Spectroscopic studies of cutaneous photosensitizing agents--X. A spin-trapping and direct electron spin resonance study of the photochemical pathways of daunomycin and adriamycin

Studies on photodegradation process of psychotropic drugs: a review

Consumption of psychotropic drugs is still increasing, especially in high-income countries. One of the most crucial consequences of this fact is significant release of them to the environment. Considerable amounts of atypical antipsychotics, benzodiazepines, antidepressants, and their metabolites were detected in river, lake, and sea water, as well as in tissues of aquatic organisms. Their ecotoxicity was proved by numerous studies. It should be noticed that interaction between psychotropic pharmaceuticals and radiation may lead to formation of potentially more toxic intermediates. On the other hand, photo-assisted wastewater treatment methods can be used as an efficient way to eliminate them from the environment. Many methods based on photolysis and photocatalysis were proposed and developed recently; nevertheless, the problem is still unsolved. However, according to recent studies, photocatalysis could be considered as the most promising and far more effective than regular photolysis. An overview on photolytic as well as homogenous and heterogeneous photocatalytic degradation methods with the use of various catalysts is presented. The photostability and phototoxicity of pharmaceuticals were also discussed. Various analytical methods were used for the photodegradation research, and this issue was also compared and summarized. Use of high-resolution multistage mass spectrometry (Q-TOF, ion trap, Orbitrap) was suggested. The combined techniques such as LC-MS, GC-MS, and LC-NMR, which enable qualitative and quantitative analyses in one run, proved to be the most valuable in this case. Assembling of MS/MS spectra libraries of drug molecules and their phototransformation products was identified as the future challenge.

Synthesis and active oxygen generation by new emodin derivatives and their gonadotropin-releasing hormone conjugates

In an attempt to develop efficient chemotherapeutic agents targeted at malignant cells that express receptors, we synthesized five new emodin derivatives and their gonadotropin-releasing hormone (GnRH) conjugates to be used as potential photoactive conjugates. Emodin was modified at its hydroxy groups and included different spacers for conjugation of the peptide. We used electron spin resonance (ESR) and spin trapping techniques to study the light-stimulated redox properties of the emodin derivatives and their GnRH conjugates. Upon irradiation, all new emodin derivatives and their conjugates stimulated the formation of singlet oxygen, that is, (1)O(2), and oxygen radicals, that is, O(2)(-)(*) and OH(*). However, substantial differences were found between the tested derivatives as to the efficacy of reactive oxygen species (ROS) production. Because of its superior ROS production properties, [d-Lys(6)(MeoEmo)]GnRH was selected as a leading conjugate. En-route to evaluate its targeting capacity, this potentially cytotoxic conjugate was tested in vitro to determine its hormonal activity and binding affinity to GnRH receptors.

Generation of free radicals by emodic acid and its [D-Lys6]GnRH-conjugate

In an attempt to develop an efficient chemotherapeutic agent targeted at malignant cells that express receptors to gonadotropin releasing hormone (GnRH) we coupled [D-Lys6]GnRH covalently to an emodin derivative, i.e. emodic acid (Emo) to yield [D-Lys6(Emo)]GnRH. Emodin is a naturally occurring anthraquinone which is widely used as a laxative and has other versatile biological activities. Physico-chemical studies employing electron paramagnetic resonance and electrochemistry of the conjugate as well as the (Emo) moiety showed that these compounds could be easily reduced either chemically, photochemically or enzymatically to their corresponding semiquinones. In the presence of oxygen the semiquinones generated reactive oxygen species (ROS), mainly superoxide and hydroxyl radicals, which were detected by the spin trapping method. Moreover, upon irradiation with visible light these compounds produced ROS and a highly reactive excited triplet state of Emo, which by itself may cause the oxidation of certain electron acceptors such as amino acids and bases of nucleic acids. Thus, [D-Lys6]GnRH-photosensitizer conjugates may be potentially used for targeted photodynamic chemotherapy aimed at treating cancer cells that carry GnRH receptors. These conjugates may also induce cytotoxicity in the dark similar to common conventional chemotherapeutic agents. The peptidic moiety, [D-Lys6]GnRH, was found to be stable toward highly reactive ROS generated either from enzymatic reduction or upon photoirradiation. The physico-chemical properties of Emo were only marginally influenced by the peptidic [D-Lys6]GnRH carrier.

