Structure and tumor-promoting activity of anthralin (1,8-dihydroxy-9-anthrone) and related compounds

Targeting mitochondria as a potential therapeutic strategy against chemoresistance in cancer

The importance of mitochondria is not only limited to energy generation but also in several physical and chemical processes critical for cell survival. Mitochondria play an essential role in cellular apoptosis, calcium ion transport and cellular metabolism. Mutation in the nuclear and mitochondrial genes, altered oncogenes/tumor suppressor genes, and deregulated signalling for cell viability are major reasons for cancer progression and chemoresistance. The development of drug resistance in cancer patients is a major challenge in cancer treatment as the resistant cells are often more aggressive. The drug resistant cells of numerous cancer types exhibit the deregulation of mitochondrial function. The increased biogenesis of mitochondria and its dynamic alteration contribute to developing resistance. Further, a small subpopulation of cancer stem cells in the heterogeneous tumor is primarily responsible for chemoresistance and has an attribute of mitochondrial dysfunction. This review highlights the critical role of mitochondrial dysfunction in chemoresistance in cancer cells through the processes of apoptosis, autophagy/mitophagy, and cancer stemness. Mitochondria-targeted therapeutic strategies might help reduce cancer progression and chemoresistance induced by various cancer drugs.

Extending the Lifetime of Organic Flow Batteries via Redox State Management

Redox flow batteries based on quinone-bearing aqueous electrolytes have emerged as promising systems for energy storage from intermittent renewable sources. The lifetime of these batteries is limited by quinone stability. Here, we confirm that 2,6-dihydroxyanthrahydroquinone tends to form an anthrone intermediate that is vulnerable to subsequent irreversible dimerization. We demonstrate quantitatively that this decomposition pathway is responsible for the loss of battery capacity. Computational studies indicate that the driving force for anthrone formation is greater for anthraquinones with lower reduction potentials. We show that the decomposition can be substantially mitigated. We demonstrate that conditions minimizing anthrone formation and avoiding anthrone dimerization slow the capacity loss rate by over an order of magnitude. We anticipate that this mitigation strategy readily extends to other anthraquinone-based flow batteries and is thus an important step toward realizing renewable electricity storage through long-lived organic flow batteries.

Anthrone and related hydroxyarenes: tautomerization and hydrogen bonding

The keto-enolization of hydroxyl-substituted naphthols and 9-anthrols has been investigated by means of CBS-QB3 calculations. An excellent agreement between experiment and theory is found for the energetics for the anthrone (5) ⇌ anthrol (6) equilibrium, with an enthalpy of tautomerization, Δ(t)H, of 3.8 kcal mol(-1). In contrast, 1-naphthol is the preferred tautomer with a Δ(t)H = -9.0 kcal mol(-1). Substitution of the hydrogens at the adjacent carbons by hydroxyl groups leads to the formation of strong intramolecular hydrogen bonds within a six-membered ring in the enones and the enols. Due to the difference in the intramolecular hydrogen bond enthalpy, Δ(HB)H(intra), the equilibrium shifts further to the enone. Thus, for 1,8-dihydroxy-anthrone (anthralin, dithranol) Δ(t)H increases to 12.7 kcal mol(-1) with an enol/enone ratio of 10(-10). The solvent effect on the 5 ⇌ 6 equilibrium has been quantified by considering the formation of intermolecular hydrogen bond(s), leading to an acidity parameter α₂(H) for anthrol of 0.42. It is shown that the hydrogen bond donating ability of bulk methanol is greatly attenuated through the formation of cyclic oligomers. The benzylic and phenolic bond dissociation enthalpies for anthrone up to anthralin suggest some antioxidant potency but the precise (radical) mechanism of action remains uncertain.

Study of the interaction of dithranol with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin in solution and in the solid state

The interaction between dithranol and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMBCyD) has been investigated in aqueous solution containing isoascorbic acid (0.2% w/v) as antioxidant and in the solid state. The interaction in the solid state was studied by differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray powder diffractometry (XPD) and a dissolution-rate method. The extent of complexation between the two substances was poor, as indicated by the low value of the slope of the linear part of the solubility curve. A phase diagram was constructed by measuring the thermal behaviour of various re-solidified physical mixtures of dithranol and of TMBCyD previously subjected to heating until melting of the TMBCyD. The loss of dithranol, owing to sublimation and degradation caused by the thermal treatment used, was less than 10%. In keeping with XPD and IR data, the phase diagram indicated that a complex was formed containing 13.7% dithranol (molar ratio 1:1) which had a congruent melting point at 164 degrees C. The drug dissolution rate from the 1:1 complex was measurable, unlike that of the corresponding physical mixture, and was significantly increased when the complex was dispersed in the glassy matrix of TMBCyD, as it was in re-solidified mixtures containing 2-7% dithranol. The results show that the solubility of dithranol is increased significantly as a consequence of its interaction with TMBCyD, despite the low extent of complexation between the two substances.

