In vitro echogenicity characterization of poly[lactide-coglycolide] (PLGA) microparticles and preliminary in vivo ultrasound enhancement study for ultrasound contrast agent application

Objectives: This work includes (1) the characterization of a reproducible poly[lactide-coglycolide] (PLGA) microparticle preparation with an optimial mean diameter and size distribution and (2) the preliminary in vivo ultrasonographic investigation of PLGA microparticles. Methods: A first series of PLGA microparticle preparations (1 to 15 mu m) was acoustically characterized on a hydrodynamic device to select the most appropriate for ultrasound contrast agent application. Preparations of 3-mu m microparticles were selected, characterized at different doses, and then injected into 20 melanoma grafted mice for contrast-enhanced power Doppler ultrasonography evaluation. Results: The 3-mu m microparticles (3.26-mu m mean diameter with 0.41-mu m standard deviation) led to in vitro enhancement of 18.3 dB at 0.62 mg/mL. In vivo experiments showed 47% enhancement of intratumoral vascularization detection after PLGA injection, significantly correlated (P < 0.0001) with preinjection intravascularization and tumoral volume. No toxicity was histologically observed. Conclusion: The 3-mu m PLGA microparticles provided significant enhancement in vitro and in vivo without any toxicity.