Sonodynamically-induced in vitro cell damage enhanced by adriamycin

Sonodynamically-induced cell damage and active oxygen generation enhanced by adriamycin (ADM) were compared in the same in vitro insonation set-up. Significant enhancement of the rates of both ultrasonically-induced cell damage and nitroxide generation was demonstrated with 40-160 microM ADM. Both rates correlated very well resulting in a correlation coefficient of more than 0.99. The enhancement of both rates was suppressed by 10 mM histidine. These results are consistent with the hypothesis that ultrasonically-generated active oxygen plays a major role in the sonodynamically-induced cell damage enhanced by ADM.

Laser photochemotherapy with anthracyclines on cultured human squamous carcinoma cells

A new treatment for cancer has been tested in vitro using light-sensitive anthracyclines followed by laser photoactivation, as described by several investigators. We previously reported 10-fold enhanced laser killing after 2 hours of incubation with daunomycin by cultured human carcinoma cells. This short-term uptake leads to drug localization in cytoplasmic and membrane sites prior to nuclear accumulation and topoisomerase inhibition. In the present study, daunomycin was incubated for 2 or 24 hours with P3 squamous carcinoma cells to directly compare cytoplasmic vs. nuclear drug targeting before and after KTP-532 laser activation. Monolayer cultures of the P3 cells sensitized with daunomycin for 2 hours, then chilled (4 degree C), and exposed to the KTP laser (532 nm, 94.2 J/cm2) had a 2- to 10-fold increased therapeutic response compared with drug or laser alone when measured by MTT tetrazolium assays. After 24 hours of incubation with daunomycin, the chemotherapeutic response of P3 tumor cells was amplified 2-fold by laser exposure. The results suggest that daunomycin and laser treatment can be combined for improved therapy of human cancer.

Laser photochemotherapy: a less invasive approach for treatment of cancer

The effectiveness of combining surgery with chemo- and radiation therapy in treatment of human cancer provides a useful model for further development of new multimodality approaches including laser photochemotherapy. Laser endoscopy often is a useful treatment for obstructive tumors in airways, but interstitial laser fiberoptics is becoming a more precise, minimally invasive alternative for ablation of unresectable or recurrent neoplasms. Combining intratumor chemotherapy with laser energy delivery via interstitial fiberoptics should be most effective using drugs activated by photothermal energy. A number of investigators have shown that anthracyclines and cis-platinum are likely candidates for light or heat activation in cancer cells. An advantage of anthracyclines is their dual role as antitumor drugs and as photosensitizers. Because they are effective chemotherapy agents without photoactivation, two approaches are possible to increase tumor responses. Maximum tolerated dose followed by photoillumination via laser fiberoptics can be used to obtain better tumor palliation. Improved treatment response to lower intratumor drug levels after laser activation also should reduce systemic toxicity. Preclinical studies and recent case reports from several groups suggest photochemotherapy with currently approved drugs and lasers may soon become an attractive alternative for treatment of recurrent tumors in cancer patients.

