Publications by authors named "Christopher M Raskett"

12 Publications

  • Page 1 of 1

In situ decellularization of a large animal saccular aneurysm model: sustained inflammation and active aneurysm wall remodeling.

J Neurointerv Surg 2021 Mar 5;13(3):267-271. Epub 2020 Oct 5.

Department of Radiology, New England Center for Stroke Research, University of Massachusetts Medical School, Worcester, Massachusetts, USA.

Objective: To investigate in situ decellularization of a large animal model of saccular aneurysm as a strategy for achieving aneurysmal growth and lasting inflammation.

Methods: 18 New Zealand White rabbits were randomized 2:1 to receive endoluminal sodium dodecyl sulfate infusion (SDS, 1% solution, 45 min) following elastase or elastase-only treatment (control). All aneurysms were measured by digital subtraction angiography every 2 weeks. Every 2 weeks, three of the rabbits (two elastase + SDS, one control) underwent MRI, followed by contrast injection with myeloperoxidase (MPO)-sensing contrast agent. MRI was repeated 3 hours after contrast injection and the enhancement ratio (ER) was calculated. Following MRI, aneurysms were explanted and subjected to immunohistopathology.

Results: During follow-up MRI, the average ER for SDS-treated animals was 1.63±0.20, compared with 1.01±0.06 for controls (p<0.001). The width of SDS-treated aneurysms increased significantly in comparison with the elastase aneurysms (47% vs 20%, p<0.001). Image analysis of thin sections showed infiltration of MPO-positive cells in decellularized aneurysms and surroundings through the 12-week observation period while control tissue had 5-6 times fewer cells present 2 weeks after aneurysm creation. Immunohistochemistry demonstrated the presence of MPO-positive cells surrounding decellularized lesions at early time points. MPO-positive cells were found in the adventitia and in the thrombi adherent to the aneurysm wall at later time points.

Conclusions: In situ decellularization of a large animal model of saccular aneurysms reproduces features of unstable aneurysms, such as chronic inflammation (up to 12 weeks) and active aneurysm wall remodeling, leading to continued growth over 8 weeks.
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http://dx.doi.org/10.1136/neurintsurg-2020-016589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8632232PMC
March 2021

High-resolution image-guided WEB aneurysm embolization by high-frequency optical coherence tomography.

J Neurointerv Surg 2021 Jul 28;13(7):669-673. Epub 2020 Sep 28.

Department of Radiology, New England Center for Stroke Research, University of Massachusetts Medical School, Worcester, Massachusetts, USA.

Background: High-frequency optical coherence tomography (HF-OCT) is an intra-vascular imaging technique capable of assessing device-vessel interactions at spatial resolution approaching 10 µm. We tested the hypothesis that adequately deployed Woven EndoBridge (WEB) devices as visualized by HF-OCT lead to higher aneurysm occlusion rates.

Methods: In a leporine model, elastase-induced aneurysms (n=24) were treated with the WEB device. HF-OCT and digital subtraction angiography (DSA) were performed following WEB deployment and repeated at 4, 8, and 12 weeks. Protrusion (0-present, 1-absent) and malapposition (0-malapposed, 1-neck apposition >50%) were binary coded. A device was considered 'adequately deployed' by HF-OCT and DSA if apposed and non-protruding. Aneurysm healing on DSA was reported using the 4-point WEB occlusion score: A or B grades were considered positive outcome. Neointimal coverage was quantified on HF-OCT images at 12 weeks and compared with scanning electron microscopy (SEM).

Results: Adequate deployment on HF-OCT correlated with positive outcome (P=0.007), but no statistically significant relationship was found between good outcome and adequate deployment on DSA (P=0.289). Absence of protrusion on HF-OCT correlated with a positive outcome (P=0.006); however, malapposition alone had no significant relationship (P=0.19). HF-OCT showed a strong correlation with SEM for the assessment of areas of neointimal tissue (R²=0.96; P<0.001). More neointimal coverage of 78%±32% was found on 'adequate deployment' cases versus 31%±24% for the 'inadequate deployment' cases (P=0.001).

