Study Of The Anti-Tumor Nucleoside Lipidic Prodrugs And Their Self-Assemblies

The lipidic prodrugs of nucleoside analogues, zidovudine （AZT） andgemcitabine （GEM）, were synthesized in this study, whose structures were designedbased on the theory of self-assembled drug delivery systems. They formed thenanoscale self-assemblies in aqueous media. The in vitro and in vivo properties ofthe self-assemblies were explored to find the design rules of the prodrugs. Thedetails are described as the followings:1. Synthesis and characterization of the lipidic prodrugsThe lipidic prodrugs were prepared from AZT and hydroxyurea as thehydrophilic segments and the fatty acids of different chains as the hydrophobicsegments, or GEM as the hydrophilic segments and cholesterol as the hydrophobicsegments to obtain cholesteryl phosphonyl gemcitabine （CPNG）. The products werecharacterized by the method of NMR. They formed the stable Langmuir monolayersat the air/water interface, where the longer the lipidic chains were, the more stablethe monolayers were.2. Preparation and properties of the self-assemblies.The optimal preparation method of self-assemblies was the tetrahydrofuran（THF） injection with the help of ultrasound after screening many methods.Transmission electron microscopy （TEM） and dynamic light scattering （DLS）method were used to characterize the self-assemblies. The self-assemblies of AZTprodrugs had the morphologies of vesicles or nanotubes with the mean sizes of60to120nm and the negatively zeta potential. CPNG formed vesicles with the mean sizeof70nm and the zeta potential of-17.6mv. A higher temperature （e.g.,100oC）could destroy the structure of self-assemblies.3. In vitro activity of the self-assembliesThe in vitro anticancer effects of the self-assemblies were investigated by theMTT method. The self-assemblies of AZT prodrugs had higher anticancer activitythan AZT and HU though the activity was not high, which indicated the release ofparent drugs from the prodrugs. CPNG self-assemblies had the significant inhibitoryeffects on the cancer cell lines95C,95D, SW620, A549, and PANC-1. The halfinhibitory concentrations (IC₅₀) were1/3-1/6of that of GEM, indicating that CPNGcould permeat into cells and be degraded to the active agents. Therefore, CPNG was selected for the further research.4. Chemical stability of CPNG self-assembliesThe chemical stability of CPNG self-assemblies in different buffer solutionsand mouse plasma were investigated using HPLC. CPNG was stable in weak acidand neutual buffers, where in the most stable pH was5.0with the half-life of770h.However, the degradation rate of CPNG in plasma was fast with the half-life of9.9h. The enzyme-catelyzing degradation was the main reason.5. Pharmacokinetics and tissue distribution of CPNG self-assembliesCPNG self-assemblies were rapidly eliminated from circulation and uptaked bythe monocyte macrophage systerm （MPS, including liver, spleen and lung） afterbolus i.v. administration.6. Pharmacodynamics of CPNG self-assembliesThe anticancer therapy showed that CPNG self-assemblies had the comparativeeffect with GEM when the same mole concentration was used on the the hepatoma（H22） tumor-bearing mice. The additive, CHS-PEG1500could inserted into CPNGself-assemblies not well, leading to CPNG self-assemblies accumulating in the MPSrather than tumor. The specific distribution of self-assemblies also resulted in weightlost.Among the prepared self-assemblies, CPNG self-assemblies were stable andhad significant anti-tumor activity. CPNG self-assemblies can permeatebiomembrane well. However, it shows weak tumor targeting.