EPR spin trapping of free radicals produced by bleomycin and ascorbate

In the presence of ascorbate, bleomycin (BLM) is converted to a redox-inactive form that is incapable of inducing DNA strand scission. We have employed EPR spin trapping with 5,5-dimethylpyrroline-1-oxide (DMPO) to examine free radical production during this process. The introduction of ascorbate to an Fe(III)BLM-DMPO system results in the formation of three EPR observable free radicals. One of these radicals is the resonance-stabilized ascorbate free radical (aH = 1.8 G) that is not spin trapped by DMPO; the other two are the result of DMPO spin trapping. These radicals appear to be two carbon-centered radicals, DMPO/.CR1, (aN1 = 15.75 G, aH1 = 22.30 G, aN/aH = 0.706) and DMPO/.CR2 (aN2 = 15.20 G, aH2 = 19.20 G, aN/aH = 0.79). Although it is not possible to identify the exact structures of the carbon-centered radicals that are spin trapped, the hyperfine splittings, as well as the aN/aH values, are characteristic of the presence of electron-withdrawing groups, such as the oxygen atom when attached to the carbon atom. In fact, these parameters are characteristic of DMPO spin trapping results obtained when sugars are subjected to oxidative insult from HO.. Thus, these BLM-ascorbate produced radicals may well be derived from the sugar moiety of BLM.

Evidence for polynuclear aggregates of ferric daunomycin. A Mössbauer, EPR, X-ray absorption spectroscopy and magnetic susceptibility study

The interaction of the antitumor agent daunomycin (DN) with ferric iron has been analysed by Mössbauer spectroscopy, EPR, extended X-ray absorption fine structure (EXAFS), and magnetic susceptibility measurements. In contrast to literature data, at millimolar iron and anthracycline concentrations no solitary Fe(DN)3 complexes are formed in appreciable amounts. The Mössbauer spectroscopic analysis revealed severe dependencies on temperature, on the preparation procedure, the time allowed for equilibration, and on the metal/ligand ratio. The Mössbauer spectra exhibit two components: a broad magnetic sextet and a quadrupole doublet at an Fe/DN molar ratio of 1:3 and exclusively a doublet at a molar ratio of 1:20, indicating an equilibrium of these two spectral components. The EPR spectra are dominated by a signal at g(eff) = 2. Double integration of the EPR signals enabled the determination of their spin density and a correlation between EPR and Mössbauer spectra. The Mössbauer sextet species is EPR invisible and corresponds to magnetically ordered polynuclear aggregates with high magnetic anisotropy. EXAFS and susceptibility measurements provide additional evidence for the formation of polynuclear aggregates of ferric daunomycin. The quadrupole doublet species in the Mössbauer spectra correlates with the g = 2 signal in EPR. This species is also related to a magnetically ordered system, exhibiting, however, superparamagnetic behavior due to less magnetic anisotropy. Since daunomycin forms dimers in aqueous solution at millimolar concentrations, we conclude that the cooperative phenomena observed in EPR and Mössbauer spectra are a consequence of its stacking effects.

Enhancement of antitumor drug cytotoxicity via laser photoactivation

We investigate the efficacy of daunomycin, some imino- and amino-substituted daunomycin analogues and the disubstituted aminoanthracenedione, mitoxantrone, in photosensitizing short-term cell kill upon irradiation in the long wavelength visible range, during incubation of Fisher rat thyroid cells with the drugs. While all compounds exhibit similar cytocidal effects on our cell line, in the absence of irradiation, administering 86 J/cm2 at wavelengths either coincident or close to drug absorption peaks causes greater enhancement in cell mortality for the 4-demethoxydaunomycin analogues than either the parent drug or its 5-imino-derivative. A lower enhancement is observed with mitoxantrone. In particular, C50 doses (i.e. concentrations that would kill 50% cells) as low as approximately 10(-9) M are found for both 6- and 11-amino 4-demethoxydaunomycin, compared with the values obtained in the absence of light, which are 2.59 x 10(-4) and 0.43 x 10(-4) M, respectively. Our previous studies of the photophysical and photochemical properties of the excited states of these drugs, and ESR and spin trapping studies of photosensitized generation of singlet oxygen, which were extended in this work to include mitoxantrone, indicate that the cytocidal effects proceed via type I rather than type II mechanisms.

