The preparation of DTPA-coupled antibodies radiolabeled with metallic radionuclides: an improved method

Preparation, characterisation and tumour targeting of cross-linked divalent and trivalent anti-tumour Fab' fragments

The monoclonal anti-CEA antibody, A5B7, has previously been administered to patients for radioimmunotherapy (RIT). Long circulation time and the formation of an immune response have limited therapeutic success in the clinic. Antibody fragments can be used to reduce the in vivo circulation time, but the best combination of fragment and radioisotope to use for therapy is far from clear. In this study we have compared the biodistribution of A5B7 IgG and F(ab')2 with chemically cross-linked divalent (DFM) and trivalent (TFM) A5B7 Fab' fragments in nude mice bearing human colorectal tumour xenografts. The cross-linkers were designed to allow site-specific labelling using yttrium 90 (90Y), a high-energy beta-emitter. We have also compared the above antibody forms conjugated to both 131I and 90Y. Both DFM and TFM were fully immunoreactive and remained intact after radiolabelling and incubation in serum at 37 degrees C for 24 h. Biodistribution results showed similar tumour uptake levels and an identical blood clearance pattern for F(ab')2 and DFM with high tumour-blood ratios generated in each case. However, unacceptably high kidney accumulation for both F(ab')2 and DFM and elevated splenic uptake of DFM labelled with 90Y was observed. Kinetic analysis of antigen binding revealed that DFM had the fastest association rate (kass = 1.6 x 10(5) Ms-1) of the antibody forms, perhaps owing to increased flexibility of the cross-linker. This advantage implies that DFM may be more suitable than F(ab')2 radiolabelled with 131I for RIT. TFM cleared from the blood significantly faster than A5B7 IgG when labelled with both 131I and 90Y, producing an improved therapeutic tumour-blood ratio. Kidney accumulation was not observed for [90Y]TFM, but a slightly higher splenic uptake was observed that may indicate reticuloendothelial system (RES) uptake. Overall, tumour uptake was higher for 90Y-labelled antibodies than for 131I-labelled antibodies. Because of the faster clearance, it should be possible to administer a higher total dose of 90Y-labelled TFM than IgG, which is attractive for RIT. Both A5B7 DFM and TFM, therefore, show favourable properties compared with their parent antibody forms.

The kinetics of MHC class I and class II expression in rat renal allografts

We have used in vivo localization of radiolabeled antibodies in a rat renal transplant model to compare the level of induction of major histocompatibility complex (MHC) class I and class II molecules in grafts undergoing rejection with grafts in which rejection was modified by cyclosporine (CsA). MHC class II expression increased in rejecting grafts, peaking on day 4, whereas a later rise in CsA-treated grafts was noted. The use of donor-specific antibodies demonstrated that this was due, in part, to a rise in class II of donor origin. No major differences in MHC class I levels were noted between the two groups until after day 4, when very little antibody localization was seen in the rejecting group. Our results suggest that therapeutic doses of CsA may not prevent the upregulation of class II that occurs during rejection, and that levels of class II are not of prognostic value in kidney transplantation.

Modification of antibody isoelectric point affects biodistribution of 111-indium-labeled antibody

We evaluated the influence of changes in charge on the biodistribution of 111In-labeled purified rabbit antihuman serum albumin (R-HSA) IgG conjugated to diethylenetriaminepentaacetic dianhydride (DTPA). Optimization of isoelectric point (pI) may influence the biodistribution profile, especially retention in vital organs, which ultimately affects radioimmunoimaging. Experiments were designed to modify the pI of R-HSA by conjugating various molar ratios of DTPA (DTPA:R-HSA ratios 5:1 to 100:1). The pI of the conjugates was determined by isoelectricfocusing (IEF). 111In-labeled DTPA:R-HSA with known pI range was injected intraperitoneally into BALB/c mice to evaluate biodistribution. There was a proportional relationship between the molar ratio of DTPA to R-HSA IgG and the number of DTPA substituted. Molar ratios of 5, 10, 20, 50 and 100 gave, on average, 2.0, 3.6, 5.1, 9.5 and 16.0 DTPA per R-HSA IgG, respectively. An anodal shift in the pI of 111In-labeled R-HSA IgG was noted with increased number of DTPA conjugation. Biodistribution studies at both 4 and 24 h showed sequential increase in the liver activity with increasing number of DTPA per antibody, whereas colon and small intestine showed a decrease in the activity at 4 h. The organ-specific increase (e.g., liver) or decrease (e.g., colon and small intestine) in the activity may depend on a critical balance of charge of a particular organ and its interaction with the amount of negative charge carried by the antibody conjugate. The results suggest that pI optimized 111In-labeled antibody could be used to increase or decrease colon and hepatic retention for more efficient radioimmunoimaging of colon tumors and their hepatic metastasis.

Serial indium-111-labelled IgG biodistribution in rat Pneumocystis carinii pneumonia: a tool to monitor the course and severity of the infection

To study the effect of new therapeutic strategies, we developed an animal model to monitor the course and severity of experimental Pneumocystis carinii pneumonia (PCP) in rats. P. carinii density scores in Giemsa-stained impression smears were used to follow P. carinii load. Indium-111 labelled IgG scintigraphy and biodistribution, histology of paraffin-embedded tissue sections, lung/body weight (L/B wt) ratio and cell count and differentiation of broncho-alveolar lavage (BAL) fluid were used as parameters of host inflammatory response. Statistically significant differences in L/B wt ratio, number of neutrophils in BAL fluid, P. carinii density score, histological extent of inflammation and 111In-IgG accumulation in the lung were seen between the rats sacrificed at various time points. 111In-IgG accumulation in the lung correlated well with L/B wt ratio and P. carinii density score and correlated moderately with number of neutrophils in BAL fluid and with the histological extent of inflammation.

Radioimmunodetection of human leukemia with anti-interleukin-2 receptor antibody in severe combined immunodeficiency mice

Anti-Tac monoclonal antibody recognizes human interleukin-2 receptor, which is overexpressed in leukemic cells of most adult T-cell leukemia (ATL) patients. To examine the potency of anti-Tac for targeting of ATL, biodistributions of intravenously administered 125I- and 111In-labeled anti-Tac were examined in severe combined immunodeficiency (SCID) mice inoculated with ATL cells. Significant amounts of radiolabeled anti-Tac were found in the spleen and thymus. The trafficking of ATL cells in SCID mice was detected using 111In-oxine-labeled ATL cells. These results were coincident with the histologically confirmed infiltration of ATL cells. The radiolabeled anti-Tac seemed potent for targeting of ATL.

