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Biomedical subjects

M J McCall

Publications and source records attributed to M J McCall.

At least 37 records · Page 2Linked to original sources
PubMed1990

Metabolism of indium chelates attached to monoclonal antibody: minimal transchelation of indium from benzyl-EDTA chelate in vivo.

The metabolism of radiolabeled antibodies is important for radioimmunoimaging and therapy. The loss of indium-111 (111In) from the chelate can pose problems in imaging and increases the radiation dose to normal tissues. We have evaluated the loss in vivo of 111In from Lym-1-benzyl-EDTA-111In (an antibody conjugated with isothiocyanato-benzyl-EDTA) in normal mice. A monoclonal antibody (CHA 255) that binds to benzyl-EDTA-indium chelates, but not to other forms of indium, was used to measure the percent of 111In remaining in the chelate. Four days after injection, 97.4 +/- 2.2% of the 111In in the liver was still in the benzyl-EDTA chelate, as was 99.4 +/- 0.7% of the 111In in the urine, and 99.1 +/- 0.7% of the 111In in the blood. Studies in vitro indicate that a benzyl-EDTA-111In-antibody-chelate conjugate is more stable in human serum than a benzyl-DTPA-111In conjugate, and that both benzyl-chelate conjugates are much more stable than an unsubstituted DTPA conjugate.

Animals↗
PubMed1990

Yttrium-90-labeled monoclonal antibody for therapy: labeling by a new macrocyclic bifunctional chelating agent.

Yttrium-90 (90Y) is a promising radiometal for therapy of cancer due to its high-energy beta emission and a physical half-life of 2.67 days. Bifunctional chelating agents based on DTPA cyclic anhydride or EDTA do not form Y(III) complexes that are stable under physiologic conditions. A new macrocyclic bifunctional chelating agent based on 1,4,7,10-tetraazacylododecane-N,N',N",N"'-tetraacetic acid (DOTA) forms a stable Y(III) complex. It was converted to p-bromoacetamidobenzyl-DOTA (BAD), and conjugated to monoclonal antibody Lym-1 via 2-iminothiolane, either as the free ligand or as the 88Y chelate. Stability studies of Lym-1-2IT-BAD-88Y in human serum in vitro showed no measurable loss of Y(III) from the ligand over a 25-day period. In Raji-tumored mice, tumor uptake was 16.8% of the injected dose per gram of tissue on Day 3. The bone uptake was 2.0, 3.6, and 2.1% injected dose per gram of tissue on Day 1, 3, and 5, respectively. The biodistribution of the control 88Y-citrate demonstrated continuous increase in bone uptake from 13.8% injected dose per gram on Day 1 to 24.9% injected dose per gram on Day 4.

Animals↗
PubMed1990

Macrocyclic chelates of radiometals for diagnosis and therapy.

Monoclonal antibody technology allows the specificity of an antibody for its antigen to be used in targeting cancer cells. Stable attachment of metal ions to antibodies by means of 'bifunctional' chelating agents can add the nuclear, physical and chemical properties of the metallic elements to these target-selective proteins. The conjugation of metals--particularly radionuclides--to monoclonal antibodies results in agents for radioimmunotherapy and other medical applications. Chelators that can hold radiometals with high stability under physiological conditions are essential to avoid excessive radiation damage to non-target cells. Derivatives of polyazamacrocycles (bearing a C-substituted functional group for antibody attachment) can exhibit remarkable kinetic inertness. We have developed a new synthetic route these macrocycles via peptide synthesis and intramolecular tosylamide ring closure. Incubation of the yttrium complex of 2-p-nitrobenzyl-1,4,7,10-tetraazacyclododecane-N,N1N",N'"-te traacetic acid (nitrobenzyl-DOTA) for 18 days in serum results in loss of so little yttrium from the complex (less than 0.5%) that the rate of loss cannot be measured under these conditions. In animal models, conjugates of this chelate with monoclonal antibodies show much lower levels of yttrium in the bone than are found with DTPA chelates prepared from the cyclic anhydride. The rates of loss of indium and cobalt from nitrobenzyl-DOTA in serum are slower than from previously studied chelates. Preliminary clinical imaging studies of 111In-labeled monoclonal antibody conjugates of DOTA show highly encouraging results.

