Ketoprofen (KP) and fenofibrate, respectively, anti-inflammatory and hypolipidemiant agents, promote anormal photosensitivity in patients and may induce photoallergic cross-reactions correlated to their benzophenone-like structure. Here, their ability to photosensitize the degradation of biological targets was particularly investigated in DNA. The photosensitization of DNA damage by KP and fenofibric acid (FB), the main metabolite of fenofibrate, and their parent compound, benzophenone (BZ), was examined on a 32P-end-labeled synthetic oligonucleotide in phosphate-buffered solution using gel sequencing experiments. Upon irradiation at lambda > 320 nm, piperidine-sensitive lesions were induced in single-stranded oligonucleotides by KP, FB and BZ at all G sites to the same extent. This pattern of damage, enhanced in D2O is characteristic of a Type-II mechanism. Spin trapping experiments using 2,2,6,6-tetramethyl-4-piperidone have confirmed the production of singlet oxygen during drug photolysis. On double-stranded oligonucleotides, highly specific DNA break occurred selectively at 5'-G of a 5'-GG-3' sequence, after alkali treatment. Prolonged irradiation led to the degradation of all G residues, with efficiency decreasing in the order 5'-GG > 5'-GA > 5'-GC > 5'-GT, in good agreement with the calculated lowest ionization potentials of stacked nucleobase models supporting the assumption of a Type-I mechanism involving electron transfer, also observed to a lesser extent with adenine. Cytosine sites were also affected but the action of mannitol which selectively inhibited cytosine lesions suggests, in this case, the involvement of hydroxyl radical, also detected by electronic paramagnetic resonance using 5,5-dimethyl-1-pyrrolidine-1-oxide as spin trap. On a double-stranded 32P-end-labeled 25-mer oligonucleotide containing TT and TTT sequences, the three compounds were found to photosensitize by triplet-triplet energy transfer the formation of cyclobutane thymine dimers detected using T4 endonuclease V.

Pyropheophorbide-a methyl ester (PPME) is a second generation of photosensitizers used in photodynamic therapy. We demonstrated that PPME photosensitization activated NF-B transcription factor in colon cancer cells. Unexpectedly, this activation occurred in two separate waves, i.e. a rapid and transient one and a second slower but sustained phase. The former was due to photosensitization by PPME localized in the cytoplasmic membrane which triggered interleukin-1 receptor internalization and the transduction pathways controlled by the interleukin-1 type I receptor. Indeed, TRAF6 dominant negative mutant abolished NF-B activation by PPME photosensitization, and TRAF2 dominant negative mutant was without any effect, and overexpression of IB kinases increased gene transcription controlled by NF-B. Oxidative stress was not likely involved in the activation. On the other hand, the slower and sustained wave could be the product of the release of ceramide through activation of the acidic sphingomyelinase. PPME localization within the lysosomal membrane could explain why ceramide acted as second messenger in NF-B activation by PPME photosensitization. These data will allow a better understanding of the molecular basis of tumor eradication by photodynamic therapy, in particular the importance of the host cell response in the treatment.

The efficiency of ruthenium complexes for photosensitizing DNA damage depends on the oxidizing character of their ligands. Here we report on the difference in behavior of tris(2.2'-bipyrazyl)ruthenium(II) (Ru[bpz]3(2+)), tris(2,2'-bipyridyl)ruthenium(II) (Ru[bipy]3(2+)) and cis-dichlorobis (2,2'-bipyrazyl)ruthenium(II) (Ru[bpz]2Cl2). Upon irradiation at 436 nm, Ru(bpz)3 (2+) was far less stable than Ru(bipy)3(2+). Ru(bpz)3(2+) in phosphate buffer containing NaCl undergoes a photoanation reaction leading to the formation of Ru(bpz)2Cl2, as previously reported also in organic media. In the presence of phage phi X174 DNA, Ru(bpz)3(2+) photosensitized the formation of single strand breaks with an efficiency that was, at the beginning of irradiation, similar to that of Ru(bipy)3(2+). After 8 min of irradiation, the cleavage efficiency of Ru(bpz)3(2+) reached a plateau that may correspond to its photode composition. For the same conditions, Ru(bpz)2Cl2 did not induce DNA breakage. Scavenging experiments showed that, in the presence of oxygen, DNA cleavage induced by Ru(bpz)3(2+) partly resulted from the formation of singlet oxygen and hydroxyl radical while in the absence of oxygen an additional mechanism involving electron transfer between the excited state of the ruthenium complex and DNA is proposed. The ICP measurement showed that Ru(bpz)3(2+) and Ru(bpz)2Cl2 gave rise to covalent binding onto DNA in contrast with Ru(bipy)3(2+), which did not bind to DNA under the experimental conditions. The results are discussed with regard to the potential use of these photosensitizers in phototherapy.

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