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Toxicity of fotemustine in rat hepatocytes and mechanism-based protection against it
N P Vermeulen1, J N Commandeur, E J Groot
1Leiden/Amsterdam Center for Drug Research, Department of Pharmacochemistry, Vrije Universiteit, Amsterdam, The Netherlands. vermeule@chem.vu.nl
Abstract:
Fotemustine is a relatively novel DNA-alkylating 2-chloroethyl-substituted N-nitrosourea (CENU) drug, clinically used for the treatment of disseminated malignant melanoma in different visceral and non-visceral tissues. Thrombocytopenia has been observed in patients treated with fotemustine and liver and renal toxicities as well. In this study, firstly the metabolism of fotemustine was investigated in vitro and secondly the undesired cytotoxicity of fotemustine as well as different ways of protection against it. In rat hepatocytes, chosen as a model system, fotemustine was shown to cause lactate dehydrogenase (LDH) leakage, glutathione (GSH) depletion, GSSG-formation and lipid peroxidation (LPO). A reactive metabolite, DEP-isocyanate, is most likely responsible for these undesired cytotoxic effects. Based on the observed cytotoxicity mechanisms, chemoprotection with several sulfhydryl-containing nucleophiles and antioxidants was investigated. The sulfhydryl nucleophiles; GSH, N-acetyl-L-cysteine (NAC) and glutathione isopropylester (GSH-IP) protected almost completely against fotemustine-induced LDH-leakage and LPO. NAC and GSH protected partly against fotemustine-induced GSH-depletion. The antioxidant, vitamin E protected completely against fotemustine-induced LPO, but only partly against fotemustine-induced LDH-leakage and not against GSH-depletion. Ebselen, a peroxidase-mimetic organoselenium compound, did not show protective effects against the cytotoxicity of fotemustine, possibly because GSH is required for the bioactivation of ebselen. It is concluded that co-administration of sulfhydryl nucleophiles, in particular NAC and GSH-IP, possibly in combination with antioxidants, such as vitamin E, are effective against the toxicity of fotemustine in vitro. It might, therefore, be worthwhile to investigate the cytoprotective potency of these agents against undesired toxicities of fotemustine in vivo as well.
Insights
Fotemustine, a melanoma drug, causes toxicity via a reactive metabolite. Sulfhydryl nucleophiles like N-acetyl-L-cysteine and glutathione isopropylester, along with vitamin E, show promise in protecting against fotemustine
Area of Science:
- Pharmacology
- Toxicology
- Biochemistry
Background:
- Fotemustine is a DNA-alkylating agent used for malignant melanoma.
- Clinical use reveals fotemustine-induced thrombocytopenia, liver, and renal toxicities.
- Understanding fotemustine's cytotoxic mechanisms is crucial for developing protective strategies.
Purpose of the Study:
- Investigate the in vitro metabolism of fotemustine.
- Identify mechanisms of fotemustine-induced cytotoxicity.
- Evaluate chemoprotective agents against fotemustine toxicity.
Main Methods:
- In vitro study using rat hepatocytes.
- Assessed fotemustine effects on lactate dehydrogenase (LDH) leakage, glutathione (GSH) depletion, GSSG-formation, and lipid peroxidation (LPO).
- Tested protection by sulfhydryl nucleophiles (GSH, N-acetyl-L-cysteine (NAC), GSH-isopropylester (GSH-IP)) and antioxidants (vitamin E, ebselen).
Main Results:
- Fotemustine induced LDH leakage, GSH depletion, and LPO in rat hepatocytes.
- A reactive metabolite, DEP-isocyanate, is implicated in fotemustine's cytotoxicity.
- NAC, GSH-IP, and GSH significantly protected against LDH leakage and LPO; NAC and GSH offered partial protection against GSH depletion.
- Vitamin E fully protected against LPO but offered partial protection against LDH leakage and no protection against GSH depletion.
- Ebselen showed no protective effects.
Conclusions:
- Sulfhydryl nucleophiles (NAC, GSH-IP) and potentially vitamin E are effective in vitro cytoprotective agents against fotemustine toxicity.
- Further in vivo investigation of these agents for fotemustine toxicity is warranted.