Formation of Inter-Strand Cross-Linkings in the Photoreactions between Furocoumarins and DNA

Abstract

A furocoumarin intercalated between two base pairs of native DNA can photoreact with two pyrimidine bases engaging both its 4',5'- and its 3,4-double bond. This fact was evidenced studying the behaviour of the fluorescence acquired by DNA during irradiation at 365 nm. When this double reaction occurs, a cross-linking is formed between the two strands of DNA, as denaturation and renaturation experiments have demonstrated. The various furocoumarin derivatives have a very diverse ability to form cross-linkages, which is independent of their photobinding capacity. This different ability is due mainly to the structure of furocoumarins and to the steric relationships that the intercalated furocoumarin molecules have with the stacked pyrimidine bases.

Design of PAP-1, a Selective Small Molecule Kv1.3 Blocker, for the Suppression of Effector Memory T Cells in Autoimmune Diseases

“…The DNA cross-linking potency of selected compounds was determined by measuring melting profiles of poly(dA-dT)-poly(dA-dT) DNA in the presence and absence of compound with and without UVA irradiation according to Dall'Acqua et al (1971). Incubation mixtures containing 10 M concentrations of the compound, 0.1 units of poly(dA-dT)-poly(dA-dT) (Sigma-Aldrich, Deisenhofen, Germany), and 1% DMSO and MOPS buffer (0.1 M; pH 7.2) were prepared in 2-ml quartz cuvettes.…”

Structure specificity of polydeoxyribonucleotides for the photoreaction with psoralen

“…A C4-cycloaddition to the 5,6-double bond of pyrimidine bases occurs: furocoumarins can photoreact either with their 3,4-or 4',5'-double bond, forming therefore two types of photoadducts. Moreover, behaving as bifunctional agents, they can form adducts, in which one furocoumarin molecule is linked with two pyrimidine bases; in this case an inter-stand crosslinking is formed in native DNA [9][10][11]. It has been shown by Cole [10] and Chandra et al [12][13][14] that the formation of inter-strand crosslinking is responsible for the photodynamic damage to biological systems by psoralen.…”

A possible mechanism of psoralen phototoxicity not involving direct interaction with DNA.

“…Typically, patients are administered MeOPso orally or Me3Pso topically and are then exposed to a measured dose of ultraviolet (UVA; 320-400 nm) irradiation. It has been hypothesized that the actions of psoralen in the skin are due to their ability to form DNA adducts following UVA light irradiation (2). Psoralens are known to intercalate into DNA in a dark reaction.…”

“…After exposure to UVA light, they form mono-and bifunctional adducts with pyrimidine bases in DNA. This results in crosslinking of psoralen between base-paired strands of DNA (1,2).…”