Thrombomodulin is preferentially expressed in Balb/c lung microvessels.

Previously, two rat monoclonal antibodies where developed which bind distinct epitopes on a murine glycoprotein, P112, which is expressed primarily in lung capillary endothelium. In this paper we show that P112 is identical to the endothelial anticoagulant protein, thrombomodulin (TM). Several lines of evidence support this conclusion. First, amino acid analysis of P112 shows a high degree of homology to TM, and both molecules exhibit the same mobility in gel electrophoresis. Second, P112 and TM share reactivity for two different monoclonal antibodies. Third, purified P112, like TM, acts as a cofactor for protein C activation. Finally, two cDNA clones identified with P112 polyclonal antiserum contain sequence identity with the known TM cDNA sequence. Quantitative analysis of TM (P112) expression using a two-site monoclonal antibody assay demonstrates that significantly higher levels of TM are found in lung in comparison with other highly vascularized organs, i.e. the kidney and liver. Quantitative Northern blot data coincides with the two-site assay data and demonstrates that the high level of TM expression in lung is not due to preferential binding of the monoclonal antibodies to lung TM but rather to increased production of TM mRNA in the lung relative to other highly vascularized organs. It is suggested that expression of TM is highest in cells from continuous endothelium.     

Production of acetylcholine receptors from TE671 cells grown on microcarriers

Summary When grown in DMEM supplemented with 10 % fetal calf serum and using Cytodex 3® as microcarriers, TE671 cells entering the stationary phase optimally expressed acetylcholine receptors. These, receptors could be conveniently extracted from cell-saturated, microbeads or monodispersed cells obtained by trypsinization of microbeads. Typically, a 500 ml-batch gave 6–7 pmol of receptors which could be used as antigen to assay anti-acetylcholine receptor antibodies in the sera of myasthenic patients.     

Analysis of differentiation antigens on normal and carcinogen-altered rat epithelial cells in vivo and in culture

Two murine monoclonal antibodies, 3BG8 and 9BG8, which were raised against a rat tracheal squamous-cell-carcinoma cell line, recognize cell-surface antigens on normal rat squamous epithelium (skin, esophagus, vagina, and cornea) as well as on carcinogen-exposed, immortalized, rat tracheal epithelial cells. Monoclonal antibody 3BG8 binds to a 115-kilodalton cell-surface protein on undifferentiated basal cells of the epithelium, while the binding of the other antibody, 9BG8, occurs in both differentiated and undifferentiated populations of normal squamous epithelium and squamous cell carcinomas. Undifferentiated tracheal carcinomas bound only the 3BG8 antibody. No binding of either antibody was detected on normal tracheal mucociliary epithelium. Only under conditions that induce squamous differentiation of rat tracheal epithelium was binding of 3BG8 and 9BG8 detected. For reasons which are not clear at present, 9BG8 dramatically inhibits the growth of normal tracheal and esophageal cells in primary culture, whereas only 3BG8 affects the growth of carcinogen-altered tracheal cell lines. Based on antigen characterization and distribution, it is concluded that the 3BG8 and 9BG8 epitopes are localized on differentiation antigens which differ from others that have been previously described.     

Radiotoxicity of bismuth-213 bound to membranes of monolayer and spheroid cultures of tumor cells

Monoclonal antibody 13A to murine CD44 was used to bind the alpha-particle emitter 213Bi to cell surfaces of cultured EMT-6 or Line 1 tumor cells. Data on kinetics and saturation of binding, cell shape and nuclear size were used to calculate the absorbed dose to the nuclei. Treatment of monolayer cells with [213Bi]MAb 13A produced a classical exponential survival curve with no apparent shoulder. Microdosimetry analyses indicated that 1.4-1.7 Gy produced a 37% surviving fraction (D0). Multicellular spheroids were shown to bind [213Bi]MAb 13A mainly on the outer cell layer. Relatively small amounts of activity added to the spheroids resulted in relatively large absorbed doses. The result was that 3-6-fold less added radioisotope was necessary to kill similar fractions of cells in spheroids than in monolayer cells. These data are consistent with the interpretation that the alpha particles from a single 213Bi atom bound to one cell can penetrate and kill adjacent cells. Flow cytometry was used to sort cells originating from the periphery or from the interior of spheroids. Cells from the outside of the [213Bi]MAb 13A exposed spheroids had a lower surviving fraction per administered activity than cells from the interior. Cells were killed efficiently in spheroids up to 20-30 cells in diameter. The data support the hypothesis that alpha-particle emitters should be very efficient at killing cells in micrometastases of solid tumors.     

