4'-Aminomethyl-4,5',8-trimethylpsoralen photochemistry: the effect of concentration and UVA fluence on photoadduct formation in poly(dA-dT) and calf thymus DNA

Spectroscopic view on the interaction between the psoralen derivative amotosalen and DNA

Psoralens are eponymous for PUVA (psoralen plus UV-A radiation) therapy, which inter alia can be used to treat various skin diseases. Based on the same underlying mechanism of action, the synthetic psoralen amotosalen (AMO) is utilized in the pathogen reduction technology of the INTERCEPT® Blood System to inactivate pathogens in plasma and platelet components. The photophysical behavior of AMO in the absence of DNA is remarkably similar to that of the recently studied psoralen 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT). By means of steady-state and time-resolved spectroscopy, intercalation and photochemistry of AMO and synthetic DNA were studied. AMO intercalates with a higher affinity into A,T-only DNA (KD = 8.9 × 10-5 M) than into G,C-only DNA (KD = 6.9 × 10-4 M). AMO covalently photobinds to A,T-only DNA with a reaction quantum yield of ΦR = 0.11. Like AMT, it does not photoreact following intercalation into G,C-only DNA. Femto- and nanosecond transient absorption spectroscopy reveals the characteristic pattern of photobinding to A,T-only DNA. For AMO and G,C-only DNA, signatures of a photoinduced electron transfer are recorded.

Tracing the Photoaddition of Pharmaceutical Psoralens to DNA

The psoralens 8-methoxypsoralen (8-MOP), 4,5',8-trimethylpsoralen (TMP) and 5-methoxypsoralen (5-MOP) find clinical application in PUVA (psoralen + UVA) therapy. PUVA treats skin diseases like psoriasis and atopic eczema. Psoralens target the DNA of cells. Upon photo-excitation psoralens bind to the DNA base thymine. This photo-binding was studied using steady-state UV/Vis and IR spectroscopy as well as nanosecond transient UV/Vis absorption. The experiments show that the photo-addition of 8-MOP and TMP involve the psoralen triplet state and a biradical intermediate. 5-MOP forms a structurally different photo-product. Its formation could not be traced by the present spectroscopic technique.

An improved 4'-aminomethyltrioxsalen-based nucleic acid crosslinker for biotinylation of double-stranded DNA or RNA

Nucleic acid crosslinkers that covalently join complementary strands of DNA/RNA have applications in both pharmaceuticals and as biochemical probes. Psoralen is a popular crosslinking moiety that reacts with double stranded DNA and RNA upon exposure to longwave UV light. The commercially available compound EZ-link psoralen-PEG3-biotin has been used in numerous studies to crosslink DNA and double-stranded RNA for genome-wide investigations. Here we present a new probe, AP3B, which uses the psoralen derivative, 4'-aminomethyltrioxsalen, to crosslink and biotinylate nucleic acids. We show that AP3B is 4 to 5 times more effective at labeling DNA in cells and produces a comparable number of crosslinks with over 100 times less compound and less exposure to UV light in vitro than EZ-link psoralen-PEG3-biotin.

DNA Intercalated Psoralen Undergoes Efficient Photoinduced Electron Transfer

The interaction of psoralens with DNA has been used for therapeutic and research purposes for decades. Still the photoinduced behavior of psoralens in DNA has never been observed directly. Femtosecond transient absorption spectroscopy is used here to gain direct insight into the photophysics of a DNA-intercalated psoralen (4'-aminomethyl-4,5',8-trimethyl-psoralen (AMT)). Intercalation reduces the excited singlet lifetime of AMT to 4 ps compared with 1400 ps for AMT in water. This singlet quenching prohibits the population of the triplet state that is accessed in free AMT. Instead, a DNA to AMT electron transfer takes place. The resulting radical pair decays primarily via charge recombination with a time constant of 30 ps. The efficient electron transfer observed here reveals a completely new aspect of the psoralen-DNA interaction.