Regional comparison of tumor vascularity and permeability parameters measured by albumin-Gd-DTPA and Gd-DTPA

Sequential albumin-Gd-DTPA and Gd-DTPA dynamic enhancement studies were performed in an animal tumor model for the comparison of regional vascularity and permeability parameters measured by these two different sizes of contrast agents. The early albumin-Gd-DTPA enhancement arises from the vascular compartment, and the averaged signal enhancement derived from the first 3 to first 6 images postinjection can be reliably used to assess vascularity. The signal intensity in the images during the period of 5-10 min post-albumin-Gd-DTPA injection shows a steady linear variation. The intercept of the linear relationship is another indicator of the vascularity and the slope represents the tumor permeability to albumin-Gd-DTPA. The Gd-DTPA enhancement study was analyzed by a two-compartmental pharmacokinetic model to calculate the regional vascularity and permeability. The permeability parameters measured from albumin-Gd-DTPA and Gd-DTPA show an excellent correlation. The vascularity parameters measured from albumin-Gd-DTPA show good linear correlation with the low vascularity groups measured by Gd-DTPA, but show saturation for the high vascularity groups. The enhancement mechanisms for both contrast agents are discussed to relate the imaging parameters to the physiological variables.

Quantitation of slow drug release from an implantable and degradable gentamicin conjugate by in vivo magnetic resonance imaging

A biodegradable model hydrogel containing a covalently bound aminoglycoside in which drug release can be monitored by magnetic resonance imaging (MRI) in vivo was developed. The hydrogel consists of the bishydroxysuccinimide ester of polyethylene glycol disuccinate cross-linked albumin, to which gentamicin and Gd-diethylenetriaminepentaacetic acid are covalently attached in stochiometric quantities. MRI allowed us to depict the three-dimensional structure of implanted gels, to accurately calculate their volumes, and thus to calculate the concentration of hydrogel-bound gentamicin. The correlation coefficient for the concentration of released gentamicin and the hydrogel volume was 0.965. Free and hydrogel-released gentamicin conjugates had similar antibiotic efficacies when tested in microbiological agar diffusion assays. In vivo, hydrogel-released gentamicin had a longer half-life in plasma than unaltered gentamicin (5.6 versus 0.7 h), presumably because of residual bound polyethylene glycol residues. Hydrogel implants into rats resulted in a prolonged (7 to 10 days) release of gentamicin and a decreased 24-h mortality in mice infected with a lethal dose of Pseudomonas aeruginosa. The results indicate the feasibility of imaging and quantitating therapeutic drug concentrations in vivo by MRI.

Dissociation of indium from indium-111-labelled diethylene triamine penta-acetic acid conjugated non-specific polyclonal human immunoglobulin G in inflammatory foci

Several investigators have reported retention of indium-111 in infectious foci after intravenous injection of 111In-labelled immunoglobulin G (IgG). With this study we intended to test the hypothesis that, upon administration of 111In-diethylene triamine penta-acetic acid (DTPA-IgG), 111In is retained in the infectious foci after dissociation from IgG. Therefore we measured the tissue distribution of double-labelled 111In-DTPA-IgG-(carbon-14) in rats with a focal infection and compared the results with corresponding data for DTPA-IgG-(14C). DTPA-conjugated IgG was labelled with 111In via citrate transchelation. 111In-DTPA-IgG and DTPA-IgG were labelled with 14C through methylation. High-performance liquid chromatography (HPLC) and instant thin-layer chromatography analysis were performed to test the in vitro stability of the labelled proteins. Young Wistar rats with a Staphylococcus aureus infection of the left calf muscle were injected intravenously with 0.2 ml of a solution containing either 0.4 MBq 111In and 30 kBq 14C or 30 kBq 14C labelled to 80 micrograms IgG. Groups of five rats were sacrificed at 2, 6, 24, and 48 h. p.i. Activity uptake was determined for plasma, urine, abscess, muscle and various other tissues. Averages and standard deviations were calculated for groups of five rats. HPLC analysis was performed on plasma and urine samples taken up to 48 h p.i. The radiochemical purity of the IgG preparations was > 95%. The labelled preparations appeared stable in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of homing, proliferation, and infiltration sites of adult T cell leukemia cells in severe combined immunodeficiency mice using radiometric techniques

To clarify the mechanism of in vivo proliferation of adult T cell leukemia (ATL) cells, we examined the organ distribution of ATL-43T cell line cells derived from original leukemic cells in severe combined immunodeficiency (SCID) mice using radiometric techniques. First, we injected 111In-oxine-labeled ATL-43T cells into SCID and CB17 mice. On day 6, significant accumulation of radioactivity was found in the spleen and thymus of SCID mice (33.3 +/- 9.4 and 10.0 +/- 3.6% injected dose/g of tissue [%ID/g], respectively) in comparison with that in CB17 mice (19.1 +/- 2.5 and 3.7 +/- 0.9%ID/g, respectively). Next, we injected radiolabeled anti-Tac monoclonal antibody (MoAb) recognizing human interleukin-2 receptor (IL-2R) alpha chain or isotype-matched control MoAb RPC5 in SCID mice bearing ATL-43T cells 4 weeks after cell inoculation. The amounts of radioactivity found in the spleen and thymus of SCID mice injected with 125I-labeled anti-Tac MoAb (22.5 +/- 6.9 and 22.8 +/- 9.6 %ID/g, respectively) were significantly higher than those in the corresponding organs of SCID mice injected with 125I-labeled RPC5 MoAb (12.0 +/- 5.1 and 7.5 +/- 4.6 %ID/g, respectively). Similar results were obtained with 111In-labeled anti-Tac MoAb. These results were consistent with the histological findings of SCID mice bearing ATL-43T cells, indicating that ATL-43T cells infiltrated preferentially into the lymphoid organs, such as the spleen and thymus, and proliferated there. Thus, the radiometric techniques employed in this study were very useful to evaluate the proliferation sites of ATL-43T cells in SCID mice. Furthermore, this murine model could give us an opportunity to test the feasibility of therapeutic application of radiolabeled anti-Tac MoAb.

Problems of delivery of monoclonal antibodies. Pharmaceutical and pharmacokinetic solutions

Monoclonal antibodies to tumour-associated antigens have great theoretical potential for the specific targeting of radioactivity and anti-neoplastic agents to tumours. The clinical success of monoclonal antibody-based cancer diagnosis and therapy depends, however, on solving a number of pharmacokinetic delivery problems. These include: (i) slow elimination of monoclonal antibodies from the blood and poor vascular permeability; (ii) low and heterogeneous tumour uptake; (iii) cross-reactivity with normal tissues; (iv) metabolism of monoclonal antibody conjugates; and (v) immunogenicity of murine forms in humans. As a result of extensive pharmaceutical and pharmacokinetic research conducted over the past 10 to 15 years, several potential solutions to these delivery problems have been identified. Blood concentrations of antibody conjugates may be reduced through regional administration, the use of antibody fragments, interventional strategies and various pre-targeting techniques. Tumour uptake may be increased through administration of higher doses, or the use of agents to increase tumour vascular permeability. Tumour retention of antibody conjugates may be improved by inhibition of metabolism, by using more stable linkage chemistry. Alternatively, normal tissue retention may be decreased through the use of metabolisable chemical linkages inserted between the antibody and conjugated moiety. Very small antigen-binding fragments and peptides that exhibit improved tumour penetration and more rapid elimination from the blood and normal tissues have been prepared by genetic engineering techniques. Chimeric (mouse/human) and human monoclonal antibodies have been developed to circumvent the problem of immunogenicity. Future research will continue to be focused on improvements in the design of monoclonal antibodies for tumour targeting, with the ultimate goal of finally uncovering the 'magic bullet' envisioned by Paul Ehrlich almost a century ago.

