Non-transferrin iron uptake by HeLa cells cultured in serum-free media with different iron sources

HeLa cells cultured in defined serum-free media supplied with iron wither in the form of diferric transferrin (transferrin-dependent cells), ferric citrate at 500 micromol/l (high-iron dependent cells) or ferric citrate at 5 micromol/l (low-iron dependent cells) accumulate iron from ferric citrate in different ways. The uptake rate in transferrin-dependent cells is always much lower in the other two lines. In all three, the uptake rate rises almost linearly with the concentration of iron up to 10 micromol/l. In high-iron dependent cells, the uptake of radiolabelled iron is suppressed by a 100-fold excess of the iron complex, whereas this same excess stimulates iron uptake in the other two lines. The same concentrations of pure citrate completely inhibit iron uptake by all three types of cell. Only high-iron dependent cells take up citrate at measurable and reproducible rates. These rates are independent on the presence of iron, and the uptake is inhibited by an unlabelled surplus. The pH-dependence of iron uptake in high-iron dependent cells is also different from that of the other cells. Low-iron dependent cells transferred to medium containing 500 micromol/l iron show increased uptake rates within 3 to 7 h, and after overnight maintenance in this medium they acquire the uptake characteristics of high-iron dependent cells. The special characteristics of iron uptake by high-iron dependent cells are paralleled by low binding activity of iron-regulatory protein to iron-responsive elements of RNA. We conclude that low-iron dependent cells maintain their iron supply from the culture medium by unspecific uptake of oligomeric complexes, while cells in media with a high content of low-molecular weight iron induce a specific uptake system which might have a protective function.

Removal of lactoferrin from plasma is mediated by binding to low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor and transport to endosomes

LDL receptor related protein (LRP) is a ubiquitously expressed cell surface receptor that binds, at least in vitro, a plethora of ligands among them alpha 2-macroglobulin and lactoferrin (Lf). The function of LRP in internalisation and distribution of ligands within cellular metabolism is still unclear. We here investigated by combined ligand- and immunoblotting the participation of LRP/alpha 2MR and its associated protein (RAP) in receptor mediated endocytosis of Lf into rat liver. We found LRP highly enriched in sucrose density gradient fractions around density 1.10 g/ml, previously characterised as endosomal fractions. RAP was concentrated in distinct fractions around density 1.14 g/ml. This separation of RAP from LRP/alpha 2MR is physiologically meaningful as RAP avidly binds to LRP/alpha 2MR and by that shuts off all ligand binding function. In endosomal fractions we found one single binding protein for 125I-labelled Lf. With a specific anti LRP/alpha 2MR antibody and ligand blotting with 125I-labelled RAP this endosomal Lf binding site was verified to be LRP/alpha 2MR. Endosomes did not bind labelled Lf when prepared from rats that received an intravenous injection of Lf (20 mg per animal) 20 min prior to preparation. Surprisingly we immunodetected Lf in these endosomes at a position around 600 kDa, comigrating with LRP/alpha 2MR. We determined Lf binding to be optimal at pH 5.8, what led us to suggest the existence of a very stable LF-LRP/alpha 2MR complex in endosomes. These data support the idea of effective binding of Lf at pH as found in inflamed tissue environment where Lf is reported to be involved in leukocyte mediated inflammation regulation.

Inhibition of thrombin and SFLLR-peptide stimulation of platelet aggregation, phospholipase A2 and Na+/H+ exchange by a thrombin receptor antagonist

A thrombin receptor has been described that is activated by thrombin cleavage generating a new N-terminus. The newly exposed SFLLR-containing "tethered-ligand" then activates the receptor. In these studies, we used 3-mercapto-propionyl-Phe-Cha-Cha-Arg-Lys-Pro-Asn- Asp-Lys-amide (Mpapeptide) as a thrombin receptor antagonist. This compound was capable of preventing both thrombin- and SFLLR-peptide-induced platelet aggregation with little effect on collagen-induced platelet aggregation. It also prevented thrombin- and SFLLRNP-induced calcium mobilization with little effect on thromboxane receptor-activated platelet Ca2+ mobilization. Platelet membrane GTPase could be activated by peptides that activated the thrombin receptor, and the thrombin receptor antagonist also prevented receptor-stimulated GTPase activity. Platelet phospholipase A2 (PLA2) activity (measured as the release of radiolabeled arachidonic acid) and Na+/H+ exchange activation were stimulated by alpha-thrombin and by SFLLR-containing peptides. Activation of both processes with low concentrations of thrombin required thrombin's anion-binding exosite, as they were not activated by similar concentrations of gamma-thrombin, and the alpha- and zeta-thrombin activation was blocked by peptides mimicking the C-terminal region of hirudin. Stimulation of PLA2 and Na+/H+ exchange by both thrombin and SFLLR-containing peptides was inhibited by the thrombin receptor antagonist Mpa-peptide. These results support the hypothesis that thrombin stimulation of PLA2 activity and Na+/H+ exchange occurs via activation of the thrombin tethered-ligand receptor. Moreover, these data are consistent with the tethered-ligand receptor mediating most actions elicited by low concentrations of alpha-thrombin involved in human platelet activation.

