Recent advances in psoralen phototoxicity mechanism

Phototoxicity─Medicinal Chemistry Strategies for Risk Mitigation in Drug Discovery

Phototoxicity is a common safety concern encountered by project teams in pharmaceutical research and has the potential to stop progression of an otherwise promising candidate molecule. This perspective aims to provide an overview of the approaches toward mitigation of phototoxicity that medicinal chemists have taken during the lead optimization phase in the context of regulatory standards for photosafety evaluation. Various strategies are laid out based on available literature examples in order to highlight how structural modification can be utilized toward successful mitigation of a phototoxicity liability. A proposed flowchart is presented as a guidance tool to be used by the practicing medicinal chemist when facing a phototoxicity risk. The description of available tools to consider in the drug design process will include an overview of the evolution of in silico methods and their application as well as structure alerts for consideration as potential phototoxicophores.

Psoralens activate and photosensitize Transient Receptor Potential channels Ankyrin type 1 (TRPA1) and Vanilloid type 1 (TRPV1)

BACKGROUND

PUVA (psoralen UVA) therapy is used to treat a variety of skin conditions, such as vitiligo psoriasis, eczema and mycosis fungoides, but it is frequently accompanied by phototoxicity leading to burning pain, itch and erythema.

METHODS

We used a combination of calcium and reactive oxygen species (ROS) imaging, patch clamp and neuropeptide release measurement to investigate whether certain ion channels involved in pain and itch signalling could be responsible for these adverese effects of PUVA.

RESULTS

Clinically used psoralen derivatives 8-methoxypsoralen (8-MOP) and 5-methoxypsoralen at physiologically relevant concentrations were able to activate and photosensitize two recombinant thermoTRP (temperature-gated Transient Receptor Potential) ion channels, TRPA1 (Transient Receptor Potential Ankyrin type 1) and TRPV1 (Transient Receptor Potential Vanilloid type 1). 8-MOP enhanced ROS production by UVA light, and the effect of 8-MOP on TRPA1 could be abolished by the antioxidant N-acetyl cysteine and by removal of critical cysteine residues from the N-terminus domain of the channel. Natively expressed mouse TRPA1 and TRPV1 both contribute to photosensitization of cultured primary afferent neurons by 8-MOP, while direct neuronal activation by this psoralen-derivative is mainly dependent on TRPV1. Both TRPA1 and TRPV1 are to a large extent involved in controlling 8-MOP-induced neuropeptide release from mouse trachea.

CONCLUSIONS

Taken together our results provide a better understanding of the phototoxicity reported by PUVA patients and indicate a possible therapeutic approach to alleviate the adverse effects associated with this therapy.

SIGNIFICANCE

Our work provides evidence for the involvement of thermoTRP channels TRPA1 and TRPV1 in the activation and photosensitization of peripheral nociceptors during PUVA (Psoralen UVA) therapy.

Phototoxicity of 7-oxycoumarins with keratinocytes in culture

Seventy-one 7-oxycoumarins, 66 synthesized and 5 commercially sourced, were tested for their ability to inhibit growth in murine PAM212 keratinocytes. Forty-nine compounds from the library demonstrated light-induced lethality. None was toxic in the absence of UVA light. Structure-activity correlations indicate that the ability of the compounds to inhibit cell growth was dependent not only on their physiochemical characteristics, but also on their ability to absorb UVA light. Relative lipophilicity was an important factor as was electron density in the pyrone ring. Coumarins with electron withdrawing moieties - cyano and fluoro at C₃ - were considerably less active while those with bromines or iodine at that location displayed enhanced activity. Coumarins that were found to inhibit keratinocyte growth were also tested for photo-induced DNA plasmid nicking. A concentration-dependent alteration in migration on neutral gels caused by nicking was observed.