Noninvasive imaging of E-selectin expression by activated endothelium in urate crystal-induced arthritis

OBJECTIVE

To assess the expression of the cytokine-inducible endothelial leukocyte adhesion molecule E-selectin during the evolution of urate crystal-induced arthritis, using a recently described radiolabeled monoclonal antibody (MAb) imaging technique.

METHODS

Monosodium urate (MSU) crystals and saline alone were injected respectively into the right (inflamed) and left (control) knees of 3 young pigs. Four hours later, 111In-labeled 1.2B6 F(ab')2 (anti-E-selectin MAb) and 125I-labeled MOPC 21 F(ab')2 (control MAb) were injected intravenously. Uptake of 1.2B6 in inflamed and control joints was assessed by scintigraphy 7 and 24 hours after intraarticular injection of MSU crystals. Immunohistochemistry studies and radioactivity counting of tissues were performed postmortem to confirm the observations from scintigraphy.

RESULTS

MAb 1.2B6 F(ab')2 scintigraphic images of the knees revealed a significantly increased uptake in the right (inflamed) knee at 7 and 24 hours postinjection, particularly over the joint space. These in vivo images were consistent with E-selectin expression in the inflamed tissue detected by immunohistochemistry and with radioactivity counts postmortem. The synovial localization ratio (inflamed:control synovium counts) was 25.4 +/- 9.7 (mean +/- SD) for the anti-E-selectin MAb compared with 2.5 +/- 0.9 for the control MAb (P < 0.05, by paired Student's t-test).

CONCLUSION

E-selectin is expressed by synovial endothelium during the evolution of urate crystal-induced arthritis and can be detected noninvasively using a radiolabeled MAb. This E-selectin imaging technique has considerable potential for the noninvasive assessment of endothelial activation in arthritis and other inflammatory rheumatic diseases.

Comparative biodistributions of indium-111-labelled macrocycle chimeric B72.3 antibody conjugates in tumour-bearing mice

A novel 111In ligand (a C-functionalised derivative of 1,4,7-triazacyclononanetriacetic acid), termed 9N3, was covalently attached to chimeric B72.3, labelled with 111In and compared with 111In-labelled chimeric B72.3 diethylenetriaminepentaacetic acid (DTPA) cyclic anhydride conjugate (cDTPA) and a C-linked derivative of DTPA (CT-DTPA) in athymic mice bearing human colon carcinoma xenografts. Significant differences in biodistribution were observed between 9N3 and cDTPA conjugates especially in the tumour uptake and blood, liver, femur and colon levels at 24, 48 and 144 h. Significantly higher tumour uptake was observed for 111In-cB72.3-9N3 compared with 111In-cB72.3-cDTPA at all time points. Radiolocalisation (RI) indices increased with time for the 9N3 conjugate but remained constant for the cDTPA conjugate. The biodistribution of 111In-labelled cB72.3-CT-DTPA was similar to that of 111In-labelled cB72.3-9N3 except for elevated kidney levels. A 12N4 macrocycle (a C-functionalised derivative of 1,4,7,10-tetraazacyclododecanetetraacetic acid) was also tested for its ability to chelate 111In and its biodistribution examined. Labelled conjugates with this macrocycle were more difficult to prepare in a stable form but gave a very similar biodistribution to the 9N3 macrocycle conjugate. Macrocycle-antibody conjugates of this type offer considerable promise for tumour imaging in patients.

90Y-labeled antibody uptake by human tumor xenografts and the effect of systemic administration of EDTA

PURPOSE

A human tumor xenograft model was used to compare the tumor and normal tissue uptake of a tumor-associated monoclonal antibody radiolabeled with 125I or 90Y.

METHODS AND MATERIALS

Nude mice bearing SC xenografts of the human colon adenocarcinoma, HT29, were injected with a mixture of 125I- and 90Y-DTPA-labeled AUA1 monoclonal antibody, which recognizes an antigen expressed on the surface of the tumor cells. In addition, the effect of systemic ethylenediaminetetraacetic acid (EDTA) administration on 90Y-labeled antibody clearance, tumor uptake of antibody and bone accumulation of 90Y was studied in a nude mouse model of intraperitoneal cancer.

RESULTS

Both the absolute amount (%id.g-1) and the tumor:normal tissue ratios were superior for the 90Y-labeled antibody, compared with the iodinated antibody, with the notable exception of bone. These results suggest that 90Y is a preferable isotope to iodine for radioimmunotherapy of solid masses, but that myelotoxicity, due to bone uptake of released 90Y, will limit the radiation dose which can be given when DTPA is used to chelate the 90Y. The 90Y-labeled antibody showed similar serum stability in vitro in the presence or absence of EDTA after incubation for up to 48 h. In vivo, urine excretion of 90Y was significantly enhanced in mice receiving daily injections of 20 mg EDTA for 3 days, commencing 2 h after intraperitoneal antibody administration, compared with control mice. There was no significant difference in the tumor uptake of 90Y-labeled antibody in EDTA-treated and control mice at any time-point up to 9 days postinjection. However, the bone levels of 90Y were significantly reduced in EDTA-treated mice at all times from 1 to 9 days.

CONCLUSION

Based on these results, it should be possible to increase the amount of 90Y-labeled antibody administered, by chelating the released 90Y with systemic EDTA to facilitate its excretion, without compromising tumor uptake of radiolabeled antibody.

Processing of antibody-radioisotope conjugates after binding to the surface of tumor cells

BACKGROUND

Previous experiments indicated that most antibodies binding to cell surface antigens are internalized gradually and degraded within lysosomes, with a half-life of degradation of approximately 1 day, for most antibodies. The research discussed in this article extended our studies to eight additional antibodies reacting with six different antigens, including three antigens anchored in the membrane by glycosyl-phosphatidylinositol. The authors also tested antibodies labeled with 111indium, as well as 125iodine, to determine whether different radiolabels would be processed differently.

METHODS

Antibodies were radiolabeled with 125I or with 111In bound to benzyl-DTPA. After binding to the surface of tumor cells in vitro, excess antibody was washed away, and the fate of the radiolabel was investigated over periods of 3-7 days. Radiolabel released into the supernatant or retained by the cells was analyzed to determine whether it was still on intact antibody.

RESULTS

In 13 of the 15 antibodies that were tested, a similar pattern of irreversible binding and gradual catabolism was observed. Iodine conjugated to antibodies was released rapidly from the cell after antibody catabolism. In contrast, the 111In was retained within the cell much longer than 125I, with the rate of degradation and release into the medium being at least fivefold slower. More than 50% of the bound 111In was still present on the cells after 7 days. Biochemical analysis of the retained 111In extracted cells after 4-6 days demonstrated that it was no longer associated with antibodies and was in a low molecular weight form, probably still associated with the chelator benzyl-DTPA.

