A BODIPY-embedding miltefosine analog linked to cell-penetrating Tat(48-60) peptide favors intracellular delivery and visualization of the antiparasitic drug

Therapeutic application of many drugs is often hampered by poor or denied access to intracellular targets. A case in point is miltefosine (MT), an orally active antiparasitic drug, which becomes ineffective when parasites develop dysfunctional uptake systems. We report here the synthesis of a fluorescent BODIPY-embedding MT analogue with appropriate thiol functionalization allowing linkage to the cell-penetrating Tat(48-60) peptide through disulfide or thioether linkages. The resulting constructs are efficiently internalized into the otherwise MT-invulnerable R40 Leishmania strain, resulting in fast parasite killing, and hence successful avoidance of the resistance. In the disulfide-linked conjugate, an additional fluoro tag on the Tat moiety allows to monitor its reductive cleavage within the cytoplasm. Terminally differentiated cells such as peritoneal macrophages, impervious to MT unless infected by Leishmania, can uptake the drug in its Tat-conjugated form. The results afford proof-of-principle for using CPP vectors to avert drug resistance in parasites, and/or for tackling leishmaniasis by modulating macrophage uptake.

Synthesis and photophysics of novel biocompatible fluorescent oxocines and azocines in aqueous solution

The spectroscopic properties in water solution of the different prototropic forms of the strongly fluorescent hemiacetal 4,9-dihydroxy-1,2-dihydro-4,11a-methanooxocino[4,5-b]benzofuran-5(4H)-one (1a, monardine), the aza analogue 4,9-dihydroxy-3,4-dihydro-1H-4,11a-methanobenzofuro[2,3-d]azocin-5(2H)-one (2a, azamonardine) and the respective 2-carboxyl derivatives (1b, 2b) have been studied by experimental and quantum-chemical methods. Monardine and carboxymonardine are the major products of new fluorogenic, room-temperature reactions of hydroxytyrosol or salvianic acid in aqueous solution, respectively, and present unique photophysical properties. Near neutral pH (pKa = 7.2) monardine switches from a weakly emitting, UV-absorbing (382 nm) neutral species to a VIS-absorbing (426 nm), blue emitting (464 nm) anion form, with a fluorescence quantum yield ϕF = 1 and single-exponential decay τF = 2.74 ns. This binary-like spectroscopic change from the neutral to the anionic form was interpreted based on time-dependent density functional theory (TDDFT) calculations as due to (i) the reversal of (n,π*) and (π,π*) lowest-lying singlet excited states, and (ii) a change in the triplet-state distribution accompanying monardine ionization which may abolish de-excitation via intersystem crossing. A similar fluorogenic reaction takes place with catecholamines such as dopamine and DOPA, to yield fluorescent azocines 2a and 2b which, depending on pH, may be present as cationic, neutral or anionic species. TDDFT computations of these forms were also carried out to assign the corresponding excitation transitions and emission properties. Besides the analytical interest of the fluorogenic reactions, the photochemical stability and biocompatibility of the bright-dark pH-controlled molecular switches 1a and 1b may facilitate novel labels and probes to be developed for superresolution fluorescence microscopy.

Drug uptake, lipid rafts, and vesicle trafficking modulate resistance to an anticancer lysophosphatidylcholine analogue in yeast

The ether-phospholipid edelfosine, a prototype antitumor lipid (ATL), kills yeast cells and selectively kills several cancer cell types. To gain insight into its mechanism of action, we performed chemogenomic screens in the Saccharomyces cerevisiae gene-deletion strain collection, identifying edelfosine-resistant mutants. LEM3, AGP2, and DOC1 genes were required for drug uptake. Edelfosine displaced the essential proton pump Pma1p from rafts, inducing its internalization into the vacuole. Additional ATLs, including miltefosine and perifosine, also displaced Pma1p from rafts to the vacuole, suggesting that this process is a major hallmark of ATL cytotoxicity in yeast. Radioactive and synthetic fluorescent edelfosine analogues accumulated in yeast plasma membrane rafts and subsequently the endoplasmic reticulum. Although both edelfosine and Pma1p were initially located at membrane rafts, internalization of the drug toward endoplasmic reticulum and Pma1p to the vacuole followed different routes. Drug internalization was not dependent on endocytosis and was not critical for yeast cytotoxicity. However, mutants affecting endocytosis, vesicle sorting, or trafficking to the vacuole, including the retromer and ESCRT complexes, prevented Pma1p internalization and were edelfosine-resistant. Our data suggest that edelfosine-induced cytotoxicity involves raft reorganization and retromer- and ESCRT-mediated vesicular transport and degradation of essential raft proteins leading to cell death. Cytotoxicity of ATLs is mainly dependent on the changes they induce in plasma membrane raft-located proteins that lead to their internalization and subsequent degradation. Edelfosine toxicity can be circumvented by inactivating genes that then result in the recycling of internalized cell-surface proteins back to the plasma membrane.

