Short interfering RNAs (siRNAs) can down-regulate protein production by site specific degradation of mRNA. We here report the in vitro efficiency of three siRNAs metalated with oxaliplatin. All siRNAs were selectively platinated in the sense Strand, and designed to target the AU-rich 3' UTR region of Wnt-5a mRNA cloned into a luciferase reporter plasmid. Two of the studied siRNAs reveal luciferase protein suppression levels well above 90% when used in nano-molar concentrations for both metalated and the corresponding native siRNA. The platinated siRNAs were also characterized with respect to thermal melting Properties, and the number of platinum adducts on the different sense strands were determined by MALDI-ToF MS. In all cases, platination was accompanied by a decrease in melting temperature. Further, the dominating oxaliplatin metalation site was the r(GpG)-adduct. The study indicates that metalation can be used as a general strategy to further expand the chemical nature of siRNAs. (C) 2008 Elsevier Inc. All rights reserved.