In vitro photoacoustic sensing of calcium dynamics with Arsenazo III.

Imaging of cellular electric potential via calcium-ion sensitive contrast agents is a useful tool, but current it lacks sufficient depth penetration. We explore contrast-enhanced photoacoustic (PA) imaging, using Arsenazo III dye, to visualize cardiac myocyte depolarization in vitro. Phantom results show strong linearity of PA signal with dye concentration (R 2 > 0.95), and agree spectrally with extinction measurements with varying calcium concentration. Cell studies indicate a significant (> 100-fold) increase in PA signal for dye-treated cells, as well as a 10-fold increase in peak-to-peak variation during a 30-second window. This suggests contrast-enhanced PA imaging may have sufficient sensitivity and specificity for depth-resolved visualization of tissue depolarization in real-time.

Therapeutic efficacy of the combination of doxorubicin-loaded liposomes with inertial cavitation generated by confocal ultrasound in AT2 Dunning rat tumour model.

The combination of liposomal doxorubicin (DXR) and confocal ultrasound (US) was investigated for the enhancement of drug delivery in a rat tumour model. The liposomes, based on the unsaturated phospholipid dierucoylphosphocholine, were designed to be stable during blood circulation in order to maximize accumulation in tumour tissue and to release drug content upon US stimulation. A confocal US setup was developed for delivering inertial cavitation to tumours in a well-controlled and reproducible manner. In vitro studies confirm drug release from liposomes as a function of inertial cavitation dose, while in vivo pharmacokinetic studies show long blood circulation times and peak tumour accumulation at 24-48 h post intravenous administration. Animals injected 6 mg kg(-1) liposomal DXR exposed to US treatment 48 h after administration show significant tumour growth delay compared to control groups. A liposomal DXR dose of 3 mg kg(-1), however, did not induce any significant therapeutic response. This study demonstrates that inertial cavitation can be generated in such a fashion as to disrupt drug carrying liposomes which have accumulated in the tumour, and thereby increase therapeutic effect with a minimum direct effect on the tissue. Such an approach is an important step towards a therapeutic application of cavitation-induced drug delivery and reduced chemotherapy toxicity.

Contribution of inertial cavitation in the enhancement of in vitro transscleral drug delivery.

In ocular drug delivery, the sclera is a promising pathway for administering drugs to both the anterior and posterior segments of the eye. Due to the low permeability of the sclera, however, efficient drug delivery is challenging. In this study, pulsed ultrasound (US) was investigated as a potential method for enhancing drug delivery to the eye through the sclera. The permeability of rabbit scleral tissue to a model drug compound, sodium fluorescein, was measured after US-irradiation at 1.1 MHz using time-averaged acoustic powers of 0.5-5.4 W (6.8-12.8 MPa peak negative pressure), with a fixed duty cycle of 2.5% for two different pulse repetition frequencies of 100 and 1000 Hz. Acoustic cavitation activity was measured during exposures using a passive cavitation detector and was used to quantify the level of bubble activity. A correlation between the amount of cavitation activity and the enhancement of scleral permeability was demonstrated with a significant enhancement in permeability of US exposed samples compared to controls. Transmission electron microscopy showed no evidence of significant alteration in viability of tissue exposed to US exposures. A pulsed US protocol designed to maximum cavitation activity may therefore be a viable method for enhancing drug delivery to the eye.

In vivo monitoring of liposomal release in tumours following ultrasound stimulation.

Dioeleoylphosphatidylethanolamine (DOPE)-based liposomes were recently reported as a new class of liposomes for ultrasound (US)-mediated drug delivery. The liposomes showed both high stability and in vitro US-mediated drug release (sonosensitivity). In the current study, in vivo proof-of-principle of US triggered release in tumoured mice was demonstrated using optical imaging. Confocal non-thermal US was used to deliver cavitation to tumours in a well-controlled manner. To detect in vivo release, the near infrared fluorochrome Al (III) Phthalocyanine Chloride Tetrasulphonic acid (AlPcS4) was encapsulated into both DOPE-based liposomes and control liposomes based on hydrogenated soy phosphatidylcholine (HSPC). Encapsulation causes concentration dependent quenching of fluorescence that is recovered upon AlPcS4 release from the liposomes. Exposure of tumours to US resulted in a significant increase in fluorescence in mice administered with DOPE-based liposomes, but no change in the mice treated with HSPC-based liposomes. Thus, DOPE-based liposomes showed superior sonosensitivity compared to HSPC-based liposomes in vivo.