Fluorescent labeling of Acanthamoeba assessed in situ from corneal sectioned microscopy

Acanthamoeba keratitis is a serious pathogenic corneal disease, with challenging diagnosis. Standard diagnostic methods include corneal biopsy (involving cell culture) and in vivo reflection corneal microscopy (in which the visualization of the pathogen is challenged by the presence of multiple reflectance corneal structures). We present a new imaging method based on fluorescence sectioned microscopy for visualization of Acanthamoeba. A fluorescent marker (MT-11-BDP), composed by a fluorescent group (BODIPY) inserted in miltefosine (a therapeutic agent against Acanthamoeba), was developed. A custom-developed fluorescent structured illumination sectioned corneal microscope (excitation wavelength: 488 nm; axial/lateral resolution: 2.6 μm/0.4-0.6 μm) was used to image intact enucleated rabbit eyes, injected with a solution of stained Acanthamoeba in the stroma. Fluorescent sectioned microscopic images of intact enucleated rabbit eyes revealed stained Acanthamoeba trophozoites within the stroma, easily identified by the contrasted fluorescent emission, size and shape. Control experiments show that the fluorescent maker is not internalized by corneal cells, making the developed marker specific to the pathogen. Fluorescent sectioned microscopy shows potential for specific diagnosis of Acanthamoeba keratitis. Corneal confocal microscopy, provided with a fluorescent channel, could be largely improved in specificity and sensitivity in combination with specific fluorescent marking.

Defeating Leishmania resistance to miltefosine (hexadecylphosphocholine) by peptide-mediated drug smuggling: a proof of mechanism for trypanosomatid chemotherapy

Miltefosine (hexadecylphosphocholine, HePC), the first orally active drug successful against leishmaniasis, is especially active on the visceral form of the disease. Resistance mechanisms are almost exclusively associated to dysfunction in HePC uptake systems. In order to evade the requirements of its cognate receptor/translocator, HePC-resistant Leishmania donovani parasites (R40 strain) were challenged with constructs consisting of an ω-thiol-functionalized HePC analogue conjugated to the cell-penetrating peptide (CPP) Tat(48-60), either through a disulfide or a thioether bond. The conjugates enter and kill both promastigote and intracellular amastigote forms of the R40 strain. Intracellular release of HePC by reduction of the disulfide-based conjugate was confirmed by means of double tagging at both the CPP (Quasar 670) and HePC (BODIPY) moieties. Scission of the conjugate, however, is not mandatory, as the metabolically more stable thioether conjugate retained substantial activity. The disulfide conjugate is highly active on the bloodstream form of Trypanosoma b. brucei, naturally resistant to HePC. Our results provide proof-of-mechanism for the use of CPP conjugates to avert drug resistance by faulty drug accumulation in parasites, as well as the possibility to extend chemotherapy into other parasites intrinsically devoid of membrane translocation systems.