Antibodies, Monoclonal↗
PubMed1989

Effect of mass of 111In-benzyl-EDTA monoclonal antibody on hepatic uptake and processing in mice.

In patients, the pharmacokinetic behavior of murine monoclonal antibodies has been observed to vary with the amount of antibody administered. It has been suggested that this reflects human recognition of the foreign mouse protein. We have found that the amount of antibody administered also influenced pharmacokinetic behavior when murine monoclonal antibody was administered to mice. p-Isothiocyanatobenzyl-EDTA, a new chelator which forms complexes with 111In that are stable in vivo, was conjugated to Lym-1, a murine anti-Burkitt's lymphoma monoclonal antibody. The pharmacokinetics of two doses (20 and 0.2 micrograms) of the 111In labeled radiopharmaceutical were studied in non-tumor bearing BALB/c mice. About 20% (0.04 microgram) of the 0.2-microgram dose, compared with 8% (1.6 micrograms) of the 20-micrograms dose, was found in the liver at 48 h after injection. Both doses demonstrated a biological half-life of approximately 120 h. At least 75% of the 111In was excreted by the kidneys, and essentially all 111In in the urine remained chelated by the EDTA portion of p-isothiocyanatobenzyl-EDTA. From these observations of a dose dependent uptake of this radiopharmaceutical by the liver we conclude that there is a recognition phenomenon in mice for this murine monoclonal antibody.

Animals↗
PubMed1989

Effect of different linkages between chelates and monoclonal antibodies on levels of radioactivity in the liver.

After injection of radiometal labeled antibodies, the radionuclide accumulates in the liver. This might be altered by a metabolizable linkage between metal chelate and antibody. Four benzyl-EDTA chelating agents were synthesized and conjugated to mouse monoclonal antibody Lym-1. Liver uptake of 111In in nontumored mice 72 h after injection was 2.2, 13.4, 7.6 and 20% for disulfide, thioether, thiourea or peptide linkages, respectively. 111In excreted in the urine was still in the benzyl-EDTA chelate form, as shown by binding to a specific anti-chelate antibody.

Animals↗
PubMed1989

Nonuniform retinal expansion during the formation of the rabbit's visual streak: implications for the ontogeny of mammalian retinal topography.

We have studied the distribution of retinal ganglion cells (RGCs) which have been retrogradely labeled from massive bilateral injections of the enzyme horseradish peroxidase into the retino-recipient nuclei of foetal and postnatal albino rabbits aged from the 24th postconceptional day (24PCD) to adulthood. The number of labeled RGCs increases from about 447,000 on the 24PCD to a peak of about 525,000 on the 27PCD. From the 29PCD to birth (31/32PCD), the number of RGCs rapidly declines to about 375,000. During the next 20 d, the number of RGCs stabilizes at about 335,000. After the 51PCD, the number of RGCs gradually declines to the adult value of about 280,000. Retinal area steadily increases from about 40 mm2 on the 24PCD to about 500 mm2 in the adult, while RGC density decreases. However, the reduction in RGC density is nonuniform: RGC density in the visual streak drops from 18,600 RGCs mm2 on the 24PCD to 4700 RGCs/mm2 in the adult, whereas RGC densities at the superior and inferior edges of the retina decreases proportionally much more (from 9300 to 105 RGCs/mm2 and from 12,000 to 170 RGCs/mm2, respectively). As a result of this differential reduction in RGC density, the streak/inferior edge ratio changes from 1.6:1 to about 28:1. In the periods from the 24PCD to the 29PCD and from the 32PCD to adulthood, the proportional increases in the streak/superior edge and streak/inferior edge RGC density ratios are linearly related to the proportional increases in retinal area. However, between the 29PCD and 32PCD, the RGC density ratios increase at a greater rate than retinal area. We conclude that (1) the centro-peripheral difference in RGC density that is already present on the 24PCD might be attributable to differential RGC generation; (2) the redistribution of RGCs between the 24PCD and adulthood is mainly due to nonuniform expansion of the retina, with minimal expansion of the visual streak and maximal expansion at the superior and inferior retinal edges; and (3) a small component of the increase in the centro-peripheral RGC density ratio, which becomes apparent between the 29PCD and 32PCD, is probably due to differential RGC loss. We discuss the pattern of retinal expansion in the rabbit and the factors which might contribute to it.

