNA-binding dye to define cell cycle stage; (2) loss of mitochondrial cardiolipin, assessed by a decrease in 10 N-nonyl acridine orange (NAO) binding; and (3) loss of mitochondrial membrane potential, assessed by a decrease in tetramethylrhodamineethylester (TMRE) binding. The results from these three assays were compared with an antibody-based assay for cleaved caspase 3. The digitonin assay and the commercially available kit gave comparable results, showing that staurosporine caused cytochrome c release in all phases of the cell cycle and clearly defining those cells that had lost DNA due to internucleosomal DNA fragmentation. The pattern of fluorescence demonstrated that the mitochondrial apoptotic pathway was either the sole or the predominant pathway to be activated and that cytochrome c release in an individual cell was all-or-nothing. However, comparison with the other assays showed that the cytochrome c release assay underestimated the true extent of apoptosis. This was caused by the selective loss of some digitonin-treated apoptotic cells. The flow cytometry assay for cytochrome c release provides valuable information but it underestimates the percentage of apoptotic cells.

C421 allele-specific ABCG2 gene amplification confers resistance to the antitumor triazoloacridone C-1305 in human lung cancer cells

The A421 ABCG2 genotype is a frequent polymorphism encoding the K141 transporter, which is associated with a significant decrease in transporter expression and function when compared to the wild type (wt) C421 allele encoding the Q141 ABCG2. Here we show that during the acquisition of resistance to the novel triazoloacridone antitumor agent C-1305 in lung cancer cells harboring a heterozygous C421A genotype, a marked C421 allele-specific ABCG2 gene amplification occurred. This monoallelic C421 ABCG2 gene amplification brought about the overexpression of both C421 ABCG2 mRNA and the transporter at the plasma membrane. This resulted in the lack of cellular drug accumulation due to increased efflux of both C1305 and C-1311, a fluorescent imidazoacridone homologue of C-1305, as well as marked resistance to these antitumor agents and to established ABCG2 substrates including mitoxantrone and SN-38. Consistently, the accumulation and sensitivity to these drugs were restored upon incubation with the potent and specific ABCG2 transport inhibitors Ko143 and fumitremorgin C. Moreover, upon transfection into HEK293 cells, the wt Q141 ABCG2 allele displayed a significantly decreased accumulation of C-1311 and increased resistance to C-1305, C-1311 and mitoxantrone, when compared to the K141 ABCG2 transfectant. Hence, the current study provides the first evidence that during the exposure to anticancer drugs, an allele-specific Q141 ABCG2 gene amplification occurs that confers a drug resistance advantage when compared to the K141 ABCG2. These findings have important implications for the selection and expansion of malignant anticancer drug resistant clones during chemotherapy with ABCG2 drugs.

A Real-Time Fluorescence Assay for Measuring N-Dealkylation

A real-time fluorescence assay system using a series of 9-N-(alkylamino)acridine derivatives (methyl, ethyl, n-propyl, n-butyl, n-pentyl, and benzyl) that are N-dealkylated to 9-aminoacridine (9AA) is described. The product, 9AA, is approximately 27-fold more fluorescent than the substrates using excitation and emission wavelengths of 405 and 455 nm, respectively. Tests using expressed CYP1A1, 1A2, 3A4, 3A5, 1B1, 2C9, 2C19, and 2D6 indicated that N-dealkylase activity is specific for CYP1A1 and CYP2D6. CYP2D6 N-dealkylated methyl, ethyl, n-propyl, and n-butyl substrates, whereas CYP1A1 N-dealkylated these plus the n-pentyl derivative. Activities using 5 microM 9-N-(alkylamino)acridine substrates ranged from 0.1 to 0.9 pmol 9AA/min/pmol P450. Kinetic constants for CYP1A1 N-dealkylation of the 9-N-(methylamino)acridine (MAA) and 9-N-(ethylamino)acridine (EAA) were K(m) 1.09 +/- 0.68 and 0.35 +/- 0.21 microM and the V(max) 61.9 +/- 48.5 and 113.8 +/- 8.4 pmol 9AA/min/pmol CYP1A1, respectively. Kinetic constants for CYP2D6 N-dealkylation of MAA and EAA were K(m) 7.9 +/- 5.4 and 3.2 +/- 1.6 microM, and V(max) 501 +/- 35.4 and 702.7 +/- 257 pmol 9AA/min/pmol CYP2D6, respectively. The experimental binding energies (DeltaG(bind)) were calculated for MAA with CYP1A1 and CYP2D6 to be -8.266 and -7.074 kcal/mol, respectively. The DeltaG(bind) values for EAA with CYP1A1 and CYP2D6 were -8.950 and -7.618 kcal/mol, respectively. The substrates were suitable for monitoring N-dealkylase activity in microsomal preparations (human, rat, and monkey hepatic preparations) and human hepatocellular carcinoma cell suspensions. Assays were conducted by monitoring reactions either in 96-well microtiter plates using a fluorescence plate reader or in cuvettes using a spectrofluorimeter.

Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.

Characterization of the ion transport activity of the budding yeast Na+/H+ antiporter, Nha1p, using isolated secretory vesicles

The Saccharomyces cerevisiae Nha1p, a plasma membrane protein belonging to the monovalent cation/proton antiporter family, plays a key role in the salt tolerance and pH regulation of cells. We examined the molecular function of Nha1p by using secretory vesicles isolated from a temperature sensitive secretory mutant, sec4-2, in vitro. The isolated secretory vesicles contained newly synthesized Nha1p en route to the plasma membrane and showed antiporter activity exchanging H+ for monovalent alkali metal cations. An amino acid substitution in Nha1p (D266N, Asp-266 to Asn) almost completely abolished the Na+/H+ but not K+/H+ antiport activity, confirming the validity of this assay system as well as the functional importance of Asp-266, especially for selectivity of substrate cations. Nha1p catalyzes transport of Na+ and K+ with similar affinity (12.7 mM and 12.4 mM), and with lower affinity for Rb+ and Li+. Nha1p activity is associated with a net charge movement across the membrane, transporting more protons per single sodium ion (i.e., electrogenic). This feature is similar to the bacterial Na+/H+ antiporters, whereas other known eukaryotic Na+/H+ antiporters are electroneutral. The ion selectivity and the stoichiometry suggest a unique physiological role of Nha1p which is distinct from that of other known Na+/H+ antiporters.