Involvement of lipid rafts in the localization and dysfunction effect of the antitumor ether phospholipid edelfosine in mitochondria

Lipid rafts and mitochondria are promising targets in cancer therapy. The synthetic antitumor alkyl-lysophospholipid analog edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine) has been reported to target lipid rafts. Here, we have found that edelfosine induced loss of mitochondrial membrane potential and apoptosis in human cervical carcinoma HeLa cells, both responses being abrogated by Bcl-x_L overexpression. We synthesized a number of new fluorescent edelfosine analogs, which preserved the proapoptotic activity of the parent drug, and colocalized with mitochondria in HeLa cells. Edelfosine induced swelling in isolated mitochondria, indicating an increase in mitochondrial membrane permeability. This mitochondrial swelling was independent of reactive oxygen species generation. A structurally related inactive analog was unable to promote mitochondrial swelling, highlighting the importance of edelfosine molecular structure in its effect on mitochondria. Raft disruption inhibited mitochondrial localization of the drug in cells and edelfosine-induced swelling in isolated mitochondria. Edelfosine promoted a redistribution of lipid rafts from the plasma membrane to mitochondria, suggesting a raft-mediated link between plasma membrane and mitochondria. Our data suggest that direct interaction of edelfosine with mitochondria eventually leads to mitochondrial dysfunction and apoptosis. These observations unveil a new framework in cancer chemotherapy that involves a link between lipid rafts and mitochondria in the mechanism of action of an antitumor drug, thus opening new avenues for cancer treatment.

Photosensitized degradation in water of the phenolic pesticides bromoxynil and dichlorophen in the presence of riboflavin, as a model of their natural photodecomposition in the environment

Within the context of environmentally friendly methods for the elimination of surface-water pollutants, the photodegradation of the phenolic pesticides bromoxynil (BXN) and dichlorophen (DCP) under simulated natural conditions has been studied. The work was done in the presence of the visible-light absorber photosensitizer riboflavin (Rf), usually present in trace quantities in natural waters. Under aerobic conditions, an efficient photooxidation of both pesticides was observed. The relatively intricate photochemical mechanism involves pesticide and oxygen consumption and, to a lesser extent, Rf degradation. The kinetic and mechanistic study supports that both H(2)O(2) and singlet molecular oxygen, O(2)((1)Δ(g)), are involved in the process. Kinetic data for the O(2)((1)Δ(g))-mediated oxidation indicate that BXN and DCP are photodegraded with this species faster than the parent compound phenol, very frequently employed as a model for aquatic contaminants, likely due to their lower pK(a) values. This observation allows the design of phenolic pesticides with different photodegradation rates under environmental conditions.

Photodegradation of bisphenol A and related compounds under natural-like conditions in the presence of riboflavin: kinetics, mechanism and photoproducts

The aerobic riboflavin (Rf)-sensitized photodegradation of the endocrine disruptor 4,4'-isopropylidenebisphenol (bisphenol A, BPA), and of the related compounds 4,4'-isopropylidenebis(2,6-dibromophenol) and 4,4'-isopropylidenebis(2,6-dimethylphenol) has been studied in water and water-methanol mixtures through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time-resolved fluorescence spectroscopy, time-resolved near-IR phosphorescence detection and laser flash photolysis techniques. Bisphenols (BPs) quench excited singlet and triplet states of Rf, with rate constants close to the diffusion limit. BPs and dissolved molecular oxygen, employed in similar concentrations, competitively quench triplet excited Rf. As a consequence, superoxide radical anion and singlet molecular oxygen (O2(1Deltag)) are produced by electron- and energy-transfer processes, respectively, as demonstrated by auxiliary experiments employing selective quenchers of both oxidative species and the exclusive O2(1Deltag) generator Rose Bengal. As a global result, the photodegradation of Rf is retarded, whereas BPs are degraded, mainly by an O2(1Deltag)-mediated mechanism, which constitutes a relatively efficient process in the case of BPA. Oxidation, dimerization and fragmentation products have been identified in the photooxidation of BPA. Results indicate that BPs in natural waters can undergo spontaneous photodegradation under environmental conditions in the presence of adequate photosensitizers.

