Oligomerized alpha-helical KALA peptides with pendant arms bearing cell-adhesion, DNA-binding and endosome-buffering domains as efficient gene transfection vectors

In this study, a number of KALA-based α-helical peptides were designed and synthesized as non-viral gene carriers. The effects of lysine and histidine residues in the pendant arms and cell-binding RGD motif on DNA binding, particle size, zeta potential, cytotoxicity and gene expression efficiency were first explored. Increasing the lysine and histidine residues reduced particle size and increased zeta potential of DNA complexes, leading to greater gene expression efficiency. In addition, the introduction of RGD group further improved gene expression level. The peptide with optimal compositions, RGDN3K6H3CKHLAKALAKALAC (RC29), was then oligomerized to form di-, tri- and tetra-RC29 via disulfide linkage. Upon oligomerization, RC29 attained a 3-dimensional long α-helical structure with pendant arm(s) extending transversally outwards. Each arm contains a cell-adhesion motif (RGD), DNA-binding and endosome-buffering domains. The α-helicity of the oligomerized peptides was evaluated by circular dichroism (CD) spectroscopy, which showed that an increased oligomerization degree led to a stronger α-helical structure. These peptides form complexes with DNA efficiently. The minimum size and maximum zeta potential of tri-RC29/DNA complexes was about 200 nm and 32.5 mV, respectively. In comparison, RC29 formed DNA complexes with a similar zeta potential, but particle size was significantly larger (355 nm). DNA complexes formed at pH 7.0 yielded higher gene expressions than those formed at pH 5.5 and 6.5. Among all the oligomerized peptides, tri-RC29 provided the highest gene expression efficiency, and its peak luciferase level was 1.5 times higher than that yielded by PEI at its optimal N/P ratio (i.e. 10). Moreover, oligomerized RC29/DNA complexes were less cytotoxic than PEI/DNA complexes. These α-helical peptides can be promising carrier for delivery of therapeutic genes in the treatment of genetic disorders.