Delivery of drug-loaded microbubbles and disruption of blood-brain barrier by focused ultrasound in a xenograft rat glioma model

Glioblastoma multiforme (GBM) is a highly malignant brain tumor. The blood-brain barrier (BBB) provides a major obstacle to chemotherapy since therapeutic doses cannot be achieved by traditional drug delivery without severe systemic cytotoxic effects. Recently, microbubble (MB)-enhanced focused ultrasound (FUS) was shown to temporally and locally disrupt the BBB thereby enhancing drug delivery into brain tumors. Here we propose the concept of smart, multifunctional MBs capable of facilitating FUS-induced BBB disruption while serving as drug carrying vehicles and protecting drugs from rapid degradation. The designed MBs had a high loading capacity (efficiency of 68.01 ± 4.35 %) for 1,3-bis(2-chloroethyl)-1- nitrosourea (BCNU). When combined with FUS (1-MHz), these BCNU-MBs facilitated local BBB disruption and simultaneously released BCNU at the target site, thus increasing local BCNU deposition. And accumulation of BCNU in the liver was reduced 5-fold due to the slow reticuloendothelial system uptake of BCNU-MBs. In tumor-bearing animals, BCNU-MBs with FUS controlled tumor progression (915.3 % to 39.6 %) and improved median survival (29 days to 32.5 days). This study provides a new approach for designing multifunctional MBs to facilitate FUS-mediated chemotherapy for brain tumor treatment.