Oral zidovudine, continuous-infusion fluorouracil, and oral leucovorin calcium: a phase I study.

A phase I clinical, pharmacologic, and biochemical evaluation of escalating oral zidovudine (AZT) given over 2 days with a fixed dose of continuous-infusion fluorouracil (800 mg/m2 per day X 3 days) and oral leucovorin calcium was performed. Eighteen patients were treated with doses of AZT ranging from 1.0 to 9.0 g/m2 per day. Nausea and vomiting were dose limiting, with a maximally tolerated dose of 7.5 g/m2 per day. Rash and mucositis occurred but were not dose limiting. A dose-related increase in peak plasma levels of AZT was observed, and the alpha half-life of AZT in plasma (75 min) was unaffected by these high doses. At doses above 4.0 g/m2 per day, trough levels significantly increased, perhaps reflecting prolonged absorption from the gut. No responses were observed; however, a significant increase in DNA single-strand breaks was observed in peripheral blood cells after a threshold dose of 4.0 g/m2 per day, confirming a biological effect of AZT in this regimen. Further trials with an intravenous formulation capable of maintaining plasma levels and circumventing dose-limiting toxicity are warranted.

Effect of vitamin E and beta-carotene on DNA strand breakage induced by tobacco-specific nitrosamines and stimulated human phagocytes.

The tobacco-specific nitrosamines (TSNAs), nitrosonornicotine (NNN) and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are metabolites of nicotine and are major carcinogens in cigarette smoke. Chronic inflammation may promote the carcinogenic effect of these nitrosamines through the generation of oxygen radicals. To evaluate the effect of oxygen radicals on TSNA-induced genetic damage, cultured human lung cells treated with NNN or NNK were exposed to stimulated human phagocytes and assayed for single-strand DNA breaks. TSNAs or stimulated phagocytes alone cause a significant increase in strand breakage which is augmented in an additive fashion when the two are combined. Pretreating the cells with vitamin E or beta carotene provided significant protection against the induction of DNA damage but vitamin E was significantly more effective than beta carotene. These data suggest a possible approach to the chemoprevention of tobacco-induced carcinogenesis.

The effect of epigallocatechin galleate and sarcophytol A on DNA strand breakage induced by tobacco-specific nitrosamines and stimulated human phagocytes.

The tobacco-specific nitrosamines (TSNAs) are metabolites of nicotine and are major carcinogens in cigarette smoke. Chronic inflammation may promote the carcinogenic effect of these nitrosamines through the generation of oxygen radicals as evidenced by an increase in DNA strand breakage in cultured human lung cells treated with stimulated human phagocytes and TSNAs. Sarcophytol A (SaA), a simple monohydroxycembratetraene isolated from marine soft coral, and (-)-epigallocatechin galleate (EGCG), one of the main constituents of green tea, both inhibit tumor promotion. To evaluate their effect on TSNA-induced genetic damage, cultured human lung cells were pretreated with SaA or EGCG and then exposed to the TSNA 4-(N-methyl-N-n-trosamino)-1-(3-pyridyl)-1-butanone (NNK) and stimulated human phagocytes and then assayed for single-strand DNA breaks. Both SaA and EGCG provided significant protection against the induction of genetic damage in these cells and may prove useful in the chemoprevention of tobacco-induced carcinogenesis.

Oxygen radicals potentiate the genetic toxicity of tobacco-specific nitrosamines.

Tobacco-specific nitrosamines (TSNAs), nitrosonornicotine (NNN) and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are metabolites of nicotine and the major carcinogens in cigarette smoke. To evaluate the effect of oxygen radicals on TSNA-induced genetic damage, MRC-5 fetal human lung cells were exposed to NNN and NNK (5 mM) and DNA single-strand breaks measured. Both NNN and NNK produced a dose-dependent increase in strand breaks up to 10 mM which was cytotoxic. In combination with enzymatically-generated oxygen radicals, strand breakage increased by approximately 50% for both NNN and NNK. Oxygen radical scavengers (superoxide dismutase, catalase, mannitol) significantly reduced the DNA damage caused by both the TSNAs and TSNAs plus oxygen radicals, suggesting that the genotoxicity is radical-mediated. Because both superoxide dismutase and catalase were protective, the hydroxyl radical may be playing an important role in the mediation of the DNA damage observed.

