Microbubble-Assisted Ultrasound for Drug Delivery to the Retina in an Ex Vivo Eye Model

Drug delivery to the retina is one of the major challenges in ophthalmology due to the biological barriers that protect it from harmful substances in the body. Despite the advancement in ocular therapeutics, there are many unmet needs for the treatment of retinal diseases. Ultrasound combined with microbubbles (USMB) was proposed as a minimally invasive method for improving delivery of drugs in the retina from the blood circulation. This study aimed to investigate the applicability of USMB for the delivery of model drugs (molecular weight varying from 600 Da to 20 kDa) in the retina of ex vivo porcine eyes. A clinical ultrasound system, in combination with microbubbles approved for clinical ultrasound imaging, was used for the treatment. Intracellular accumulation of model drugs was observed in the cells lining blood vessels in the retina and choroid of eyes treated with USMB but not in eyes that received ultrasound only. Specifically, 25.6 ± 2.9% of cells had intracellular uptake at mechanical index (MI) 0.2 and 34.5 ± 6.0% at MI 0.4. Histological examination of retinal and choroid tissues revealed that at these USMB conditions, no irreversible alterations were induced at the USMB conditions used. These results indicate that USMB can be used as a minimally invasive targeted means to induce intracellular accumulation of drugs for the treatment of retinal diseases.</p

Ultrasound and microbubbles for the treatment of ocular diseases : From preclinical research towards clinical application

The unique anatomy of the eye and the presence of various biological barriers make efficacious ocular drug delivery challenging, particularly in the treatment of posterior eye diseases. This review focuses on the combination of ultrasound and microbubbles (USMB) as a minimally invasive method to improve the efficacy and targeting of ocular drug delivery. An extensive overview is given of the in vitro and in vivo studies investigating the mechanical effects of ultrasound-driven microbubbles aiming to: (i) temporarily disrupt the blood–retina barrier in order to enhance the delivery of systemically administered drugs into the eye, (ii) induce intracellular uptake of anticancer drugs and macromolecules and (iii) achieve targeted delivery of genes, for the treatment of ocular malignancies and degenerative diseases. Finally, the safety and tolerability aspects of USMB, essential for the translation of USMB to the clinic, are discussed.Peer reviewe

The Effect of Microbubble-Assisted Ultrasound on Molecular Permeability across Cell Barriers

The combination of ultrasound and microbubbles (USMB) has been applied to enhance drug permeability across tissue barriers. Most studies focused on only one physicochemical aspect (i.e., molecular weight of the delivered molecule). Using an in vitro epithelial (MDCK II) cell barrier, we examined the effects of USMB on the permeability of five molecules varying in molecular weight (182 Da to 20 kDa) and hydrophilicity (LogD at pH 7.4 from 1.5 to highly hydrophilic). Treatment of cells with USMB at increasing ultrasound pressures did not have a significant effect on the permeability of small molecules (molecular weight 259 to 376 Da), despite their differences in hydrophilicity (LogD at pH 7.4 from -3.2 to 1.5). The largest molecules (molecular weight 4 and 20 kDa) showed the highest increase in the epithelial permeability (3-7-fold). Simultaneously, USMB enhanced intracellular accumulation of the same molecules. In the case of the clinically relevant anti- C-X-C Chemokine Receptor Type 4 (CXCR4) nanobody (molecular weight 15 kDa), USMB enhanced paracellular permeability by two-fold and increased binding to retinoblastoma cells by five-fold. Consequently, USMB is a potential tool to improve the efficacy and safety of the delivery of drugs to organs protected by tissue barriers, such as the eye and the brain.Peer reviewe

Ultrasound and Microbubbles Mediated Bleomycin Delivery in Feline Oral Squamous Cell Carcinoma-: An In Vivo Veterinary Study

To investigate the feasibility and tolerability of ultrasound and microbubbles (USMB)-enhanced chemotherapy delivery for head and neck cancer, we performed a veterinary trial in feline companion animals with oral squamous cell carcinomas. Six cats were treated with a combination of bleomycin and USMB therapy three times, using the Pulse Wave Doppler mode on a clinical ultrasound system and EMA/FDA approved microbubbles. They were evaluated for adverse events, quality of life, tumour response and survival. Furthermore, tumour perfusion was monitored before and after USMB therapy using contrast-enhanced ultrasound (CEUS). USMB treatments were feasible and well tolerated. Among 5 cats treated with optimized US settings, 3 had stable disease at first, but showed disease progression 5 or 11 weeks after first treatment. One cat had progressive disease one week after the first treatment session, maintaining a stable disease thereafter. Eventually, all cats except one showed progressive disease, but each survived longer than the median overall survival time of 44 days reported in literature. CEUS performed immediately before and after USMB therapy suggested an increase in tumour perfusion based on an increase in median area under the curve (AUC) in 6 out of 12 evaluated treatment sessions. In this small hypothesis-generating study, USMB plus chemotherapy was feasible and well-tolerated in a feline companion animal model and showed potential for enhancing tumour perfusion in order to increase drug delivery. This could be a forward step toward clinical translation of USMB therapy to human patients with a clinical need for locally enhanced treatment

Altitude and management affect soil fertility, leaf nutrient status and Xanthomonas wilt prevalence in enset gardens

