Study Of Mitoxantrone Hydrochloride Long-circulating Thermosensitive Liposomes

In recent years, due to the high incidence and high mortality, cancer poses a seriousthreat to human health and life. Surgery, radiotherapy and chemotherapy are commonlyused for cancer treatment. Among them, chemotherapy plays a major role on theelimination of system tiny tumor metastasis, the system complementary therapies as wellas to prolong the lives of patients. However, the poor stability of the physical andchemical properties of the drug, the short half life in vivo as well as the seriouslysystemic side effects limited its clinical use. The pharmaceutics development such as thegrowth of the liposomes can achieve the accumulation of the drug in the specific tissue invivo, improve the deficient of the chemotherapy, reduce the systemic side effects andenhance curative effect. Especially the thermosensitive liposomes can make the drugrelease at the cancer cite by heating the tissue.In this study, the anthracycline antineoplastic drug Mitoxantrone hydrochloride (DHAQ)was selected as the model drug. Its long-circulating thermosensitive liposomes (M-LTL)were prepared by film separation and pH gradient method, and a systemic study onM-LTL was made. Firstly, pharmaceutical characteristic of DHAQ was investigatedsystemically, such as solubility in different medium, precipitation in different medium,pKa, and so on. Secondly, the prearation technology of the liposome and itsphysic-chemical properties were studied in this paper. Dextran G-50microcolumncentrifugation was used to separate the drug unencapsulated from the drug-containingliposomes.And the reproducibility in the amplified technology was also evaluated. Inaddition,the freeze-thawing stability, long-term stability of M-LTL stored at4℃and-20℃, compativility in clinical was also studied. At last, the pharmacodynamicsevaluation of the M-LTL was also studied. At last, the pharmacodynamics evaluation ofthe M-LTL was conducted. Tumor-bearing mouse model was founded by subcutancousgraft of H22cancr cell.And the tumor inhibitory efficiency was calculated by using thetumor growth curve and the tumor inhibitory rate as the main index.DHAQ showed the different precipitation properties with varing the buffer salt solutions. The precipitation of DHAQ which formulated with buffer salt after loading into theliposomes can dissolve and free drug can be released when the temperature increased to42℃, at which the liposomes phase transition happened. Free drugs were not easy to leakout when stored at lower temperature, due to DHAQ existing in colloidal stateprecipitation. Three different active-loading methods were studied, pH gradient methodmediated by citric acid solution was taken for its simpleness, reproducibility and highencapsulating efficiency. According to single factor study, drug/lipid ratio, formulation oflipids, pH of hydration medium mainly affect the encapsulating efficiency, while stabilityof M-LTL at-20℃was primarily affected by the kind and concentration of protectiveagent. The optimized formulation were as follows：drug concentration2.0mg/mL；drug/lipid1：15； DPPC/MSPC86：5；300mM pH3.0citrate buffer was used as thehydration medium；the protectant concentration was10%/20%(inner/outer of theliposomes). The study on physic-chemical properties of M-LTL showed that the meanparticle size of the liposome was92nm. The content of DHAQ and the average EE was1.98mg/mL and99.8%, respectly. Freezing-thawing process, dilution and filtrationshowed slight influence on its stability. When the M-LTL was stored at4℃or-20℃for6months the mean particle diameter increased about11nm and19nm with drug contentdecreasing3.7%and9.1%respectively. Therefore, M-LTL storing at4℃was morestable. The in vitro release test of M-LTL demonstrated that the drug release amount wasnot more than5%at37℃in15min, while about60%of the total drug released at42℃in5min. The in vivo test demonstrated that the tumor inhibitory rate of M-LTL heatinggroup had significant difference (P<0.05) compared with M-LTL heating-free group,injection(M-I) and normal saline group, which mean tumor inhibitory rate was81.5%while the other two groups only61.1%and40.1%. In summary,the preparation techniquewas stable and repeatable. The results demonstrated that M-LTL is temperature-sensitiveremarkably and could increase the release in vivo to increase the local concentration ofdrugs.