Effect of polyethylene glycol linker chain length of folate-linked microemulsions loading aclacinomycin A on targeting ability and antitumor effect in vitro and in vivo.

To establish a novel formulation tumor-targeted drug carrier of lipophilic antitumor antibiotics, aclacinomycin A (ACM), folate-linked microemulsions were prepared and investigated both in vitro and in vivo. Three kinds of folate-linked microemulsions with different polyethylene glycol (PEG) chain lengths loading ACM were formulated with 0.24 mol% folate-PEG(2000)-distearoylphosphatidylethanolamine (DSPE), folate-PEG(5000)-DSPE, and folate-lipid (without PEG linker) in microemulsions. In vitro studies were done in a human nasopharyngeal cell line, KB, which overexpresses the folate receptor (FR), and a human hepatoblastoma cell line, [FR(-)] HepG2. In vivo experiments were done in a KB xenograft by systemic administration of folate-linked microemulsions loading ACM. The association of folate-linked microemulsions to KB cells could be blocked by 2 mmol/L free folic acid. Selective FR-mediated cytotoxicity of folate-linked microemulsions loading ACM was obtained in KB but not in HepG2 cells. The association of the folate-PEG(5000)-linked microemulsion and folate-PEG(2000)-linked microemulsion with the cells was 200- and 4-fold higher, whereas their cytotoxicity was 90- and 3.5-fold higher than those of nonfolate microemulsion, respectively. The folate-PEG(5000)-linked microemulsions showed 2.6-fold higher accumulation in solid tumors 24 hours after i.v. injection and greater tumor growth inhibition than free ACM. These findings suggest that a folate-linked microemulsion is feasible for tumor-targeted ACM delivery. This study shows that folate modification with a sufficiently long PEG chain on emulsions is an effective way of targeting emulsion to tumor cells.