(334bk) Redesign and Develop Effective Liposomal Formulation for Prodrug Delivery through Synchrotron X-Ray Studies of Molecular Interactions

Capecitabine is an anticancer chemotherapy prodrug and is widely used in pharmaceutical industry to treat patients with metastatic colorectal cancer. Through two-step enzyme catalyzed degradation, capecitabine is converted to 5FU, which is an effective drug. Despite the longer half-life of the prodrug, current problems are high dose and toxicity. Many efforts had been made to increase the efficacy of the drug in terms of controlled and sustained release and thus, lower the dosage. Specifically, liposomal nanoparticle is an attractive approach to achieve those goals; however, the unique molecular structure of the prodrug makes it difficult to prepare stable nanoformulations with high drug loading and long-term stability.

In this study, we modified the prodrug molecule by attaching a cetyl chloroformate to the 5- fluorouracil head group through a simple one-pot reaction. The new prodrug (5FU-PAL) has bigger hydrophobic domain and behaves as an amphiphilic molecule at the interface. We have optimized a liposomal formulation of 5FU-PAL for prolonged blood circulation and sustained release based on the understanding of molecular interactions between 5FU-PAL and lipids, which was achieved by using synchrotron X-ray reflectivity and grazing incidence X-ray diffraction (GIXD) integrated with a Langmuir trough. Monolayer packing of 5FU-PALwith saturated neutral lipid dipalmitoyl-phosphatidylcholine (DPPC), positively charged lipid 1,2-stearoyl-3-trimethylammonium-propane (DSTAP), negatively charged lipid 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), unsaturated neutral lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and unsaturated positively charged lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) were investigated. It was found that 5FU-PAL interacts strongly with positively charged lipid, especially in the head group region where the electron density of positively charged lipid increased upon adding the prodrug while the electron density of neutral and negatively charged lipid decreased. Furthermore, adding the prodrug molecule caused the packing at the air-water interface to become tighter. In addition, 5FU-PAL at the air-water interface folded into multiple layers with highly ordered crystal structures. The studied could precisely quantify the maximum drug loading in the liposomal formulation with a stable structure.