Antagonism in effectiveness of evofosfamide and doxorubicin through intermolecular electron transfer.

Hypoxic cells pose a problem in anticancer chemotherapy, in which often drugs require oxygen as an electron acceptor to bring about the death of actively cycling cells. Bioreductive anticancer drugs, which are selectively activated in the hypoxic regions of tumours through enzymatic one-electron reduction, are being developed for combination with chemotherapy-, radiotherapy- and immunotherapy-containing regimens to kill treatment-resistant hypoxic cells. The most clinically-advanced bioreductive drug, evofosfamide (TH-302), which acts by releasing a DNA-crosslinking mustard, failed to extend overall survival in combination with doxorubicin, a topoisomerase II inhibitor, for advanced soft tissue sarcoma in a pivotal clinical trial. However, the reasons for the lack of additive efficacy with this combination are unknown. Here, we show that the radical anion of evofosfamide undergoes electron transfer to doxorubicin in kinetic competition to fragmentation of the radical anion, thus suppressing the release the cytotoxic mustard. This electron transfer process may account, at least in part, for the lack of overall survival improvement in the recent clinical trial. This study underlines the need to consider both redox and electron transfer chemistry when combining bioreductive prodrugs with other redox-active drugs in cancer treatment.

Pentamidine antagonizes the benznidazole's effect in vitro, and lacks of synergy in vivo: Implications about the polyamine transport as an anti-Trypanosoma cruzi target.

Benznidazole is the first-line drug used in treating Chagas disease, which is caused by the parasite Trypanosoma cruzi (T. cruzi). However, benznidazole has limited efficacy and several adverse reactions. Pentamidine is an antiprotozoal drug used in the treatment of leishmaniasis and African trypanosomiasis. In T. cruzi, pentamidine blocks the transport of putrescine, a precursor of trypanothione, which constitutes an essential molecule in the resistance of T. cruzi to benznidazole. In the present study, we describe the effect of the combination of benznidazole and pentamidine on isolated parasites, mammalian cells and in mice infected with T. cruzi. In isolated trypomastigotes, we performed a dose-matrix scheme of combinations, where pentamidine antagonized the effect of benznidazole, mainly at concentrations below the EC50 of pentamidine. In T. cruzi-infected mammalian cells, pentamidine reversed the effect of benznidazole (measured by qPCR). In comparison, in infected BALB/c mice, pentamidine failed to get synergy with benznidazole, measured on mice survival, parasitemia and amastigote nest quantification. To further explain the in vitro antagonism, we explored whether pentamidine affects intracellular trypanothione levels, however, pentamidine produced no change in trypanothione concentrations. Finally, the T. cruzi polyamine permease (TcPAT12) was overexpressed in epimastigotes, showing that pentamidine has the same trypanocidal effect, independently of transporter expression levels. These results suggest that, in spite of the high potency in the putrescine transport blockade, TcPAT12 permease is not the main target of pentamidine, and could explain the lack of synergism between pentamidine and benznidazole.

Concomitant Benznidazole and Suramin Chemotherapy in Mice Infected with a Virulent Strain of Trypanosoma cruzi.

Although suramin (Sur) is suggested as a potential drug candidate in the management of Chagas disease, this issue has not been objectively tested. In this study, we examined the applicability of concomitant treatment with benznidazole (Bz) and suramin in mice infected with a virulent strain of Trypanosoma cruzi. Eighty 12-week-old male C57BL/6 mice were equally randomized in eight groups: (i) noninfected mice (negative control) and mice infected with T. cruzi Y strain receiving (ii) no treatment (positive control), (iii) Bz, 100 mg/kg of body weight per day, (iv) Sur, 20 mg/kg/day, and (v to viii) Sur, 20 mg/kg/day, combined with Bz, 100, 50, 25, or 5 mg/kg/day. Bz was administered by gavage, and Sur was administered intraperitoneally. Sur dramatically increased the parasitemia, cardiac content of parasite DNA, inflammation, oxidative tissue damage, and mortality. In response to high parasitic load in cardiac tissue, Sur stimulated the immune system in a manner typical of the acute phase of Chagas disease, increasing tissue levels of gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) and inducing a preferential IgG2a anti-T. cruzi serum pattern. When Sur and Bz were combined, the infection severity was attenuated, showing a dose-dependent Bz response. Sur therapy had a more harmful effect on the host than on the parasite and reduced the efficacy of Bz against T. cruzi infection. Considering that Sur drastically reinforced the infection evolution, potentiating the inflammatory process and the severity of cardiac lesions, the in vivo findings contradicted the in vitro anti-T. cruzi potential described for this drug.