Modification of DNA bases by anthralin and related compounds

Modification of bases in calf thymus DNA by treatment with the antipsoriatic drug anthralin was studied. The products of DNA bases were identified and their yields measured by gas chromatography-mass spectrometry with selected ion monitoring. Treatment of calf thymus DNA with anthralin significantly enhanced the amount of modified bases above control levels. Purine bases were modified to products identical with those known to be typical of DNA damage induced by hydroxyl radicals. The yields of Fapy-adenine, 8-hydroxyadenine, Fapy-guanine, and 8-hydroxyguanine were maximally increased at an anthralin concentration of 75 microM. A variety of structural analogues of anthralin were also tested at 75 microM were either weaker or stronger hydroxylating agents. It is likely that damage to DNA bases induced by anthrones contributes to their antiproliferative activity. The pharmacological implications of these characteristics of the action of anthralin on DNA bases are discussed.

Inhibition of anthralin-caused skin tumor promotion and interleukin-1 alpha production by potent immunosuppressant FK506

The effect of FK506, a potent immunosuppressive agent, on 7,12-dimethylbenz[alpha]anthracene-initiated and anthralin-promoted skin tumor formation was examined in CD-1 mice. A topical application of 0.1 mumol FK506 to mouse skin 15 min prior to each anthralin treatment markedly inhibited skin tumor formation. Anthralin stimulated IL-1 alpha production in primary cultured mouse epidermal cells, and the peak IL-1 alpha level was observed at 6 h after the stimulation. Anthralin also stimulated IL-1 alpha release into culture medium. Both production and release of Il-1 alpha were markedly inhibited by FK506 (0.1 or 1 microM). FK506 (1 microM) alone neither affected IL-1 alpha production nor its release. It may be possible that the inhibition of IL-1 alpha production by FK506 is related to its anti-tumor-promoting action.

Myeloperoxidase as a biomarker of skin irritation and inflammation

Topical exposure to many occupational and environmental chemicals is often accompanied by the induction of a cutaneous inflammatory response characterized by the influx of polymorphonuclear leucocytes (PMNs). In this study, the accumulation of myeloperoxidase (MPO), an enzyme found at high content in PMNs, was used as a biomarker to assess the inflammatory response to a number of well characterized skin irritants and tumour promoters. Of the chemicals examined, there was a good agreement between MPO accumulation and morphometric indicators of PMNs. Therefore, it was suggested that MPO accumulation could be an additional and useful toxicological tool for determining the dermal irritancy of chemicals.

The antipsoriatic drug, anthralin, inhibits protein kinase C--implications for its mechanism of action

In psoriatic patients, anthralin is known to attenuate lesional inflammation, but often generates perilesional dermatitis. This phenomenon is well reflected by the contrasting action of anthralin on human leukocytes. The release of reactive oxygen species (ROS) is inhibited by anthralin in phorbol ester-activated leukocytes, whereas anthralin directly induces this cellular response in unstimulated cells. In order to elaborate further the underlying mechanisms, we compared the kinetics of anthralin and different well-characterized stimuli, including the phorbol ester, phorbol-12-myristate-13-acetate, in this test system. Compared with standard stimuli, anthralin only marginally induced the release of ROS from human leukocytes and displayed different kinetics. Protein kinase C (PKC), the major cellular phorbol ester receptor, is considered to be involved in the regulation of this cellular response. Furthermore, its involvement in the pathophysiology of psoriasis has been suggested. Therefore, we also investigated the effects of anthralin on purified PKC. Anthralin was found to inhibit the enzyme activity in a dose-dependent manner but not to display any stimulatory effects. The present results provide first evidence that the therapeutic activity of anthralin, at least in part, might be mediated by inhibition of PKC.

