Photochemical properties of ofloxacin involved in oxidative DNA damage:: A comparison with rufloxacin

Photodegradation of ofloxacin (OFX) under aerobic conditions gives rise to N-demethylation, mainly involving coupling of radical cation OFX.+ with superoxide radical anion. Although H2O2 is produced as a byproduct, oxidative damage to DNA to give 8-OH-dGuo is associated with a type II mechanism. When the photosensitizing potentials of OFX and rufloxacin (RFX) are compared under the same conditions, the latter is shown to produce a much higher degree of DNA oxidation despite the close structural similarity. This is explained by a decrease of the triplet energy when sulfur instead of oxygen is attached to position 8 of the fluoroquinolone ring system. As a consequence, phosphate anions are able to quench OFX triplet but not RFX triplet; this reveals that the reaction medium has a strong influence on the photochemistry of OFX and hence on its photobiological properties.