Fluorescent labelling of closely-spaced aldehydes induced in DNA by bleomycin-Fe(III).
OBJECTIVE
To test the ability of FARPhC and FARP, two novel fluorescent reagents, to label aldehyde-containing sites (principally abasic sites) generated in DNA by the radiomimetic drug bleomycin, and to use fluorescent energy transfer from FARPhc (donor) to FARP (acceptor) to quantitate such closely-spaced sites.


METHODS
FARPhc, 7-hydroxycoumarin-3-carboxylic acid (((((amino-oxymethyl) carbonyl) hydrazino) carbonylethyl) amide) was synthesized with a protocol similar to the one recently reported for FARP (a fluorescein-based probe).


RESULTS
Both FARPhc and FARP form stable oxime bonds with the open-chain aldehydes generated upon acidic depurination of DNA. Plasmid DNA exposed to bleomycin-Fe(III)-ascorbate undergoes extensive strand breakage, and upon subsequent reaction with FARPhc and/or FARP it becomes fluorescently labelled, indicating the generation of aldehyde-containing sites. The binding of the probes to calf thymus or plasmid DNA results in significant fluorescent energy transfer among closely-spaced fluorophores, as revealed by the fluorescence increase following digestion of fluorescently labelled samples with nuclease P1. The fluorescent quenching is most evident when both FARPhc and FARP are used simultaneously to trap aldehyde sites. When single-stranded oligonucleotides engineered to contain either one or two closely spaced bleomycin binding sites are exposed to bleomycin and then fluorescently labelled, the oligonucleotides demonstrate significantly increased fluorescent energy transfer with two binding sites indicating a dependence of aldehyde site generation and clustering on the local sequence of a single strand.


CONCLUSIONS
A new detection method for DNA damage induced by bleomycin following fluorescent labelling of aldehyde group-containing sites (FLAGS) and their clustering via fluorescent energy transfer is demonstrated. The method is applicable to any form of DNA. This work may lead to a general approach for the quantification of multiply damaged sites in DNA, a subset of DNA lesions that may have major biological significance.
Chakrabarti
S
S
Joint Center for Radiation Therapy and Dana Farber Cancer Institute, Harvard Medical School, Boston, MA 02215, USA.
Mahmood
A
A
Makrigiorgos
G M
GM
D000447:Aldehydes / Q000737:chemistry*; D000818:Animals; D001205:Ascorbic Acid; D001761:Bleomycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002417:Cattle; D004247:DNA / Q000737:chemistry / Q000187:drug effects*; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000737:chemistry; D004278:DNA, Superhelical / Q000737:chemistry; D003854:Deoxyribonucleotides / Q000737:chemistry; D005452:Fluoresceins / Q000737:chemistry; D005456:Fluorescent Dyes; D006834:Hydrazines / Q000737:chemistry; D015394:Molecular Structure; D010091:Oximes / Q000737:chemistry; D015719:Single-Strand Specific DNA and RNA Endonucleases; D013050:Spectrometry, Fluorescence; D014468:Umbelliferones / Q000737:chemistry
C121151:5-(((2-(carbohydrazino)methyl)thio)acetyl)aminofluorescein aminooxyacetyl hydrazide; C106879:7-hydroxycoumarin-3-carboxylic acid; C121150:7-hydroxycoumarin-3-carboxylic acid (((((aminooxymethyl)carbonyl)hydrazino)carbonylethyl)amide); D000447:Aldehydes; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D003854:Deoxyribonucleotides; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006834:Hydrazines; D010091:Oximes; D014468:Umbelliferones; C023503:iron bleomycin; D001761:Bleomycin; D004247:DNA; D015719:Single-Strand Specific DNA and RNA Endonucleases; D001205:Ascorbic Acid