Ga-67 and Fe-59 distributions in mice

Tissue distributions of i.v.-injected Ga-67 citrate and [59Fe] ferric citrate were measured in normal mice and in lymphoid-tumor hosts. The study arose out of previously reported tissue-culture work showing marked transferrin stimulation of Ga-67 and Fe-59 uptakes by cultured cells from mouse lymphoid tumors. In vivo, however, no obvious correlation was found between Ga-67 and Fe-59 tissue distributions; indeed, Ga-67 showed high affinity for tumor tissue and low affinity for hemopoietic tissues, while for Fe-59 the reverse applied. Taken together, these comparisons of kinetics and distributions for Ga-67 and Fe-59 suggest that a tissue's avidity for Ga-67 is strongly influenced by other factors besides the cell population's capacity for transferrin interactions.

Iron-dextran enhancement of 67Ga-concentration in abscess relative to normal tissue

Iron-dextran (Imferon) significantly increases the concentration of 67Ga in abscess relative to muscle, when given intravenously to abscess bearing rabbits 24 hr after intravenous, carrier-free 67Ga-citrate. This increase is achieved by accelerating the clearance of 67Ga from the blood.

The medical use of gallium radionuclides: a brief history with some comments

The use of gallium radionuclides in nuclear medicine dates back to the late 1940s, following the observation in toxicologic studies that gallium tended to localize to a high degree at sites of osteogenic activity. Initial attempts in the early 1950s to use 72Ga for clinical diagnosis and therapy of malignant bone lesions were unproductive. However, the basic information gained then in the preclinical and clinical investigations was quite instrumental in generating the present-day use of gallium radionuclides as effective radiopharmaceutical agents. Although initial clinical trials of 72Ga were unproductive, subsequent studies with 68Ga and 67Ga, together with advances in nuclear medical instrumentation, resulted in the identification of gallium radionuclides as effective tumor- and abscess-localizing agents. A major factor in the recognition of the peculiar biologic properties of gallium radionuclides was the existence of a carrier (stable isotope) effect. Also, it appears from basic studies of the mechanism(s) of the uptake of gallium in tumor tissue that the biodistribution of gallium involves many essential biologic processes. The future use of gallium radionuclides may, therefore, actually very well fall more into the field of basic biologic investigations rather than into the field of nuclear medical diagnosis.

Mechanisms of localization of gallium-67 in tumors

The mechanism of tumor localization of gallium-67 (67Ga) is not known with certainty, although much information has been derived regarding the biodistribution and subcellular fate of 67Ga in a variety of tumors and other tissues from experimental animals. After intravenous administration, 67Ga is bound to transferrin in the blood, and distributed to liver, lacrimal glands, salivary glands, and soft tissue tumors. Within the cells of the liver and tumors, gallium is found in lysosomes, and rough endoplasmic reticulum. Within these organelles, 67Ga is bound to a variety of macromolecules, including transferrin, ferritin, and a 45,000 molecular weight glycoprotein. Recent studies of tumor cells growing in tissue culture suggest an important role for transferrin in 67Ga tumor uptake. This uptake is mediated by a transferrin specific cellular receptor.

Studies on gallium accumulation in inflammatory lesions: II. Uptake by Staphylococcus aureus: concise communication

Gallium-67 was demonstrated to be taken up in significant amounts by a number of common micro-organisms. The mechanism of gallium-67 uptake was studied in S. aureus. It is found to involve two separate processes. One is insensitive to temperature or metabolic inhibitors, and is not inhibited by a high concentration of nonradioactive gallium. This process probably operates through nonspecific binding of Ga-67 to components of S. aureus. The second process is not inhibited by metabolic inhibitors either, but it is temperature-sensitive and is inhibited by high concentrations of stable gallium. This component of the Ga-67 uptake is most likely due to a carrier-mediated transport system (facilitated transfer).

Accumulation and localization of gallium-67 in various types of primary lung carcinoma

The uptake and location of Ga-67 were investigated in 15 primary pulmonary carcinomas. The accumulation in the tumor was determined by scintigraphy of the patient, grain counts over fields of tumor cells in autoradiographs of tumor-tissue samples, and gamma counts in specimens of the tumor. Good correlation was found between the results obtained with these three methods. The relationship between accumulation of Ga-67 in the tumor and the histologic type of tumor was also studied. Undifferentiated carcinomas, and tumor cells in squamous-cell carcinomas showed significantly more Ga-67 than tumor cells in adenocarcinomas. No correlation was found between the presence of inflammatory infiltrates in or around the tumor and the grade of the scintigraphic images. In the autoradiograms, lymphocytes, plasma cells, granulocytes, and macrophages showed less radioactivity than the tumor cells--or none at all. Collagen fibers appeared to have bound some Ga-67, but necrotic areas showed no uptake.

