On the Chemical Reactivity of Molecules with Membrane Lipids: An Experimental and Theoretical Approach

Abstract

It is now well-established that the reactivity of membrane associated molecules, such as CADs (cationic amphiphilic drugs), with membrane lipids is influenced by the disposition of each molecule in the membrane rather than its lipophilicity. The reactions involving CADs and phospholipids such as POPC include lipidation and hydrolysis. Some CADs promote lipid hydrolysis, whereas others either decree the rate or have no effect on lipid chemical stability. Lipidation involves the transfer of an acyl group from the glycerol part of the lipid to a reactive group on the CAD. Lipidation and hydrolysis reactions both lead to the formation of lysolipids. This project aims to investigate the factors of drug reactivity towards lipid membranes.

This project involves both experimental and theoretical work to understand drug reactivity factors with POPC lipids. A range of isotopically enriched reactive compounds have been synthesised. These compounds vary in the rates of lysolipid formation that they induce in POPC membranes. Furthermore, a novel synthetic methodology has been developed to incorporate an 15N isotope into molecules with aniline functionality, and its applicability to clinically relevant molecules. 1D and 2D solid-state NMR data is presented which enables the interactions of each labelled molecule with POPC lipids to be probed via close contact distance measurements. Atomistic molecular dynamics (MD) simulations provide corroborating information on the preferred depth and orientation of the molecules in the lipid bilayer. QM/MM simulations are used to locate the reactive intermediates and the transition state in each bond forming and bond breaking process along the reaction pathway. These calculations were successful in being able to predict reactive and non-reactive conformations of drugs in the membrane interface. The MD and DFT results correlate well with ssNMR data in showing how orientation and depth of partitioning influence drug-lipid reactivity.