Opponent: Professor Ines Neundorf, Institute of Biochemistry, University of Cologne, Zuelpicher Str. 47a, D-50674 Cologne, Germany. e-mail: ines.neundorf@uni-koeln.de

Abstract

Glioblastoma multiforme is the most aggressive form of malignant brain tumor with poor prognosis. The efficacy of brain cancer treatment by chemotherapeutics is limited by the blood-brain barrier (BBB) which blocks almost all the macromolecules to transport into the brain. Delivery of the large molecules such as proteins and nucleic acids across the BBB is a great challenge for brain-targeted drug delivery. To overcome this obstacle, cell-penetrating peptides (CPPs) were used as vectors for delivery of nucleic acids across the BBB targeting glioblastomas. The CPPs have shown such promising carriers to deliver various cargoes ranging from small molecules to large molecules across the cell membrane. This thesis is focused on the development of glioblastoma-targeting vectors based on modifications of the CPPs and the targeting peptides. The peptide-based vectors were developed to improve the transport of the nucleic acids across the BBB and specifically target glioblastomas.

In this thesis, a series of peptide-based vectors targeting glioblastomas were synthesized and modified with targeting peptides by either covalent conjugation or non-covalent complex. The delivery of plasmid DNA (pDNA) in the complex with the peptide-based vectors was studied in the in vitro model of the BBB. The role of receptors expressed on the BBB was investigated. Scavenger receptors class A and B were found to be expressed on the BBB, and they were involved in the delivery of the pDNA across the BBB model. Moreover, various targeting peptides were modified with hexaglutamate to form a non-covalent complex with the CPPs for small-interfering RNA (siRNA) delivery to glioblastoma cells. The non-covalent complex of the CPP and the targeting peptide showed greater gene-silencing efficiency than the consecutively covalent conjugation of the CPP and the targeting peptide for siRNA delivery to glioblastoma cells. Lastly, a number of novel, amphipathic peptides were developed based on the model amphipathic peptide called PepFect 20-28. The prediction of the biological effect of the designed peptides using quantitative structure-activity relationship model showed a correlation with the experimental data.

In the study, the modified CPPs with the targeting peptides showed promising vectors for delivery of nucleic acids across the BBB model. The CPP-based carriers with homing peptide strategy have a potential for the BBB shuttle and the use as a glioblastoma-targeted drug carrier in the in vivo studies and the clinical applications