Biomedical subjects

C F Meares

Publications and source records attributed to C F Meares.

At least 91 records · Page 5Linked to original sources

PubMed1988

Chelate radiochemistry: cleavable linkers lead to altered levels of radioactivity in the liver.

Bifunctional chelating agents based on benzyl-EDTA bind 111In stably under physiological conditions. Available evidence indicates that the indium is cleared from the body in its original chelated form. Initial studies of a series of antibody-chelate conjugates joined by different molecular linkers show that the 111In biodistribution is strongly dependent on the nature of the linker. Linkers containing thiourea, thioether, peptide, ester, and disulfide groups were compared in healthy BALB/c mice. The disulfide linker led to particularly rapid clearance of 111In from the liver, and from the whole body. Results did not appear to be as favorable as those currently obtainable with reversible radiolabelling techniques, in which the 111In chelate is bound non-covalently to the antibody and a competing hapten is used to displace it when desired. However, the concept of a metabolically cleavable linker is sound. Further exploration is needed to produce a conjugate with the desired properties.

Animals↗

PubMed1988

Copper-67-labeled monoclonal antibody Lym-1, a potential radiopharmaceutical for cancer therapy: labeling and biodistribution in RAJI tumored mice.

Copper-67 (67Cu) is one of the most promising radiometals for radioimmunotherapy because of its 61.5 hr physical half-life, abundant beta particles, and gamma emissions suitable for imaging. However, 67Cu is readily transferred from the usual chelates of EDTA or DTPA to albumen. We developed a new macrocycle (6-p-nitrobenzyl-TETA) to chelate copper. Bifunctional chelating agent p-bromoacetamidobenzyl-TETA was conjugated to Lym-1, a monoclonal antibody against human B cell lymphoma, without significantly altering its immunoreactivity. This conjugate was stably labeled with 67Cu under conditions chosen to optimize the yield of a high specific activity radiopharmaceutical. The biodistribution in RAJI tumor bearing mice demonstrated significant tumor uptake (14.7% ID per gram) and extended residence time (120 hr) in contrast to normal organs. After 24 hr, radioactivity was continuously cleared from all tissues except the tumor. This study suggests 67Cu labeled Lym-1 to be a promising radiopharmaceutical for potential use for radioimmunotherapy of B cell lymphoma.

Animals↗

PubMed1988

Pre-targeted immunoscintigraphy of murine tumors with indium-111-labeled bifunctional haptens.

A method of tumor imaging utilizing the nonspecific accumulation of antibody through leaky capillaries is described, in which the antibody and the radiolabel are administered separately. Nonradioactive antibody is given first (pre-targeted), and allowed adequate time to reach maximum tumor concentration. Depending on the antibody, this may take several days. At the time of maximum tumor concentration of nonradioactive antibody, the blood is quickly cleared of excess circulating nonradioactive antibody using a special i.v. "chase". The radiolabel then is given and imaging done in 1 to 3 hr. The use of short lived tracers (hours) to image antibodies that localize slowly (days) in-vivo is made possible by this method.

Animals↗

PubMed1987

The interaction of anions with native and phenylglyoxal-modified human serum transferrin.

The interaction of various anions with human serum transferrin was investigated due to the concomitant binding of iron and a synergistic anion to form the transferrin-anion-iron complex. Two tetrahedral oxyanion oxidizing agents, periodate and permanganate, were found to partially inactivate transferrin when used at equimolar ratios of oxidizing agent to protein active sites. Hypochlorite, a strong oxidizing agent with little structural similarity to periodate and permanganate, had little effect on iron-binding activity when used at similar low molar ratios of reagent to transferrin active sites. Transferrin treated with a 3:1 molar ratio of periodate or permanganate to active sites lost 74 or 67% of its iron-binding capacity, respectively. The composition of the buffer affected the extent of transferrin inactivation by periodate and permanganate; for example, the extent of inactivation by periodate was threefold greater in a borate buffer than in a phosphate buffer. Comparative oxidations in buffer systems suggest the following order of affinity of three buffer anions for the apotransferrin metal-binding center: phosphate greater than bicarbonate greater than borate. The interaction of phosphate ions with the iron-transferrin complex was also examined due to the increased susceptibility to periodate inactivation of iron-saturated transferrin in phosphate buffer (M. H. Penner, R. B. Yamasaki, D. T. Osuga, D. R. Babin, C. F. Meares, and R. E. Feeney (1983) Arch. Biochem. Biophys. 225, 740-747). The apparent destabilization of the iron-transferrin complex in phosphate buffer was found to be due to the competitive removal of iron by phosphate from the iron-protein complex. We found that phenylglyoxal-modified Fe-transferrin, with no loss of bound iron, was much more resistant to iron removal by phosphate and other competitive chelators.