In Vitro Alternatives and Phototoxicity Testing. II. Effects of Reactive Oxygen Species in In Vitro Phototoxicity Assays

The effects of reactive oxygen species (including singlet oxygen) in two in vitro phototoxicity assays — the 3T3 cell neutral red uptake phototoxicity (3T3 NRU PT) assay and the photohaemolysis assay — were assessed by using scavengers. Fifteen test substances, which had previously been shown to be phototoxic in vitro, were assessed. Eleven of these produced singlet oxygen. The major factor in the photodynamic reaction of bithionol was thought to be a Type I reaction, because bithionol did not produce singlet oxygen and did not react to histidine. Acridine was regarded as a Type II substance, because of the evident effect of histidine as a scavenger. 8-Methoxypsoralen and 5-methoxypsoralen produced singlet oxygen, but their actions were not affected by the scavengers. In this study, we confirmed that reactive oxygen species have great effects in in vitro phototoxicity, and that the 3T3 NRU PT assay can be used to detect effects which are thought to be the direct reaction of an excited photosensitiser to biological substrates (Type III reaction), for example, 8-methoxypsoralen. Therefore, we suggest that photohaemolysis and phototoxicity could be used to evaluate the photodynamic mechanisms of photosensitising chemicals.

4,6,4'-trimethylangelicin shows high anti-proliferative activity on DU145 cells under both UVA and blue light

OBJECTIVES

Furocoumarins (psoralens and angelicins) have been already used under ultraviolet A light (UVA) for the treatment of skin diseases and cutaneous T-cell lymphoma. Besides their high anti-proliferative activity, some severe long-term side effects have been observed, for example genotoxicity and mutagenicity, likely strictly related to the formation of crosslinks. It has been demonstrated that blue light (BL) activation of 8-methoxypsoralen, an FDA-approved drug, leads to less mutagenic monoadducts in the DNA. So far, in this work the less toxic and more penetrating BL is proposed to activate 4,6,4'-trimethylangelicin (TMA), an already known UVA photoactivatable compound.

MATERIALS AND METHODS

Photocleavage, crosslink formation and oxidative damage were detected in pBR322 plasmid DNA treated with 300.0 μmol/L TMA activated with various exposures of BL. Anti-proliferative activity, reactive oxygen species (ROS) formation and activation status of some signalling pathways involved in cell growth and apoptosis were verified on DU145 cells treated with 5.0 μmol/L TMA plus 2.0 J/cm² of BL.

RESULTS

Under BL-TMA, no mutagenic crosslinks, no photocleavage and neither photooxidative lesions were detected on isolated plasmid DNA. TMA showed high anti-proliferative activity on DU145 cells through induction of apoptosis. Besides ROS generation, the proapoptotic effect seemed to be related to activation of p38 and inhibition of p44/42 phosphorylation. Interestingly, the decrease in nuclear β-catenin was coupled with a significant dropping of CD44-positive cells.

CONCLUSION

Overall, our results indicate that TMA can be activated by BL and may be considered for targeted phototherapy of prostate cancer lesions.

Phototherapy and Combination Therapies for Vitiligo

Vitiligo is a disease characterized by disappearance of melanocytes from the skin. It can negatively influence the physical appearance of affected individuals, and may profoundly affect a person's psychosocial function and quality of life. Therefore, vitiligo should not be considered as merely a condition that affects a patient's appearance, but needs to be actively treated in patients who seek medical help. Phototherapy has been used as the main treatment modality for patients with vitiligo. Different forms of phototherapy for vitiligo include broadband UVB, narrowband UVB, excimer light and excimer laser, and psoralen plus UVA.

Phosphor for phototherapy: Review on psoriasis

We review developments in the field of phototherapy in terms of the treatment wavelength, dosimetry and phosphor used for different dermatoses. We attempt to categorize skin lesions and diseases by morphology, focusing on conditions that can be treated using phototherapy and photochemotherapy. Recent research and review articles are studied, the treatments explained and information on phototherapy that is applicable to psoriasis and other diseases is tabulated. The clinical features, epidemiology, epitalogy and various types of psoriasis, together with the therapies available to treat them are reported. Needs-based research has been carried out on narrow and broad band UVB wavelength-emitting phosphors and psoralen combined with UVA (PUVA) depending upon the disease undergoing treatment. Somewhat detailed descriptions of the different types of therapies used in the treatment of psoriasis are given. Phototherapy is shown to be a good therapeutic option for various types of skin diseases. The use of natural therapy has diminished as more people move towards artificial phototherapy like narrow band UVB, broad band UVB, PUVA and targeted phototherapy. The main advantages of these treatments are that they are safe and reduce erythema following treatment. Regarding safety issue the targated phototherapy pay more attention towards researcher.

Antiproliferative activity of 8-methoxypsoralen on DU145 prostate cancer cells under UVA and blue light

The use of photoactivatable 8-methoxypsoralen (8-MOP) as potential focal treatment towards prostate cancer cells is proposed here.