CONCLUSIONS

Different radiolabels are processed by tumor cells differently, after catabolism of the antibody to which they originally were conjugated. The data suggest that the prolonged retention of 111In, relative to that of 125I, is due not to deiodination of iodine conjugates, but rather to intracellular retention of catabolic products containing 111In, perhaps within lysosomes. The use of radioisotopes that are retained within cells after antibody internalization and degradation may improve both radioimmunodetection and radioimmunotherapy of cancer.

MRI contrast enhancement by Gd-DTPA-monoclonal antibody in 9L glioma rats

To achieve a tissue-specific enhancement in diagnosis of brain tumor, a magnetic resonance imaging (MRI) study was performed using conjugate of Gd-DTPA and monoclonal antibody (MoAb) against 9L glioma cells. Fisher 344 strain rats were used for this study. MoAb against 9L glioma cells was conjugated with Gd-DTPA according to the method of Hnatowich et al. (1983) and used for the MRI study. The gadolinium (Gd) concentration in the Gd-MoAb injected to the rats was 0.01-0.03 mmol/kg. The enhancement effect increased gradually and persisted for 24 hours after the injection. This was longer than Gd-DTPA, which showed a peak of enhancement effect within 30 minutes after injection and was washed out within 120 min. This result was compatible with scintigraphy studies using 125I labeled anti 9L monoclonal antibody, in which the accumulation of the 125I antibody increased at 24, 48 and 72 hours after the injection. By using tumor-specific contrast agents such as Gd-MoAb, it may be possible to differentiate among tumor, perifocal edema and radiation injury.

In vitro activity of immunoconjugates between cisplatin and an anti-CA125 monoclonal antibody on ovarian cancer cell lines

Cis-diammine dichloro platinum (II) (CDDP), is a highly potent antineoplastic agent that is used in the treatment of ovarian cancer. However, the clinical use of CDDP is restricted by its severe side effects. In order to reduce these side effects and to enhance its therapeutic efficacy, we developed specific immunoconjugates consisting of the murine monoclonal antibody OC125 and CDDP, using diethylene triamine pentaacetic acid (DTPA) as a linker. The coupling efficiencies of the different preparations synthesized, varied between 1.10 +/- 0.42 and 2.65 +/- 1.60 mol of CDDP per mol of antibody protein. Despite the chemical modification of the antibody molecule, specific binding activity of the OC125-CDDP conjugates toward the CA125 antigen was maintained as was demonstrated by means of immunohisto-/cytochemical staining of frozen sections of ovarian cancer tissue, amniotic epithelium, and the CA125 positive ovarian cancer cell line NIH:OVCAR 3. The antiproliferative activity of the immunoconjugates was tested against the human ovarian cancer cell lines NIH:OVCAR 3 and SKOV 3, applying a kinetic crystal violet microassay. Despite the promising results obtained with the specific immunostaining of the target cells, no significant antiproliferative activity of our immunoconjugates against the cell lines tested was observed. One possible explanation for the lack of antitumor activity could be the fact that CA125 is released in large amounts by the NIH:OVCAR 3 cells. This may have prevented an efficient immunotargeting of the cancer cells by the formation of soluble immune complexes.

Targeting of tumours with murine and reshaped human monoclonal antibodies against placental alkaline phosphatase: immunolocalisation, pharmacokinetics and immune response

Anti-tumour monoclonal murine and humanised (reshaped human) antibodies (H17E2 and Hu2PLAP, respectively) against placental alkaline phosphatase (PLAP), radioactively labelled with indium-111 (111In) and iodine-123 (123I), were evaluated for their ability to localise mainly testicular and ovarian tumours in sequential pilot studies of the Hammersmith Oncology Group. 33 patients with active primary and/or metastatic testicular cancer were studied with the [111In]- or [123I]H17E2 antibody. 8 patients with testicular cancer were studied with the same antibody after being rendered free of disease after induction chemotherapy and surgical resection of residual tumour. 3 additional patients, 2 with ovarian cancer and 1 with testicular seminoma, were studied with [111In]H17E2 via a macrocyclic chelating agent (DOTA). 7 patients; 5 with ovarian cancer, 1 with breast cancer, and 1 with gastric cancer, received the reshaped human Hu2PLAP antibody [111In]DOTA labelled. One of these was imaged twice, with H17E2- and Hu2PLAP-DOTA-111In, respectively. In the initial 33 patients with active primary and/or metastatic testicular cancer, the presence of tumour was confirmed and correlated well with conventional radiological diagnostic methods, and in addition, the antibody scan revealed the presence of active disease in 2 patients with negative conventional imaging, but elevated serum tumour markers. In the 8 patients with complete remission (CR), imaging studies with the radiolabelled antibody did not show any localisation. The best images were obtained at 24 and 48 h after the [123I]- and [111In]H17E2, respectively. None of these patients developed human anti-mouse antibody responses (HAMA). Successful imaging with the reshaped human antibody, Hu2PLAP-DOTA-111In, was seen in 3 patients with PLAP-positive tumours (2 ovarian and 1 gastric cancer). The 3 negative patients were 1 in complete remission, 1 with PLAP-negative tumour and 1 who cleared the Hu2PLAP antibody immediately after infusion due to the presence of anti-chelating agent (anti-DOTA) antibodies from a previous H17E2-DOTA-111In scan. One patient with PLAP-negative breast carcinoma had a false-positive scan with Hu2PLAP, showing localisation to the pleural effusion. Antibody pharmacokinetics showed a mean t1/2 beta = 73.1 +/- 30.2 h (n = 5) for Hu2PLAP versus t1/2 beta = 27.2 +/- 5.9 h (n = 3) for H17E2 (P < 0.05). 2 patients receiving Hu2PLAP were excluded due to the rapid clearance of the radiolabel as a result of the presence of high HAMA and anti-chelate antibody levels, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Polyclonal 111In-IgG, 125I-LDL and 125I-endothelin-1 accumulation in experimental arterial wall injury

To test iodine-125 labelled low-density lipoprotein (125I-LDL), polyclonal indium-111 labelled immunoglobulin G (111In-IgG) and iodine-125 labelled endothelin-1 uptake in metabolically active atheromatous plaques after arterial wall injury, we performed balloon de-endothelialization of carotid arteries or abdominal aortas in 24 New Zealand male rabbits which were fed with a normal diet (n = 14) or a hypercholesterolaemic diet (n = 10) after surgery. Six weeks later the animals were injected with 200 microCi of 125I-LDL and/or with 100 microCi of 111In-IgG or with 9 microCi of 125I-endothelin-1. Forty-eight hours later the animals were sacrificed. Carotid arteries and aortas were removed, counted and fixed for autoradiography and light microscopy examination. Contralateral carotid arteries and thoracic aortas served as controls. Significant 111In-IgG uptake was observed in the injured arteries at autoradiography, with localization mainly in the healing edges, and at well counting. The percentage of the injected dose per gram (%D.inj/g) was 0.0188 +/- 0.06 versus 0.0059 +/- 0.003 in controls (P < 0.05). There was no difference in 111In-IgG uptake between arteries with injury alone and those with active atheroma formation at the site of the injury. Significant 125I-LDL uptake was observed only when lipid deposition was present at light microscopy (%D.inj/g of 0.0024 +/- 0.0005 vs. 0.0010 +/- 0.0003 in controls, P < 0.05). 125I-endothelin-1 accumulation was observed in four of five injured aortas both at autoradiography, with diffuse localization, and at well counting (%D.inj/g of 0.0012 +/- 0.0004 in the abdominal aortas vs 0.0008 +/- 0.0003 in the thoracic aortas).(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex sympathetic dystrophy of the hand: an excessive inflammatory response?

