טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHollander Amit
SubjectDevelopment of Lipid Carriers for Drug Delivery
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor Professor Dganit Danino
Full Thesis textFull thesis text - English Version


Abstract

Drug delivery systems are used to improve pharmacological and therapeutic properties of drugs. They aim to encapsulate, safely deliver and efficiently release the drug at desired location and desired rate. The materials of which they are made may be characterized by size, shape, charge, composition and more. The most clinically established systems used for drug delivery consist of lipids.

Cochleates are lipid microstructures, consisting of negatively charged phospholipid bilayers rolled up into cigar-like spiral rolls through the interaction with multivalent counterions as bridging agents. This lipid-based system was shown to have potential as a drug carrier, in particular, for oral delivery.

I investigated the structure of these cochleates, made of DOPS, negatively charged lipid, and calcium, which drives complex formation. By using cryo-TEM and cryo-SEM, I was able to explore structural details of the cochleates at length scales ranging from the nano to the micro-scale. I revealed the nano-layers during cochleate formation, thus, making evidence for cochleates formation mechanism

I further hypothesized that the calcium ions may be replaced by the drug itself. Few antibiotics from the aminoglycosides family were examined and my hypothesis was proved by one of them, gentamicin. The encapsulation of gentamicin is expected to enhance its bioavailability and reduce the drug dose in the treatment of genetic diseases, associated with nonsense mutations. Ex-vivo experiments in HEK-293 cells supported this expectation.

I also investigated the intermediate structures of this system by changing the lipid to drug ratio. The most common structure was found to be multi-lamellar vesicle (MLV), which was also formed after changing preparation technique or pH. Another interesting intermediate, liposomes with an inner snake-like structure, was found and may imply on an early stage of MLV production, influenced mainly by pH gradient.

In another lipid system, I examined the co-encapsulation of positively charged active antimicrobial agents of the OAK (oligo-acyl-lysyl) family together with positively charged antibiotics, into negatively charged lipid matrix, designed to simultaneously deliver both drugs, safely and effectively. This co-encapsulation strategy was previously shown to synergistically reduce the minimal inhibition concentration (MIC) and improve the antibiotic effect, thus may serve as a new medical tool for overcoming microbial resistance to antibiotic.

I showed that elongated MLVs were produced and that the investigated OAK is responsible for the elongation effect. Surprisingly, the micro-scale elongated structures displayed better drug delivery capability than the nano-scale spherical structures in a systemic efficacy study in infected mice.