Contribution of hydrazines-derived alkyl radicals to cytotoxicity and transformation induced in normal c-myc-overexpressing mouse fibroblasts

Abstract

Several hydrazine derivatives (HD) tested so far have pharmacological activities, but many also have toxic side effects, including carcinogenesis. Their toxicity has been ascribed to carbocations (via formation of azoxy intermediates), alkyl radicals or reactive oxygen species. Cytotoxicity and transformation by carbocations is widely accepted, but the role of alkyl radicals is still questioned. We have investigated the cytotoxicity of HD to mouse fibroblasts in three activation systems in which enhanced alkyl radical formation is demonstrated by electron spin resonance/spin-trapping. Cytotoxicity was assayed by inhibition of [3H-methyl]thymidine uptake into DNA of Balb/c 3T3 and/or Myc 9E fibroblasts (normal Balb/c 3T3 cells over-expressing the c-myc proto-oncogene). Based on the results obtained in the cytotoxicity assays we also investigated the transforming potential of procarbazine (PCZ) and methylhydrazine (MeH) activated by horseradish peroxidase (HRP) using the Myc 9E cell line, which aims at the activation of a second cooperating oncogene. Our results show that: (i) cytotoxicity of HD to mouse fibroblasts is increased by HRP activation of MeH, phenelzine and PCZ, which displayed enhanced alkyl radical formation, but not of 1,2-dimethylhydrazine (DMH), which did not produce increased alkyl radical formation under these conditions; (ii) cytotoxicity of neutrophil-activated MeH (producing a 10-fold higher concentration of methyl radicals), is more pronounced than DMH; (iii) MeH and DMH activated by prolonged auto-oxidation in 24-h incubations have comparable cytotoxicity and alkyl radical formation; and (iv) PCZ and MeH activation by HRP to alkyl radicals increased the transformation induced in Myc 9E cells. Taken together, our results strongly support a role for hydrazine-derived alkyl radicals in HD-induced cytotoxicity and cell transformation.

Mechanisms of Anti-Cancer Agents Emphasis on Oxidative Stress and Electron Transfer

“…Metabolic studies performed with monosubstituted derivatives support the route shown in Fig. (14) [203][204][205].…”

“…This sequence bears analogy to that described in the Peroxides section. Alternatively, evidence exists for a DNA alkylating pathway [204].…”

Brown seaweeds protect against azoxymethane-induced hepatic repercussions through up-regulation of peroxisome proliferator-activated receptor gamma and attenuation of oxidative stress

“…Several studies revealed that AOM is a potent carcinogen for the liver (Chastre et al 2012) and at low doses induce hepatotoxicity with ductular hyperplasia (Shan et al 2008;Khurana et al 2010). Although derived from a rare plant and human exposure to AOM is infrequent, exposure to structurally related hydrazine compounds that are found in herbicides, rocket fuels, tobacco and drugs is common (Gamberini et al 1998). Therefore, by use of AOM-induced hepatic injury in mice we conducted the present study to elucidate the role of brown seaweeds in mitigating AOM-induced hepatotoxicity.…”

Assessment and Validation of US EPA's OncoLogic® Expert System and Analysis of Its Modulating Factors for Structural Alerts

“…Hydrazine derivatives are activated to reactive intermediates, such as free radicals and carbocations, through a variety of cellular oxidative metabolic pathways. Aliphatic azo and azoxy species are intermediates in the activation pathways of hydrazine [15].…”