Psoralen Derivatives with Enhanced Potency.

Psoralen is a furocoumarin natural product that intercalates within DNA and forms covalent adducts when activated by ultraviolet radiation. It is well known that this property contributes to psoralen's clinical efficacy in several disease contexts, which include vitiligo, psoriasis, graft-versus-host disease and cutaneous T-cell lymphoma. Given the therapeutic relevance of psoralen and its derivatives, we attempted to synthesize psoralens with even greater potency. In this study, we report a library of 73 novel psoralens, the largest collection of its kind. When screened for the ability to reduce cell proliferation, we identified two derivatives even more cytotoxic than 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), one of the most potent psoralens identified to date. Using MALDI-TOF MS, we studied the DNA adduct formation for a subset of novel psoralens and found that in most cases enhanced DNA binding correlated well with cytotoxicity. Generally, our most potent derivatives contain positively charged substituents, which we believe increase DNA affinity and enhance psoralen intercalation. Thus, we provide a rational approach to guide efforts toward further optimizing psoralens to fully capitalize on this drug class' therapeutic potential. Finally, the structure-activity insights we have gained shed light on several opportunities to study currently underappreciated aspects of psoralen's mechanism.

UV doses of young adults.

Since 1986, people have been informed that they get about 80% of their lifetime ultraviolet (UV) dose by the age of 18. This belief originated from the mathematical conclusion that diligent use of sunscreens (sun protection factor 15 or higher) during the first 18 years of life would reduce the lifetime incidence of nonmelanoma skin cancers by 78%. These data were misconstrued to mean that individuals also got about 80% of their lifetime dose of UV by the age of 18 (linear relationship). However, these calculations were based on the incidence of nonmelanoma skin cancers being related to the square of the UV dose. Careful analysis of UV exposure data shows that Americans actually get less than 25% of their lifetime UV dose by the age of 18. This finding also appears to be true worldwide because Australia, UK and The Netherlands report a similar UV exposure pattern. UV-initiated damage early in life can be promoted by subsequent exposures to progress into tumors later in life. For example, the nonmelanoma skin cancer, squamous cell carcinoma, is dependent on the cumulative UV dose. Thus, a better educational approach for reducing skin cancers would be to instruct fair-skinned individuals to protect themselves throughout their lives from being exposed to too much UV radiation.

UVA and UVB-Induced 8-Methoxypsoralen Photoadducts and a Novel Method for their Detection by Surface-Enhanced Laser Desorption Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF MS).

UVA-activated psoralens are used to treat hyperproliferative skin conditions due to their ability to form DNA photoadducts, which impair cellular processes and may lead to cell death. Although UVA (320-400 nm) is more commonly used clinically, studies have shown that UVB (280-320 nm) activation of psoralen can also be effective. However, there has been no characterization of UVB-induced adduct formation in DNA alone. As psoralen derivatives have a greater extinction coefficient in the UVB region (11 800 cm(-1)  M(-1) at 300 nm) compared with the UVA region (2016 cm(-1)  M(-1) at 365 nm), a greater extent of adduct formation is expected. SELDI-TOF, a proteomic technique that combines chromatography with mass spectrometry, was used to detect photoadduct formation in an alternating A-T oligonucleotide. 8-Methoxypsoralen (8-MOP) and DNA solutions were irradiated with either UVA or UVB. An adduct peak was obtained with SELDI-TOF. For UVB-activated 8-MOP, the extent of adducts was three times greater than for UVA. HPLC ESI-MS analysis showed that UVB irradiation yielded high levels of 3,4-monoadducts (78% of total adducts). UVA was more effective than UVB at conversion of 4',5'-monoadducts to crosslinks (17% vs 4%, respectively). This report presents a method for comparing DNA binding efficiencies of interstrand crosslink inducing agents.

Photochemotherapy of vascular cells with 8-methoxypsoralen and visible light: differential effects on endothelial and smooth muscle cells.

BACKGROUND: The long-term efficacy of percutaneous transluminal coronary angioplasty is limited by the restenosis which occurs in approximately 40% of patients, usually within 6 months of the procedure. PURPOSE: The present study was designed to evaluate the effects of 8-methoxypsoralen (8-MOP) activated with visible light on the properties of bovine aortic smooth muscle cells (SMC) and endothelial cells (EC) in vitro. METHODS: Cells were seeded in polystyrene wells, allowed to attach over a 24-h period, incubated with 1, 20, or 50 microg/ml 8-MOP and then exposed to 12 J/cm2 visible light (447 nm). Cell counts were performed for up 14 days (n = 4-6 wells per time point), and each experiment was performed in triplicate. Cellular migration, morphology, and size were also analyzed. RESULTS: The lowest 8-MOP dose (1 microg/ml) had no significant effect on SMC proliferation, while the highest dose (50 microg/ml) induced cytostasis. An intermediate dose of 8-MOP (20 microg/ml) produced a transient and reversible inhibition of proliferation. There was no significant effect on proliferation of EC at lowest dose of 8-MOP (1 microg/ml). However, in contrast to the SMC experiments, a transient and reversible inhibition of EC proliferation was seen at both 20 and 50 microg/ml 8-MOP. CONCLUSIONS: These experiments demonstrate that while 8-MOP photoactivated with 447 nm visible light can reversibly inhibit the proliferation of both SMC and EC in a dose-dependent fashion, SMC are more sensitive to the treatment than EC.