Aldehydes↗

PubMed1987

Comparative serum stability of radiochelates for antibody radiopharmaceuticals.

Serum incubation of monoclonal antibodies chelate labeled by DTPA, benzyl-EDTA and benzyl-TETA with 111In, 57Co, and 67Cu demonstrated marked differences in their stability. In serum, 111In-benzyl-EDTA-antibody was more stable than 111In-DTPA-antibody. Cobalt-57 or 67Cu chelated antibody were less stable than either 111In chelated antibody; 67Cu was only firmly attached to the antibody as 67Cu-benzyl-TETA-antibody. The relative stability of the radiometal chelated antibodies was paralleled by the relative stability in serum of the radiometal chelates themselves. These in vitro studies suggest that in vivo behavior of metal chelates exposed to a complex protein environment cannot be predicted by classical equilibrium constants.

Antibodies, Monoclonal↗

PubMed1986

RNA contacts subunits IIo and IIc in HeLa RNA polymerase II transcription complexes.

Subunits of RNA polymerase II that come into contact with nascent RNA transcripts have been determined by photoaffinity labeling. Transcription was carried out in a cell-free extract in the presence of 4-thio-UTP, and utilized the major late promoter of adenovirus-2 DNA. The transcript length was limited by inclusion of the chain terminator 3'-O-methyl-GTP. Transcription complexes were irradiated with near-UV light (lambda greater than 300 nm) to specifically photoactivate 4-thio-uridine. After photocross-linking, radiolabeled proteins were separated by electrophoresis, blotted onto nitrocellulose, and visualized by autoradiography. Specific photoaffinity labeling of enzyme subunits IIo and IIc was observed. In some experiments, radiolabeled IIa was also detected. Based on the level of photoaffinity labeling of subunits IIo and IIa, relative to their concentration in the transcription reaction, the transcriptional activity of RNA polymerase IIO appears to be greater than 10 times that of IIA. RNA attached to subunits IIo and IIc was estimated to be 16-40 nucleotides in length, whereas RNA attached to subunit IIa was approximately 27-40 nucleotides long. Photoaffinity labeling was sensitive to alpha-amanitin, and required DNA containing an RNA polymerase II promoter.

Adenoviridae↗

PubMed1986

Accessibility of the leading end of ribonucleic acid in transcription complexes.

A photoaffinity-protection technique has been developed to study the accessibility of the leading (5') end of nascent RNA as it passes through the transcription complex formed by Escherichia coli RNA polymerase and phage T7 DNA. The macromolecules contacted by the leading (5') end of the growing RNA chain in the transcription complex have been determined previously by photoaffinity labeling experiments using aryl azides attached to the leading end of nascent RNA [Hanna, M. M., & Meares, C. F. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 4238-4242]. By using thiols to reduce accessible photoprobes, we have modified the photoaffinity technique so that it tests the accessibility of the leading end of nascent RNA to small molecules in solution, as a function of RNA chain length. We examined in detail RNA molecules containing 11-50 nucleotides, whose 5' ends label the beta and beta' enzyme subunits with good yield. The thiol's accessibility to the leading end of each transcript was determined by comparing the RNAs cross-linked to beta beta' in thiol-treated samples to controls not treated with thiol. Incubation with 1 mM dithiothreitol for 5 min reduced approximately 36% of the 5'-azides on RNAs 11-13 bases long and approximately 43% on RNAs 28-37 bases long but practically none of the 5'-azides on RNAs 40-43 bases long. Also notable was the reduction of 34 +/- 1% of the 5'-azides on RNA 12 bases long but only 14 +/- 2% on the 14-base RNA; on the T7 A1 promoter, the leading end of the transcript diverges from the DNA template when the chain is between 12 and 14 bases long.

