Nucleotide excision repair in the human ovarian carcinoma cell line (2008) and its cisplatin-resistant variant (C13*).

Repair of cisplatin-damaged DNA was investigated in a human ovarian carcinoma cell line (2008) and its cisplatin-resistant variant (C13*) using a host-cell reactivation (HCR) assay. The HCR of cisplatin-damaged adenovirus (Ad) was not significantly different in C13* cells compared to 2008 cells. The cisplatin concentrations required to reduce the amount of viral DNA replicated to 50% were 0.12 +/- 0.02 microM and 0.10 +/- 0.01 microM after 48 h of repair in 2008 and C13* cells respectively. Similarly, the cisplatin concentration required to reduce the expression of a reporter gene inserted in the viral DNA was not significantly altered in C13* cells compared to the parental line (IC50 values were 0.28 +/- 0.04 microM in 2008 cells and 0.17 +/- 0.06 microM in C13* cells after 48 h of repair). Pretreatment of the cells with cisplatin, immediately prior to Ad infection, did not significantly alter the HCR of cisplatin-damaged Ad in either cell type. In addition, a cisplatin-sensitive variant derived from the C13* cells, namely the RH4 cells, did not differ significantly from either the 2008 or C13* cells in their ability to reactivate cisplatin-damaged Ad. Furthermore, a component of the nucleotide excision repair (NER) pathway, DNA polymerase alpha, was investigated using the competitive inhibitor aphidicolin. The combination of cisplatin and aphidicolin resulted in similar synergistic growth inhibition in both the 2008 and C13* cells providing additional support to the HCR results which suggest that enhanced NER is not responsible for the cisplatin resistance in C13* cells.

A sensitive fluorometric assay for protein-bound DOPA and related products of radical-mediated protein oxidation.

Oxidative attack on proteins results in the hydroxylation of tyrosyl residues to protein-bound DOPA (3,4-dihydroxyphenylalanine). Existing methods for assaying protein-bound DOPA have poor sensitivity and numerous possible interferences, such that accurate determination (especially of very low DOPA concentrations) has required time-consuming acid hydrolysis and HPLC analysis with fluorometric detection. This work presents a sensitive and selective assay for peptide or protein-bound o-benzoquinones derived from DOPA based on fluorometric detection of ethylenediamine derivatives. Detection limits for protein-bound DOPA are in tbe range 0.53-4.70 ng/mL for the assay mixture, corresponding to sample DOPA concentrations of 0.59-5.30 ng/mL (representing a minimum of 6-54 pmole detected), depending on the particular protein/peptide under study. The assay response increases linearly with DOPA concentration, and also with the extent of radical exposure of the protein. The assay is a simple and fast way to assess DOPA formation and thus oxidative damage in a protein.

Factors involved in the down-regulation of cytochrome P450 during Listeria monocytogenes infection.

The activation of host defense mechanisms has been shown to cause a depression in hepatic cytochrome P450-mediated metabolism in rodents and humans. In a previous study, it was demonstrated that the Gram-positive bacteria Listeria monocytogenes causes a down-regulation of hepatic cytochrome P450 and related substrate metabolism as a result of a pretranslational depression of apoprotein synthesis. The objectives of this study were to determine whether the effect of listeria on hepatocyte cytochrome P450 involves hepatic nonparenchymal cells and whether the hemolysin, secreted only by hemolytic forms of the bacteria, plays any part in mediating this effect. Total cytochrome P450 levels as well as ethoxyresorufin-O-dealkylase (EROD) and benzyloxyresorufin-O-dealkylase (BROD) activities were significantly reduced in hepatic microsomes isolated from mice infected in vivo for 48 h with 15U listeria, whereas the same dose of the avirulent non-hemolytic M3D strain had no effect. Listeria (15U) significantly depressed hepatocyte EROD and BROD activities after 24 h incubations with liver cell cultures containing hepatocytes and nonparenchymal cells, as the result of both a direct effect on the hepatocyte and an interaction of listeria with hepatic nonparenchymal cells. The M3D strain of listeria had no effect on cytochrome P-450-mediated metabolism in isolated cells, confirming that hemolysin is an essential component of the mechanism responsible for the down-regulation of cytochrome P450 during listeria infections.

