Preparation, characterization, and in vitro pH-sensitivity evaluation of superparamagnetic iron oxide nanoparticle-misonidazole pH-sensitive liposomes.

BACKGROUND: The use of misonidazole (MISO), the first and a potential hypoxic tumor cell radiosensitizer, has been limited by peripheral neurotoxicity, thus discouraging phase III clinical trials.

OBJECTIVE: To develop a targeted drug delivery and tracing system with pH-sensitive liposomes (SpHLs) and superparamagnetic iron oxide nanoparticles (SPIONs) to counter MISO-related adverse effects and to enable tracing under magnetic resonance.

METHODS: SPION-MISO-SpHLs were prepared by a reverse evaporation and freeze-thawing method. HPLC and phenanthroline spectrophotometry were established for MISO and Fe determination. The characterization and in vitro pH-sensitivity of SPION-MISO-SpHLs were evaluated.

RESULTS: The maximal entrapment efficiencies of MISO and SPIONs in SPION-MISO-SpHLs were 30.2% and 23.7%, respectively. The cumulative release rates of MISO and SPIONs were respectively 2.49 and 2.47 times higher in pH 5.5 than in pH 7.4 buffer. The mean particle size of SPION-MISO-SpHLs was 950 nm. The zeta potential was -58.9 mV in pH 7.4 buffer and 36.3 mV in pH 5.5 buffer. SEM imaging showed that SPION-MISO-SpHLs had similar spherical morphologies. SPIONs were packed in the center of liposomes and were well dispersed in a TEM graph. Magnetization curve showed that SPION-MISO-SpHLs retained superparamagnetic properties. SPION-MISO-SpHLs were compared with MISO+SPION+blank liposome in hypoxia and control groups of A549 cells. MISO and SPION concentrations in culture medium showed significant differences between the same concentration groups (P <0.0001) and at different times (P <0.0001).

CONCLUSION: SPION-MISO-SpHLs possess pH-dependent release ability and superparamagnetism, and thus provides a system for targeted delivery and tracing under magnetic resonance.