In 23 patients with reflex sympathetic dystrophy (RSD) of the hand, scintigraphy with indium-111 labeled human non-specific polyclonal immunoglobulin G (In-111-IgG) was performed to investigate whether inflammatory characteristics are present in RSD. Both blood flow and accumulation over 48 h were assessed. Nineteen patients had increased flow to the affected hand, and 3 had decreased flow. One patient had bilateral RSD. Exercise provoked aggravation of complaints and signs in all patients. The affected/non-affected hand ratio (target-to-background, T/B) immediately before and after exercise did not change significantly. The T/B ratios 48 h after In-111-IgG injection were significantly higher in patients with RSD less than 5 months than in patients with RSD existing 5 months or longer. The T/B ratios 24 and 48 h after In-111-IgG injection were not correlated with the flow T/B ratios. In fact, 2 of the 3 patients with a decreased flow showed excess accumulation on the late images. Significantly more patients with early RSD, existing less than 5 months, had a positive In-111-IgG scintigraphy (14 of 17) than the patients with late RSD (1 of 6). Increased vascular permeability for macromolecules, an important characteristic of inflammation, appears to play a role in the development of RSD. This phenomenon is not flow-dependent.

Intravesical administration of indium-111-labelled HMFG2 monoclonal antibody in superficial bladder carcinomas

Tumour-associated HMFG2 monoclonal antibody (MAb) was labelled with indium-111 and administered intravesically to 20 patients with known or suspected superficial bladder carcinoma. The antibody solution was kept in the bladder for 1 hr and was then washed out. Cystoscopy was performed at 2 and 24 hr after instillation. Radioactivity of tumour and normal tissue obtained from the bladder during cystoscopy and cells recovered from urine after the instillation were counted in a gamma-counter. Conventional histology, immunocytochemistry and autoradiography were also performed. Mean uptake at 2 and at 24 hr was higher in tumours than in normal samples. Autoradiography showed selective accumulation of radioactivity in cells which expressed the antigen detected by the HMFG2 MAb. There was no correlation of tumour uptake with the grade of tumour. No radioactivity was found in the blood of patients after the instillation. Based on dosimetric calculations, however, the radiation dose that can be delivered to the tumours is not sufficient to be cytotoxic, possibly due to inadequate penetration and retention by tumour tissue. Nevertheless, the significant difference between antibody uptake by the tumours and that by normal urothelium, observed in our study, allow for the possibility of using this approach therapeutically.

Lymphocytic gastritis: an unusual cause of hypoproteinaemia

Lymphocytic gastritis (LG) is a disorder characterized by diffuse infiltration of the gastric epithelium by small lymphocytes. Its cause remains largely unknown, although several arguments favour an immune origin. Hypoproteinaemia induced by leakage of plasma proteins into the gastric lumen is a rare complication of LG. We report here on three cases of LG whose presenting symptom was lower limb oedema secondary to hypoproteinaemia. The diagnosis was based on radiological, endoscopic and histopathological findings. Radionuclide studies allowed confirmation of the loss of proteins in the stomach. Therapy with omeprazole or H2-receptors antagonists proved to be successful. The relationship between LG and varioliform gastritis is reviewed.

Preparation and in vitro evaluation of "no-carrier-added" 18F-labeled biotin

This paper will describe the preparation of "no-carrier-added" 18F-labeled biotin where the radiolabel bound to an aromatic moiety is described. This has been accomplished by preparation of [18F]fluorobenzylbromide (yield 20-30%) and its reaction with biotin-LC-hydrazide. This yielded "no-carrier-added" radiolabeled biotin (5-10%) which was then purified by reversed phase HPLC. The pure product was found to bind to avidin, thereby demonstrating retention of its biological integrity. Thus this product is potentially useful for imaging tumor tissue following injection of avidin coupled MoAbs.

Imaging and dosimetry determinations using radiolabeled antibodies

Numerous studies using radiolabeled antibodies for imaging and therapy of lymphoma have been reported (Table 4). The targeting of lymphoma associated antigens with MoAb appears to be more favorable than the targeting of antigens on epithelial tumor. Antigen abundance may not be the overriding factor in this favorable targeting, since the number of antigenic sites per cell are often in the same range or lower than those targeted in epithelial tumors. This improved targeting is likely related to the greater access of antibody to the target antigen in lymph nodes, bone marrow, circulation, and other sites. With certain antibodies, trafficking of the cells targeted with the radiolabeled antibody may also result in favorable localization [19]. While the most frequently used isotope for imaging and therapy has been 131I, certain limitations have been observed, including its high-energy gamma rays and resulting lower resolution, and the frequent occurrence of dehalogenation [21,25,98]. Many of the antigens expressed by lymphomas undergo antigenic modulation. Antigens that undergo modulation may be targeted successfully, but once modulation occurs the antibody is broken down and the iodine is rapidly excreted from the cells. While this rapid release from normal organs is an advantage, it is an undesirable event at the tumor site. In contrast to the case of 131I MoAb, modulation may be an advantage for targeting with 111In labeled antibodies, since the radioactive metals are retained for longer periods at the tumor sites; even if the antibody is broken down, the 111In is not easily excreted from the cells [52]. Among the most consistent and favorable targeting observed to date is that seen with 111In T101 in CTCL. These studies have shown concentration of 111In in tumor of 10-100 times that seen in other tumor systems using iodinated antibodies. Unfortunately no studies have followed this lead and performed the necessary comparisons between 111In and 131I MoAb to determine if this is a consistent finding. The use of 99mTc labeled MoAb for imaging lymphomas is in its infancy, although preliminary reports appear promising [71]. While in epithelial tumors preferential tumor targeting may take more than 48 hours in lymphomas, targeting is usually seen within the first 24 hours, which is within the window of imaging time for 99mTc. Therefore, further evaluation of 99mTc antibodies should be performed. Determination of the optimum dose of antibody for imaging has been attempted. Studies using various anti-lymphoma directed antibodies have shown widely varying biodistribution and variable dose-response curves.(ABSTRACT TRUNCATED AT 400 WORDS)

