Delivery of water-soluble drugs using acoustically triggered perfluorocarbon double emulsions

Abstract

Purpose: Ultrasound can be used to release a therapeutic payload encapsulated within a perfluorocarbon (PFC) emulsion via acoustic droplet vaporization (ADV), a process whereby the PFC phase is vaporized and the agent is released. ADV-generated microbubbles have been previously used to selectively occlude blood vessels in vivo. The coupling of ADV-generated drug delivery and occlusion has therapeutically synergistic potentials.

Methods: Micron-sized, water-in-PFC-in-water (W(1)/PFC/W(2)) emulsions were prepared in a two-step process using perfluoropentane (PFP) or perfluorohexane (PFH) as the PFC phase. Fluorescein or thrombin was contained in the W(1) phase.

Results: Double emulsions containing fluorescein in the W(1) phase displayed a 5.7±1.4-fold and 8.2±1.3-fold increase in fluorescein mass flux, as measured using a Franz diffusion cell, after ADV for the PFP and PFH emulsions, respectively. Thrombin was stably retained in four out of five double emulsions. For three out of five formulations tested, the clotting time of whole blood decreased, in a statistically significant manner (p < 0.01), when incubated with thrombin-loaded emulsions exposed to ultrasound compared to emulsions not exposed to ultrasound.

Conclusions: ADV can be used to spatially and temporally control the delivery of water-soluble compounds formulated in PFC double emulsions. Thrombin release could extend the duration of ADV-generated, microbubble occlusions.

Fig. 1

The Kytox 157L FS is first converted into an acid chloride and then reacted with PEG-diamine to form a copolymer via amide linkages.

Fig. 2

Micrographs of a W₁/PFC/W₂ emulsion containing fluorescein in the W₁ phase. The left image is an overlay of both visible and fluorescent micrographs. The scale bar is 8 μm. The structure of the W₁/PFC/W₂ emulsion – water droplets containing fluorescein within a globule of PFC - can be clearly seen in the right image, which displays a 100 μm diameter globule.

Fig. 3

In vitro release profiles of PFP (left) and PFH (right) double emulsions containing fluorescein at 37°C. In each case, the release profiles obtained from the emulsion, with and without ADV, are compared to a solution of fluorescein of equal concentration. The fluorescein concentration for the PFP and PFH emulsions are 0.6 mg/mL and 0.3 mg/mL, respectively.

Fig. 4

Reference curve displaying the activated clotting time (ACT) for canine blood, stored with citrate-phosphate-dextrose (CPD) solution, as a function of thrombin concentration.

Fig. 5

Anticoagulative effect of the Krytox-PEG copolymer used in the thrombin emulsions. A blank emulsion, containing Krytox-PEG copolymer was mixed with thrombin solution. An aliquot of the resulting mixture, containing 1 IU thrombin, was added to blood containing CPD. Points marked with an asterisk (*) indicate copolymer levels that are not statistically different than control case (i.e. without copolymer).

Fig. 6

The effect of ADV (3.5 MHz, 3.7 μs pulse duration, 10 ms PRP, 4.7 MPa peak rarefactional pressure, 11.3 MPa peak compressional pressure, 5 minute exposure) on the ACT for five different thrombin formulations. Cases where the ACT was statistically different after ADV are denoted by an asterisk (*).