The binding parameters of radiolabelled monoclonal F (ab′)2 and Fab′ fragments relative to immunoglobulin G in reactions with surface-bound antigens

The binding parameters of iodine-125-labelled intact monoclonal immunoglobulin G (IgG), F(ab)₂ and Fab fragments were compared. The study was carried out with the two monoclonal antibodies (MoAbs) K13 and K16 specific for human Ig light chains K and , respectively. When testing the ¹²⁵I-MoAbs against monodisperse polymer particles coated with the specific antigens, the K_a for the F(ab)₂ fragments were similar to that for IgG, while the K_a for the Fab fragments were reduced to 10%–20% of that for IgG. The number N of effective target sites revealed with Fab was higher than with F(ab)₂ and IgG, presumably because less surface area is occupied by the small Fab molecules. The immunoreactive fraction F ranged according to IgG > F(ab)₂ > Fab. The explanation of the moderate difference between the K_a of the monoclonal Fab and the divalent IgG and F(ab)₂ was that the divalent molecules were not divalently attached to the particles. When testing the same antibody preparations against human lymphoma cells producing Ig with light chains K or , the binding results were less reliable than when particles were utilised, presumably due to antigen shedding. Different MoAbs vary in their loss of immunoreactivity due to enzymatic degradation and the radiolabelling procedure. The preparation of the radiolabelled fragments should therefore be optimized for each MoAb, and evaluation is necessary before injection. Artificial targets with a low leakage of antigen, like the monodisperse polymer particles here applied, are recommended for the in vitro evaluation of the immunoreactivity of labelled MoAb preparations.     

Quantification of nicotinic acetylcholine receptors in human brain using [123I]5-I-A-85380 SPET

The purpose of this study was to assess the utility of a new single-photon emission tomography ligand, [¹²³I]5-iodo-3-[2(S)-2-azetidinylmethoxy]pyridine (5-I-A-85380), to measure regional nAChR binding in human brain. Six healthy nonsmoker subjects (two men and four women, age 33±15 years) participated in both a bolus (dose: 317±42 MBq) and a bolus plus constant infusion (dose of bolus: 98±32 MBq, B/I=6.7±2.6 h, total dose: 331±55 MBq) study. The study duration was 5–8 h and 14 h in the former and the latter, respectively. Nonlinear least-squares compartmental analysis was applied to bolus studies to calculate total (V_T) and specific (V_S) distribution volumes. A two-tissue compartment model was applied to identify V_S. V_T was also calculated in B/I studies. In bolus studies, V_T was well identified by both one- and two-tissue compartment models, with a coefficient of variation of less than 5% in most regions. The two-compartment model gave V_T values of 51, 22, 27, 32, 20, 19, 20, and 17 ml cm^–3 in thalamus, cerebellum, putamen, pons, and frontal, parietal, temporal, and occipital cortices, respectively. The two-compartment model did not identify V_S well. B/I studies provided poor accuracy of V_T measurement, possibly due to deviations from equilibrium conditions. These results demonstrate the feasibility of quantifying high-affinity type nAChRs using [¹²³I]5-I-A-85380 in humans and support the use of V_T measured by bolus studies.     

Radiolabelling of monoclonal antibodies: Optimization of conjugation of DTPA to F(ab′) 2-fragments and a novel measurement of the degree of conjugation using Eu(III)-labelling

F(ab) ₂ fragments (at concentrations of 5–30 mg/ml) derived from monoclonal antibodies raised against human prostate specific acid phosphatase were derivatized with a bicyclic anhydride of diethylenetriaminepentaacetic acid (cDTPAA) in the molar ratios of cDTPAA/F(ab) ₂ of 1:1, 5:1, 10:1 or 50:1. The most optimal product, aimed at radioimaging of prostatic cancer was obtained when the antibody fragment concentration was at least 10 mg/ml and the molar ratio of cDTPAA to F(ab) ₂ was 5:1 cDTPAA was added dissolved in dimethylsulfoxide (DMSO). Under these conditions, 1.8–2.2 DTPA molecules/F(ab) ₂ molecule were bound, giving a coupling efficiency of 37%–44%, and the labelling efficiency with ¹¹¹In (3 mCi/1 mg protein) was 95%±3% (n=7). The antibody fragment completely retained its immunoreactivity measured by radioimmunoassay and showed no aggregation when studied using sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE).For evaluation of the degree of conjugation of DTPA to the antibody fragment, a novel technique was developed relying on the use of EuCl₃, and the measurement of europium fluorescence employing time resolved fluorometry. Results by EuCl₃ labelling were identical to those obtained by the conventional ¹¹¹InCl₃ labelling method.     