Ultrafast purification and reconstitution of His-tagged cysteine-less Escherichia coli F1Fo ATP synthase

His-tagged cysteine-less F1Fo ATP synthase from Escherichia coli was purified using Ni-NTA affinity chromatography. During the purification procedure the loss of total ATPase activity did not exceed 50%, and the extent of purification was about 80-fold. The purified enzyme was essentially free of other proteins, was highly active in ATP hydrolysis (75 units/mg at pH 8 and 37 degrees C), and was sensitive to N,N'-dicyclohexylcarbodiimide (70%). Incorporation of F1Fo into soybean liposomes yielded well-coupled and highly active proteoliposomes. The entire procedure, from the disruption of cells by French press to the preparation of proteoliposomes, took only about 8 h. Some improvements in procedures for the estimation of rates of both ATP hydrolysis and ATP-dependent 9-amino-6-chloro-2-methoxyacridine (ACMA) fluorescence quenching are described.

Binding of an aminoacridine derivative to a GAAA RNA tetraloop

RNA tetraloops are common secondary structural motifs in many RNAs, especially ribosomal RNAs. There are few studies of small molecule recognition of RNA tetraloops although tetraloops are known to interact with RNA receptors and proteins, and to form nucleation sites for RNA folding. In this paper, we investigate the binding of neomycin, kanamycin, 2,4-diaminoquinazoline, quinacrine, and an aminoacridine derivative (AD1) to a GAAA tetraloop using fluorescence spectroscopy. We have found that AD1 and quinacrine bind to the GAAA tetraloop with the highest affinity of the molecules examined. The equilibrium dissociation constant of the AD1-GAAA tetraloop complex was determined to be 1.6 microM. RNase I and lead acetate footprinting experiments suggested that AD1 binds to the junction between the loop and stem of the GAAA tetraloop.

Physiological ligands ADP and Pi modulate the degree of intrinsic coupling in the ATP synthase of the photosynthetic bacterium Rhodobacter capsulatus

The proton-pumping and the ATP hydrolysis activities of the ATP synthase of Rhodobacter capsulatus have been compared as a function of the ADP and P(i) concentrations. The proton pumping was measured either with the transmembrane pH difference probe, 9-amino-6-chloro-2-methoxyacridine, or with the transmembrane electric potential difference probe, bis(3-propyl-5-oxoisoxazol-4-yl)pentamethine oxonol, obtaining consistent results. The comparison indicates that an intrinsic uncoupling of ATP synthase is induced when the concentration of either ligand is decreased. The half-maximal effect was found in the submicromolar range for ADP and at about 70 microM for P(i). It is proposed that a switch from a partially uncoupled state of ATP synthase to the coupled state is induced by the simultaneous binding of ADP and P(i).

[Study of the cholinesterase active site using a fluorescent probe]

We studied fluorescence of 9-amino-1,2,3,4-tetrahydroacridine hydrochloride (tacrine) in the presence of serum cholinesterase. Quenching of tacrine fluorescence dependent on cholinesterase activity has been revealed. A quenching mechanism is proposed; it includes formation of a complex and charge transfer mediated by excited tacrine molecule as well as indole of tryptophan residue from the periphery of cholinesterase active site.

Molecular mechanism of the enzymatic oxidation investigated for imidazoacridinone antitumor drug, C-1311

The imidazoacridinone derivative, C-1311, is an antitumor agent that has been under phase I of clinical trial. The work presented here aims to elucidate the molecular mechanism of the enzymatic oxidative activation of this drug in such a model metabolic system, where the covalent binding to DNA was previously demonstrated. The oxidative activation of C-1311 was performed with HRP/H(2)O(2) and MPO/H(2)O(2) systems. The obtained final products of such transformations were separated and analysed by HPLC. The structures of the products were identified by means of ESI-MS and NMR. It was demonstrated that C-1311 was oxidised with HRP and MPO in the manner dependent on the drug:H(2)O(2) ratio and the drug was more susceptible to HRP oxidation than to MPO. Structural studies showed compounds C0 and C1 to be the result of dealkylation, which occurred in the amino groups of the side chain. The structures of C3 and C4 products were identified as dimers, whose monomers held the imidazoacridinone core. The activation of the imidazoacridinone ring system in position ortho to 8-hydroxyl group was necessary to form such dimers. We suggest that similar mechanism of C-1311 activation should occur in the presence of DNA when, instead of the dimer formation, the covalent binding to DNA, showed earlier for this drug, was formed. Since peroxidase-type enzymes are present in the cell nucleus of tumour cells the activation mechanisms of the C-1311 proposed here may be expected to take place in the cellular environment in vivo.

Reactive oxygen species affect mitochondrial electron transport complex I activity through oxidative cardiolipin damage

The aim of this study was to investigate the influence of reactive oxygen species (ROS) on the activity of complex I and on the cardiolipin content in bovine heart submitochondrial particles (SMP). ROS were generated through the use of xanthine/xanthine oxidase (X/XO) system. Treatment of SMP with X/XO resulted in a large production of superoxide anion, detected by acetylated cytochrome c method, which was blocked by superoxide dismutase (SOD). Exposure of SMP to ROS generation resulted in a marked loss of complex I activity and to parallel loss of mitochondrial cardiolipin content. Both these effects were completely abolished by SOD+catalase. Exogenous added cardiolipin was able to almost completely restore the ROS-induced loss of complex I activity. No restoration was obtained with other major phospholipid components of the mitochondrial membrane such as phosphatidylcholine and phosphatidylethanolamine, nor with peroxidized cardiolipin. These results demonstrate that ROS affect the mitochondrial complex I activity via oxidative damage of cardiolipin which is required for the functioning of this multisubunit enzyme complex. These results may prove useful in probing molecular mechanisms of ROS-induced peroxidative damage to mitochondria, which have been proposed to contribute to those pathophysiological conditions characterized by an increase in the basal production of reactive oxygen species such as aging, ischemia/reperfusion and chronic degenerative diseases.