A bifunctional HBED-derivative for labeling of antibodies with 67Ga, 111In and 59Fe. Comparative biodistribution with 111In-DPTA and 131I-labeled antibodies in mice bearing antibody internalizing and non-internalizing tumors

To investigate whether bifunctional ligands containing chelating structures other than EDTA and DTPA and metallic radiotracers other than 111In will reduce the non-specific radioactivity uptake in the liver during immunoscintigraphy, we synthetized an isothiocyanato-substituted phenolic polyaminocarboxylic acid (HBED-CI) for labeling of MAbs with 67Ga, 111In and 59Fe. Biodistribution of HBED-CI-labeled MAbs was compared to that of 131I and 111In-DTPA labeled MAbs in nude mice bearing tumors, which differ with regard to intracellular internalization and catabolism of the corresponding MAb-antigen complex. In the liver a continuous radioactivity excretion for 67Ga-HBED-CI-labeled MAbs was observed with kinetics that parallel 131I clearance after administration of 131I-MAbs, while 111In-HBED-CI-labeling led to a constant 111In liver level quite similar to that of 111In-DTPA-MAbs. In tumors, 67Ga-HBED-CI-MAb uptake again paralleled that of 131I-MAbs, showing continuous accumulation in tumor tissues when internalization of the MAb-antigen complex was not involved. A much lower uptake, which peaked between 24 and 48 h, was found in the case of MAb-antigen internalization. 111In of 111In-HBED-CI- and 111In-DTPA-labeled MAbs continuously accumulated in both types of tumors. Compared with 111In-DTPA-MAbs, an improvement in tumor-to-liver ratios, due to the reduced liver radioactivity associated with 67Ga-HBED-CI-labeled MAbs, could only be obtained with non-internalizing tumors. The time course of radioactivity distribution in the liver and in MAb-internalizing tumors after administration of 67Ga-HBED-CI-, 111In-HBED-CI- and 111In-DTPA-labeled MAbs further indicates a dominating influence of the metallic radiotracer rather than the ligand on retention or excretion of radioactivity in MAb-catabolizing tissues.

Evaluation of biological response modifiers in the enhancement of tumor uptake of technetium-99m labeled macromolecules. A preliminary report

Imaging tumors with radioactive monoclonal antibodies remains attractive but continues to be challenging. With the hypothesis that the use of biological response modifiers (BRMs) may augment the tumor uptake, technetium-99m(99mTc)-labeled tumor necrosis factor (TNF) and nuclear histone specific TNT-1-F(ab')2 were evaluated in tumor bearing mice given a single dose of interferon (IFN). Ukrain or pokeweed mitogen as BRMs. As early as 1.5 h post injection (p.i.) of the radioactive macromolecules, the absolute tumor uptake (% administered dose/g) of each agent was enhanced (e.g., TNF, control = 1.8 +/- 0.4, Ukrain = 3.2 +/- 0.5, P = 0.006) and tumor to muscle ratios were elevated (e.g., TNF, control a 4.1 +/- 2.2, interferon 8.3 +/- 2.7, P = 0.01). The absolute tumor uptake remained practically unchanged at 4 h p.i. Generally with BRMs, the blood clearance was rapid and tumor/blood ratios and tumor/muscle ratios were higher than in the control group, increasing to greater than 200% for IFN as a BRM. The early enhancement in tumor uptake of macromolecules, leading to excellent delineation of tumors by scintigraphy is highly encouraging and warrants further studies to explore the full potential of BRMs.

In vitro stability of EDTA and DTPA immunoconjugates of monoclonal antibody 2G3 labeled with indium-111

Monoclonal antibody 2G3 directed against a high molecular weight glycoprotein on breast and ovarian cancer cells was conjugated with bicyclic DTPA (or EDTA) anhydride or benzyl isothiocyanate DTPA (benzyl DTPA) and labeled with 111In. DTPA anhydride was more reactive with the antibody than benzyl DTPA, and kinetics of labeling with 111In were more rapid for DTPA substituted 2G3 than for benzyl DTPA substituted 2G3. On the other hand, 111In-2G3 conjugates prepared using DTPA anhydride were subject to more extensive dimerization and higher losses in immunoreactivity than those prepared using benzyl DTPA. On the basis of measurement of transchelation to transferrin, the stability of 111In-2G3 prepared using DTPA anhydride or benzyl DTPA did not differ during incubation in human plasma for 6 days at 37 degrees C. These results suggest that an important advantage of benzyl DTPA over DTPA anhydride for preparing 111In-labeled antibodies is the prevention of intermolecular (and intramolecular) crosslinking during conjugation which ultimately leads to alterations in conformation and losses in immunoreactivity of the radioimmunoconjugate.

The evaluation of 186Re-labeled antibodies using N2S4 chelate in vitro and in vivo using tumor-bearing nude mice

We have recently described a method for radiolabeling monoclonal antibodies, with metallic radionuclides using a new chelating agent N2S3. Using this chelate the monoclonal antibodies Lym-1 and B72.3 were labeled with 186Re and their biological integrity was evaluated in vitro and in vivo. 186Re-labeled antibodies using N2S4 methodology were found to be stable in human serum and retained their immunoreactivity. Intravenous administration of 0.5 mCi 186Re-labeled antibodies resulted in partial or complete regression of tumor tissue in mice.

Synthesis of a monoclonal antibody-indium-111-porphyrin conjugate

Antibodies were labelled with indium-111 with a view to their use in the radio-immunodetection of cancers. The covalent coupling between indium-111 porphyrin and monoclonal antibodies (IgG and F(ab')2 fragment) was achieved using the ester activated method [N-hydroxy-succinimide/1-ethyl-3-(3-dimethylaminopropyl)carbodiimide]. After purification, this provided conjugated with specific activities of 6 muCi/micrograms Mab (9.3 molecules per Mab) or 1 muCi/microgram (F(ab')2 fragment (1.5 molecule per F(ab')2). ELISA procedures suggested the full retention of immunoreactivity by the radiolabelled antibodies.

Biodistribution of a monoclonal antibody (RNL-1) against the neural cell adhesion molecule (NCAM) in athymic mice bearing human small-cell lung-cancer xenografts

The purpose of this investigation was to determine the targeting potential of the murine monoclonal antibody (MAb) RNL-1 for human small-cell lung cancer (SCLC) in a nude mouse model. RNL-1 is preferentially reactive with SCLC and lung carcinoids, and was classified as a cluster-1 MAb as defined by the International Workshop on Small-Cell Lung-Cancer Antigens. From the intercellular location of the target antigen and its reactivity with 3T3 cells transfected with nucleic acid sequences encoding for the neural cell adhesion molecule (NCAM), it was concluded that RNL-1 is directed against NCAM. RNL-1 was radiolabelled with either 125iodine or 111indium and injected into nude mice bearing NC1-H82 SCLC xenografts. The biodistribution of the radiolabels was determined up to 120 hr post injection. Maximum tumour accretion for 111In-RNL-1 was 11.8%ID/g and 6.5%ID/g for 125I-RNL-1. The accumulation of 111In-RNL-1 could be visualized clearly by gamma scintigraphy without background subtraction techniques. Autoradiographs of whole-body sections from animals injected with 125I-RNL-1 showed that activity in the SCLC xenografts was mainly peripheral, suggesting that tumour uptake is dependent on the vascularization of the tumour tissue.

