Ultrastructural morphology (transmission electron microscopy) and localisation of
cisplatin-induced
platinum (Pt)-
DNA adducts (immunoelectron microscopy) were analysed in the human
small cell lung cancer cell line
GLC(4) and its 40-fold in vitro acquired
cisplatin-resistant subline GLC(4)-CDDP, which is characterised by, among other things, a decreased
DNA platination. Immunolabelling of Pt-
DNA adducts was performed with the polyclonal antibody GPt, known to detect the main Pt-containing intrastrand and interstrand
DNA adducts. Morphological analysis of
GLC(4) and GLC(4)-CDDP at the ultrastructural level showed cells with a high nucleus/cytoplasm ratio with the majority of nuclei containing one or more nucleoli. GLC(4)-CDDP showed, in contrast to
GLC(4), an extensive Golgi apparatus and an increased number of mitochondria.
DNA platination was detectable in both
GLC(4) and GLC(4)-CDDP. Immunoelectron microscopy showed Pt-
DNA adducts primarily in the nucleus, preferentially at loci with high-density
chromatin (e.g.
heterochromatin, pars granulosa around nucleoli, condensed
DNA in proliferating and apoptotic cells), and in mitochondria. The level of detectable Pt-
DNA adducts was cell cycle status-dependent. In both cell lines, Pt-
DNA adduct levels increased from non-dividing interphase cells to dividing cells and were highest in cells undergoing apoptosis. Overall localisation of Pt-
DNA adducts was comparable in
GLC(4) and GLC(4)-CDDP cells.