Photodegradation of the acaricide abamectin: a kinetic study

The acaricide abamectin is a mixture of two colorless homologues in a molar ratio of at least 4:1 with the same structure of macrocyclic lactone. The kinetics of its degradation under direct (254 nm) and dye-sensitized (>400 nm) photoirradiation in methanol solution has been studied by UV-vis spectrophotometry, potentiometric detection of dissolved oxygen, stationary fluorescence, laser flash photolysis, and time-resolved detection of singlet molecular oxygen (O2((1)Delta(g))) phosphorescence. The results indicate that the degradation is very efficient under direct irradiation with UV light (254 nm), with a quantum yield of 0.23. On the contrary, under visible-light irradiation, using the natural pigment riboflavin or the synthetic dye rose bengal as sensitizers, the degradation is very inefficient and proceeds through a O2((1)Delta(g))-mediated mechanism, with a bimolecular rate constant for the overall O2((1)Delta(g)) quenching (the sum of physical and chemical quenching) of 5.5 x 10(5) M(-1) s(-1). This value is similar to those reported for the rate constants of the reactions of O2((1)Delta(g)) with isolated double bonds or conjugated dienes and points to similar processes in the case of abamectin.

Synthesis, Photophysical Properties, and Laser Behavior of 3-Amino and 3-Acetamido BODIPY Dyes

The asymmetrically substituted BODIPY dyes 9a and 9b have been synthesized through a key redox step involving the alpha-nitroso derivative of the starting pyrrol. Both dyes emit fluorescence with quantum yields of ca. 0.7, but only 8b behaves as a good laser dye, with an efficiency of 48% in ethanol solution.

The phenyltetraene lysophospholipid analog PTE-ET-18-OMe as a fluorescent anisotropy probe of liquid ordered membrane domains (lipid rafts) and ceramide-rich membrane domains

The conjugated phenyltetraene PTE-ET-18-OMe (all-(E)-1-O-(15'-phenylpentadeca-8',10',12',14'-tetraenyl)-2-O-methyl-rac-glycero-3-phosphocholine) is a recently developed fluorescent lysophospholipid analog of edelfosine, (Quesada et al. (2004) J. Med. Chem. 47, 5333-5335). We investigated the use of this analog as a probe of membrane structure. PTE-ET-18-OMe was found to have several properties that are favorable for fluorescence anisotropy (polarization) experiments in membranes, including low fluorescence in water and moderately strong association with lipid bilayers. PTE-ET-18-OMe has absorbance and fluorescence properties similar to those of diphenylhexatriene (DPH) probes, with about as large a difference between its fluorescence anisotropy in liquid disordered (Ld) and ordered states (gel and Lo) as observed for DPH. Also like DPH, PTE-ET-18-OMe has a moderate affinity for both gel state ordered domains and Lo state ordered domains (rafts). However, unlike fluorescent sterols or DPH (Megha and London (2004) J. Biol. Chem. 279, 9997-10004), PTE-ET-18-OMe is not displaced from ordered domains by ceramide. Also unlike DPH, PTE-ET-18-OMe shows only slow exchange between the inner and outer leaflets of membrane bilayers, and can thus be used to examine anisotropy of an individual leaflet of a lipid bilayer. Since PTE-ET-18-OMe is a zwitterionic molecule, it should not be as influenced by electrostatic interactions as are other probes that do not cross the lipid bilayer but have a net charge. We conclude that PTE-ET-18-OMe has some unique properties that should make it a useful fluorescence probe of membrane structure.

Kinetics and Mechanism of the Sensitized Photodegradation of Uracil-Modeling the Fate of Related Herbicides in Aqueous Environments†

