Synthesis of a radiolabeled diglyceride 3-[ 18 F]fluorodipalmitoyl-1,2-glycerol ( 18 F-fluorodipalmitin, [ 18 F]FDP) and its potential as a reagent for radiolabeling long-circulating liposomes were investigated. The incorporation of 18 F into the lipid molecule was accomplished by nucleophilic substitution of p-toluenesolfonyl moiety with a decay corrected yield of 43 ± 10% (n = 12). Radiolabeled long-circulating PEG-coated liposomes were prepared using a mixture of DPPC, cholesterol, DSPE-PEG2000 (61:30:9) and [ 18 F]FDP with a decay corrected yield of 70 ± 8% (n = 4). PET imaging and biodistribution studies were performed with free [ 18 Liposomes are vesicles composed of one or more concentric phospholipid bi-layers and such vesicles have been widely investigated as possible drug carriers [1,2]. Prolonged blood circulation of the liposomes is achieved with the addition of a polyethylene glycol (PEG) coating, which efficiently minimizes their removal by macrophages of the reticuloendothelial system [3][4][5][6]. Liposomes with various target-specific ligands attached to their surface are being investigated for targeted drug delivery [1,2,7]. Liposomes labeled with radioisotopes such as 99m Tc, 186 Re, 67 Ga, 111 In, and 18 F were previously employed to study the biodistribution of different types of liposomes in various animal models using scintigraphy, SPECT and PET. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Materials and Methods GeneralThe solvents and chemicals were purchased from Aldrich (Milwaukee, WI). The 1 H and 13 C NMR spectra were recorded using a Bruker Avance 500 spectrometer and the chemical shifts are reported relative to TMS. Analytical reversed-phase HPLC was performed using a Phenomenex Jupiter 5μ C4 300A column ( . The size distribution of liposomes was determined using a particle size analyzer Nanotrac NPA150 purchased from Microtrac Inc. (North Largo, FL). The lipid concentration was determined using a Phospholipids B kit purchased from Wako Chemicals, Inc. (Richmond, VA). Synthesis of 3-tosyl-1,2-dipalmitoyl glycerol (2)The precursor 2 was prepared according to the previously published procedure [32] from 1,2-dipalmitoyl-sn-glycerol (1) and 4-toluenesulfonyl chloride. The crude product was subsequently purified by recrystalization from hexane. 1 mL). The content of the vial was dissolved in anhydrous acetonitrile (0.35 mL) and transferred into a suspension of 2 (5.5 mg) in anhydrous acetonitrile (0.5 mL). The reaction mixture was heated to 100 ºC for 20 minutes and allowed to cool to room temperature for 5 min...

No abstract

Interest in ultrasound contrast agents (lipid-shelled microbubbles) as delivery vehicles is increasing; however, the biodistribution of these agents remains uncharacterized, both with and without ultrasound. In this study, an 18 F-labeled lipid ([ 18 F]fluorodipalmitin), incorporated in microbubble shells, was used as a dynamic microPET probe for quantitative 90-minute biodistribution measurements in male Fischer 344 rats (n = 2). The spleen retained the highest concentration of radioactive lipid at ~2.6 percent-injected dose per cubic centimeter (% ID/cc) and the liver demonstrated the largest total accumulation (~17 % ID). The microbubble pharmacokinetic profile differed from free lipid, which is rapidly cleared from blood, and liposomes, which remain in circulation. Additionally, region of interest (ROI) analysis over 60 minutes post-ultrasound treatment quantified the delivery of lipid by therapeutic ultrasound from microbubbles to kidney tissue (n = 8). The ultrasound sequence consisted of a 200 kPa, 5.3 MHz radiation force pulse followed by a 1.6 MPa, 1.4 MHz fragmentation pulse and was applied to one kidney, while the contralateral kidney served as a control. ROI-estimated activity in treated kidneys was slightly but significantly greater at 0 and 60 minutes than in untreated kidneys (p = 0.0012 and 0.0035, respectively). This effect increased with the number of microbubbles injected (p = 0.006). In summary, [ 18 F]fluorodipalmitin was used to characterize the biodistribution of contrast microbubble shells and the deposition of lipid was shown to be locally increased after insonation.

Bioencapsulation of living cells into silica materials derived from the sol–gel process has resulted in novel hybrid living materials with exciting functionalities. Despite the many successes in this field, long-term viability and activity of the encapsulated cells remain a significant obstacle to producing practical and robust devices, e.g., whole-cell-based biosensors. We report the first study on the effects of various media additives and the metabolic phase of encapsulated cells on long-term viability and the rate of inducible gene expression. Saccharomyces cerevisiae (S. cerevisiae) cells, genetically engineered to produce yellow fluorescent protein (YFP) in response to galactose, were encapsulated in poly(glycerol) silicate derived matrices. Surprisingly, we find that addition of media components to the glycerol-silica matrix adversely impacted long-term viability in all cases studied, with a 1.3, 1.4, or 5.4 fold decrease in viability after only 9 days of storage in matrices containing yeast peptone dextrose (YPD), yeast peptone (YP, no glucose), or Synthetic Complete (SC) +2% glucose media, respectively. These findings are attributed to the media components inducing exit of the cells from the more robust quiescent state, and the metabolic production of toxic byproducts. Encapsulated cells from exponential culture exhibited inducible reporter gene expression rates approximately 33% higher than cells from stationary cultures. Addition of media components to the silica matrix increased gene expression rates under certain conditions. These results further elaborate on other silica matrix encapsulated living cell studies, and provide important design parameters for developing effective living cell-based biosensors for case-specific detection applications.

In this letter, we present a simple one-step, versatile, scalable chemical vapor deposition (CVD)-based process for the encapsulation and stabilization of a host of single or multicomponent supramolecular assemblies (proteoliposomes, microbubbles, lipid bilayers, and photosynthetic antennae complexes and other biological materials) to form functional hybrid nanobiomaterials. In each case, it is possible (i) to form thin silica layers or gels controllably that enable the preservation of the supramolecular assembly over time and under adverse environmental conditions and (ii) to tune the structure of the silica gels so as to optimize solute accessibility while at the same time preserving functional dynamic properties of the encapsulated phospholipid assembly. The process allows precise temporal and spatial control of silica polymerization kinetics through the control of precursor delivery at room temperature and does not require or produce high concentrations of injurious chemicals that can compromise the function of biomolecular assemblies; it also does not require additives. This process differs from the conventional sol-gel process in that it does not involve the use of cosolvents (alcohols) and catalysts (acid or base).