Studies On The Macromolecular Prodrug Of Fluorouracil And Its Liposome

Oral colon-specific delivery system is naturally of value for the topical treatment of diseases of colon such as ulcerative colitis, Crohn's disease, or colorectal cancer, whereby high local concentration can be achieved while minimizing side effects.It is confirmed that intraluminal fluorouracil chemotherapy in colon adjuvent to surgery for colorectal-cancer can improve the therapy index, decrease the side-effect and improve the patent's lifetime. Based on this investigation, we synthesized a macromolecular prodrug of fluorourcil with a bility of colon-specific released drug delivery system.Dextrans are glucose polymers which have been used for more than 50 years as plasma volume expanders. Recently, dextrans have also been investigated for delivery of drugs, proteins, enzymes and imaging agents.Fluorouracil-acetic acid (FUAC) was synthesized following the literature method. Fluorouracil acetic acid (FUAC) was then chemcally bound to dextran in the mixed solvent (FA/DMF/DCM=10:9:1, v/v/v) catalyzed by DMAP and DCC. The obtained conjugate was confirmed by the analysis of UV, IR and NMR spectrum. The absence of free drug in the conjugate was proved by gel filtration chromatography on Sephadex G-25.The ionization constant (pKa) of fluorouracil-acetic acid was 2.692±0.025 determined by the the potentiometric titration. The saturated solubility of FUAC in water at 20℃is 1.55 g/100 ml water.The chemical stability of polymeric prodrug obtained was investigated in various buffer solution at 37℃and 60℃respectively. The result indicated that the polymeric drug was more stable in acidic condition with pH range from 1.24 to 5.66 and decomposed at slight alkaline condition. The hydrolysis rate increased with the ionic strength increase from 0.1 to 0.5 M. The rate constants for the hydrolysis reaction of the conjugate in 0.1 M phosphate buffer solution at pH 6.84 at 37°C and 60°C were calculated. The observed activation energy (E_obs ) was 88.73±6.00 KJ/mol calculated from the Arrhenius Equation. This was indicative for the breakage of a sigma bond, proving once again that FUAC was covalently bond to the polymeric backbone not merely dispersed or wrapped into polymer. The degree of substitued was determined by the ratio of the raction materials.The liposomes of FUAC-dextran conjugates and tegafur were prepared by thin film dispersion method. Through the single factor analysis and the orthogonal design experiment, the best experimental condition is obtained with the 84.5％of encapsulation efficiency for FUAC-dextran conjugates liposome. Through the single factor analysis and the orthogonal design experiment, the best experimental condition is obtained with the 37.5％of encapsulation efficiency for tegafur liposome. The reason for the difference of the encapsulation efficiency was explained.The pharmacokinetics of FUAC was investigated after oral administration of FUAC at 100 mg·kg^-1 body or oral administration of FUAC-dextran conjugates at 100 mg·kg^-1 body (based FUAC) in rat. The AUC for the FUAC was 846±513 mg·l^-1·min and hardly determined the concentration of the FUAC in plasma.The macromolecular prodrug was incubated with the dilution contents of rat gastro-intestinal tract at 37℃to investigate the release of FUAC from the macromolecular prodrug. The macromolecular prodrug with DS 10.3％exhibited the colon localizations release characteristics. But the macromolecular prodrugs with DS 15.1％FUD-70 AND DS 30.2％FUD-40 do not showed the colon localizations release characteristics.The concentratin of FUAC in colon and caecum reached the highest at 4 h after oral administartion of FUAC at 50 mg·kg^-1 body weight, after then decrease rapidly. But the concentratin of FUAC in colon and caecum reached the highest at 4 h and kept at high level for a long time from 4 to 12 h after oral administartion of FUAC-dextran conjugate(DS: 10.3％, FUD-70) at 50 mg·kg^-1 body weight (based on FUAC). The AUC of FUAC after oral administration of the conjugates was twice as that of FUAC solution. This result indicated that the macromolecular prodrug was promising for oral colon drug delivery system.