Comparative Studies of UV-induced DNA Cleavage by Analogues of iodoHoechst 33258

Abstract

Following the earlier demonstration that iodo-Hoechst 33258 sensitizes DNA and cells to UVA, presumably mediated by formation of a carbon-centred radical on the ligand upon dehalogenation, three isomeric analogues of iodo-Hoechst 33258 have now been studied. The isomers differ in the location of the iodine atom in the phenyl ring of the ligand, relative to the site of attachment of the bibenzimidazole moiety, and are accordingly denoted ortho-, meta- and para-iodoHoechst. Comparison of the ligands with respect to induction of DNA ssb in pBR322 DNA revealed a wide range of activity; (D37's vary by a factor of 37), decreasing in the order: ortho- > meta- and para- > iodoHoechst 33258. Preliminary dehalogenation studies suggest that the higher activity of the ortho isomer results more from increased cross-section for dehalogenation than from increased efficiency of strand breakage per dehalogenation event. However, the chemistry of strand breakage by the ortho-isomer is distinctive, and tentatively assigned to initial attack at the 1'-deoxyribosyl carbon; the other two isomers, like iodo-Hoechst 33258, attack the 5'-carbon. The results are discussed in terms of the spectrum of DNA strand breakage chemistry associated with ionizing radiation, and the potential of DNA strand breaking agents such as the iodoHoechst compounds to study the chemical and biological consequences of the different subclasses of initial DNA damage.

Assessment of molecular binding of Hoechst 33258 analogues into DNA using docking and MM/GBSA approach

“…Comparison of o-, m-and p-iodoHoechst with respect to DNA strand breakage in plasmid DNA indicated remarkable differences in photopotency [13]. The ortho isomer was found to be more efficient than the meta and para isomers [14,15]. Moreover, the photo-induced cytotoxicity by these analogues in K562 cells also displays similar results [16].…”

Activation of multiple DNA repair pathways by sub-nuclear damage induction methods

“…Sensitization of DNA can be accomplished by incorporation of a halogenated thymidine analogue in combination with Hoechst (Limoli and Ward, 1993;Paull et al, 2000;Rogakou et al, 1999), by incorporation of halogenated Hoechst (Martin et al, 1994;Martin et al, 1990) or of halogenated thymidine analogues alone (Lukas et al, 2003;Tashiro et al, 2000). Halogenation is thought to be required for DSB induction.…”

Fluorescently-labelled CPD and 6-4PP photolyases: new tools for live-cell DNA damage quantification and laser-assisted repair

“…Using laser pulses as short as 12.5 s, with relatively low laser power, allowed us to efficiently photo-reactivate DNA damage in live cell imaging experiments (Figure 5). Of note, while the 405 nm laser light can also be used to generate DNA damage, (85,86), the laser intensity used for efficient PR is more than 10-fold lower than the intensities required to induce DNA damage (74). Our results indicated that PR is rather specific for 405 nm laser, as PLs were not efficiently activated by the 488 nm laser at settings normally used for imaging GFP-tagged factors (Supplementary Figure S5C-H).…”