Verschiedene 99mTc-Generatoreluate: Auswirkungen auf die radiochemische Reinheit der Markierungsprodukte

Ziel der Arbeit war es, relativ empfindliche Kits, die sich durch niedrigen Zinngehalt (HMPAO) oder komplizierte chemische Abläufe bei der Markierung (MAG3) auszeichnen, auf ihre Markierbarkeit mit verschiedenen Generatorelua-ten zu testen. Die radiochemische Reinheit der Markierungsprodukte der verschiedenen kommerziellen Kits (HMPAO: Amersham Buchler, MAG3: Mallinckrodt) wurde nach Anweisungen des Herstellers nach Zusatz des 99mTc04̄-Eluates von Tc-Generatoren der Firmen Amersham Buchler, Mallinckrodt und CIS-Biointernational bestimmt. Die Bestimmung der radiochemischen Reinheit erfolgte unter Verwendung radioanalytischer Verfahren wie High Performance Liquid Chromatography, Dünnschicht- und Papierchromatographie sowie Umkehrphasenchromatographie. Die Qualität der drei verschiedenen Generatoreluate war zur Markierung von HMPAO und MAG3 ausreichend. Die geringfügigen Qualitätsunterschiede beschränken den Einsatz in der nuklearmedizinischen Routine nicht.

Erste klinische Erfahrungen bei der Tumordiagnostik mit radioaktiven Lanthanid-Komplexen

Bei 70 Patienten wurde geprüft, ob 169Yb-markierte Metall-Ligand-Komplexe ähnlich wie bei vorangegangenen tierexperimentellen Studien in unterschiedlichen Tumoren gespeichert werden. Das zeitliche Verhalten dieser Radiopharmaka in Tumoren, im Skelett und in der Leber erlaubte eine gute bis ausgezeichnete szintigraphische Geschwulstdarstellung bei 61/70 Fällen. Eine diagnostisch aussagefähig interpretierbare Darstellung wurde in der Mehrzahl der Studien schon 2-5 h nach der i.v. Injektion der radioaktiven Verbindung möglich. Eine Anzahl von Läsionen wurde gefunden, für die mit anderen Methoden kein äquivalenter Befund vorlag. Diese Befunde wurden als Metastasen interpretiert.

Die Kinetik von rezeptorvermittelter Radiotoxizität des 16α-[125I]-Iodöstradiol-3,17ß

Ziel: Es wurden radiozytotoxische Effekte von 16α-[125l]-lodöstradi- ol-3,17ß ü 125 I]E) an MCF-7-Mammakarzinom-Zellen in Abhängigkeit von der Inkubationszeit in dem Zeitraum zwischen 1 und 24 h untersucht. Methoden: Der Rezeptorstatus der Zellen wurde durch immunhisto- chemische Färbung bestimmt. Die Akkumulation von [125|]E wurde in Gegenwart und Abwesenheit von nichtradioaktivem Östradiol sowie [127I]E und in Östrogenrezeptor (ER)-negativen im Vergleich zu ER-positiven Zellen getestet. Die Ermittlung der subzellulären Verteilung erfolgte in 0,25 M Saccharose durch Ultrazentrifugation. Die Radiozytotoxizität wurde unter den verschiedenen Versuchsbedingungen durch Standard- Kolonie-Assays nach Inkubation mit [125I]E (1.85 kBq/ml-55.5 kBq/ml) für 1, 2, 4, 8, 12 und 24 h ermittelt. Ergebnisse: Eine deutliche Zytotoxizität wurde nur bei Inkubation ER-positiver Zellen mit [125I]E gefunden. Das Maximum lag bei einer Reduktion der Überlebensfraktion auf 20-25% bei Radioaktivitätskonzentrationen im Inkubationsmedium von >37 kBq/ml. Diese maximalen Effekte wurden nach Inkubationszeiten von 8 h gefunden. Eine Verlängerung der Inkubationszeit führte zu keiner weiteren Verstärkung der Toxizität. Schlußfolgerungen: Die Ergebnisse zeigen, daß die Radioaktivität an die Östrogenrezeptoren gebunden wurde. Infolge ihrer Kernlokalisation haben Radioöstrogene, die sehr niederenergetische Elektronen (Auger-Elektronen) emittieren, therapeutische Relevanz durch ER-vermittelte Entfaltung zellinaktivierender, ionisierender Strahlung ohne Beeinflussung benachbarter Zellen. Allerdings sollte anstelle von 125l das kürzerlebige 123l zur Markierung zum Einsatz kommen, da die entscheidenden Strahleneffekte innerhalb von 8 h erfolgen.

Zusammenhänge zwischen Eigenschaften von 131I-Therapiekapseln und der Radioiodkinetik

Ziel: Es sollte das Auftreten nichtreproduzierbarer Meßwerte bei Radioiodtest und Radioiodkinetik unter 131l-Therapie geklärt werden. Methoden: Der lodgehalt der Kapseln wurde kolonmetrisch und mit der Aktivierungsanalyse bestimmt. Die Messung der radiochemischen Reinheit erfolgte mittels HPLC und Elektrophorese. Das Löseverhalten der Kapseln wurde unter unterschiedlichen Bedingungen überprüft. Ergebnisse: Der lodgehalt der Kapseln schwankte zwischen 0,8 und ca. 100 μg/Kapsel. Die radiochemische Reinheit der Kapseln differierte ebenfalls (75%-99,5%). Hauptverunreinigung war lodat. Das Löseverhalten war ebenfalls unterschiedlich. Schlußfolgerung: Zusätzliches nichtradioaktives lod in den Therapiekapseln könnte eine Ursache verminderter Radioiodaufnahme unter Therapie sein.

Synthese tumoraffiner Yb-169- und Y-90-Porphyrin-Komplexe und tierexperimentelle Untersuchung verschiedener Yb-169-Porphyrine

Ziel: Es wurde untersucht, ob eine Einführung radioaktiver Isotope von Yb und Y in ausgewählte Porphyrine möglich ist. Außerdem sollten erste Daten zur Bioverteilung von radioaktiven Yb-169-Porphyrin-Komplexen gewonnen werden. Methoden: Die Synthesen der Metall-Porphyrin-Komplexe erfolgten mit geträgerten Radiometallen. Erste Tierversuche wurden an Mammakarzinom-tragenden Mäusen durchgeführt. Die Organe wurden 5 und 24 h nach i.v.-lnjektion im Bohrlochdetektor gemessen. Ergebnisse: Es konnten vier Yb-169-Porphyrin-Komplexe und Y-90-Porphyrin-Komplexe in nicht trägerfreier Form synthetisiert werden. Dies wurde anhand der Absorptionsspektren sowie mittels DC und HPLC bewiesen. Je nach Komplex lagen die Tumor/Untergrund-Verhältnisse im Durchschnitt zwischen 2 und 20. Schlußfolgerung: Die synthetisierten radioaktiven Metall-Porphyrin-Komplexe zeigen eine deutliche Tumoraffinität, die bei weiterer Verbesserung der Synthese (Ziel: Trägerreduzierung, andere Radionuklide) eine Tumorszintigraphie und vielleicht -therapie ermöglichen könnte.

