title: Metabolism of melphalan by rat liver microsomal glutathione S-transferase.
abstract: One of the major problems in the treatment of human cancer is the phenomenon of drug resistance. Increased glutathione (gamma-glutamylcysteinylglycine, GSH) conjugation (inactivation) due to elevated level of cytosolic glutathione S-transferase (GST) is believed to be an important mechanism in tumor cell resistance. However, the potential involvement of microsomal GST in the establishment of acquired drug resistance (ADR) remains uncertain. In our experiments, a combination of liquid chromatography/electrospray ionization/mass spectrometry (LC/ESI/MS) was employed for structural characterization of the resulting conjugates between GSH and melphalan, one of the alkylating agents. The spontaneous reaction of 1mM melphalan with 5mM GSH at 37 degrees C in aqueous phosphate buffer for 1h gave primarily the monoglutathionyl and diglutathionyl melphalan derivatives, with small amounts of mono- and dihydroxy melphalan derivatives. We demonstrated that rat liver microsomal GST presented a strong catalytic effect on the reaction as determined by the increase of monoglutathionyl and diglutathionyl melphalan derivatives and the decrease of melphalan. We showed that microsomal GST was activated by melphalan in a concentration- and time-dependent manner. Microsomal GST which was stimulated approximately 1.5-fold with melphalan had a stronger catalytic effect. Thus microsomal GST may play a potential role in the metabolism of melphalan in biological membranes, and in the development of ADR.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, 310031 Hangzhou, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Ye
authors.forename: Yijia
authors.initials: Y
authors.lastname: Lou
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D005033:Ethylmaleimide; D008401:Gas Chromatography-Mass Spectrometry; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008558:Melphalan / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D018906:Antineoplastic Agents, Alkylating; D005982:Glutathione Transferase; D005978:Glutathione; D005033:Ethylmaleimide; D008558:Melphalan