The Pre-clinical Research Of Paclitaxel-loaded Nanostructure Lipid Carriers

BACKGROUND Paclitaxel is the diterpene product obtained from the needles and bark of the Pacific Yew (Taxus brevifolia ) to be used as a potent anti-tumor drug. It can block cells in the late G2-mitotic phase of the cell cycle by stabilizing the microtubule cytoskeleton. Because Paclitaxel is lipophilic and possesses very low water solubility (less than 2μg/mL), the drug is dissolved in a 50:50 mixture of Cremophor EL and ethanol. However, Cremophor may induce the hypersensitivity and many other serious side effects, it is necessary to develop the Cremophor EL-free formulations to overcome these problems. In the present study we have developed a new carrier system of nanostructure lipid particle to delivery paclitaxel (TAX-NLC) for improving the solubility of paclitaxel, increasing the enveloping efficiency and enhancing drug loading capacity.OBJECTIVE to get the higher qualified 125I labeled TAX tracer for the radionuclide trace experiment, to investigate the pharmacokinetics and the tissue distributions of the TAX-NLC in nude mice bearing human KB tumor cells and in macaques, to evaluate the anti-tumor efficacy of TAX-NLC initially.METHODS The modified Ch-T labeling method will be used for getting high qualified 125I-TAX tracer. The IR was used to identify the product. HPLC and paper chromatography were used to determine its radiochemical purities. The stabilities of 125I-TAX in vitro were monitored by trichloroacetic acid (TCA) precipitation. The 125I -TAX-NLC was prepared by high pressure homogenization-hot homogenization by entrapped 125I- TAX. The TAX-NLC labeled with 125I - paclitaxel at the dose 75 mg/m2 were injected to nude mice bearing human tumor (KB cell line) xenografts and macaques via tail vein and left forelimb vein, respectively. After the injection, serial blood samples and organs of mice were collected at various time intervals, and the 125I activities in the organs, including blood and tumor, were counted. The serial blood samples of macaques were collected from right forelimb vein at various time intervals too, but the distribution of TAX-NLC in macaques was imaged by SPECT (IRIX, Marconi). The pharmacokinetics parameters were calculated by DAS 2.1 software. Furthermore, the comparable anti-tumor efficacy of TAX-NLC was observed by calculating the weights and volumes of xenografts initially.RESULTS The labeled products has been identified by IR spectra, and the radio chemical purity was more than 95%, the tracer was stable in the serum and ethanol. at room temperature and 4℃. The blood pharmacokinetics of TAX-NLC exhibited a characteristic distribution and elimination response for macromolecules in mice and macaques, which could be described by a bi-exponential process. The plasma concentration of the TAX-NLC in nude mice and macaques was declined as a three-compartment model. The parameters in nude mice were below: half-lives 0.399 h(t1/2α), 3.711 h( t1/2β), 60.117 h( t1/2γ), AUC(0-∞) 546.135 mg/L*h. Because of the big difference between the macaques, the parameters in macaques were below respectively: t1/2αwere 0.105h and 0.158h,the t1/2βwere 6.845 and 3.128h, and the t1/2γwere 72.66 and 29.27. AUC(0-t) were 614.105 and 310.473 mg/L*h. CL were 0.1 and 0.194 L/h/m2. The main tissues distribution of TAX-NLC were live, spleen, lung in nude mice, and the concentration of TAX-NLC in tumor (KB cell line) xenografts reached to 9.6 ug per gram tumor, it was three times more than opposite muscles. However, the main tissues distributions of TAX-NLC in macaques scanned by SPECT were gallbladder, live, urinary bladder, spleen, and heart. The excretion of TAX in the macaques was by bile and urine.The anti-tumor efficacy of TAX-NLC was similar as free TAX, but the TAX-NLC was better about the bioavailability.CONCLUSIONS These studies indicate that The TAX-NLC was a perspective carrier system. The TAX-NLC had a prolonged circulating time, and the main elimination organs were gallbladder and kidneys. The Paclitaxel could be concentrated on the tumor xenografts by the TAX-NLC carrier system. This formulation could serve as a promising approach for cancer therapy.