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Pulsed-High Intensity Focused Ultrasound and Low Temperature–Sensitive Liposomes for Enhanced Targeted Drug Delivery and Antitumor Effect

Authors' Affiliations: ¹ Diagnostic Radiology Department, Clinical Center and ² Tumor Angiogenesis Section, Surgery Branch, National Cancer Institute, NIH, Bethesda, Maryland

Requests for reprints: Victor Frenkel, Molecular Imaging Lab, NIH Clinical Center, Room 1N306a, Building 10, 10 Center Drive, Bethesda, MD 20892. Phone: 301-402-5710; Fax: 301-496-9933; E-mail: vfrenkel{at}cc.nih.gov.

Purpose: To determine if pulsed-high intensity focused ultrasound (HIFU) could effectively serve as a source of hyperthermia with thermosensitive liposomes to enhance delivery and efficacy of doxorubicin in tumors.

Experimental Design: Comparisons in vitro and in vivo were carried out between non–thermosensitive liposomes (NTSL) and low temperature–sensitive liposomes (LTSL). Liposomes were incubated in vitro over a range of temperatures and durations, and the amount of doxorubicin released was measured. For in vivo experiments, liposomes and free doxorubicin were injected i.v. in mice followed by pulsed-HIFU exposures in s.c. murine adenocarcinoma tumors at 0 and 24 h after administration. Combinations of the exposures and drug formulations were evaluated for doxorubicin concentration and growth inhibition in the tumors.

Results: In vitro incubations simulating the pulsed-HIFU thermal dose (42°C for 2 min) triggered release of 50% of doxorubicin from the LTSLs; however, no detectable release from the NTSLs was observed. Similarly, in vivo experiments showed that pulsed-HIFU exposures combined with the LTSLs resulted in more rapid delivery of doxorubicin as well as significantly higher i.t. concentration when compared with LTSLs alone or NTSLs, with or without exposures. Combining the exposures with the LTSLs also significantly reduced tumor growth compared with all other groups.

Conclusions: Combining low-temperature heat-sensitive liposomes with noninvasive and nondestructive pulsed-HIFU exposures enhanced the delivery of doxorubicin and, consequently, its antitumor effects. This combination therapy could potentially produce viable clinical strategies for improved targeting and delivery of drugs for treatment of cancer and other diseases.

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