Phototherapy and photochemotherapy for psoriasis

Phototherapy is a first-line option for the treatment of moderate to severe psoriasis. Systematic reviews indicate near comparable efficacy of the different forms of phototherapy. Localized phototherapy can be an adjunctive treatment of recalcitrant plaques during systemic treatment of psoriasis. More than 200 psoralen-UV-A therapy treatment sessions is associated with an increased risk of keratinocytic cancers, whereas no increased risk has been demonstrated for narrow-band UV-B therapy. The mechanism of action of phototherapy in psoriasis is via inhibition of keratinocyte proliferation; induction of apoptosis in keratinocytes, dendritic, and T cells; and inhibition of Th1 and Th17 pathways, but activation of Th2.

Synthesis, reactions and biological activities of furochromones: a review

Furochromone derivatives are important synthetic targets which showed a myriad of interesting biological activities. Ammi visnaga (Umbelliferae) is the most famous source of these derivatives, which has been used in folk medicine for millennia targeting different ailments. Since the isolation of furochromone derivatives, different synthetic methodologies were developed for their preparation. Despite the recent interesting findings on this class of compounds, the chemical literatures lack a comprehensive summary on the synthetic methodologies and biological activities of furochromone derivatives. This review highlights recent advances in furochromones chemistry by discussing different synthetic procedures developed for the preparation of naturally occurring derivatives as well as other unique derivatives which showed promising biological activities. It also sheds light on the most common reactions of furochromone derivatives and the utilization of these derivatives as the blocks for many biologically active compounds.

Modulation of the UVB-induced lethality by furocoumarins in Staphylococcus aureus

Furocumarins (FCs) are photoactive compounds capable of binding to DNA, and once excited by UVA light (∼365nm), they form photoadducts which can lead to mutagenicity and lethality. However, the biological effects of FCs combined with UVB light (312nm) is still little investigated. In the present study, the lethal effect of UVB light alone and combined with different concentrations of 8-methoxypsoralen (8-MOP), 4,5',8-trimethylpsoralen (TMP) and 3-carbethoxypsoralen (3-CPs) was evaluated in a strain of Staphylococcus aureus. 8-MOP-UVB and TMP-UVB were more effective in inducing lethality compared to UVB alone, indicating that these FCs act as photosensitizing agents for UVB. The increase in concentration of 8-MOP resulted in a greater mortality. On the contrary, a decrease in mortality was found with an increase in TMP concentration. 3-CPs protected bacteria against damage induced by UVB, which can be attributed to the inhibition of cyclobutyl pyrimidine dimer formation. The different modulatory effects on lethality induced by UVB shown by the FCs tested could be related to differences in the specificity of each compound for particular nucleotide sequences, as well as other chemical characteristics of each molecule could influence the number and types of adducts formed, contributing to the photosensitizing or photoprotective effects observed.

Molecular Mechanisms of UV-Induced Apoptosis and Its Effects on Skin Residential Cells: The Implication in UV-Based Phototherapy

The human skin is an integral system that acts as a physical and immunological barrier to outside pathogens, toxicants, and harmful irradiations. Environmental ultraviolet rays (UV) from the sun might potentially play a more active role in regulating several important biological responses in the context of global warming. UV rays first encounter the uppermost epidermal keratinocytes causing apoptosis. The molecular mechanisms of UV-induced apoptosis of keratinocytes include direct DNA damage (intrinsic), clustering of death receptors on the cell surface (extrinsic), and generation of ROS. When apoptotic keratinocytes are processed by adjacent immature Langerhans cells (LCs), the inappropriately activated Langerhans cells could result in immunosuppression. Furthermore, UV can deplete LCs in the epidermis and impair their migratory capacity, leading to their accumulation in the dermis. Intriguingly, receptor activator of NF-κB (RANK) activation of LCs by UV can induce the pro-survival and anti-apoptotic signals due to the upregulation of Bcl-xL, leading to the generation of regulatory T cells. Meanwhile, a physiological dosage of UV can also enhance melanocyte survival and melanogenesis. Analogous to its effect in keratinocytes, a therapeutic dosage of UV can induce cell cycle arrest, activate antioxidant and DNA repair enzymes, and induce apoptosis through translocation of the Bcl-2 family proteins in melanocytes to ensure genomic integrity and survival of melanocytes. Furthermore, UV can elicit the synthesis of vitamin D, an important molecule in calcium homeostasis of various types of skin cells contributing to DNA repair and immunomodulation. Taken together, the above-mentioned effects of UV on apoptosis and its related biological effects such as proliferation inhibition, melanin synthesis, and immunomodulations on skin residential cells have provided an integrated biochemical and molecular biological basis for phototherapy that has been widely used in the treatment of many dermatological diseases.

