James R. Bading

Clearance of Alzheimer’s amyloid-β1-40 peptide from brain by LDL receptor–related protein-1 at the blood-brain barrier

Elimination of amyloid-ss peptide (Ass) from the brain is poorly understood. After intracerebral microinjections in young mice, (125)I-Ass(1-40) was rapidly removed from the brain (t(1/2) </= 25 minutes), mainly by vascular transport across the blood-brain barrier (BBB). The efflux transport system for Ass(1-40) at the BBB was half saturated at 15.3 nM, and the maximal transport capacity was reached between 70 nM and 100 nM. Ass(1-40) clearance was substantially inhibited by the receptor-associated protein, and by antibodies against LDL receptor-related protein-1 (LRP-1) and alpha(2)-macroglobulin (alpha(2)M). As compared to adult wild-type mice, clearance was significantly reduced in young and old apolipoprotein E (apoE) knockout mice, and in old wild-type mice. There was no evidence that Ass was metabolized in brain interstitial fluid and degraded to smaller peptide fragments and amino acids before its transport across the BBB into the circulation. LRP-1, although abundant in brain microvessels in young mice, was downregulated in older animals, and this downregulation correlated with regional Ass accumulation in brains of Alzheimers disease (AD) patients. We conclude that the BBB removes Ass from the brain largely via age-dependent, LRP-1-mediated transport that is influenced by alpha(2)M and/or apoE, and may be impaired in AD.

Imaging of Cell Proliferation: Status and Prospects

Increased cellular proliferation is an integral part of the cancer phenotype. Several in vitro assays have been developed to measure the rate of tumor growth, but these require biopsies, which are particularly difficult to obtain over time and in different areas of the body in patients with multiple metastatic lesions. Most of the effort to develop imaging methods to noninvasively measure the rate of tumor cell proliferation has focused on the use of PET in conjunction with tracers for the thymidine salvage pathway of DNA synthesis, because thymidine contains the only pyrimidine or purine base that is unique to DNA. Imaging with 11C-thymidine has been tested for detecting tumors and tracking their response to therapy in animals and patients. Its major limitations are the short half-life of 11C and the rapid catabolism of thymidine after injection. These limitations led to the development of analogs that are resistant to degradation and can be labeled with radionuclides more conducive to routine clinical use, such as 18F. At this point, the thymidine analogs that have been studied the most are 3′-deoxy-3′-fluorothymidine (FLT) and 1-(2′-deoxy-2′-fluoro-1-β-d-arabinofuranosyl)-thymine (FMAU). Both are resistant to degradation and track the DNA synthesis pathway. FLT is phosphorylated by thymidine kinase 1, thus being retained in proliferating cells. It is incorporated by the normal proliferating marrow and is glucuronidated in the liver. FMAU can be incorporated into DNA after phosphorylation but shows less marrow uptake. It shows high uptake in the normal heart, kidneys, and liver, in part because of the role of mitochondrial thymidine kinase 2. Early clinical data for 18F-FLT demonstrated that its uptake correlates well with in vitro measures of proliferation. Although 18F-FLT can be used to detect tumors, its tumor-to-normal tissue contrast is generally lower than that of 18F-FDG in most cancers outside the brain. The most promising use for thymidine and its analogs is in monitoring tumor treatment response, as demonstrated in animal studies and pilot human trials. Further work is needed to determine the optimal tracer(s) and timing of imaging after treatment.

Hyperspectral and multispectral bioluminescence optical tomography for small animal imaging

For bioluminescence imaging studies in small animals, it is important to be able to accurately localize the three-dimensional (3D) distribution of the underlying bioluminescent source. The spectrum of light produced by the source that escapes the subject varies with the depth of the emission source because of the wavelength-dependence of the optical properties of tissue. Consequently, multispectral or hyperspectral data acquisition should help in the 3D localization of deep sources. In this paper, we describe a framework for fully 3D bioluminescence tomographic image acquisition and reconstruction that exploits spectral information. We describe regularized tomographic reconstruction techniques that use semi-infinite slab or FEM-based diffusion approximations of photon transport through turbid media. Singular value decomposition analysis was used for data dimensionality reduction and to illustrate the advantage of using hyperspectral rather than achromatic data. Simulation studies in an atlas-mouse geometry indicated that sub-millimeter resolution may be attainable given accurate knowledge of the optical properties of the animal. A fixed arrangement of mirrors and a single CCD camera were used for simultaneous acquisition of multispectral imaging data over most of the surface of the animal. Phantom studies conducted using this system demonstrated our ability to accurately localize deep point-like sources and show that a resolution of 1.5 to 2.2 mm for depths up to 6 mm can be achieved. We also include an in vivo study of a mouse with a brain tumour expressing firefly luciferase. Co-registration of the reconstructed 3D bioluminescent image with magnetic resonance images indicated good anatomical localization of the tumour.