Metabolic transformation and mechanism of action of mononitroso caffeidine- a new interpretation.

Although caffeine is not carcinogenic, its hydrolysed product, caffeidine causes human cancer, possibly through endogenous nitrosation to form mononitroso caffeidine (MNC). MNC undergoes enzymatic demethylation and reacts with cellular nucleophiles, notably DNA, via the formation of a putative imidazole diazonium ion. Its interaction with proteins has not been reported. The present work is based on the hypothesis that some active metabolites of MNC covalently interact with cellular DNA and/or proteins to initiate carcinogenesis. We report here the synthesis of a possible reactive metabolite of MNC, viz., N, 1-methyl-4(N-methyl-N-nitrosamino)-imidazole-5-carboxylic acid (MNIC). Its structure has been determined by uv, ir, nmr and mass spectral analyses and its interaction with egg albumin and human serum protein has been examined by uv and CD spectroscopy. We concluded that metabolic activation of MNC occurs through the formation of MNIC. Avoiding consumption of salted tea or coffee that prevents the intake of caffeidine will possibly eliminate the risk of MNC carcinogenicity.

CCK-8S systemic administration blocks the 7-nitroindazole-induced effects on the EEG of striatum and globus pallidus: a FFT analysis in the rat.

BACKGROUND: Nitric oxide (NO) and cholecystokinin (CCK) are involved in the modulation of several neurotransmitter systems in the basal ganglia, and a functional interaction between their modulatory effects could be hypothesised. MATERIALS AND METHODS: We studied the effects exerted by the administration of 7-nitroindazole (7-NI) (50 mg kg(-1) i.p.), a selective inhibitor of neuronal NO synthase, on the depth EEG activity of the striatum and of the globus pallidus in both not pre-treated and sulphated CCK octapeptide (CCK-SS)-treated (100 nM kg(-1) i.p.) rats. Striatal and pallidal depth EEG power spectra were examined by means of a Fast Fourier Transform analysis. RESULTS: Striatal depth recordings showed a marked increase of % power of slow standard rhythms after 7-NI systemic treatment. In contrast, pallidal recordings revealed an increase of % power of rapid standard rhythms after i.p. injection of 7-NI. The same modifications were not evidenced in CCK-8S pre-treated rats after 7-NI administration. CONCLUSION: The results show an influence exerted by peripheral CCK on the nitrergic modulation of the bioelectric activities of the striatum and of the globus pallidus. This effect could be of particular interest in the light of NO and CCK involvement in the neuroprotective mechanisms.

Prevention of benznidazole-induced prolonging effect on the pentobarbital sleeping time of rats using different thiol-containing compounds.

Benznidazole (BZ) is a nitroimidazolic chemotherapeutic agent employed against the acute and indeterminate phase of Chagas' disease, a tropical sickness afflicting more than twenty million people in Latin America. BZ has serious toxic side effects forcing people to stop treatment. These effects were attributed to the nitroreductive metabolic activation of BZ to a hydronitroxide radical or the hydroxylamine, which would covalently bind to cellular components. One of these deleterious effects is the prolongation on the pentobarbital sleeping time of rats. This results from the covalent binding of BZ reactive metabolites, arisen during its nitroreductive metabolism, to the phospholipid component of the mixed function oxidase which biotransform the barbiturate. In this study, the potential ability of different thiol containing drugs to trap BZ reactive metabolites and to prevent BZ effect on the pentobarbital sleeping time was tested. Our HPLC studies evidenced that cysteine, N-acetylcysteine, penicillamine and glutathione were able to trap BZ reactive metabolites in vitro to produce one or two adducts. Reduced lipoic acid instead, decreased the intensity of the nitroreductive process without leading to detectable adducts. The in vivo administration of the thiol drugs, at dosage regimes available in literature, was able to markedly prevent the BZ prolongation effect on the sleeping time. Whether these thiols might prevent other BZ toxic effects without harming its chemotherapeutic actions remains to be established.

In vivo protective role of antioxidants against genotoxicity of metronidazole and azanidazole.

