Functionalization of Pt(IV)–Ammines Enables Site-Directed Covalent Modification of mRNA

Developing chemical toolkits for mRNA modification has remained an immense challenge driven by inherent difficulties in targeting mRNA molecules. Antisense oligonucleotides (ASOs) offer a promising framework for targeting specific mRNA sequences, yet they do not possess the capacity to alter the covalent structure of mRNA except through enzyme-mediated hydrolysis. The requirement of relying on an enzyme for modifying mRNA incurs several limitations on the application, design, and delivery of ASOs. To address these limitations, we developed a Pt(IV)-ASO strategy that combines the reactivity of platinum with the sequence specificity of ASOs to covalently modify nucleic acids, including short RNA and mRNA, in a selective, enzyme-free manner. Access to Pt(IV)-ASO constructs was made possible by an innovative equatorial Pt(IV) ammine functionalization strategy, allowing for conjugation of carboxylic acids directly to the Pt core. Reactivity with 21-mer RNA and full-length mRNA by Pt-ASO con-structs was demonstrated, and the covalently modified products were characterized using a suite of orthogonal techniques, such as electrophoretic mobility shift assay, MALDI-TOF MS, temperature-dependent dissociation assay, and RT-qPCR. Constructs were optimized for their reactivity and selectivity, allowing for Pt(IV)-PMO constructs with sub-nanomolar IC50 values in an RNA competition assay. This Pt(IV)-ASO plat-form facilitates new avenues for RNA modification by providing a strategy for covalent modification of nucleic acids with potential applications for molecular biology research.