Tandem mass spectrometry for characterization of covalent adducts of DNA with anticancer therapeutics

The chemotherapeutic activities of many anticancer and antibacterial drugs arise from their interactions with nucleic acid substrates. Some of these ligands interact with DNA in a way that causes conformational changes or damage to the nucleic acid targets, ultimately altering recognition by key DNA-specific enzymes, interfering with DNA transcription or prohibiting replication, and terminating cell growth and proliferation. The design and synthesis of ligands that bind to nucleic acids remains a dynamic field in medicinal chemistry and pharmaceutical research. The quest for more selective and efficacious DNA-interactive anticancer chemotherapeutics has likewise catalyzed the need for sensitive analytical methods that can provide structural information about the nature of the resulting DNA adducts and provide insight into the mechanistic pathways of the DNA/drug interactions and the impact on the cellular processes in biological systems. This review focuses on the array of tandem mass spectrometric strategies developed and applied for characterization of covalent adducts formed between DNA and anticancer ligands.

Identification of new scavengers for hydroxyl radicals and superoxide dismutase by utilising ultraviolet A photoreaction of 8-methoxypsoralen and a variety of mutants of Escherichia coli: implications on certain diseases of DNA repair deficiency

8-Methoxypsoralen+UVA (ultraviolet light of 320-400 nm) known as PUVA has been in use for a number of years for the treatment of psoriasis and vitiligo. The treatment possibly works on the basis of UVA photoactivated 8-methoxypsoralen binding to DNA forming both single strand and double strand type damage. We have used Escherichia coli as model system in studying PUVA induced DNA damage and repair. It has been known for some time that the photoactivated 8-methoxypsoralen, besides intercalating with DNA, generates at least two reactive oxygen species (ROS): hydroxyl radicals and superoxide anions, and also singlet oxygen. In this study it has been found that, in E. coli, malate dehydrogenase, succinate dehydrogenase and NADH:ubiquinone oxidoreductase can protect cells from PUVA killing presumably by scavenging these ROS. Possible mechanisms have been proposed for these enzymes as cell protectors. Studies also suggest the potential for the use of PUVA in the treatment of a large number of human diseases. This study also finds that, unlike 8-methoxypsoralen, trioxsalen (4,5',8-trimethylpsoralen, another derivative of psoralens) does not generate ROS by UVA photoactivation; and hence the mode of action of trioxsalen and PUVA overlaps only in the binding of these molecules to DNA in the presence of UVA.

Screening for ocular phototoxicity

Normally light transmission through the eye is benign and serves to direct vision and circadian rhythm. However, with very intense light exposure, or with ambient light exposure to the aged eye and/or young or adult eye in the presence of light-activated (photosensitizing) drugs or dietary supplements, cosmetics, or diagnostic dyes, light can be hazardous, leading to blinding disorders. Light damage to the human eye is avoided because the eye is protected by a very efficient antioxidant system and the chromophores present absorb light and dissipate its energy. After middle age, there is a decrease in the production of antioxidants and antioxidant enzymes and an accumulation of endogenous chromophores that are phototoxic. The extent to which a particular exogenous photosensitizing substance is capable of producing phototoxic side effects in the eye depends on several parameters, including (1) the chemical structure; (2) the absorption spectra of the drug; (3) binding of the drug to ocular tissue (lens proteins, melanin, DNA); and (4) the ability to cross blood-ocular barriers (amphiphilic or lipophilic). For instance, compounds that have either a tricyclic, heterocyclic, or porphyrin ring structure and are incorporated into ocular tissues are potentially phototoxic agents in the eye. The extent to which these substances might damage the eye (photoefficiency) can be predicted using in vitro and photophysical techniques. With simple, inexpensive testing, compounds can be screened for their potential ocular phototoxicity at the developmental stage. It may be that a portion of the molecule can be modified to reduce phototoxicity while leaving the primary drug effect intact. Preclinical safety testing may prevent ocular side effects that can range from mild, reversible blurred vision to permanent blindness.