The mutagenicity of metronidazole and azanidazole has been extensively reported. Previous experiments demonstrated, by means of the intrasanguineous host-mediated assay, that they significantly induced mutagenicity in liver, kidney and lung of mice. The treatment of mice with butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT) by two different routes of administration (i.p. injection and oral intubation) significantly reduced liver- and kidney-mediated mutagenicity of azanidazole and metronidazole. No significant differences were observed between the routes of treatment in terms of protective effect on genotoxicity of azanidazole in the considered organs, whereas i.p. administration was the most suppressive on the mutagenicity of metronidazole. Even if BHT was the most effective agent in preventing mutation induction in mice, a detectable toxicity, in terms of increased mutagenicity, was evaluated in the liver. Evidence of lung abnormalities was also seen. The results suggest that the possible adverse effects on biological systems limit the prophylactic use of BHA and BHT in preventing the action of chemical carcinogens in man.

Misonidazole neurotoxicity in rats: Part II. Effect of pre- and intermittent treatment with pentobarbital on misonidazole neurotoxicity in the rat.

Rats pretreated for 5 days with 50 mg/kg of pentobarbital tolerated statistically significant higher doses of misonidazole before the onset of misonidazole-induced neurotoxicity than rats treated intermittently with the same dose of pentobarbital. Presumably in pretreated rats, pentobarbital induced an increase in the activities of hepatic microsomal enzymes that led to a more rapid metabolism of misonidazole than in rats treated only intermittently.

In vitro inhibition of misonidazole toxicity and melphalan chemopotentiation by metyrapone.

Overnight exposure of Chinese hamster cells, V-79-753B, to 10(-3)M metyrapone protected them against the hypoxiamediated toxicity of 10(-2)M misonidazole. This protection was accompanied by an increase in radiation resistance. There was no appreciable change in the oxygen-enhancement ratio, nor in the amount of sensitisation produced by 10(-3)M misonidazole. Treatment of cells with metyrapone (10(-3)M) or dexamethasone (1 microgram ml-1 [approximately 2 X 10(-6)M]) prior to exposure first to 5 X 10(-3)M misonidazole in hypoxia and then to melphalan in air, substantially decreased the amount of chemopotentiation produced by the sensitiser, although the toxicity of melphalan alone was not affected in cells treated with either compound. Cells pretreated with either metyrapone or dexamethasone had 2-3 times more glutathione than control cells. This increase in GSH could not explain the change in radiation response, since cells pretreated with 5 X 10(-5)M flurbiprofen, a non-steroidal anti-inflammatory agent, had similarly high GSH levels, but their radiation response is similar to that of untreated cells (Millar et al, 1981). Neither dexamethasone nor flurbiprofen affected cell growth, whilst metyrapone markedly decreased the growth of cells. The results are discussed in terms of possible mechanism(s).

Protection against misonidazole-induced toxicity in vitro by non-steroidal anti-inflammatory agents.

Overnight exposure of Chinese hamster cells, V-79-753B, to certain non-steroidal anti-inflammatory agents (NSAIA) including indomethacin (5 x 10(-5)M), benoxaprofen (5 x 10(-5)M) or aspirin (10(-4)M) protected against misonidazole-induced toxicity both in air and in hypoxia at 37 degrees C. In no instance was the radiosensitivity of cells affected by these treatments nor was there any effect on the amount of acute hypoxic cell radiosensitization produced by 1.0 mM misonidazole. There was no protection against misonidazole-induced toxicity when cells were pretreated with theophylline (10(-3)M). Protection against misonidazole-induced toxicity by benoxaprofen was not reversed by the addition of 1 microgram/ml prostaglandin E1 or F1 alpha. The results are discussed in terms of possible mechanisms.

Flurbiprofen, a non-steroid anti-inflammatory agent, protects cells against hypoxic cell radiosensitizers in vitro.

Overnight exposure of Chinese hamster cells (V79-753B) to 5 x 10(-5) M flurbiprofen (2-(2-fluoro-4-biphenyl)propionic acid) in vitro reduced the cytotoxic effects of misonidazole, 1-methyl-4-nitro-5-phenoxysulphonylimidazole (NSC 38087) and nitrofurantoin, both in air and in hypoxia at 37 degrees C. Flurbiprofen did not alter the cells' uptake of 14C-misonidazole, nor did it affect the radiosensitivity of aerobic or anaerobic cells, or the degree of hypoxic-cell radiosensitization produced by the sensitizers. When flurbiprofen-treated cells were exposed to melphalan there was no protection against cytotoxicity. These data suggest that flurbiprofen may inhibit the catabolism of radiosensitizers to toxic products and indicate the need to examine whether it will protect against misonidazole-induced toxicity in vivo.