Investigation of the Internalization of Fluorescently Labeled Lipophilic siRNA into Cultured Tumor Cells

Abstract

The attachment of lipophilic molecules of natural origin, which have natural means for cell internalization, to small interfering RNA (siRNA) is an effective way of delivering siRNA to cells for biomedical purposes in vitro and in vivo. Earlier, we showed that the attachment of cholesterol to the 5'-end of the sense strand of nuclease-resistant siRNA through the optimized linker allows it to penetrate the cells and suppress the expression of the target gene. However, the effectiveness of the conjugates is different for cells of different origin, and in hematopoietic cells, they are not active, despite effective accumulation. In this work, we investigated the accumulation of fluorescently labeled cholesterol conjugates of siRNA using endocytosis inhibitors and showed that fluorescently labeled 5'-cholesterol conjugate of siRNAs penetrate KB-3-1 and K562 cells in several ways whose contribution differs depending on cell type and the presence of serum. In a serum-free medium, it was found that macropinocytosis and clathrin-dependent endocytosis contribute to the accumulation of the conjugate in KB-3-1 cells, while clathrin-dependent endocytosis makes the main contribution in K562 cells, while inhibitors of different types of endocytosis do not reduce the biological activity of the conjugate without a fluorescent label.