Transport of vitamin C in animal and human cells

The transport systems of animal and human tissues for vitamin C are reviewed with respect to their properties. It emerges that pure diffusion plays only a very minor role while a variety of more or less specific transporters is found on cellular membranes. Although most tissues prefer the reduced ascorbate over the oxidized dehydroascorbic acid and have high-affinity transporters for it, there are several examples for the reversed situation. Special attention is given to similarity or identity with glucose transporters, especially the GLUT-1 and the sodium-dependent intestinal and renal transporters, and to the very widespread dependence of ascorbate transport on sodium ions. The significance of ascorbate transport for vitamin C-requiring and nonrequiring species as well as alterations in states of disease can be seen from ample experimental evidence.

Interaction of a doxorubicin-transferrin conjugate with isolated transferrin receptors

It is shown that transferrin-doxorubicin conjugates bind to isolated transferrin receptors. The receptors were isolated from human full-term placenta by solubilization of trophoblast plasma membranes with the nonionic detergent C12E8 and then by affinity chromatography on a diferric transferrin-coupled Sepharose CL-4B column. The binding affinity of such conjugate was similar to that of transferrin. Dissociation of conjugate from the isolated receptor occurred with time-dependent kinetics similar to those of transferrin when the experimental conditions mimicking the physiological steps of transferrin recycling were consecutively applied. These results support the idea that a) binding of such conjugates is primarily governed by the interaction between the transferrin part of the conjugates and the transferrin receptor, and b) it is not the transferrin receptor itself which participates in the putative secondary interaction between the receptor-bound conjugates and plasma membrane.

Monodehydroascorbate reductase activity in the surface membrane of leukemic cells. Characterization by a ferricyanide-driven redox cycle

A transmembrane monodehydroascorbate reductase activity with a high affinity in the subpicomolar concentration range of the free radical can be measured at the surface of erythroleukemic cells using a ferricyanide-driven redox cycle. The activity is dependent on the membrane potential and can therefore only be found in intact cells. It is independent of the glutathione content of the cells. Thenoyltrifluoroacetone is an efficient inhibitor of the activity, whereas ouabain, monensin and tetraethylammonium show no effect. Cells are able to generate ascorbate from dehydroascorbic acid. This explains why both forms of vitamin C show practically the same affinity for the redox cycle but why it does not drive the redox cycle by itself because it is much slower and is not inhibited by thenoyltrifluoroacetone. The reductase activity is independent of the degree of differentiation of the leukemic cells.

No enzymatic activities are necessary for the stabilization of ascorbic acid by K-562 cells

We disprove that living cells stabilize ascorbate by the activity of a trans plasma membrane semidehydroascorbate reductase. The two processes show different specificities for both substrate and inhibitor. Not only cells but also cell-conditioned buffers stabilize ascorbate as long as compounds with molecular weights above 10 kDa are not removed. The effect is most probably due to chelation of traces of transition metals.

NAD(P)H:ferric iron reductase in endosomal membranes from rat liver

Endosomes isolated from rat liver, characterized by high enrichment of endocytosed ligand after liver perfusion, displayed ferric reductase activity with higher affinity for NADH (1.7 microM) than for NADPH (7.1 microM). The ferric-NTA complex was reduced by NADH with a molar stoichiometry of 2:1 for the iron complex to pyridine nucleotide ratio under near anaerobic conditions. Superoxide radicals were not apparently involved in the reduction of ferric iron under these conditions, despite measurable generation of superoxide under aerobic atmosphere. The reaction was inhibited by sulfhydryl reagents, was heat labile, and may account for reduction of ferric to ferrous iron during hepatic iron uptake from transferrin or from other iron sources.

