Long circulating nanoparticles of etoposide using PLGA‐MPEG and PLGA‐pluronic block copolymers: characterization, drug‐release, blood‐clearance, and biodistribution studies

The anti‐leukemic drug, etoposide (ETO), has variable oral bioavailability ranging from 24–74% with a short terminal half‐life of 1.5 h i.v. necessitating continuous infusion for 24–34 h for the treatment of leukemia. In the present study, etoposide‐loaded PLGA‐based surface‐modified nanoparticles (NPs) with long circulation were designed as an alternative to continuous i.v. administration. PLGA‐mPEG and PLGA‐PLURONIC copolymers were synthesised and used to prepared ETO‐loaded NPs by high‐pressure homogenization. The mean particle size of ETO‐loaded PLGA‐MPEG nanoparticles was 94.02±3.4 nm, with an Entrapment Efficiency (EE) of 71.2% and zeta potential value of −6.9±1.3 mV. ETO‐loaded PLGA‐pluronic nanoparticles had a mean particle size of 148.0±2.1 nm, an EE of 73.12±2.7%, and zeta potential value of −21.5±1.6 mV. In vitro release of the pure drug was complete within 4 h, but was sustained up to 7 days from PLGA‐mPEG nanoparticles and for 5 days from PLGA‐pluronic nanoparticles. Release was first order and followed non‐Fickian diffusion kinetics in both instances. ETO and ETO‐loaded PLGA nanoparticles labeled with 99m Tc were used in blood clearance studies in rats where the two coated NPs, 99m Tc‐ ETO‐PLGA‐PLU NP and 99m Tc‐ ETO‐PLGA‐mPEG NP, were found to be available in higher concentrations in the circulation as compared to the pure drug. Biodistribution studies in mice showed that ETO‐loaded PLGA‐MPEG NP and PLGA‐PLURONIC NP had reduced uptake by the RES due to their steric barrier properties and were present in the circulation for a longer time. Moreover, the NPs had greater uptake in bone and brain where concentration of the free drug, ETO, was negligible. Drug delivered from these NPs could result in a single i.v. injection that would release the drug for a number of days, which would be potentially beneficial and in better control of leukemia therapy. Drug Dev Res 71: 228–239, 2010.