title: Novel sulfobutyl ether cyclodextrin gradient leads to highly active liposomal irinotecan formulation.
abstract: OBJECTIVE
  Liposomal delivery of irinotecan could provide protection against drug hydrolysis, deliver more active lactone form to tumours and prolong irinotecan exposure time. Nevertheless, conventional drug-loading technologies have typically resulted in undesired drug retention properties. To resolve the problem, a modified gradient loading method was developed and the resulting formulations were evaluated in a systemic manner.
  
  
  METHODS
  Irinotecan was loaded into liposomes using a novel sulfobutyl ether beta-cyclodextrin (sbe-CD) gradient. The effect of drug-to-lipid ratio (D/L) and polyethylene glycol (PEG) grafting density were investigated. Drug release experiments were performed in ammonium-containing medium based on the fluorescence dequenching phenomenon of irinotecan. Pharmacokinetic studies were performed in normal balb/c mice treated with different formulations. To compare the anti-tumour effect of different formulations, an RM-1 prostate cancer model was used. Acute toxicity studies were performed in healthy female c57 mice.
  
  
  RESULTS
  Irinotecan could be encapsulated into liposomes with >90% loading efficiency at a high drug-to-lipid mass ratio (>0.5). In-vitro release experiments revealed that sbe-CD anion was more able to retain irinotecan than sulfate. Moreover, the elevated D/L ratio elicited decreased drug release kinetics. Both trends had also been observed when the effects of anions and D/L ratio on half-life of irinotecan were assessed. Pegylated liposomal irinotecan loaded with sbe-CD/triethylammonium gradient had irinotecan half-life values ranging from 9.4 to 13.1 h, surpassing vesicles prepared by the triethylammonium sulfate method (∼4.5 h). In the RM-1 tumour model, all the liposomal irinotecan formulations were more therapeutically active than free irinotecan and the formulation with a high D/L ratio was the most efficacious. Moreover, the high D/L formulation might be less toxic than free irinotecan based on acute toxicity studies.
  
  
  CONCLUSIONS
  The novel sbe-CD gradient could mediate effective irinotecan loading and improve irinotecan retention, thus resulting in highly active liposomal irinotecan formulations. The improvement in drug retention might be associated with the formation of complicated aggregates inside vesicles.
authors.affiliation: CSPC ZhongQi Pharmaceutical Technology (Shijiazhuang) Co., Ltd, Shijiazhuang, China. lcllib@hotmail.com
authors.forename: ChunLei
authors.initials: C
authors.lastname: Li
authors.forename: JingXia
authors.initials: J
authors.lastname: Cui
authors.forename: CaiXia
authors.initials: C
authors.lastname: Wang
authors.forename: YanHui
authors.initials: Y
authors.lastname: Li
authors.forename: Lan
authors.initials: L
authors.lastname: Zhang
authors.forename: Xian
authors.initials: X
authors.lastname: Xiu
authors.forename: YongFeng
authors.initials: Y
authors.lastname: Li
authors.forename: Na
authors.initials: N
authors.lastname: Wei
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
mesh_terms: D000645:Ammonium Sulfate / Q000737:chemistry; D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000627:therapeutic use; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D002214:Capsules; D005260:Female; D006207:Half-Life; D000077146:Irinotecan; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011092:Polyethylene Glycols / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D013678:Technology, Pharmaceutical / Q000379:methods; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D000970:Antineoplastic Agents; D002214:Capsules; D008055:Lipids; D008081:Liposomes; D047392:beta-Cyclodextrins; C093196:SBE4-beta-cyclodextrin; D011092:Polyethylene Glycols; D000077146:Irinotecan; D000645:Ammonium Sulfate; D002166:Camptothecin