PHOTOCHEMICAL AND PHOTOBIOLOGICAL STUDIES OF A FURONAPHTHOPYRANONE ASA BENZO-SPACED PSORALEN ANALOG IN CELL-TREE AND CELLULAR DNA

Photobiological activities of the benzo-spaced psoralen analog furonap hthopyranone 3 have been investigated in cell-free and cellular DNA. T he molecular geometry parameters of 3 suggest that it should not form interstrand crosslinks with DNA, With cell-free DNA no evidence for cr osslinking but also not for monoadduct formation was obtained; rather, the unnatural furocoumarin 3 induces oxidative DNA modifications unde r near-UVA irradiation, The enzymatic assay of the photosensitized dam age in cell-free PM2 DNA revealed the significant formation of lesions sensitive to formamidopyrimidine DNA glycosylase (Fpg protein), In th e photooxidation of calf thymus DNA by the furonaphthopyranone 3, 0.29 +/- 0.02% 8-oxo-7,8-dihydroguanine (8-oxoGua) was observed, With 2'-d eoxyguanosine (dGuo), the guanidine-releasing photooxidation products oxazolone and oxoimidazolidine were formed predominately, while 8-oxod Guo and 4-HO-8-oxodGuo were obtained in minor amounts, The lack of a s ignificant D2O effect in the photooxidation of DNA and dGuo reveals th at singlet oxygen (type II process) plays a minor role; control experi ments with tert-butanol and mannitol confirm the absence of hydroxyl r adicals as oxidizing species, The furonaphthopyranone 3 (E-red = -1.93 +/- 0.03V) should act in its singlet-excited state as electron accept or for the photooxidation of dGuo (Delta G(ET) ca -5 kcal/mol), which corroborates photoinduced electron transfer (type I) as a major DNA-ox idizing mechanism. A comet assay in Chinese hamster ovary (CHO) AS52 c ells demonstrated that the psoralen analog 3 damages cellular DNA upon near-UVA irradiation; however, no photosensitized mutagenicity was ob served in CHO AS52 cell cultures.