Abstract 3772: Passive tumor targeting with drug-loaded liposomes: Experimental evidences that size does matter
Authors: Fanciullino Raphaelle , Giacometti Sarah , Milano Gerard , Piccerelle Philippe , Ciccolini Joseph 
Published: August 2012

Abstract
Background Liposomes encapsulating anticancer agents are to date the only nano-objects used in clinical oncology. Drug-loaded liposomes are expected to exhibit a higher specificity towards malignant tissues because they can theoritically leak out of the blood vessels in the tumour surrounding, a phenomenon known as the Enhanced Permability Retention (EPR) effect, a.k.a. passive targeting. Here, we have developed a range of experiments designed to investigate how liposome size will impact on their distribution in the body and their ability to target tumors eventually. Methods: experiments were carried out in swiss nu/nu female mice orthotopically xenografted with the human breast cancer MDA-231-LUC+ model. Tumor localization and size was monitored by 3D bioluminescence after injecting 150 mg/mg luciferine I.P. Four different batches of LipoFufol, a stealth liposomal formulation of modulated 5-FU, were prepared. Changes in sonication parameters (frequency, duration) generated different sizes ranging from 10 up to 1 000 nm in diameter. Inclusion of a fluorescent tag (ie, DIR) in the liposomes membrane allowed their monitoring in mice over 10 days. Double bioluminescence/fluorescence detection was finally performed to evaluate the liposome accumulation in the tumors throughout time. Response at 10-day was evaluated through caspase-3 expression. Additionally, plasma drug monitoring of liposomal 5-FU was performed in Wistar rats and compared with the pharmacokinetics of the free drug. Results: Biodistribution study using different sizes of DIR-labelled LipoFufol confirmed that both distribution and accumulation phases depend on the liposome size. Pegylation allowed to partly bypass the liver. Liver uptake was observed between 3 and 6 hours. Smaller liposomes tend to reach faster the tumor tissues and to accumulate there throughout time. Several days (ie, one week) after a single injection, tumors were the only tissue with detectable liposomes. A delay in reaching the tumor was observed when LipoFufol size was ranging between 80-120 nm. When Liposomal diameter was superior to 120 nm, a decrease in the extravasation within the tumor led to a reduced tumoral accumulation as compared with &lt;100 nm liposomes. A marked trend was observed between tumor acculation of LipoFufol and response, thus demonstrating that preliminary biodistribution phase is a major issue for ensuring a maximal efficacy in tumor-bearing animals. When administered in rats, 80 nm stealth liposomal 5-FU exhibited markedly reduced clearance (ie, –50%) and prolonged half-life as compared with free 5-FU, thus confirming that encapsulation does optimize the pharmacokinetics profile of the drugs. Conclusions: Our present data suggest that size considerations are critical when designing nano-objects in oncology, and that 80 nm objects are required to achieve a better selectivity towards tumor tissues with higher efficacy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3772. doi:1538-7445.AM2012-3772