Conclusion: HF-OCT visualizes features that can determine adequate device deployment to prognosticate early aneurysm occlusion following WEB implantation and can be used to longitudinally monitor aneurysm healing progression.
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http://dx.doi.org/10.1136/neurintsurg-2020-016447DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8205185PMC
July 2021

Acute Thrombus Burden on Coated Flow Diverters Assessed by High Frequency Optical Coherence Tomography.

Cardiovasc Intervent Radiol 2020 Aug 8;43(8):1218-1223. Epub 2020 May 8.

New England Center for Stroke Research, Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave N, SA-107R, Worcester, MA, 01655, USA.

Purpose: The implantation of flow diverters requires administration of dual anti-platelet therapy, posing the potential for complications. The p48MW HPC (phenox, Bochüm, Germany) hydrophilic-coated flow diverting stent is designed to be anti-thrombotic, thus opening the potential for single anti-platelet therapy. We deploy a novel intravascular high-resolution imaging technique, high-frequency optical coherence tomography (HF-OCT), to study in an animal model the acute thrombus formation on coated p48MW devices versus uncoated control devices.

Methods: Three pigs were implanted with 4 flow diverters each, two test hydrophilic-coated devices, and two control uncoated devices (p48MW). Each pig was treated with a different anti-platelet regime: no anti-platelet therapy, aspirin only, aspirin and clopidogrel. Twenty minutes after the flow diverter was implanted, an HF-OCT data set was acquired. Acute clot formed on the flow diverter at each covered side branch was measured from the HF-OCT slices. Factors considered to be important were the device type (pHPC versus bare metal), aspirin, clopidogrel, and vessel location. A linear model was constructed from the significant factors.

Results: Both coating (p < 0.001) and aspirin (p = 0.003) were significantly related to reduction in clot burden, leading to an approximate 100-fold and 50-fold reduction in clot, respectively.

Conclusions: This study shows the power of HF-OCT not only in the detection of clot but also the quantification of clot burden. In an animal model, the pHPC-coated p48MW significantly reduced acute thrombus formation over jailed side branches as compared to the bare metal p48MW that was nearly eliminated when combined with aspirin administration.
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http://dx.doi.org/10.1007/s00270-020-02482-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8209672PMC
August 2020

Essential role of the small GTPase Ran in postnatal pancreatic islet development.

PLoS One 2011 17;6(11):e27879. Epub 2011 Nov 17.

Prostate Cancer Discovery and Development Program, The Wistar Institute, Philadelphia, Pennsylvania, United States of America.

The small GTPase Ran orchestrates pleiotropic cellular responses of nucleo-cytoplasmic shuttling, mitosis and subcellular trafficking, but whether deregulation of these pathways contributes to disease pathogenesis has remained elusive. Here, we generated transgenic mice expressing wild type (WT) Ran, loss-of-function Ran T24N mutant or constitutively active Ran G19V mutant in pancreatic islet β cells under the control of the rat insulin promoter. Embryonic pancreas and islet development, including emergence of insulin(+) β cells, was indistinguishable in control or transgenic mice. However, by one month after birth, transgenic mice expressing any of the three Ran variants exhibited overt diabetes, with hyperglycemia, reduced insulin production, and nearly complete loss of islet number and islet mass, in vivo. Deregulated Ran signaling in transgenic mice, adenoviral over-expression of WT or mutant Ran in isolated islets, or short hairpin RNA (shRNA) silencing of endogenous Ran in model insulinoma INS-1 cells, all resulted in decreased expression of the pancreatic and duodenal homeobox transcription factor, PDX-1, and reduced β cell proliferation, in vivo. These data demonstrate that a finely-tuned balance of Ran GTPase signaling is essential for postnatal pancreatic islet development and glucose homeostasis, in vivo.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027879PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3219697PMC
May 2012

Exploiting the mitochondrial unfolded protein response for cancer therapy in mice and human cells.