Enhanced depletion of lens reduced glutathione Adriamycin in riboflavin-deficient rats

The anticancer drug Adriamycin has photosensitizing properties which potentially may be detrimental to lens tissue. Since reduced glutathione (GSH) serves to protect lens from photo-oxidative stress and dietary riboflavin is required by glutathione reductase to regenerate GSH, we investigated whether Adriamycin intensifies the depletion of GSH levels in rat lens during dietary riboflavin deficiency. Three-week-old rats were divided into two groups. One group was fed a diet deficient in riboflavin (less than 1 ppm) and the other group was pair-fed a control diet containing adequate riboflavin (8.5 ppm). After 6-12 weeks of dietary treatment, half the animals in each dietary group received Adriamycin (8 mg/kg/day) intraperitoneally for 3 days. After killing the rats, lenses were removed, and GSH content and glutathione reductase activity were measured in freshly prepared homogenates. To determine the extent of systemic oxidative stress and the degree of riboflavin deficiency, glucose-6-phosphate dehydrogenase and glutathione reductase activities, respectively, were measured in erythrocytes. In lens of rats fed the riboflavin-sufficient diet, treatment with Adriamycin did not diminish GSH content or alter glutathione reductase activity. In confirmation of reports by others, lenses of animals fed the riboflavin-deficient diet had diminished GSH levels, lower basal glutathione reductase activity, and elevated glutathione reductase activity coefficients compared to those of animals pair-fed the control diet. The present study shows that in riboflavin-deficient rats, Adriamycin exacerbated the depletion of GSH but did not reduce further glutathione reductase activity. The implications of these findings are that nutritional deficiencies, in particular riboflavin deprivation, may pose a potential risk to lenticular tissue following Adriamycin treatment.

Photosensitization by selected anticancer agents

Novel anticancer anthrapyrazoles and anthracenediones are available as alternatives to the cardiotoxic clinical agents, doxorubicin and daunorubicin. Certain representatives of these new classes of compounds possess photosensitizing properties. The structural features influencing the photophysical parameters of these agents are discussed. Photosensitizing reactions involving singlet oxygen production, free radical formation, decomposition of hydrogen peroxide and organic hydroperoxides, oxidation of certain biochemical electron donors, DNA damage and killing of human leukemic cells in vitro in the presence of photoactive anthrapyrazoles, anthracenediones and anthracyclines are described.

Cell photosensitization by 5-iminodaunomycin activated with red light

5-Iminodaunomycin, an anthracycline antitumor drug exhibiting an absorption peak at 595 nm, is shown to photosensitize in vitro cell kill. The photoactivation is performed irradiating the culture dishes during the incubation with the drug for 2 h with 34 mW/cm2 intensity, that is with light doses of up to 245 J/cm2. Long-term effects of administering 50 ng/ml and light for 2 h are studied in terms of growth curves. We show that photoactivation enhances the dark toxicity by a factor of about 10. Immediate cell death is produced by irradiating the cells in the presence of higher drug concentrations (e.g., 1000 ng/ml) which, however, are not toxic in the short term if administered in the dark. The viable cell percentage decreases at increasing light doses, being about 0.6% at the maximum dosage. Administering lower light doses, such as 30 J/cm2, which corresponds to an exposure duration of 15 min, has a short-term effect on the cell survival that strongly depends on the timing of the exposures within the incubation period.

Adriamycin-catalyzed aerobic photooxidation of NAD dimers to NAD+

The photooxidation of the dimers of nicotinamide adenine dinucleotide, (NAD)2, is catalyzed by adriamycin under aerobic conditions. (NAD)2 and O2 react in 1:1 molar ratio to yield 2 mol of NAD+. Experiments carried out by irradiating at 340 and 485 nm, corresponding to the absorption maxima of (NAD)2 and adriamycin, respectively, clearly indicate that the process is primed by photoexcitation of adriamycin. The key step of the process is the redox reaction between (NAD)2 and adriamycin with formation of the semiquinone radical anion, identified by the EPR spectrum. The semiquinone is then oxidized back to adriamycin by oxygen with formation of the superoxide radical.