Development of anti-CD30 radioimmunoconstructs (RICs) for treatment of Hodgkin's lymphoma

Objectives: Comparison of the binding affinity to a CD30-positive Hodgkin lymphoma (HL) cell line and biodistribution in HL bearing mice of new anti-CD30 radioimmunoconjugates (RICs) of varying structure and labelling nuclides. Methods: The antibodies Ki-4 and 5F11 were radioiodinated by the chloramine T method or labelled with 111In via p-NCSBenzyl- DOTA. In addition, the Ki-4-dimer was investigated in the iodinated form. The RICs were analyzed for retained immunoreactivity by immunochromatography. In-vitro binding studies were performed on CD30-positive L540 cell lines. For in-vivo biodistribution studies, SCID mice bearing human HL xenografts were injected with the various radioimmunoconjugates. After 24 h, activities in the organs and tumour were measured for all 5 RICs. Tumour-free animals were studied in the same way with 131I- Ki-4 24 h p. i. The three RICs with the highest tumour/background ratios 24 h p.i. (131I-Ki-4, 131I–5F11, 111In-bz- DOTA-Ki-4) were analysed further at 48 h and 72 h. Results: All the RICs were successfully labelled with high specific activities (28–47 TBq/ mmol) and sufficient radiochemical yields (> 80%). Scatchard plot analysis proved high tumour affinity (KD = 20–220 nmol/l). In-vivo tumour accumulation in % of injected dose per g tissue (%ID/g) lay between 2.6 (131I-5F11) and 12.3 % ID/g (131I-Ki-4) with permanently high background in blood. Tumour/blood-ratios of all RICs were below one at all time points. Conclusions: In-vitro tumour cell affinities of all RICs were promising. However, in-vivo biokinetics tested in the mouse model did not meet expectations. This highlights the importance of developing and testing further new anti-CD30 conjugates.

Radioimmunotherapy with yttrium-90 ibritumomab tiuxetan

90Y-ibritumomab tiuxetan (Zevalin®) is currently approved for radioimmunotherapy of patients with relapsed or refractory follicular non-Hodgkin’s lymphoma pretreated with rituximab. Future directions are the combined use of 90Y-ibritumomab tiuxetan as part of the initial treatment and as first-line multi-agent therapy of relapsed disease. Current studies investigate patients with other than follicular indolent histologies, e. g. diffuse large cell lymphoma. Labelling of 90Y ibritumomab tiuxetan is a safe procedure, the radiochemical purity is not disturbed by a higher room temperature or by metallic impurity. Quality control is recommended by thin layer chromatography (TLC), strips >15 cm are favourable. TLC cannot distinguish between the correctly radiolabelled antibodies and radiocolloid impurity. If necessary, additional HPLC should be performed. Radiocolloid impurities are absorbed to the solid phase and do not reach the eluate. If the radiochemical purity test is insufficient (<95%), the additional cleaning using EconoPac 10 DG columns (Biorad, Hercules, CA, USA) is a reliable procedure to reduce the percentage of free radionuclide. However, this procedure is not part of the approval.

Exhalation of 1-131 after radioiodine therapy: time dependence and chemical form

Aim: The change of both amount and chemical forms of radioiodine exhaled in the air of rooms with patients on the therapy ward should be investigated depending on radioactivity applied, time after application, and kind of thyroid disease. Methods: The air of ward-rooms of 62 patients with thyroid carcinoma, Graves’ Disease, and autonomy which received different therapy doses, was investigated with an portable constant air flow sampler. Different chemical iodine species (organic, elemental, aerosol bound) were collected during 8 hr in various filters until 3 days after application of the radioiodine capsule, according to their chemical form. The radioactivity in the filters was measured with a well counter on defined time points after application. Results: The radioactivity exhaled was between 0,008 and 0,03% related to activity of radioiodine applied. The percentage of radioiodine exhaled related to the activity applied, differed significantly depending on disease and changed as follows: Grave’s Disease > autonomy > carcinoma. The exhalation of radioiodine became stronger with increasing applied activities and showed an exponential decrease with time. The most part of radioiodine was present in organic bound form. This organic portion decreased with time in favour of the other iodine species. Conclusion: The degree of accumulation of radioiodine orally applied within thyroid seems to be in direct proportion to the extend of its exhalation. Further measurements directly in the breathing air of RIT-patients are necessary, in order to clarify the relationship between degree of thyroid uptake and quantity as well as chemical form of radioiodine exhaled.

Administration of additional inactive iodide during radioiodine therapy for Graves' disease

Aim: Graves' hyperthyroidism and antithyroid drugs empty the intrathyroid stores of hormones and iodine. The consequence is rapid 131I turnover and impending failure of radioiodine therapy. Can administration of additional inactive iodide improve 131I kinetics? Patients, methods: Fifteen consecutive patients, in whom the 48 h post-therapeutically calculated thyroid dose was between 150 and 249 Gy due to an unexpectedly short half-life, received 3 × 200 μg inactive potassium-iodide (127I) daily for 3 days (Group A), while 17 consecutive patients with a thyroid dose of ≥ 250 Gy (Group B) served as the non-iodide group. 48 hours after 131I administration (M1) and 4 or 5 days later (M2) the following parameters were compared: effective 131I half-life, thyroid dose, total T3, total T4, 131I-activity in the T3- and T4-RIAs. Results: In Group A, the effective 131I half-life M1 before iodine (3.81 ± 0.93 days) was significantly (p <0.01) shorter than the effective 131I half-life M2 (4.65 ± 0.79 days). Effective 131I half-life M1 correlated with the benefit from inactive 127I (r = –0.79): Administration of 127I was beneficial in patients with an effective 131I half-life M1 of <3 or 4 days. Patients from Group A with high initial specific 131I activity of T3 and T4 showed lower specific 131I activity after addition of inactive iodine compared with patients from the same group with a lower initial specific 131I activity of T3 and T4 and compared with the patient group B who was given no additional inactive iodide. This correlation was mathematically described and reflected in the flatter gradient in Group A (y = 0.5195x + 0.8727 for 131I T3 and y = 1.0827x – 0.4444 for 131I T4) and steeper gradient for Group B (y = 0.6998x + 0.5417 for 131I T3 and y = 1.3191x – 0.2901 for 131I T4). Radioiodine therapy was successful in all 15 patients from Group A. Conclusion: The administration of 600 μg inactive iodide for three days during radioiodine therapy in patients with Graves' hyperthyroidism and an unexpectedly short half-life of <3 or 4 days was a safe and effective alternative to the administration of a second radioiodine capsule