J Clin Invest 2011 Apr;121(4):1349-60

Prostate Cancer Discovery and Development Program, Philadelphia, Pennsylvania, USA.

Fine tuning of the protein folding environment in subcellular organelles, such as mitochondria, is important for adaptive homeostasis and may participate in human diseases, but the regulators of this process are still largely elusive. Here, we have shown that selective targeting of heat shock protein-90 (Hsp90) chaperones in mitochondria of human tumor cells triggered compensatory autophagy and an organelle unfolded protein response (UPR) centered on upregulation of CCAAT enhancer binding protein (C/EBP) transcription factors. In turn, this transcriptional UPR repressed NF-κB-dependent gene expression, enhanced tumor cell apoptosis initiated by death receptor ligation, and inhibited intracranial glioblastoma growth in mice without detectable toxicity. These data reveal what we believe to be a novel role of Hsp90 chaperones in the regulation of the protein-folding environment in mitochondria of tumor cells. Disabling this general adaptive pathway could potentially be used in treatment of genetically heterogeneous human tumors.
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http://dx.doi.org/10.1172/JCI44855DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3069780PMC
April 2011

Preclinical characterization of mitochondria-targeted small molecule hsp90 inhibitors, gamitrinibs, in advanced prostate cancer.

Clin Cancer Res 2010 Oct 28;16(19):4779-88. Epub 2010 Sep 28.

Department of Cancer Biology, University of Massachusetts Medical School, Worcester, USA.

Purpose: This study aimed to characterize the preclinical activity of the first class of combinatorial, mitochondria-targeted, small molecule heat shock protein-90 (Hsp90) inhibitors, gamitrinibs, in models of hormone-refractory, drug-resistant, localized, and bone metastatic prostate cancer in vivo.

Experimental Design: Mitochondrial permeability transition, apoptosis, and changes in metabolic activity were examined by time-lapse videomicroscopy, multiparametric flow cytometry, MTT, and analysis of isolated mitochondria. Drug-resistant prostate cancer cells were generated by chronic exposure of hormone-refractory PC3 cells to the Hsp90 inhibitor 17-allylaminogeldanamycin (17-AAG). The effect of gamitrinibs on s.c. or intratibial prostate cancer growth was studied in xenograft models. Bone metastatic tumor growth and bone parameters were quantified by micro-computed tomography imaging.

Results: In the NCI 60-cell line screening, gamitrinibs were active against all tumor cell types tested, and efficiently killed metastatic, hormone-refractory, and multidrug-resistant prostate cancer cells characterized by overexpression of the ATP binding cassette transporter P-glycoprotein. Mechanistically, gamitrinibs, but not 17-AAG, induced acute mitochondrial dysfunction in prostate cancer cells with loss of organelle membrane potential, release of cytochrome c, and caspase activity, independently of proapoptotic Bcl-2 proteins Bax and Bak. Systemic administration of gamitrinibs to mice was well tolerated, and inhibited s.c. or bone metastatic prostate cancer growth in vivo.

Conclusions: Gamitrinibs have preclinical activity and favorable safety in models of drug-resistant and bone metastatic prostate cancer in vivo.
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http://dx.doi.org/10.1158/1078-0432.CCR-10-1818DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2948625PMC
October 2010

Global targeting of subcellular heat shock protein-90 networks for therapy of glioblastoma.

Mol Cancer Ther 2010 Jun 25;9(6):1638-46. Epub 2010 May 25.

