Disposition of ultrasound sensitive polymeric drug carrier in a rat hepatocellular carcinoma model.

RATIONALE AND OBJECTIVES: A doxorubicin-loaded microbubble has been developed that can be destroyed with focused ultrasound resulting in fragments, or "nanoshards" capable of escaping through the leaky tumor vasculature, promoting accumulation within the interstitium. This study uses a rat liver cancer model to examine the biodistribution and tumoral delivery of this microbubble platform compared with de novo drug-loaded polymer nanoparticles and free doxorubicin. MATERIALS AND METHODS: Microbubbles (1.8 μm) and 217-nm nanoparticles were prepared containing 14-C labeled doxorubicin. Microbubbles, nanoparticles, a combination of the two, or free doxorubicin were administered intravenously in rats bearing hepatomas, concomitant with tumor insonation. Doxorubicin levels in plasma, organs, and tumors were quantified after 4 hours and 7 and 14 days. Tumors were measured on sacrifice and evaluated with autoradiography and histology. RESULTS: Animals treated with microbubbles had significantly lower plasma doxorubicin concentrations (0.466 ± 0.068%/mL) compared with free doxorubicin (3.033 ± 0.612%/mL, P = .0019). Drug levels in the myocardium were significantly lower in animals treated with microbubbles compared to free doxorubicin (0.168%/g tissue vs. 0.320%/g, P = .0088). Tumors treated with microbubbles showed significantly higher drug levels than tumors treated with free doxorubicin (2.491 ± 0.501 %/g vs. 0.373 ± 0.087 %/g, P = .0472). These tumors showed significantly less growth than tumors treated with free doxorubicin (P = .0390). CONCLUSIONS: Doxorubicin loaded microbubbles triggered with ultrasound provided enhanced, sustained drug delivery to tumors, reduced plasma and myocardium doxorubicin levels, and arresting tumor growth. The results suggest that in situ generation of nano particles provides a superior treatment over injection of free drug and also de novo synthesized nanoparticles.