Anthracycline antibiotic blockade of SV40 T antigen helicase action.
We previously showed that anthracycline antibiotics potently block SV40 large T antigen helicase; in the present study, we describe the kinetics and the structure-activity characteristics of this process. The concentration vs effect data for helicase blockade were fitted by the Hill equation to yield nearly parallel log-concentration effect curves for a series of active anthracycline antibiotics. The effective concentration for 50% helicase blockade (EC50) values ranged from 0.34 microM for daunorubicin to 40.8 microM for 3'-deaminodaunorubicin. Clinically inactive 3'-N-acyl anthracyclines produced no blockade. The Hill constants for the blockade ranged from 1.1 to 1.6 for the entire series of active anthracyclines, indicating no positive cooperativity and suggesting that a single molecule of bound drug is sufficient to block helicase action. The EC50 values for several clinically effective anthracyclines showed a relationship to the average DNA binding constants for these drugs, and Lineweaver-Burk analysis of the blockade kinetics indicated non-competitive inhibition. The kinetics of the blockade indicated that the anthracycline, DNA, and helicase form a ternary complex that is irreversible under the reaction conditions. This mechanism may be central to the cytotoxic and anti-cancer activities of anthracycline antibiotics and may be useful in understanding the enzymatic mechanism of DNA helicase action.
Bachur
N R
NR
University of Maryland Cancer Center, University of Maryland School of Medicine, Baltimore 21201, USA.
Lun
L
L
Sun
P M
PM
Trubey
C M
CM
Elliott
E E
EE
Egorin
M J
MJ
Malkas
L
L
Hickey
R
R
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D004265:DNA Helicases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D012313:RNA / Q000096:biosynthesis; D013329:Structure-Activity Relationship
D000903:Antibiotics, Antineoplastic; D000952:Antigens, Polyomavirus Transforming; D004791:Enzyme Inhibitors; D012313:RNA; D000251:Adenosine Triphosphatases; D004265:DNA Helicases