Department of Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

Drug discovery for complex and heterogeneous tumors now aims at dismantling global networks of disease maintenance, but the subcellular requirements of this approach are not understood. Here, we simultaneously targeted the multiple subcellular compartments of the molecular chaperone heat shock protein-90 (Hsp90) in a model of glioblastoma, a highly lethal human malignancy in urgent need of fresh therapeutic strategies. Treatment of cultured or patient-derived glioblastoma cells with Shepherdin, a dual peptidomimetic inhibitor of mitochondrial and cytosolic Hsp90, caused irreversible collapse of mitochondria, degradation of Hsp90 client proteins in the cytosol, and tumor cell killing by apoptosis and autophagy. Stereotactic or systemic delivery of Shepherdin was well tolerated and suppressed intracranial glioma growth via inhibition of cell proliferation, induction of apoptosis, and reduction of angiogenesis in vivo. These data show that disabling Hsp90 cancer networks in their multiple subcellular compartments improves strategies for drug discovery and may provide novel molecular therapy for highly recalcitrant human tumors.
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http://dx.doi.org/10.1158/1535-7163.MCT-10-0097DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2884083PMC
June 2010

Sorafenib exerts anti-glioma activity in vitro and in vivo.

Neurosci Lett 2010 Jul 12;478(3):165-70. Epub 2010 May 12.

Department of Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.

Despite conventional treatment strategies glioblastoma, the most common malignant primary brain tumor, has a bad prognosis with median survival times of 12-15 months. In this study, the efficacy of sorafenib (Nexavar, BAY43-9006), a multikinase inhibitor, on glioblastoma cells was evaluated both in vitro and in vivo. Treatment of established or patient-derived glioblastoma cells with low concentrations of sorafenib caused a dramatic dose dependent inhibition of proliferation (IC(50), 1.5 microM) and induction of apoptosis and autophagy. Sorafenib inhibited phosphorylation of signal transducer and activator of transcription 3 (Stat3) and expression of cyclins, D and E. In contrast, AKT was not modulated by sorafenib. Most important, systemic delivery of sorafenib was well tolerated, and significantly suppressed intracranial glioma growth via inhibition of cell proliferation, induction of apoptosis and autophagy, and reduction of angiogenesis. Furthermore, intracranial growth inhibition by sorafenib was accompanied by a significant reduction in ph-Stat3 (Tyr 705) levels. In summary, sorafenib has potent anti-glioma activity in vitro and in vivo.
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http://dx.doi.org/10.1016/j.neulet.2010.05.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198851PMC
July 2010

IAP regulation of metastasis.

Cancer Cell 2010 Jan;17(1):53-64

Department of Cancer Biology, Prostate Cancer Discovery and Development Program, University of Massachusetts Medical School, Worcester, MA 01605, USA.

Inhibitor-of-Apoptosis (IAP) proteins contribute to tumor progression, but the requirements of this pathway are not understood. Here, we show that intermolecular cooperation between XIAP and survivin stimulates tumor cell invasion and promotes metastasis. This pathway is independent of IAP inhibition of cell death. Instead, a survivin-XIAP complex activates NF-kappaB, which in turn leads to increased fibronectin gene expression, signaling by beta1 integrins, and activation of cell motility kinases FAK and Src. Therefore, IAPs are direct metastasis genes, and their antagonists could provide antimetastatic therapies in patients with cancer.
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http://dx.doi.org/10.1016/j.ccr.2009.11.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2818597PMC
January 2010

Molecular dependence of estrogen receptor-negative breast cancer on a notch-survivin signaling axis.

Cancer Res 2008 Jul;68(13):5273-81

Department of Cancer Biology and the Cancer Center, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

Despite progress in the management of breast cancer, the molecular underpinnings of clinically aggressive subtypes of the disease are not well-understood. Here, we show that activation of Notch developmental signaling in estrogen receptor (ER)-negative breast cancer cells results in direct transcriptional up-regulation of the apoptosis inhibitor and cell cycle regulator survivin. This response is associated with increased expression of survivin at mitosis, enhanced cell proliferation, and heightened viability at cell division. Conversely, targeting Notch signaling with a peptidyl gamma-secretase inhibitor suppressed survivin levels, induced apoptosis, abolished colony formation in soft agar, and inhibited localized and metastatic tumor growth in mice, without organ or systemic toxicity. In contrast, ER+ breast cancer cells, or various normal cell types, were insensitive to Notch stimulation. Therefore, ER- breast cancer cells become dependent on Notch-survivin signaling for their maintenance, in vivo. Therapeutic targeting of this pathway may be explored for individualized treatment of patients with clinically aggressive, ER- breast cancer.
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http://dx.doi.org/10.1158/0008-5472.CAN-07-6673DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2652573PMC
July 2008

Activated checkpoint kinase 2 provides a survival signal for tumor cells.

