Investigation and optimization of liposome formulation for use as drug carrier for the anticancer agent Camptothecin

Abstract

In this thesis, the method development and investigation of different liposomal formulations to incorporate and retain Camptothecin (CPT) is described. CPT is a potent anticancer drug that has shown to be active against a broad spectrum of cancers. However, due to its challenging physicochemical properties, like poor water solubility, severe toxic effects to normal tissues and instability, its clinical development has been limited for nearly 40 years. A strategy to overcome CPT’s challenging properties is to use liposome-based carrier system. By taking advantage of this carrier system, we may solubilise CPT in the phospholipid bilayer of liposomes, protect it from blood proteins and achieve a selective drug accumulation in tumor tissues or tumor-associated cells by enhanced permeability and retention effect (EPR). A good liposome formulation of clinical utility must fulfil two important criteria. The liposomal drug carrier must incorporate CPT in the liposomal bilayer in a relevant therapeutic concentration and be able to retain the drug within the liposome to make it bioavailable at the target site after i.v. administration. The focus of this thesis was to study different liposomal formulations and their ability to incorporate and retain CPT. Screening of eight different liposome formulations with respect to association with CPT was performed. The 1,2-di-oleyl-3 trimethyl-ammonium-propane (DOTAP) containing formulations showed superior incorporation capacity, giving an CPT incorporation of 250 µg/130 µmoles lipid. The DOTAP containing formulations exhibited as well a trend toward higher retention ability in serum compared to the other formulations. Although they showed better retention ability, only 25 % of the drug was associated with the liposomes, which is far from being optimal. One of the important criteria mentioned above for liposomes as drug delivery systems is their ability to remain stable in blood circulation for prolonged time in order to reach the specific target and to avoid rapid clearance by RES after i.v. injection. To achieve this, PEG decoration on the liposome surface can be employed. We chose to PEGylate DOTAP formulations in order to get a better understanding of this system. PEGylation lead, as expected, to increased stability of the liposomes, however a reduced incorporation capacity was observed. The presence of 1 % and 10 % PEG gave better retention and slower leakage from the liposomes. We conclude that DOTAP inclusion in our liposomes increased the incorporation of CPT into the lipid bilayer, that liposomal retention in our current formulations must be improved, and while PEGylation is necessary in order to prevent rapid in vivo clearance, the inclusion of PEG reduces incorporation, and therefore further studies are needed in order to improve incorporation of CPT in PEGylated liposomes.