Caitlin W Burke

University of Virginia, Charlottesville, Virginia, United States

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Publications (9)45.86 Total impact

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    ABSTRACT: The ultrasound (US)-targeted delivery of systemically administered drug and gene-bearing nanoparticles has emerged to become a robust area of investigation with clear clinical potential. Such approaches typically entail the concurrent injection of contrast agent microbubbles (MBs) and nanoparticles, followed by the application of US to the region of interest. US-activated MBs disrupt the surrounding microvessel, permitting nanoparticle delivery with precise spatial localization. Our group has previously shown that US-targeted nanoparticle delivery can amplify collateral artery growth, that the binding of nanoparticles to MBs enhances nanoparticle delivery, that non-viral gene nanocarrier transfection is dependent on both MB diameter and US pressure, and that solid tumor growth can be controlled by the US-targeted delivery of 5 FU nanoparticles. More recent studies center on developing MRI-guided focused ultrasound (FUS) for nanoparticle delivery across the blood brain-barrier (BBB), which is the foremost impediment to drug treatment for most central nervous system diseases. Importantly, densely PEGylated nanoparticles that have been specifically designed to penetrate brain tissue (i.e., brain-penetrating nanoparticles, BPNs) are capable of crossing the BBB after it is opened with FUS and MBs, thereby supporting the use of gene- and drug-bearing BPNs in combination with MR-guided FUS in treating disorders and pathologies of the CNS.
    The Journal of the Acoustical Society of America 11/2013; 134(5):4047. · 1.65 Impact Factor
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    ABSTRACT: Nanoparticle drug delivery vehicles may eventually offer improved tumor treatments; however, nanoparticle delivery from the bloodstream to tumors can be hindered by poor convective and/or diffusive transport. We tested whether poly(lactic-co-glycolic acid) nanoparticle delivery can be improved by covalently linking them to ultrasound-activated microbubbles in a "composite-agent" formulation and whether drug (5-fluorouracil)-loaded nanoparticles delivered in this fashion inhibit the growth of tumors that are typically not responsive to intravenously administered 5-fluorouracil. After intravenous composite-agent injection, C6 gliomas implanted on Rag-1(-/-) mice were exposed to pulsed 1MHz ultrasound, resulting in the delivery of 16% of the initial NP dose per gram tissue. This represented a 5-to-57-fold increase in nanoparticle delivery when compared to multiple control groups. 5 fluorouracil-bearing nanoparticle delivery from the composite-agent formulation resulted in a 67% reduction in tumor volume at 7 days after treatment, and animal survival increased significantly when compared to intravenous soluble-5 fluorouracil administration. We conclude that nanoparticle delivery from ultrasound-activated composite agents may improve tumor treatment by offering a combination of better targeting, enhanced payload delivery, and controlled local drug release.Molecular Therapy (2013); doi:10.1038/mt.2013.259.
    Molecular Therapy 10/2013; · 7.04 Impact Factor
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    ABSTRACT: Our goal was to enhance ultrasound (US)-targeted skeletal muscle transfection through the use of poly(ethyleneglycol) (PEG)/polyethylenimine (PEI) nanocomplex gene carriers and adjustments to US and microbubble (MB) parameters. C57BL/6 mice received an intravenous infusion of MBs and either "naked" luciferase plasmid or luciferase plasmid condensed in PEG/PEI nanocomplexes. Pulsed ultrasound (1MHz; 0.6MPa or 0.8MPa) was applied to the right hindlimb for 12min. Luciferase activity in both hindlimbs was assessed at 3, 5, 7, and 10days post-treatment by bioluminescent imaging. When targeted to hindlimb using unsorted MBs and 0.6MPa US, 7days after treatment, we observed a >60-fold increase in luciferase activity in PEG/PEI nanocomplex-treated muscles over muscles treated with "naked" plasmid DNA. Luciferase activity was consistently greater after treatment with PEG/PEI nanocomplexes at 0.6MPa as compared to 0.8MPa. The combination of small diameter MBs and 0.6MPa US also resulted in significantly greater gene expression when compared to concentration matched intramuscular injections, a control condition in which considerably more PEG/PEI nanocomplexes were present in tissue. This result suggests that, in addition to facilitating PEG/PEI nanocomplex delivery from the bloodstream to tissue, US enhances transfection via one or more secondary mechanisms, including increased cellular uptake and/or trafficking to the nucleus of PEG/PEI nanocomplexes. We conclude that PEG/PEI nanocomplexes may be used to markedly enhance the amplitude of US-MB-targeted skeletal muscle transfection and that activating "small" MBs with a moderate level (0.6MPa) of acoustic pressure can further enhance these effects.