The dye-sensitized photodegradation of uracil (UR), the parent compound of several profusely employed herbicides, has been studied as a model of their environmental fate. In order to mimic conditions frequently found in nature, aqueous solutions of UR have been irradiated with visible light in the presence of the natural sensitizer riboflavin (Rf). The results indicate that UR is photostable in acid media, but is quickly degraded in pH 7 or pH 9 solutions, where singlet molecular oxygen [O2(1Delta(g))] and, to a lesser extent, superoxide radical anion (O2*-)-both species photogenerated from triplet excited Rf, 3Rf*-participate in the photodegradation. At pH 7, UR is slowly degraded through an O2*- -mediated mechanism, whereas Rf disappears through its reaction with O2(1Delta(g)) and, in the form of 3Rf*, with UR. On the contrary, at pH 9 Rf is photoprotected through two processes: its regeneration from the formed Rf radical species-a back electron transfer that also produces O2*- -and the elimination from the medium of O2(1Delta(g)) by its reaction with UR. The overall result of the preservation of ground state Rf is the continuity of the photosensitized process and, hence, of the UR degradation. Media with higher pH values could not be employed due to the fast photodegradation of Rf. With rose bengal (RB) as photosensitizer, the rate constants found for the overall interaction between UR and the photogenerated O2(1Delta(g)) were in the range 5 x 10(5) M(-1) s(-1) (at pH 7) to 1.3 x 10(8) M(-1) s(-1) (in 1 M NaOH aqueous solution, mainly physical quenching). The maximum O2(1Delta(g)0-mediated photooxidation efficiencies with RB were reached at pH 11, where only the O2(1Delta(g)0-reactive quenching with UR was observed.

Synthesis of 16-mercaptohexadecylphosphocholine, a miltefosine analog with leishmanicidal activity

The alkylphosphocholine miltefosine (n-hexadecylphosphocholine, MT) has been introduced recently as a very effective drug for the oral treatment of human leishmaniasis. However, the parasiticidal mechanism of MT at a molecular level is far from being understood. Here we report the synthesis and biological characterization of 16-mercaptohexadecylphosphocholine, a thiol analog of MT which was designed to facilitate the search of MT interacting targets within the parasite by a variety of analytical methods. This analog presents the same leishmanicidal effect as the parent drug against Leishmania donovani promastigotes and Leishmania pifanoi axenic amastigotes, and has been used to develop an affinity chromatography method to attempt the isolation of putative Leishmania proteins that bind to the phosphocholine part of the molecule.

Dye-sensitized photodegradation of the fungicide carbendazim and related benzimidazoles

The present work studies the visible-light-promoted photodegradation of the colorless fungicide carbendazim (methyl 2-benzimidazolecarbamate) and several 2-substituted benzimidazoles (SBZ's), in water or water-methanol solution, in the presence of air and, as a photosensitizer, the synthetic xanthene dye Rose Bengal (RB) or the natural pigment riboflavin (Rf). The results indicate that the degradation of each particular SBZ depends on its chemical structure and on the sensitizer employed. In the presence of RB, the degradation always operates via a singlet molecular oxygen (O(2)((1)Delta(g)))-mediated mechanism, through a highly efficient process, as deduced from the comparison of the rate constants for physical and chemical quenching of O(2)((1)Delta(g)). In the presence of Rf, the visible-light irradiation of any of the studied SBZ's produces a series of competitive processes that depend on the relative concentrations of Rf and SBZ. These processes include the quenching of excited singlet and triplet Rf states by the SBZ and the generation of both O(2)((1)Delta(g)) and superoxide radical anion (O(2)(-)), the latter generated by electron transfer from excited Rf species to the dissolved oxygen. The overall result is the photodegradation of the SBZ and the photoprotection of the sensitizer.

Dynamics of bolaamphiphilic fluorescent polyenes in lipid bilayers from polarization emission spectroscopy

The rotational motions of the biamphiphilic polyenes (bolapolyenes) dimethyl all-(E)-octacosa-10,12,14,16,18-pentaenedioate (DE28:5) and dimethyl all-(E)-tetratriaconta-13,15,17,19,21-pentaenedioate (DE34:5), with head-to-head distances of 34 and 42A, respectively, have been examined by fluorescence anisotropy methods. The membrane-spanning bolapolyenes, which contain a central emitting pentaene group tethered to two methoxycarbonyl opposite polar heads by symmetric C(8) (DE28:5) and C(11) (DE34:5) polymethylene chains, were dispersed in lipid bilayers of DPPC or DMPC, and the stationary and picosecond-resolved emission was recorded as a function of temperature. In fluid-phase DMPC bilayers, three relaxation times could be determined, assigned to fast (0.2 and 2ns) single-bond isomerization processes localized on the alkyl chains, and to whole-molecule oscillations ( approximately 11ns), respectively. The anisotropy decay parameters were further analyzed in terms of a diffusive model for wobbling in a Gaussian ordering potential, to assess the anchoring effect of the symmetric polar heads. In this way, the average rotational diffusion constant of the bolapolyenes, D( perpendicular), could be estimated as 0.022-0.026rad(2) ns(-1) (DMPC bilayers, 35 degrees Celsius), a value that is only 1/3 of that corresponding to the related pentaene fatty acid spanning a single membrane monolayer. In contrast, the amplitude of the equilibrium orientational distribution (theta(half-cone) approximately 50 degrees ) is very similar for both the transmembrane and the single-headed polyenes. The reorientational oscillations of the central emitting group in the bolapolyenes necessarily would produce large-amplitude (2-5A) and very fast (ns) translational motions of the polar heads.