PET and [18F]-FDG in oncology: A clinical update

Positron emission tomography (PET) has become a very useful adjunct to anatomic imaging techniques, adding unique information to the characterization of disease. The whole-body PET FDG technique developed over the last few years has surpassed most expectations with respect to its utility in clinical oncology. The large spectrum of neoplasms that now can be studied with this approach makes it an essential clinical imaging tool in diagnosis and management for many patients with cancer. The metabolic information provided by this technique is complementary to results from standard clinical and morphological examinations. It may be anticipated that through application of the multi-modality imaging approach, significant advances in medical care will come.

Bioactivity and Safety of IL13Rα2-Redirected Chimeric Antigen Receptor CD8+ T Cells in Patients with Recurrent Glioblastoma

Purpose: A first-in-human pilot safety and feasibility trial evaluating chimeric antigen receptor (CAR)–engineered, autologous primary human CD8+ cytotoxic T lymphocytes (CTL) targeting IL13Rα2 for the treatment of recurrent glioblastoma (GBM). Experimental Design: Three patients with recurrent GBM were treated with IL13(E13Y)-zetakine CD8+ CTL targeting IL13Rα2. Patients received up to 12 local infusions at a maximum dose of 108 CAR-engineered T cells via a catheter/reservoir system. Results: We demonstrate the feasibility of manufacturing sufficient numbers of autologous CTL clones expressing an IL13(E13Y)-zetakine CAR for redirected HLA-independent IL13Rα2-specific effector function for a cohort of patients diagnosed with GBM. Intracranial delivery of the IL13-zetakine+ CTL clones into the resection cavity of 3 patients with recurrent disease was well-tolerated, with manageable temporary brain inflammation. Following infusion of IL13-zetakine+ CTLs, evidence for transient anti-glioma responses was observed in 2 of the patients. Analysis of tumor tissue from 1 patient before and after T-cell therapy suggested reduced overall IL13Rα2 expression within the tumor following treatment. MRI analysis of another patient indicated an increase in tumor necrotic volume at the site of IL13-zetakine+ T-cell administration. Conclusions: These findings provide promising first-in-human clinical experience for intracranial administration of IL13Rα2-specific CAR T cells for the treatment of GBM, establishing a foundation on which future refinements of adoptive CAR T-cell therapies can be applied. Clin Cancer Res; 21(18); 4062–72. ©2015 AACR.

Cerebrovascular Accumulation and Increased Blood‐Brain Barrier Permeability to Circulating Alzheimer's Amyloid β Peptide in Aged Squirrel Monkey with Cerebral Amyloid Angiopathy

Abstract: Senescent squirrel monkey is a valuable model to study pathogenesis of cerebrovascular amyloid angiopathy (CAA). Cerebrovascular sequestration and blood‐brain barrier (BBB) permeability to 125I‐amyloid β(1‐40) synthetic peptide (sAβ1‐40) were studied in adult versus aged squirrel monkey 1 h after a single intravenous injection. In aged monkey, the half‐time of elimination of sAβ1‐40, te1/2, was prolonged by 0.6 h, the systemic clearance, ClSS, was reduced from 1.8 to 1.1 ml/min/kg, and the mean residence time of intact peptide in the circulation was increased by 1 h (45%). In adult monkey, cerebrovascular sequestration of intact sAβ1‐40 was significant, and the BBB permeability was 18.6‐fold higher than for inulin. In aged monkey, the sequestration of intact sAβ1‐40 by cortical and leptomeningeal microvessels and the BBB permeability were increased by 5.9, 1.8‐, and 2.1‐fold, respectively, in the presence of an unchanged barrier to inulin. In brain parenchyma of aged animals, 76.1% of circulating sAβ1‐40 remained intact versus 45.7% in adult. We conclude that multiple age‐related systemic effects, i.e., reduced body elimination and systemic clearance of sAβ1‐40, and reduced peripheral metabolism, may act in concert with BBB mechanisms, i.e., increased transendothelial transport and microvascular accumulation of blood‐borne sAβ1‐40, and reduced brain metabolism to enhance the development of CAA.

Perfusion of colorectal hepatic metastases. Relative distribution of flow from the hepatic artery and portal vein