    Journal of Controlled Release 07/2012; 162(2):414-21. · 7.63 Impact Factor
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    ABSTRACT: Intravenously injected nanoparticles can be delivered to skeletal muscle through capillary pores created by the activation of microbubbles with ultrasound; however, strategies that utilize coinjections of free microbubbles and nanoparticles are limited by nanoparticle dilution in the bloodstream. Here, improvement in the delivery of fluorescently labeled ≈150 nm poly(lactic-co-glycolic acid) nanoparticles to skeletal muscle is attempted by covalently linking them to albumin-shelled microbubbles in a composite agent formulation. Studies are performed using an experimental model of peripheral arterial disease, wherein the right and left femoral arteries of BalbC mice are surgically ligated. Four days after arterial ligation, composite agents, coinjected microbubbles and nanoparticles, or nanoparticles alone are administered intravenously and 1 MHz pulsed ultrasound was applied to the left hindlimb. Nanoparticle delivery was assessed at 0, 1, 4, and 24 h post-treatment by fluorescence-mediated tomography. Within the coinjection group, both microbubbles and ultrasound are found to be required for nanoparticle delivery to skeletal muscle. Within the composite agent group, nanoparticle delivery is found to be enhanced 8- to 18-fold over 'no ultrasound' controls, depending on the time of measurement. A maximum of 7.2% of the initial nanoparticle dose per gram of tissue was delivered at 1 hr in the composite agent group, which was significantly greater than in the coinjection group (3.6%). It is concluded that covalently linking 150 nm-diameter poly(lactic-co-glycolic acid) nanoparticles to microbubbles before intravenous injection does improve their delivery to skeletal muscle.
    Small 04/2011; 7(9):1227-35. · 7.82 Impact Factor
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    ABSTRACT: In this study, the authors sought determine whether microbubble (MB) destruction with pulsed low duty cycle ultrasound can be used to reduce brain tumor perfusion and growth through nonthermal microvascular ablation. Studies using C57BLJ6/Rag-1 mice inoculated subcutaneously with C6 glioma cells were approved by the institutional animal care and use committee. Microbubbles were injected intravenously, and 1 MHz ultrasound was applied with varying duty cycles to the tumor every 5 seconds for 60 minutes. During treatment, tumor heating was quantified. Following treatment, tumor growth, hemodynamics, necrosis, and apoptosis were measured. Tumor blood flow was significantly reduced immediately after treatment, with posttreatment flow ranging from 36% (0.00002 duty cycle) to 4% (0.01 duty cycle) of pretreatment flow. Seven days after treatment, tumor necrosis and apoptosis were significantly increased in all treatment groups, while treatment with ultrasound duty cycles of 0.005 and 0.01 inhibited tumor growth by 63% and 75%, respectively, compared with untreated tumors. While a modest duty cycle-dependent increase in intratumor temperature was observed, it is unlikely that thermal tissue ablation occurred. In a subcutaneous C6 glioma model, MB destruction with low-duty cycle 1-MHz ultrasound can be used to markedly inhibit growth, without substantial tumor tissue heating. These results may have a bearing on the development of transcranial high-intensity focused ultrasound treatments for brain tumors that are not amenable to thermal ablation.
    Journal of Neurosurgery 01/2011; 114(6):1654-61. · 3.15 Impact Factor
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    Caitlin W Burke, Richard J Price
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    ABSTRACT: We are developing minimally-invasive contrast agent microbubble based therapeutic approaches in which the permeabilization and/or ablation of the microvasculature are controlled by varying ultrasound pulsing parameters. Specifically, we are testing whether such approaches may be used to treat malignant brain tumors through drug delivery and microvascular ablation. Preliminary studies have been performed to determine whether targeted drug-bearing nanoparticle delivery can be facilitated by the ultrasound mediated destruction of "composite" delivery agents comprised of 100nm poly(lactide-co-glycolide) (PLAGA) nanoparticles that are adhered to albumin shelled microbubbles. We denote these agents as microbubble-nanoparticle composite agents (MNCAs). When targeted to subcutaneous C6 gliomas with ultrasound, we observed an immediate 4.6-fold increase in nanoparticle delivery in MNCA treated tumors over tumors treated with microbubbles co-administered with nanoparticles and a 8.5 fold increase over non-treated tumors. Furthermore, in many cancer applications, we believe it may be desirable to perform targeted drug delivery in conjunction with ablation of the tumor microcirculation, which will lead to tumor hypoxia and apoptosis. To this end, we have tested the efficacy of non-theramal cavitation-induced microvascular ablation, showing that this approach elicits tumor perfusion reduction, apoptosis, significant growth inhibition, and necrosis. Taken together, these results indicate that our ultrasound-targeted approach has the potential to increase therapeutic efficiency by creating tumor necrosis through microvascular ablation and/or simultaneously enhancing the drug payload in gliomas.
