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2 -Deoxynucleoside conjugates of 13α-estrone were synthesized by applying the copper-catalyzed alkyne-azide click reaction (CuAAC). For the introduction of the azido group the 5 -position of the nucleosides and a propargyl ether functional group on the 3-hydroxy group of 13α-estrone were chosen. The best yields were realized in our hands when the 3 -hydroxy groups of the nucleosides were protected by acetyl groups and the 5 -hydroxy groups were modified by the tosyl-azide exchange method. The commonly used conditions for click reaction between the protected-5 -azidonucleosides and the steroid alkyne was slightly modified by using 1.5 equivalent of Cu(I) catalyst. All the prepared conjugates were evaluated in vitro by means of MTT assays for antiproliferative activity against a panel of human adherent cell lines (HeLa, MCF-7 and A2780) and the potential inhibitory activity of the new conjugates on human 17β-hydroxysteroid dehydrogenase 1 (17β-HSD1) was investigated via in vitro radiosubstrate incubation. Some protected conjugates displayed moderate antiproliferative properties against a panel of human adherent cancer cell lines (the protected cytidine conjugate proved to be the most potent with IC 50 value of 9 µM). The thymidine conjugate displayed considerable 17β-HSD1 inhibitory activity (IC 50 = 19 µM).

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There is a pressing need to develop ways to deliver therapeutic macromolecules to their intracellular targets. Certain viral and bacterial proteins are readily internalized in functional form through lipid raft‐mediated/caveolar endocytosis, but mimicking this process with protein cargoes at therapeutically relevant concentrations is a great challenge. Targeting ganglioside GM1 in the caveolar pits triggers endocytosis. A pentapeptide sequence WYKYW is presented, which specifically captures the glycan moiety of GM1 (KD = 24 nm). The WYKYW‐tag facilitates the GM1‐dependent endocytosis of proteins in which the cargo‐loaded caveosomes do not fuse with lysosomes. A structurally intact immunoglobulin G complex (580 kDa) is successfully delivered into live HeLa cells at extracellular concentrations ranging from 20 to 160 nm, and escape of the cargo proteins to the cytosol is observed. The short peptidic WYKYW‐tag is an advantageous endocytosis routing sequence for lipid raft‐mediated/caveolar cell delivery of therapeutic macromolecules, especially for cancer cells that overexpress GM1.

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