Study On Self-assemblies Of Zidovudine Lipid Prodrugs

It is necessary that drugs permeate cell membrane and enter cell for action in the cell. Water-solubility drugs through lipophilic derivation could improve cell membrane permeability, but it is difficult of lipophilic drugs to delivery in the body fluid. In order to solve the problems of cell membrane permeability and body fluid delivery of drugs in vivo, self-assemblies, take drugs to the targets directly and make them safe and efficient, belongs to a novel drug delivery system. Self-assembled drug delivery system (SADDS) was investigated in this paper using hydrophilic zidovudine (3'azido-3'-deoxythymidine, AZT) as a model drug. AZT was lipophilic derivated and then self-assemblies of AZT lipid prodrugs (CPNZ) were prepared. The main contents were described in detail as follows:1. Synthesis of lipidic prodrug. Four lipidic prodrugs of anti-HIV nucleoside zidovudine were designed and synthesized, that is, 5′-tetradecanylphosphonyl-zidovudine(TPZ),5′-hexadecanylphosphonyl-zidovudine(HPZ),5′- o c t a d e c a n y l p h o s p h o n y l - z i d o v u d i n e ( O P Z ) a n d5′-cholesterylphosphonyl-zidovudine (CPNZ) and one key intermediate was AZT 5′-o-hydrogenphosphonate (PZT).2. Characterization of lipidic prodrug. Solubility of OPZ and CPNZ was measured and hydrogen bonding and hydrophobic interaction are the key factors to determine solubility. The found LogP of OPZ and CPNZ in n-octanol/phosphate buffer solution (pH 7.4) system were 0.552 and 0.928, which were higher than Log P of AZT (0.0913), which suggested the lipophilicity of prodrug was greatly increased. The predicted Log P of OPZ and CPNZ were 7.33 and 8.89, which were different from the found ones. It suggested the prodrug could distribute in the interface of oil and water, that is, the prodrug possessed typical amphiphilic properties.3. Preparation and characterization of CPNZ self-assemblies. Several methods were used to prepare CPNZ self-assemblies. Through prescription screening and optimization, CPNZ self-assemblies, a kind of suspension system of highly dispersed, high level and homogeneous, were prepared with EtOH injection method. The mechanism of self-assembly was presumed through a serious of microcosmic morphology and size determination: CPNZ molecules self-assembled to spherical vesicles by the hydrophobic interaction of cholesteryl moieties and under the action of the hydrogen bonding of phosphonyl nucleoside. The apparent particle size of CPNZ self-assemblies was about 100 nm. The surface Zeta potential was -20.3mV.4. Physical stability of CPNZ self-assemblies. Physical stability was investigated through heating , high pressure, centrifugation (<10000rpm) and storing at -4℃. The results indicated they could aggregate, precipitate and content of CPNZ also decreased sharply, When CPNZ self-assemblies were heated and under high pressure. However, CPNZ self-assemblies were stable to a great extent through high speed centrifugation (<10000rpm). Content of CPNZ did not drop at -4℃for one month. High concentration (>20mg/ml) self-assemblies could redisperse easily with water.5. Chemical stability of CPNZ self-assemblies. Chemical stability of CPNZ self-assemblies in buffer solutions of different pH, plasma of different animals and tissue homogenates of rabbit were all investigated, using an assay method of HPLC. CPNZ in CPNZ self-assemblies hydrolyzed quickly in strong acid and strong base buffer solution, but kept stable for a long period in neutral and weak acid surrounding in which t1/2 was more than 315 h, and in plasma of animals and tissue homogenates of rabbit, the hydrolysis of CPNZ was a bit faster with t1/2 of less than 20 h. However, the hydrolysis rate of CPNZ in a variety of animals was unmarkedly different. But the degradation rate of CPNZ in tissue homogenates of rabbit was very different. t1/2 in liver and spleen homogenates were less than 2 h, t1/2 in lung homogenates was ca. 10 h. 6. Pharmacokinetics and tissue distribution of CPNZ self-assemblies. After single bolus iv administration to rabbits and rats, CPNZ self-assemblies were eliminated quickly from blood circulation, distribution t1/2 in rabbits and rats were 4.37 min and 4.22min, respectively. elimination t1/2 in rabbits and rats were 48 min and 114min, respectively. It suggested that CPNZ self-assemblies had some longevity in the blood. Which was attributed to CHS-PEG1500, With regard to macrophage system, especially liver and spleen targeting and sustained releasing effects were shown in two animals. The CPNZ concent in liver occupied more than 50% and 42% of dose at 0.5h after bolus iv administration of CPNZ self-assemblies to rabbits and rats, respectively. Self-assemblies were targeted to liver, spleen and lung of rabbits and rats. The elimination t1/2 in liver and spleen of rabbits were 21h and 11h. The elimination t1/2 in liver, spleen and lung of rats were 25h, 15h and 11h.The concentration of AZT, the parent drug, was low, which mainly resulted from the rate of hydrolysis of CPNZ was much slower than the elimination of AZT and degradation products AZT in cells could phosphorylate by intracellular kinases.A highly dispersed, homogeneous, stable self-assemblies of zidovudine lipidic prodrugs was prepared in this paper. A nano-size, ordered structure formed under the action of hydrophobic interaction and hydrogen bonding was proved. The self-assemblies were uptaked by monocyte macrophage quickly in rabbits and rats and sustainedly degraded into AZT.