Retention efficacy and release of radioiodine in fume hoods

Procedures to determine the release of hazardous gaseous substances including radioactive iodine are covered by different norms such as the European standard EN 14175 and the German national standard DIN 25466. The detection of sulphur hexafluoride (SF₆) is required to comply with the prescribed methodology. The detection limit of this test is 4.5·10^-7 mol/m³ in exhaust air. This detection limit would represent a very high activity in the region of 0.27 TBq/m³ leading to an unacceptable risk. We therefore developed a test using a filter system, consisting of a combination of filters capable of separating various chemical forms of airborne radioiodine. Air samples were collected directly in front of the fume hood and in the laboratory beside two different fume hoods of a similar construction with a final activated carbon filter for retention of radioiodine. Particular attention was therefore paid to air samples taken after passage over the filters. Significant differences in the degree of retention of iodine were found between the two fume hoods investigated. In one test a malfunction of the fume hood was demonstrated. In this case 0.148 × 10^-3% of the total released activity per m³ air was found 1 cm in front of the hood sash. A remarkably high fraction of the activity released in the fume hood (1.3 × 10^-3%/m³ air) was measured after the activated carbon filter. In the ambient air, values of up to 8.6 × 10^-6% pro m³ laboratory air sampled were measured, despite a 6-8-fold air exchange. The selected procedure is a factor of 10¹¹ (Schomäcker et al., 2001) more sensitive than the standard recommended methods (EN 14175). The standard test prescribed by the DIN/EN failed to reveal any inadequacy in the protective function of the radionuclide hood with respect to radioiodine retention.

The effectiveness of wastewater treatment in nuclear medicine: Performance data and radioecological considerations

For planned and ongoing storage of liquid radioactive waste in a designated plant for a nuclear medicine therapy ward (decontamination system/decay system), detailed knowledge of basic parameters such as the amount of radioactivity and the necessary decay time in the plant is required. The design of the plant at the Department of Nuclear Medicine of the University of Cologne, built in 2001, was based on assumptions about the individual discharge of activity from patients, which we can now retrospectively validate. The decontamination factor of the plant is at present in the order of 10^-9 for ¹³¹I. The annual discharges have been continuously reduced over the period of operation and are now in the region of a few kilobecquerels. This work emphasizes the high efficacy of the decontamination plant to reduce the amount of radioactivity released from the nuclear medicine ward into the environment to almost negligible levels.

Influence of iodine supply on the radiation-induced DNA-fragmentation

The protective effect of stable iodide against radiation on thyroid cells was investigated. One physiological effect of stable iodine is well-rooted: stable iodine leads to a reduced thyroid uptake of radioactive iodine. This work wants to focus on an intrinsic effect of stable iodine by which DNA-damage in cells is prevented. To investigate this intrinsic effect thyroid cells (FRTL-5) were externally irradiated by use of a linear accelerator (LINAC) applying energy doses of 0.01 Gy-400 Gy and by incubation with various activity concentrations of ¹³¹I (0.1-50 MBq/ml for 24 h). We added stable iodine (NaI) to the cells prior to external irradiation and investigated the effect of the concentration of stable iodine (1, 5, 15 μg/ml). In order to clarify whether thyroid cells have a distinctive and iodine-dependent reaction to ionizing radiation, keratinocytes (HaCaT) without NIS were exposed in the same way. As indicators for the cellular reaction, the extent of DNA fragmentation was determined (Roche, Mannheim, Germany). Both cell types showed distinct ability for apoptosis as proven with camptothecin. The addition of "cold" iodine from 1 to 15 μg/ml without irradiation ("negative control") did not change the response in both cell types. Plausibly, the radio-sensitivity of both cell types did increase markedly with increasing radiation dose but the radiation effect is diminished if iodine is added to the thyroid cells beforehand. The DNA-damage in thyroid cells after addition of cold iodine is reduced by a factor of 2-3. The skin cells did not show an significant change of radio-sensitivity depending on the presence of cold iodine. Elementary iodine possibly acts as a radical scavenger and thus markedly reduces the secondary radiation damage caused by the formation of cytotoxic radicals. This intrinsic radioprotective effect of iodine is seen only in cells with NIS.

Exhalation of 131I after radioiodine therapy: Dosimetric considerations based on measurements in exhaled air

It is well known that a considerable amount of radioiodine is exhaled after radioiodine therapy (RIT) leading to unwanted radiation exposure through inhalation for non-involved persons. This study focuses on the amount of exhalation in the breath-out air of RIT-patients and the dosimetric consequences. Furthermore, the correlation between radioiodine uptake and exhalation was investigated. The radioiodine species were collected in a filter system and quantified over time by measurements with a scintillation counter. The dosimetric implications were then studied for different exposure scenarios. Of the activity administered to the patient, approximately 10^-3% (50-110 ppm) is exhaled. The radioiodine inhalation taking place following exhalation in the vicinity yields doses of up to 500 μSv (children, staying with the patient immediately after application and for the next 8 h). Three days after administration the doses are significantly reduced. This study lays emphasis on previous assumptions that exhalation depends on thyroid storage. Regardless of the type of thyroid disease, the predominant form exhaled is organic radioiodine. The amount of exhaled radioiodine is small but from the point of view of radiation protection, by no means negligible immediately after administration. Radiation doses received by incorporation of exhaled radioiodine can easily exceed 100 μSv soon after administration of radioiodine. Three days after RIT the radioactivity can still be measured in the exhaled air but even at maximum, the annual doses lie far below 10 μSv and are thus comparatively low.

Administration of additional inactive iodide during radioiodine therapy for Graves' disease: who might benefit?

AIM

Graves' hyperthyroidism and antithyroid drugs empty the intrathyroid stores of hormones and iodine. The consequence is rapid 131I turnover and impending failure of radioiodine therapy. Can administration of additional inactive iodide improve 131I kinetics?

PATIENTS, METHODS

Fifteen consecutive patients, in whom the 48 h post-therapeutically calculated thyroid dose was between 150 and 249 Gy due to an unexpectedly short half-life, received 3 x 200 microg inactive potassium-iodide (127I) daily for 3 days (Group A), while 17 consecutive patients with a thyroid dose of > or = 250 Gy (Group B) served as the non-iodide group. 48 hours after 131I administration (M1) and 4 or 5 days later (M2) the following parameters were compared: effective 131I half-life, thyroid dose, total T3, total T4, 131I-activity in the T3- and T4-RIAs.