Characteristics and modulation of dithranol (anthralin)-induced skin irritation in the mouse ear model

Dithranol-induced skin irritation and the modulatory effects of different pharmacological agents were studied using the mouse ear model. A single topical application of dithranol caused a dose-dependent skin irritation which resulted in delayed swelling of the mouse ear with two separate peak responses, 1-2 and 6-10 days after application. The irritation was most effectively and persistently inhibited by topical treatment with corticosteroids, the free radical scavenger DL-alpha-tocopherol (DLAT) and the serotonin antagonist metergoline. The effect of corticosteroids, however, was slightly diminished during the second peak irritation. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA), the dual lipoxygenase and cyclo-oxygenase inhibitor tolfenamic acid and the cyclo-oxygenase inhibitor indomethacin as well as trifluoperazine retained their inhibitory activity. Of these compounds, indomethacin was active only during the first irritation peak, NDGA during both peaks and trifluoperazine principally during the second peak. Retinoic acid did not inhibit the ear swelling. The results confirm and extend the observations that the formation of free radicals is essential for dithranol inflammation. The inflammation can also be suppressed by inhibiting the formation of arachidonic acid or its pro-inflammatory metabolites.

Spectroscopic studies of cutaneous photosensitizing agents--XV. Anthralin and its oxidation product 1,8-dihydroxyanthraquinone

The photochemistry (Type I and II) of anthralin and its photo-oxidation product 1,8-dihydroxyanthraquinone (1,8-DHAQ) has been studied in ethanol, acetonitrile and dimethylsulfoxide using spin-trapping and direct detection of singlet oxygen (1O2) luminescence techniques. In ethanol, where it exists in its neutral form (AN), anthralin does not undergo either Type I or II reactions upon UV-irradiation. In contrast, irradiation of anthralin in acetonitrile, a solvent in which anthralin is partially converted to its corresponding mono-anion (AN-), generates both superoxide and singlet oxygen. Irradiation of anthralin in dimethylsulfoxide, where the AN- form is present in substantial quantity, generates superoxide and solvent derived radicals but no detectable singlet oxygen. UV-irradiation of 1,8-DHAQ in ethanol and acetonitrile produces both superoxide and singlet oxygen in significant yields. In dimethylsulfoxide, on the other hand, only superoxide and solvent derived radicals are observed. The 1O2 quantum yield for AN- and 1,8-DHAQ in acetonitrile were determined to be 0.14 and 0.88 relative to rose bengal in the same solvent. These findings suggest that the AN photosensitization occurs via Type I and II pathways, is solvent dependent and involves AN- as well as its oxidation product 1,8-DHAQ, which is a more potent generator of both singlet oxygen and superoxide.

Studies on the contact sensitizing activity of dithranol (anthralin) and 10-butyryl dithranol (butantrone)

The contact sensitizing activity of dithranol and butantrone (10-butyryl dithranol) was studied in 3 animal models: the guinea pig maximization test (GPMT), the closed patch test (CPT), and the mouse ear swelling test (MEST) in 2 different mouse strains. In the GPMT, both dithranol and, to a greater extent, butantrone showed sensitizing potential. Because butantrone was less irritant, the concentrations used were 10x higher than those of dithranol. In the CPT, only butantrone was slightly positive. In the MEST, with both CF-1 and Balb/c mice, dithranol caused less swelling of the test ear after challenge than butantrone. According to the evaluation criteria of the MEST, only butantrone caused sensitization in 50% of the CF-1 mice and in 40% of the Balb/c mice. Thus, the GPMT was the only test which indicated the minor contact sensitizing potential of dithranol. On the other hand, the 10-butyryl analogue of dithranol showed undoubtedly stronger contact sensitizing potential than the parent compound in all tests. Therefore, as compared to dithranol, an increased risk of sensitization should be considered.

Formation of DNA adducts in the skin of psoriasis patients, in human skin in organ culture, and in mouse skin and lung following topical application of coal-tar and juniper tar

Preparations of coal-tar and juniper tar (cade oil) that are used in the treatment of psoriasis are known to contain numerous potentially carcinogenic polycyclic aromatic hydrocarbons (PAH). Evidence of covalent binding to DNA by components of these mixtures was sought in a) human skin biopsy samples from 12 psoriasis patients receiving therapy with these agents, b) human skin explants maintained in organ culture and treated topically with the tars, and c) the skin and lungs of mice treated with repeated doses of the formulations following the regimen used in the clinic. DNA was isolated from the human and mouse tissues and digested enzymically to mononucleotides. 32P-Post-labeling analysis revealed the presence of aromatic DNA adducts in the biopsy samples at levels of up to 0.4 fmol total adducts/microgram DNA. Treatment of human skin in organ culture produced similar levels of adducts, while treatment with dithranol, a non-mutagenic therapeutic agent, resulted in chromatograms indistinguishable from those from untreated controls. In mouse skin, coal-tar ointment and juniper tar gave similar DNA adduct levels, with a similar time-course of removal: maximum levels (0.5 fmol/microgram DNA) at 24 h after the final treatment declined rapidly to 0.05 fmol/microgram at 7 d, thereafter declining slowly over the succeeding 25 d. However, while coal-tar ointment produced only very low levels of adducts in mouse lung (less than 0.03 fmol/microgram DNA), juniper tar produced adducts at a high level (0.7 fmol/microgram DNA) that were persistent in this tissue. These results provide direct evidence for the formation of potentially carcinogenic DNA damage in human and mouse tissue by components of these therapeutic tar preparations.

