Microbubble Agents: New Directions.

Microbubble ultrasound contrast agents have now been in use for several decades and their safety and efficacy in a wide range of diagnostic applications have been well established. Recent progress in imaging technology is facilitating exciting developments in techniques such as molecular, 3-D and super resolution imaging and new agents are now being developed to meet their specific requirements. In parallel, there have been significant advances in the therapeutic applications of microbubbles, with recent clinical trials demonstrating drug delivery across the blood-brain barrier and into solid tumours. New agents are similarly being tailored toward these applications, including nanoscale microbubble precursors offering superior circulation times and tissue penetration. The development of novel agents does, however, present several challenges, particularly regarding the regulatory framework. This article reviews the developments in agents for diagnostic, therapeutic and "theranostic" applications; novel manufacturing techniques; and the opportunities and challenges for their commercial and clinical translation.

US Molecular Imaging of Acute Ileitis: Anti-Inflammatory Treatment Response Monitored with Targeted Microbubbles in a Preclinical Model.

Purpose To evaluate whether dual-selectin-targeted US molecular imaging allows longitudinal monitoring of anti-inflammatory treatment effects in an acute terminal ileitis model in swine. Materials and Methods The Institutional Animal Care and Use Committee approved all animal studies. Fourteen swine with chemically induced acute terminal ileitis (day 0) were randomized into the following groups: (a) an anti-inflammatory treatment group (n = 8; meloxicam, 0.25 mg per kilogram of body weight; prednisone, 0.5 mg/kg) and (b) a control group (n = 6; saline). US molecular imaging was performed with a clinical US machine after intravenous injection of clinically translatable dual P- and E-selectin-targeted microbubbles (5 × 108/kg). Three inflamed bowel segments per swine were imaged at baseline, as well as on days 1, 3, and 6 after treatment initiation. At day 6, bowel segments were analyzed ex vivo for selectin expression levels by using quantitative immunofluorescence. Results After induction of inflammation, US molecular imaging signal increased at day 1 in both animal groups (P < .001). At day 3, signal in the treatment group decreased (P < .001 vs day 1), while signal in control animals did not significantly change (P = .18 vs day 1) and was higher (P = .001) compared with that in the treatment group. At day 6, signal in the treatment group further decreased and remained lower (P = .02) compared with that in the control group. Immunofluorescence confirmed significant (P ≤ .04) downregulation of both P- and E-selectin expression levels in treated versus control bowel segments. Conclusion Dual-selectin-targeted US molecular imaging allows longitudinal monitoring of anti-inflammatory treatment effects in a large-animal model of acute ileitis. This supports further clinical development of this quantitative and radiation-free technique for monitoring inflammatory bowel disease. © RSNA, 2018 Online supplemental material is available for this article.

Use of capillary electrophoresis as a versatile tool to measure interaction constants between a KDR-binding PEGylated lipopeptide and pegylated phospholipid micelles.

In the frame of our molecular imaging activities, a PEGylated lipopeptide has been developed as a specific ligand for the human vascular endothelial growth factor receptor 2, which is considered as one of the important molecular marker of angiogenesis. In this study, the potential of affinity capillary electrophoresis (ACE) is evaluated to measure the interactions of an active PEGylated lipopeptide, its hydrolysis product and its precursor consisting of a peptide structure with different micelles including Brij-35, Tween-20, and pegylated phospholipids. Given the amphiphilic structure of the PEGylated lipopeptide, a MEKC method allowing the simultaneous separation of the compounds of interest was set up, using low percentages of acetonitrile. Analytes were resolved using a BGE consisting of 100 mM borate buffer pH 9.0, 1 mM Brij, and 25% acetonitrile. Optimized conditions were then used to perform ACE experiments. The affinity constants of the analytes with the micelles were calculated on the basis of their mobility decrease when surfactant concentration increased in the electrolyte. The use of different linearization models to estimate affinity constants was discussed and comparison of different surfactants was reported. PEGylated lipopeptide interacted more strongly with pegylated phospholipid micelles than with Brij-35 or Tween-20. Moreover, it is likely that the chemical structure of the compounds, and particularly the lipidic part of the molecules, significantly affects the interaction with micelles. In conclusion, the ACE method can be readily applied to investigate interactions of our targeting lipopeptides with various micelles currently used for the preparation of pharmaceutical vehicles.