Rune Nilsson

Fractionation of rat IgG subclasses and screening for IgG Fc-binding to bacteria

The four IgG subclasses of the rat, IgGl, IgG2a, IgG2b and IgG2c, were purified from normal serum by a combination of protein A-affinity chromatography and DEAE-cellulose chromatography. Purified, radiolabelled preparations of IgG were tested for binding to Gram-positive bacteria representing five different Fc-receptor (FcR) types. Distinct rat subclass-specific Fc-binding was noted to bacterial species belonging to different Fc-receptor types. Staphylococcus aureus (FcR I) strains bind IgGl and IgG2c as shown by others. Group C and G Streptococci (FcR III) bind all four subclasses of rat IgG. Streptococcus zooepidemicus strains (FcR V) also bind all four subclases but only to a lower degree. Human group A Streptococci (FcR II) and bovine group G Streptococci (FcR IV) do not bind any of the rat IgG subclasses. Elution studies on two strains. Staphylococcus aureus, Cowan I, and human group G Streptococcus, G 148, showed that both thiocyanate and pH-elution might be useful for the fractionation of IgG subclasses bound to bacterial cells. The present work indicates the possible use of bacterial cells as solid-phase absorbents in immunological studies of rat IgG.

Quantitative analysis of rat Ig (sub) classes binding to cell surface antigens

An indirect 125I-labeled protein A assay for detection of cell surface-bound rat immunoglobulins is presented. The assay is quantitative and rapid and detects as little as 1 ng of cell surface-bound Ig. It discriminates between antibodies belonging to different IgG subclasses, IgM and IgA. We describe the production and specificity control of the reagents used and show that the test can be used for quantitative analysis. A large number of sera from untreated rats are tested to evaluate the frequency of falsely positive responses and variation due to age, sex and strain of rat. With this test it is relatively easy to quantitate the binding of classes and subclasses of rat immunoglobulins in a small volume (6 μl) of untreated serum.

High-dose radioimmunotherapy combined with extracorporeal depletion in a syngeneic rat tumor model†

The aim of the current study was to investigate the possibility of increasing the maximal tolerated dose (MTD) of a tumor‐selective radiolabeled antibody when radioimmunotherapy (RIT) is combined with extracorporeal depletion of radioimmunoconjugates from the circulation. Furthermore, the authors evaluated whether this increase in dose improved the therapeutic effect on solid manifest tumors in an immunocompetent animal model.

Determining maximal tolerable dose of the monoclonal antibody BR96 labeled with 90Y or 177Lu in rats: establishment of a syngeneic tumor model to evaluate means to improve radioimmunotherapy.

Purpose: To evaluate therapeutic strategies, it is essential to use biological models reflecting important aspects of the clinical situation. The aim of the present study was to compare the maximal tolerable dose of the monoclonal antibody BR96 labeled with 90Y or 177Lu in immunocompetent rats. Maximal tolerable dose was defined as the highest activity that allows 100% of the animals to survive without clinical signs, such as infections, bleeding, or diarrhea, and with <20% loss in body weight. Experimental Design: Increasing activity levels of BR96 labeled with 90Y or 177Lu were administered to groups of rats. Blood parameters, body weight, and general performance were monitored for 8 weeks. Results: Two days postinjection, all groups had decreased leukocyte counts down to 5% to 15% of initial values. Initiation of recovery (at 14-21 days) showed a dose-response relationship. All groups, except the group given the highest activity of 90Y, had complete resolution in their leukopenia. The decrease in platelets was delayed to days 7 to 14 postinjection with a dose-dependent response regarding both severity of the nadir (10-40% of initial value) and the start of recovery. Animals in the groups given the highest activities of both 90Y and 177Lu exhibited skin infections on day 21. Conclusions: The results showed good reproducibility and dose-dependent toxicity for both radionuclides, indicating that the maximal tolerable dose for 177Lu–BR96 (1,000 MBq/kg) is 1.7 times that for 90Y–BR96 (600 MBq/kg) in rats. This model makes it feasible to evaluate strategies to escalate therapeutic doses to tumors without increasing normal tissue toxicity.

Improving radioimmonotargeting of tumors. Variation in the amount of L6 MAb administered, combined with an immunoadsorption system (ECIA).

Extracorporeal immunoadsorption (ECIA) is a new method for the selective removal of circulating radiolabeled monoclonal antibodies (MAb) from plasma to increase the uptake in tumor versus normal tissues (T/N-ratio). To ascertain whether the amount of MAb affects T/N ratios immediately and 24 h after ECIA, we used a rat model with two tumor sites--one intramuscular (im) and one below the subrenal capsule (SR). Extracorporeal immunoadsorption was done with an avidin-agarose column after injection of 125I-labeled biotinylated L6 MAb. The animals received 10, 50 or 250 micrograms of L6 only (controls), or followed by ECIA. The efficacy of the procedure in removing plasma activity was 80-95%. For both tumor sites, the highest T/N-ratios were obtained with 10 micrograms L6. All T/N-ratios significantly improved for SR tumors by a factor ranging from 3.2 (lung) to 12.6 (bone marrow). The T/N-ratios were still elevated 24 h after ECIA. Injection of larger amounts of MAb, probably causing a higher degree of tumor saturation, will not necessarily improve the T/N ratio after ECIA.