GM-CSF: modulation of biochemical and cytotoxic effects of tiazofurin in HL-60 cells

Cytokines, such as granulocyte macrophage colony stimulating factor (GM-CSF) or interleukin-3 (IL-3) recruit quiescent cells into the cell cycle and sensitize these cells towards cell cycle specific chemotherapeutic agents. We examined the in vitro effects of GM-CSF on HL-60 cells and tested its modulatory influence on biochemical and cytotoxic effects seen with tiazofurin, a potent and specific inhibitor of IMP dehydrogenase. Incubation of HL-60 cells with 500 U/ml GM-CSF for 4 d enhanced cell proliferation, which was accompanied by a significant increase in IMP dehydrogenase activity (from 2.22 in control cells to 3.70 nmol/mg/h in cells pretreated with GM-CSF). When HL-60 cells were incubated with 100 microM tiazofurin for 2 h, intracellular GTP decreased to 46% of untreated control cells. In HL-60 cells pretreated with GM-CSF, GTP pools decreased to 38% of control after incubation with tiazofurin which is 69% of the predicted value for additive effect. The MTT chemosensitivity assay yielded significantly decreased IC50 values for tiazofurin in HL-60 cells, preincubated with GM-CSF (IC50 decreased from 13 microM to 10 microM). Therefore our results suggest that combination therapy with GM-CSF and tiazofurin may be beneficial for the treatment of refractory leukaemia patients.

Hypolipidemic activity of HOE-402 is mediated by stimulation of the LDL receptor pathway

HOE-402 (4-amino-2-[4,4-dimethyl-2-oxo-1-imidazolidinyl]-pyrimidine-5-N- [trifluoromethylphenyl]-carboxamide-monohydrochloride) has been shown to exhibit hypolipidemic action in heterozygous Watanabe heritable hyperlipidemic rabbits. In all animals, elevated cholesterol levels were reduced to normal (from 3.0 to 1.5 mmol/L) after 3 weeks of HOE-402 treatment. This was due entirely to reduction of low density lipoprotein (LDL) cholesterol and was paralleled by accelerated removal of plasma 125I-LDL. This reduction of LDL levels was not found in homozygous LDL receptor-defective animals, emphasizing the necessity of a functional LDL receptor system for the hypolipidemic action. The effect of HOE-402 on LDL receptor activity in the cultured hepatoma cell line HepG2 was also determined. When cells were incubated with plasma from treated animals (containing cholesterol 1.5 mmol/L and HOE-402 80 ng/mL), high-affinity cell-surface binding sites for LDL were induced more than threefold, as shown by Scatchard analysis of cell-surface binding data. Induction of the LDL receptor was detectable after 6 hours and was 300% after 18 hours. This induction was specific for LDL, as 125I-transferrin and [59Fe]transferrin were internalized normally in HOE-402-treated cells. The increase of LDL receptor protein was related to induced LDL receptor mRNA levels (400%), as shown by quantification of Northern blotting experiments. These findings suggest that HOE-402 mediated its hypolipidemic action mainly via the LDL receptor pathway. It enhanced mRNA levels for LDL receptor, hence increasing its synthesis, which subsequently resulted in reduced plasma LDL levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of conjugation of doxorubicin to transferrin on the iron uptake by K562 cells via receptor-mediated endocytosis

