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)

Abstract

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 (320-400nm) is more commonly used clinically, studies have shown that UVB (280-320nm) 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 (11800cm(-1) M(-1) at 300nm) compared with the UVA region (2016cm(-1) M(-1) at 365nm), 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.