Blood Pharmacokinetics of Various Monoclonal Antibodies Labeled with a New Trifunctional Chelating Reagent for Simultaneous Conjugation with 1,4,7,10-Tetraazacyclododecane-N,N′,N″,N‴-Tetraacetic Acid and Biotin before Radiolabeling

Purpose: Knowledge of the blood pharmacokinetics of monoclonal antibodies is crucial in deciding the optimal time for starting the administration of a “clearing agent” or using a “clearing device.” The primary purpose was to investigate whether the pharmacokinetics of various antibodies labeled with the same chelator and 111In differed significantly after i.v. injection in immunocompetent rats. A new trifunctional chelator called “1033” containing a biotin and a radiometal chelation moiety is introduced, making it possible to use only one conjugation procedure for the antibody. Experimental Design: Sixty-five non–tumor-bearing rats were included and divided into four groups (I-IV). The blood pharmacokinetics was investigated for rituximab, BR96, and trastuzumab labeled with 1033 and 111In (I-III). The whole-body activity and activity uptake in muscle, liver, and kidney, which might explain differences in the early pharmacokinetics in blood, were also measured. hMN14 labeled with another chelator [1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA)], but with the same radionuclide (111In-biotin-DOTA-hMN14), was studied (IV). The blood pharmacokinetics from another 15 tumor-bearing rats was compared with those of non–tumor-bearing rats (III) by injection of 111In-1033-BR96. Results: No statistical difference was detected between the groups regarding the blood pharmacokinetics of rituximab, BR96, or trastuzumab. The pharmacokinetics and biodistribution of 111In-biotin-DOTA-hMN14 exhibited a clear difference compared with others. There were no significant differences in the blood pharmacokinetics of 111In-1033-BR96 between tumor-bearing rats and non–tumor-bearing rats. Conclusions: Different antibodies labeled with the trifunctional chelator 1033 and 111In did not exhibit different blood pharmacokinetics, which means that the pharmacokinetics could be predicted irrespective of the IgG1 antibody chosen. A small tumor burden did not change the pharmacokinetics of the radioimmunoconjugates.

Improved Tumor Targeting and Decreased Normal Tissue Accumulation through Extracorporeal Affinity Adsorption in a Two-Step Pretargeting Strategy

Purpose: Evaluation of the possibilities of reducing the accumulation of radiolabeled streptavidin in radiosensitive organs by extracorporeal affinity adsorption (ECAT). Experimental Design: Rats were injected with biotinylated antibody and subjected to removal of the antibodies from the circulation by ECAT 24 h after injection (avidin column). Animals were then injected with 111In-1,4,7,10-tetra-azacylododecane N,N′,N″,N‴-tetraacetic acid (DOTA)-streptavidin. In a third step, animals were subjected to a second ECAT 8 h after injection to remove the DOTA-streptavidin from the circulation (biotin column). Biodistribution and tumor targeting of DOTA-streptavidin 24 h after injection was determined. Results: Elimination of biotinylated antibody by ECAT before injection of DOTA-streptavidin increased the tumor targeting by 50%. In addition, the levels of DOTA-streptavidin in liver and lymph nodes were reduced by 60%, which implied a 4.3- and 3.8-fold increase of tumor-to-liver and tumor-to-lymph node ratios, respectively. By doing a second ECAT to remove DOTA-streptavidin from the circulation, accumulation in normal tissues was reduced. However, this latter ECAT also reduced tumor accumulation by 25% (mostly corresponding to radioactivity in the circulation). Conclusions: ECAT was efficient as a means of removing biotinylated antibodies and would probably also be efficient for the clearance of streptavidin-conjugated antibodies. Conversely, the use of ECAT for removal of radiolabeled streptavidin seems not to offer any advantage.

Use of Monte Carlo simulations with a realistic rat phantom for examining the correlation between hematopoietic system response and red marrow absorbed dose in Brown Norway rats undergoing radionuclide therapy with (177)Lu- and (90)Y-BR96 mAbs.