The influence of conjugation of doxorubicin to holotransferrin on the receptor-mediated endocytosis of and on the iron uptake from transferrin was studied using K562 cells. 125I-labelled transferrin and doxorubicin-transferrin conjugates were used in the binding, dissociation, and ligand-exchange experiments at 0 degree C, and 59Fe,125I-labelled (double-labelled) ligands were used in the endocytosis, iron uptake, and recycling experiments at 37 degrees C. The binding affinity of conjugates was about half of that of transferrin. Binding of 125I-labelled ligands was blocked by both unlabelled ligands to the same degree, however, it was not blocked at all by an 8000-fold excess of doxorubicin. After saturation bindings, slightly more 125I-labelled conjugates dissociated from the surface of cells than transferrin. Exchange of 125I-labelled ligands for unlabelled ligands resulted in different EC50 values (defined as the concentration of unlabelled ligand at which half as much radioligand is exchanged for unlabelled ligand as would be exchanged at infinitely high concentration of unlabelled ligand under similar assay conditions). While transferrin exchanged transferrin with an EC50 value close to the binding affinity, conjugates exchanged conjugates with much lower efficiency. The heterolog exchange experiments yielded EC50 values inbetween the two extrema. For studying iron uptake, K562 cells were loaded with the double-labelled ligands either at 37 degrees C (endosome-loading only) or at 0 degree C (surface-loading only). Results obtained for the endocytosis of, the iron uptake from, and the recycling of double-labelled ligands indicate that (a) the rate of iron uptake is smaller from conjugates than from transferrin, (b) there are at least two parallel recycling processes for both ligand.receptor complexes, and (c) each time constant characterizing the different steps of iron uptake via receptor-mediated endocytosis is smaller for conjugates than for transferrin (or, the half times characterizing the different steps are higher for conjugates than for transferrin). Endocytosis and iron uptake were unaffected by free doxorubicin (12.5 microM) or colchicine (1 mM). Benzyl alcohol (30 mM) slowed down the rate of both endocytosis and iron uptake, while dithiothreitol (5 mM) decreased the rate of iron uptake and increased the rate of endocytosis. N-Ethylmaleimide (1 mM) completely stopped both endocytosis and iron uptake. The results suggest that the binding of conjugates to the surface of cells is governed by the binding of the transferrin part of conjugates to the transferrin receptor. However, conjugation of doxorubicin to transferrin seems to influence all properties of transferrin.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding and function of a potent new thromboxane receptor antagonist, BMS 180,291, in human platelets

Binding and function of BMS 180,291 ([(+)1S-(1 alpha,2 alpha,3 alpha,4 alpha)]-2-[[3-[4-[(n-pentylamino)carbonyl]-2-oxazolyl]-7- oxabicyclo[2.2.1] hept-2-yl]methyl]benzenepropanoic acid]) in human platelets was examined. Kinetic determination of [3H]BMS 180,291 binding produced ligand-receptor association and dissociation rates of 1.4 x 10(7) +/- 0.2 M-1 x min-1 (n = 5) and 0.04 +/- 0.005 min-1 (n = 5), respectively. The resultant Kd was 3.1 +/- 1.1 nM (n = 5). Saturation binding analysis in platelet membranes was consistent with a single class of [3H]BMS 180,291 binding sites with a Kd of 3.6 +/- 0.19 nM (n = 4) and a binding site maxima (Bmax) of 2099.1 +/- 70.3 fmol/mg of protein (n = 4). Specific [3H]BMS 180,291 binding was inhibited by thromboxane A2/endoperoxide receptor antagonists and agonists with a rank order of potency of: BMS 180,291 > or = SQ 29,548 = I-BOP race 15-(1 alpha,2 beta(5Z), 3 alpha(1E,3S),4 alpha) d7-[3-(3-hydroxy-4-(p-iodophenoxy)-1-butenyl)-7- oxabicyclo[2.2.1]hept-2-yl]5-heptenoic acid) > or = BM 13,505 > or = SQ 30,741 = U 44,609 > U 46,619 >> BM 13,177. Prostaglandin E2 and prostacyclin did not appreciably inhibit the specific binding of [3H]BMS 180,291. BMS 180,291 (10 nM-5 microM) shifted the I-BOP-induced platelet shape change curve to the right in a parallel manner without reduction of the maximal response (KB = 13 +/- 3.5 nM; pA2 = 8 +/- 0.2; slope = -1.0 +/- 0.05), whereas 30 nM drug decreased the maximal I-BOP-induced platelet aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of doxorubicin-conjugated transferrin to U937 cells

Binding of transferrin (Trf) and its doxorubicin-conjugated forms (Conj) to U937 cells at 0 degrees C were compared using 125I-labelled Trf or Conj. The apparent binding affinity (Ka) of Conj to the surface of U937 cells was (1.9 +/- 0.4).10(8) l/mol; it is about 40% of that of Trf [(5.0 +/- 1.2).10(8) l/mol]. Binding of 125I-labelled ligands was blocked by the unlabelled ligands to the same degree, however, it was not blocked by a great excess of doxorubicin (Dox). N-ethylmaleimide caused about 10% inhibition while dithiothreitol was without effect. Dissociation of 125I-labelled ligands in the presence of different concentrations of unlabelled ligands (Trf and Conj in the all 4 variations) resulted in different R50 values (the concentration of the unlabelled ligand where 50% of the radiolabelled ligand was released). While Trf displaced Trf with an R50 value close to the binding affinity, Conj displacement by Conj occurred with much lower efficiency. The heterolog displacement experiments yielded R50 values in between the two extrema. These results suggest that 1) binding of Conj to the surface of cells is governed by the binding of the Trf part of Conj to the transferrin receptor, 2) -SH groups are not involved in the binding, and 3) a second interaction between the Conj and some constituent(s) of the plasma membrane may modify the binding of Conj in comparison to that of Trf.

