Antitumor effect of palmitic acid‐conjugated DsiRNA for colon cancer in a mouse subcutaneous tumor model

We investigated the in vitro and in vivo RNAi efficacy in colon cancer cells of C16‐DsiRNA targeting endogenous β‐catenin, which is active during cancer cell development and is associated with the growth of cancer. C16‐DsiRNA exhibited a strong target gene‐silencing effect, high cellular uptake, and execellent nuclease resistance in vitro. Likewise, C16‐DsiRNA showed strong inhibition of the growth of tumor formed in our subcutaneous tumors mouse model, and this in vitro RNAi effect lasted up to 15 days.

Abstract

In this study, we synthesized Dicer substrate siRNA conjugated with palmitic acid at the 5'‐end of the sense strand (C16‐DsiRNA), and examined its RNAi effect on β‐catenin as a target gene in a colon cancer cell line, HT29Luc, both in vitro and in vivo. We examined the in vitro RNAi effect in HT29Luc cells and found that C16‐DsiRNA strongly inhibited expression of the β‐catenin gene in comparison with non‐modified DsiRNA. Also, high membrane permeability of C16‐DsiRNA was exhibited, and it was confirmed that most of the C16‐DsiRNA was localized in cytoplasm of HT29Luc cells. In regard to the in vivo RNAi effect, C16‐DsiRNA complexed with Invivofectamine targeting the β‐catenin gene was locally administered to a subcutaneous tumor formed by implantation of HT29Luc cells into the subcutis of nude mice; we evaluated the effect by measuring the bioluminescence increase, which reflects tumor growth, using an in vivo imaging system. As a result, C16‐DsiRNA strongly inhibited the growth of tumors formed in subcutis of nude mice compared with non‐modified DsiRNA, and this in vivo RNAi effect lasted up to 15 days. Our results suggest that C16‐DsiRNA should be vigorously pursued as a novel nucleic acid medicine for clinical treatment of cancer.

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