The relevance of secondary radicals in the mode of action of anthralin

The formation of free radicals during the reaction of anthralin analogues with peroxidizing polyunsaturated lipids was monitored by ESR spectroscopy. The biological effect of the different compounds was assessed by their ability to inhibit respiration of cultured human keratinocytes. C(10)-monosubstituted analogues of anthralin exhibited a strong antirespiratory effect and produced a cascade of radicals. Abstraction of the hydrogen atom at C(10) led to the generation of primary radicals which further decomposed into secondary radicals similar to those observed with anthralin itself. 10, 10'-disubstituted analogues of anthralin did not form any paramagnetic species during reaction with peroxidizing lipids while decomposition of a 2,7-disubstituted anthralin derivative under the same conditions resulted in primary, but not secondary radical species. Since both types of disubstituted analogues are devoid of antirespiratory activity we postulate that the antimitochondrial and thus antiproliferative activity of anthralin and its analogues is associated with their capacity to form secondary radicals during their decomposition.

Investigations of anthralin free radicals in model systems and in skin of hairless mice

The antipsoriatic compound anthralin (1.8-dihydroxy-9-anthrone) is converted in skin into several oxidized products, including persistent free radicals that are not well characterized. Anthralin oxidation was investigated by electron spin resonance spectroscopy in a biological system and in a chemical system. Free radical formation in the skin of hairless mice is reduced by the antioxidant tocopherol. The data indicate that tocopherol acts by interfering with free radical formation rather than by scavenging persistent anthralin radicals directly. The skin radicals do not correspond to 10-anthranyl, the initial paramagnetic anthralin oxidation product. Similar radicals obtained in skin are formed by anthralin exposed to ultraviolet light or alkaline solution and by mitochondria and microsomes. The pertinent skin radical is attributed to products derived from anthralin dark structures, the final oxidation products of anthralin. It is suggested that resonance stabilized, paramagnetic polycyclic hydrocarbons are the compounds detected. Their stability and low reactivity indicate a low potential for cutaneous irritation and tumor promotion. Reactive oxygen species, which have been reported to be formed concomitantly during oxidation of anthralin, and the initially formed highly reactive 10-anthranyl radical are more potent candidates for mediating tumor promotion and inflammation.

Anthralin-derived transients--I. The triplet state and the products of its reaction with oxygen in benzene

Direct laser excitation in benzene of 1,8-dihydroxy-9-anthrone (anthralin) does not lead to transient species with lifetimes in the nanosecond time regime or longer. The triplet state has been produced in benzene by pulse radiolysis and characterised in terms of its absorption spectrum (lambda max 560 nm), natural lifetime (11 microseconds), self-quenching properties (kmicrosecond = 2.6 x 10(7) l mol-1 s-1) and triplet energy (234 kJ mol-1). There is no tendency in the non-polar medium for production of either the triplet or ground state in a tautomeric form. The observed triplet state reacts with oxygen with a typical rate constant, 2.2 x 10(9) l mol-1 s-1. The products of this reaction are singlet oxygen (approximately 64%) and the anthralin radical (approximately 14%).

