Cytochrome P450 isozymes 3A4 and 2B6 are involved in the in vitro human metabolism of thiotepa to TEPA.

PURPOSE: To establish the cytochrome P450 (CYP) isozymes involved in the metabolism of the alkylating agent, thiotepa, to the pharmacologically active metabolite, TEPA. METHODS: In vitro chemical inhibition studies were conducted by incubating thiotepa and pooled human hepatic microsomes in the presence of known inhibitors to CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. Studies were also performed with cloned, expressed CYP3A4, CYP2A6, CYP2E1 and CYP2B6 microsomes, and anti-CYP2B6 monoclonal antibody. RESULTS: Known CYP3A4 inhibitors reduced TEPA production. Inhibition with CYP2E1 inhibitors was inconsistent. All other inhibitors produced little or no change in TEPA formation. Cloned, expressed CYP2B6 and CYP3A4 microsomes catalyzed TEPA formation, whereas CYP2A6 and CYP2E1 did not. Incubation of thiotepa with anti-CYP2B6 antibody and cloned, expressed CYP2B6 microsomes resulted in reductions in the formation of TEPA, but no change in TEPA formation occurred in human liver microsomes. CONCLUSIONS: Thiotepa is metabolized in human liver microsomes by CYP3A4 (major) and CYP2B6 (minor). There is a potential for CYP-mediated drug interactions with thiotepa. Pharmacokinetic variability of thiotepa may be related to expression of hepatic CYP isozymes.

[1,4-dihydroisonicotinic acid (1,4-DHINA) derivatives, inhibitors of chemical mutagenesis]. / Proizvodnye 1,4-digidroizonikotinovoi kisloty (1,4-DGINK)-- ingibitory khimicheskogo mutageneza.

The paper summarizes the results of studies into the modifying effect of some 1,4-dihydroisonicotinic acid (1,4-DHINA) derivatives during chemical mutagenesis in eukaryotic organisms. The compounds under study are effective in reducing the incidence of point and chromosomal mutations induced by ethylmethane sulfonate (EMS) in Drosophila sex cells, displaying the specificity of the influence depending on some factors. The effects of these antimutagens on the formation and repair of chromosomal breaks were studied during mutagenized sperm storage in Drosophila female receptacula semenis. A relation was found between the female sensitivity to antimutagens and the appropriate modifying effect, on the one hand, and the oocytic genotype, on the other. The protective effect of one of 1,4-DHINA derivatives against alkylating agents (EMS and Thiophosphamide) was confirmed by in vivo experiments in mice and in cultured human lymphocytes. The revealed mechanisms of modified chemical mutagenesis both in the Drosophila sex cells and in the mammalian somatic cells are in favour of those of protective action, which are mediated by the antimutagenic cell system, as well as, perhaps, by repair processes.

[Study of the antimutagenic properties of Angelica archangelica by the micronucleus test]. / Izuchenie antimutagennykh svoistv dudnika lekarstvennogo (Angelica archangelica L.) mikroiadernym testom.

The antimutagenic activity Angelica archangelica L. water and alcohol extracts thio-tepa against mutagenicity was investigated by the micronucleus test in mouse bone marrow and peripheral blood cells. The reduction of thio-tepa mutagenic activity was more prominent when the extracts were injected 2-hours before thio-tepa treatment as it could be seen at the simultaneous treatment. The observed reduction of micronucleus frequencies was up to 77%. No genotoxic effects of Angelica extracts had been seen at the concentrations 50-100 mg/kg.

In vivo effects of single or combined dietary antimutagens on mutagen-induced chromosomal aberrations.

The food components chlorophyllin, beta-carotene and alpha-linolenic acid (in its methyl ester form) were tested in Chinese hamsters for antimutagenic activity on the powerful mutagen thio-tepa. Each of these natural protective compounds inhibited by 70-85% the clastogenic effects induced by the mutagen. When 2 or 3 of these antimutagens were administered simultaneously no additive effects were observed. alpha-Linolenic acid methyl ester was the most effective antimutagen under the experimental conditions.

Enhancement and attenuation of cytogenetic damage by vitamin C in cultured human lymphocytes exposed to thiotepa or L-ethionine.

Vitamin C (vit C) at 2 mM enhanced sister chromatid exchange (SCE) frequencies induced by Thiotepa (THIO) or L-ethionine (L-ETH) in cultured human lymphocytes. However, when vit C was tested at 0.02 mM and 0.2 mM a rather protective effect on SCE rates induced by THIO or L-ETH was identified. Vit C (2 mM) caused a cell division delay in cultures treated with THIO or L-ETH. Division delays caused by THIO or L-ETH were reversed in the presence of 0.02 mM or 0.2 mM vit C. Mitotic indices (MIs) in cultures treated with THIO or L-ETH continued to be suppressed in the presence of 2 mM vit C. However, vit C at 0.02 mM reversed suppression of MIs caused by L-ETH or THIO. These findings illustrate the complexity of the interactions of vit C in biological systems and indicate that with different concentrations vit C can cause or prevent genetic toxicity.

Use of intravesical cisplatin and mitomycin-C for recurrent transitional cell carcinoma of bladder refractory to thiotepa.