GATE Validation of Standard Dual Energy Corrections in Small Animal SPECT-CT

This paper addresses ¹²³I and ¹²⁵I dual isotope SPECT imaging, which can be challenging because of spectrum overlap in the low energy spectrums of these isotopes. We first quantify the contribution of low-energy photons from each isotope using GATE-based Monte Carlo simulations for the MOBY mouse phantom. We then describe and analyze a simple, but effective method that uses the ratio of detected low and high energy ¹²³I activity to separate the mixed low energy ¹²³I and ¹²⁵I activities. Performance is compared with correction methods used in conventional tissue biodistribution techniques. The results indicate that the spectrum overlap effects can be significantly reduced, if not entirely eliminated, when attenuation and scatter is either absent or corrected for using standard methods. In particular, we show that relative activity levels of the two isotopes can be accurately estimated for a wide range of organs and provide quantitative validation that standard methods for spectrum overlap correction provide reasonable estimates for reasonable corrections in small-animal SPECT/CT imaging.     

LaPO4 nanoparticles doped with actinium-225 that partially sequester daughter radionuclides

Nanoscale materials have been envisioned as carriers for various therapeutic drugs, including radioisotopes. Inorganic nanoparticles (NPs) are particularly appealing vehicles for targeted radiotherapy because they can package several radioactive atoms into a single carrier and can potentially retain daughter radioisotopes produced by in vivo generators such as actinium-225 ((225)Ac, t(1/2) = 10 d). Decay of this radioisotope to stable bismuth-209 proceeds through a chain of short-lived daughters accompanied by the emission of four α-particles that release >27 MeV of energy. The challenge in realizing the enhanced cytotoxic potential of in vivo generators lies in retaining the daughter nuclei at the therapy site. When (225)Ac is attached to targeting agents via standard chelate conjugation methods, all of the daughter radionuclides are released after the initial α-decay occurs. In this work, (225)Ac was incorporated into lanthanum phosphate NPs to determine whether the radioisotope and its daughters would be retained within the dense mineral lattice. Further, the (225)Ac-doped NPs were conjugated to the monoclonal antibody mAb 201B, which targets mouse lung endothelium through the vasculature, to ascertain the targeting efficacy and in vivo retention of radioisotopes. Standard biodistribution techniques and microSPECT/CT imaging of (225)Ac as well as the daughter radioisotopes showed that the NPs accumulated rapidly in mouse lung after intravenous injection. By showing that excess, competing, uncoupled antibodies or NPs coupled to control mAbs are deposited primarily in the liver and spleen, specific targeting of NP-mAb 201B conjugates was demonstrated. Biodistribution analysis showed that ～30% of the total injected dose of La((225)Ac)PO(4) NPs accumulated in mouse lungs 1 h postinjection, yielding a value of % ID/g >200. Furthermore, after 24 h, 80% of the (213)Bi daughter produced from (225)Ac decay was retained within the target organ and (213)Bi retention increased to ～87% at 120 h. In vitro analyses, conducted over a 1 month interval, demonstrated that ～50% of the daughters were retained within the La((225)Ac)PO(4) NPs at any point over that time frame. Although most of the γ-rays from radionuclides in the (225)Ac decay chain are too energetic to be captured efficiently by SPECT detectors, appropriate energy windows were found that provided dramatic microSPECT images of the NP distribution in vivo. We conclude that La((225)Ac)PO(4)-mAb 201B conjugates can be targeted efficiently to mouse lung while partially retaining daughter products and that targeting can be monitored by biodistribution techniques and microSPECT imaging.     

HIV-1 gp41 and gp160 are hyperthermostable proteins in a mesophilic environment. Characterization of gp41 mutants.

