Synthesis of Passerini-3CR Polymers and Assembly into Cytocompatible Polymersomes.

The versatility of the Passerini three component reaction (Passerini-3CR) is herein exploited for the synthesis of an amphiphilic diblock copolymer, which self-assembles into polymersomes. Carboxy-functionalized poly(ethylene glycol) methyl ether is reacted with AB-type bifunctional monomers and tert-butyl isocyanide in a single process via Passerini-3CR. The resultant diblock copolymer (P1) is obtained in good yield and molar mass dispersity and is well tolerated in model cell lines. The Passerini-3CR versatility and reproducibility are shown by the synthesis of P2, P3, and P4 copolymers. The ability of the Passerini P1 polymersomes to incorporate hydrophilic molecules is verified by loading doxorubicin hydrochloride in P1DOX polymersomes. The flexibility of the synthesis is further demonstrated by simple post-functionalization with a dye, Cyanine-5 (Cy5). The obtained P1-Cy5 polymersomes rapidly internalize in 2D cell monolayers and penetrate deep into 3D spheroids of MDA-MB-231 triple-negative breast cancer cells. P1-Cy5 polymersomes injected systemically in healthy mice are well tolerated and no visible adverse effects are seen under the conditions tested. These data demonstrate that new, biodegradable, biocompatible polymersomes having properties suitable for future use in drug delivery can be easily synthesized by the Passerini-3CR.

Biocompatible Unimolecular Micelles Obtained via the Passerini Reaction as Versatile Nanocarriers for Potential Medical Applications.

A Passerini three-component polymerization was performed for the synthesis of amphiphilic star-shaped block copolymers with hydrophobic cores and hydrophilic coronae. The degree of polymerization of the hydrophobic core was varied from 5 to 10 repeating units, and the side chain ends were conjugated by performing a Passerini-3CR with PEG-isocyanide and PEG-aldehyde (950 g/mol). The resulting amphiphilic star-shaped block copolymers contained thioether groups, which could be oxidized to sulfones in order to further tune the polarity of the polymer chains. The ability of the amphiphilic copolymers to act as unimolecular micellar encapsulants was tested with the water-insoluble dye Orange II, the water-soluble dye Para Red and the macrolide antibiotic azithromycin. The results showed that the new copolymers were able to retain drug cargo at pH levels corresponding to circulating blood and selectively release therapeutically effective doses of antibiotic as measured by bacterial cell kill. The polymers were also well-tolerated by differentiated THP-1 macrophages in the absence of encapsulated drugs.

An Update on Isocyanide-Based Multicomponent Reactions in Polymer Science.

Developments and progress in polymer science are often inspired by organic chemistry. In recent years, multicomponent reactions-especially the Passerini and Ugi reactions-have become very important tools for macromolecular design, mainly due to their modular character. In this review, the versatility of the Passerini and Ugi reactions in polymer science is highlighted by discussing recent examples of their use for monomer synthesis, as polymerization techniques, and for postpolymerization modification, as well as their suitability for architecture control, sequence control, and sequence definition.

Endoplasmic reticulum retention of the large splice variant of the UDP-galactose transporter is caused by a dilysine motif.

Nucleotide-sugar transporters supply mainly the Golgi glycosyltransferases with substrates. Some glycosyltransferases in the endoplasmic reticulum (ER), however, also use activated sugars. Recent studies have demonstrated that UDP-galactose (UDP-Gal) is the substrate for the ER resident ceramide-galactosyltransferase (cer-GalT) and cells expressing cer-GalT are able to retain the UDP-Gal transporter (UGT) by physical contacts formed between the two proteins. Here, we describe a second active mechanism for ER localization of the UGT. The UGT is produced in two splice forms UGT1 and UGT2. The proteins vary only at their extreme C-termini but show strikingly different intracellular distribution. Although N-terminally epitope tagged forms of UGT1 localize exclusively to the Golgi, similar constructs of UGT2 show both ER and Golgi localization. The dilysine motif KVKGS contained in UGT2 can be demonstrated to be responsible for the dual localization because: (1) disturbance of the signal via site specific mutation or C-terminal extension completely shifts the transporter to the Golgi, (2) transfer of the dilysine motif is sufficient to redistribute the Golgi CMP-sialic acid transporter to the ER, and (3) replacement of KVKGS by the strong ER retention signal KKNT is sufficient to completely retain UGT2 in the ER.

Molecular cloning of two Arabidopsis UDP-galactose transporters by complementation of a deficient Chinese hamster ovary cell line.

Nucleotide-sugar transporters (NSTs) form a family of structurally related transmembrane proteins that transport nucleotide-sugars from the cytoplasm to the endoplasmic reticulum and Golgi lumen. In these organelles, activated sugars are substrates for various glycosyltransferases involved in oligo- and polysaccharide biosynthesis. The Arabidopsis thaliana genome contains more than 40 members of this transporter gene family, of which only a few are functionally characterized. In this study, two Arabidopsis UDP-galactose transporter cDNAs (UDP-GalT1 and UDP-GalT2) are isolated by expression cloning using a Chinese hamster ovary cell line (CHO-Lec8) deficient in UDP-galactose transport. The isolated genes show only 21% identity to each other and very limited sequence identity with human and yeast UDP-galactose transporters and other NSTs. Despite this low overall identity, the two proteins clearly belong to the same gene family. Besides complementing Lec8 cells, the two NSTs are shown to transport exclusively UDP-galactose by an in vitro NST assay. The most homologous proteins with known function are plant transporters that locate in the inner chloroplast membrane and transport triose-phosphate, phosphoenolpyruvate, glucose-6-phosphate, and xylulose 5-phosphate. Also, the latter proteins are members of the same family, which therefore has been named the NST/triose-phosphate transporter family.