Histologic alterations produced by chrysarobin (1,8-dihydroxy-3-methyl-9-anthrone) in SENCAR mouse skin: relationship to skin tumor promoting activity

Histologic changes induced in SENCAR skin following a single treatment with chrysarobin (1,8-dihydroxy-3-methyl-9-anthrone) exhibited differences in time course from that observed with 12-O-tetradecanoylphorbol-13-acetate (TPA). Although not significantly different, maximum elevations in epidermal thickness, total number of nucleated epidermal cells, and dark basal keratinocytes (DCs) induced by 220 nmol chrysarobin occurred at 96 h after treatment, while those induced by 3.4 nmol TPA occurred at 48 h. Both compounds elicited comparable inflammatory responses. Twice-weekly applications of chrysarobin for 2.5 weeks induced a moderate hyperplasia, increase in total nucleated epidermal cells, and increased DCs at 48 and 96 h after the last treatment, with a higher value for these parameters occurring at 48 h. Interestingly, the magnitude of these changes was similar to that observed after a single application. In contrast, twice-weekly applications of TPA induced a dramatic, potentiated induction of epidermal hyperplasia and DCs. Once-weekly applications of chrysarobin led to a potentiated induction of both hyperplasia and DCs compared to the twice-weekly treatment regimen and also more effectively promoted epidermal papillomas in previously initiated SENCAR mice. Skin sections from mice treated with chrysarobin displayed overt signs of epidermal toxicity including altered basal cell morphology and a decreased number of basal cells per 125 micron of basement membrane. Hyperplasia induced by multiple but not single treatments with chrysarobin and TPA correlated quantitatively with their papilloma promoting activity. In addition, the data suggest that epidermal toxicity may play a role in tumor promotion by anthrones.

Anthralin, a non-phorbol tumor promoter, fails to inhibit metabolic cooperation in mutant human fibroblasts, but inhibits phytohemagglutinin-induced lymphocyte blastogenesis in vitro

Two (among many) of the hypotheses put forward to explain mechanisms of action of tumor promoters are: (1) immunosuppression of the host; and (2) inhibition of intercellular junctional communication. Murine spleen cells were exposed for 30 min to various concentrations of anthralin (1,8-dihydroxy-9-anthrone), a polyphenolic non-phorbol promoter, and 1,8-dihydroxyanthraquinone (1,8-DHAQ), an inactive congener. Phytohemagglutinin (PHA)-induced T cell blastogenesis, an indicator of lymphocyte function, was then assessed in vitro. Exposure to anthralin resulted in a concentration-dependent suppression of lymphocyte proliferation with complete suppression occurring at 1 microM. The inactive congener, 1,8-DHAQ, failed to suppress lectin-induced blastogenesis at concentrations up to 10 microM. Dithiothreitol (DTT), a sulfhydryl (SH) compound, failed to protect against the suppression of lymphocyte function by anthralin. In addition, anthralin failed to inhibit in vitro microtubule assembly, a SH-dependent process, in a crude rat brain extract. Finally, unlike 12-O-tetradecanoylphorbol-13-acetate (TPA), the most potent skin tumor promoter known, anthralin failed to inhibit metabolic cooperation between mutant human fibroblasts as assayed by [14C]citrulline incorporation. In summary, the data suggest that anthralin may act as a tumor promoter by suppressing immune parameters, a property which is shared by the phorbol esters.

Cocarcinogenic and tumor-promoting capabilities of anthralin

Numerous chemicals to which humans are exposed either therapeutically or as a result of living in an industrial environment constitute a potential threat as carcinogens, mutagens, and/or tumor promoters and cocarcinogens. Anthralin, and antipsoriatic agent, acts as a tumor promoter for Balb/c-3T3 mouse embryo cell cultures that were previously exposed to a low dose of either benzo-a-pyrene (BaP), an indirect-acting carcinogen needing metabolic conversion for its carcinogenic action, or beta-propiolactone (BPL), a direct-acting carcinogen which needs no metabolic conversion. As a cocarcinogen, i.e., when exposure of cells to anthralin was simultaneous with exposure to the carcinogen, anthralin enhanced neoplastic transformation only when the carcinogen was BaP. Several explanations are explored. The possibility that cocarcinogens and tumor promotion occur by separate mechanisms is suggested.

Toxicological studies with dithranol and its 10-acyl analogues

The oral LD50 values of an antipsoriatic drug, dithranol, were 1542 mg/kg in NMRI mice and 3216 mg/kg in Wistar rats. Three 10-acyl analogues of dithranol (10-acetyl, 10-propionyl and 10-butyryl dithranol or butantrone) were more toxic both in mice and rats. They were mutagenic only in TA1537 of the five Salmonella typhimurium strains tested. None of them were mutagenic in two Escherichia coli strains. Butantrone was least toxic to test bacteria and had the lowest mutagenic activity on TA1537. In metaphase analysis of in vitro treated human lymphocytes, dithranol, 10-acetyl dithranol and 10-propionyl dithranol produced significant increases in the number of chromosome and chromatid gaps but without a clear dose-response relationship, and without inducing significant breaks. Butantrone did not cause significant increases in gaps or breaks. In the mouse micronucleus test, dithranol and butantrone caused no increases in micronucleated polychromatic or normochromatic erythrocytes, indicating lack of clastogenic activity in vivo at maximum tolerated doses. Hence, dithranol and its 10-acyl analogues have a weak mutagenic activity in vitro. The mutagenic activity of butantrone is lower than that of the other analogues and dithranol.