Currentaspects of psoriasis phototherapy

The review covers current aspects of ultraviolet therapy for patients suffering from psoriasis. It describes mechanisms of action as well as early and remote side effects of the current phototherapy methods. The review also presents data from literature about the risk of their cancerogenicity. It also discusses approaches to the optimization of phototherapy in view of risks and benefits for the patient.

Slt2 (Mpk1) MAP kinase is involved in the response of Saccharomyces cerevisiae to 8-methoxypsoralen plus UVA

The bifunctional furocoumarin 8-methoxypsoralen (8-MOP) is a well established drug in the photochemotherapy of psoriasis and other skin diseases. In eukaryotic cells, this compound intercalates into DNA and undergoes photocycloaddition with pyrimidines to form monoadducts and interstrand crosslinks initiating a cascade of events leading to cytotoxic, mutagenic and carcinogenic responses. In yeast cells, exposure to 8-MOP plus UVA induces transcription of a large set of genes, and cellular reaction is different from an overall DNA damage response and specific to 8-MOP/UVA [M. Dardalhon, W. Lin, A. Nicolas, D. Averbeck, Specific transcriptional responses induced by 8-methoxypsoralen and UVA in yeast, FEMS Yeast Res. 7 (2007) 866-878]. To further define the relationship between induced genes and genotoxic consequences after 8-MOP/UVA treatment, the survival responses of mutants deleted for genes that are specifically induced by 8-MOP plus UVA were analysed in terms of survival. Six mutants deleted for RAD51, RAD54, DUN1, DIN7, already known to be implicated in DNA damage responses, and for SLT2/MPK1 and PDE2 involved in cell wall stress responses, were found sensitive to 8-MOP plus UVA treatment. Further characterization of slt2 mutant provides evidence for the existence of an 8-MOP/UVA response in yeast in which the yeast Slt2 MAPK pathway is implicated. Activation by 8-MOP plus UVA of this MAP kinase previously observed at the transcriptional level is now confirmed at the protein level. In addition to sensitivity to 8-MOP/UVA, yeast cells lacking SLT2 show reduced survival after 3-carbethoxypsoralen plus UVA and 1,6-dioxapyrene plus UVA. Osmotic support could suppress the sensitivities to these genotoxic agents, suggesting that these sensitivities are related to cell integrity defects and/or cell wall defects.

A theoretical insight into the photophysics of psoralen

Psoralen photophysics has been studied on quantum chemistry grounds using the multiconfigurational second-order perturbation method CASPT2. Absorption and emission spectra of the system have been rationalized by computing the energies and properties of the low-lying singlet and triplet excited states. The S1 pipi* state has been determined to be responsible of the lowest absorption and fluorescence bands and to initially carry the population in the photophysical processes related to the phototherapeutic properties of psoralen derivatives. The low-lying T1 pipi* state is, on the other hand, protagonist of the phosphorescence, and its prevalent role in the reactivity of psoralen is suggested to be related to the elongation of the pyrone ring C3-C4 bond, where the spin density is distributed on both carbon atoms. Analysis of energy gaps and spin-orbit coupling elements indicates that the efficient photophysical process leading to the population of the lowest triplet state does not take place at the Franck-Condon region but along the S1 relaxation path.

Specific transcriptional responses induced by 8-methoxypsoralen and UVA in yeast

Treatment of eukaryotic cells with 8-methoxypsoralen plus UVA irradiation (8-MOP/UVA) induces pyrimidine monoadducts and interstrand crosslinks and initiates a cascade of events leading to cytotoxic, mutagenic and carcinogenic responses. Transcriptional activation plays an important part in these responses. Our previous study in Saccharomyces cerevisiae showed that the repair of these lesions involves the transient formation of DNA double-strand breaks and the enhanced expression of landmark DNA damage response genes such as RAD51, RNR2 and DUN1, as well as the Mec1/Rad53 kinase signaling cascade. We have now used DNA microarrays to examine genome-wide transcriptional changes produced after induction of 8-MOP/UVA photolesions. We found that 128 genes were strongly induced and 29 genes strongly repressed. Modifications in gene expression concern numerous biological processes. Compared to other genotoxic treatments, c. 42% of the response genes were specific to 8-MOP/UVA treatment. In addition to common DNA damage response genes and genes induced by environmental stresses, a large fraction of 8-MOP/UVA response genes correspond to membrane-related functions.