HIV gp41(24-157) unfolds cooperatively over the pH range of 1.0-4.0 with T(m) values of > 100 degrees C. At pH 2.8, protein unfolding was 80% reversible and the DeltaH(vH)/DeltaH(cal) ratio of 3.7 is indicative of gp41 being trimeric. No evidence for a monomer-trimer equilibrium in the concentration range of 0.3-36 micro m was obtained by DSC and tryptophan fluorescence. Glycosylation of gp41 was found to have only a marginal impact on the thermal stability. Reduction of the disulfide bond or mutation of both cysteine residues had only a marginal impact on protein stability. There was no cooperative unfolding event in the DSC thermogram of gp160 in NaCl/P(i), pH 7.4, over a temperature range of 8-129 degrees C. When the pH was lowered to 5.5-3.4, a single unfolding event at around 120 degrees C was noted, and three unfolding events at 93.3, 106.4 and 111.8 degrees C were observed at pH 2.8. Differences between gp41 and gp160, and hyperthermostable proteins from thermophile organisms are discussed. A series of gp41 mutants containing single, double, triple or quadruple point mutations were analysed by DSC and CD. The impact of mutations on the protein structure, in the context of generating a gp41 based vaccine antigen that resembles a fusion intermediate state, is discussed. A gp41 mutant, in which three hydrophobic amino acids in the gp41 loop were replaced with charged residues, showed an increased solubility at neutral pH.     

Quantitative Tomography of Early-Onset Spontaneous AA Amyloidosis in Interleukin 6 Transgenic Mice

Mice that constitutively express the human interleukin 6 (huIL6) protein from a heritable transgene (H2-L^d-IL-6) express high levels of the acute-phase reactant, serum amyloid protein A, a liver-derived apoprotein of high-density lipoprotein that is the precursor of AA amyloid. Typically at approximately 5 mo of age B6(C)- Tg(H2-L^d-IL-6)Kish (H2/huIL-6) animals begin to develop splenic deposits of AA amyloid, which progress to involve the liver, kidney, and vasculature, ultimately resulting in death due to severe systemic AA amyloidosis at 8 to 9 mo of age. These mice provide a robust model in which to study novel therapeutic and diagnostic imaging agents for AA amyloidosis. We recently have noted a change in onset of spontaneous disease, as evidenced by 2 female transgenic mice that were found moribund at only 5 mo of age. Extensive hepatosplenic amyloid deposits in both mice were identified and quantified by single-photon emission computed tomography, which further revealed heterogeneous distribution of radiotracer in the spleen indicating a distinction between amyloid-laden red pulp and the disease-free lymphoid follicles. The AA nature of the deposits was evidenced immunohistochemically and by mass spectrometric analyses of extracted amyloid fibrils. Our studies have documented the manifestation of early-onset, severe, spontaneous AA amyloidosis in 2- to 5-mo-old H2/huIL-6 mice; we hypothesize that this disease is due to genetic rather than environmental factors.Abbreviations: au, arbitrary units; CT, computed tomography; huIL6, human interleukin 6; SAP, serum amyloid P; SPECT, single photon emission computed tomography; sAA, serum amyloid AAA amyloidosis is the most common form of systemic amyloid disease in animals, occurring in cheetah,^5,36 shar-pei dogs,^8,11 sheep,^10,34 goats,³⁴ ducks,¹³ cats,^45,46 hamsters,^20,35 dolphins,⁷ common marmosets³⁰ and, especially, mice.^2,4,15,20 Typically, this disorder results from overproduction of an acute-phase reactant termed serum amyloid protein A (sAA), the amyloidogenic precursor protein, which is synthesized almost exclusively by hepatocytes.^3,26,33,39 Serum amyloid protein A binds heparan sulfate proteoglycan and laminin within the basement membrane and modulates cholesterol metabolism.^29,37,44For more than 50 y mice have been used as an experimental model for AA, whereby animals are injected with a proinflammatory stimulus, such as silver nitrate, casein solution, Freund adjuvant, or lipopolysaccharide to generate an acute-phase response.¹⁵ Variations of this experimental model are used to study the etiology of amyloidosis and for the discovery and testing of novel therapies.^22,25,47 One drawback, however, is the need to provide repeated chemical injections, with attendant toxicity, to maintain the pathology. Cessation of the inflammatory stimulus results in slow but progressive resorption of the amyloid deposits.²⁵As an alternative approach, we characterized and maintained a line of mice that express the human IL6 (huIL6) protein from a stably inserted transgene. The B6(C)- Tg(H2-L^d-IL-6)Kish (H2/huIL-6) strain was derived at the National Institutes of Health by introgressive backcrossing of the original H2-L^d-IL-6 Tg C57BL/6 transgenic mice^42,43 onto the Balb/c background for more than 20 generations.²⁸ These mice constitutively express the huIL6 transgene under the control of the mouse major histocompatibility complex class 1 (H2-L^d) promoter. The transgene segregates with an autosomal pattern of Mendelian inheritance.⁴³ Because of the role of IL6 in maintenance of the inflammatory response and lymphocyte proliferation during the immune response, early generations of these transgenic animals had high sAA levels and an extensive lymphocytosis with development of polyclonal plasma cell proliferation in 56% of mice at 18 mo of age.²⁸Human IL6 serum levels in the early generations of this transgenic line were 0.5 to 1 ng/mL⁴³; however, backcrossed Balb/c mice bred in our facility for approximately 2 y had approximately 300-fold higher with circulating huIL6 levels at 8 wk of age (0.3 to 1 µg/mL).⁴¹ In response to the proinflammatory huIL6 cytokine, the mice experience a chronic inflammatory state that results in increased concentrations of circulating sAA-conjugated high-density lipoprotein. The spontaneous onset of AA amyloidosis in these mice typically occurred at age 5 mo, presenting first as perifollicular deposits in the spleen only detectable histologically by biopsy.⁴¹ Over the course of the next 3 to 4 mo, amyloid was detected in the periportal vasculature and sinusoids within the liver, tongue, heart and intestinal villi, as well as renal interstitium, glomerulae, and papilla. In addition, cast nephropathy was commonly observed, as was extramedullary hematopoiesis and splenomegaly due to amyloidosis or lymphoid hyperplasia (or both) resulting from the elevated IL6 concentrations.We previously documented the nature of the amyloid in H2/huIL-6 mice immunohistochemically by using AA-specific monoclonal antibodies.⁴¹ In addition, we used liquid chromatography-coupled mass spectrometry to show that isolated tissue-derived AA fibrils were comprised of a truncated form of sAA containing the first 77 N-terminal amino acids (residues 1 to 77).⁴¹ No evidence of apolipoproteins AI and AII or immunoglobulin light chain has been found during immunohistochemical examination and liquid chromatography-coupled mass spectrometry of the amyloid extracted from these mice. In addition, the organ distribution of the disease was visualized through whole-body single-photon emission computed tomography (SPECT imaging) by using the amyloidophilic protein serum amyloid P component (SAP) as a tracer;^17,18,48,49 however, quantitative analysis of AA deposition from high-resolution (‘single-pinhole’) SPECT data was not possible.Recently, we have noted that several of our H2/huIL-6 mice exhibited a phenotype indicative of severe amyloidosis at as early as 3 to 5 mo of age. Here we present imaging-based case studies of 2 kindred animals that became moribund at approximately 5 mo of age. SPECT images for which iodinated SAP was used as a tracer revealed hepatosplenic AA amyloid deposits, which were quantified by using a novel image-based approach and were of sufficiently high resolution to discriminate the amyloid-laden red pulp from the amyloid-free lymphoid follicles of the spleen.     