Triplet state characteristics and singlet oxygen generation properties of anthracyclines

The triplet states of adriamycin (Ad), daunomycin (D) and two daunomycin analogues, daunomycinone (Dc) and daunomycin N-trifluoroacetamide (DAc), have been studied using laser flash photolysis and pulse radiolysis techniques. Triplet lifetimes, molar absorption coefficients, energy levels and quantum yields have been obtained for Dc and DAc, and estimated for D and Ad. Time-resolved near-infrared singlet oxygen luminescence measurements have been carried out on D, Ad and 5-iminodaunomycin (5-ID) in 2H2O solution and Dc in benzene solution at room temperature. Singlet oxygen quenching by the water-soluble anthracyclines was observed and a second-order rate constant of approx. 10(8) M-1.s-1 obtained. Electron spin resonance experiments have demonstrated that D photoexcited at lambda less than or 365 nm gives rise to singlet oxygen as shown by its reaction with 2,2,6,6-tetramethyl-4-piperidone to give the corresponding nitroxyl radical. Although all the anthracyclines studied have the ability to photosensitize the formation of singlet oxygen, the quantum yields are very low (phi delta approximately 0.02-0.03), suggesting that these anthracyclines would be poor photodynamic sensitisers.

Photochemistry of aqueous solutions of benzazolo[3,2-a]quinolinium salts. A spin-trapping study using 17O-enriched water and oxygen

The photolysis of buffered aqueous solutions containing the quinolinium salts, 3-nitro-7-ethyl-benzimidazolo[3,2-a]quinolinium perchlorate (NEBQClO4) and 3-nitrobenzothiazolo[3,2-a]quinolinium chloride (NBQCl), at 344 and 365 nm, respectively, was studied in the presence of the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). Only a water-derived DMPO-OH.spin-adduct was obtained for both of these salts, at a DMPO concentration of 14 mM, as confirmed by H2 17O-enriched water experiments. A photosolvated intermediate is postulated as the OH donating species. Lower steady-state concentrations of the spin adduct were obtained in argon-saturated solutions, implying that oxygen gas is at least partially necessary in the water-derived DMPO-OH formation. Evidence for superoxide ion formation was obtained by the DMPO-17OH spin-adduct formation during the photolysis of NBQCl in an 17O-enriched oxygen atmosphere in the presence of 150 mM DMPO. An increase in the DMPO-OH steady-state concentration was observed if the photolysis of NBQCl was performed in the presence of superoxide dismutase (SOD). Our results suggest that this effect is due to the SOD inhibition of the destruction of DMPO-OH.by superoxide ion.

O2- photogenerated from aqueous solutions of tetracycline antibiotics (pH 7.3) as evidenced by DMPO spin trapping and cytochrome c reduction

UV-irradiation of several tetracycline antibiotics in aqueous buffer (pH 7.3) resulted in the generation of the superoxide anion radical (O2-) which was detected by cytochrome c reduction and by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide and was inhibited by superoxide dismutase. A comparison of the O2- yields from the tetracyclines examined showed the trend chlortetracycline (CTC) greater than oxytetracycline (OXY) greater than demeclocycline (DEM) much greater than (doxycycline (DOXY) = tetracycline (TC) = minocycline (MINO) = 0). This trend is in reasonable agreement with clinical reports that CTC, OXY and DEM are potent photosensitizers, TC is only weakly phototoxic whereas MINO is not. These findings suggest that the O2- production may be involved in tetracycline-induced phototoxicity. While the two methods for O2- detection gave comparable results for most of the tetracyclines, the spin trapping technique was clearly superior for DOXY which reduced cytochrome c in the dark.