| Objective The aim of this investigation was to testify the selective affinity of sulfadiazine(SF) to tumor cells, and to develop tumor targeted drug delivery system for flourouracil(5Fu) using sulfadiazine as the cairrer. Antitumor activity and acute toxic effect of the tumor targeted drug delivery system were also observed.Methods (1) Ploy(ethylene glycol)(PEG) was conjugated to the terminal sulphonyl amino group of sulfadiazine through ring-opening polymerization of ethylene oxide by anion initiation using sulfadiazine as parent compound. Molecular weight of SFPEG was measured by viscometry. (2) SFPEG was labeled by 99MTc via diethylenetriamine pentoacetic acid(DTPA). Labeling efficiency was determined by paper chromatography. Nude mice bearing human nasophargngeal cell line CNE2 was used to evaluate the biodistribution of SFPEG. The tumor bearing mice were sacrificed at 6h after 99mTcSFPEGDTPA was injected though tail-vein. Tumor, liver, spleen, kidney, bone marrow, muscle and heart were obtained from the tumor bearing mice and the radioactivity present on each sample was measured by liquid scintillation counting. Tumor to non-tumor ratios were caculated. SPECT imaging study was also conducted at 24h and 48h after the administration of 99mTcSFPEGDTPA. (3) 5Fu was subjected to reaction with trichloromethyl chloroformate(TCF) to prepare chloroformyl 5Fu, which was linked to a spacer hydroxyl group of PEG that served as a macromolecular linking arm between SF and 5Fu. The content of 5Fu in the conjugate was determined by ultraviolet spectrophotometry. Spectrum of ultraviolet and infrared along with differential scanning calorimetry were employed to identify the structure of the conjugate of SFPEG-end capped 5Fu. (4) MTT colorimetric assay was applied to detect cytotoxicity of SFPEGSFu in CNE2 cell and human normal liver cell line LO2 in vitro. 5Fu and SFPEG+5Fu(30:1,m/m) were contrasted as the postive treatment. Antitumor activity of SFPEG5Fu in vivo was evaluated in mice bearing H22 hepatoma.The tumor bearing mice were randomly divided into four groups, the group of 0.9% NaCl solution, SFPEG5Fu, 5Fu, and SFPEG+5Fu(30:l,m/m). The group of 0.9% NaCl solution served as a control group. The other three groups were treated intravenously with 20mg/Kg (equivalent dose of 5Fu) of SFPEG5Fu, 5Fu, SFPEG+5Fu (30:1,m/m) respectively once a day for 5 days. Tumor inhibitory rates of each group were compared. Survival times of mice in all groups were observed and also compared. (5) Healthy mice were treated with maximum dose and maximum volume of SFPEG5Fu for only once and were sacrificed on 14th day. Autopsy examination was performed. Liver, spleen, kidney, lung, pancreas, heart, stomach, intestine and sternum were obtained and routine pathological examination was conducted to observe its acute toxic effect of SFPEG5Fu.Results (1) Reaction time of polymerization was shortened with increasing temperature according to the preliminary results. Yielding rate and molecular weight were also increased with increasing temperature. The optimum time and temperature observed were found to be 100℃-110℃ and 46h-48h. (2) Labeling efficiency was over 90% as determined by paper chromatography in two different mobile phase. Radioactivity of the tumor tissue was increased significantly at 6h post injection and was higher than the non-tumor tissues except kidney. T/NT ratios ranged from 3.27:1 to 4.53:1. Image of the tumor was viewed distinctly at 48h post injection. (3) Structure analysis confirmed the linkage between 5Fu and SF via PEG. The drug loading content of the conjugate was 3.27% according to the regression equation C265 = 18.80A - 1.195. (4) SFPEG5Fu appeared an obvious dosage and effect relatio on CNE2 cell in vitro, when the concentration and culture time increased, SFPEG5Fu increased the ability of killing and suppressing the cells(P<0.01). On the action time of 72h, tumor suppressing rates of SFPEG5Fu were lower than those of 5Fu(P < 0.01), which demonstrated the mild loss of antitumor efficiency in vitro when 5Fu w...
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