Photodegradation of hydroxylated N-heteroaromatic derivatives in natural-like aquatic environments. A review of kinetic data of pesticide model compounds

In the present review, the results published by our group and others related with the study of the kinetic behavior and, in some cases, the mechanism of the dye-promoted photooxygenation of several hydroxypyridines, hydroxyquinolines and hydroxypyrimidines--some of them with the basic molecular structures of known pesticides, and of a few non-hydroxylated model compounds, are compiled and discussed. The main aim was to examine the experimental conditions that maximize the photodegradation efficiencies of all these compounds, under dye-sensitized photooxidation conditions similar to those frequently found in nature, with a natural dye sensitizer such as riboflavin (vitamin B2), a pigment habitually present in natural waters. The usual mechanism of action of this compound is rather complex, in many cases with the concurrent involvement of the oxidative species singlet molecular oxygen (O2(1Deltag)) and superoxide radical anion. In order to simplify the study of the processes, the results found using the synthetic dye Rose Bengal (RB), a sensitizer that generates O2(1Deltag) with high efficiency, are also discussed. RB and similar O2(1Deltag)-generators could be used for the efficient non-natural photodegradation of related pesticides in aqueous solutions under controlled conditions.

Fluorescent phenylpolyene analogues of the ether phospholipid edelfosine for the selective labeling of cancer cells

Edelfosine (ET-18-OCH3), a synthetic antitumor ether lipid, is taken up by malignant but not by normal cells, triggering apoptosis in a large variety of human tumor cells. The synthesis of the first fluorescent edelfosine analogue (6), with apoptotic activity comparable to that of the parent drug, is described. Fluorescence microscopy experiments show that 6 selectively labels human cancer cells, accumulating into specific domains of the plasma membrane.

Macromolecular accessibility of fluorescent taxoids bound at a paclitaxel binding site in the microtubule surface

The macromolecular accessibility of the paclitaxel binding site in microtubules has been investigated using a fluorescent taxoid and antibodies against fluorescein, which cannot diffuse into the microtubule lumen. The formation of a specific ternary complex of microtubules, Hexaflutax (7-O-{N-[6-(fluorescein-4'-carboxamido)-n-hexanoyl]-l-alanyl}paclitaxel) and 4-4-20 IgG (a monoclonal antibody against fluorescein) has been observed by means of sedimentation and electron microscopy methods. The kinetics of binding of the antibody to microtubule-bound Hexaflutax has been measured. The quenching of the observed fluorescence is fast (k+ 2.26 +/- 0.25 x 10(6) m(-1) s(-1) at 37 degrees C), indicating that the fluorescein groups of Hexaflutax are exposed to the outer solvent. The velocity of the reaction is linearly dependent on the antibody concentration, indicating that a bimolecular reaction is being observed. Another fluorescent taxoid (Flutax-2) bound to microtubules has also been shown to be rapidly accessible to polyclonal antibodies directed against fluorescein. A reduced rate of Hexaflutax quenching by the antibody is observed in microtubule-associated proteins containing microtubules or in native cellular cytoskeletons. It can be concluded that the fluorescent taxoids bind to an outer site on the microtubules that is shared with paclitaxel. Paclitaxel would be internalized in a further step of binding to reach the known luminal site, this step being blocked in the case of the fluorescent taxoids. Because the fluorescent ligands are able to induce microtubule assembly, binding to the outer site should be enough to induce assembly by a preferential binding mechanism.