RESULTS

In Group A, the effective 131I half-life M1 before iodine (3.81 +/- 0.93 days) was significantly (p < 0.01) shorter than the effective 131I half-life M2 (4.65 +/- 0.79 days). Effective 131I half-life M1 correlated with the benefit from inactive 127I (r = -0.79): Administration of 127I was beneficial in patients with an effective 131I half-life M1 of <3 or 4 days. Patients from Group A with high initial specific 131I activity of T3 and T4 showed lower specific 131I activity after addition of inactive iodine compared with patients from the same group with a lower initial specific 131I activity of T3 and T4 and compared with the patient group B who was given no additional inactive iodide. This correlation was mathematically described and reflected in the flatter gradient in Group A (y = 0.5195x + 0.8727 for 131I T3 and y = 1.0827x - 0.4444 for 131I T4) and steeper gradient for Group B (y = 0.6998x + 0.5417 for 131I T3 and y = 1.3191x - 0.2901 for 131I T4). Radioiodine therapy was successful in all 15 patients from Group A.

CONCLUSION

The administration of 600 microg inactive iodide for three days during radioiodine therapy in patients with Graves' hyperthyroidism and an unexpectedly short half-life of <3 or 4 days was a safe and effective alternative to the administration of a second radioiodine capsule.

[Radioimmunotherapy with yttrium-90 ibritumomab tiuxetan. Clinical considerations, radiopharmacy, radiation protection, perspectives]

90Y-ibritumomab tiuxetan (Zevalin) is currently approved for radioimmunotherapy of patients with relapsed or refractory follicular non-Hodgkin's lymphoma pretreated with rituximab. Future directions are the combined use of 90Y-ibritumomab tiuxetan as part of the initial treatment and as first-line multi-agent therapy of relapsed disease. Current studies investigate patients with other than follicular indolent histologies, e. g. diffuse large cell lymphoma. Labelling of 90Y ibritumomab tiuxetan is a safe procedure, the radiochemical purity is not disturbed by a higher room temperature or by metallic impurity. Quality control is recommended by thin layer chromatography (TLC), strips >15 cm are favourable. TLC cannot distinguish between the correctly radiolabelled antibodies and radiocolloid impurity. If necessary, additional HPLC should be performed. Radiocolloid impurities are absorbed to the solid phase and do not reach the eluate. If the radiochemical purity test is insufficient (<95%), the additional cleaning using EconoPac 10 DG columns (Biorad, Hercules, CA, USA) is a reliable procedure to reduce the percentage of free radionuclide. However, this procedure is not part of the approval.

[Hodgkin's lymphoma in nuclear medicine: diagnostic and therapeutic aspects]

Today, diagnostic and therapeutic strategies of Hodgkin lymphoma (HL) with positron emission tomography and radioimmunotherapy include state-of-the-art nuclear medicine which require the cooperation between oncology and nuclear medicine. The benefit of FDG-PET in HL patients with residual tumor masses consists of its high negative predictive value in the therapy control of the disease. The concept of waitful watching in patients with PET-negative residual masses after BEACOPP-chemotherapy will be evaluated in a large multicenter trial of the GHSG (German Hodgkin Study Group). Radioimmunotherapy has been performed in patients with CD20-positive Non-Hodgkin lymphoma for 10 years with promising results. HL is also an excellent target for immunotherapy due to the expression of antigens such as CD25 and CD30. Thus, a new radioimmunoconstruct consisting of the murine anti-CD30 antibody Ki-4 labeled with iodine-131 was developed for patients with relapsed or refractory HL.

Hodgkin’s lymphoma in nuclear medicine: diagnostic and therapeutic aspects

Today, diagnostic and therapeutic strategies of Hodgkin lymphoma (HL) with positrone emission tomography and radioiummunotherapy include state-of-the-art nuclear medicine which require the cooperation between oncology and nuclear medicine. The benefit of FDG-PET in HL patients with residual tumor masses consists of its high negative predictive value in the therapy control of the disease. The concept of waitful watching in patients with PET-negative residual masses after BEACOPPchemotherapy will be evaluated in a large multicenter trial of the GHSG (German Hodgkin Study Group). Radioimmunotherapy has been performed in patients with CD20-positive Non-Hodgkin lymphoma for 10 years with promising results. HL is also an excellent target for immunotherapy due to the expression of antigens such as CD25 and CD30. Thus, a new radio-immunoconstruct consisting of the murine anti-CD30 antibody Ki-4 labeled with iodine-131 was developed for patients with relapsed or refractory HL.

High cervical spinal cord stimulation (CSCS) increases regional cerebral blood flow after induced subarachnoid haemorrhage in rats

The effects of high cervical spinal cord stimulation (cSCS) on regional cerebral blood flow (rCBF) were investigated after experimentally induced subarachnoid haemorrhage (SAH) in rats by the means of (99m)Tc-HMPAO. The experiments were carried out on a total of 24 Wistar rats, divided in three groups [group I: control without SAH, group II: SAH, group III: SAH and cSCS]. (99m)Tc-HMPAO was administered intravenously (group II/group III) 48 hours after induction of SAH. In group III, (99m)Tc-HMPAO was given after 3 hours of cSCS. All animals were sacrificed 30 minutes after application on (99m)Tc-HMPAO. Radioactivities were determined in blood, cerebrum and cerebellum. The ratio cerebrum/blood and cerebellum/blood was calculated to ascertain "extraction rate" in the sample differentially. The following mean values were calculated for the cerebellum/blood ratio: Group I: 1.06, SD: 0.21; Group II: 0.66, SD: 0.21; Group III: 1.00, SD: 0.37. Comparing the mean values a highly significant difference could be found between group II and III (p = 0.007) and between group I and II (p = 0.0019), respectively. Calculations of the cerebrum/blood ratio revealed similar results. After SAH cSCS enhances cerebral and cerebellar blood flow in rats. Possibly, cSCD constitutes a new therapeutic approach in the treatment of disturbed regional cerebral blood flow after SAH.