Superficial transitional cell carcinoma of the bladder (TCCaB) has a high incidence of recurrence. Intravesical thiotepa is the drug used most often for treatment. Intravesical mitomycin-C also has shown promise. Cisplatin has proven activity in patients with metastatic TCCaB and in experimental bladder cancer models. Patients who have no response to one intravesical agent such as thiotepa may respond to other agent(s) such as mitomycin-C or cisplatin. In this report we have evaluated 10 patients with superficial recurrent TCCaB who showed no response to intravesical thiotepa and were subsequently treated with mitomycin-C or cisplatin. Six patients were treated with cisplatin and 4 with mitomycin-C. The 4 treated with mitomycin-C had complete response or partial response within three months. Of the 6 treated with cisplatin, 4 had complete response within three months, and 2 had no response.

Anticlastogenic effect of beta-carotene in Chinese hamsters. Time and dose response studies with different mutagens.

beta-Carotene exhibited dose-dependent anticlastogenic effects on aberrations induced by the direct-acting mutagens thio-TEPA, methyl methanesulfonate and busulfan in the in vivo chromosome aberration test (bone marrow cells, Chinese hamsters). No effect was seen when retinol was used. Apparent differences in the action of beta-carotene on aberrations induced by the three applied mutagens may be due to differences in the solubility of the compounds and to the different routes of administration.

[Arsenic trioxide inhibition of the thiophosphamide induction of mutations in mouse germ and somatic cells]. / Ingibirovanie trioksidom mysh'iaka induktsii mutatsii tiofosfamidom v polovykh i somaticheskikh kletkakh myshi.

After single i. p. injection of arsenic trioxide, at the dosage range of 1/4 to 1/40 LD50 into hybrid mice (CBA X C57B1/6J)F1, no induction of dominant lethals in male germ cells was observed. However, it led to an increase in the number of micronuclei in the erythrocytes of bone marrow. Treatment with the effective dose of thioTEPA, causing an increase in the number of dominant lethals in male germ cells and in the number of micronuclei in the erythrocytes of bone marrow, followed by injection of arsenic trioxide, resulted in inhibition of the mutagenic activity of thioTEPA. This inhibition increased proportionally with the dose of arsenic trioxide.

The apparent decrease in thiotepa-induced chromosome aberrations in human lymphocytes caused by an effect of WR2721 on the cell cycle as found by the definitively determined division method.

Antimutagenic radioprotective compounds have been reported to decrease the yield of chemically induced chromosome aberrations even when administered long before the chemical mutagen thio-TEPA. Because thio-TEPA can induce aberrations in all parts of the cell cycle, it seemed likely that the apparent decrease in aberrations was the result of an effect of the antimutagen on the progression of cells through the cell cycle so that cells treated in the more sensitive stage would be scored. To test this possibility human lymphocytes were treated with the protective compound WR2721 and then thio-TEPA. The cells were grown in the presence of 5-bromodeoxyuridine, which allows the definitive determination of metaphases from cells that divided once, twice, or three times after treatment. The yield of aberrations observed in first division cells was the same whether or not the protector was present. A decrease in aberration yields appeared only in rapidly cycling cells that were in the second division at the time of fixation. Labeling experiments showed that in this rapidly dividing population fewer of the metaphase cells had been in G2 when thio-TEPA was added. The results indicate that part of the decrease in aberration yields obtained by treatment with an antimutagen several hours before the addition of a mutagen is an artifact of cell selection.

[Modelling modification of chemical mutagenesis in human cells. III. Linear index of protection as the standardized criterion of modification]. / Modelirovanie modifikatsii khimicheskogo mutageneza v kletkakh cheloveka. Soobshchenie III. Lineinyi pokazatel' zashchity--unifitsirovannyi kriterii modifikatsii.

The effect of substances with radioprotective activity, APAETP 2,3 (aminopropylaminoethylthiophosphoric acid 2,3), APAETP 3,3 and cystaphos, on chromosome aberrations, induced by thioTEPA in the culture of human lymphocytes was investigated. It is shown that the obtained curves "concentration -- effect" for thioTEPA can be described by equations rho = 1 -- e-(KC + alpha)2 and X = E -(KC + alpha)2 --1 for aberrant cells and for chromosome breaks in the presence of the investigated substances. On the basis of comparison of angle coefficients of regression the unificated characteristic of the efficiency of chemical mutagenesis is proposed: the linear protection index (LPI), with generalizes the effect of modificators in chemical mutagenesis.

[Modeling modification of chemical mutagenesis in human cells. 1. Elimination of chromosomal aberrations]. / Modelirovanie modifikatsii khimicheskogo mutageneza v kletkakh cheloveka. Soobshchenie I. Eliminatsiia aberratsii khromosom.

Elimination of chromosome aberrations was studied in populations of dividing cells. For this purpose, on the basis of the corresponding theory of Carrano-Heddle assuming the Poisson distribution, a theory is advanced by the authors based on geometrical distribution, describing the distribution of lesions caused by the action of tioTEF. Parameters of elimination are obtained observed in case of addition of a protector, aminopropy-laminoethylthiophosphoric acid (APAETF) in a lymphocyte culture of human peripheral blood. It is shown that the addition of the protector diminishes the probability of the transmission of chromosome aberrations to daughter cells.