Cytotoxicity of a transferrin-adriamycin conjugate to anthracycline-resistant cells

Conjugates of adriamycin coupled to transferrin by glutaraldehyde are cytotoxic to human promyelocytic (HL-60) and erythroleukemic (K562) cells. Growth inhibition of adriamycin-sensitive cells, as evaluated by thymidine incorporation and the MTT-assay, was higher for conjugates than for free adriamycin. The cytotoxicity toward adriamycin-resistant K562 and HL-60 cells was 3-fold and more than 10-fold higher, respectively, for the transferrin-adriamycin conjugate than for the free drug. The effect of the conjugate was dependent on its adriamycin content, i.e., on its conjugation number.

Lactoferrin specifically inhibits endocytosis of chylomicron remnants but not alpha-macroglobulin

Our recently found nonlipoprotein inhibitor of chylomicron remnant uptake, lactoferrin, has been investigated in vivo and in vitro. Lipoprotein lipase extracted triglycerides from chylomicrons, doubly labeled with [3H]retinol/[14C]oleate, in the presence of lactoferrin normally. The subsequent uptake of remnants into liver was retarded considerably. In the intact rat, chylomicron remnants (CRs), predominantly labeled in the apoB48 moiety by 125I, were excluded from the hepatic endosomal compartment in the presence of lactoferrin as shown in subcellular fractionation studies of rat livers. In tissue culture, internalization of [125I]chylomicron remnants was inhibited in the presence of 14 pM lactoferrin by 70%. Upon removal of lactoferrin, internalization was rapidly restored. Protease digestion eliminated the inhibitory effect completely. Modification of arginine residues with cyclohexanedione reversibly removed the inhibitory potency of lactoferrin. We located by molecular modeling an alpha-helical segment in lactoferrin on the exposed surface of the molecule containing the sequence Arg-X-X-Arg-Lys-X-Arg, which resembles the receptor recognition structure in apolipoprotein E (apoE). This firmly established ligand correspondence with apoE, the candidate ligand for CR recognition by the receptor. Finally, the postulated second function of low density lipoprotein receptor-related protein, uptake of alpha-2-macroglobulin (alpha 2M) was found to be distinct from lipoprotein binding, since lactoferrin inhibited CR but not alpha 2M internalization. In addition, CR uptake was not affected by alpha 2M. We conclude that if a bifunctional receptor were to operate, its diverse functions were exerted by independently operating substructures. The results of our in vivo and cell culture experiments are, however, entirely compatible with the existence of two receptors as well.

Ascorbate-mediated transmembrane electron transport and ascorbate uptake in leukemic cell lines are two different processes

Transmembrane reduction of extracellular oxidants by K562 and U937 leukemic cells was stimulated by catalytic amounts of ascorbate or dehydroascorbate. This stimulation was not due to transport of ascorbate in different redox states in and out of the cells. The membrane redox cycle was strictly dependent on the presence of the cells at every stage, and showed high affinity for ascorbate with simple linear kinetics. Metabolic inhibitors and sulfhydryl reagents inhibited this stimulation. Ascorbate uptake was also dependent on oxidation, but in a very different manner and with much lower affinity for ascorbate. The uptake was non-saturable in the concentration range used. There was some release of ascorbate from the cells, which cannot account for an appreciable part of the reduction of extracellular electron acceptors.