Tumor localization and in vivo antitumor activity of the immunoconjugate composed of anti-human colon cancer monoclonal antibody and mitomycin C-dextran conjugate

The tissue distribution and in vivo antitumor activity of a novel monoclonal antibody-mitomycin C conjugate (A7-MMCD) composed of anti-human MAb A7 and MMC-dextran conjugate were investigated using tumor-bearing mice. A7-MMCD was prepared via an anionic dextran intermediate for the purpose of keeping the non-specific uptake by the reticuloendothelial system to a minimum. 111In-labeled A7-MMCD showed about a 5-times-greater accumulation in SW1116 (targeted tumor) than in S180 (non-targeted tumor) 48 h after injection, and produced a tumor-to-blood ratio which was 3 times higher in SW1116-bearing mice than in S180-bearing mice 96 h after injection. Accumulations in the liver, spleen, and kidney were also observed to some extent. Pharmacokinetic analysis revealed that A7-MMCD had nearly the same properties in the body as MMCDan (MMCD with an anionic charge), i.e., those of a negatively charged macromolecule. Both A7-MMCD and MMCDan had relatively similar tissue uptake rate indices for the liver and spleen. The tumor uptake rate index for SW1116 was about 2.5 times greater than that for S180, and the total amount of 111In-A7-MMCD accumulated in SW1116 was calculated to be approximately 5 times greater than the amount in S180. These results indicated that A7-MMCD could achieve site-specific targeting in the body. Furthermore, in the therapeutic experiment using SW1116 implanted subcutaneously, A7-MMCD suppressed tumor growth significantly, compared to free MMC and MMCDan. These results suggest that in designing an monoclonal antibody-drug conjugate via an intermediary, the physicochemical properties of intermediate macromolecules must also be taken into consideration to obtain a high degree of efficacy in vivo.

The in vivo release of 90Y from cyclic and acyclic ligand-antibody conjugates

Yttrium binding ligands DOTA, caDTPA and CT-DTPA were each conjugated to monoclonal antibody B72.3, labelled with 90Y and injected into mice in order to assess the in vivo inertness of the antibody-linked 90Y-ligand complexes. Levels of 90Y in femur shafts of the DOTA-B72.3 mice were low, being approximately 7 and 44%, respectively, of levels in the femur shafts of the caDTPA-B72.3 and CT-DTPA-B72.3 treated mice. This finding demonstrates the greater inertness and by implication the greater suitability for immunotherapy of the DOTA-90Y complex.

Synthesis and preliminary evaluation of a new chelate N2S4 for use in labeling proteins with metallic radionuclides

The successful attachment of various metallic radionuclides such as 99mTc to monoclonal antibodies for targeting tumor tissue in vivo depends upon the development and use of suitable bifunctional chelating agents. We have successfully synthesized a new N2S4 (compound 4) chelate. This chelate forms a stable complex with 99mTc and is capable of coupling to different proteins. The N2S4 compound is quite stable if kept as a hydrochloride salt and is coupled to antibody under neutral conditions with better than 95% efficiency without the loss of immunoreactivity.

A PAC study of the binding of 111In to a monoclonal antibody via the macrocyclic molecule 1,4,7-triazacyclononanetriacetic acid

Time integral and time differential PAC measurements have been made from samples of 111In bound to the functionalized 9N3 macrocycle, and 111In bound to the monoclonal antibody AUA1 via the macrocycle, over the temperature range 80-350 K. Values obtained for the integrated perturbation coefficient G22 (infinity) clearly illustrate the effects which the antibody has on the angular correlation of the gamma-rays emitted by the 111In decay. Measurements of the quadrupole frequency in the 111In-9N3-AUA1 samples show a transition temperature between 250 and 275 K which was not detected in the 111In-9N3. An arrhenius plot of the temperature dependence of the correlation time for the 111In-9N3 yielded a value of 0.10 +/- 0.01 eV for the activation energy associated with molecular re-orientation, whilst a Debye plot indicated an effective volume of (10 +/- 1) x 10(-27) m3 for the same sample. Extrapolation of the Debye plot suggests a high relaxation constant which may be attributed to internal vibrational modes in the macrocycle. Comparisons are made with similar work on the plasma protein transferrin.

90Y.B72.3 against pancreatic cancer: dosimetric and biological analysis

Nude mice xenografted with a human pancreatic carcinoma cell line were injected with yttrium-90 (90Y) conjugated to diethylene triaminepenta acetic acid (DTPA) alone, and DTPA covalently linked to a monoclonal antibody, B72.3. The animals were sacrificed in temporal sequence to evaluate isotope distribution. Dosimetry was carried out using the principles outlined in MIRD and ICRU Report 32. Results are expressed as percent uptake per unit mass in organs and tumor and as relative absorbed dose normalized to 90Y uptake in liver at 7 hr. When conjugated to B72.3, an 8-fold increase in isotope localization in the tumor was noted by 24 hr. When the relative absorbed dose is calculated for 90Y and 90Y.B72.3, a 26-fold increase in tumor dose is noted for the 90Y conjugate. Normal tissues show no to modest (less than 5x) enhanced dose with 90Y.B72.3. B72.3, therefore, deserves further investigation as a potential monoclonal antibody for targeting therapeutic radioisotopes and possibly diagnostic radioisotopes to pancreatic cancer. Radiobiological aspects of the low dose rates from radioimmunotherapy are discussed.

In vitro uptake 153gadolinium and gadolinium complexes by hyaline articular cartilage

This in vitro study evaluated whether Gadolinium (Gd) penetrates into hyaline cartilage and would be incorporated into vital chondrocytes. Hyaline joint cartilage of rabbits was exposed to radioactive 153GdCl3 and to a radioactive 153Gd-DTPA-BSA-complex (DTPA, diethylene-triaminepentaacetic acid; BSA, bovine serum albumine). In addition an exchange experiment with radioactive 153GdCl3 versus Gd-DTPA-di-N-methylglucamine (Magnevist) was performed. Incorporation of 153GdCl3 into neuroblastoma cells, connective tissue cells and chondrocytes was tested. The results showed that the depth and extent of incorporation of Gd depends on the molecular mass and time of exposure. 153Gd-DTPA-BSA complexes exhibited an incorporation rate of maximal 11% +/- 2.8% up to the middle third of the cartilage within 24 h with almost no incorporation (2 +/- 1.9%) for the deep layer. The exchange experiment revealed no uptake of Gd for the deep layer. The maximal incorporation rate of 153GdCl3 into vital chondrocytes was 6.3%. These data indicate that under the condition of MR-arthrography, Gd-DTPA-di-N-methylglucamine will not be absorbed into the deep layers of hyaline cartilage and will not be incorporated into vital chondrocytes.