Photodegradation of the herbicide Norflurazon sensitised by Riboflavin. A kinetic and mechanistic study

The kinetics and mechanism of the Riboflavin (Rf)-promoted photochemical degradation with visible light of the herbicide Norflurazon (NF) has been studied by time-resolved and stationary techniques. Using light of wavelength higher than 400 nm--a region where NF is totally transparent--and with concentrations of Rf and NF of ca. 0.02 and 1 mM, respectively, only the excited triplet state of Rf ((3)Rf*) is quenched by NF, in competition with dissolved ground state triplet oxygen, O(2)((3)Sigma(g)(-)). NF degradation mainly occurs by reaction with superoxide radical anion O(2)(-) formed through two electron transfer steps: from NF to (3)Rf*, yielding Rf radical anion, and from this anion to O(2)((3)Sigma(g)(-)), regenerating ground state Rf. Although singlet molecular oxygen is also produced, NF only quenches this oxidative species in a physical mode. The global result is the photoprotection of the sensitiser and the photodegradation of NF.

Intracellular triggering of Fas aggregation and recruitment of apoptotic molecules into Fas-enriched rafts in selective tumor cell apoptosis

We have discovered a new and specific cell-killing mechanism mediated by the selective uptake of the antitumor drug 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH₃, Edelfosine) into lipid rafts of tumor cells, followed by its coaggregation with Fas death receptor (also known as APO-1 or CD95) and recruitment of apoptotic molecules into Fas-enriched rafts. Drug sensitivity was dependent on drug uptake and Fas expression, regardless of the presence of other major death receptors, such as tumor necrosis factor (TNF) receptor 1 or TNF-related apoptosis-inducing ligand R2/DR5 in the target cell. Drug microinjection experiments in Fas-deficient and Fas-transfected cells unable to incorporate exogenous ET-18-OCH₃ demonstrated that Fas was intracellularly activated. Partial deletion of the Fas intracellular domain prevented apoptosis. Unlike normal lymphocytes, leukemic T cells incorporated ET-18-OCH₃ into rafts coaggregating with Fas and underwent apoptosis. Fas-associated death domain protein, procaspase-8, procaspase-10, c-Jun amino-terminal kinase, and Bid were recruited into rafts, linking Fas and mitochondrial signaling routes. Clustering of rafts was necessary but not sufficient for ET-18-OCH₃–mediated cell death, with Fas being required as the apoptosis trigger. ET-18-OCH₃–mediated apoptosis did not require sphingomyelinase activation. Normal cells, including human and rat hepatocytes, did not incorporate ET-18-OCH₃ and were spared. This mechanism represents the first selective activation of Fas in tumor cells. Our data set a framework for the development of more targeted therapies leading to intracellular Fas activation and recruitment of downstream signaling molecules into Fas-enriched rafts.

Rose Bengal–Sensitized Photooxidation of the Dipeptides l-Tryptophyl-l-Phenylalanine, l-Tryptophyl-l-Tyrosine and l-Tryptophyl-l-Tryptophan: Kinetics, Mechanism and Photoproducts¶

The Rose Bengal-sensitized photooxidations of the dipeptides l-tryptophyl-l-phenylalanine (Trp-Phe), l-tryptophyl-l-tyrosine (Trp-Tyr) and l-tryptophyl-l-tryptophan (Trp-Trp) have been studied in pH 7 water solution using static photolysis and time-resolved methods. Kinetic results indicate that the tryptophan (Trp) moiety interacts with singlet molecular oxygen (O(2)((1)Delta(g))) both through chemical reaction and through physical quenching, and that the photooxidations can be compared with those of equimolecular mixtures of the corresponding free amino acids, with minimum, if any, influence of the peptide bond on the chemical reaction. This is not a common behavior in other di- and polypeptides of photooxidizable amino acids. The ratio between chemical (k(r)) and overall (k(t)) rate constants for the interaction O(2)((1)Delta(g))-dipeptide indicates that Trp-Phe and Trp-Trp are good candidates to suffer photodynamic action, with k(r)/k(t) values of 0.72 and 0.60, respectively (0.65 for free Trp). In the case of Trp-Tyr, a lower k(r)/k(t) value (0.18) has been found, likely as a result of the high component of physical deactivation of O(2)((1)Delta(g)) by the tyrosine moiety. The analysis of the photooxidation products shows that the main target for O(2)((1)Delta(g)) attack is the Trp group and suggests a much lower accumulation of kynurenine-type products, as compared with free Trp. This is possibly because of the occurrence of another accepted alternative pathway of oxidation that gives rise to 3a-oxidized hydrogenated pyrrolo[2,3-b]indoles.