Proportional anatomical stereotactic atlas for visual interpretation of brain SPET perfusion images

A semi-automatic method was developed to determine the anterior (AC) and posterior (PC) commissures on brain single-photon emission tomographic (SPET) perfusion images, and then to draw the proportional anatomical Talairach's grid on each axial SPET image. First, the AC-PC line was defined on SPET images from the linear regression of four internal landmarks (frontal pole of the brain, inferior limit of the anterior corpus callosum, sub-thalamic point and occipital pole). Second, the SPET position of AC and PC points on the AC-PC line was automatically determined from measurements made on hard copies of magnetic resonance (MR) images of the patients. Finally, a proportional Talairach's grid was automatically drawn on each axial SPET image. To assess the accuracy of localization of AC and PC points, co-registered technetium-99m hexamethylpropylene amine oxime SPET and MR images from 11 subjects were used. The mean displacements between estimated points on SPET and true points on MRI (x=sagittal, y=frontal and z=axial displacement) were calculated. The mean displacements (in mm) were x=–1.4±1.8, y=–1.7±3.3 and z=–1.1±2.5 for AC, and x=–1.8±1.8, y=0.3±3.2 and =–1.3±2.7 for PC. These displacements represented an error of less than 5 mm at the anterior or posterior pole of the brain or at the vertex. Intra- and inter-observer comparisons did not reveal significant differences in mean displacements. Thus, this semi-automatic method results in reproducible and accurate stereotactic localization of SPET perfusion abnormalities. This method can be used routinely for repeat follow-up studies in the same subject as well as in different individuals without requiring SPET MRI co-registration.     

Die Abhängigkeit des Faktors β von der Konzentrationshöhe

Zusammenfassung Die Begriffe des Konzentrationsabfalles \ und des Reduktionsfaktors sowie die Variationsbreiten dieser Größen werden diskutiert.Die mittlere Abbaugeschwindigkeit während langer Zeitspannen lag bei Blutalkoholkonzentrationen oberhalb 1,5 mindestens bei 0,16, wenn der errechnete Höchstwert (r = 0,7) annähernd erreicht wurde.Die statistische Auswertung von den 4118 Einzelentnahmen und den Entnahmen in zeitlichem Abstand bei 922 Personen zeigt die am häufigsten beobachtete Blutalkoholkonzentration bei 1,8und ein mittleres \₆₀ von 0,184.Der Faktor nimmt mit steigender Blutalkoholkonzentration zu. Die Unterschiede zwischen den Bereichen 0,41—1,2 und oberhalb 2,0 sind statistisch gesichert, die mittleren \₆₀-Werte von 0,17 bzw. 0,203 damit signifikant.Auszugsweise vorgetragen auf dem Kongreß für Gerichtliche und Soziale Medizim 1954 in Kiel.     

Alterations in an indium-111 Fab′ under conditions of utilization

This study was conducted to investigate alterations that occur in an indium/111 Fab of a monoclonal antibody following its in vivo administration. Patients were infused with 111 In-Fab of the monoclonal antibody ZCE-025. Serum and urine specimens were collected from these patients. Starting materials, serum, urine and controls samples were studied by electrophoresis. Animal distribution studies were performed in normal Balb/c mice and, in some cases, nude mice bearing a carcinoembryonic antigen (CEA)/producing human colon tumour since the antibody targets CEA. The studies indicated that the molecule circulated almost totally intact for at least 4 h and to a considerable extent for 24 h, with some evidence for in vivo fragmentation by 24 h. Evidence was also obtained suggesting the formation of a high molecular weight species in some patients. Shortly after infusion, some of the ¹¹¹In in the urine appeared as the intact Fab, but within hours the majority migrated electro-phoretically as low molecular weight species. We conclude that while the majority of the ¹¹¹In-Fab of this particular antibody remains intact and immunoreactive following its administration, the molecule is structurally changed to some degree shortly after its infusion into humans. Since each monoclonal antibody is unique, the degree and rapidity of degradation of its Fab in vivo could vary markedly from the above and possibly adversely effect its utility as a radiopharmaceutical. Offprint requests to: S.E. Halpern Funded by the Veterans Administration     

Improvement of brain single photon emission tomography (SPET) using transmission data acquisition in a four-head SPET scanner