Effects of electrical stimulation of the Gasserian ganglion on regional cerebral blood flow after induced subarachnoid hemorrhage in pigs evaluated by 99mTc-HMPAO-SPECT

It could be demonstrated that cervical spinal cord stimulation increases cerebral blood flow. The effects of electrical stimulation of the trigeminal ganglion in the acute phase of SAH in pigs were investigated. The experiments were carried out on 11 domestic pigs divided in two groups (group I: SAH [n = 5]; group II: SAH and trigeminal stimulation [n = 6]). In all animals a native SPECT was performed. The Gasserian ganglion was exposed for inserting the stimulation electrode. SAH was induced by injecting 10 ml autologous blood through a catheter placed in the suprasellar cistern. 30 minutes after SAH-induction electrical stimulation was started for two hours in group II (2.8-4.5 V, 50 Hz, 300 microseconds). 99mTc-HMPAO (400-540 MBq) was injected intravenously 110 minutes later. In group I 99mTc-HMPAO was applied after the same time interval. 80 minutes later SPECT was performed. Data were processed to calculate the uptake of radioactivity (%/kg tissue weight). The mean values were calculated for the different groups: native animal examination (%/kg tissue weight): 0.6343; group I: 0.468; group II: 0.6533. Comparing the mean values a highly significant difference between group I and group II (p < 0.01) and between native examination and group I (p < 0.01) could be found. No statistical significance could be detected on comparing the left/right-ratio in any ROI. The electrical stimulation of the Gasserian ganglion leads to a significantly increased uptake of 99mTc-HMPAO after induced SAH. Maybe the stimulation of the Gasserian ganglion constitutes a new therapeutic modality treating disturbed rCBF after SAH.

[Exhalation of I-131 after radioiodine therapy (RIT): time dependence and chemical form]

AIM

The change of both amount and chemical forms of radioiodine exhaled in the air of rooms with patients on the therapy ward should be investigated depending on radioactivity applied, time after application, and kind of thyroid disease.

METHODS

The air of ward-rooms of 62 patients with thyroid carcinoma, Graves' Disease, and autonomy which received different therapy doses, was investigated with an portable constant air flow sampler. Different chemical iodine species (organic, elemental, aerosol bound) were collected during 8 hr in various filters until 3 days after application of the radioiodine capsule, according to their chemical form. The radioactivity in the filters was measured with a well counter on defined time points after application.

RESULTS

The radioactivity exhaled was between 0.008 and 0.03% related to activity of radioiodine applied. The percentage of radioiodine exhaled related to the activity applied, differed significantly depending on disease and changed as follows: Grave's Disease > autonomy > carcinoma. The exhalation of radioiodine became stronger with increasing applied activities and showed an exponential decrease with time. The most part of radioiodine was present in organic bound form. This organic portion decreased with time in favour of the other iodine species.

CONCLUSION

The degree of accumulation of radioiodine orally applied within thyroid seems to be in direct proportion to the extend of its exhalation. Further measurements directly in the breathing air of RIT-patients are necessary, in order to clarify the relationship between degree of thyroid uptake and quantity as well as chemical form of radioiodine exhaled.

Use of myocardial imaging agents for tumour diagnosis--a success story?

The search for new radiopharmaceuticals for tumour diagnosis usually proceeds on the basis of rational concepts drawing on the latest advances in molecular biology. Using this approach, radioactive peptide hormones, antibodies and oligonucleotides have been developed that are used increasingly in nuclear medicine for diagnostic and therapeutic purposes. This article, however, focusses on a group of radiopharmaceuticals whose use in tumour diagnosis was not the outcome of a methodical development programme but rather the result of a chance discovery. These radiopharmaceuticals, thallium-201 and technetium-99m labelled 2-methoxyisobutylisonitrile (MIBI), tetrofosmin and furifosmin, were first developed through extensive research efforts for cardiac imaging, but during their worldwide application for myocardial scintigraphy they were accidentally found to accumulate in tumours. Intensive studies were then begun on cell cultures in an attempt to discover the cause of their uptake into tumours. The aim was to compare the effectiveness of the radiopharmaceuticals for tumour diagnosis in a range of indications and to investigate the various mechanisms by which they are taken up into tumours. While the more favourable radiophysical properties of 99mTc-MIBI render it superior to 201Tl for many diagnostic purposes, neither 99mTc-tetrofosmin nor 99mTc-furifosmin has yet proved suitable for clinical routine examinations, although the former has found limited application. In the case of 99mTc complexes, the breakthrough came with the experimental finding that these substances are substrates of P-glycoprotein, a product of the human multidrug resistance gene (MDR1). The concentration of 99mTc complexes in tumour cells is a function of a passive, membrane potential-dependent influx into and a P-glycoprotein-controlled efflux out of the tumour cell. Preliminary studies suggest that in vivo detection of MDR may even be possible. There is also evidence that the P-glycoprotein-mediated transport system can be blocked competitively. However, it will be some time before a system can be developed for detection of MDR on a routine basis.

[Synthesis of tumor affinity label Yb-169- and Y-90- porphyrin complexes and animal experimental investigations with various Yb-169-porphyrins]

AIM

It should be shown, that it is possible to insert radioactive isotopes of Yb and Y into some selected porphyrins. Besides, first informations about the biodistribution of Yb-169-por-phyrin-complexes should be obtained.

METHODS

Carrier added radioactive isotopes were used for the synthesis of the metal porphyrin complexes. The animal experiments were done with mamma carcinoma bearing mice. The activity of the organs was determined 5 and 24 h after i.v. injection in a well counter.

RESULTS

Four Yb-169-porphyrin complexes and Y-90-porphyrin complexes could be synthesized in non-carrier-free form. This was verified by absorption spectra, TLC and HPLC. Depending on the complex, the average tumour/background ratios were between 2 and 20.

CONCLUSION

The synthesized radioactive metal-porphyrin complexes showed a clear tumour-affinity which could be used for tumour scintigraphy or perhaps therapy if the synthesis is improved (goal: reduction of carrier, other radionuclides).

[Kinetics of receptor-mediated radiotoxicity of 16alpha-[125I]-iodostradiol-3,17beta]

AIM

The radiocytotoxic effects in estrogen receptor (ER) containing MCF-7 cells of a mamma carcinoma were investigated following incubation with [125I]E ranging from 1 h to 24 h.

METHODS

The receptor status of the cells was confirmed by immunohistochemical staining. The accumulation of [125I]E in MCF-7 cells was tested in the presence and absence of radioinert E and [127I]E and in ER-negative cells in comparison to ER-positive cells. The subcellular distribution was investigated in 0.25 M Saccharose by ultra centrifugation. The radiocytotoxicity was assessed in ER-positive and negative cells by a standard colony forming assay after incubating with [125I]E (1.85 kBq/ml-55.5 kBq/ml) for 1, 2, 4, 8, 12, and 24 h.

RESULTS

A significant cytotoxicity was observed only when ER-rich MCF-7-cells were incubated with [125I]E alone. The maximal cytotoxic effect was a reduction of survival fraction to 20-25%. This was achieved at radioactivity concentrations > 37 kBq/ml. Maximal effect was seen after 8 h incubation, extension of incubation time did not further increase toxicity.

