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. 2019 Aug 23;40(11):1373–1385. doi: 10.1038/s41401-019-0287-8

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — Illustration of the esterase-responsive charge‐reversal polymer (ERP) and its lipid‐coated esterase-responsive polyplexes with TRAIL plasmid for cancer gene therapy. a The ERP is a PEI whose amines are quaternized with propionic 4‐acetoxybenzyl ester. Hydrolysis of the phenolic acetate triggers the elimination of p-hydroxymethylphenol and consequent conversion of the cationic polymer into a zwitterionic form. b ERP condenses plasmid DNA into the polyplexes, which are easily coated with DC-Chol/DOPE lipids to form lipidic esterase‐responsive polyplexes (LERPs). After i.p. injection into nude mice bearing HeLa cell-derived tumors, tumor cells internalize LERPs into the cytosol, which is rich in esterases. The LERPs disassemble and release the polyplexes to allow the esterases to trigger the charge reversal of the ERP and thus plasmid release. These free plasmids enter the nucleus for effective gene expression, inducing apoptosis when delivering the TRAIL gene. In tumor fibroblasts, the low esterase level cannot efficiently induce the charge reversal process, and the TRAIL plasmids will not be expressed, preventing WNT16B production. Reprinted with permission from [56]