Effect of application frequency on epidermal ornithine decarboxylase induction by chrysarobin in SENCAR mice

Ornithine decarboxylase (ODC EC 4.1.1.17) induction in mouse epidermis after single or multiple topical applications of chrysarobin differed from that following topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA). Following a single application of 220 nmol chrysarobin, ODC activity began to rise at 24 h reaching a peak at 56 h and returned to normal after 96 h. When 5 separate applications of 220 nmol chrysarobin were applied in multiple application protocols, an alteration in the ODC induction response was observed. With a once per week or twice per week application protocol, ODC was elevated in a multiphasic manner giving multiple peaks of activity after the last application. Interestingly, the magnitude of ODC induction was greater using the once per week, compared to the twice per week, application protocol. Preliminary results indicate that a once per week application protocol is more effective than a twice per week protocol for promoting the development of skin papillomas in SENCAR mice. Thus, the magnitude of the induced ODC response with chrysarobin, although low compared to TPA, correlated with tumor promoting activity.

Simultaneous quantitation of 1,8,9-anthracenetriol, 1,8-dihydroxy-9,10-anthraquinone, and 1,8,1',8'-tetrahydroxy-10,10'-dianthrone by reversed-phase high-performance liquid chromatography

A sensitive and specific reversed-phase high-performance liquid chromatographic method was developed for the simultaneous analysis of anthralin (1,8,9-anthracenetriol) and its known degradation products: quinone (1,8-dihydroxy-9,10-anthraquinone) and dimer (1,8,1',8'-tetrahydroxy-10,10'-dianthrone). The method provides for rapid and simple quantitation of nanogram amounts of the three compounds. The molar absorptivities for anthralin in different solvents and solvent systems, including the mobile phase, are presented.

Induction of intestinal tumours in rats by chrysazin

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Effect of 1,8-dihydroxy-9-anthrone (anthralin) on rat hepatic ornithine decarboxylase activity in vivo

Intraperitoneal injection of the non-phorbol tumor promoter anthralin (1,8-dihydroxy-9-anthrone) in male rats resulted in an increase of hepatic ornithine decarboxylase (ODC) activity. Maximal activity was observed 8 h after promoter administration reaching levels about 30 times over control. The kinetics of anthralin dependent ODC induction differed markedly from that by either 12-O-tetradecanoylphorbol-13-acetate (TPA) or phenobarbital (PB) (Bisschop et al., Carcinogenesis 2 (1981) 1282). With anthralin a slow decrease of ODC back to control level is observed approximately within 22 h. In contrast, ODC induction mediated by other tumor promoters like TPA and PB decreased to control levels within 4-6 hours. Administration of a second dose of anthralin 8 h after the first dose prevented the activity decrease as normally observed after a single dose of a tumor promoter. This effect lasted at least 10 h. ODC activity induction occurred in a dose-dependent manner being linear from 10-2000 micrograms anthralin/kg body wt. Pretreatment of the animals either with actinomycin D or with cycloheximide completely blocked anthralin mediated ODC induction suggesting that de novo ODC-mRNA synthesis and subsequent translation is involved in this process.

Role of oxygen radicals in tumor promotion

Tumor promoters provoke the elaboration of oxygen radicals by direct chemical generation and through the indirect activation or alteration of cellular sources including membrane oxidases, peroxisomes, and electron transport chains in mitochondria and endoplasmic reticulum. Although direct measurement of amplified oxygen radical production in response to tumor promoters in target tissues remains problematic, studies with scavengers of reactive oxygen species demonstrate inhibition of biochemical and biological sequelae of tumor promoter exposure and provide strong presumptive evidence for oxygen radical involvement in this late stage of carcinogenesis. The critical macromolecular targets for these oxygen radicals remain undefined; however, they may include lipids, DNA, DNA repair systems, and other enzymes.

