Triggered drug release from liposome-microbubble pendant complexes: From model systems to tumor therapy in a murine adenocarcinoma model

Liposome-microbubble complexes allow delivery of drugs that cannot be otherwise associated with the bubble shell: water-soluble drugs and proteins. We prepared liposome-microbubble pendants by decorating biotinylated microbubbles with biotinylated liposomes via streptavidin. A model dye calcein was used as a model release marker. Using focused ultrasound (Philips TIPS, 1 MHz, 7 MPa) we were able to release ~30% of the entrapped dye. For an enzyme thrombin, ~11% of the entrapped material was released following pendant insonation. In vivo tumor therapy was performed with doxorubicin-liposome-microbubble pendants in a subcutaneous MC38 murine adenocarcinoma model. Doxorubicin was loaded in liposomes via an ammonium citrate gradient procedure. By using larger liposomes, >>80nm (as in Doxil/Lipodox), we prepared pendants carrying ~1 pg doxorubicin per particle. To avoid tumor blood flow stoppage caused by high-power insonation of microbubbles in tumor vasculature, we applied continuous sine wave ultrasound (Bi...