Antigenotoxic effects of three essential oils in diploid yeast (Saccharomyces cerevisiae) after treatments with UVC radiation, 8-MOP plus UVA and MMS

Essential oils (EOs) extracted from medicinal plants such as Origanum compactum, Artemisia herba alba and Cinnamomum camphora are known for their beneficial effects in humans. The present study was undertaken to investigate their possible antigenotoxic effects in an eukaryotic cell system, the yeast Saccharomyces cerevisiae. The EOs alone showed some cytotoxicity and cytoplasmic petite mutations, i.e. mitochondrial damage, but they were unable to induce nuclear genetic events. In combination with exposures to nuclear mutagens such as 254-nm UVC radiation, 8-methoxypsoralen (8-MOP) plus UVA radiation and methylmethane sulfonate (MMS), treatments with these EOs produced a striking increase in the amount of cytoplasmic petite mutations but caused a significant reduction in revertants and mitotic gene convertants induced among survivors of the diploid tester strain D7. In a corresponding rho0 strain, the level of nuclear genetic events induced by the nuclear mutagens UVC and 8-MOP plus UVA resulted in the same reduced level as the combined treatments with the EOs. This clearly suggests a close relationship between the enhancement of cytoplasmic petites (mitochondrial damage) in the presence of the EOs and the reduction of nuclear genetic events induced by UVC or 8-MOP plus UVA. After MMS plus EO treatment, induction of these latter events was comparable at least per surviving fraction in wildtype and rho0 cells, and apparently less dependent on cytoplasmic petite induction. Combined treatments with MMS and EOs clearly triggered switching towards late apoptosis/necrosis indicating an involvement of this phenomenon in EO-induced cell killing and concomitant decreases in nuclear genetic events. After UVC and 8-MOP plus UVA plus EO treatments, little apoptosis and necrosis were observed. The antigenotoxic effects of the EOs appeared to be predominantly linked to the induction of mitochondrial dysfunction.

Photoreaction of skin-sensitizing trimethyl psoralen with lipid membrane models

The concerted photoreaction between trimethyl psoralen (TMP) and isomeric model compounds of oleic acid methyl ester (OAME) and eadilic acid methyl ester (EAME) are explored using density functional theory. The S(1) surfaces all reveal large barriers (25-31 kcal/mol) to reach the decay channels, whereas the S(2) surfaces differ considerably between the furan and pyrone side adducts. For the pyrone side adducts, a small barrier to reach the intersection between the S(1) and S(2) states is found, followed by a small second barrier on the S(1) surface to the low-lying decay channel. For the furan-side adducts, no such intersection between S(1) and S(2) is seen, which thus prevents these products from being formed in high yields. The photoinduced cycloaddition is more favorable between OAME and the pyrone side double bond of TMP than for any of the other systems, which agrees with the experimental findings that this is formed in the highest yield. The computed UV absorption spectra of TMP and the TMP(pyrone)-OAME cycloadduct agree well with the experimental spectra.

Assignment of the 1H and 13C NMR signals of some benzofurocoumarins

The complete 1H and 13C NMR assignment of four 6,7-benzo-fused furocoumarins (1-4) and three 3,4-benzo-fused furocoumarins (5-7) has been performed using 1D and 2D NMR techniques, including COSY, HMQC and HMBC experiments.