Uptake and endocytic pathway of transferrin and iron in perfused rat liver

Uptake and distribution of transferrin and iron in perfused rat liver are dependent on perfusion temperature, time and uptake affinity. Transferrin passes at least two different compartments on its receptor-mediated recycling pathway, which are separable by centrifugation in a shallow Nycodenz gradient. Perfusion at lowered temperature (16 degrees C) is sufficient for internalization of transferrin and iron. Passage of radiolabelled iron to other than endosomal compartments as well as recycling of labelled transferrin are largely suppressed at this perfusion temperature, as much less is released by further perfusion with unlabelled transferrin than at 4 degrees C where the ligand is largely washed off the surface, or 37 degrees C, where the recycling pathway is operating. But also at lowered temperature only a part of the iron in endosomal fractions can be assigned to transferrin. A considerable part of the total uptake of transferrin and iron can be attributed to low-affinity mechanisms even at very low transferrin concentrations. Transferrin receptors are concentrated in endosomal fractions in comparison to fractions representing different plasma membrane domains of the liver. Endosomal fractions specifically display detergent-activated NADH-acceptor oxidoreductase which may be part of the iron uptake system.

Targeting, dosimetry, and radioimmunotherapy of B-cell lymphomas with iodine-131-labeled LL2 monoclonal antibody

Sixteen patients with non-Hodgkin's lymphoma were infused with 6.2 to 58.2 mCi (0.2 to 3.9 mg) doses of radioactive iodine (131I)-labeled LL2 immunoglobulin G (IgG) or F(ab')2, in order to study antibody distribution, pharmacokinetics, dosimetry, toxicity, tumor targeting, and therapy. LL2 is a murine IgG2a monoclonal antibody (MAb) reactive with B cells and non-Hodgkin's B-cell lymphoma. In a series of five assessable therapy patients, doses as small as 30 mCi 131I-LL2 IgG or F(ab')2 resulted in tumor responses (two partial remissions, two mixed and minor responses, and one no response), while one patient receiving diagnostic doses as low as 6.2 mCi showed a partial remission for 1 year and a complete remission after a second low radiation dose. No acute toxicities were noted, and only myelotoxicity accompanied therapeutic doses, with grade IV marrow toxicity seen in three of seven patients receiving total doses of about 50 mCi. Dosimetry calculations showed spleen and tumor dose rules of about 4.6 cGy/mCi, which was three to four times the dose to other organs. Despite the administration of relatively low doses of LL2 (0.2 to 3.9 mg), 82% of 60 known extrasplenic lymphoma sites were imaged. Serum clearance showed an average distribution half-life (T1/2) of 2.1 hours and an elimination T1/2 of 32.0 hours. The average total-body clearance T1/2 was 43 to 45 hours. LL2's antigenic target does not appear to be shed in high amounts into the circulation. Three of eight patients having at least two injections showed a human antimouse antibody response. These patients may have been presensitized to animal protein. An interesting observation in this study was the marked drop in circulating B lymphocytes after the administration of radioiodinated LL2 or anticarcinoembryonic antigen MAbs, suggesting that this is a nonspecific radiation effect and not necessarily related to the binding of MAb to normal B cells.

Plasma membrane Fe2-transferrin reductase and iron uptake in K562 cells are not directly related

Receptor-mediated endocytosis and recycling of transferrin is partly inhibited by the ferrous iron chelator bipyridine, which almost completely blocks iron uptake. Bipyridine causes iron release at the cell surface, but inhibition of iron uptake is also due to a blockage of its passage through the endosomal membrane. The rate of release of iron to bipyridine is decreased by the competing electron acceptor ferricyanide and by amiloride, but not by iron uptake inhibiting acidotropic amines. Transferrin reduction at the plasma membrane may be artificially induced by presence of a ferrous chelator and caused by low-affinity transmembrane NAD(P)H oxidoreductase.

Murine monoclonal antibodies against carcinoembryonic antigen: immunological, pharmacokinetic, and targeting properties in humans