Kinetic study of the riboflavin-sensitised photooxygenation of two hydroxyquinolines of biological interest

4-Hydroxyquinoline (4-OHQ) and 8-hydroxyquinoline (8-OHQ), two compounds of interest because of their bioactivity and their structural relation with bioactive products, are effectively photooxygenated when irradiated with visible light in the presence of riboflavin (Rf) (vitamin B2) in solution in air-saturated water-methanol (9:1). Rf behaves as a dye-sensitiser, since both quinolines are transparent to visible light. 8-OHQ degrades about five times faster than 4-OHQ. Kinetic data obtained through time-resolved and stationary detection of Rf-electronically excited states indicate that a superoxide radical anion-mediated mechanism exclusively operates for 4-OHQ, whereas singlet molecular oxygen--mainly--plus superoxide radical anion is the species that reacts with 8-OHQ. The sensitiser Rf, which is known to photodegrade under visible-light aerobic irradiation, is regenerated in the presence of any of the quinolines through an electron transfer process that produces superoxide radical anion. The overall picture indicates that both quinolines act as sacrificial scavengers of the photogenerated oxygen species, thus preventing the photodegradation of Rf.

Photophysical and lasing properties of new analogs of the boron-dipyrromethene laser dye pyrromethene 567 incorporated into or covalently bounded to solid matrices of poly(methyl methacrylate)

The photophysical, lasing and thermostability properties of newly synthesized analogs of the commercial dye pyrromethene 567 (PM567) have been measured in polymeric matrices of poly(methyl methacrylate) both when used as a dopant and when covalently bounded to the polymeric chain. These analogs have an acetoxy or a polymerizable methacryloyloxy group at the end of a polymethylene chain at Position 8 of the PM567 chromophore core. Clear correlations between photophysical and lasing characteristics are observed. Linking chain lengths with three or more methylene units give the highest fluorescence quantum yields (as high as 0.89) and lasing efficiencies (as high as 41%). The covalent linkage of the chromophore to the polymeric chain via the methacryloyloxy group improves the photostability of the PM567 chromophore.

Methacrylate-tethered analogs of the laser dye PM567--synthesis, copolymerization with methyl methacrylate and photostability of the copolymers

The synthesis and characterization of new analogs of the laser dye PM567 (4,4-difluoro-1,3,5,7,8-pentamethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene) with the 8-position substituted by a linear chain with n methylenes (n = 1, 3, 5, 10 or 15) tethered with an acetoxy or methacryloyloxy group (PnAc and PnMA, respectively) is described. The monomeric dyes PnMA have been successfully copolymerized with methyl methacrylate (MMA), yielding linear copolymers of high optical quality where the covalently bonded chromophore is separated from the polymeric main chain by a spacer of variable length. The photostability of the solid polymeric materials under UV (310 nm) irradiation (method ASTM G 53-77) has been compared with those of the model dyes PnAc and PM567 as solid solutions in poly-MMA (PnAc-PMMA and PM567-PMMA, respectively). In all the cases, the chromophore bound to the polymer is more photostable than that simply dissolved in the same polymer, with photodegradation quantum yields in the range 2.3 x 10(-5) to 4.8 x 10(-5), which was interpreted as due to additional modes for the dissipation of the absorbed energy along the polymeric chain. In both polymer solutions and copolymers, the length of the polymethylene chain has low or null influence on the photostability. In ethanol solution, PnAc model dyes with polymethylene chains with three or more methylene groups show about the same photostability; this is of an order of magnitude higher than that of the parent dyes P1Ac and PM567 in the same solvent.