Doxorubicin and gamma rays increase the level of DNA topoisomerase IIalpha in nuclei of normal and xeroderma pigmentosum fibroblasts

Time-targeted therapy (TTT): proof of principle using doxorubicin and radiation in a cultured cell system

We test the hypothesis that a pulse of the anti-cancer agent doxorubicin renders cells more sensitive to ionizing radiation in a strongly time-specific, dose-specific manner. We have treated cultured cells from a human tumor line, HepG2, with graded doses of two agents: doxorubicin (Dox) and ionizing radiation (XR), delivered in sequence-specific, time-specific, dose-specific patterns. We observe a strong increase in cell killing, up to 120 fold, between pulsed treatment with Dox followed exactly 4 hours later with acute XR. This effect is more pronounced for larger doses of irradiation (>7.5 Gy). These data demonstrate proof of principal in a model system that timing between agents may be an exceptionally important variable in using combined, multi-modal therapy in the treatment of cancer. Since the levels of Dox needed to induce substantial increases in cellular radiosensitivity may be achievable in vivo, we suggest that this phenomenon, which we refer to as time-targeted therapy (TTT), be considered for translation into the clinic if preclinical studies identify appropriate timing and toxicity for combined of Dox XR can be overcome.

Protein kinase C delta activates topoisomerase IIalpha to induce apoptotic cell death in response to DNA damage

DNA topoisomerase II is an essential nuclear enzyme that modulates DNA processes by altering the topological state of double-stranded DNA. This enzyme is required for chromosome condensation and segregation; however, the regulatory mechanism of its activation is largely unknown. Here we demonstrate that topoisomerase IIalpha is activated in response to genotoxic stress. Concomitant with the activation, the expression of topoisomerase IIalpha is increased following DNA damage. The results also demonstrate that the proapoptotic kinase protein kinase C delta (PKCdelta) interacts with topoisomerase IIalpha. This association is in an S-phase-specific manner and is required for stabilization and catalytic activation of topoisomerase IIalpha in response to DNA damage. Conversely, inhibition of PKCdelta activity attenuates DNA damage-induced activation of topoisomerase IIalpha. Finally, aberrant activation of topoisomerase IIalpha by PKCdelta is associated with induction of apoptosis upon exposure to genotoxic agents. These findings indicate that PKCdelta regulates topoisomerase IIalpha and thereby cell fate in the genotoxic stress response.

Intranucleolar localization of DNA topoisomerase II? is a distinctive feature of necrotic, but not of apoptotic, Jurkat T-cells

Two distinct types of cell death have been described: apoptosis and necrosis. However, it is becoming increasingly clear that the differences between these two types are far less numerous than initially thought. Morphological analyses might provide important information to distinguish apoptotic from necrotic samples. We recently reported that in necrotic, but not apoptotic, HL-60 human myeloid leukaemia cells, the nuclear protein topoisomerase IIalpha concentrated in nucleoli. In order to ascertain whether or not this phenomenon was restricted to a peculiar cell type or could be detected also in cells of lymphoid lineage, we performed an investigation aimed at defining the localization of topoisomerase IIalpha in apoptotic and necrotic Jurkat human T lymphoblastoid cells. Immunofluorescence staining demonstrated that topoisomerase IIalpha was excluded from the condensed chromatin of apoptotic cells, whereas in necrotic cells it was localized in discrete nuclear dots. Immuno-electron microscopy analysis showed that topoisomerase IIalpha was undetectable in nucleoli of normal and apoptotic cells, whereas it was present in the nucleolus of necrotic cells irrespectively of the type of inducer used (ethanol, H(2)O(2), HgCl(2)). Taken together, our findings identify topoisomerase IIalpha as a potential morphological marker useful to discriminate between apoptotic and necrotic cells.

Influence of vitamin D3 metabolites on cell proliferation and cytotoxicity of adriamycin in human normal and neoplastic cells

The common features of biological activity displayed by vitamin D family members and adriamycin suggest the possibility of synergistic effects of the combination of these compounds. Until now, the mechanisms responsible mainly for adriamycin cytotoxic action have not been indicated. Therefore, observation of the possible common cell targets for adriamycin and vitamin D metabolites could shed more light on the mechanisms of cytotoxic activity of adriamycin. In the present study, the influence of calcidiol (25-hydroxyvitamin D(3)) and calcitriol (1alpha,25-dihydroxyvitamin D(3)) on the proliferation and cytotoxicity of adriamycin was studied. The following cell lines were tested: normal human fibroblasts-CRL 1502, human melanoma cells-ME18 and its subline-ME18/R, resistant to adriamycin. As was shown, 72 h of incubation with calcidiol or calcitriol, both at 10 microM, inhibited growth (to approx. 60%) only of the ME18 cells. Dose and time dependence of this effect has been confirmed. Antiproliferative events did not correlate with an increase of adriamycin cytotoxicity. It was noted that calcidiol and calcitriol had no significant influence on the adriamycin IC(50) values in any cell lines tested. These results point to the divergent mechanisms of action of adriamycin and vitamin D(3) metabolites.

DNA repair capacity after gamma-irradiation and expression profiles of DNA repair genes in resting and proliferating human peripheral blood lymphocytes

DNA repair plays an important role in maintaining genomic integrity, and deficiencies in repair function are known to promote cancer development. Several studies have used the individual capacity to repair DNA damage in peripheral blood lymphocytes (PBLs) as a cancer risk marker. As the cell's ability to remove DNA damage may be correlated with proliferative activity, it is an important question whether quiescent or dividing cells should be used in such studies. The aim of our study was to compare DNA repair capacity and expression profiles of 70 known DNA repair genes, both in resting and phytohemagglutinin (PHA) stimulated human PBLs. Using the comet assay, gamma-radiation-induced DNA damage and repair in lymphocytes was analyzed. No difference, neither in the rate of radiation-induced DNA damage nor in DNA repair capacity between PHA-stimulated and non-stimulated PBLs was observed. Stimulated cells, however, showed significantly elevated values for background damage. Transcriptional profiles of repair genes were analyzed using cDNA arrays. Hybridization experiments were performed with mRNA isolated from both unstimulated and PHA-stimulated PBLs. More than 70% of all evaluated genes had constant expression levels. Twelve genes responded with a more than two-fold increase of transcripts to the mitogenic stimulus. Most of the up-regulated repair enzymes are also known to play a role in DNA replication. In conclusion, the data presented here suggest that all repair proteins needed for the repair of gamma-irradiation induced DNA-damage, that can be detected by the alkaline comet assay, are already present in G0 cells at sufficient amounts and do not need to be induced once lymphocytes are stimulated to start cycling. Our results thus do not support a general increase in DNA repair activity of PBLs by PHA stimulation, and the use of stimulated PBLs in molecular epidemiological studies on DNA repair of gamma-irradiation induced DNA damage seems not to be mandatory.