CONCLUSION

The results suggest that the radioactivity was bound to ER. Through their nuclear localization radioestrogens tagged with radionuclides emitting very low energy electrons (Auger electrons) bear potential for therapy by ER-mediated deposition of lethal doses of ionizing radiation to single cells without affecting neighbouring cells. But, instead of 125I the shorter-living 123I shall be used for labelling because the deciding radiation effectes occur within the first 8 h.

[Influence on extratumoral organ activities of tumor-affinity samarium-153 preparations]

AIM

Possibilities to exercise an influence on the biodistribution of a tumor-affine 153Sm-preparation, samarium-153-nitrilotriacetate (NTA), were tested.

METHODS

Animals experiments on tumor-bearing mice after additional application of EDTMP (ethylenediamine tetramethylene phosphonate) for the reduction of extratumorale liver-radioactivity and yttrium chloride for the reduction of unwanted underground radioactivity in bone were carried out. Furthermore, the combination of both measurements was tested.

RESULTS

The biodistribution of 153Sm-NTA showed a rather low tumor-radioactivity of app. 0.72%/g. The additional EDTMP-application caused a dose-dependent decrease of the underground-radioactivity in liver especially if given 2 h in advance or simultaneously. The additional application of the stable yttrium salt reduced the bone radioactivity on simultaneous increase of liver- and spleen-radioactivity and practically unchanged tumor-radioactivity. The combined use of EDTMP together with the bone-affine metal salt led to a reduction of liver radioactivity on simultaneous reduction of bone radioactivity.

CONCLUSIONS

The background radioactivity can be reduced on unchanged tumor-radioactivity by combined Na-EDTMP/YCl3-application. The present results do not allow a therapeutic exploitation because of the low tumor accumulation.

Beeinflussung extratumoraler Organaktivitäten von tumoraffinen Samarium-153-Zuhereitungen

Ziel: Es sollten Einflußmöglichkeiten auf die Bioverteilung einer tumoraffinen 153Sm-Zubereitung, von Samarium-153 Nitrilotriazetat (NTA), getestet werden. Methoden: Es wurden Tierexperimente an tumortragenden Mäusen nach Zusatzapplikation von EDTMP (Ethylendiamintetra-methylenphosphonat) zur Reduktion der extratumoralen Leber-Radioaktivität bzw. stabilem Yttriumchlorid zur Verminderung unerwünschter Untergrund-Radioaktivität im Knochen durchgeführt. Ebenfalls wurde die Kombination beider Maßnahmen getestet. Ergebnisse: Die Bioverteilung der 153Sm-NTA-Kontrollgruppe zeigte 24 h p.i. eine Tumoraktivität von nur ca 0.72%/g. Die EDTMP-Zusatzapplikation bewirkte eine dosisabhängige Senkung der Untergrundaktivität in der Leber, besonders bei gleichzeitiger Gabe oder Präapplikation. Die zusätzliche Gabe stabilen Yttriumsalzes reduzierte die Knochen-Radioaktivität bei gleichzeitiger Erhöhung der Leber- sowie Milz-Radioaktivität und praktisch gleichbleibender Tumoraktivität. Die kombinierte Anwendung von EDTMP gemeinsam mit YCI3 führte zu einer Reduktion der Leberaktivität bei gleichzeitiger Verminderung der Knochenaktivität und unveränderter Tumorakkumulation. Schlußfolgerungen: Die Background-Radioakti-vität kann bei gleichbleibender Tumorradioaktivität durch kombinierte Na-EDTMP/YCI3-Applikation reduziert werden. Die vorliegenden Ergebnisse lassen aber wegen der geringen Tumorspeicherung keine therapeutische Nutzung zu.

[Relationship between properties of 131I therapy and radioiodine kinetics]

AIM

The reason of unreproducible data under diagnosis and therapy with radioiodine should be elucidated.

METHODS

The iodine content of the capsules was tested by a colorimetric method and by activation analysis. Radiochemical purity was determined by HPLC and by electrophoresis. Solubility of the capsules was investigated under different conditions.

RESULTS

The iodine content of the capsules varied between 0.8 and appr. 100 micrograms/capsule. The radiochemical purity of the capsule iodine varied between 75% and 99.5% (main contamination: iodate). The solubility of the capsules differed.

CONCLUSION

Additional non-radioactive iodine in the therapy capsules could be one reason of the reduced radioiodine-uptake under therapy.

[Detection of multi-focal breast carcinoma using 2[18F] fluoro-deoxy-D-glucose positron emission tomography (FDG-PET)]

The elevated rate of glycolysis in malignomas compared to normal tissues can be visualised by positron-emission-tomography (PET) using 2[18F]fluoro-deoxy-D-Glucose (FDG). Based on the case of a 38-year old woman with multifocal carcinoma of the right breast (pT1 c pN0 M0, G2) as a vehicle, we describe a FDG-PET procedure which is comparable to established methods of nuclear medicine (e.g. bone scan) with regard to patient's burden and time consumption and could be used on a routine basis. This technique allowed correct assessment of suspicious breast findings and visualised multifocal growth of a tumour which was judged to be a unifocal breast cancer by conventional methods of clinical examination, mammography and ultrasound.

Qualitative [18F]FDG positron emission tomography in primary breast cancer: clinical relevance and practicability

Positron emission tomography (PET) using fluorine-18 2-deoxy-2-fluoro-d-glucose (FDG) is of potential value for the diagnosis of malignant tumours. The aim of this study was to evaluate the use of FDG PET in patients with breast tumours, appraising its applicability in visualising primary carcinomas and regional metastases in a clinical setting. Results of FDG PET were compared with those of mammography, breast ultrasonography and histology in 30 patients with inconclusive breast findings. For PET, transmission and emission images were taken in one or two scan positions, depending on the available time and the clinical status of patients. PET showed focal FDG uptake with high contrast in 21 of 23 primary carcinomas. In one patient, only PET correctly visualized multifocal disease (three foci, O 0.4-1 cm). The accuracy of PET in the detection of primary breast cancer was 90%, and in the detection of involved axillary lymph nodes, 94%. All metastases (lymph nodes, lungs, bones, soft tissues) covered by the field of view and demonstrated by other methods (X-ray, computed tomography, magnetic resonance imaging, bone scan) showed FDG uptake. In three patients, only PET initiated further diagnostic procedures. The results indicate that FDG PET can provide a rapid diagnostic study (45-60 min) and allows accurate tumour staging of several organ systems for primary tumour and metastases with a single imaging study in a routine clinical setting.

