Enhancement of the stability of BCNU using self-emulsifying drug delivery systems (SEDDS) and in vitro antitumor activity of self-emulsified BCNU-loaded PLGA wafer

Abstract

The main purpose of this study was to develop self-emulsifying drug delivery systems (SEDDS) for the improvement of the stability of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) after released from poly (d,l-lactide-co-glycolide) (PLGA) wafer and to evaluate its in vitro antitumor activity against 9L gliosarcoma cells. The in vitro stability test of BCNU was characterized by the BCNU amount in phosphate buffered saline (PBS, pH 7.4) at 37 °C. SEDDS increased in vitro half-life of BCNU up to 130 min compared to 45 min of intact BCNU. Self-emulsified (SE) BCNU was fabricated into wafers with flat and smooth surface by compression molding. In vitro release of BCNU from SE BCNU-loaded PLGA wafer was prolonged up to 7 days followed first order release kinetics. Beside, the cytotoxicity of SE BCNU-loaded PLGA wafer against 9L gliosarcoma cells was higher than intact BCNU-loaded PLGA wafer which is more susceptible to hydrolysis. SE BCNU degraded much more slowly than the intact BCNU in PLGA matrix at 25 °C. These results strongly suggest that the self-emulsion system increased the stability of BCNU after released from PLGA wafer. From these results, it could be expected that the penetration depth of BCNU could be improved in brain tissue using self-emulsion system.

Introduction

The localized, controlled delivery of anticancer agents using biodegradable polymeric implant is an alternative to the systemic administration of chemotherapeutic agents for treating malignant brain tumors. Gliadel^® made of poly 1,3-bis(p-carboxyphenoxy)propane-sebacic acid copolymer (polyanhydride, PA) and 1,3-bis(2-chloroethyl)-1-nitrosourea (carmustine, BCNU) as a chemotherapeutic agent has been commercialized in treating malignant brain tumors (Dang et al., 1996, Sampath and Brem, 1998). However, the conventional therapies cannot extend the median survival of patients significantly because these tumors tend to recur within 2 cm of treated site (Chasin et al., 1990).

In our previous study, we applied BCNU-loaded poly(d,l-lactide-co-glycolide) (PLGA) wafer to study for brain tumor, because PLGA has been approved for drug delivery use by the Food and Drug Administration (FDA). Long-term delivery of BCNU (Seong et al., 2002), the BCNU release behavior with the changes of various dimension of wafer (Chae et al., 2004) and additives (An et al., 2002a, An et al., 2002b, Lee et al., 2003), cytotoxicity against various tumor cell lines (Seong et al., 2003, Lee et al., 2004) and in vivo anti-tumor activity were investigated. But it has been reported that BCNU presents very short penetration distance because it gets drained out of the system before being able to diffuse to any appreciable distance (Wang et al., 1999).

BCNU is known to cross the BBB due to its low molecular weight and lipophilicity (Paoletti, 1984). However, its effectiveness was hindered by both dose-limiting side effects and relatively short half-life (<20 min, in plasma) (Loo et al., 1966). The exposure of BCNU released from matrix is very brief; therefore, the penetration depth is very short (2–3 mm in brain tissue). Improving the permeation depth of BCNU in brain tissue is very important for treating brain tumor effectively. One of the ways to improve the penetration depth of BCNU is enhancing the stability of BCNU released from matrix against hydrolysis in vitro and in vivo.

One of the technological resources used to improve the permanence of drugs more largely at the site of action, in this case, is the use of emulsions. The self-emulsified drug delivery system (SEDDS) prepared from oil, a surfactant, and possibly one or more hydrophilic solvents or co-surfactants (Holm et al., 2003, Kang et al., 2004) when exposed to aqueous media under condition of gentle agitation, such as body fluid and blood (Tarr et al., 1987, He et al., 2003) to retard exposure of BCNU from aqueous media. SEDDS were mainly used to improve the bioavailability of poor water soluble drug compounds (Humberstone and Charman, 1997, Kommuru et al., 2000). Moreover, the drug dissolution into oil components was diffused without any activity in the mean time of forming emulsion, because of the presence of a surfactant, which can adsorb on the oil droplet surface (Dickinson and Matsumura, 1994).

In objective of this study, SEDDS of BCNU was developed for enhancing the stability of BCNU. The self-emulsified (SE) BCNU was incorporated into PLGA wafer as a new polymeric implant. In vitro release pattern of BCNU from SE BCNU-loaded PLGA wafers and cytotoxicity according to droplet size and stability of the SE BCNU-loaded PLGA wafer against 9L gliosarcoma cells were assessed.