title: Replacing Mn(2+) with Co(2+) in human arginase i enhances cytotoxicity toward l-arginine auxotrophic cancer cell lines.
abstract: Replacing the two Mn(2+) ions normally present in human Arginase I with Co(2+) resulted in a significantly lowered K(M) value without a concomitant reduction in k(cat). In addition, the pH dependence of the reaction was shifted from a pK(a) of 8.5 to a pK(a) of 7.5. The combination of these effects led to a 10-fold increase in overall catalytic activity (k(cat)/K(M)) at pH 7.4, close to the pH of human serum. Just as important for therapeutic applications, Co(2+) substitution lead to significantly increased serum stability of the enzyme. Our data can be explained by direct coordination of l-Arg to one of the Co(2+) ions during reaction, consistent with previously reported model studies. In vitro cytotoxicity experiments verified that the Co(2+)-substituted human Arg I displays an approximately 12- to 15-fold lower IC(50) value for the killing of human hepatocellular carcinoma and melanoma cell lines and thus constitutes a promising new candidate for the treatment of l-Arg auxotrophic tumors.
authors.affiliation: Department of Chemical Engineering, University of Texas, Austin, 78712, USA.
authors.forename: Everett M
authors.initials: EM
authors.lastname: Stone
authors.forename: Evan S
authors.initials: ES
authors.lastname: Glazer
authors.forename: Lynne
authors.initials: L
authors.lastname: Chantranupong
authors.forename: Paul
authors.initials: P
authors.lastname: Cherukuri
authors.forename: Robert M
authors.initials: RM
authors.lastname: Breece
authors.forename: David L
authors.initials: DL
authors.lastname: Tierney
authors.forename: Steven A
authors.initials: SA
authors.lastname: Curley
authors.forename: Brent L
authors.initials: BL
authors.lastname: Iverson
authors.forename: George
authors.initials: G
authors.lastname: Georgiou
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism* / Q000627:therapeutic use*; D001119:Arginase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000627:therapeutic use*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003035:Cobalt / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy; D008345:Manganese / Q000378:metabolism*; D008545:Melanoma / Q000188:drug therapy; D009369:Neoplasms / Q000188:drug therapy*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000970:Antineoplastic Agents; D003035:Cobalt; D008345:Manganese; D001119:Arginase