title: Determination of the activity of maleimide-functionalized phospholipids during preparation of liposomes.
abstract: Numerous examples exist in the literature for the use of maleimide-thiol-reactions in the area of functionalized nanoparticles. Although the hydrolysis tendency of maleimides is well-known, qualitative and quantitative information on the stability and reactivity of maleimide groups during preparation and in final formulations are missing. This is surprising, since hydrolysis of maleimides prevents nanoparticle functionalization and results in an increase of negative surface charge due to the hydrolysis product maleic acid. In this study we investigated the stability of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[maleimide-2000] (DSPE-PEG2000-Mal) during the preparation of liposomes via two common preparation methods, which can be distinguished by the insertion of DSPE-PEG2000-Mal during or after the liposome formation process (pre-insertion and post-insertion process). The liposomes prepared by the pre-insertion method had 63% active maleimide groups remaining on their surface. The activity decreased dramatically during the purification process down to 32%. The preparation by post-insertion showed minimal effects with regard to maleimide activity. 76% of maleimide groups were active and therefore available for coupling reaction. By identifying active maleimide groups on the surface of the final formulations, the presented work revealed the dramatic impact of preparation methods on the activity of maleimide groups.
authors.affiliation: Merck KGaA, Chemical & Pharmaceutical Development, Frankfurter Straße 250, 64293 Darmstadt, Germany. Electronic address: Mira.Oswald@merckgroup.com.
authors.forename: Mira
authors.initials: M
authors.lastname: Oswald
authors.affiliation: Merck KGaA, Chemical & Pharmaceutical Development, Frankfurter Straße 250, 64293 Darmstadt, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Geissler
authors.affiliation: University of Regensburg, Dept. for Pharmaceutical Technology, Universitätsstraße 31, 94030 Regensburg, Germany. Electronic address: Achim.Goepferich@chemie.uni-regensburg.de.
authors.forename: Achim
authors.initials: A
authors.lastname: Goepferich
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods; D016503:Drug Delivery Systems / Q000379:methods; D008081:Liposomes / Q000737:chemistry*; D008301:Maleimides / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D008081:Liposomes; D008301:Maleimides; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D013438:Sulfhydryl Compounds; C107570:polyethylene glycol-distearoylphosphatidylethanolamine; C043592:maleimide; D011092:Polyethylene Glycols
keywords: DSPE-PEG(2000)-Mal; Liposomes; Maleimide activity