We have examined three 131I-labeled murine monoclonal antibodies (MAbs) against carcinoembryonic antigen (CEA), NP-2, NP-3, and NP-4, after i.v. injection in patients with diverse cancers. Although the MAbs had a similar tumor-targeting ability, several important features were discovered that have led us to the selection of one of these MAbs for further clinical evaluation. We found that it is important to evaluate MAbs with a high immunoreactivity. For example, the MAb NP-2 was used initially in patients with an immunoreactivity between 35 and 50%. Although the tumor-imaging properties of this MAb compared favorably with the affinity-purified, goat anti-CEA antibody that we used previously, further purification of NP-2 to an immunoreactivity greater than 70% uncovered a previously unknown cross-reactivity with human granulocytes. It was also discovered that the MAbs differed in their ability to complex with CEA in the blood. Plasma samples were analyzed by gel filtration at 1 or 24 h after injection. The formation of complexes with circulating CEA was dependent on the CEA:MAb ratio in the blood. NP-3 complexed to a greater degree with CEA than NP-4, but NP-2 did not complex with CEA even at CEA:NP-2 ratios of 55 to 1. NP-3 commonly showed enhanced uptake in the colon by external scintigraphy, and examination of the radioactivity in the stool showed that most of the radioactivity was associated with whole IgG and large-sized fragments of NP-3. We also compared the rate of elimination of radioactivity from the blood for all of the MAbs and compared the clearance of NP-3 to NP-4 at three different ranges of MAb protein doses (less than 1.0 mg, 1 to 5 mg, and 5 to 20 mg). The blood clearance rate for NP-3 was fastest among the other MAbs at protein doses exceeding 1.0 mg. Patients given less than 1.0 mg of NP-4 had a significantly (P less than 0.005) shorter elimination half-life than patients given more than 1.0 mg of NP-4. By virtue of NP-4's good targeting properties in patients and its limited complexation with circulating CEA, it was selected as the MAb of choice for CEA tumor imaging.

Clinical studies of cancer radioimmunodetection with carcinoembryonic antigen monoclonal antibody fragments labeled with 123I or 99mTc

Seventy-three patients with diverse cancers containing carcinoembryonic antigen received 123I-labeled anti-carcinoembryonic antigen monoclonal antibody F(ab')2 fragment [38 patients], 99mTc-labeled anti-carcinoembryonic antigen monoclonal antibody Fab' fragment [23 patients], or both reagents at different times [6 patients] for evaluation of antibody targeting and imaging [radioimmunodetection (RAID)], using planar and single-photon emission computed tomography. The results indicated that antibody fragments are preferred for early tumor imaging (within 24 h). Rapid targeting and clearance from blood and normal organs of the antibody fragments (blood median t1/2 elimination of 26.5 and 13.2 h for the F(ab')2 and Fab' fragments respectively) permitted the use of short-lived radionuclides, such as 123I (13.3 h) and 99mTc (6 h), and confirmed that selective antibody accretion in tumors occurred very soon after administration, such as between 2 and 5 h. Scan interpretations at 24 h for the 123I-labeled F(ab')2 and at 2-5 h for the 99mTc-labeled Fab' revealed overall sensitivities, on a tumor site basis, of 95.9 and 94.9%, respectively. On a site basis, the overall accuracies were 94.2 and 93.8% for the 123I and 99mTc immunoconjugates, respectively. In the 6 patients studied with both radioimmunoconjugates, a high concordance in detection was found. Both imaging agents also revealed a high number of putatively new tumor sites not disclosed by other radiological methods at the time of the RAID studies, of which 40.0 and 20.5% were subsequently confirmed as tumor for the 123I and 99mTc agents, respectively, within an 11-month follow-up period. This represented 24 proven occult tumor sites in 19 patients given the 123I-immunoconjugate and 16 proven occult tumor sites in 9 patients receiving the 99mTc agent. The new lesions were found up to 17 and 7 months earlier for 123I-RAID and 99mTc-RAID, respectively, than with other detection methods. The smallest tumors identified were below 0.5 cm, especially with the 99mTc immunoconjugate and single-photon emission computed tomography imaging. The findings of this study confirm previous evidence that RAID is a safe and a potentially useful new method of cancer detection. Despite the excellent results with the 123I-F(ab')2 antibody fragment, its poor availability and high cost limit its clinical use. Therefore, the 99mTc agent, which is made by an instant, 1-step, 1-vial, direct labeling method, appears to be the method of choice for rapid and accurate detection of cancer by RAID.

[Prophylactic antibiotic therapy using oxacillin (Bristopen) in pediatric orthopedic surgery]

The aim of this study was to evaluate the efficiency of oxacillin in the prophylaxis of bone infections in orthopaedic surgery in children. Staphylococcus is the usual pathogen in orthopaedics. This is the reason of our choice: oxacillin. 420 patients are included: 195 control patients did not receive any prophylactic antibiotherapy; 225 patients received oxacillin. The oxacillin treatment started at anaesthetic induction and was carried on for 72 hours. In the control group, 7 superficial and 4 deep infections were observed, while a single superficial infection was noted in the oxacillin-treated group. This easy and inexpensive prophylactic treatment gave excellent results. We think that it should be systematically administered in orthopedic surgery to ensure as little complication as possible to the child.