In Vitro And In Vivo Studies Of A Novel Drug Carrier Based On Lipid Emulsion For Paclitaxel Delivery

It is estimated that approximately 40%or more of active substances being identified through drug discovery programs are poorly soluble in water,especially for several chemotherapy agents.Paclitaxel is highly lipophilic and poorly water-soluble drug(<1?g/mL).The first formulation of PTX is Taxol(?).Cremophor EL and ethanol(50:50,v/v)were used as solvent of PTX,which have serious side effects,including allergic reactions,neurotoxicity and cardiac toxicity.In recent years,although extensive researches of nanoparticles have been designed and developed,these studies have many difficult to achieve clinical transformation.Nanoscale drug carriers have shown particularly promise in increasing the solubility and monitoring therapeutic efficacy of poorly water-soluble drugs.However,only a few quantity of the drug could be loaded into the nanocarrier due to the poor stability and extraction of RES organs.It was found that lipid emulsion was capable to incorporate large quantity of high lipophilic and poor water-soluble drugs.In this study,PTX was used as a model drug and incorporated into a marketable lipid emulsion.Prior to use,4mL of PTX-PEG400 was diluted with 96mL of 20%lipid emulsion.This two-vial formulation of PTX-loaded lipid emulsion was prepared from the aspect of the separation of drug and carrier.Meanwhile,it was hoped to solve PTX and the drawbacks of its traditional formulation,to solve the stability issue of traditional drug-loaded lipid emulsion and the extraction of RES organs.Therefore,the objective of this study was to functionally evaluate the in vitro and in vivo characteristics of this novel lipid emulsion drug delivery systems.First,drug content,particle size and pH were measured as the stability indexes of TPLE and CPLE in the stability study.The results showed that the maximum stability time of CPLE was 15h.TPLE could be stable within 10h with PTX content>98%and a mean emulsion droplet diameter of 220nm.At each time point,there were no significant changes and differences in terms of pH and particle size between these two formulations.Although the stability time of CPLE was longer than TPLE,it was not enough for the industrial production and clinical use.However,TPLE,which was mixed with blank lipid emulsion,could avoid the drawbacks of stable time.Secondly,in vitro releases of PTX from TPLE and CPLE containing the same quantity of drug were carried out in a Pharmaceutical Dissolution Tester using basket-rotating method.The results showed that the release kinetics of TPLE and CPLE both exhibited a biphasic pattern characterized by a fast initial burst release during the first 4h,then followed by a slow,sustained release.At the determined time intervals,it was found that PTX released faster from TPLE than CPLE.After 10h,the accumulated PTX was found to be 36.119±4.41%and 27.86±3.76%of the total amount for TPLE and CPLE,respectively.Furthermore,experimental results of in vivo tissue distribution and antitumor activity showed that the distribution of drugs in the same preparations of PTX in nude mice organizations are liver>kidney>lung>spleen>heart>tumor.TPLE could significantly reduce the PTX distribution in the liver and spleen,when compared with CPLE,while the concentration of TPLE in the tumor was higher than CPLE,clearly indicating that the TPLE distribution in the RES organs(such as liver and spleen)was reduced.The cumulative toxicity to these organs also could be reduced.Higher concentration of PTX in the tumor tissue could in part increase the antitumor effects of TPLE.Two independent in vivo antitumor studies have shown that tumor inhibition rate was that:TPLE(30mg/kg)>TPLE(15mg/kg)>CPLE(15mg/kg)>TPLE(7.5mg/kg).At equal doses of PTX(15mg/kg),the tumor growth rate of mice treated with TPLE was significantly lower(p<0.01),compared to CPLE treatment group.Tumor growth was inhibited to such an extent that the volume of tumor treated with TPLE,at the last day,was either 26%in A2780 ovarian group or 12%in Bcap37 breast group smaller than those treated with CPLE,respectively.Finally,the phase distribution of PTX was detected in the three phases of emulsion system.The result showed that PTX in TPLE was mainly dissolved in the oil phase and fewer PTX was located in the phospholipoid layer when compared with CPLE.There was no significant difference of PTX distribution in the aqueous phase both in TPLE and CPLE(p>0.05).To evaluate the above result,the probe of Flutax-1 was used as a mark to detecte PTX phase distribution by phase distribution and CLSM studies.The results clearly suggested that Flutax-1 was mainly located in the oil phase and phospholipids layer,higher amount of Flutax-1 could be incorporated in the oil phase and phospholipids layer of CPLE than that of TPLE.However,there was no significant difference of fluorescent intensity was observed in the aqueous phase of TPLE and CPLE systems.These results could explain the difference of in vitro release result of two types of PTX emulsions.Overall,this study evaluated the in vitro and in vivo characteristics of TPLE and CPLE.TPLE system exerts its full clinical advantages and the results of our study collectively suggest the potent value of this nanocarrier in the development of drug delivery sy'stems.