Attenuation coefficient maps (-maps) are a useful way to compensate for non-uniform attenuation when performing single photon emission tomography (SPET). A new method was developed to record single photon transmission data and a-map for the brain was produced using a four-head SPET scanner. Transmission data were acquired by a gamma camera opposite to a flood radioactive source attached to one of four gamma cameras in the four-head SPET scanner. Attenuation correction was performed using the iterative expectation maximization algorithm and the-map. Phantom studies demonstrated that this method could reconstruct the distribution of radioactivity more accurately than conventional methods, even for a severely non-uniform-map, and could improve the quality of SPET images. Clinical application to technetium-99m hexamethylpropylene amine oxime (HMPAO) brain SPET also demonstrated the usefulness of this method. Thus, this method appears to be promising for improvement in the image quality and quantitative accuracy of brain SPET.This work was presented in part at the World Congress on Medical Physics and Biomedical Engineering, 7–12 July 1991, Kyoto, Japan     

Positive 131Cesium scanning in parathyroid adenoma

In a case of primary hyperparathyroidism, a palpable nodule, at the base of the right lobe of the thyroid, proved cool during ^99mTc scanning, but hot when scanned with radiocesium. The uptake of this tracer was higher than the uptake of ⁷⁵Se-selenomethionine after suppression with T₃.The authors discuss the possibility of cases of false-positive radiocesium uptake in extrathyroid nodules, and in particular, the use of this tracer for the detection of parathyroid adenoma by scanning.     

Agreement between emergency physician diagnosis and radiologist reports in patients discharged from an emergency department with community-acquired pneumonia

To evaluate the level of concurrence between radiologist reports and the diagnosis of community-acquired pneumonia (CAP) in patients discharged from an emergency department (ED), a retrospective chart audit of patients discharged with a diagnosis of pneumonia or possible pneumonia from the ED during a 2-year period was conducted. Emergency physician (EP) and radiology report (RR) diagnoses were categorized as pneumonia, possible pneumonia, non-pneumonia and normal, and categories from each were compared. 815 charts were analyzed. Of 671 EP diagnoses of pneumonia, 304 (45.3%) RRs reported pneumonia and 82 (12.2%), possible pneumonia. Of 815 EP diagnoses of pneumonia or possible pneumonia, 426 (52.3%) RRs were in agreement, while 216(26.5%) were of diagnoses other than pneumonia and 173 (21.1%) were read as normal. EPs and radiologists frequently disagree on whether a patient has pneumonia or not. Perhaps it is time to revisit the gold standard status of plain chest X-ray.Presented at the 9th International Conference of Emergency Medicine, Edinburgh, Scotland, 17–21 June, 2002.     

Non-invasive assessment of distribution volume ratios and binding potential: tissue heterogeneity and interindividually averaged time-activity curves

Due to the stochastic nature of radioactive decay, any measurement of radioactivity concentration requires spatial averaging. In pharmacokinetic analysis of time-activity curves (TAC), such averaging over heterogeneous tissues may introduce a systematic error (heterogeneity error) but may also improve the accuracy and precision of parameter estimation. In addition to spatial averaging (inevitable due to limited scanner resolution and intended in ROI analysis), interindividual averaging may theoretically be beneficial, too. The aim of this study was to investigate the effect of such averaging on the binding potential (BP) calculated with Logans non-invasive graphical analysis and the simplified reference tissue method (SRTM) proposed by Lammertsma and Hume, on the basis of simulated and measured positron emission tomography data {[¹¹C]d-threo-methylphenidate (dMP) and [¹¹C]raclopride (RAC) PET}. dMP was not quantified with SRTM since the low k ₂ (washout rate constant from the first tissue compartment) introduced a high noise sensitivity. Even for considerably different shapes of TAC (dMP PET in parkinsonian patients and healthy controls, [¹¹C]raclopride in patients with and without haloperidol medication) and a high variance in the rate constants (e.g. simulated standard deviation of K ₁=25%), the BP obtained from average TAC was close to the mean BP (error <5%). However, unfavourably distributed parameters, especially a correlated large variance in two or more parameters, may lead to larger errors. In Monte Carlo simulations, interindividual averaging before quantification reduced the variance from the SRTM (beyond a critical signal to noise ratio) and the bias in Logans method. Interindividual averaging may further increase accuracy when there is an error term in the reference tissue assumption E=DV ₂–DV (DV ₂ = distribution volume of the first tissue compartment, DV = distribution volume of the reference tissue). This can be explained by the fact that the distribution volume ratio (DVR=DV/DV) obtained from averaged TAC is an approximation for DV/DV rather than for DVR/n. We conclude that Logans non-invasive method and SRTM are suitable for heterogeneous tissues and that discussion of group differences in PET studies generally should include qualitative and quantitative assessment of interindividually averaged TAC.     