Relation between platinum-DNA adducts and complete remission in adult acute nonlymphocytic leukemia.

The purpose of this study was to determine the relationship between platinum-DNA adducts in leukemic cells and the success of remission induction therapy in adult patients with acute nonlymphocytic leukemia (ANLL). Freshly isolated cells from pre-treatment bone marrow aspirates of 14 patients were incubated with cisplatin in vitro and the amount of platinum bound to DNA was determined using a competitive ELISA procedure and an antibody directed against platinum-modified DNA. Platinum-DNA adduct levels discriminated well between complete remission (CR) and remission failure (RF) patients, treated with mitoxantrone, cytosine arabinoside +/- carboplatin.

Cross-resistance to cisplatin in cells resistant to photofrin-mediated photodynamic therapy.

This study shows that a Photofrin-induced photodynamic therapy-resistant variant (RIF-8A) of a radiation-induced fibrosarcoma-1 cell line (RIF-1) is cross-resistant to cis-diamminedichloroplatinum(II) (cisplatin). This is the first study to show cross-resistance to cisplatin in photodynamic therapy-resistant variants in vitro. Resistance does not appear to be the result of elevated glutathione levels since neither the resistant variant (RIF-8A) nor the parental line (RIF-1) varied in total glutathione levels. However, cisplatin-DNA adduct levels differed significantly between the two cell types. Immediately following a 1-h exposure to cisplatin (50 microM), RIF-1 cells contained 44.6 +/- 2.0 (SEM) pg platinum/micrograms DNA while RIF-8A cells contained 24.8 +/- 6.3 pg platinum/micrograms DNA. In addition, the resistant variant had decreased plasma and mitochondrial membrane potentials. The plasma and mitochondrial membranes of the resistant variant accumulated 3- and 3.6-fold less rhodamine 123, respectively. The difference in rhodamine 123 accumulation could not be attributed to elevated P-glycoprotein expression because both the parental line and the variant contained similar amounts of P-glycoprotein. In conclusion, alterations in the plasma and/or mitochondrial membrane potentials may provide cells with a survival advantage when challenged with either photodynamic therapy or cisplatin in vitro. This appears to be a novel mechanism of resistance.

Mechanism of hepatic cytochrome P450 modulation during Listeria monocytogenes infection in mice.

There have been numerous reports of altered drug clearance during episodes of viral infection and during the clinical use of recombinant interferons, but there have been very few reports regarding the effect of active bacterial infections on cytochrome P450-mediated metabolism. The objective of this study was to determine the mechanism by which the Gram-positive bacteria Listeria monocytogenes causes a depression of cytochrome P450-mediated biotransformation in mice. After induction with beta-napthoflavone, hepatic microsomal cytochrome P450 levels were reduced by 40% and ethoxyresorufin-O-dealkylase (EROD) activity was decreased by 65% in mice infected for 48 hr. The loss of EROD activity was accompanied by losses of cytochrome P450IA apoenzyme and cytochrome P450IA mRNA. Listeria infection did not affect total mRNA levels, as determined by oligo(dT)18 hybridization. The time course of these effects demonstrated that an up-regulation of cytochrome P450IA preceded the loss of this isozyme and that changes in cytochrome P450IA mRNA preceded the changes in apoenzyme levels and EROD activity. In hepatic microsomes from uninduced mice, cytochrome P450 levels and the rates of dealkylation of ethoxyresorufin, benzyloxyresorufin, pentoxyresorufin, and aminopyrine were significantly reduced, by 40-60%, after 48 hr of infection. The decrease in aminopyrine-N-demethylase activity was accompanied by a loss of cytochrome P450IID9 mRNA after 48 hr of infection. Cytochrome P450IID9 mRNA levels returned to normal after 96 hr of infection, whereas aminopyrine-N-demethylase activity was still decreased at this time. No up-regulation of cytochrome P450IID9 occured before the loss of this isozyme. The results of this study indicate that the changes in the levels of cytochrome P450IA and cytochrome P450IID9 that are observed during L. monocytogenes infection occur at a pretranslational step. If other bacteria have a similar capacity to depress cytochrome P450 by such a mechanism, then drugs with narrow therapeutic indices should be administered with caution during infectious diseases caused by bacteria or viruses.