Crystal structure of 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide bound to d(CGTACG)2: implications for structure-activity relationships of acridinecarboxamide topoisomerase poisons

The structure of the complex formed between d(CGTACG)2 and 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide, an inactive derivative of the antitumour agents N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 9-amino-DACA, has been solved to a resolution of 1.8 A using X-ray crystallography. The complex crystallises in the space group P6(4 )and the final structure has an overall R factor of 21.9%. A drug molecule intercalates between each of the CpG dinucleotide steps with its side chain lying in the major groove, and its protonated morpholino nitrogen partially occupying positions close to the N7 and O6 atoms of guanine G2. The morpholino group is disordered, the major conformer adopting a twisted boat conformation that makes van der Waals contact with the O4 oxygen of thymine T3. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of guanine G2. Sugar rings are found in alternating C3'-exo/C2'-endo conformations except for cytosine C1 which is C3'-endo. Intercalation perturbs helix winding throughout the hexanucleotide compared with B-DNA, steps 1 and 2 being unwound by 10 and 8 degrees, respectively, while the central TpA step is overwound by 11 degrees. An additional drug molecule lies at the end of each DNA helix linking it to the next duplex to form a continuously stacked structure. The protonated morpholino nitrogen of this 'end-stacked' drug hydrogen bonds to the N7 atom of guanine G6, and its conformationally disordered morpholino ring forms a C-H...O hydrogen bond with the guanine O6 oxygen. In both drug molecules the 4-carboxamide group is internally hydrogen bonded to the protonated N10 atom of the acridine ring. We discuss our findings with respect to the potential role played by the interaction of the drug side chain and the topoisomerase II protein in the poisoning of topoisomerase activity by the acridinecarboxamides.

Direct photocleavage of HIV-DNA by quinacridine derivatives triggered by triplex formation

Amino-p-quinacridine compounds (PQs) have been shown to stabilize strongly and specifically triple-helical DNA. Moreover, these derivatives display photoactive properties that make them efficient DNA cleavage agents. We exploited these two properties (triplex-specific binding and photoactivity) to selectively cleave a double-stranded (ds)DNA sequence present in the HIV-1 genome. Cleavage was first carried out on a linearized plasmid (3300 bp) containing the HIV polypurine tract (PPT) that allowed targeting by a triplex-forming oligonucleotide (TFO). PQ(3)(), the most active compound of the series, efficiently cleaved double-stranded DNA in the vicinity of the PPT when this sequence had formed a triplex with a 16-mer TFO. Investigation of the cleavage at the molecular level was addressed on a short DNA fragment (56 bp); the photoinduced cleavage by PQ(3)() occurred only in the presence of the triple helix. Nevertheless, unusual cleavage patterns were observed: damage was observed at guanines located 6-9 bp away from the end of the triple helical site. This cleavage is very efficient (up to 60%), does not require alkaline treatment, and is observed on both strands. A quinacridine-TFO conjugate produced the same cleavage pattern. This observation, along with others, excludes the hypothesis of a triplex-induced allosteric binding site of PQ(3 )()adjacent to the damaged sequence and indicates that PQ(3 )()preferentially binds in the vicinity of the 5'-triplex junction. Irradiation in the presence of TFO-conjugates with acridine (an intercalative agent) and with the tripeptide lys-tryp-lys led to a complete inhibition of the photocleavage reaction. These results are interpreted in terms of competitive binding and of electron-transfer quenching. Together with the findings of simple mechanistic investigations, they led to the conclusion that the photoinduced damage proceeds through a direct electron transfer between the quinacridine and the guanines. This study addresses the chemical mechanism leading to strand breakage and characterizes the particular photosensitivity of the HIV-DNA target sequence which could be an oxidative hot spot for addressed photoinduced strand scission by photosensitizers.

Enzymatic activation of a new antitumour drug, 5-diethylaminoethylamino-8-hydroxyimidazoacridinone, C-1311, observed after its intercalation into DNA

The imidazoacridinone derivative, C-1311, is a new antitumour agent that exhibits strong antitumour activity against experimental colorectal cancer and has been selected for entry into clinical trial. The compound has previously been shown to have DNA non-covalent binding properties in vitro and to bind irreversibly to DNA of tumour cells. The latter effect has also been observed in a cell-free system, but only in the presence of activated enzymes. The present studies were aimed at finding out whether and in what way the enzymatic activation of C-1311 and its non-covalent binding to DNA influence or depend on each other. Enzymatic activation was performed with a model system containing horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) and was followed by UV-VIS spectroscopy and by HPLC with UV-VIS and electrospray ionisation mass spectrometry detection. DNA non-covalent binding was studied in the cell-free system by means of an unwinding assay and UV-VIS spectroscopy. It was shown that C-1311 was oxidised by the HRP/H2O2 system in a manner dependent on the drug:H2O2 ratio. In the case of ratios of 1:3 and 1:5, the reaction gave highly reactive species that were quickly transformed into the further products p2 and p3 that were unable to intercalate into DNA. In the presence of DNA, C-1311 first intercalated into DNA and the intercalated compound was then oxidised. This oxidation was directed to only one product. Therefore, DNA seems to play the role of a "scavenger" of the reactive oxidation product(s) yielded from the intercalated drug and prevents its further deactivation. We conclude that, under the conditions studied, intercalation of C-1311 into DNA is followed by its HRP-mediated activation, giving rise to the intercalated species that might irreversibly bind to DNA. Since peroxidase-type enzymes are present in the cell nucleus, the proposed sequence of events may also be expected to take place in the cellular environment in vivo.

Protein-free parallel triple-stranded DNA complex formation

A 14 nt DNA sequence 5'-AGAATGTGGCAAAG-3' from the zinc finger repeat of the human KRAB zinc finger protein gene ZNF91 bearing the intercalator 2-methoxy,6-chloro,9-amino acridine (Acr) attached to the sugar-phosphate backbone in various positions has been shown to form a specific triple helix (triplex) with a 16 bp hairpin (intramolecular) or a two-stranded (intermolecular) duplex having the identical sequence in the same (parallel) orientation. Intramolecular targets with the identical sequence in the antiparallel orientation and a non-specific target sequence were tested as controls. Apparent binding constants for formation of the triplex were determined by quantitating electrophoretic band shifts. Binding of the single-stranded oligonucleotide probe sequence to the target led to an increase in the fluorescence anisotropy of acridine. The parallel orientation of the two identical sequence segments was confirmed by measurement of fluorescence resonance energy transfer between the acridine on the 5'-end of the probe strand as donor and BODIPY-Texas Red on the 3'-amino group of either strand of the target duplex as acceptor. There was full protection from OsO(4)-bipyridine modification of thymines in the probe strand of the triplex, in accordance with the presumed triplex formation, which excluded displacement of the homologous duplex strand by the probe-intercalator conjugate. The implications of these results for the existence of protein-independent parallel triplexes are discussed.