Transferrin promotion of 67Ga and 59Fe uptake by cultured mouse myeloma cells

Radiotracer 67Ga-citrate is used as a tumor-seeking agent in clinical imaging investigations although fundamental reasons for its high uptake in certain malignant lesions remain unexplained. The mechanism by which 67Ga becomes concentrated in tumor cells has been investigated by comparing 67Ga and 59Fe uptake by cultured mouse myeloma cells with particular reference to uptake stimulation by transferrin. Concentrations of human transferrin down to 2 microgram/ml greatly stimulated cellular uptake of both tracers, whereas bovine transferrin proved relatively inactive. The rates of stimulated uptake of both tracers were similar as was their high degree of retention by cells, but their quantitative dependencies on transferrin concentration showed characteristic differences. Pretreatment of human transferrin with saturating amounts of nonradioactive Fe3+ canceled its ability to promote 59Fe uptake, but it had little effect on its promotion of 67Ga uptake. Further increase in the amount of added Fe3+ did cause a progressive depression of 67Ga uptake, but this effect probably relates to the iron distribution in the whole-cell culture system including the fetal calf serum component of cell growth medium. The results suggest that 67Ga and 59Fe reveal different aspects of the interaction of transferrin with cells.

[Study of distribution of 169Yb, 69Ga and 111In in tumor tissues by macroautoradiography; comparison between viable and necrotic tumor tissues]

The localization of 169Yb, 67Ga and 111In in tumor tissues was determined macroautoradiographically. 169Yb-citrate and 111In-citrate were injected intravenously to the rats subcutaneously transplanted Yoshida sarcoma and were injected intraperitoneally to the mice subcutaneously transplanted Ehrlich tumor. These animals were sacrificed 3, 24 and 48 hours after injection. These tumor tissues were frozen in n-hexane (-70 degrees C) cooled with dry ice-acetone. After this, these frozen tumor tissues were cut into serial thin sections (10 micron) in the cryostat (-20 degrees C). One of the slice of these sections was then placed on X-ray film and this film was developed after exposure of several days. On the other hand, next slice of these sections were then stained using the hematoxylin and eosin. From the observations of these autoradiogram and H-E stained slice, the following results were obtained. Concentration of 169Yb, 67Ga and 111In was predominant in viable tumor tissue rather than in necrotic tumor tissue, regardless of time after the administration. 67Ga and 111In were distributed uniformly in viable tumor tissue, but deposition of 169Yb was observed more avidly in viabl tumor tissue neighboring to necrotic tumor.

Quantitative estimation of 67Ga citrate in hypofunctioning thyroid nodules

Quantitation of 67Ga citrate activity was performed in 11 subjects who underwent surgery for nonfunctioning, cold thyroid nodules. Radioactivity was measured in blood and in excised nodular and paranodular tissue at approximately 48 hours after the injection. Eight subjects were histologically benign, nonfunctioning nodules had no significant concentration of Ga. Their nodular/blood activity ratio was 1.6. In two patients with thyroid cancer, a higher activity was observed (mean 4.5/1). One patient with Hashimoto's thyroiditis also revealed a high concentration of Ga (5.3/1). Findings suggest that 67Ga citrate has a lesser affinity for benign cold nodules than for malignant and inflammatory lesions. More clinical experience is necessary before the significance of these observations can be assessed.

Gallium-67 scintigraphy in multisystem malignant melanoma

In a prospective study of the value of gallium-67 scintigraphy in cases of multisystem malignant melanoma, 69 scans were obtained for 36 patients. No abnormality was found in 18 scans; in only 3 was there other evidence of disease. Of 54 sites of disease demonstrated by scintigraphy, 40 were correlated with other investigations: biopsy (5), surgery (7), autopsy (7), radiographic (13), or clinical (8). Metastatic melanoma was found in 37 (69%) of the sites; no such disease was found in 3 (5.7%). The life expectancy of patients with an abnormal scan was shorter than that of patients with a normal scan. Gallium studies reliably indicated the extent of multisystem melanoma, and are of value in clinical management.

Unilateral breast uptake of 67Ga from breast feeding

Unilateral 67Ga uptake was observed in the left breast of a 23-year-old woman who had nursed her infant on that side for 10 months. Careful clinical examination and follow-up failed to reveal any evidence of breast disease. Unilateral breast feeding should be considered in the differential diagnosis of asymmetric 67Ga localization in the breast.

