Study On The Self-assembled Systems Of Gemcitabine Lipid Prodrugs

Malignant tumor was the most common disease and the frequently encountered disease to threaten human healthy. Chemotherapy iwas also the major method for treating tumor.But most chemotherapeutics existed effect dose-dependent,enough medicine dose displayed notable antitumor effect,but it also genrtated toxic and side-effect.Antitumor drug delivery directly to the tumor position has already become the hot spot of research.Self-assembled drug delivery systems(SADDS)were prepared from amphiphilic conjugates of hydrophilic drugs and lipids through self-assembling into orderer highly dispering aggregates in the aqueous media .The amphiphilic nature of SADDS lead to strong affinity and permeability with biomembranes .Meanwhile,The property of high disrersion lead to targets efficiently.In this paper,Gemcitabine(2'-deoxy-2',2'-difluorocytidine,dFdC)was selected as model drug.GEM was lipophilic derivated and then self-assemblies of GEM lipid prodrugs were prepared.The main contents were described in details as follows:1. Synthesis and characteristics of anti-tumor prodrug.GEM derivatives ,4-N-stearoyl–gemcitabine (OPG), 4-N-lauroyl–gemcitabine (lAG),4-N-tetradecanoyl-gemcitabine(TDG), 4,4'-N-dipentadecanoyl-gemcitabine (PDDG) were designed and synthesized. The solubility of the prodrug was measured, of which the hydrogen bonding and hydrophobic interaction were the key factors. The lipophilicity of prodrug was greatly increased. the formation and characterization of its langmuir monolayers were investigated. It showed well-defined isotherms.2. Preparation and characteristics of anti-tumor amphiphilic prodrug self-assemblies. Many methods were used to prepare OPG self-assemblies. A kind of homogeneous suspension system with highly dispersion and high concentration were prepared by THF injection method. The mean particle size of OPG self-assemblies was about 202 nm. The surface Zeta potential was -29.2 mV.3. Physical Stability of anti-tumor amphiphilic prodrug self-assemblies. Physical stability was investigated through heating, high pressure, centrifugation (<10000 rpm) and storing at room temperature. The results indicated the content of OPG decreased sharply when OPG self-assemblies were heated and under high pressure. However, OPG self-assemblies were stable to a great extent through high speed centrifugation and storing at room temperature. High concentration (>8 mg/mL) self-assemblies could redisperse easily with water.4. Chemical stability of OPG self-assembliesChemical stability of OPG self-assemblies in buffer solutions of different pH, plasma of different animals and tissue homogenates of mice were all investigated using an assay method of HPLC. OPG self-assemblies hydrolyzed quickly in pH 2.0,pH5.5,pH9.0,pH12.0 buffers.but kept relative stable for a long period in neutral ,which t1/2 =37h. the hydrolysis of OPG in the plasma of animals was different. The hydrolysis rate of OPG in the plasma of human was fast. The hydrolysis rate of OPG in the plasma of mouse and rabbit were slow.The degradation rate of OPG in mice was adequate. t1/2 was 22 h.5. Pharmacokinetics and tissue distribution of OPG self-assemblies After single bolus of iv administration to normal mice, OPG self-assemblies were eliminated quickly from blood circulation to liver and spleen .The distribution t1/2 and elimination t1/2 were 1.2 and 56.7 min. The Kunming mice models with Hepatoma (H22) were established. After iv administration to tumor-beared Kunming mice, OPG self-assemblies were also distributed quickly from blood circulation to liver and spleen.distribution t1/2 and elimination t1/2 in mice were 1.4 and 15.4min, respectively.It hasn't achieved expecting effect tumor targeting.6. Pharmacodynamics experiments of OPG self-assemblies in Hepatoma (H22) tumor–bearing Kunming mice. After iv administration of Hepatoma (H22) tumor to Kunming mice successively and the evaluation index was the body weight and tumor volume. The results showed that the OPG self assemblies group had signant significant difference comparing to the negative control group (p<0.05). It demonstrated that OPG self assemblies had antitumor effect. But OPG self assemblies group and the GEM control group had no significant difference (p>0.05), It demonstrated that OPG self assemblies had no significant tumor targeting.Two reasons resulted in no significant tumor targeting:The size of self assemblies and distribution of self assemnlies to blood;On the other hand,The tumor EPR effect related to the molecular weight ,enough large molecular weight had strong EPR effect。...