A novel form of intercalation involving four DNA duplexes in an acridine-4-carboxamide complex of d(CGTACG)(2)

The structures of the complexes formed between 9-amino-[N:-(2-dimethyl-amino)butyl]acridine-4-carboxamide and d(CG(5Br)UACG)(2) and d(CGTACG)(2) have been solved by X-ray crystallography using MAD phasing methodology and refined to a resolution of 1.6 A. The complexes crystallised in space group C222. An asymmetric unit in the brominated complex comprises two strands of DNA, one disordered drug molecule, two cobalt (II) ions and 19 water molecules (31 in the native complex). Asymmetric units in the native complex also contain a sodium ion. The structures exhibit novel features not previously observed in crystals of DNA/drug complexes. The DNA helices stack in continuous columns with their central 4 bp adopting a B-like motif. However, despite being a palindromic sequence, the terminal GC base pairs engage in quite different interactions. At one end of the duplex there is a CpG dinucleotide overlap modified by ligand intercalation and terminal cytosine exchange between symmetry-related duplexes. A novel intercalation complex is formed involving four DNA duplexes, four ligand molecules and two pairs of base tetrads. The other end of the DNA is frayed with the terminal guanine lying in the minor groove of the next duplex in the column. The structure is stabilised by guanine N7/cobalt (II) coordination. We discuss our findings with respect to the effects of packing forces on DNA crystal structure, and the potential effects of intercalating agents on biochemical processes involving DNA quadruplexes and strand exchanges. NDB accession numbers: DD0032 (brominated) and DD0033 (native).

Three-dimensional structures of Drosophila melanogaster acetylcholinesterase and of its complexes with two potent inhibitors

We have crystallized Drosophila melanogaster acetylcholinesterase and solved the structure of the native enzyme and of its complexes with two potent reversible inhibitors, 1,2,3,4-tetrahydro-N-(phenylmethyl)-9-acridinamine and 1,2,3,4-tetrahydro-N-(3-iodophenyl-methyl)-9-acridinamine--all three at 2.7 A resolution. The refined structure of D. melanogaster acetylcholinesterase is similar to that of vertebrate acetylcholinesterases, for example, human, mouse, and fish, in its overall fold, charge distribution, and deep active-site gorge, but some of the surface loops deviate by up to 8 A from their position in the vertebrate structures, and the C-terminal helix is shifted substantially. The active-site gorge of the insect enzyme is significantly narrower than that of Torpedo californica AChE, and its trajectory is shifted several angstroms. The volume of the lower part of the gorge of the insect enzyme is approximately 50% of that of the vertebrate enzyme. Upon binding of either of the two inhibitors, nine aromatic side chains within the active-site gorge change their conformation so as to interact with the inhibitors. Some differences in activity and specificity between the insect and vertebrate enzymes can be explained by comparison of their three-dimensional structures.

Uptake of acridinecarboxamide derivatives by L1210 cells

The uptake of six 9-aminoacridinecarboxamide derivatives by L1210 cells in relation to their lipophilicity and cytotoxic activity was studied. The amount of acridines taken up by cells was estimated by fluorimetric measurements. It was found that the uptake efficiency of this class of compounds by cells depends on the size of carboxamide residue as well as on position of the substituent. The increase of size of carboxamide chain resulted in the loss of capability of acridines to penetrate cell membrane. Cytotoxic effects of acridines were well correlated with the level of drugs accumulated by cells, whereas no clear correlation between uptake and lipophilicity was observed. It is concluded that uptake of 9-aminoacridinecarboxamides is the most important factor determining their antiproliferative activity.

Endotoxin pretreatment in vivo increases the mitochondrial respiratory capacity in rat hepatocytes

Administration of sublethal doses of endotoxin produces tolerance to subsequent oxidative stress in diverse animal models. Although endotoxin induces antioxidant enzymes, particularly manganous superoxide dismutase (Mn-SOD), the phenomenon of tolerance remains incompletely understood. Previously I determined that endotoxin treatment in rats increased lung mitochondrial respiration-dependent (i.e., independent of Mn-SOD) scavenging of superoxide anion. Because nonenzymatic scavenging of superoxide anion correlates with the mitochondrial membrane energy gradient, I hypothesized that endotoxin increases the mitochondrial transmembrane potential. Endotoxin treatment (500 micrograms/kg intraperitoneally 48 h earlier) increased the hepatocyte mitochondrial transmembrane potential as determined by two separate methods: the intramitochondrial sequestration of triphenylmethylphosphonium (electrical potential or delta psi) and the fluorescence intensity of the hepatocyte mitochondria when stained with rhodamine-123 and examined by confocal microscopy. These findings suggest that endotoxin treatment increased the total mitochondrial membrane potential per hepatocyte. In parallel, endotoxin treatment increased the fluorescence intensity of hepatocyte mitochondria after staining with 10-N-nonyl-acridine orange, a dye that binds to the mitochondrial inner membrane independently of the transmembrane potential. This suggests that an increase in mitochondrial inner membrane mass is responsible for the net increase in inner membrane potential per cell following endotoxin pretreatment. These findings complement previous studies in which endotoxin treatment increased the mitochondrial-specific antioxidant Mn-SOD and support the more recent finding that endotoxin treatment also increased nonenzymatic scavenging of superoxide by lung mitochondria. Taken, together, these observations suggest that mitochondrial biogenesis, and the subsequent increase in both enzymatic and nonenzymatic scavenging of superoxide anion, is a central feature of endotoxin-mediated tolerance to oxidative stress.

Flow cytometric analysis of reticulated platelets: evidence for a large proportion of non-specific labelling of dense granules by fluorescent dyes

The labelling of platelets with thiazole orange (TO) has been utilized by various laboratories to determine the percentage of reticulated platelets within whole blood or platelet-rich plasma (PRP). A proportion of TO labelling, however, is not entirely mRNA specific and remains to be fully defined. Almost half of the total TO-positive signal within normal platelets (n = 5) was shown to be abrogated upon degranulation with 80 microM thrombin receptor activating peptide (TRAP) (P = 0.006), strongly suggesting that platelet granules are non-specifically labelling with dye. We have confirmed this hypothesis by studying TO labelling of platelets within whole blood from dense granule deficient patients, e.g. Hermansky-Pudlak syndrome (HPS) (n = 5) and storage pool disease (SPD) (n = 4). The levels of TO-positive platelets were found to be significantly lower than normal (P = 0.0003 and P = 0.0002 respectively), but not significantly different from TRAP degranulated platelets. Upon degranulation of HPS and SPD platelets there was very little further reduction in the TO signal. Incubation of normals and SPD whole blood with different concentrations of either TO or coriphosphine-O confirmed that dense granules were non-specifically labelling even at high concentrations of both dyes. These findings suggest that although TO labelling is in part RNA specific, the dense granular pool of nucleotides appears to cause a substantial amount (approximately 50%) of non-specific labelling observed under these conditions of assay. This can easily be controlled for by a degranulation step with a non-enzymatic platelet agonist such as TRAP, and may have important consequences for the eventual standardization. clinical utilization and automation of reticulated platelet assays.