Animals↗
PubMed1988

The intrinsic curvature of DNA in solution.

We propose a detailed quantitative scheme for explaining the anomalous electrophoretic mobility in polyacrylamide gels of repeating sequence DNA. We assume that such DNA adopts a superhelical configuration in these circumstances, and migrates less quickly than straight DNA of the same length because it can only pass through larger holes. The retardation is maximal when the length of the DNA reaches one superhelical turn, but is less for shorter pieces. We attribute the curvature of the superhelix to different angles of roll at each kind of dinucleotide step, i.e. an opening up of an angle by an increased separation on the minor-groove side. The main effect is due to a difference of about 3 degrees in roll values between AA/TT and other steps, together with a difference of about 1 degree in the angle of helical twist: we deduce these values explicitly from some of the available data on gel-running. The scheme involves a simple calculation of the superhelical parameters for any given repeating sequence, and it gives a good correlation with all of the available data. We argue that these same base-step angular parameters are also consistent with observations from X-ray diffraction of crystallized oligomers, and particularly with the recent data on CGCA6GCG from Nelson et al. We are concerned here with the intrinsic curvature of unconstrained DNA, as distinct from the curvature of DNA in association with protein molecules; and this paper represents a first attempt at an absolute determination.

Adenine↗
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

Peak density and distribution of ganglion cells in the retinae of microchiropteran bats: implications for visual acuity.

We have estimated the total number, distribution and peak density of retinal ganglion cells (RGCs) in retinal wholemounts of several species of microchiropteran (echolocating) bats. The estimates are based on counts of Nissl-stained, presumed RGCs. The total number of presumed RGCs varies among the species: from about 4,500 in Rhinolophus rouxi to about 120,000 in Macroderma gigas. In addition, in two species (Nyctophilus gouldi and M. gigas), the estimates are based on counts of positively identified RGCs retrogradely labelled with the enzyme horseradish peroxidase injected into the retinorecipient nuclei. In these two species, the numbers and distributions of retrogradely labelled RGCs and Nissl-stained presumed RGCs are very similar. In all six species studied, the peak-density regions of presumed (or positively identified) RGCs are located in the inferotemporal retinae, and the RGC isodensity lines tend to be horizontally elongated. However, the RGC densities in the high-density regions are only 2-4 times greater than those in the low-density regions in the superior retinae. The somal sizes of RGCs vary from 5 to 16 micron in diameter and are unimodally distributed. There is no indication of the existence of distinct morphological classes of RGCs. The axial lengths of microchiropteran eyes vary from 1.8 mm in R. rouxi to 7.0 mm in M. gigas. For all species the posterior nodal distance (PND) was assumed to be 0.52 of the axial length of the eye. This assumption is based on the analysis of published data concerning schematic eyes of nocturnal vertebrates. These derived values of the PNDs allowed us to calculate the retinal magnification factors and the number of RGCs per degree of visual angle. From these, the upper limits of visual acuity were derived on the basis of the assumptions of the sampling theorem. The estimated upper limits of visual acuity of the six species of echolocating bats vary from about 0.35 cycles/degree in R. rouxi to about 2 cycles/degree in M. gigas. This range is quite similar to the range of visual acuities in murid rodents.

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

Structural analysis of a reconstituted DNA containing three histone octamers and histone H5.