[Biokinetics of tumor-affinity yttrium preparations--2]

After demonstrating that the application form 87Y-NTA-EDTMP-Ca is superior to the so far used citrate form of yttrium especially regarding the tumour/liver and tumour/bone ratios, the relationships between the concentrations of the components in the 87Y-NTA-EDTMP-Ca mixture and the 87Y biokinetics were investigated in tumour-bearing mice. The increase of the EDTMP and Ca2+ concentrations by several orders of magnitude caused no significant changes of tumour radioactivity but a clear radioactivity decrease in the liver, spleen and bone, respectively. The increase of the NTA concentration led also to a radioactivity decrease in all organs and tissues investigated. A significant radioactivity reduction in the tumour could be observed only after administration of rather high NTA amounts. Considerations of the tumour/background ratios depending on different compositions of the injection mixture showed the possibility of optimizing radionuclide biodistribution.

Untersuchung zur Biokinetik tumoraffiner Yttrium-Zubereitungen - 2. Teil

Nachdem gezeigt wurde, daß die Applikationsform 87Y-NTA-EDTMP-Ca der bisher verwendeten Zitratform des Yttriums insbesondere hinsichtlich der Tumor/Leber- und Tumor/Femur-Verhältnisse überlegen ist, wurden die Zusammenhänge zwischen der Konzentration der Komponenten in dem 87Y-NTA-EDTMP-Ca-Gemisch und der Veränderung der 87Y-Biokinetik an tumortragenden Mäusen untersucht. Die Erhöhung der EDTMP- und Ca2+-Konzentrationen verursachten keine signifikanten Veränderungen der Tumorradioaktivität, aber eine deutliche Verringerung der Radioaktivität in Leber und Milz bzw. Knochen. Die Erhöhung der NTA-Konzentration führte auch zu einer Abnahme der Radioaktivität in allen untersuchten Organen und Geweben (im Tumor nach Applikation relativ hoher NTA-Mengen). Die Betrachtungen der Tumor/Untergrund-Verhältnisse in Abhängigkeit unterschiedlicher Zusammensetzungen des Injektionsgemisches zeigten, daß es möglich ist, die Bioverteilung des Radionuklids zu optimieren.

[99mTc-generator eluates: effects on the radiochemical purity of the labelling products]

Relatively sensitive kits--which are known for low tin content (HMPAO) or for a complicated chemical labelling procedure (MAG3)--were tested for their efficiency of labelling with eluates of different generators. The radiochemical purity of the labelling products was determined according to the manufacturer's instructions (HMPAO: Amersham Buchler, MAG3: Mallinckrodt Diagnostica) after adding the 99mTcO4- eluates from the different Tc-generators (Amersham Buchler, Mallinckrodt Diagnostica, CIS Biointernational). The radiochemical purity was determined by using radioanalytical methods such as high performance liquid chromatography, thin layer chromatography, paper chromatography and reversed phase chromatography. The quality of the three different generator eluates was sufficient for the labelling of HMPAO and MAG3. The small differences in quality did not limit the use in nuclear medical routine.

[Initial results in tumor diagnosis with radioactive lanthanide complexes]

Clinical investigations have been made in 70 patients to determine whether 169Yb-labelled metal ligand complexes accumulate in various tumors as was shown by previous animal experiments. The time course of these radiopharmaceuticals in tumors, the skeleton and the liver permitted a good to excellent tumor imaging in 61/70 cases. Even 2-5 h after intravenous injection of the radioactive compound, a meaningful diagnosis could be made in the majority of cases. A number of lesions were found for which no equivalent findings were available with other methods. They were therefore interpreted as metastases.

[Long term biokinetics of 169Yb following injection as citrate, hydroxyethylethylenediaminetetraacetate and nitrilotriacetate]

169Yb complexes with known biokinetics in tumour-bearing mice up to 48 h p.i. were injected into healthy mice to study the radionuclide biodistribution in various organs and tissues for 672 h after injection, in order to obtain reliable biokinetic data in an animal model, not affected by tumour-growth, as a basis for the calculation of biological half-life and dose distribution. The results demonstrated the existence of at least two components with different biological half-lives in the organs and tissues investigated. The effective half-lives of these components decreased with increasing stability of the complexes administered. The effective half-life of the fast component was a few hours and that of the slow one between about 200 and 800 h.

[The effect of ethylenediaminetetramethylenephosphonate on the biodistribution of tumor-seeking radionuclides]

It is well known that after application of radioactive complexes for tumour diagnosis or therapy, such as 67Ga-citrate or radiolanthanide complexes (167Tm- or 169Yb-nitrilotriacetate, -citrate, -alpha-hydroxyisobutyrate, 90Y-citrate, etc.) activity is accumulated not only in the tumour but also in other organs, above all liver and bone. This is the main obstacle to their medical use. Recently published results encouraged us to use ethylenediaminetetramethylene phosphonate (EDTMP) for the reduction of extratumoural liver activity. The results show that even small amounts of EDTMP (1-2 mg/kg BW) reduce the activity deposition in the liver by about one order of magnitude. EDTMP provoked elimination of activity from tumour, skeleton and other tissues but not to the same extent as from the liver. Tumor/liver activity ratios > 5 are achievable in this manner.

[The effect of bone-seeking metal salts on the biodistribution of tumor-seeking heavy metal complexes]

This work attempted to overcome the problem of unwanted bone radioactivity after injection of tumour-affine heavy-metal compounds (prototype 169Yb-citrate) by pre-application of stable yttrium- and calcium-compounds into tumour-bearing mice in doses of 1 mg metal/kg body weight. The pre-application of stable yttrium and calcium resulted in a smaller bone radioactivity. The most favourable results were achieved by injecting the metal salts simultaneously at or within 5 h before the 169Yb-citrate. On the other hand a strong radioactivity increase in the RES (liver and spleen) by a factor of 2 to 4 was observed after yttrium-preapplication.

Langzeitbiokinetik des 169Yb nach Injektion als Zitrat, Hydroxyethylethylen- diamintetraazetat und Nitrilotriazetat

169Yb-Komplexe mit bekannter Biokinetik in tumortragenden Mäusen bis zu 48 h nach Injektion wurden gesunden Mäusen intravenös injiziert und die Bioverteilung in Organen und Geweben bis zu 672 h nach Injektion untersucht. Durch diese Langzeituntersuchungen in einem durch Tumorwachstum unbeeinflußten Tiermodell sollten zuverlässige biokinetische Daten als Basis für Berechnungen der biologischen Halbwertszeit und der Dosisverteilung in verschiedenen Organen und Geweben erhalten werden. Die Ergebnisse der Radionuklidelimination aus Organen und Geweben bzw. der -exkretion mit dem Urin zeigten, daß mindestens zwei Komponenten vorliegen, deren effektive Halbwertszeiten mit zunehmender Stabilität der verabreichten Komplexe kürzer werden. Sie liegen für die »schnelle« Komponente bei wenigen Stunden und für die »langsame« Komponente zwischen 200 und 800 h.