Anthralin: historical and current perspectives

Anthralin was first synthesized in 1916. Earlier, a natural product, chrysarobin, originally derived from the South American araroba tree, had been used to treat psoriasis. Anthralin was first used in Germany, and later in the Ingram regimen in Britain, but it has never been popular with American dermatologists. This is probably due to the side effects of staining and irritation of the skin. Attempts to reduce these using low concentration, short contact therapy, and concomitant steroid therapy, have been only partially successful. It may be that better instruction of patients and physicians will lead to wider use of this effective topical agent for the treatment of psoriasis. The mode of action of anthralin is thought to be either through its effect on deoxyribonucleic acid (DNA), probably mitochondrial DNA, which reduces cell turnover, or through its effects on various enzyme systems, including those of polyamine synthesis and respiration. The aims of this review are to discuss historical aspects of anthralin and to update its chemistry, pharmacology, and clinical usage.

Recent advances in the treatment of psoriasis

Because psoriasis is a disease of unknown etiology, all treatments are based on empirical experience and diverse scientific theories. Although there is no present cure for psoriasis, many forms of therapy are effective in control of the disorder. These range from topical medications such as tar, anthralin, corticosteroids; phototherapy and photochemotherapy; systemic medication, including cytotoxic agents; and vitamin A analogues or retinoids. This report focuses on modifications of existing therapies based on advances in basic science knowledge and technology, combination therapies, as well as new therapeutic agents and new approaches to the treatment of psoriasis.

Anthralin: chemical instability and glucose-6-phosphate dehydrogenase inhibition

The chemical stability of the antipsoriatic drug, anthralin (1,8-dihydroxy-9-anthrone), in solution has been studied using high-performance liquid chromatographic analysis. The time course for decomposition in solution has been correlated with that of the inhibition of glucose-6-phosphate dehydrogenase, one of the most widely documented biochemical properties associated with anthralin. Solutions of anthralin in aqueous buffer (37 degrees, pH 7.5, under light protection) completely within 4 hr giving the 10,10'-dimer (40%), no detectable 1,8-dihydroxy-9,10-anthraquinone, and a greatly increased potency of inhibition of glucose-6-phosphate dehydrogenase. This increased inhibitory potency could not be explained by formation of the dimer which, like anthralin and its quinone, were shown to be only weak inhibitors of the enzyme. In acetone solution exposed to light and air, anthralin decomposed completely within 4 days, in part via the dimer as intermediate. The final solution had the characteristic color of anthralin-brown, contained the quinone (20%), and like decomposed aqueous solutions of anthralin, completely inhibited glucose-6-phosphate dehydrogenase. The results show that neither anthralin, nor either of its two identified decomposition products, is the potent toxic species against glucose-6-phosphate dehydrogenase.

The effect of topical drugs on mouse ear epidermal transglutaminase activity

The response of mouse ear epidermal transglutaminase to single applications of anthralin, retinoic acid (both 59 micrograms/ear) or fluocinolone acetonide (2 micrograms/ear) was determined. Anthralin and retinoic acid caused inflammation and accumulation of epidermal protein and DNA, whereas fluocinolone acetonide resulted in ear thinning and decreased epidermal protein and DNA. Treatment with either anthralin or retinoic acid caused increases in absolute amounts of epidermal transglutaminase activity/ear. Anthralin increased this parameter 70-100% above acetone-treated controls from 48 hr through 7 days. Retinoic acid-treated ears showed a slower initial increase but peaked at 4 times control level by 96 hr before returning to normal at 7 days. Fluocinolone acetonide treatment had no effect on this parameter. The specific activity of epidermal transglutaminase (total epidermal transglutaminase/total soluble epidermal protein) was decreased by retinoic acid treatment; was maintained at normal levels by anthralin (except for the 7-day point where it decreased 50%); and was dramatically stimulated by fluocinolone acetonide. In the latter case, specific activity was more than 5 x control by 96 hr and still near this level at 7 days. Epidermal transglutaminase activity is a marker of differentiation, and protein and DNA accumulation an indication of growth. Thus, at the doses studied, retinoic acid favors growth over differentiation, anthralin maintains a normal to near normal ratio of growth to differentiation, and fluocinolone acetonide strongly favors differentiation over growth.