    Journal of Visualized Experiments 01/2010;
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    ABSTRACT: Bone marrow-derived cells (BMCs) and inflammatory chemokine receptors regulate arteriogenesis and angiogenesis. Here, we tested whether arteriolar remodeling in response to an inflammatory stimulus is dependent on BMC-specific chemokine (C-C motif) receptor 2 (CCR2) expression and whether this response involves BMC transdifferentiation into smooth muscle. Dorsal skinfold window chambers were implanted into C57Bl/6 wild-type (WT) mice, as well as the following bone marrow chimeras (donor-host): WT-WT, CCR2(-/-)-WT, WT-CCR2(-/-), and EGFP(+)-WT. One day after implantation, tissue MCP-1 levels rose from "undetectable" to 463 pg/mg, and the number of EGFP(+) cells increased more than 4-fold, indicating marked inflammation. A 66% (28 microm) increase in maximum arteriolar diameter was observed over 7 days in WT-WT mice. This arteriolar remodeling response was completely abolished in CCR2(-/-)-WT mice but largely rescued in WT-CCR2(-/-) mice. EGFP(+) BMCs were numerous throughout the tissue, but we found no evidence that EGFP(+) BMCs transdifferentiate into smooth muscle, based on examination of >800 arterioles and venules. BMC-specific CCR2 expression is required for injury/inflammation-associated arteriolar remodeling, but this response is not characterized by the differentiation of BMCs into smooth muscle.
    Arteriosclerosis Thrombosis and Vascular Biology 10/2009; 29(11):1794-801. · 6.34 Impact Factor
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    ABSTRACT: Chemokine (C-C motif) receptor-2 (CCR2) regulates arteriogenesis and angiogenesis, facilitating the MCP-1-dependent recruitment of growth factor-secreting bone marrow-derived cells (BMCs). Here, we tested the hypothesis that the BMC-specific expression of CCR2 is also required for new arteriole formation via capillary arterialization. Following non-ischemic saphenous artery occlusion, we measured the following in gracilis muscles: monocyte chemotactic protein-1 (MCP-1) in wild-type (WT) C57Bl/6J mice by ELISA, and capillary arterialization in WT-WT and CCR2(-/-)-WT (donor-host) bone marrow chimeric mice, as well as BMC transdifferentiation in EGFP(+)-WT mice, by smooth muscle (SM) alpha-actin immunochemistry. MCP-1 levels were significantly elevated 1 day after occlusion in WT mice. In WT-WT mice at day 7, compared to sham controls, arterial occlusion induced a 34% increase in arteriole length density, a 46% increase in SM alpha-actin(+) vessels, and a 45% increase in the fraction of vessels coated with SM alpha-actin, indicating significant capillary arterialization. However, in CCR2(-/-)-WT mice, no differences were observed between arterial occlusion and sham surgery. In EGFP(+)-WT mice, EGFP and SM alpha-actin never colocalized. We conclude that BMC-specific CCR2 expression is required for skeletal muscle capillary arterialization following arterial occlusion; however, BMCs do not transdifferentiate into smooth muscle.
    Angiogenesis 09/2009; 12(4):355-63. · 4.41 Impact Factor
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    ABSTRACT: Therapeutic strategies in which recombinant growth factors are injected to stimulate arteriogenesis in patients suffering from occlusive vascular disease stand to benefit from improved targeting, less invasiveness, better growth-factor stability, and more sustained growth-factor release. A microbubble contrast-agent-based system facilitates nanoparticle deposition in tissues that are targeted by 1-MHz ultrasound. This system can then be used to deliver poly(D,L-lactic-co-glycolic acid) nanoparticles containing fibroblast growth factor-2 to mouse adductor muscles in a model of hind-limb arterial insufficiency. Two weeks after treatment, significant increases in both the caliber and total number of collateral arterioles are observed, indicating that the delivery of nanoparticles bearing fibroblast growth factor-2 by ultrasonic microbubble destruction may represent an effective and minimally invasive strategy for the targeted stimulation of therapeutic arteriogenesis.
    Small 09/2008; 4(10):1769-77. · 7.82 Impact Factor