Enset (Ensete ventricosum) is a productive, drought-tolerant and multipurpose food security crop grown in the densely populated Ethiopian highlands. It is a so-called orphan crop, and its production suffers from a lack of information on proper soil fertility management and its interaction with bacterial wilt disease caused by the pathogen Xanthomonas campestris pv. musacearum. The aim of this study was therefore to assess soil–plant nutrient variation within enset home gardens at three altitudes (ranging from 2000 to 3000m above sea level – a.s.l.) in the Gamo highlands and investigate whether this variation affects disease prevalence. Altitude in the rift valley covaries with soil leaching, and plant available P, Ca and Mg in soils significantly raised with decreasing altitude. Soil carbon and most nutrients reached very high levels in the gardens, whereas the more distant outfields were severely nutrient deprived. Differences in management intensity within the garden caused soil pH, conductivity, total organic carbon, total N and available P, K, Ca, Mg, Mn and Fe levels to significantly decline with distance from the house; yet, this decrease in soil nutrients was not mirrored in a response of foliar nutrient content, except for N. Hence, over-fertilization is likely, and establishing evidencebased nutrient recommendations for enset would benefit soil quality and productivity both in the gardens and in the outfields. Disease prevalence was high in the study area, with one-third of the farms affected in the recent past. Although more experimental work is needed to exclude confounding factors, our data indicate that the effects of altitude, P fertilization, micronutrients and K-Ca-Mg balance are promising avenues for further investigation into Xanthomonas wilt disease susceptibility

The Effect of Microbubble-Assisted Ultrasound on Molecular Permeability across Cell Barriers

The combination of ultrasound and microbubbles (USMB) has been applied to enhance drug permeability across tissue barriers. Most studies focused on only one physicochemical aspect (i.e., molecular weight of the delivered molecule). Using an in vitro epithelial (MDCK II) cell barrier, we examined the effects of USMB on the permeability of five molecules varying in molecular weight (182 Da to 20 kDa) and hydrophilicity (LogD at pH 7.4 from 1.5 to highly hydrophilic). Treatment of cells with USMB at increasing ultrasound pressures did not have a significant effect on the permeability of small molecules (molecular weight 259 to 376 Da), despite their differences in hydrophilicity (LogD at pH 7.4 from −3.2 to 1.5). The largest molecules (molecular weight 4 and 20 kDa) showed the highest increase in the epithelial permeability (3-7-fold). Simultaneously, USMB enhanced intracellular accumulation of the same molecules. In the case of the clinically relevant anti- C-X-C Chemokine Receptor Type 4 (CXCR4) nanobody (molecular weight 15 kDa), USMB enhanced paracellular permeability by two-fold and increased binding to retinoblastoma cells by five-fold. Consequently, USMB is a potential tool to improve the efficacy and safety of the delivery of drugs to organs protected by tissue barriers, such as the eye and the brain

Ultrasound-directed enzyme-prodrug therapy (UDEPT) using self-immolative doxorubicin derivatives

Background: Enzyme-activatable prodrugs are extensively employed in oncology and beyond. Because enzyme concentrations and their (sub)cellular compartmentalization are highly heterogeneous in different tumor types and patients, we propose ultrasound-directed enzyme-prodrug therapy (UDEPT) as a means to increase enzyme access and availability for prodrug activation locally. Methods: We synthesized β-glucuronidase-sensitive self-immolative doxorubicin prodrugs with different spacer lengths between the active drug moiety and the capping group. We evaluated drug conversion, uptake and cytotoxicity in the presence and absence of the activating enzyme β-glucuronidase. To trigger the cell release of β-glucuronidase, we used high-intensity focused ultrasound to aid in the conversion of the prodrugs into their active counterparts. Results: More efficient enzymatic activation was observed for self-immolative prodrugs with more than one aromatic unit in the spacer. In the absence of β-glucuronidase, the prodrugs showed significantly reduced cellular uptake and cytotoxicity compared to the parent drug. High-intensity focused ultrasound-induced mechanical destruction of cancer cells resulted in release of intact β-glucuronidase, which activated the prodrugs, restored their cytotoxicity and induced immunogenic cell death. Conclusion: These findings shed new light on prodrug design and activation, and they contribute to novel UDEPT-based mechanochemical combination therapies for the treatment of cancer

The role of ultrasound and magnetic resonance in local drug delivery.

International audienceLocal drug delivery has recently attracted much attention since it represents a strategy to increase the drug concentration at the target location and decrease systemic toxicity effects. Ultrasound can be used in different ways to trigger regional drug delivery. It can cause the local drug release from a carrier vehicle and the local increase of cell membrane permeability either by a mechanical action or by a temperature increase. Ultrasound contrast agents may enhance these effects by means of cavitation. Ultrasound can be focused deep inside the body into a small region with dimensions on the order of 1 mm. Several types of drug microcarriers have been proposed, from nano- to micrometer sized particles. The objective of real-time imaging of local drug delivery is to assure that the delivery takes place in the target region, that the drug concentration and the resulting physiological reaction are sufficient, and to intervene if necessary. Ultrasound and nuclear imaging techniques play an important role. MRI is rather insensitive but allows precise targeting of (focused) ultrasound, can provide real-time temperature maps, and gives access to a variety of imaging biomarkers that may be used to assess drug action. Examples from recent articles illustrate the potential of the principles of ultrasound-triggered local drug delivery