Is glutathione the major cellular target of cisplatin? A study of the interactions of cisplatin with cancer cell extracts

Abstract

Cisplatin is an anticancer drug whose efficacy is limited because tumors develop resistance to the drug. Resistant cells often have elevated levels of cellular glutathione (GSH), believed to be the major cellular target of cisplatin that inactivates the drug by binding to it irreversibly, forming [Pt(SG)2] adducts. We show by [1H,15N] HSQC that the half-life of 15N labeled cisplatin in whole cell extracts is ∼75 min, but no Pt-GSH adducts were observed. When the low molecular mass fraction (<3 kDa) of the extracts was incubated with cisplatin, binding toGSHwas observed probably due to removal of high molecular mass platinophiles. Two-thirds of the Pt adducts formed in whole cell extracts, had a molecular mass > 3 kDa. [Pt(SG)2] cannot account for more than 20% of the Pt adducts. The concentration of reduced thiols in the high molecular mass fraction of the extracts is six times higher than in the low molecular mass fraction. © 2009 American Chemical Society.