Focused ultrasound influence on calcein-loaded thermosensitive stealth liposomes

Abstract

Focused ultrasound (FUS) is a versatile technology for non-invasive thermal therapies in oncology. Indeed, this technology has great potential for local heat-mediated drug delivery from thermosensitive liposomes (TSLs), thus improving therapeutic efficacy and reducing toxicity profiles. In the present study we evaluated the influence of FUS parameters on the release of calcein from TSLs used to model a hydrophilic drug. Quantitative calcein release from TSLs (DPPC/CHOL/DSPE-PEG2000: 90/5/5) and non-thermosensitive liposomes (NTSLs) (DPPC/CHOL/DSPE-PEG2000: 65/30/5) was measured by spectrofluorimetry after both water bath and FUS-induced in vitro heating. The heating of TSLs at 42 °C in a water bath resulted in a maximum calcein release of 45%. No additional calcein release was observed at temperatures above 42 °C. A similar percentage of calcein release was achieved when TSLs were exposed to 1 MHz sinusoidal waves at peak negative pressure of 1.5 MPa, 40% duty cycle, for 10 min (i.e. above 42 °C). No release was detected when NTSLs were heated in a water bath. For both TSLs and NTSLs, the calcein release was increased by more than 10% for acoustic pressures ranging from 1.5 MPa to 2 MPa. This additional release was attributed to the mechanical stress generated by FUS, which was sufficient to disrupt the liposomal membrane. Furthermore, analysis of cryo-TEM images showed a significant decrease in liposome size (14%) induced by the thermal effect, whereas the liposome diameter remained unaffected by the FUS-triggered non-thermal effects.

• Drug delivery
• focused ultrasound
• mechanical stress
• mild hyperthermia
• thermosensitive liposomes

Acknowledgements

The authors thank Michalakis Averkiou (University of Cyprus) for providing FUS transducer, Mario Ries and Roel Deckers (UMC Utrecht), Justin Tessié (IPBS-CNRS UMR 5089, Toulouse) for fruitful discussions, Sylvie Attucci (Inserm U-1100, Tours) for her technical assistance in spectrofluorimetry, Jacqueline Butterworth for proofreading the manuscript.

Declaration of interest

This research work was funded by the Agence Nationale pour la Recherche (ANR-10-TecSan-007), the European Commission FP7 Program SONODRUGS (NMP4-LA-2008-213706) and FEDER PRESAGE (3431 – 35438). Institut Galien Paris-Sud is a member of the Laboratory of Excellence LERMIT supported by a grant from ANR (ANR-10-LABX-33). The authors alone are responsible for the content and writing of the paper.