Immunoelektrophoretische Differenzierung der Proteine faulen Leichenblutes

Zusammenfassung Leichenblute verschiedener Fäulnisgrade wurden immunoelektrophoretisch untersucht. Für die Differenzierung der einzelnen Blutplasmafraktionen wurden Anti-Humanserum vom Kaninchen und die spezifischen Antiseren der Behringwerke gegen die nachstehend aufgeführten Proteine benutzt: Präalbumin, Albumin, ₁-Lipoprotein, ₂-Makroglobulin, ₂-Lipoprotein, ₁-Globulin (Transferrin),-Lipoprotein, Fibrinogen, ₂-A-Globulin, ₂-M-Globulin,- Globulin.Infolge der mangelnden Proportionalität zwischen Fortschritt der Fäulnis und Leichenalter gestattet die Immunoelektrophorese des Leichenblutes keine Todeszeitbestimmung.Albumin und- Globulin widerstehen der Fäulnis am längsten. Es folgen ₂-Makroglobulin, Transferrin und Fibrinogen. Die Proteine, die am reichlichsten im Menschenblut vorhanden sind, lassen sich im faulen Leichenblut auch am längsten nachweisen. Die Proteolyse folgt jedoch nicht nur quantitativen Gesetzen. Die Lipoproteine bilden insofern eine Ausnahme, als sie früher durch die Fäulnis eliminiert werden, als es ihrem Anteil am Gesamtprotein entspricht.Die Eiweißkörper des faulen Leichenblutes weisen im Vergleich zu ihren Homologen frischer Blutproben z. T. Veränderungen der Wanderungsgeschwindigkeit auf. Bei erhaltener Antigenstruktur treten Bruchstücke in Erscheinung, die mit dem Antiserum in ungleichmäßig geschwungenen oder aufgesplitterten Linien präcipitieren.Im Doppeldiffusionstest nachOuchterlony ließen sich im Vergleich zu den frischen Homologen keine Veränderungen der Antigenkomponenten der Proteine des faulen Leichenblutes nachweisen.Mit Unterstützung der Deutschen Forschungsgemeinschaft, der hiermit unser herzlicher Dank ausgesprochen wird.In Anlehnung an einen Vortrag auf der Tagung der Deutschen Gesellschaft für Gerichtliche und Soziale Medizin vom 30. 9. bis 3. 10. 62 in Münster (Westf.).Herrn Professor G.Weyrich zum 65. Geburtstag gewidmet.     

Rechtsdogmatische und forensischpsychiatrische Aspekte des Willensproblems

Zusammenfassung Die unterschiedlichen Bedeutungen des Willensbegriffs und die sich daraus ergebenden psychologischen, psychiatrischen und rechtsdogmatischen Fragen werden diskutiert.

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Summary The different meanings of the conception of purposely action and the resulting problems in psychology, psychiatry and penal law are discussed.

     

γ-Glutamyltransferase test as a new tool for identification of seminal stains

Summary A simple qualitative method for identification of seminal stains based on a high activity of -glutamyltransferase (-GTP) in human semen is described. It employs the release of -naphthylamine from N--glutamyl--naphthylamide by the -GTP action; -naphthylamine couples with Fast Garnet GBC salt to produce a strong brownish-red color. The data on its simplicity, specificity, and stability show that the present method is suitable for medicolegal examination of seminal stains as a preliminary test.     

Comparison of FP-CIT SPECT with F-DOPA PET in patients with de novo and advanced Parkinson’s disease

Purpose Diagnosis of Parkinsons disease (PD) can be difficult. F-DOPA PET is able to quantify striatal dopa decarboxylase activity and storage capacity of F-dopamine, but is expensive and not generally available. FP-CIT binds to the dopamine transporter, and FP-CIT SPECT is cheaper and more widely available, but has a lower resolution. The aim of this study was to compare these two methods in the same patients with different stages of PD to assess their power in demonstrating deficits of the striatal dopaminergic system.Methods Thirteen patients with de novo PD and 17 patients with advanced PD underwent FP-CIT SPECT and static F-DOPA PET. After data transfer to standard stereotactic space, a template with regions of interest was used to sample values of the caudate, putamen and an occipital reference region. The outcome value was striato-occipital ratios. Patients were clinically examined in the off state (UPDRS-III and H&Y stage).Results Good correlations were found between striatal F-DOPA uptake and striatal FP-CIT uptake (r=0.78) and between putaminal F-DOPA uptake and putaminal FP-CIT uptake (r=0.84, both p<0.0001). Both striatal uptake of FP-CIT and that of F-DOPA correlated moderately with H&Y stage (=–0.52 for both techniques), UPDRS-III (=–0.38 for F-DOPA; =–0.45 for FP-CIT) and disease duration (=–0.59 for F-DOPA; =–0.49 for FP-CIT, all p<0.05).Conclusion FP-CIT values correlate well with F-DOPA values. Both methods correlate moderately with motor scores and are equally able to distinguish patients with advanced PD from patients with de novo PD.     