DNA, Viral↗

PubMed1986

The sigma subunit of RNA polymerase contacts the leading ends of transcripts 9-13 bases long on the lambda PR promoter but not on T7 A1.

The sigma subunit of RNA polymerase is responsible for specific initiation of RNA synthesis at promoter sites on DNA. sigma dissociates shortly after initiation. Photoaffinity-labeling experiments performed on transcription complexes with two different DNA promoters, which have highly homologous control sequences upstream from the transcribed regions, have revealed that the sigma subunit of RNA polymerase is contacted by the 5' ends of quite different lengths of nascent RNA in each transcription complex. On the other hand, the labeling of subunits beta beta' is quite similar for both promoters, and the alpha subunit is not labeled in either case. The results of transcription experiments on the phage lambda PR promoter show that sigma can be photoaffinity labeled by RNA chains that are 9-13 nucleotides long and thus remains associated with the core enzyme at least to that point. But on the A1 promoter of phage T7 DNA, photoaffinity labeling of sigma ceases with the trinucleotide. Thus release of sigma from the vicinity of nascent RNA depends not merely on the length but on the sequence of the transcript. For the T7 A1 promoter, sigma labeling ceases while the leading end of the RNA is still base paired to the DNA template; thus, it appears that there is at least one site on the enzyme that interacts with the growing transcript/template hybrid, in a sequence-dependent way, to effect sigma release.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophage lambda↗

PubMed1986

Metabolizable 111In chelate conjugated anti-idiotype monoclonal antibody for radioimmunodetection of lymphoma in mice.

The relative biological properties of 111In-labeled monoclonal antibodies (MoAb) coupled with a conventional bifunctional chelate (BC) and a new, enzyme metabolizable, bifunctional chelate (BCM) were investigated. A rat IgG2a MoAb against idiotype from a mouse B-cell lymphoma was utilized. Mice bearing B-cell lymphomas in the subcutaneous tissues of the flank were given IV-injections of labeled MoAb and imaged or killed for organ counting at 24 h or 48 h. Rat anti-dinitrophenyl IgG2a MoAb and non-specific polyclonal mouse IgG were used as controls. Compared to BC, the use of BCM resulted in a substantial decrease in blood background activity, a shorter biological half-life and an increase in tumor to blood ratio at the expense of a moderate decrease in absolute tumor uptake. The versatile chemistry of these C-1 substituted bifunctional chelates provides a variety of possible enzyme cleavable moieties for further investigation.

Animals↗

PubMed1986

Chelating agents for the binding of metal ions to antibodies.

The development and applications of bifunctional chelating agents are reviewed, with emphasis on the preparation of radiolabeled monoclonal antibodies suitable for use in vivo. Major principles and practical aspects of the chemical procedures are outlined, and new results of interest for future work are described.

Antibodies, Monoclonal↗

PubMed1986

Serum stability of 67Cu chelates: comparison with 111In and 57Co.

Simple chelates and chelate conjugated monoclonal antibodies labeled with 111In, 57Co and 67Cu demonstrate marked differences in stability when exposed to a serum environment. Among these radiometals, on DTPA, the order of stability is 111In greater than 57Co much greater than 67Cu. On benzyl-EDTA, the order of stability is 111In congruent to 57Co much greater than 67Cu. Among those investigated, the only serum stable 67Cu chelate found was 67Cu-TETA. The order of stability observed for 57Co vs 67Cu is contrary to published equilibrium constants. These in vitro studies suggest that the in vivo behavior of metal chelates exposed to a complex molecular environment may not be predicted by classically determined equilibrium constants.

Antibodies, Monoclonal↗

PubMed1986

Monoclonal antibodies as reversible equilibrium carriers of radiopharmaceuticals.

