Research Of 7-ethyl-10-hydroxycamptothecin Palmitic Acid Ester Long-circulating Liposome

7-etyl-10-hydroxycamptothecin(SN38)is an alkaloid with high anti-tumor activity,But,the poor solubility and pH-dependent hydrolysis limits the clinical application of SN38.This study intends to combine the advantages of chemical modification and long-circulating liposome,by structural modification to prepare a lipid soluble prodrug of SN38,and incorporated it into liposome to overcome the shortcomings of SN38 and improve the anti-tumor effect.In this study,7-ethyl-10-hydroxycamptothecin palmitic acid ester from the reaction of SN38 and palmitoyl chloride,yield of SN38-PA was about 98%,SN38-PA was confirmed through NMR spectrometry and LC/MS.SN38-PA partition coefficient was determined by shake-flask method,0.1M citrate buffer solution was saturated with 1-octanol thoroughly,SN38-PA exhibited a lipophilicify LogP of about 7.92.The sephadex column chromatography was used to determinate the entrapment efficiency of SN38-PA liposome.The film dispersion method,reverse phase evaporation and injection method were used to prepare the SN38-PA liposome,respectively.Single factors had been done and the central composite design was used to optimize the prescription.Finally the SN38-PA liposome was prepared by film evaporation method,the better prescription was that the ration of phospholipid(Lipoid E PC S)and drug ratio was 12.5:1(W / W),ration of phospholipid(Lipoid E PC S)and cholesterol was 2.5:1(W / W),content of DSPE-PEG2000 was 0.5%.The average particle diameter was 80.13 nm,average Zeta potential was-33.53 mv,average entrapment efficiency was 99.11%.In phosphate buffer solution,compared to CPT-11,SN38-PA has a higher rate of closed lactone ring,after 12 h the lactone ring of SN38-PA was more than 95%,while the lactone ring of CPT-11 was only about 20%.Compared to CPT-11,SN38-PA can be rapidly degraded in rat plasma in vitro,after 24 h the degradation ratio of SN38-PA was about 98%,while the CPT-11 was only about 12%.Compared to CPT-11,SN38-PA has a higher plasma concentration and can rapidly metabolized in rats.It can also produce more active metabolite SN38,the area under the curve of SN38 from SN38-PA was 9.92 times(P <0.001),the half-life was significantly longer(P <0.05),and the clearance rate were significantly smal er(P <0.001),when compared to SN38 from CPT-11.Detected the distribution of CPT-11,SN38-PA and SN38 in various mice tissues(heart,liver,spleen,lung,kidney,rectum,tumor),compared to CPT-11 the SN38-PA had more active metabolite SN38 in each tissues,the concentrat ion and AUC in each tissues was higher than CPT-11.Finally,we valuated the pharmacodynamic differences between SN38-PA liposome and CPT-11 injection in vivo.Under the same dose the anti-tumor inhibition rate of SN38-PA liposome was almost 1.61 times when compared with CPT-11 injection,and the anti-tumor inhibition rate of the lowest dose of SN38-PA liposome was also significantly higher than CPT-11 injection(P <0.05).Based on mice body weight changes,we can see that both CPT-11 injection and SN38-PA liposome had some toxicity.The pathology slices indicated that the cell necrosis of SN38-PA liposome was more seriously than CPT-11 injection when at the same dose.In general,SN38-PA liposome has higher anti-tumor effect.