Mechanism of 67Ga accumulation in normal rat liver lysosomes

67Ga accumulates in various malignant tumors and parenchymatous tissues. It was found to be associated with the soluble fraction of lysosomes (11). The present work investigates the mechanism of 67Ga accumulation in normal liver cells. Lysosomes were isolated from rat liver after intravenous injection of carrier free 67Ga. The soluble lysosomal fraction was obtained by sonication followed by centrifugation at 105,000 xg for 2 hrs. Gel filtration on Sephadex G 25 superfine was carried out on the soluble lysosomal fraction in order to investigate the stability of the 67Ga-protein complex within the lysosomes under EDTA treatment. After treatment with 1 mM/l EDTA a considerable amount of the protein bound radioactivity was found to be liberated. In further experiments the 67Ga binding lysosomal proteins were fractionated by electrophoresis on 7% polyacrylamide gels (0.5 cm x 5.5 cm). After staining with Coomassie blue 18 separated protein bands were apparent. 67Ga distribution within the gels was assessed by direct counting of radioactivity in gel slices. A considerable amount of the intralysosomal protein bound radioactivity migrated with a relative mobility of 0.36 corresponding to a protein band of molecular weight 85,000--90,000. This peak corresponded to the peak of 67Ga-labelled purified transferrin in control gels. These data were confirmed by immunoelectrophoresis combined with autoradiography: within the soluble lysosomal fraction a slight transferrin line could be identified. We conclude that 67Ga which is transported in the blood by transferrin (23) and taken up by the hepatic cell through endocytosis (32) is accumulated in the lysosomes associated with transferrin and its degraded fragments.

Lack of gallium uptake in primary hepatic amyloidosis

99mTc-sulfur colloid and 67Ga citrate hepatic scintigrams showed matching defects in a patient with diffuse primary amyloidosis. Amyloidosis should be added to the usual differential diagnosis of such matching lesions which includes cysts, fibrosis, most benign tumors, and occasional metastatic lesions which do not concentrate gallium.

Gallium-67 distribution in pregnant mammals

Studies on the distribution of 67Ga in pregnant rabbits showed a marked concentration of the isotope in uterine tissue and flushings of 5-day pregnant rabbits 24 hours after isotope injection. The isotope no longer localized throughout the uterine tissues and flushings on injection of 7- to 8-day pregnant rabbits but was specifically associated with the blastocysts and sites of implantation. As the gestation time progressed 67Ga increasingly concentrated in placental and mammary tissue while the concentration in serum and thymus tissue decreased. The marked concentration in placental tissue was readily discernible on total-body scans of pregnant rabbits. Column chromatography of uterine washings and placental extracts from pregnant rabbits and thymus extracts from estrous rabbits showed most of the isotope associated with moieties greater than or equal to 200,000 MW whereas the isotope in "milk" and extracts of mammary tissue was bound to components of 25,000-35,000 MW. Extracts of thymus from pregnant rats showed a marked, selective loss of 67Ga binding in two peaks of approximately 50,000 and 120,000 MW compared to the chromatographic profile of extracts from normal rat thymus.

A clinical comparison of the tumour-imaging radiopharmaceuticals 67Gallium-citrate and 111Indium-labelled bleomycin

Two tumour-imaging agents, 67Gallium-citrate and 111Indium-bleomycin have been assessed in a clinical trial. Both the quality of tumour image and correlation with known sites of disease has been compared by scanning with the two agents in a variety of malignant diseases. In addition, comparative uptakes of the agents have been measured in biopsy samples. In 28 scanning examinations using the agents sequentially, 67Gallium-citrate provided a more satisfactory tumour image and had closer clinical correlation with known sites of disease in 14 cases. Scans were felt to be of similar quality in 14 cases. There were no examples where 111Indium-bleomycin scans were found to be superior to 67Gallium-citrate. A number of biopsy samples of spleen, liver and lymph nodes were obtained from patients undergoing staging laparotomies for lymphomas in whom small doses of 67Gallium-citrate and 111Indium-bleomycin had been injected shortly before operation. Seven of the spleen samples were infiltrated with tumour and five of these contained less 67Ga than 111In; in contrast four of the five tumour-infiltrated lymph nodes showed 67Ga concentrations greater than those of 111In. It is concluded that 67Gallium-citrate is a more useful tumour-imaging agent than 111Indium-bleomycin, at least for lesions situated above the diaphragm. The value of 111Indium-bleomycin in the demonstration of abdominal malignancies has not been fully assessed in this study. Trials of new tumour imaging agents should as far as possible be compared directly with the best available alternative agent in a controlled study.

Distribution of 67Ga in organs of mice with lymphoid leukaemia

Distribution of 67Ga in different organs of A/H mice bearing a lymphatic leukaemia was examined. Mice received 10(6) leukaemia cells intravenously and groups of 6 mice were sacrificed every other day. Twenty-four hours before sacrifice, the mice received intraperitoneal injection of 67Ga. Spleen, lymph nodes, liver, left kidney, lung, left femur, and a sample of blood were taken, to determine their radioactivity. The maximum of 67Ga uptake was on the 7th day after transplantation of the leukaemia, whereas before death it declined to the values observed in control mice without leukaemia. The changes are interpreted in terms of the ability of leukaemia cells and of macrophages to bind 67Ga.