Biodistribution of iodine-125 tyramine transforming growth factor α antisense oligonucleotide in athymic mice with a human mammary tumour xenograft following intratumoral injection

The Watson-Crick base pairing rule provides the underlying principle for the antisense (AS) approach to inhibiting gene expression. Transforming growth factor (TGF) was the first growth factor to be associated with tumorigenesis, thus making the TGF (mRNA) a potential target for AS therapy and offering the potential for monitoring of the progression of malignancy by non-invasive imaging with radiolabelled AS phosphodiester. Probe labelling and biodistribution were studied in the present report. A 23-mer oligonucleotide sequence was synthesized and grafted in 5 with a tyramine group which was further radioiodinated. The radiolabelled AS was injected intratumorally in mammary tumour-bearing BALB/c mice (3 weeks after inoculation of 7·10⁶ NS2T2A mammary cells). Biodistribution was monitored by sequential scintigraphy and organ radioactivity after autopsy. The 5 tyramine group allowed specific and stable radiolabelling of the AS with¹²⁵I. The¹²⁵I AS oligonucleotide was rapidly cleared from the tumour by intestine and kidneys. Four hours after intratumoral injection, 6.5%±1.5% of the dose was retained in the tumour as non-degraded¹²⁵I AS. It is concluded that 5 tyraminylated AS provides information on the biodistribution of AS oligonucleotide following intratumoral injection. These data will contribute to the pharmacology of AS oligonucleotides which can be used for therapy.     

Immunohistochemical dynamics of leukotoxin (9.10-eooxv-12-octadecenoic acid) in lungs of rats

This paper investigates the immunohistochemical dynamics of leukotoxin (9,10-epoxy-12-octadecenoic acid, LTx) in the lungs of rats exposed to hyperoxia with or without paraquat. The rats were treated with 100% oxygen or ambient air for 24. 48, 72 and 96 h in the presence or absence of a low or high dose paraquat (1,1-di-methyl-4,4-bipyridinium, PQ) injection. Immunostaining for LTx demonstrated positive reactions in the neutrophils that showed a progressive increase in intensity of staining with time in all groups exposed to 100% oxygen and in the group with high dose PQ, but the positive findings were weak in the group injected with low dose PQ only. We found the positive immunostaining reaction not only in neutrophils but also in alveolar macrophages. This indicates that LTx is produced by alveolar macrophages as well as by neutrophils depending on the treatment period under hyperoxic conditions, suggesting that LTx is an important chemical mediator in pulmonary diseases.     

In vitro and in vivo characterisation of nor-β-CIT: a potential radioligand for visualisation of the serotonin transporter in the brain

Radiolabelled 2-Cabomethoxy-3-(4-iodophenyl)tropane (-CIT) has been used in clinical studies for the imaging of dopamine and serotonin transporters with single-photon emission tomography (SPET). 2-Carbomethoxy-3-(4-iodophenyl)nortropane (nor--CIT) is a des-methyl analogue of -CIT, which in vitro has tenfold higher affinity (IC₅₀=0.36 nM) to the serotonin transporter than -CIT (IC₅₀=4.2 nM). Nor--CIT may thus be a useful radioligand for imaging of the serotonin transporter. In the present study iodine-125 and carbon-11 labelled nor--CIT were prepared for in vitro autoradiographic studies on post-mortem human brain cryosections and for in vivo positron emission tomography (PET) studies in Cynomolgus monkeys. Whole hemisphere autoradiography with [¹²⁵I]nor--CIT demonstrated high binding in the striatum, the thalamus and cortical regions of the human brain. Addition of a high concentration (1 M) of citalopram inhibited binding in the thalamus and the neocortex, but not in the striatum. In PET studies with [¹¹C]nor--CIT there was rapid uptake of radioactivity in the monkey brain (6% of injected dose at 15 min) and high accumulation of radioactivity in the striatum, thalamus and neocortex. Thalamus to cerebellum and cortex to cerebellum ratios were 2.5 and 1.8 at 60 min, respectively. The ratios obtained with [¹¹C]nor--CIT were 20%–40% higher than those previously obtained with [¹¹C]-CIT. Radioactivity in the thalamus and the neocortex but not in the striatum was displaceable with citalopram (5 mg/kg). In conclusion, nor--CIT binds to the serotonin transporter in the primate brain in vitro and in vivo and has potential for PET and SPET imaging of the serotonin transporter in human brain.     

