1. Replacing Mn2+ with Co2+ in Human Arginase I Enhances Cytotoxicity toward <scp>l</scp>-Arginine Auxotrophic Cancer Cell Lines
- Author
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Robert M. Breece, Paul Cherukuri, David L. Tierney, Lynne Chantranupong, Everett Stone, Brent L. Iverson, George Georgiou, Steven A. Curley, and Evan S. Glazer
- Subjects
Carcinoma, Hepatocellular ,Arginine ,Auxotrophy ,Chemical biology ,Gene Expression ,Antineoplastic Agents ,Biology ,Biochemistry ,Article ,Cell Line, Tumor ,Neoplasms ,Enzyme Stability ,Escherichia coli ,Humans ,Enzyme kinetics ,Cytotoxicity ,Melanoma ,Cell Proliferation ,chemistry.chemical_classification ,Manganese ,Arginase ,Cell growth ,Liver Neoplasms ,Cobalt ,General Medicine ,In vitro ,X-Ray Absorption Spectroscopy ,Enzyme ,chemistry ,Molecular Medicine ,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.
- Published
- 2010
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