PURPOSE Biokinetic and dosimetry studies in laboratory animals often precede clinical radionuclide therapies in humans. A reliable evaluation of therapeutic efficacy is essential and should be based on accurate dosimetry data from a realistic dosimetry model. The aim of this study was to develop an anatomically realistic dosimetry model for Brown Norway rats to calculate S factors for use in evaluating correlations between absorbed dose and biological effects in a preclinical therapy study. METHODS A realistic rat phantom (Roby) was used, which has some flexibility that allows for a redefinition of organ sizes. The phantom was modified to represent the anatomic geometry of a Brown Norway rat, which was used for Monte Carlo calculations of S factors. Kinetic data for radiolabeled BR96 monoclonal antibodies were used to calculate the absorbed dose. Biological data were gathered from an activity escalation study with (90)Y- and (177)Lu-labeled BR96 monoclonal antibodies, in which blood cell counts and bodyweight were examined up to 2 months follow-up after injection. Reductions in white blood cell and platelet counts and declines in bodyweight were quantified by four methods and compared to the calculated absorbed dose to the bone marrow or the total body. RESULTS A red marrow absorbed dose-dependent effect on hematological parameters was observed, which could be evaluated by a decrease in blood cell counts. The absorbed dose to the bone marrow, corresponding to the maximal tolerable activity that could safely be administered, was determined to 8.3 Gy for (177)Lu and 12.5 Gy for (90)Y. CONCLUSIONS There was a clear correlation between the hematological effects, quantified with some of the studied parameters, and the calculated red marrow absorbed doses. The decline in body weight was stronger correlated to the total body absorbed dose, rather than the red marrow absorbed dose. Finally, when considering a constant activity concentration, the phantom weight, ranging from 225 g to 300 g, appeared to have no substantial effect for the estimated absorbed dose.PURPOSE Biokinetic and dosimetry studies in laboratory animals often precede clinical radionuclide therapies in humans. A reliable evaluation of therapeutic efficacy is essential and should be based on accurate dosimetry data from a realistic dosimetry model. The aim of this study was to develop an anatomically realistic dosimetry model for Brown Norway rats to calculate S factors for use in evaluating correlations between absorbed dose and biological effects in a preclinical therapy study. METHODS A realistic rat phantom (Roby) was used, which has some flexibility that allows for a redefinition of organ sizes. The phantom was modified to represent the anatomic geometry of a Brown Norway rat, which was used for Monte Carlo calculations of S factors. Kinetic data for radiolabeled BR96 monoclonal antibodies were used to calculate the absorbed dose. Biological data were gathered from an activity escalation study with90 Y- and 177 Lu-labeled BR96 monoclonal antibodies, in which blood cell counts and bodyweight were examined up to 2 months follow-up after injection. Reductions in white blood cell and platelet counts and declines in bodyweight were quantified by four methods and compared to the calculated absorbed dose to the bone marrow or the total body. RESULTS A red marrow absorbed dose-dependent effect on hematological parameters was observed, which could be evaluated by a decrease in blood cell counts. The absorbed dose to the bone marrow, corresponding to the maximal tolerable activity that could safely be administered, was determined to 8.3 Gy for177 Lu and 12.5 Gy for 90 Y. CONCLUSIONS There was a clear correlation between the hematological effects, quantified with some of the studied parameters, and the calculated red marrow absorbed doses. The decline in body weight was stronger correlated to the total body absorbed dose, rather than the red marrow absorbed dose. Finally, when considering a constant activity concentration, the phantom weight, ranging from 225 g to 300 g, appeared to have no substantial effect for the estimated absorbed dose.

Repeated Radioimmunotherapy with 177Lu-DOTA-BR96 in a Syngeneic Rat Colon Carcinoma Model

AIM Fractionation is generally used as a mean to improve radioimmunotherapy (RIT). Since RIT is considered suitable for small-volume disease, the aim of the current study was to investigate whether repeated administration of (177)Lu-labeled mAb BR96 was tolerated and could delay or prevent metastatic disease after complete remission of the tumor obtained by the first administration. METHODS Immunocompetent rats bearing a syngeneic colon carcinoma were first treated with 400 MBq/kg (177)Lu-DOTA-BR96, an activity resulting in complete response in 29 of 30 animals. On day 21, two groups of rats were given an additional activity of 150 or 350 MBq/kg resulting in total administered activities corresponding to 0.9 and 1.3 times the maximal tolerated dose. RESULTS The additional treatment resulted in tolerable myelotoxicity; however, the frequency of metastatic disease and survival were not affected. Immunohistochemistry demonstrated binding of the BR96 antibody to tissue sections of analyzed metastases. CONCLUSIONS In our model, development of metastatic disease after treatment of the manifest tumor was not prevented by an additional treatment with the same radioimmunoconjugate. Therefore, the antibody should be labeled with a more suitable radionuclide for treatment of metastases. The repeated targeted therapy was well tolerated in aspects of myelotoxicity.

Antigen-independent binding of rat immunoglobulins in a radioimmunoassay. Solutions to an unusual background problem

A high non-specific binding of immunoglobulins to plastic surfaces was noted with a number of rat sera, when tested in an indirect 125I-labeled protein-A assay for detection of cell-surface-bound rat immunoglobulins of various classes and IgG subclasses. This type of non-specific binding was found with all types of Ig. The degree of binding varied with the type of test plate used and fluctuated with time among sera drawn sequentially from the same donors. Coating test wells with fetal calf serum supplemented with BSA, gelatin or fibrinogen did not eliminate the reactions. The immunoglobulins bind directly to the polystyrene, and not to antigens present in fetal calf serum or autoantigens in rat serum. Two different approaches were used to eliminate the nonspecific reaction. When living cells were used as target antigens, exclusively cell-bound radioactivity was eluted with the non-ionic detergent Nonidet P40, which solubilizes the cell membrane without breaking the protein-A/rabbit IgG, rabbit IgG/rat Ig, or rat Ig/plastic interactions. When rat serum antibodies are tested on target antigens adsorbed on non-tissue culture grade plates, non-specific binding may be avoided by including 0.05% Tween 20 in the incubation mixture.