Enhanced nuclear delivery and cytotoxic activity of hydroxycamptothecin using o/w emulsions

Hydroxycamptothecin-Emulsions (HCPT-E), being a promising delivery system for intravenous applications, were prepared. Here we evaluated the relation of cytotoxicity and intracellular drug amounts. The mechanism of the enhanced antiproliferative activity was also investigated.

In vitro cytotoxic potential were assessed by the methyl thiazol tetrazolium (MTT) assay. The capability of emulsions to preserve lactone form of HCPT and the time course of subcellular (cytoplasm and nuclei) drug distribution in vitro of HCPT-E were quantified by a reversed-phase HPLC assay.

MTT results showed that the antiproliferative activity of HCPT-E was stronger than that of HCPT-Injections (HCPT-I) which is presently used in clinic. IC50 values of HCPT-E was much lower, by 4 and 7 times than those of HCPT-I. HeLa cells treated with HCPT-E for 4 h exhibited a considerable morphology change and displayed a hint of apoptotic cell death at 72 h. The lactone is the key position in HCTP molecule which is sensitive to pH. Lactone ring of HCPT in HCPT-E was stable for longer time than that of HCPT-I in the presence of human plasma or culture medium. Both the nuclear and cytoplasmic level of HCPT in HeLa cells exposed to HCPT-E at each time were higher by 18 to 33 times than those treated with HCPT-I. Drug amounts of nuclei was higher than that of cytoplasm in HeLa cells incubated with HCPT-E while it was reverse in HeLa cells exposed to HCPT-I.

HCPT-E improved stability of HCPT, enhanced uptake, changed its intracellular distribution in favor of accumulating in the intracellular targets.