We have prepared monoclonal antibodies (MoAbs) with the specific ability to bind metal chelates such as 111In benzyl EDTA. One, 10, 50 and 100 micrograms MoAb CHA255 Kb = 4 X 10E9 was complexed with 111In BLEDTA II, BLEDTA IV, and benzyl EDTA and injected i.v. in Balb/c mice with KHJJ tumor. The biological half-life by whole body counting was profoundly altered for all three compounds; from minutes to hours with 10 micrograms; to days with 100 micrograms. Tumor uptake increased 50 fold at 24 h with increasing MoAb but satisfactory tumor concentrations (3% per g) and tumor/blood ratios (1.8:1) were obtained with an amount equivalent to 7 mg for a human. Blood level and whole body activity were decreased 30-50% within 3 h or i.v. injection of a "flushing" dose of unlabeled indium benzyl EDTA, increasing tumor/blood ratios to 50:1.

Animals↗

PubMed1986

Distribution of ions around DNA, probed by energy transfer.

Measurements of the effect of DNA on rates of bimolecular energy transfer between ions provide a direct indication of how cations cluster in regions near DNA and how anions are repelled from the same regions. Energy transfer from luminescent lanthanide ions (in the "rapid-diffusion" limit) probes collision frequencies that are dependent on the equilibrium spatial distributions of ions. The addition of 1 mM DNA (phosphate) to a 2 mM salt solution increases the overall collision frequency between monovalent cations by a factor of 6 +/- 1.5; it increases the divalent-monovalent cation collision frequency by a factor of 29 +/- 3; and it decreases the divalent cation-monovalent anion collision frequency by a factor of 0.24 +/- 0.03. Comparisons are made with the changes in collision frequencies predicted by several different theoretical descriptions of ion distributions. The closest agreement with experimental results for monovalent ions at 1 mM DNA is obtained with a static accessibility-modified discrete charge calculation, based on a detailed molecular model of B-DNA. At high DNA concentration (10 mM), the best results are obtained by numerical solutions of the Poisson-Boltzmann equation for a "soft-rod" model of DNA. Poisson-Boltzmann calculations for a "hard-rod" model greatly overestimate the effects of DNA on collision frequencies, as does a calculation based on counterion-condensation theory.

Animals↗

PubMed1986

Metal decomposition rates of 111In-DTPA and EDTA conjugates of monoclonal antibodies in vivo.

We have studied the metal chelate decomposition rates in vivo in both 111In-labelled benzyl EDTA and DTPA (bicyclic anhydride) conjugates of monoclonal anti-IAk IgG2a with identical Ka = 1 X 10(11)M-1 in both Ag+ve and Ag-ve mice. Twenty mu Ci was given i.v. and whole body counting done immediately and daily for 10 days, with six to eight mice in each group. Half the mice in each group received i.p. injections of 5.0 mg CaNa2 EDTA chase (Versenate) to facilitate urinary excretion of free 111In. 50% of control 111In-citrate remained at nine days but only 8% with chase. No significant loss of 111In with chase occurred with C1 substituted EDTA conjugates. A 19% increase in excretion was demonstrated with the chase in mice given DTPA conjugates (1.9% per day). While this will not interfere with radioimmunoimaging up to 24 h after injection, waiting periods of a week or longer will produce significant background of free 111In in the reticuloendothelial system, RES. 111In-EDTA stability was important in accurate metabolic rate measurements of anti-IAk; T1/2 = 7.0 days in Ag-ve mice, T1/2 = 9.3 days in Ag-ve mice. It will be important to measure the in vivo rates for each new metal complex, especially those intended for therapy such as Y-90.

Animals↗

PubMed1985

Photo-induced nicking of deoxyribonucleic acid by ruthenium(II)-bleomycin in the presence of air.

A new metallobleomycin, ruthenium(II)-bleomycin A2 was prepared. When irradiated at 366 nm the ruthenium complex (1-10 microM) was found to break a 121-base pair DNA restriction fragment at specific sites (usually the pyrimidine residues located at the 3'-side of guanine). Care was taken to rule out complications due to the presence of trace amounts of iron. Photo-induced damage by cobalt-bleomycin in the presence of light, and redox-mediated damage by bleomycin and iron produced DNA cleavage at sites similar to ruthenium-bleomycin. In contrast to cobalt-bleomycin, ruthenium-bleomycin required oxygen as well as light to cause significant damage to DNA.