Analysis of the imidazoacridinone C1311 by high-performance liquid chromatography

The imidazoacridinone C1311 has shown anti-tumour activity both in vitro and in vivo, prompting its acceptance for Phase I clinical trials. A high-performance liquid chromatography method using fluorescence detection has been developed for the analysis of C1311 in mouse and human plasma and mouse tissue samples. This method is selective, sensitive (limit of detection of 1 ng ml-1) and reproducible, with recoveries of > 90%, C1311 was stable over 8 h, at 25 degrees C, in plasma, tumour homogenate, saline and a range of buffers (pH 3.0-8.0). The compound was highly protein bound (> 90%) in plasma which may have important consequences in the pharmacokinetics of the drug.

32P-post-labelling analysis of nucleobases involved in the formation of DNA adducts by antitumor 1-nitroacridines

Adducts generated in vitro by the reaction of 1-nitroacridines with poly(dN)s in the presence of dithiothreitol were used to identify a kind of nucleic base involved in the formation of individual adducts. The patterns of chromatographic spots corresponding to modified nucleotides obtained by 32P-post-labelling assay for synthetic homopolymers of four deoxyribonucleotides were compared with the fingerprints detected in the case of calf thymus DNA reacted with 1-nitroacridines under conditions in which the formation of identical DNA adducts as in cellular models was demonstrated in earlier investigations. Both compounds studied (Ledakrin and C-857) turned out to bind covalently only with purine nucleotides. Ledakrin formed with dG four and C-857 five different adducts. All of them were also detected in ctDNA. The incubation with poly(dA) resulted in four Ledakrin-dA species, two of which were found in ctDNA, and in two C-857-dA adducts that were not, however, observed in DNA containing samples. Modification of purines accounted for all adducts observed in ctDNA. For both compounds studied, the level of total binding to poly(dA) was about one order of magnitude lower than to poly(dG) for which it was comparable with the extent of ctDNA modification. This indicates that dG represents a preferential site of covalent binding of 1-nitroacridines to DNA.

Nucleic acid specificity of an acridine derivative permits its use for flow cytometric analysis of the cell cycle

3-amino-6-methoxy-9-(2-hydroxyethylamine) acridine (AMHA) is an acridine derivative, which is easily excited in near ultraviolet and which emits a bright green fluorescence. The dye was preferentially incorporated into nucleic structures as attested by microscopic and cytometric analyses after RNase and DNase treatments. The affinity for RNA seemed low and similar to that observed for propidium iodide. AMHA was quickly accumulated in fixed cells, and in appropriate concentrations (10-50 microM) was a DNA- and RNA-specific dye. AMHA probably exhibits an adenine-thymine specificity, as suggested by its quenching after bromodeoxyuridine uptake: the fluorescence quenching was similar to that obtained for Hoechst 33258. After cell treatment by RNase and in the presence of MgCl2, AMHA staining allowed flow cytometric analysis of the cell-cycle distribution. The resulting histograms were similar to those obtained with propidium iodide (CV near 3.5%, and similar cell cycle distribution). Thus, AMHA is a suitable fluorescent dye for efficient analysis of the cell cycle by flow cytometry.

The acridine ring selectively intercalated into a DNA helix at various types of abasic sites: double strand formation and photophysical properties

The interactions between the intercalating agent and the three types of abasic sites: abasic frameshift, apurinic and apyrimidinic, were investigated. 9-amino-6-chloro-2-methoxyacridine (ACMA), whose spectroscopic properties are strongly perturbed by the environment, was selected as the intercalating agent. The optically pure threoninol derived from the reduction of L-threonine was used as an artificial abasic site mimicking the ring-opened natural ribose. In order to secure the selective intercalation to the adjacent abasic site, ACMA and the abasic site were connected through a tri- pentamethylene linker. These modified oligonucleotides covalently linked to an ACMA molecule at the internucleotide site having the same base-sequence were synthesized using the acridine-phosphoramidites. Although all the modified oligonucleotides lack a nucleobase at the intervening position, these double strands showed high thermal stability. The pentamethylene linker and the apyrimidinic systems were especially stabilized. At the same time, sharpness of the absorption spectra and a new fluorescent band of the acridine, due to the fixation of the environment around ACMA, were observed. Therefore, it is concluded that the acridine binds preferentially to the apyrimidinic site rather than the frameshift abasic site and that the surroundings of the acridine are strictly fixed at the microenvironmental level.

Photochemical and photophysical studies of 3-amino-6-iodoacridine and the inactivation of lambda phage

The photochemistry and photophysics of 3-amino-6-iodoacridine (Acr-I) was studied. Photolysis (350 nm) of Acr-I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr-I hydrochloride is shown to bind to calf thymus DNA and to the self-complementary dinucleotide cytidylyl-(3'-5')-guanosine (CpG) miniduplex in a manner similar to that of proflavine (Acr-NH2), a known DNA intercalator. The Acr-I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr-NH2. The efficiency of Acr-I-sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr-I/(CpG)2 complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen- or peroxyl radical-mediated process. Photolysis of Acr-I in the presence of a mononucleotide (GMP) or a non-self-complementary dinucleotide (uridylyl-[3'-5']-cytidine-UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr-NH2/(CpG)2 complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of lambda phage sensitized by Acr-I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr-I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C-I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.

ATP synthase from bovine heart mitochondria: reconstitution into unilamellar phospholipid vesicles of the pure enzyme in a functional state

A highly purified and monodisperse preparation of proton-translocating F1F0-ATPase from bovine heart mitochondria is an assembly of 16 unlike polypeptides. This preparation has been reconstituted in the presence of various detergents into unilamellar phospholipid vesicles. Incorporation of the enzyme into vesicles increases the ATP hydrolase activity of the enzyme by 10-20-fold, depending on the detergent, and the highest activities of ATP hydrolysis, 70 units/mg, were obtained by reconstitution from dodecylmaltoside or CHAPS. This activity is mostly sensitive to inhibitors that act on the F0 membrane sector of the complex. From the quenching of the pH-sensitive probe, 9-amino-6-chloro-2-methoxyacridine, it was shown that the reconstituted enzyme was able to form a transmembrane proton gradient in an ATP-dependent manner. By co-reconstitution of the enzyme with bacteriorhodopsin, it was demonstrated that in the presence of a light-induced proton gradient the enzyme can synthesize ATP from ADP and phosphate. Therefore, the characteristic biological functions of the F1F0-ATPase in mitochondria have been demonstrated with the purified enzyme. Thus, in terms of both its physical and biochemical properties, the purified enzyme fulfils important pre-requisites for formation of two- and three-dimensional crystals.