Inhibition of the hepatocyte uptake of radiolabelled monoclonal antibodies by chelating agents

The imaging of small abdominal tumours with indium 111 labelled monoclonal antibodies (MAbs) is often obscured by the uptake of activity into the heptocytes of normal liver tissue. A model has therefore been developed to analyse reagents which may inhibit the hepatocyte uptake of 111In-MAb whilst preserving tumour uptake. Primary rat hepatocyte cultures and an epithelial membrane antigen (EMA) expressing tumour cell line (MCF7), recognised by the EMA-specific MAb ICR2, were obtained in tissue culture. Monolayers of both cells were incubated with the 111In-MAb with or without the additional reagents and the cell uptake then measured and expressed per milligram of cell protein using a Lowry protein assay. No preferential reduction in hepatocyte uptake was noted by incubating cells with either saturated or unsaturated transferrin. The chelating agent, diethylene triamine penta-acetic acid (DTPA), however, significantly reduced the uptake of activity in hepatocytes but not the tumour cell line (P less than 0.05). An optimum concentration and time period for incubating DTPA with labelled MAb was established. The mean hepatocyte uptake was reduced by 80% with a 1 h incubation with 1 mM DTPA. These results suggest that DTPA may have a role in reducing the liver uptake of radioactivity in patient studies using 111In-MAb.

Effect of isoelectric point on biodistribution and inflammation: imaging with indium-111-labelled IgG

Electrostatic effects play an important role in protein interactions and may alter the biodistribution of antibodies. To study the effect of molecular charge of the biodistribution and infection imaging properties of human polyclonal immunoglobulin G (IgG), its isoelectric point was varied by changing the level of diethylene triamine penta-acetic acid (DTPA) substitution: 0.8, 0.9, 3.7, 5.1 and 5.9 DTPA/IgG. Biodistributions of the different IgG preparations were determined at 10 min, 1, 6, 24, and 48 h post injection in normal rats, and infection imaging properties were determined in rats with Escherichia coli thigh infections. The biodistribution was significantly affected by pI. The immunoglobulin preparations with 0.9 and 3.7 DTPA/IgG showed faster clearance from the circulation and generally lower accumulation in most organs. The images had a target-to-background ratio of approximately 1.3-2.3:1. These results suggest that even though targeting is not affected by the level of DTPA substitutions, preparations with 0.9 and 3.7 DTPA/IgG may be superior imaging agents because of reduced accumulation by background organs.

Multi-centre immunoscintigraphic study using indium-111-labelled CEA-specific and/or 19-9 monoclonal antibody F(ab')2 fragments

Six European nuclear medicine centres performed immunoscintigraphy first retrospectively in 34 patients using indium-111-labelled carcinoembryonic antigen (CEA)-specific and/or 19-9 F(ab')2 fragments. Results for sensitivity and specificity in tumour sites were 94% and 87%, respectively, for the pelvis and 73% and 100% for the extrahepatic abdomen. A second prospective series concerned 58 other patients previously operated on for colorectal adenocarcinoma (27 colon, 31 rectum). Two-thirds of these patients had a suspected recurrence signalled by an isolated rise in tumour markers, and 46 patients examined by immunoscintigraphy, X-ray computed tomography and ultrasonography were found to have a recurrence (a total of 62 tumour sites). Sensitivity and specificity with immunoscintigraphy were 90% and 97%, respectively, for the pelvis and 62% and 95% for the extrahepatic abdomen. For 29 patients injected with CEA-specific fragments, sensitivity was 90% and specificity 94% for the pelvis. For 25 patients injected with 19-9 fragments, pelvic sensitivity and specificity were 80% and 100%, respectively, whereas sensitivity for the extrahepatic abdomen was only 29% since several cases of peritoneal carcinosis were not visualized. In the prospective series, comparison of the three imaging techniques for all tumour sites (including liver and in 5 cases thorax) gave a sensitivity and specificity of 82% and 91%, respectively, for immunoscintigraphy, 52% and 95% for X-ray computed tomography and 59% and 100% for ultrasonography. These results thus confirm the advantage of using 111In-labelled CEA-specific or 19-9 to visualize and localize recurrences of colorectal cancer.

Carbohydrate-derivatized immunoconjugate of the anti-(carcinoembryonic antigen) monoclonal antibody C46: immunohistological reactivity and pharmacokinetic comparison with a randomly derivatized C46 immunoconjugate

In this study, a site-specific glycyl-tyrosyl-(N-epsilon-diethylenetriaminepentaacetic acid)-lysine (GYK-DTPA) immunoconjugate of the anti-carcinoembryonic antigen monoclonal antibody C46 (C46-GYK-DTPA) was characterized by immunohistological and immunofluorescence methods for reactivity with normal and neoplastic human tissues. In addition, pharmacokinetic studies assessed the ability of C46-GYK-DTPA labeled with 111In to localize to and image human tumor xenografts in nude mice. The native antibody and the site-specific immunoconjugate exhibited similar patterns of reactivity with normal human tissues. C46 did not bind to the surface of normal human granulocytes, which indicates lack of reactivity with normal cross-reacting antigen. C46-GYK-DTPA reacted with 100% of the colon, breast and renal carcinomas examined and with two of three lung carcinomas, but did not react with any sarcomas, melanomas or lymphomas examined. Intravenously administered C46-GYK-DTPA-111In rapidly localized to and imaged LS174T human colon adenocarcinoma xenografts in nude mice, reaching maximal levels of about 25% of injected dose/g tumor within 1 day. No unusual localization to any non-tumor tissue or organ was seen; the level of radioactivity in the normal tissues and organs was at or below that in the blood. The accessible binding sites in 1 g tumors appeared to be saturated at an antibody dose between 100 micrograms and 1000 micrograms/mouse. Further, in a direct in vivo comparison, the site-specific conjugate C46-GYK-DTPA had more favorable pharmacokinetics and better tumor localization than a randomly derivatized C46 immunoconjugate (C46-DTPA). These findings suggest that the site-specific immunoconjugate C46-GYK-DTPA may be useful in the diagnosis and therapy of colon cancer and other adenocarcinomas expressing carcinoembryonic antigen.

Proton relaxation enhancement of albumin, immunoglobulin G, and fibrinogen labeled with Gd-DTPA

Bovine serum albumin, immunoglobulin G, and fibrinogen were labeled with Gd-DTPA using a bifunctional chelating agent DTPA anhydride. The protein-(Gd-DTPA) conjugates had 1.4- to 2.0-fold greater longitudinal relaxivities at 0.02 and 0.44 T than the relaxivity of plain Gd-DTPA. The increase of longitudinal relaxivity was not directly related to the size of carrier protein. Up to 50 Gd-DTPA chelates per protein, longitudinal relaxivity of the conjugates was proportional to the concentration of Gd and independent of the Gd/protein ratio.