title: Enzymatic release of antitumor ether lipids by specific phospholipase A2 activation of liposome-forming prodrugs.
abstract: An enzymatically activated liposome-based drug-delivery concept involving masked antitumor ether lipids (AELs) has been investigated. This concept takes advantage of the cytotoxic properties of AEL drugs as well as the membrane permeability enhancing properties of these molecules, which can lead to enhanced drug diffusion into cells. Three prodrugs of AELs (proAELs) have been synthesized and four liposome systems, consisting of these proAELs, were investigated for enzymatic degradation by secretory phospholipase A(2) (sPLA(2)), resulting in the release of AELs. The three synthesized proAELs were (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphocholine (1-O-DPPC), (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphoethanolamine poly(ethylene glycol)(350) (1-O-DPPE-PEG(350)), and 1-O-DPPE-PEG(2000) of which 1-O-DPPC was the main liposome component. All three phospholipids were synthesized from the versatile starting material (R)-O-benzyl glycidol. A phosphorylation method, employing methyl dichlorophosphate, was developed and applied in the synthesis of two analogues of (R)-1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphoethanolamine poly(ethylene glycol). Differential scanning calorimetry has been used to investigate the phase behavior of the lipid bilayers. A release study, employing calcein encapsulated in non-hydrolyzable 1,2-bis-O-octadecyl-sn-glycero-3-phosphocholine (D-O-SPC) liposomes, showed that proAELs, activated by sPLA(2), perturb membranes because of the detergent-like properties of the released hydrolysis products. A hemolysis investigation was conducted on human red blood cells, and the results demonstrate that proAEL liposomes display a very low hemotoxicity, which has been a major obstacle for using AELs in cancer therapy. The results suggest a possible way of combining a drug-delivery and prodrug concept in a single liposome system. Our investigation of the permeability-enhancing properties of the AEL molecules imply that by encapsulating conventional chemotherapeutic drugs, such as doxorubicin, in liposomes consisting of proAELs, an increased effect of the encapsulated drug might be achievable due to an enhanced transmembrane drug diffusion.
authors.affiliation: Department of Chemistry and LiPlasome Pharma A/S, Technical University of Denmark, Building 207, DK-2800 Lyngby, Denmark. than@kemi.dtu.dk
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Andresen
authors.forename: Jesper
authors.initials: J
authors.lastname: Davidsen
authors.forename: Mikael
authors.initials: M
authors.lastname: Begtrup
authors.forename: Ole G
authors.initials: OG
authors.lastname: Mouritsen
authors.forename: Kent
authors.initials: K
authors.lastname: Jørgensen
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D002152:Calorimetry, Differential Scanning; D004355:Drug Stability; D004987:Ethers / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D005452:Fluoresceins / Q000737:chemistry; D006461:Hemolysis; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes; D010539:Permeability; D010741:Phospholipases A / Q000737:chemistry* / Q000378:metabolism; D054467:Phospholipases A2; D010742:Phospholipid Ethers / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D011092:Polyethylene Glycols / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D011355:Prodrugs / Q000138:chemical synthesis* / Q000737:chemistry / Q000633:toxicity; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: C484862:1-O-hexadecyl-2-palmitoyl-sn-glycero-3-phosphoethanolamine poly(ethylene glycol); D000970:Antineoplastic Agents; D004987:Ethers; D005452:Fluoresceins; D008051:Lipid Bilayers; D008081:Liposomes; D010742:Phospholipid Ethers; D011355:Prodrugs; D011092:Polyethylene Glycols; C082824:1-hexadecyl-2-palmitoyl-sn-glycero-3-phosphocholine; D010741:Phospholipases A; D054467:Phospholipases A2; C007740:fluorexon