Discrimination of lesion removal of N-methylpurine-DNA glycosylase revealed by a potent neutralizing monoclonal antibody

N-Methylpurine-DNA glycosylase (MPG), a ubiquitous DNA repair enzyme, initiates excision repair of several N-alkylpurine adducts, induced by alkylating chemotherapeutics, and deaminated and lipid peroxidation-induced purine adducts. We have generated monoclonal antibodies (moAbs) against human MPG. Twelve independent hybridoma clones were characterized, which, except 520-16A, are identical based on epitope exclusion assay. Four moAbs, including 520-2A, 520-3A, 520-16A, and 520-26A, have high affinity (K(D) approximately 0.3-1.6nM), and their subtypes were IgG(2a), IgG(1), IgG(2a), and IgG(2b), respectively. moAb 520-3A recognizes the sequence (52)AQAPCPRERCLGPP(66)T, an epitope exclusively present in the N-terminal extension of human MPG. We found that moAb 520-3A significantly inhibited MPG's enzymatic activity towards different substrates, such as hypoxanthine, 1,N(6)ethenoadenine and methylated bases, which represent different classes of DNA damage, however, with different efficiencies. Real-time binding experiments using surface plasmon resonance (SPR) spectroscopy showed that the pronounced inhibition of activity was not in the substrate-binding step. Single turnover kinetics (STO) revealed that the inhibition was at the catalytic step. Since we found that this antibody has an epitope in the N-terminal tail, the latter appears to have an important role in substrate discrimination, however, with a differential effect on different substrates.