Novel sulfobutyl ether cyclodextrin gradient leads to highly active liposomal irinotecan formulation

作者：Li, ChunLei^*; Cui, JingXia; Wang, CaiXia; Li, YanHui; Zhang, Lan; Xiu, Xian; Li, YongFeng; Wei, Na; Zhang, Li; Wang, Ping

来源：Journal of Pharmacy and Pharmacology, 2011, 63(6): 765-773.

DOI：10.1111/j.2042-7158.2011.01272.x

• drug loading
• irinotecan
• liposomes
• sulfobutyl ether cyclodextrin
• therapeutic index

Objectives
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.
Key findings
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 (similar to 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.

• 出版日期2011-6
• 单位河北化工医药职业技术学院; 河北医科大学