Air↗

PubMed1985

Diffusion-enhanced lanthanide energy-transfer study of DNA-bound cobalt(III) bleomycins: comparisons of accessibility and electrostatic potential with DNA complexes of ethidium and acridine orange.

Energy transfer in the "rapid-diffusion" limit reflects the equilibrium properties of a donor-acceptor system. Rates of energy transfer from freely diffusing terbium chelates to DNA-binding chromophores change dramatically when DNA is added; energy transfer from an electrically neutral chelate is reduced because the energy acceptor becomes partially buried in DNA, while energy transfer from a positive chelate is increased because of electrostatic attraction. The rate constants for energy transfer to DNA-bound chromophores from a positively charged terbium chelate, relative to those from a neutral chelate, were used to estimate the following values for the electrostatic potential near the surface of each DNA-bound acceptor at 298 K in the presence of 1.0 mM added salt (in units of -e/kT): acridine orange, 4.54 +/- 0.11; ethidium, 4.66 +/- 0.07; green Co(III) bleomycin A2, 4.06 +/- 0.11; orange Co(III) bleomycin A2, 3.11 +/- 0.10. Smaller numbers indicate less negative potentials; these can be due to a combination of (1) positive charge on the chromophore, (2) location of the chromophore [particularly Co(III) bleomycin] away from the DNA phosphates, and/or (3) separation of DNA phosphate negative charges by an intercalator. The magnitudes of the individual rate constants indicate that all the DNA-bound chromophores can be directly encountered by the terbium probes. Energy-transfer rate constants from a neutral terbium chelate to DNA-bound and free acceptors can provide a measure of the accessibility of the terbium probe to each bound chromophore. The ratios of these rate constants were as follows: acridine orange, 0.17 +/- 0.01; ethidium, 0.27 +/- 0.02; green form of Co(III) bleomycin A2, 0.48 +/- 0.06; orange form of Co(III) bleomycin A2, 0.71 +/- 0.06. These results are consistent with the probable differences in binding mechanisms for the intercalating chromophores (ethidium and acridine orange) as compared to the Co(III) bleomycins (in which the relevant chromophores are nonintercalating metal centers). In addition, all the results imply that the green Co(III) bleomycin chromophore binds closer to DNA than the orange; this provides a first step toward understanding the structural basis for the different biological properties of these metallobleomycins. Control experiments and theoretical considerations necessary to establish the validity of the results are also presented.

Acridine Orange↗

PubMed1985

Interaction of oxidized chicken ovotransferrin with chicken embryo red blood cells.

Iron-saturated chicken ovotransferrin was chemically oxidized with NaIO4, converting 50% of its methionine residues to their sulfoxide derivatives while maintaining 95% of its iron-binding activity. The oxidized chicken ovotransferrin was able to deliver iron to the chicken embryo red blood cell for heme synthesis. From competition experiments, oxidized diferric chicken ovotransferrin was estimated to be approx. 65% as efficient as unmodified diferric chicken ovotransferrin at competing with diferric (55Fe2) chicken ovotransferrin for the iron-donating sites of the chicken embryo red blood cells. The presence of apo chicken ovotransferrin preparations (native or oxidized) in the incubation medium had little effect on the rate of iron incorporation into heme from diferric chicken ovotransferrin. The effect of modifying the periodate-susceptible methionine residues in chicken ovotransferrin was small but significant. These methionine residues do not appear critical for the interaction of chicken ovotransferrin with the chicken embryo red blood cell receptors, the incorporation of chicken ovotransferrin into the cell, or the release of iron from chicken ovotransferrin for heme synthesis.

Animals↗

PubMed1985

Copper chelates as probes of biological systems: stable copper complexes with a macrocyclic bifunctional chelating agent.

Monoclonal antibodies tagged with chelated metal ions have numerous potential applications. Here we report the synthesis of a new "bifunctional" metal chelator, 6(p-bromoacetamidobenzyl)-1,4,8,11-tetraazacyclotetradecane- N,N',N",N"' -tetraacetic acid, which can be covalently attached to proteins and which binds copper stably in human serum under physiological conditions. In contrast, other reagents based on ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid rapidly lose copper to serum albumin under the same conditions.

Chelating Agents↗