The importance of portal circulation in the delivery of drugs and nutrients to colorectal hepatic metastases is controversial. Using 13N (nitrogen 13) amino acids and ammonia with dynamic gamma camera imaging, we demonstrate, for the first time in human beings, a quantitative advantage of hepatic artery compared with portal vein infusion. Eleven patients were studied by hepatic artery injection, five patients were studied by portal vein injection, and two patients had injections through both routes. Data collected from the liver for 10 minutes after rapid bolus injection of 13N L‐glutamate, L‐glutamine, or ammonia were compared with 99mTc (technetium) macroaggregated albumin (MAA) images produced after injection through the hepatic artery or portal vein at the same session. Tumor regions defined from 99mTc sulfur colloid scans were compared with nearby liver areas of similar thickness. For the 13N compounds, the area‐normalized count rate at first pass maximum (Qmax) and the tissue extraction efficiency were computed. The tumor/liver Qmax ratios for MAA and 13N compounds were highly correlated. Both tumor and liver extracted more than 70% of the nitrogenous compounds. The tumor/liver Qmax ratios reflect the relative delivery of injected tracer per unit volume of tissue. After hepatic artery injection the Qmax ratio was 1.03 ± 0.33 (mean ± SD), significantly exceeding the Qmax ratio of 0.50 ± 0.34 after portal vein injection (P < 0.003). Therefore, (1) more than twice as much of a nutrient substrate is delivered per volume of tumor relative to liver by the hepatic artery as by the portal vein; (2) the high extraction efficiency demonstrates that the hepatic artery flow is nutritive; and (3) the delivery of substance in solution (such as nutrients or drugs) to tumor and liver tissue correlates with the distribution of colloids such as macroaggregated albumin after hepatic arterial and portal venous injection.

Circulating amyloid-β peptide crosses the blood–brain barrier in aged monkeys and contributes to Alzheimer's disease lesions

1. We studied cerebrovascular sequestration and blood-brain barrier (BBB) permeability to [125I]- or [123I]-labeled amyloid-beta peptides (A beta) in aged rhesus and aged squirrel monkey, the nonhuman primate models of cerebral beta-amyloidosis and cerebrovascular amyloid angiopathy (CAA), respectively. 2. In aged rhesus, the half-time of elimination of [125I]A beta 1-40, t1/2e, was faster by 1.34 h, the systemic clearance, Clss, increased by 4.21 ml/min/kg and the mean residence time of intact peptide in the circulation shortened by 2 h. 3. Cerebrovascular sequestration of [125I]A beta 1-40 was significant in aged squirrel monkey (20.8 ml/g x 10(2)), but undetectable in the rhesus. 4. The permeability surface area product, PS, for [14C]inulin was low in both species (0.11-0.18 ml/g/s x 10(6)) indicating an intact barrier. 5. The BBB permeability to A beta 1-40 was 34.8- and 13.7-fold higher than for [14C]inulin in aged squirrel and rhesus, respectively, suggesting a specialized A beta transport across the BBB. 6. The single photon computed emission tomography studies confirmed a saturable [123I]A beta 1-40 transport at the BBB in primates (Km = 40 nM). 7. Brain autoradiographic analysis of [125I]A beta 1-42 or [125I]A beta 1-40 after intracarotid infusions of radiotracers confirmed co-localization of the signal with A beta-immunoreactive plaques in rhesus monkeys. 8. Metabolism of [125I]A beta 1-40 in brain and plasma was slower in aged squirrel compared to aged rhesus, by 2.9- and 2.6-fold, respectively. 9. Thus, transport of circulating A beta across the BBB contributes to brain parenchymal accumulation of amyloid in aged nonhuman primates. Negligible capillary binding, rapid systemic and brain degradation, and accelerated body elimination of blood-borne A beta, may prevent the development of CAA in rhesus in contrast to squirrel monkeys.

Brain Clearance of Alzheimer's Amyloid-β40 in the Squirrel Monkey: A SPECT Study in a Primate Model of Cerebral Amyloid Angiopathy

Squirrel monkey is a valuable model to study pathogenesis of cerebrovascular amyloid angiopathy (CAA). Previous studies suggested that circulating amyloid- β 40 peptide (A β 40) crosses the blood-brain barrier (BBB) and may therefore enhance cerebrovascular amyloidosis in aged squirrel monkeys. In the present study, we used single photon emission computed tomography (SPECT) to determine elimination of 123 I-A β 40 and 99m Tc-DTPA, an extracellular marker, from the brain in squirrel monkeys at different age. Following intracerebral microinfusions, the time-activity brain clearance curves indicated bi-exponential removal of 123 I-A β 40 with an initial rapid washout (1.1 ≤ t 1/2 ≤ 2.7 h). This, plus the observed appearance of 123 I-radioactivity in plasma suggest significant brain-to-blood transport. In contrast, 99m Tc-DTPA was removed slowly by brain interstitial fluid bulk flow (monoexponential decay with 6.8 ≤ t 1/2 ≤ 16.8 h) . A comparison of three middle aged (11-16 years old) vs. two old (22 yrs old) monkeys was consistent with an age-related decline in the BBB capacity to remove 123 I-A β from the brain. This correlated with an age-dependent increase in A β 40/42 cerebrovascular immunoreactivity and amyloid deposition. Thus, vascular clearance plays an important role in reducing A β levels in the squirrel monkey brain and impaired A β 40 elimination across the BBB may contribute to the development of CAA.

Spontaneous and Controllable Activation of Suicide Gene Expression Driven by the Stress-Inducible Grp78 Promoter Resulting in Eradication of Sizable Human Tumors

GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.