Cp. Saris et al., IN-VITRO FORMATION OF DNA-ADDUCTS BY CISPLATIN, LOBAPLATIN AND OXALIPLATIN IN CALF THYMUS DNA IN SOLUTION AND IN CULTURED HUMAN-CELLS, Carcinogenesis, 17(12), 1996, pp. 2763-2769
Two interesting representatives of a new generation of platinum-based
cytostatic drugs that are currently being tested in clinical trials ar
e lobaplatin [1,2-diaminomethylcyclobutane platinum(II) lactate] and o
xaliplatin [1,2-diaminocyclohexane platinum (II) oxalate], Since littl
e is known about the DNA adduct formation of these compounds, we studi
ed their formation in DNA in vitro in calf thymus DNA and in cells, Th
e major adducts formed in vitro were the Pt-GG and Pt-AG intrastrand c
rosslinks. The latter adducts could be detected using a recently devel
oped P-32-postlabelling method. Using both this assay and atomic absor
ption spectroscopy, it was shown that there is a substantially higher
rate of the in vitro adduct formation by cisplatin, compared with loba
platin and oxaliplatin, Platinum concentrations required to obtain 90%
cell kill during a 2 h incubation of A2780 cells were 15 mu M for cis
platin and oxaliplatin and 22 mu M for lobaplatin, Using an antiserum
originally raised against cisplatin-treated DNA, we were also able to
detect platinum-DNA adducts induced by lobaplatin and oxaliplatin, Max
imal nuclear staining for all three compounds was observed after a 4 h
post-incubation period, The nuclear staining level induced by cisplat
in was about 10-fold higher than after lobaplatin and oxaliplatin trea
tment, GG and AG adducts, measured by P-32-postlabelling, also showed
maximum levels at about 4 h after treatment, Relative GG peak levels w
ere 4:1:3 for cisplatin, lobaplatin and oxaliplatin, respectively, The
ratios of GG over AG intrastrand crosslinks in the A2780 cells were n
ot significantly different for the various compounds, In conclusion, t
he P-32-postlabelling technique has been shown to be appropriate for a
dduct analysis, not only for the classical Pt compounds cisplatin and
carboplatin but also for novel platinum compounds like lobaplatin and
oxaliplatin. Results indicated large differences in reactivity of the
latter compounds to DNA in vitro, compared with cisplatin, This differ
ence was smaller in cells, suggesting enhancement of adduct formation
by certain cellular mechanisms and/or compounds. From these studies, n
o conclusions can be drawn with respect to the cytotoxicity of the dif
ferent Pt-GG and Pt-AG intrastrand crosslinks formed by these compound
s.