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.

Evaluation of an Ultrasound-Guided Focused Ultrasound CMUT Probe for Targeted Therapy Applications

“…For TSL release, one will focus on the pressure amplitude at the expense of the focal spot. In this case, a PTP pressure of 3 MPa can be achieved, which is in line with the minimum target value defined by [29]. This consideration is in agreement with the temperature elevation measured thereafter, since the TSLs melting temperature …”

“…More precisely, sonoporation and the triggered release of thermosensitive liposomes (TSLs) [28] were targeted. Whereas sonoporation generally requires a relatively low peak negative pressure (PNP), the mild hyperthermia required to reach the melting phase transition temperature of the TSLs is more challenging to generate at 1 MHz: [29] showed that this temperature, typically approximately 42˚C, can be reached at 1 MHz, More detailed information about the design stage, the manufacturing process and the choice of the CMUT geometry are given by [27]. …”

Molecular Study of Ultrasound-Triggered Release of Fluorescein from Liposomes

“…2 due to the addition of cholesterol is a decrease in T m values when the DSPC membrane contains up to 33 mol% of cholesterol. This behavior is in agreement with literature data performed on liposome membranes made of DNPC 57 (di24:1c15 PC, 1,2-dinervonoyl-sn-glycero-3-phosphocholine), HSPC 58 (Hydrogenated soybean phosphatidylcholine made approximately of 85% DSPC and 15% DPPC), di17:0 PC 59 (1,2-diheptadecanoyl-sn-glycero-3-phosphocholine), DPPC, 11,52,60 and DOPC. 61 This effect can be explained by the fact that the addition of cholesterol rearranges the membrane structure: both L α and L β phases are progressively disappearing upon the addition of cholesterol to be progressively replaced by a homogeneous liquid ordered or L o phase.…”

A cMUT probe for ultrasound-guided focused ultrasound targeted therapy

“…Novell et al also showed in another study [43] that identical temperatures can be obtained with different pressure amplitudes by tuning the duty cycle. Because previous reports showed that cMUTs can operate in CW mode [35], the excitation conditions could be tuned a posteriori to fulfill the heating requirements in the ROI if the performances of LF arrays were found to be lower than expected.…”