Medullary-thyroid-carcinoma imaging in an animal model: Use of radiolabeled anticalcitonin F(ab′)2 and meta-iodobenzylguanidine

Radiolabeled anti-calcitonin (CT) immunoglobulin fragments (¹³¹I-anti-CT F(ab)₂) and meta-iodobenzylguanidine (¹³¹I-mIBG) were injected into nude mice with a transplanted medullary thyroid carcinoma (MCT). ¹³¹I-Anti-CT F(ab)₂ proved to be unsuitable for MCT scintigraphic imaging. However, a high mIBG uptake was observed in MCTs, but not in control tumors (mesothelioma). The uptake of mIBG was not modified by the presence of reserpine or pentagastrine. These results are discussed, and it is suggested that mIBG could be an APUD-system marker.     

Methamphetamin—ein Metabolit der Appetitzügler Benzphetamin und Furfenorex

Zusammenfassung Die Appetitzügler Didrex (1) [1-Phenyl-2-(N, N-methyl-benzyl-amino)propan — Benzphetamin] und Frugalan (2) [1-Phenyl-2-(N, N-methyl-furfuryl-amino)propan = Furfenorex] werden — wie GC-MS-Analysen ergaben — beim Menschen zu Methamphetamin (3) (1-Phenyl-2-methylamino-propan) metabolisiert. Käufliche Muster beider Präparate enthielten neben anderen Verunreinigungen Spuren von Methamphetamin (3).

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Summary The anorectics Didrex (1) [1-Phenyl-2-(N, N-methyl-benzyl-amino)propane = Benzphetamine] and Frugalan (2) [1-Phenyl-2-(N, N-methyl-furfuryl-amino)propane = Furfenorex] are metabolized to methamphetamine (3) (1-Phenyl-2-methylamino-propane) in man as demonstrated by GC-MS-analysis. Commercially available samples of the two drugs contained — besides other impurities — traces of methamphetamine (3).

Institut für Rechtsmedizin der Universität Göttingen.     

Comparison of IgG and F(ab′)2 fragments of bispecific anti-RCC×anti-DTIn-1 antibody for pretargeting purposes

Purpose An effective pretargeting strategy was developed for renal cell carcinoma (RCC) based on a biologically produced bispecific monoclonal antibody: anti-RCC×anti-DTPA(In) (bsMAb: G250×DTIn-1). Tumour uptake of a ¹¹¹In-labelled bivalent peptide after pretargeting with bsMAb G250×DTIn-1 was relatively high compared with that in other pretargeting systems using chemically coupled F(ab)₂ fragments. Here, we investigated the effect of the bsMAb form in the pretargeting strategy.Methods To determine the optimal interval between the administration of each of the bsMAb forms and the ¹¹¹In-labelled bivalent peptide, the biodistribution of the radioiodinated bsMAb forms was studied in athymic mice with subcutaneous SK-RC-1 RCC tumours. Since tumour targeting of the radiolabelled peptide depends on the bsMAb form and dose, a bsMAb dose escalation study was carried out for both bsMAb forms. Under optimised conditions, the biodistribution of the ¹¹¹In label in mice with pretargeted RCC was determined from 4 h up to 7 days p.i.Results The optimal interval between the two administrations was 72 h for the bsMAb IgG and 4 h for the bsMAb F(ab)₂. The optimal bsMAb dose for intact IgG was 67 pmol and the optimal bsMAb F(ab)₂ dose was 200 pmol. Targeting of the pretargeted RCC with 4 pmol ¹¹¹In-labelled bivalent peptide revealed high tumour uptake with both bsMAb forms.Conclusion With the pretargeting strategy, using either bsMAb IgG or bsMAb F(ab)₂, very efficient peptide targeting of the tumour was obtained. Uptake and retention of the radiolabel in the tumour with the pretargeting approach are not affected by the bsMAb form used.