Previous work has shown that DNA and the histone proteins will combine to form structures of a complex, yet definite nature. Here, we describe three experiments aimed at a better understanding of the interactions of DNA with the histone octamer and with histone H5. First, there has been some question as to whether the methylation of DNA could influence its folding about the histone octamer. To address this point, we reconstituted the histone octamer onto a 440 base-pair DNA of defined sequence at various levels of cytosine methylation, and also onto the unmethylated DNA. The reconstituted structures were probed by digestion with two different enzymes, micrococcal nuclease and DNase I. All samples were found to contain what appear to be three histone octamers, bound in close proximity on the 440 base-pair DNA. The cutting patterns of micrococcal nuclease and DNase I remain the same in all cases, even if the DNA has been extensively methylated. The results show, therefore, that methylation has little, or no, influence on the folding of this particular DNA about the histone octamer. Second, there has been concern as to whether the base sequence of DNA could determine its folding in a long molecule containing several nucleosomes, just as it does within any single, isolated nucleosome core. In order to deal with this problem, we cut the 440 base-pair DNA into three short fragments, each of nucleosomal length; we reconstituted each separately with the histone octamer; and then we digested the reconstituted complexes with DNase I for comparison with similar data from the intact 440 base-pair molecule. The results show that the folding of this DNA is influenced strongly by its base sequence, both in the three short fragments and in the long molecule. The rotational setting of the DNA within each of the three short fragments is as predicted from a computer algorithm, which measures its homology to 177 known examples of nucleosome core DNA. The rotational setting of the DNA in the 440 base-pair molecule remains the same as in two of the three short fragments, but changes slightly in a third case, apparently because of steric requirements when the nucleosomes pack closely against one another. Finally, there has been little direct evidence of where histone H5 binds within a DNA-octamer complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1987

Differential retinal growth appears to be the primary factor producing the ganglion cell density gradient in the rat.

We have studied the distribution of retinal ganglion cells (RGCs) that had been retrogradely labelled from bilateral injections of horseradish peroxidase into the retino-recipient nuclei of albino rats aged from the 22nd postconceptional day (22PCD-day of birth) to adulthood. During the period in which most (85%) of the naturally occurring RGC loss takes place (22-26 PCD) the distribution of RGCs remains almost uniform. Between the 26 and 32PCD (11th postnatal day), the peak RGC density decreases by only 20% while the RGC density at the superior retinal periphery decreases by 80%. In the same period a centro-peripheral RGC density difference of 4:1 becomes apparent. We have interpreted these changes to be due to a phase of rapid differential retinal growth (with more growth occurring at the retinal periphery). Thereafter the reduction in RGC density (and presumably retinal growth) is more uniform resulting by adulthood in a centro-peripheral RGC density ratio of 5:1.

Aging↗
PubMed1987

Changes in the numbers of retinal ganglion cells and optic nerve axons in the developing albino rabbit.

In albino rabbits aged from the 16th postconceptional day (16PCD) to adulthood, the number of axons in the optic nerves were estimated from sample areas totalling 1-12% of the cross-sectional area of the nerve. On the 16PCD there are about 20,000 axons in the optic stalk. The number of axons in the retrobulbar part of the optic nerve reaches a peak value of 766,000 on the 23PCD, and then decreases to about 350,000 by the 32PCD (the day of birth). The number of axons does not change between the 32PCD and 50PCD, but thereafter it slowly decreases, reaching the adult number (294,000) by the 84PCD. A similar trend is apparent in pigmented animals. Thus, on the 25PCD there are 736,000 axons in the retrobulbar part of the optic nerve and the number decreases to 428,000 by the 31PCD. In the adult pigmented rabbit there are 280,000 axons in the optic nerve. In animals younger than the 32PCD, growth cones are present, and the number of axons in the prechiasmal part of the optic nerve was 8-22% lower than in the retrobulbar part of the same nerve. These observations suggest that there is a continued outgrowth of axons from the eye towards the target nuclei. By the 32PCD, the numbers of axons in the retrobulbar and prechiasmal parts of the nerve were very similar, suggesting that by this age all axons had reached the chiasm. The numbers of retinal ganglion cells (RGCs) labelled by massive injections of horseradish peroxidase into the retino-recipient nuclei were estimated in albino rabbits aged from the 24PCD to adulthood. RGCs were counted in evenly spaced sample areas totalling 4-11% of the retinal area. On the 24PCD, the number of labelled RGCs (500,000) was lower than the number of axons in the optic nerve (probably because not all RGC axons had reached their target nuclei by this age). However, by the 27PCD the number of labelled RGCs (550,000) was very similar to the number of prechiasmal axons (568,000). At all ages thereafter, the numbers of both RGCs and axons were very similar, with adult RGC numbers (about 291,000) being reached by the 85PCD. We conclude that axon loss in the rabbit optic nerve after the 27PCD is almost certainly due to the elimination (presumably death) of the parent RGCs, and we suggest that RGC death is also the most likely cause of axon loss prior to the 27PCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
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

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

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↗