Fundamentals of the psoralen-based Helinx technology for inactivation of infectious pathogens and leukocytes in platelets and plasma

Psoralens plus ultraviolet A (UVA) light inactivate viruses and bacteria as well as leukocytes. A system employing the synthetic psoralen compound amotosalen hydrochloride (S-59), in combination with UVA light, is being developed to decontaminate platelet concentrates and plasma in a blood-bank setting. S-59 is a heterocyclic psoralen compound that reacts by a three-step process with nucleic acids (NAs): (1) S-59 intercalates into the double helix; (2) upon illumination with long-wavelength ultraviolet light (UVA), it covalently attaches to a single strand, forming a monoadduct; and (3) additional illumination causes a photoreaction of the monoadduct with the second NA strand, resulting in an interstrand crosslink. The reaction occurs with the genomic material of DNA- and RNA-based viruses and occurs in genomes that are single stranded as well as double stranded. Inactivation rate is related to genome size. Large genomes such as those in leukocytes are far more susceptible to inactivation than are viruses such as hepatitis B virus (HBV), which is inactivated (>10(5) logs) under conditions being developed for blood-bank use. The efficiency of the process is affected by a number of practical considerations such as solution components and light source. The S-59 photochemical treatment process (PCT) has been optimized for platelet concentrates as currently processed for transfusion.

Effects of hydroxyl radical scavengers on relaxation of supercoiled DNA by aminomethyl-trimethyl-psoralen and monochromatic UVA photons

The ability of scavengers of hydroxyl radical (OH radical) to modulate the photosensitized relaxation (induction of the first single-strand break) of supercoiled plasmid DNA with UVA photoactivated 4'-aminomethyl-4,5',8-trimethylpsoralen was examined by comparing the dose reduction factor (DRF: the ratio of fluence required to induce the same degree of relaxation in the absence to the presence of OH radical scavengers). The addition of mannitol, azide, acetate, or formate at concentrations inversely proportional to the value of the rate constants for the scavenging of OH radicals partially attenuated the supercoiled DNA relaxation. The degrees of protection afforded by the four scavengers in the presence of AMT photoactivated by either 334 nm or 365 nm monochromatic photons were similar, giving an average DRF of about 0.25 in all cases. Given the diverse chemical nature of the scavengers and their wide range of concentrations utilized, these findings are evidence for the involvement of a Type I photosensitization in the induction of DNA single-strand breaks by photoactivated AMT.

Psoralen-mediated virus photoinactivation in platelet concentrates: enhanced specificity of virus kill in the absence of shorter UVA wavelengths

Treatments with psoralens and long-wavelength ultraviolet radiation (UVA, 320-400 nm; PUVA) have shown efficacy for virus sterilization of platelet concentrates (PC). Our laboratory has employed the psoralen derivative 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), and we have found that platelet integrity is best preserved when rutin, a flavonoid that quenches multiple reactive oxygen species, is present during AMT/UVA treatment of PC. In this report, we examine the effects of different UVA spectra under our standard PC treatment conditions (i.e. 50 micrograms/mL AMT, 0.35 mM rutin and 38 J/cm2 UVA). Added vesicular stomatitis virus (VSV; > or = 5.5 log10) was completely inactivated with the simultaneous maintenance of the platelet aggregation response (> 90% of control) when a UVA light source with transmission mainly between 360 and 370 nm (narrow UVA1) was used. In contrast, with a broad-band UVA (320-400 nm; broad UVA) light source, the aggregation response was greatly compromised (< 50% of control) with only a minor increase in the rate of VSV kill. With this lamp, platelet function could be improved to about 75% of the control by adding a long-pass filter, which reduced the transmission of shorter (< or = 345 nm) UVA wavelengths (340-400 nm; UVA1). At equivalent levels of virus kill, aggregation function was always best preserved when narrow UVA1 was used for PUVA treatment. Even in the absence of AMT, and with or without rutin present, narrow UVA1 irradiation was better tolerated by platelets than was broad UVA.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Methoxypsoralen photoadduct formation in complementary oligonucleotides containing a cross-linkable site

The complete profile of 8-methoxypsoralen photoadduct formation in complementary oligonucleotides (5'-GAGTATGAG and 5'-CATAC) has been determined. Equimolar solutions of the oligonucleotides were irradiated at 4 degrees C in order to stabilize the mini-double helix. Photomodified oligonucleotides were separated by reversed phase chromatography on a Vydac C4 column. Photoadduct formation favored the 5'TAT site in the 9mer over the 5'ATA site in the 5mer by a factor of two. Split-dose studies showed that the monoadducts formed on GAGTATGAG were preferentially converted to cross-links by an additional UVA exposure.