Cancer Res 2006 Dec;66(24):11576-9

Department of Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

Tumor cells often become resistant to DNA damage-based therapy; however, the underlying mechanisms are not yet understood. Here, we show that tumor cells exposed to DNA damage counteract cell death by releasing the antiapoptotic protein, survivin, from mitochondria. This is independent of p53, and requires activated checkpoint kinase 2 (Chk2), a putative tumor suppressor. Molecular or genetic targeting of Chk2 prevents the release of survivin from mitochondria, enhances DNA damage-induced tumor cell apoptosis, and inhibits the growth of resistant in vivo tumors. Therefore, activated Chk2 circumvents its own tumor-suppressive functions by promoting tumor cell survival. Inhibiting Chk2 in combination with DNA-damaging agents may provide a rational approach for treating resistant tumors.
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http://dx.doi.org/10.1158/0008-5472.CAN-06-3095DOI Listing
December 2006

Antileukemic activity of shepherdin and molecular diversity of hsp90 inhibitors.

J Natl Cancer Inst 2006 Aug;98(15):1068-77

Department of Cancer Biology and Cancer Center, University of Massachusetts Medical School, LRB428, 364 Plantation Street, Worcester, MA 01605, USA.

Background: Heat shock protein 90 (Hsp90) is a molecular chaperone that is involved in signaling pathways for cell proliferation, survival, and cellular adaptation. Inhibitors of Hsp90 are being examined as cancer therapeutic agents, but the molecular mechanism of their anticancer activity is still unclear. We investigated Hsp90 as a therapeutic target for acute myeloid leukemia (AML) by use of the Hsp90 inhibitor shepherdin (a novel peptidyl antagonist of the interaction between Hsp90 and survivin, which is a regulator of cell proliferation and cell viability in cancer).

Methods: We studied protein interactions by molecular dynamics simulations and conducted competition experiments by use of enzyme-linked immunosorbent assay (ELISA). Shepherdin[79-83], a novel variant carrying the survivin sequence from Lys-79 through Gly-83, or its scrambled peptide was made permeable to cells by adding the antennapedia helix III carrier sequence. Apoptosis, Hsp90 client protein expression, and mitochondrial dysfunction were evaluated in AML types (myeloblastic, monocytic, and chronic myelogenous leukemia in blast crisis), patient-derived blasts, and normal mononuclear cells. Effects of shepherdin on tumor growth were evaluated in AML xenograft tumors in mice (n = 6). Organ tissues were examined histologically.

Results: Shepherdin[79-83] bound to Hsp90, inhibited formation of the survivin-Hsp90 complex, and competed with ATP binding to Hsp90. Cell-permeable shepherdin[79-83] induced rapid (within 30 minutes) and complete (with concentrations inducing 50% cell death of 24-35 microM) killing of AML types and blasts, but it did not affect normal mononuclear cells. Shepherdin[79-83] made contact with unique residues in the ATP pocket of Hsp90 (Ile-96, Asp-102, and Phe-138), did not increase Hsp70 levels in AML cells, disrupted mitochondrial function within 2 minutes of treatment, and eliminated the expression of Hsp90 client proteins. Shepherdin[79-83] abolished growth of AML xenograft tumors (mean of control group = 1698 mm3 and mean of treated group = 232 mm3; difference = 1466 mm3, 95% confidence interval = 505.8 to 2426; P = .008) without systemic or organ toxicity and inhibited Hsp90 function in vivo.

Conclusions: Shepherdin is a novel Hsp90 inhibitor with a unique mechanism of anticancer activity.
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http://dx.doi.org/10.1093/jnci/djj300DOI Listing
August 2006
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