Understanding and Exploiting Drug Reactivity with Lipid Membranes

Research has shown that lipid membranes may be far from inert. The reactions between cationic amphiphilic drugs and glycerophospholipids yield lysolipids and lipidated drug molecules, with membrane-drug reactivity dependent on the structure of the drug molecule. Thus, it may be possible to design membrane reactivity into proto-drugs for use in drug delivery to highly lipophilic areas which have been challenging to target, such as the brain. As a first objective, this work aimed to determine the source of acyl groups of lipidated propranolol in vivo. Here, exogenously supplemented 13C-labelled oleic acid was successfully incorporated into 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine molecules of Hep G2 lipid membranes. We found direct evidence for a 13C-oleyl lipidated adduct following incubation with propranolol, formed via a reaction with 13C-labelled 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine of lipid membranes. As a second objective to probing the scope of lipid membrane-drug reactivity, we have synthesised and characterised novel cyclopropane functionalised fatty acids and silyl-protected precursors for use as dienophiles in bio-orthogonal inverse electron demand Diels-Alder reactions. Cyclisations between cyclopropene-functionalised fatty acids and fluorescently-conjugated dienes represent a new avenue of single-molecule, real-time, in vivo lipid tracking using confocal microscopy without disrupting nascent cellular metabolism. Our findings and novel bio-orthogonal probes bring us closer to elucidating the nature of lipid membrane-drug reactivity. Such understanding is key to exploiting the nascent lipid membrane activity as a new modality for advanced drug delivery.