Conformers of acetylcholinesterase: a mechanism of allosteric control

Rate control in acetylcholinesterase (AChE) involves a single anionic site whose anionic center controls rate-related biochemical and conformational changes in the E (free enzyme) and EA (acylated enzyme) conformers. Change in conformer structure and biochemistry affect binding, acylation, and hydrolysis. It is significant that the anionic-esteratic intersite distance is not altered during conformer change as E is converted to EA. In this enzyme system, cationic acetylcholine and anionic AChE are true structural, functional, and biochemical counterparts. The anionic center in the E conformer lies at the bottom of a sterically restricted, hydrophobic cleft < 8 A wide at the top and > 3 A wide at the bottom, while the anionic center in the EA conformer is relatively open. It is characterized by a decrease in the relative binding of hydrophobic cations and by an ability to bind large organic cations. Binding of acetylcholine, H+, or organic cations at the anionic site controls k2(acylation) in the E conformer and k3(hydrolysis) in the EA conformer. Acetylcholine binding forms the ES complex in which the cation maximizes k2. In the EAS complex, the cation reduces k3 and provides allosteric control. Anionic site structure and biochemistry and the effect of pH on k2 and k3 differentiates AChE from butyrylcholinesterase. This comprehensive study of kinetic and thermodynamic processes in AChE was made possible by the synthesis and/or use of families of over 30 cationic and acylation probes of known stereochemistry. They act as rulers of the E and EA conformers of AChE and provide comparative data on kinetic-based and thermodynamic-based constants. Cationic inhibitors affect decarbamylation rates in AChE and provide an additional set of comparative data related to the mechanism of substrate hydrolysis by AChE. Acridine araphanes are unique neural receptor and cholinergic enzyme probes. Their parallel plane and coplanar conformations are related to bridge length. Two parallel plane acridine araphanes are pure uncompetitive inhibitors of AChE. Scatchard plots of the binding of methylacridinium and 9-aminoacridine with the E conformer and 9-aminoacridine with the EA conformer indicate binding at a single anionic site. No ternary complex (EII or EAII) from two-site binding was detected. In AChE, nonspecific, low-level binding at surface ionic and hydrophobic areas is ubiquitous. Binding affinity differences greater than two orders of magnitude distinguish binding at the anionic site from low level binding at surface moieties. Surface binding provides environmental and stability changes in the enzyme but does not modify the fundamental biochemistry of the E and EA conformers.

Inhibition by SKF-525A of the aldehyde oxidase-mediated metabolism of the experimental antitumour agent acridine carboxamide

Oxidation of the experimental anti-tumour agent N-[(2'-dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601316; acridine carboxamide) to the 9(10H)acridone, followed by ring hydroxylation and glucuronidation, appears to be the main pathway of detoxication of AC in the rat and mouse. The acridone formation has been further characterized in vitro using an enzyme-enriched fraction where activity per milligram protein is increased approximately 10-fold compared with the cytosolic fraction. Inhibition by amsacrine [4'-(9-acridinylamino)methanesulphon-m-anisidide; NSC 249992] and menadione (50% inhibition at 6.4 and 1.8 microM, respectively) but not allopurinol (to 30 microM) indicates that the activity is due to aldehyde oxidase, without the involvement of xanthine oxidase. Interestingly, acridone formation in both the cytosolic and enzyme-enriched fractions is highly sensitive to the classical cytochrome P450 inhibitor SKF-525A [proadifen hydrochloride; 2'-(diethylamino)ethyl 2,2-diphenylpentenoate] (50% inhibition at 9.2 and 1.9 microM, respectively). Further analysis indicates mixed non-competitive type inhibition by SKF-525A (K(is), 0.3 microM; K(ii), 4.9 microM). Little or no inhibition was seen with cimetidine, metyrapone or methimazole. No NADPH-dependent acridone formation was observed with the microsomal fraction. These data indicate that acridone formation previously observed in isolated rat hepatocytes and in vivo is most likely due to aldehyde oxidase rather than cytochrome P450.

Metabolism of the experimental antitumor agent acridine carboxamide in the mouse

The metabolism of the experimental antitumor agent acridine carboxamide (AC) has been examined in the male BDF1 mouse. [3H]AC was administered at the optimal single intraperitoneal dose for antitumor activity (410 mumol/kg body weight) and the metabolites in urine, bile, and feces characterized using reversed-phase HPLC. In urine (0-24 hr) the main product appears to be a glucuronide, also present in bile, with lesser amounts of AC, AC-N-oxide, and at least 10 minor products. Biliary excretion of AC metabolites (examined after removal of the gallbladder at the appropriate times) is greatest at 1-2 hr after treatment when at least 14 products are detected, including AC, AC-N-oxide, and other products with UV/visible spectra characteristic of ring hydroxylated and/or acridone derivatives. In feces (0-24 hr) no AC-N-oxide is detected, the major metabolites being two polar species and AC. These polar species are both present in urine and bile where they are increased on incubation with crude beta-glucuronidase. These aglycones have been identified as the 7-hydroxy-9(10H)acridone derivatives of AC and N-monomethyl-AC by [1H]NMR and mass spectrometry. Thus the main pathways of elimination of AC appear to be 1) N-oxidation and 2) 9(10H)acridone formation plus 7-hydroxylation of both AC and its N-demethylated product followed by glucuronidation. Reduction of AC-N-oxide in the gut may allow reabsorption of AC. Both the back-reduction and reabsorption of AC, and enterohepatic circulation of the 7-hydroxyacridone derivatives may contribute to the slow elimination of AC metabolites.

Rat hepatocyte-mediated metabolism of the experimental anti-tumour agent N-[2'-(dimethylamino)ethyl]acridine-4-carboxamide

1. Metabolism of the experimental antitumour agent N-[2'-(dimethylamino)-ethyl]acridine-4-carboxamide (AC) has been studied in isolated rat hepatocytes using 3H-AC. 2. The major primary metabolites of AC (150 microM) are the 9(10H)acridone, N-oxide and N-monomethyl derivatives. The equivalent 9(10H)acridone derivatives are also formed from AC-N-oxide and N-monomethyl-AC followed by formation of the 7-hydroxy-9(10H)acridone derivatives of AC and N-monomethyl-AC. A similar pattern of metabolism was observed on incubation of AC-N-oxide. 3. Inhibition studies with SKF 525A (250 microM) and methimazole (250 microM) indicate that N-demethylation is mainly catalysed by cytochrome P450 whereas N-oxidation is mediated mainly by flavin-containing monooxygenases. Both primary and secondary acridone formation were also inhibited by SKF 525A as was the back-reduction of AC-N-oxide to AC. 4. These results show that the rat hepatocyte system is a suitable model for further characterization of the metabolism of AC.

