The Research Of Tumor-targeted Water-soluble Paclitaxel Prodrugs

Paclitaxel is a powerful anticancer agent isolated from the trunk bark of the PacificYew tree. However its poor solubility has limited its use in cancer therapy. Currentformulation for intravenous injection used clinically contains Cremophor EL which cancause a series of side-effects. In order to solve this problem, a tumor-targeted drugdelivery system which used clinical plasma volume expander-Hydroxyethyl starch (HES)as a carrier conjugating with paclitaxel was designed. The main research works are asfollows:(1) The prodrugs were prepared by conjugating paclitaxel with hydroxyethyl starchthrough a heterbifounction linker of3-(2-pyridyldithio)-propanoic acid (PDP). The threeproducts of different content of paclitaxel were synthesized by controlling the ratio of rawmaterials. Intermediates and target compounds were characterized by Proton NuclearMagnetic Resonance (1H-NMR) and Fourier Transform Infrared Spectroscopy (FT-IR).The results showed it was confirmed that paclitaxel was successfully attached to the chainof hydroxyethyl starch. The degrees of substitution (DS) of PDP in the intermediates of3-(2-pyridyldithio)-propanoic acid-hydroxyethyl starch (HES-PDP) were respectively5.4%,9.9%and23.2%through Proton Nuclear Magnetic Resonance (1H-NMR).(2) The physical and chemical properties of prodrugs such as drug content, watersolubility, self-assembly were studied. The drug content was determined through the usageof reducing agent dithiothreitol (DTT) to reduce prodrugs and following by analysis ofhigh performance liquid choromatography (HPLC). The result showed the drug content ofthree different prodrugs was respectively5.8%,11.3%and12.8%. The water solubilitywas determined by solubilizing prodrugs with water gradually and the result showed threedifferent prodrugs which used the chain of hydroxyethyl starch as the carrier could largelyimprove the solubility of paclitaxel. The prodrugs nanoparticles were prepared andcharacterized by dynamic light scattering (DLS) and transmission electron microscope(TEM). The results showed the prodrugs could self-assemble to form sphericalnanoparticles which had the sructrue of core/shell. The average diameter of thenanoparticles was143.6~223.0nm, decreasing with rising of the drug content.(3) The drug release behaviors of prodrugs in various Glutathione (GSH)concentrations (2μmol/L,10mmol/L) which were analog of plasma and intracellularGSH levels were studied. The results showed three different prodrugs exhibited the GSH dependent release kinetics in various GSH concentrations. The conjugates were stable at2μmol/L GSH concentration while showing the significant amount of drug release atintracellular GSH concentration.(4) In vitro anti-tumor effect of prodrug was measured by the method of MTT. Theresults showed intermediate HES-PDP was nearly nontoxic but the prodrug showed drugdependent cytotoxicity, namely cell viability decreased with the rising of drugconcentration. The conjugate showed less cytotoxicity at lower drug concentration whileexhibited close anti-tumor effect at higher drug concentration compared with freepaclitaxel.