Synthesis and characterisation of ultrasound imageable heat-sensitive liposomes for HIFU therapy

Abstract

Background/Objective: Novel approaches allowing efficient, readily translatable image-guided drug delivery (IGDD) against solid tumours is needed. The objectives of this study were to: 1) develop echogenic low temperature sensitive liposomes (E-LTSLs) loaded with an ultrasound (US) contrast agent (perfluoropentane, PFP), 2) determine the in vitro and in vivo stability of contrast agent encapsulation, 3) co-encapsulate and characterise doxorubicin (Dox) E-LTSL, and cellular uptake and cytotoxicity in combination with high intensity focused ultrasound (HIFU). Method: E-LTSLs were loaded passively with PFP and actively with Dox. PFP encapsulation in E-LTSL was determined by transmission electron microscopy (TEM), and US imageability was determined in tissue-mimicking phantoms and mouse tumour model. Dox release from E-LTSL in physiological buffer was quantified by fluorescence spectroscopy. Cellular uptake and cytotoxicity of E-LTSL in the presence of HIFU-induced mild hyperthermia (∼40–42 °C) was determined in a 3D tumour spheroid model. Results: TEM and US confirmed that the PFP emulsion was contained within LTSLs. Phantom and animal studies showed that the E-LTSLs were echogenic. Temperature versus size increase and Dox release kinetics of E-LTSLs demonstrated no difference compared to LTSL alone. Dox release was <5% within 1 h at baseline (25 °C) and body (37 °C) temperatures, and was >99% under hyperthermia. E-LTSL plus HIFU achieved significantly greater Dox uptake in spheroids and cytotoxicity compared to body temperature. Conclusion: A stable US-imageable liposome co-loaded with Dox and PFP for in vivo IGDD was developed. Data suggest that HIFU can induce cellular uptake and toxicity with E-LTSLs.

• HIFU
• Echogenic heat-sensitive liposome
• Perfluoropentane
• Image Guided Drug Delivery
• Tumor
• Spheroid

Declaration of interest

Research reported in this publication was supported by the Center for Veterinary Health Sciences Seed Support, National Cancer Institute of the National Institutes of Health under Award Number R15CA179369, and the Oklahoma Center for Advancement in Science and Technology (OCAST). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or OCAST. We thank Dr. Jack Dillwith and Robin Madden for providing core-facility support and technical expertise.