Development of artificial ribonucleases

Antisense oligonucleotides offer a new way of treating genetically based diseases by interfering with protein expression on the mRNA level. First generation phosphorothioate antisense oligonucleotides have shown promising results in animal experiments and several compounds are currently being tested in the clinics against a variety of diseases. Nevertheless, improvements of various aspects of the technology, such as stability, reduction of length and target affinity of oligonucleotides, are still highly desirable. As a consequence, a large number of chemical modifications of antisense compounds has been reported during the last decade. Unlike phosphorothioates, however, most second generation modifications do not induce degradation of messenger RNA by an RNase H-based mechanism, which is in most cases an essential component of antisense activity. An alternative approach to enable degradation of the mRNA comprises the covalent attachment of RNA cleaving groups to modified oligonucleotides. Macrocyclic lanthanide complexes, in combination with modified antisense oligonucleotides, can be used to specifically cleave mRNA. The preparation, properties and use of such artificial ribonucleases are highlighted. In particular, the design and preparation of constructs cleaving RNA with multiple turn-over is described.