Zofia Walter

Induction of DNA-protein cross-links by platinum compounds.

Abstract The differences between cis- and trans-diamminedichloroplatinum II (DDP) in forming DNA-protein cross-links in isolated human lymphocytes were investigated. Both cis- and trans-DDP can induce DNA-protein cross-links. We show that cis-DDP forms complexes between DNA and proteins faster than trans-DDP. This results from an increase in the quantity of DNA and platinum together with an increase in drug concentration. Under the same conditions trans-DDP causes a decrease in DNA-forming complexes with proteins. After a 12 h incubation of lymphocytes we observe a similar level of DNA in DNA-protein crosslinks induced by DDP isomers, but more platinum appears in complexes induced by trans- DDP. The results obtained demonstrate that the antitumor drug - cis-DDP and the clinically ineffective trans-DDP induce links between DNA and proteins in a different manner. We suggest that the therapeutic activity of ds-DDP can in part arise from rapidly forming DNA-protein complexes which can destroy the most important cellular processes, such as replication and transcription.

Immunospecific protein of 34.5 kDa from DNA-protein cross-links induced by cis- and trans-diamminedichloroplatinum.

Cis ‐diamminedichloroplatinum(II) (cis ‐DDP) is one of the most often used anticancer drugs. It is generally accepted that the antitumor activity of the drug results from its interactions with DNA. Trans ‐diamminedichloroplatinum(II) (trans ‐DDP) also binds to DNA effectively, but is clinically ineffective. In the present work the lymphocyte nuclear proteins that participate in DNA—protein cross‐links induced by cis ‐ and trans ‐DDP are investigated. In lymphocytes which are incubated without platinum compounds there are DNA‐binding proteins in the range of 45–71kDa. It is shown that additional proteins of 28, 30, 34.5, 45 and 120kDa are cross‐linked with DNA in lymphocytes after 2‐h incubation with cis ‐DDP at concentrations of 0.1 and 0.5mM. Trans ‐DDP does not bind additional proteins to DNA after the same incubation time. Electrophoretic analysis shows that trans ‐DDP binds much more of the same nuclear proteins to DNA than cis ‐DDP after 12‐h incubation. In this study a test for the identification of 34.5kDa protein is also undertaken. This protein appears in the samples obtained after 12‐h incubation of lymphocytes with cis ‐ and trans ‐DDP at 0.5 and 1mM, especially. The protein of 34.5kDa from cross‐links induced by 1mM trans ‐DDP is recognized by antibodies against the protein of the same molecular weight from the nuclear matrix of the lymphocytes. The results obtained here are discussed in relation to the biological activity of diamminedichloroplatinum isomers.

Interaction of Organophosphorus Insecticide Methylparathion with Calf Thymus DNA and a Synthetic DNA Duplex

Abstract The interaction of an organophosphorus insecticide methylparathion (O.O-dimethyl 0-4-nitrophenyl phosphorothioate) with double-stranded DNA was characterized by UV and circular dichroism (CD) spectroscopy. Two kinds of DNA were employed: calf thymus DNA (CT DNA) and a synthetic two-stranded oligomer of sequence 5′-d(TTGGATCCGAATT-CAAGCTT)-3′ Melting curves and CD spectra were taken for the DNAs in the presence of the insecticide at methylparathion/DNA base pair molar ratio of 0.5. The insecticide evoked a decrease of the melting temperature and a broadening of the transition range for CT DNA. Similar effects were observed for the synthetic oligomer but they were less pronounced than in the case of CT DNA. Methylparathion evoked a slight shift and an increase in the amplitude of the negative band in the CD spectra of both DNAs. Obtained results indicate that methylparathion may perturb the thermal stability and conformation of DNA, which is an evidence that the insecticide has an ability to interact directly with DNA.

Chromium Incorporated in RNA and DNA

The objective of this study was to examine the effect of Cr(III) (chromium chloride) and Cr(VI) (potassium dichromate) on RNA and DNA-chromium adducts formation in isolated nucleic acids and isolated pig lymphocytes. The incubation of cells with potassium dichromate and chromium chloride at concentrations of 10 and 100 μm results in binding of a 1.2-1.9 fold greater number of chromium atoms to nuclear DNA than to total cellular RNA. The incubation of total cellular RNA and nuclear DNA isolated from lymphocytes with CrCl3 and K2Cr2O7 yielded a binding of 1.1-1.6 fold more of Cr atoms to RNA than to DNA. The number of chromium atoms bound to nucleic acids is higher after incubation with K2Cr2O7 than with CrCl3 in both experimental systems.