Inhibition of DNA replication and repair by anthralin or danthron in cultured human cells

The comparative effects of the tumor promoter anthralin and its analog, danthron, on semiconservative DNA replication and DNA repair synthesis were studied in cultured human cells. Bromodeoxyuridine was used as density label together with 3H-thymidine to distinguish replication from repair synthesis in isopycnic CsCl gradients. Anthralin at 1.1 microgram inhibited replication in T98G cells by 50%. In cells treated with 0.4 or 1.3 microM anthralin and additive effect was observed on the inhibition of replication by ultraviolet light (254 nm). In cells irradiated with 20 J/m2, 2.3 microM anthralin was required to inhibit repair synthesis by 50%. Thus there was no selective inhibitory effect of anthralin on repair synthesis. Danthron exhibited no detectable effect on either semiconservative replication or repair synthesis at concentrations below about 5.0 microM. Neither compound stimulated repair synthesis in the absence of ultraviolet irradiation. Thus, anthralin and danthron do not appear to react with DNA to form adducts that are subject to excision repair. Although both compounds appear to intercalate into supercoiled DNA in vitro to a limited extent, the degree of unwinding introduced by the respective drugs does not correlate with their relative effects on DNA synthesis in vivo. Therefore the inhibitory effect of anthralin on DNA replication and repair synthesis in T98G cells does not appear to result from the direct interaction of the drug with DNA.

Metabolism of [14C]emodin in the rat

1. Absorption, excretion, tissue distribution and metabolism of the anthraquinone [14C]emodin was studied after a single oral administration (approx. 50 mg/kg) to rats. 2. Urinary excretion amounted to 18(+/- 5)% dose in 24 h and to 22(+/- 6)% in 72 h. 3. Metabolites found in pooled urine (0-72 h) were mostly free anthraquinones (emodin and emodic acid, 16% dose); 3% was conjugated and 3% was non-extractable radioactivity. 4. In 24 h, 48 +/- 11% and in 120 h, 68 +/- 8% dose was excreted in the faeces, mostly in the free anthraquinone form. 5. In two cannulated rats biliary excretion reached a maximum at approx. 6 h and amounted to 49% dose within 15 h; 70% of biliary activity was in the form of conjugated emodin. 6. The content of radioactivity in most organs decreased significantly between 3 and 5 days. In kidneys, however, the 14C activity was still equiv. to 4.33 p.p.m. emodin after five days. Mesenterium and fat tissue showed increasing 14C activity from 72 to 120 h.

A review of the genetic effects of naturally occurring flavonoids, anthraquinones and related compounds

Two classes of common phenolic plant pigments, the anthraquinones and the flavonols, contain many members mutagenic in the Salmonella/mammalian microsome assay. Several reports on the mutagenicity or other genetic or "carcinogenic" effects of these compounds have appeared in the literature or have been presented at various scientific meetings. The object of this review paper is to assess the present state of knowledge with respect to the genetic toxicity of these agents and their dietary intake and metabolic fate in man. Such information is necessary for formulating an assessment of genetic or carcinogenic risk to man posed by these agents.

Separation, identification, and quantitation of anthralin and its decomposition products

Anthralin and its decomposition products were separated by both column chromatographic and TLC techniques. Two decomposition products were characterized by TLC, melting-point data, and UV and IR spectroscopy. Pure anthralin and its decomposition products also were determined quantitatively.

Mutagenesis by 9,10-anthraquinone derivatives and related compounds in Salmonella typhimurium

Ninety 9,10-anthraquinone (AQ) derivatives and related anthracene derivatives were screened for mutagenicity with five Salmonella typhimurium tester strains with and without mammalian microsomal activation. About 35% of the compounds tested are considered to be mutagenic. Three patterns of mutagenesis were apparent. (1)Direct frameshift mutagenesis by certain AQ compounds bearing free hydroxyl groups. The most potent were anthragallol (1,2,3-trihydroxy-AQ), purpurin (1,2,4-trihydroxy-AQ) and anthraufin (1,5-dihydroxy-AQ). Some hydroxy-AQ compounds exhibited activation by mammalian microsomal preparations, particularly at lower concentrations, and the majority of mutagenic hydroxy-AQs appeared to revert strain TA1537 (his 3076) specifically.(2)Frameshift mutagenesis by certain AQ compounds with primary amino and, in a few cases, with secondary amino groups. Mammalian microsomes invariably potentiated frameshift mutagenesis, and activity with strain TA100 (sensitive to base pair substitution) is seen in a few cases, e.g. 1,2-diamino-AQ. (3)AQ compounds with one or more nitro groups. These derivatives exhibit the least specificity with regard to tester strain reverted and to microsomal activation. All seven nitro-AQ's tested were mutagenic. In those compounds with mixed "mutagenic" functional groups, the type of mutagenesis observed is usually N02 greater than 0H greater than NH2. AQs bearing halogens, sulfonate or alkyl groups were non-mutagenic, as were AQs substituted solely with secondary amines.