NLA-1: a 2-nitroimidazole radiosensitizer targeted to DNA by intercalation

Targeting of electron affinic radiosensitizers to DNA via reversible non-covalent intercalative binding has potential for increasing sensitizer concentrations locally at the DNA target while decreasing accessibility to reductases responsible for bioactivation and cytotoxicity. We have prepared an DNA-targeted acridine-linked 2-nitroimidazole (NLA-1) as an example of such a compound. NLA-1 binds reversibly to DNA with an affinity similar to 9-aminoacridine, and is approximately 1000 times more potent than MISO as a cytotoxin, despite a similar reduction potential. It shows less enhancement of cytotoxicity under hypoxia (5- to 6-fold) than does MISO (approximately 11-fold), but is a potent hypoxia-selective radiosensitizer in AA8 cells with a concentration for an enhancement ratio of 1.6 (C1.6) of 9 microM. The mean intracellular concentration at the C1.6 is 400 microM, on which basis its potency is about twice that of MISO. The in vitro therapeutic index (aerobic cytotoxic potency/hypoxic C1.6) of NLA-1 is approximately 6-fold lower than that for MISO. NLA-1 lacks radiosensitizing activity against SCCVII or EMT6 tumors in vivo at the maximum tolerated dose (MTD) of 100 mumol.kg-1.

Cytosol mediated metabolism of the experimental antitumor agent acridine carboxamide to the 9-acridone derivative

The acridine antitumor agent N-[2'-(dimethylamino)ethyl]acridine-4-carboxamide (AC; NSC 601316; acridine carboxamide) is oxidized efficiently in vitro by rat and mouse hepatic cytosolic fractions. Under these conditions the oxidase activity has an apparent Km of 11 microM towards AC. A single product is formed which has been identified as the corresponding 9(10H)-acridone carboxamide by 1H-NMR and mass spectrometry. Inhibition with menadione and amsacrine, but not allopurinol, indicates that this reaction is most likely to be catalysed by aldehyde oxidase (EC 1.2.3.1). Several AC analogues with modifications to the side chain (the N-oxide, N-monomethyl-, and amino-derivatives) are also metabolized to the equivalent acridone product but the 7-hydroxylated and 4-carboxylic acid acridine derivatives are not.

Subcellular distribution of a nitroxide spin-labeled netropsin-acridine hybrid in living KB cells: Electron Spin Resonance Study

NETGA is an hybrid derivative which possesses an intercalating heterocyclic nucleus related to amsacrine and a minor groove binding squeletton related to netropsin. Cellular uptake of this drug has been studied by Electron Spin Resonance (ESR) spectroscopy using a spin-label derivative of NETGA (SL-NETGA). ESR determination of the kinetics of the drug repartition between the cytoplasm and nucleus showed that NETGA accumulated very rapidly and predominantly in the nucleus. Analysis of the anisotropic ESR spectra recorded in the nuclear compartment are in agreement with a strong binding of the drug to the DNA besides confirmed by a maximum delta Tm of 12 degrees C between the spin-label compound-DNA complex and the DNA alone.

Free energy calculation on base specificity of drug--DNA interactions: application to daunomycin and acridine intercalation into DNA

We present the results of free energy perturbation/molecular dynamics studies on B-DNA.daunomycin and B-DNA.9-aminoacridine complexes as well as on B-DNA itself in order to calculate the free energy differences between complexes having different base pair sequences. The results generally reproduce the trends observed experimentally, i.e., preferences of acridine and daunomycin to bind to a specific base sequence in the DNA. This is encouraging, given the simplicity of the molecular mechanical/dynamical model in which solvent is not explicitly included.

Molecular recognition between oligopeptides and nucleic acids. DNA sequence specificity and binding properties of an acridine-linked netropsin hybrid ligand

The binding to DNA of a mixed function ligand (NETGA) is described, in which a potential intercalating group, an acridine moiety, is incorporated at the carboxyl terminus of the minor groove binding oligopeptide netropsin skeleton. Scatchard analysis of absorption data provided evidence of two modes of binding to DNA with K1 = 9.1 x 10(5) M-1 at low r values (0.003-0.1), and a binding site size n = 10, indicative of binding of both moeities. At high binding ratios (greater than 0.1), K2 = 0.9 x 10(5) M-1 and n = 5 corresponding to external binding. Complementary strand MPE footprinting on a pBR322 restriction fragment showed NETGA binds to 5'-AAAT like netropsin. It causes enhanced cleavage by MPE, particularly at G-C rich sequences and remote from the preferred binding sites. Viscometry measurements provided evidence for biphasic modes of the two binding portions of NETGA. Fluorescence polarization and linear dichroism measurements were in accord with distinct modes of interaction of the acridine (intercalation) and oligopeptide (minor groove binding) portions of NETGA. LD measurements on NETGA indicate that the oligopeptide moiety (netropsin-like) has an orientation typical of minor groove binders, whereas the degree of intercalation of the acridine group is decreased by association of the oligopeptide moiety.

DNA intercalating properties of tetrahydro-9-aminoacridines. Synthesis and 23Na NMR spin-lattice relaxation time measurements

A series of 9-(arylamino)-1,2,3,4-tetrahydroacridines, including the tetrahydro m-AMSA [N-[4-(acridin-9-yl-amino)-3- methoxyphenyl]methanesulfonamide] derivative, has been synthesized. 23Na NMR spin-lattice relaxation rate (1/T1) measurements have been used to study whether these hydrogenated acridines were capable of intercalative binding to calf thymus DNA. The results have been compared to corresponding measurements for 9-aminoacridine, m-AMSA, and MgCl2. All compounds studied were capable of intercalative binding to DNA. However, it was found that the interaction was strongly influenced by substituents on the 9-arylamino group. Thus, tetrahydro m-AMSA was found to intercalate much more weakly with DNA than m-AMSA. Removal of the 3'-methoxy substituent of the 9-arylamino group resulted in intercalation in DNA that was almost as strong as that for m-AMSA.

