In vivo photoreaction of a chiral cobalt complex: DNA cleavage by Co(DIP)3(3+) in mammalian cells.
The chiral complex tris (diphenylphenanthroline) cobalt (III) (Co(DIP)3(3+) provides a photoreactive probe for chromatin structure in mammalian cells. The complex, which upon photoactivation cleaves DNA in a conformation-specific fashion in vitro, is shown also to cleave DNA in vivo upon irradiation with ultraviolet light (greater than 300 nm). delta- and lambda-Co (DIP)3(3+) isomers are taken up efficiently into cultured Chinese hamster ovary cells and concentrate within cell nuclei. In the absence of light the complexes are toxic to the cells (10% survival at approximately 300 nM), but after ultraviolet irradiation, the toxicity is markedly (greater than 10-fold) increased. The synergism between irradiation and Co(DIP)3(3+) administration may lie in photoreactions with DNA elicited by the cobalt complex. Alkaline sucrose gradient analysis of DNA from cells exposed to lambda-Co(DIP)3(3+) and irradiation show single-stranded DNA fragmentation under conditions where little cleavage is seen in cells either incubated with lambda-Co(DIP)3(3+) or irradiated with greater than 300 nm A ultraviolet light. Cellular DNA is cleaved with lower efficiency than naked DNA, likely due to decreased accessibility of sites in vivo. Hybridization of fragments obtained from the alkaline sucrose gradients to a probe specific for the amplified dihydrofolate reductase gene reveals a similar distribution of dhfr sequences and total DNA, indicating that the family of conformations recognized by lambda-Co(DIP)3(3+) are dispersed throughout the genome.
Chapnick
L B
LB
Department of Biological Sciences, Columbia University, New York, NY 10027.
Chasin
L A
LA
Raphael
A L
AL
Barton
J K
JK
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002499:Centrifugation, Density Gradient; D003035:Cobalt; D006224:Cricetinae; D004247:DNA / Q000187:drug effects* / Q000528:radiation effects; D009942:Organometallic Compounds / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D010618:Phenanthrolines / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D010777:Photochemistry; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics; D014466:Ultraviolet Rays
D009942:Organometallic Compounds; D010618:Phenanthrolines; D003035:Cobalt; C046724:tris(diphenylphenanthroline)cobalt(III); D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase