title: Synthesis and characterisation of ultrasound imageable heat-sensitive liposomes for HIFU therapy.
abstract: 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).
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Danny
authors.initials: D
authors.lastname: Maples
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Kevin
authors.initials: K
authors.lastname: McLean
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Kaustuv
authors.initials: K
authors.lastname: Sahoo
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Ryan
authors.initials: R
authors.lastname: Newhardt
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Perumal
authors.initials: P
authors.lastname: Venkatesan
authors.affiliation: b Center for Interventional Oncology, National Institutes of Health , Bethesda , Maryland , USA.
authors.forename: Bradford
authors.initials: B
authors.lastname: Wood
authors.affiliation: a Center for Veterinary Health Sciences, Oklahoma State University , Stillwater , Oklahoma and.
authors.forename: Ashish
authors.initials: A
authors.lastname: Ranjan
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000627:therapeutic use; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004317:Doxorubicin / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000627:therapeutic use; D005466:Fluorocarbons / Q000008:administration & dosage* / Q000493:pharmacokinetics; D057086:High-Intensity Focused Ultrasound Ablation; D006358:Hot Temperature; D006801:Humans; D008081:Liposomes; D008297:Male; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000628:therapy*; D010420:Pentanes
chemical_list: D000903:Antibiotics, Antineoplastic; D003287:Contrast Media; D004317:Doxorubicin; D005466:Fluorocarbons; D008081:Liposomes; C008806:perfluoropentane; D010420:Pentanes
keywords: Echogenic heat-sensitive liposome; HIFU; Image Guided Drug Delivery; Perfluoropentane; Spheroid; Tumor