Correlation of brain levels of 9-amino-1,2,3,4-tetrahydroacridine (THA) with neurochemical and behavioral changes

9-Amino-1,2,3,4-tetrahydroacridine (THA) has been reported to cause improvement in patients with senile dementia of the Alzheimer's type. We have examined some effects of THA in vitro and in vivo to define its mechanism of action. In vitro, THA inhibits acetylcholinesterase (AChE) (IC50 = 223 nM) and blocks [3H]AFDX-116 (M2) and [3H]telenzepine (M1) binding (IC50 s of 1.5 and 9.1 microM respectively). In vivo levels of THA were 10-fold higher in brain than plasma following 3.2 mg/kg i.p., a dose which was found to be active in reversing amnesia induced by scopolamine assessed in T-maze tests in rats and passive avoidance tests in mice. Additionally, these brain concentrations were above the IC50 of THA for AChE inhibition. THA (5.6-17.8 mg/kg i.p.) also elevated acetylcholine levels in the rat CNS. THA-induced side effects were blocked by the central muscarinic antagonist, scopolamine, but not by the peripheral antagonists methscopolamine and glycopyrrolate, nor by nicotinic antagonists. We conclude that brain AChE inhibition by THA is sufficient to explain its purported therapeutic activity in Alzheimer's disease and that its favorable brain/plasma distribution in vivo may account for its central cholinergic action without inducing the severe peripheral cholinergic effects typically seen with other AChE inhibitors.

Synthesis, biological activity and DNA interaction of anilinoacridine and bithiazole peptide derivatives related to the anti-tumor drugs m-AMSA and bleomycin

The synthesis of two depsipeptides including a peptide metal-chelating moiety (Gly-His-Lys) and a moiety with DNA affinity, namely either glycyl-anilino-9-aminoacridine 1 or 2'-(2-aminoethyl)-4-methoxycarbonyl-2",4'-bithiazole 2, has been carried out. The goal was to introduce separately on the same molecule the two factors contributing to the biological activity of many anti-tumor drugs. The interaction of both drugs with DNA has been studied and the acridine ring of 1 was found to intercalate in the double helix. The production of free radicals has been evidenced by spin-trapping for 1 although both compounds were revealed to be good copper-chelating agents. In vitro cytostatic activity and inhibition of [3H]-thymidine incorporation were obtained for 1 while 2 exhibited no activity in both tests. In view of these results, it can be pointed out that the anti-tumor properties of such drugs rely (1) on their ability to reach and to bind DNA and (2) on redox mechanisms involving interactions between the drugs, metals and molecular oxygen. The latter phenomenon leads to the formation of active radical species, able to degrade the DNA.

32P-post-labeling analysis of DNA adduct formation by antitumor drug nitracrine (Ledakrin) and other nitroacridines in different biological systems

A 32P-post-labeling method has been employed to detect DNA adducts formed by derivatives of nitro-9-aminoacridine in both cellular and non-cellular systems. The treatment of HeLa S3 cells in culture or Ehrlich ascites tumor cells in vivo with nitracrine and two other antitumor 1-nitro-9-aminoacridines, denoted C-857 and C-1006, resulted in covalent binding of these compounds to cellular DNA. Each derivative studied gave rise to a distinct pattern of adduct spots and the similarity of the respective adduct profiles was noted for the both cellular models. Calf thymus DNA samples modified in vitro with nitracrine and C-857 in the presence of either rat hepatic microsomal fraction or dithiothreitol yielded chromatographic profiles resembling those obtained in the cellular systems, suggesting similarity in the DNA adduct structures. There were also neither qualitative nor quantitative differences in calf thymus DNA modification by these two 1-nitro derivatives between aerobic and anaerobic conditions, thus the reduction of a nitro group seems not to be the only determinant of covalent binding to DNA in vitro. No DNA adduct formation was detected in the cellular systems used with 2-nitro and 4-nitro isomers of nitracrine that are devoid of cytotoxic activity, which provides further evidence that both covalent binding and DNA crosslinking, but not intercalation, are responsible for cytotoxic and antitumor properties of 1-nitro-9-aminoacridines.

In vitro binding of nitracrine to DNA in chromatin

In the presence of sulfhydryl compounds nitracrine, an anticancer drug, binds covalently to DNA. The accessibility of DNA in chromatin both to nitracrine and to 8-methoxypsoralen, which was used as a reference compound in this study, when assayed in NaCl concentrations from 0 to 2 M show similar characteristics. The initial decrease reaches a minimum at 0.15 M NaCl above which dissociation of non-histone proteins and histones at higher ionic strengths is demonstrated by an increase in accessible sites. The relative accessibility of DNA in chromatin to nitracrine is, however, lower than that found for 8-methoxypsoralen. Partial dissociation of chromatin with 0.7 M NaCl increases the accessibility of DNA in chromatin when assayed in the absence of NaCl but has no apparent influence when estimated at ionic strength close to physiological conditions.

Identification of 9-hydroxylamine-1,2,3,4-tetrahydroacridine as a hepatic microsomal metabolite of tacrine by high-performance liquid chromatography and electrochemistry

Amperometric detection using a dual-electrode thin-layer cell in the series configuration can aid in the identification of unknown components in complicated samples by voltammetric characterization. This is shown by studying the metabolism of tacrine by rat hepatic microsomes using high-performance liquid chromatography with electrochemical detection. The major metabolite detected in microsomal incubations did not co-elute with any standard acridine available and was produced in too small a quantity for mass spectral characterization. Tentative identification of this metabolite as 9-hydroxylamine-1,2,3,4-tetrahydroacridine was made by electrochemical characterization. The electrochemistry of the metabolite was compared to that of the hydroxylamine produced and studied by cyclic voltammetry.

A sodium/proton antiporter in chromaffin-granule membranes

Chromaffin granules, the secretory vesicles of the adrenal medulla, have a Na+/H+ exchange activity in their membranes which brings their proton gradient into equilibrium with a Na+ gradient. This explains why Na+ is mildly inhibitory to amine transport (which is driven by the H+ gradient) The activity can be demonstrated by using accumulation of 22Na+ in response to a pH gradient that is either imposed by diluting membrane 'ghosts' into alkaline media, or generated by ATP hydrolysis. It can also be monitored indirectly by fluorescence measurements in which the pH inside 'ghost' is monitored by quenching of a fluorescent weak base. This method has been used to monitor Na+ entry into acid-loaded 'ghosts' of H+ entry into methylamine accumulation. The exchanger appears to be reversible and non-electrogenic, with a stoichiometry of 1:1. Using an indirect assay we measured an apparent Km for Na+ of 4.7 mM, and a Ki for amiloride, a competitive inhibitor, of 0.26 mM. Direct assays using 22Na+ suggested a higher Km. Ethylisopropylamiloride was not inhibitory.