RNA interference in mammalian cells by siRNAs modified with morpholino nucleoside analogues

siRNAs modified with morpholino nucleoside analogues were synthesized and their biological properties were examined in details. The gene silence abilities of modified siRNAs were correlated to the positions of the modifications, some of which appeared to be more potent than the native siRNA. The 3'-end modification improved the stability of siRNAs in serum significantly. Furthermore, the dose-response and time-course experiments demonstrated that the siRNAs with 3'-end modification have potent gene silence activity at lower concentration and prolonged action time. These favorable properties make the morpholino modified siRNA a potentially useful tool in therapeutic applications.