Sequence and length optimization of membrane active coiled coils for triggered liposome release.

Defined and tunable peptide-lipid membrane interactions that trigger the release of liposome encapsulated drugs may offer a route to improving the efficiency and specificity of liposome-based drug delivery systems, but this require means to tailor the performance of the membrane active peptides. In this paper, the membrane activity of a de novo designed coiled coil peptide has been optimized with respect to sequence and size to improve release efficiency of liposome encapsulated cargo. The peptides were only membrane active when covalently conjugated to the liposomes. Two amino acid substitutions were made to enhance the amphipathic characteristics of the peptide, which increased the release by a factor of five at 1 µM. Moreover, the effect of peptide length was investigated by varying the number of heptad repeats from 2 to 5, yielding the peptides KVC2-KVC5. The shortest peptide (KVC2) showed the least interaction with the membrane and proved less efficient than the longer peptides in releasing the liposomal cargo. The peptide with three heptads (KVC3) caused liposome aggregation whereas KVC4 proved to effectively release the liposomal cargo without causing aggregation. The longest peptide (KVC5) demonstrated the most defined α-helical secondary structure and the highest liposome surface concentration but showed slower release kinetics than KVC4. The four heptad peptide KVC4 consequently displayed optimal properties for triggering the release and is an interesting candidate for further development of bioresponsive and tunable liposomal drug delivery systems.

Tuning Liposome Membrane Permeability by Competitive Coiled Coil Heterodimerization and Heterodimer Exchange.

Membrane-active peptides that enable the triggered release of liposomal cargo are of great interest for the development of liposome-based drug delivery systems but require peptide-lipid membrane interactions that are highly defined and tunable. To this end, we have explored the possibility to use the competing interactions between membrane partitioning and heterodimerization and the folding of a set of four different de novo designed coiled coil peptides. Covalent conjugation of the cationic peptides triggered rapid destabilization of membrane integrity and the release of encapsulated species. The release was inhibited when introducing complementary peptides as a result of heterodimerization and folding into coiled coils. The degree of inhibition was shown to be dictated by the coiled coil peptide heterodimer dissociation constants, and liposomal release could be reactivated by a heterodimer exchange to render the membrane bound peptide free and thus membrane-active. The possibility to tune the permeability of lipid membranes using highly specific peptide-folding-dependent interactions delineates a new possible approach for the further development of responsive liposome-based drug delivery systems.