Effects of the modulating agent WR2721 and its main metabolites on the formation and stability of cisplatin-DNA adducts in vitro in comparison to the effects of thiosulphate and diethyldithiocarbamate.
The influence of the modulating agent WR2721, its active thiol-metabolite WR1065 and the symmetrical disulphide WR33278 on the in vitro formation and stability of cis-diamminedichloroplatinum(II) (cisplatin, CDDP)-DNA adducts was investigated and compared with the effects of the highly nucleophilic modulating agents diethyldithiocarbamate (DDTC) and thiosulphate (TS). Salmon sperm DNA (0.5 mg/mL) was incubated with 25 micrograms/mL (83 microM) cisplatin for 1 hr in 50 mM phosphate buffer, pH 7.2 at 37 degrees in the absence or presence of modulating agent. DDTC and TS were potent inhibitors of the platination of the DNA (95 and 89%, respectively, with 4.2 mM of modulating agent). The WR-compounds were also remarkably active in the inhibition of DNA platination. Prevention of adduct formation in the presence of 4.2 mM WR-compound decreased in the order WR1065 (74%) greater than WR33278 (63%) greater than WR2721 (51%). The prevention of CDDP-DNA adduct formation by WR1065 was strongly concentration-dependent up to 4.2 mM but at higher concentrations this protection hardly increased at all. In the presence of the modulating agents, increased levels of CDDP monofunctionally bound to a guanine residue were observed with a simultaneous decrease in the relative abundance of bifunctional adducts. All modulators were also able to reverse part of the CDDP-DNA adducts formed. After a 2-hr incubation of already platinated salmon sperm DNA with 4.2 mM of modulating agent, the removal of Pt from DNA amounted to about 43% with DDTC, 28% with WR1065 and 13-14% with TS, WR2721 and WR33278. Even CDDP bifunctionally bound to two adjacent guanines in the same DNA strand, which is considered to be a very stable adduct, was partly reversed. Our observations suggest that WR2721, especially when administered prior to or concomitantly with CDDP, can be expected to protect those tissues from CDDP-induced damage to DNA that are able to efficiently dephosphorylate WR2721 followed by uptake of the thiol metabolite WR1065. This stresses the importance of a selective formation and uptake of WR1065 by non-tumour tissues for the successful use of WR2721 as a protective agent in combination with platinum-based cancer chemotherapy.
Treskes
M
M
Department of Oncology, Free University Hospital, Amsterdam, The Netherlands.
Nijtmans
L G
LG
Fichtinger-Schepman
A M
AM
van der Vijgh
W J
WJ
D004999:Amifostine / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002021:Buffers; D002945:Cisplatin / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D018736:DNA Adducts; D004050:Ditiocarb / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008624:Mercaptoethylamines / Q000378:metabolism / Q000494:pharmacology; D012474:Salmon; D013885:Thiosulfates / Q000494:pharmacology*
D002021:Buffers; D018736:DNA Adducts; D008624:Mercaptoethylamines; D013885:Thiosulfates; C057270:cisplatin-DNA adduct; C020174:N-(2-mercaptoethyl)-1,3-diaminopropane; D004247:DNA; D004050:Ditiocarb; D004999:Amifostine; D002945:Cisplatin; C045611:WR 33278