DNA targeted UVA photosensitization: characterization of an extremely photopotent iodinated minor groove binding DNA ligand

Previous studies have described UVA-induced DNA strand breakage at the binding sites of iodinated DNA minor groove binding bisbenzimidazoles. The DNA breakage, presumably mediated by the carbon-centred ligand radical produced by photodehalogenation, was also shown to be cytotoxic. The earlier studies included a comparison of three ligand isomers, designated ortho-, meta- and para-iodoHoechst, and the efficiency of photo-induction of strand breaks in plasmid DNA proved to be much higher for the ortho-isomer. We have now extended the comparison of the three isomers with respect to photo-induced cytotoxicity in K562 cells. Although the relationship between the extent of nuclear uptake and the concentration of the ligand in the medium was similar for the three isomers, assay of in situ dehalogenation in drug-treated cells indicated that the apparent cross-section for dehalogenation of the ortho-isomer was greater than 5-fold higher than that for the meta- and para-isomers. Also, analysis of clonogenic survival data showed that the dehalogenation event associated with ortho-iodoHoechst was a more efficient mediator of UVA-induced cytotoxicity in K562 cells than that for meta- or para-iodoHoechst. The number of dehalogenation events associated with 50% cell-kill for ortho-iodoHoechst (1.23+/-0.04 x 10(4)) was less than that for the para- (3.92+/-0.29 x 10(4)) and meta- (11.6+/-0.90 x 10(4)) isomers. Thus it is concluded that the photopotency of ortho-iodoHoechst, which is an important feature in the context of its potential use in clinical phototherapy, is due not only to more efficient UVA-mediated dehalogenation of the ligand, but also to greater cytotoxic potency per dehalogenation event.

Vibronic absorption, fluorescence, and phosphorescence spectra of psoralen: a quantum chemical investigation

Excited state potential energy hypersurfaces of 7H-furo[3,2-g][1]benzopyran-7-one (psoralen) have been explored employing (time-dependent) Kohn-Sham density functional theory. At selected points, we have determined electronic excitation energies and electric dipole (transition) moments utilizing a combined density functional/multireference configuration interaction method. Spin-orbit coupling has been taken into account employing an efficient, non-empirical spin-orbit mean-field Hamiltonian. Franck-Condon factors have been computed for vibrational modes with large displacements in the respective Dushinsky transformations. The simulated band spectra closely resemble experimental band shapes and thus validate the theoretically determined nuclear structures at the S(0), S(1), and T(1) minima. In the S(1) (pi(HOMO)-->pi*(LUMO)) state, the lactone bond of the pyrone ring is significantly elongated. From excited vibrational levels of the S(1) state a conical intersection between a (pi-->sigma*) excited state and the electronic ground state may be energetically accessible. Fast non-radiative decay via this relaxation pathway could explain the low fluorescence quantum yield of psoralen. The T(1) (pi(HOMO-1)-->pi*(LUMO)) exhibits a diradicaloid electronic structure with a broken C(5)-C(6) double bond in the pyrone ring. A variational multireference spin-orbit configuration interaction procedure yields a phosphorescence lifetime of 3 s, in excellent agreement with experimental estimates.

Protective effect of furocoumarins against 254-nm ultraviolet in Staphylococcus aureus

For Staphylococcus aureus, pretreatment with furocoumarins (FCs) protect cells against killing by far ultraviolet light (FUV; approximately 254 nm). This protective effect was evident in the repair-proficient, parental strain as well as in the repair-deficient variants in the following order of efficacy: 4,5'',8-trimethylpsoralen << 8-methoxypsoralen congruent with angelicin < 3-carbethoxypsoralen. The extent of protection was greater in the parental strain, indicating that despite the protective effect, a certain number of lethal lesions are nevertheless produced, which would be repaired with greater efficiency in such a strain than in the repair-deficient ones. This protective effect could be attribute to the inhibition of the formation of cyclobutyl pyrimidine dimers. Although the energy-transfer concept could explain the inhibition of pyrimidine dimer formation, and thus the protective effect of FC against FUV, we cannot rule out the possibility that the differences in degree of protection afforded by the FC employed here are related to a subtle and complex combination of effects.

HPLC comparison of supercritical fluid extraction and solvent extraction of coumarins from the peel of Citrus maxima fruit

The efficiency of carbon dioxide supercritical fluid extraction (SFE) of the biologically active compounds imperatorin, meranzin and meranzin hydrate from the fruit peel of Citrus maxima Merr. has been compared with that of solvent extraction with acetone. Under the best SFE conditions tested for the three coumarins, which involved extraction at 50 degrees C and 27.6 MPa, the extractive efficiencies were 84, 76 and 18% for imperatorin, meranzin and meranzin hydrate, respectively. The presence of modifiers significantly affected the extraction efficiency: the highest extraction efficiency of the three coumarins was obtained with ethanol as modifier.