Der Einfluß von knochenaffinen Metallsalzen auf die Bioverteilung tumoraffiner Schwermetallkomplexe

Diese Arbeit versucht, das Problem der unerwünschten Knochenradioaktivität nach Injektion tumoraffiner, radioaktiver Schwermetallverbindungen (Prototyp: 169Yb-Zitrat) durch Prämedikation mit stabilen Yttrium-oder Kalziumverbindungen in tumortragenden Mäusen in Dosen von 1 mg/kg Körpergewicht zu überwinden. Die Prämedikation mit stabilem Yttrium oder Kalzium resultiert in geringeren Knochenradioaktivitäten. Die besten Ergebnisse wurden erreicht, wenn die Metallsalze gleichzeitig oder bis 5 h vor 169Yb-Zitrat injiziert wurden. Andererseits wurde eine starke Radioaktivitätserhöhung um den Faktor 2-4 im RES (Leber, Milz) nach Prämedikation mit Yttrium beobachtet.

Der Einfluß von Ethylendiamin- tetramethylenphosphonat auf die Bioverteilung tumoraffiner Radionuklide

Es ist bekannt, daß nach Applikation radioaktiver Komplexe für Tumordiagnostik oder -therapie, wie 67Ga-Zitrat oder Radiolanthanid-Komplexe (167Tm- oder 169Yb-Nitrilotriazetat, -Zitrat, -α-Hydroxyisobutyrat, 90Y-Zitrat etc.) die Aktivität nicht nur im Tumor, sondern auch in anderen Organen, vor allem in Leber und Knochen, akkumuliert wird. Dieses Verhalten ist das Haupthindernis für eine medizinische Nutzung. Kürzlich publizierte Ergebnisse gaben Veranlassung, Ethylendiamintetramethylenphosphonat (EDTMP) zur Reduktion der extratumo- ralen Leberaktivität einzusetzen. Die Ergebnisse zeigen, daß schon kleine EDTMP-Mengen (1–2 mg/kg KG) zur Verringerung der Leberaktivität um ca. eine Größenordnung ausreichen. EDTMP verursachte eine verstärkte Radionuklidelimination aus Tumor, Skelett und anderen Geweben, aber in viel geringerem Ausmaß als aus der Leber. Tumor/Leber-Quotienten > 5 sind auf diese Weise erreichbar.

[The effect of Ca-diethylenetriamine pentaacetate on the bio-behavior of tumor-affine metal complexes]

The complexon CaDTPA was injected into tumour-bearing mice in concentrations of 0.05, 0.1, 0.3, and 0.6 mole/l (pH:6) 30 min after the 169Yb-injection. 100 microliters of a 0.3 M CaDTPA solution were injected at different time points (simultaneously, 2, 5, 10, 20, 30, 40 and 50 min, 1, 1.25, 1.5, 2.5 and 10 h) after 169Yb-citrate injection. The animals were killed 24 h after radionuclide administration. A strong radioactivity decrease was observable 24 h p.i. not only in blood, liver, spleen, muscle and bone but also in the tumour if CaDTPA was administered within the first 2 h after ytterbium injection. Thereafter no change in radioactivity could be achieved by DTPA. A time phase in which the Yb could be eliminated from the tissues by means of DTPA (time intervals < 2 h) was distinguishable from a time phase in which it was not attainable for DTPA (time intervals > 5 h). This indicates that the incorporation of Yb into the cells is completed after 5 h and that the metals are intracellularly bound, probably to the lysosomes. Improvements of the scintigraphic tumour detection cannot be expected from the use of complexons.

Der Einfluß von Ca-Diethylentriaminpentaacetat auf das Bioverhalten tumoraffiner Metallkomplexe

Das Komplexon CaDTPA wurde tumortragenden Mäusen in Konzentrationen von 0.05, 0.1, 0.3 und 0.6 mol/l 30 min nach Applikation von 169Yb-Zitrat injiziert. 100 µl einer 0.3 M CaDTPA-Lösung wurden zu unterschiedlichen Zeitpunkten (gleichzeitig, 2, 5, 10, 20, 30, 40 und 50 min, 1, 1.25, 1.5, 2.5 und 10 h) nach 169Yb-Zitrat-lnjektion injiziert. Die Tiere wurden 24 h nach Radionuklidgabe getötet. Ein starker Radioaktivitätsabfall, nicht nur in Blut, Leber, Milz, Muskel und Knochen, sondern auch im Tumor konnte 24h p.i. dann beobachtet werden, wenn CaDTPA innerhalb von 2 h nach Ytterbiuminjektion gegeben wurde. Danach wurde durch DTPA keine Radioaktivitätsänderung mehr erreicht. Eine Zeitphase, in welcher Yb von den Geweben eliminierbar war (Zeitintervalle <2 h), konnte von einer Zeitphase abgegrenzt werden, in welcher Yb nicht mehr für DTPA erreichbar war (Zeitintervalle >5 h). Das zeigt, daß die Yb-Inkorporation in die Zellen nach 5 h abgeschlossen ist und die Metalle intrazellulär, wahrscheinlich in den Lysosomen, gebunden sind. Verbesserungen des szintigraphischen Tumornachweises können von der Verwendung von Komplexonen nicht erwartet werden.

Stabilities of lanthanide-protein complexes

After incubation of both serum and HSA solutions with radioactive lanthanide complexes the binding constants of the corresponding lanthanide-protein complexes formed in the protein solutions under physiologic conditions, pH: 7.4, temperature: 310 K, isotonic ionic strength: 0.15 mol/L, were determined. The association constants of the lanthanide-protein complexes formed both in serum and HSA-solutions are equal within the experimental error. In conclusion, serum albumin binding predominates for the radiolanthanides. With the decrease of the ionic radii from 1.034 A (Ce) to 0.858 (Yb) the association constants increased by five orders of magnitude from 1 g Kpr = 4.90 (Ce) to 1 g Kpr = 9.54 (Yb). Further, a serum fractionation with alcohol was carried out to prove that the albumin fraction of serum is responsible for the lanthanide binding in blood.

The influence of isotopic and nonisotopic carriers on the biodistribution and biokinetics of M3+-citrate complexes

The influence of carrier amounts of Fe, Ga, and Tm on the biodistribution of 67Ga-, 59Fe-, and 167Tm-citrate in mice was investigated. Our results suggest that 167Tm, unlike 67Ga and 59Fe, is not transported by transferrin in the blood. Of the three radioisotopes tested, 167Tm had the highest tumor/background ratio (10 h after the injection). The application of Fe carrier led to an enhancement of the elimination of 67Ga from the blood and muscles, resulting in a better tumor/background ratio.