Translocation of chromosomes 16 and 18 in oxygen radical-transformed human lung fibroblasts.

Human lung fibroblasts (MRC5) were treated chronically with the oxygen radical-generating system hypoxanthine plus xanthine oxidase and assayed for malignant transformation in the soft agar colony assay. After a thrice weekly exposure to oxygen radicals for 4 and 5 weeks, there was a significant number of transformants compared to controls. In 4 separate experiments, karyotypes of the malignant transformants were examined. 22/75 metaphases exhibited karyotypic abnormalities and in 13/22 of the abnormal karyotypes, a t16:18 (p13.3,q21) translocation was observed. This genetic lesion may represent a marker for oxygen radical-induced malignant transformation in mammalian cells.

Niacin prevents DNA strand breakage by adenosine deaminase inhibitors.

The adenosine deaminase inhibitors deoxycoformycin and erythro-9-(2-hydroxy-3 nonyl) adenine (EHNA) induce single-strand DNA breaks in cultured human lymphocytes. Deoxycoformycin produced a significant number of strand breaks (4-fold increase compared to controls) and EHNA induced strand breaks in a dose-dependent manner. Strand breaks stimulate repair by poly(ADP-ribosylation) which requires NAD+ as a cofactor. Niacin is a precursor of NAD+ and when preincubated with human lymphocytes prior to exposure to adenosine deaminase inhibitors, strand breakage was reduced significantly. The administration of niacin may represent an approach to decreasing the toxicity associated with these agents.

Hydroxy- and hydroperoxy-6,8,11,14-eicosatetraenoic acids induce DNA strand breaks in human lymphocytes.

Oxygen radical-induced genetic damage may be mediated by products of lipid peroxidation, in particular, arachidonic acid. Hydroxy- and hydroperoxyeicosatetraenoic acids (HETEs and HPETEs) are intermediates in the metabolism of arachidonic acid to the leukotrienes. Several isomeric hydroxy- and hydroperoxy-6,8,11,14-eicosatetraenoic acids were evaluated for their ability to cause DNA single-strand breaks in human lymphocytes. Both HETEs and HPETEs induced strand breaks in a dose-dependent fashion at concentrations of 5, 10 and 20 microM. At each concentration, HETEs were more effective in producing breakage than the corresponding HPETEs. Each of the isomeric forms used were equally effective in producing strand breaks. Antioxidants (superoxide dismutase, catalase and mannitol) were protective. Iron chelation by desferrioxamine suppressed strand breakage by 45% and an additional 33% inhibition was observed upon the addition of the calcium chelator EGTA.

High-dose intravenous zidovudine with 5-fluorouracil and leucovorin. A phase I trial.

BACKGROUND: The inhibition of pyrimidine metabolism by 5-fluorouracil (5-FU) enhances the anti-cancer effects of zidovudine (formerly called AZT) in in vitro and in vivo model systems without additive toxicity. Zidovudine-induced DNA damage correlates with cytotoxicity. METHODS: A Phase I trial of high-dose continuous-infusion intravenous zidovudine therapy in combination with 5-FU and leucovorin therapy was performed. Eighteen patients with advanced malignant tumors were treated with 43 courses of oral leucovorin (50 mg every 4 hours); continuous-infusion 5-FU (800 mg/M2/day) for 72 hours (3 days); and zidovudine, begun 24 hours after the start of 5-FU and leucovorin, for 48 hours, and terminating with the end of the 5-FU infusion. Zidovudine plasma levels and zidovudine-induced DNA damage were assessed. RESULTS: Zidovudine administered in doses of 2-20 g/M2/day, added no obvious toxicity to the basic chemotherapeutic treatment with 5-FU and leucovorin but resulted in a dose-dependent biologic effect manifested by an increase in DNA strand breaks in peripheral blood cells. At doses greater than 15 g/M2/day, altered plasma kinetics of zidovudine were observed; plasma zidovudine levels increased dramatically in relation to the dose of zidovudine. Limitations in drug administration restricted administration of higher intravenous doses without achieving a maximally tolerated dose. No responses were seen in this heavily pretreated population. CONCLUSIONS: Based on the results of preclinical studies, plasma zidovudine levels greater than those achieved at the maximal dose (133 microns) are required for increased anti-cancer activity with 5-FU. Additional studies using a bolus or rapid infusion as a method of achieving higher peak levels are indicated.