Light-dependent mutagenesis by benzo[a]pyrene is mediated via oxidative DNA damage

Benzo[a]pyrene (B[a]P) is an environmental carcinogenic polycyclic aromatic hydrocarbon (PAH). Mammalian enzymes such as cytochrome P-450s and epoxide hydrase convert B[a]P to reactive metabolites that can covalently bind to DNA. However, some carcinogenic compounds that normally require metabolic activation can also be directly photoactivated to mutagens. To examine whether B[a]P is directly mutagenic in the presence of light, we exposed Salmonella typhimurium strains with different DNA repair capacities to B[a]P and white fluorescent light at wavelengths of 370-750 nm. B[a]P plus light significantly enhanced the number of His+ revertants. Mutagenesis was completely light-dependent and required no exogenous metabolic activation. The order of mutability of strains with different DNA repair capacities was strain YG3001 (uvrB, mutMST) >> strain TA1535 (uvrB) > strain YG3002 (mutMST) > strain TA1975. The uvrB gene product is involved in the excision repair of bulky DNA adducts, and the mutMST gene encodes 8-oxoguanine (8-oxoG) DNA glycosylase, which removes 8-oxoG from DNA. Introduction of a plasmid carrying the mOgg1 gene that is the mouse counterpart of mutMST substantially reduced the light-mediated mutagenicity of B[a]P in strain YG3001. B[a]P plus light induced predominantly G:C --> T:A and G:C --> C:G transversions. We propose that B[a]P can directly induce bulky DNA adducts if light is present, and that the DNA adducts induce oxidative DNA damage, such as 8-oxoG, when exposed to light. These findings have implications for the photocarcinogenicity of PAHs.

Design of PAP-1, a selective small molecule Kv1.3 blocker, for the suppression of effector memory T cells in autoimmune diseases

The lymphocyte K+ channel Kv1.3 constitutes an attractive pharmacological target for the selective suppression of terminally differentiated effector memory T (TEM) cells in T cell-mediated autoimmune diseases, such as multiple sclerosis and type 1 diabetes. Unfortunately, none of the existing small-molecule Kv1.3 blockers is selective, and many of them, such as correolide, 4-phenyl-4-[3-(methoxyphenyl)-3-oxo-2-azapropyl]cyclohexanone, and our own compound Psora-4 inhibit the cardiac K+ channel Kv1.5. By further exploring the structure-activity relationship around Psora-4 through a combination of traditional medicinal chemistry and whole-cell patch-clamp, we identified a series of new phenoxyalkoxypsoralens that exhibit 2- to 50-fold selectivity for Kv1.3 over Kv1.5, depending on their exact substitution pattern. The most potent and "drug-like" compound of this series, 5-(4-phenoxybutoxy)psoralen (PAP-1), blocks Kv1.3 in a use-dependent manner, with a Hill coefficient of 2 and an EC50 of 2 nM, by preferentially binding to the C-type inactivated state of the channel. PAP-1 is 23-fold selective over Kv1.5, 33- to 125-fold selective over other Kv1-family channels, and 500- to 7500-fold selective over Kv2.1, Kv3.1, Kv3.2, Kv4.2, HERG, calcium-activated K+ channels, Na+,Ca2+, and Cl- channels. PAP-1 does not exhibit cytotoxic or phototoxic effects, is negative in the Ames test, and affects cytochrome P450-dependent enzymes only at micromolar concentrations. PAP-1 potently inhibits the proliferation of human TEM cells and suppresses delayed type hypersensitivity, a TEM cell-mediated reaction, in rats. PAP-1 and several of its derivatives therefore constitute excellent new tools to further explore Kv1.3 as a target for immunosuppression and could potentially be developed into orally available immunomodulators.

Synthesis and photocytotoxic activity of new alpha-methylene-gamma-butyrolactone-psoralen heterodimers

The synthesis of a new alpha-methylene-gamma-butyrolactone-psoralen heterodimer 2 is reported. Its photoantiproliferative activity and skin phototoxicity were compared with that of 5-methoxypsoralen (5-MOP) and another heterodimer 1. Both derivatives show a significant phototoxicity toward malignant cell lines including melanoma cells A375 compared to their intrinsic cytotoxicity in the dark. Both compounds were found to be nonphototoxic on mice skin and therefore could be active potential drugs in photochemotherapy.