Synthesis of folate-labeled siRNAs from a folate derivative phosphoramidite

With the recent success of GalNAc and the need for extra-hepatic RNAi delivery systems, other receptor-targeting ligands, like folate, have gained increased attention. The folate receptor is an important molecular target in cancer research, as it is overexpressed on numerous tumours while having limited expression in non-malignant tissues. Despite the promise of folate conjugation as a delivery platform in cancer therapeutics, its application in RNAi has been limited by sophisticated, and often expensive, chemistry. Here, we report a straightforward and cost-effective strategy to synthesize a novel folate derivative phosphoramidite for siRNA incorporation. In the absence of a transfection carrier, these siRNAs were selectively taken up by folate receptor-expressing cancer cell lines and displayed potent gene-silencing activity.