Riitta Mustonen

Effects of commercial chlorophenolate, 2, 3, 7, 8-TCDD, and pure phenoxyacetic acids on hepatic peroxisome proliferation, xenobiotic metabolism and sister chromatid exchange in the rat

The induction of hepatic peroxisome proliferation and drug metabolizing enzymes and of sister chromatid exchange (SCE) in lymphocytes was studied in male Han/Wistar rats after exposing them for 2 weeks to a commercial chlorophenolate formulation (Ky-5) (100mg/kg/ day), to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD; 0.05–5 μg/kg/wk) and to the pure phenoxyacetic acids, 2,4-dichlorophenoxyacetic acid (2,4-D; 100 mg/kg/day) and 2-chloro-4-methylphenoxyacetic acid (MCPA; 100 mg/kg/day). The chlorophenolate formulation and pure 2,4-D and MCPA caused significant increases in the number of peroxisomes in liver cells, although the average size of peroxisomes was not affected, whereas the effect of even the highest dose of 2,3,7,8-TCDD remained small. This finding indicates that dioxin impurities do not account for the peroxisome proliferation induced by chlorophenolate. The relative weight of the liver increased significantly in rats treated with the chlorophenolate formulation and with 2,3,7,8-TCDD (5.0 and 0.5 μg/kg). The pattern of induction of xenobiotic metabolizing enzymes showed some differences between chlorophenolate treatment and 2,3,7,8-TCDD treatment. Furthermore, the effects of pure phenoxyacetic acids were different from that seen with chlorophenolate and 2,3,7,8-TCDD. The highest dose of 2,3,7,8-TCDD increased the frequency of SCE in circulating lymphocytes slightly, but significantly.

DNA adducts in experimental cancer research

SummaryThe role of DNA adducts in the initiation of cancer is scrutinized in this presentation. Work on the activation of oncogenes, particularly on ras, has provided new evidence to link DNA adducts and tumour formation. Polycyclic hydrocarbons and nitroso compounds can cause activation of ras oncogenes through a defined point mutation. The properties of two DNA binding agents, styrene oxide and cisplatin are discussed. Styrene oxide is a versatile electrophile causing numerous adducts; cisplatin has a high specificity towards guanine-N-7 and cross-link formation. Finally, the relation of specific adducts to carcinogenic potency as defined by TD50 values is investigated. For small alkyl groups, O-alkylation of bases correlates with potency but among others, particularly the bulky carcinogens, 7-alkylguanines appear as correlates of potency. Most such potent agents forming 7-alkylguanines induce depurination and imidazole ring-opening.

32P-Postlabelling of 7-methyl-dGMP ring-opened 7-methyl-dGMP and platinated dGpdG

The 32P-postlabelling technique introduced by Randerath and coworkers was used to investigate the efficiency of the phosphorylation reaction by T4 polynucleotide kinase using three synthesized adducts: 7-methyl-dGMP, ring-opened 7-methyl-dGMP and platinated dGpdG. The methylated substrates were detected at sub-fmol sensitivities. 7-Methyl-dGMP was quantitatively phosphorylated at these low concentrations. The efficiency of phosphorylation of the ring-opened product was less (about one order of magnitude) and that of Pt(dGpdG) about three orders of magnitude less. These results show that T4 polynucleotide kinase phosphorylation is an efficient reaction with 7-methyl-dGMP and with ring-opened 7-methyl-dGMP, even though in the latter case longer incubation times may have to be used to boost the reaction towards completion. By contrast, the low level of phosphorylation with Pt(dGpdG) does not appear encouraging for quantitative determination requiring a high sensitivity.

Determination of cis-diamminedichloroplatinum (II) in plasma proteins and hemoglobin of cancer patients

A study was conducted to determine the levels of cis-diamminedichloroplatinum (II) (cisplatin) in plasma proteins and hemoglobin of cancer patients after cisplatin chemotherapy. Thirty-seven cancer patients with different type of cancers (lung, esophageal, urinary tract, and testicular cancer, melanoma, osteosarcoma etc) received cisplatin 32–110 mg/m2 either as a single intravenous infusion or as infusions given on 5 consecutive days. Blood samples were classified according to time from previous cisplatin infusion. They included a total of 103 samples taken before the cisplatin infusion, immediately after infusion, 1, 2 or 3–5 days after infusion or 2–3, 4, or 5–7 weeks after infusion. Platinum (Pt) concentration in plasma proteins and hemoglobin was measured by atomic absorption spectroscopy (AAS). The data showed a correlation between the dose of cisplatin and the concentrations of Pt in plasma proteins and hemoglobin of cancer patients. Plasma proteins bound more cisplatin than hemoglobin, the respective maxima in the patients receiving > 50 mg/m2 being 27.7 and 1.6 ng/mg protein in samples drawn immediately after treatment. The kinetics of disappearance of Pt from plasma proteins showed several components; the initial half-life was about 5–7 days. The disappearance of Pt from hemoglobin showed a single component of a half-life of 12–14 days.

Cisplatin Binding to Plasma Proteins and Hemoglobin in Cancer Patients

The antitumor activity of cisplatin (cis-diamminedichloroplatinum (II)) is thought to involve binding to cellular protein and nucleic acids (Roberts and Thomson 1979). The purpose of this study was to investigate using atomic absorption spectroscopy (AAS) the correlation between cisplatin dose and Pt concentrations in blood proteins (plasma proteins and hemoglobin) of cancer patients undergoing chemotherapy.