COVALENT SEQUESTRATION OF MELPHALAN BY METALLOTHIONEIN AND SELECTIVE ALKYLATION OF CYSTEINES

Rabbit liver metallothionein-2 is shown to form covalent bonds with th e anticancer agent melphalan, in support of the hypothesis that covale nt sequestration by metallothionein constitutes one mechanism for the cross-resistance acquired by cancer patients to therapeutic alkylating agents. Among 20 cysteines in the 2-domain protein, 89% of the first alkylation reaction occurs with 2 that cochelate a zinc cation in the carboxy domain. Computer-supported docking studies indicate a favorabl e binding site for melphalan near these cysteine sulfhydryl groups. Al though folded metallothionein-2 is resistant to trypsin cleavage, alky lation by 1 mol of melphalan allows cleavage by trypsin between the tw o globular domains.