Carcinogenesis, Vol 18, 1767-1774, Copyright © 1997 by Oxford University Press
MJ Welters, M Maliepaard, AJ Jacobs-Bergmans, RA Baan, JH Schellens, J Ma, WJ van der Vijgh, JM Braakhuis and AM Fichtinger-Schepman
For the improvement of chemotherapy with platinum (Pt)-containing drugs a
sensitive assay to detect the induced Pt-DNA adducts is needed. Therefore,
the 32P-postlabelling assay, described by Blommaert and Saris (Nucleic
Acids Res., 1995, 23, 1300-1306), to detect the major adducts Pt-GG and
Pt-AG has substantially been improved and compared with ELISA and AAS. For
the quantification of the adducts, TpT was added as an internal standard
immediately after isolation of the Pt- adducts from digested DNA samples.
It was found that 32P-labelling of both GpG and ApG, the dinucleotides
obtained after deplatination of the adducts, was equally efficient as that
of TpT. To isolate the Pt- adducts on basis of a positive charge, the pH of
DNA digests was adjusted to approximately 3 prior to separation by strong
cation- exchange chromatography. For the subsequent deplatination a volume
of only 12 microl of 0.2 M NaCN was used, which did not interfere with the
following labelling step. The quantification of the 32P-labelled
dinucleotides was performed by phosphorimaging of spots after separation on
TLC as well as by 32P-counting of fractions collected after separation by
HPLC. The method was used to determine adduct levels in in vitro
cisplatin-treated DNA and in DNA isolated from cisplatin-treated cultured
cells, tumor xenografts from cisplatin- treated mice, and from white blood
cells and (tumor) tissues from cisplatin-treated patients. The results show
a significant correlation with the adduct levels as determined with atomic
absorption spectroscopy (high levels) or with specific antibodies (low
levels). This assay appears to be useful for the determination of low
levels of Pt-adducts in small DNA samples as present in clinical specimens
such as blood and tumor tissue, but also in buccal mucosal cells and fine
needle aspirates.
ARTICLES
Improved 32P-postlabelling assay for the quantification of the major platinum-DNA adducts
Toxicology Division, TNO Nutrition and Food Research Institute, Zeist, The Netherlands.
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