The role of transferrin in the in vivo uptake of gallium-67 in a canine tumor

Gallium-67 as a Tumor-seeking Agent in Lymphomas - a Review

Background

At present 67Ga can be considered one of the most widely used viability radiotracers. There is general consensus in the literature that 67Ga has the highest clinical value in the management of lymphoma patients.

Methods

We critically discuss the role of gallium scintigraphy in lymphoma patients on the basis of the experience of the Nuclear Medicine Division at the National Cancer Institute of Milan.

Results and Conclusions

The sensitivity of gallium scan is very high (80-90%) in the staging and follow-up of Hodgkin's disease, and the method is also of great importance in the follow-up of lymphoma patients. We recommend scintigraphy to study the residual mediastinal mass after treatment. Our experiences during the follow-up of 189 lymphoma patients clearly showed the superior performance of gallium scan compared to MRI in the study of the mediastinal region after treatment. Sensitivity and specificity were both very high (90% and 96.9% vs 88.7% and 89.2%, respectively). Gallium scintigraphy can also be used to study the disease-free interval, posttreatment survival, early signs of recurrence and treatment response times. Comparison of the survival curves of 33 patients with diffuse large cell Non-Hodgkin's lymphoma examined at the National Cancer Institute showed a statistically significant difference (logrank test, P=0.0125) between patients with positive and those with negative gallium scan after 4-6 cycles of chemotherapy.

Imaging features of ocular adnexal lymphoproliferative disease

PURPOSE

To evaluate the imaging characteristics of a cohort of patients with ocular adnexal lymphoproliferative disease (OALD).

METHODS

A noncomparative retrospective review between 1992 and 1995 and prospective study from 1995 to 2005 of the clinical, imaging and treatment of 105 patients presenting to tertiary orbital referral centre presenting with OALD.

RESULTS

One hundred and five patients (mean age 61 years, range 11-90 years) with equal gender distribution were included. Fifty-three were primary and 52 were secondary. Computed tomography (CT) usually showed a well-circumscribed lesion of greater than brain density, moulding to adjacent tissues with moderate enhancement. Aggressive histology was associated with bone destruction, while moulding was associated with indolent histology (P<0.005).MRI in OALD showed intermediate signal intensity on T1- and T2-weighted images and moderate enhancement with gadolinium. Gallium scanning sensitivity to detect ocular adnexal disease was 25 and 57% for systemic involvement. Positron emission tomography (PET) upstaged (71%) of patients with systemic lymphoproliferative involvement, having a higher sensitivity than CT in detecting distant disease (86 vs 72%).

CONCLUSIONS

CT and/or MRI are essential in the evaluation of OALD and can be used to establish that an orbital lesion may be lymphoprolifetaive in nature. Further, these imaging modalities may predict the behaviour of the lymphoma in certain cases. Gallium scanning provides no additional information to CT and does not influence patient treatment. PET represents an important addition to the assessment of OALD with real impact on patient management.

The Entering of Indium-111 and Iron-59 into the Hepatocytes from Partially Hepatectomized Rats Differ from That of Gallium-67

We recently suggested that the transferrin (Tf)-gallium-67 (67Ga) complex dissociated on the surface of the hepatocytes after partial hepatectomy and free 67Ga bound to heparan sulfate in the extracellular matrix. In the present study, we investigated whether the entering of indium-111 (111In) and iron-59 (59Fe) with high affinity to transferrin differed from the entering of 67Ga by the hepatocytes after partial hepatectomy. 111In was almost taken by the plasma and little taken by the red blood cell. On the other hand, the uptake of 59Fe by the red blood cell was higher than plasma. The uptake of 59Fe by the bone marrow was significantly higher than that of 111In. The uptake of 111In and 59Fe by the liver tissue was reached a maximum 2 d after partial hepatectomy but the uptake ratio of 111In was lower than that of 59Fe. We suspected that the uptake of 59Fe by the liver tissue was the highest because of the high binding affinity of Tf-59Fe to Tf-receptor. The entering of 111In and 59Fe into the hepatocytes was also reached a maximum 2 d after partial hepatectomy but the ratio of 59Fe was slightly lower than that of 111In. These results suggested that the binding affinity to Tf could have played a crucial role in the differences of the entering of 111In, 59Fe and 67Ga into the hepatocytes of partially hepatectomized rats.

Hypoxia as a factor for 67Ga accumulation in tumour cells

Recent reports have demonstrated that hypoxia induces the up-regulation of transferrin receptor expression in tumour cells. Tumour cells take up 67Ga in the form of a 67Ga-transferrin complex via transferrin receptors. As a result, we attempted to determine the influence of hypoxic conditions on 67Ga uptake in tumour cells. B16 melanoma cells and LS180 colon cancer cells were incubated in 95% air/5% CO2 or 95% N2/5% CO2 for 1 h at 37 degrees C. Cellular uptake of 67Ga citrate was subsequently determined at 20, 40, 60 and 90 min. Uptake of the 67Ga-transferrin complex pre-chelated in vitro was similarly assessed. The effect of hypoxia on 67Ga binding to serum proteins was also investigated. Both B16 and LS180 cells displayed increased cellular uptake of 67Ga citrate in N2 gas in comparison to that in air (P < 0.0001). Hypoxia more prominently influenced cellular uptake of Ga-transferrin relative to that of 67Ga citrate (P < 0.0001). Hypoxia did not affect the percentages of 67Ga radioactivity bound to protein in medium supplemented with fetal calf serum, indicating that the results were not caused by the alteration of 67Ga-transferrin formation. These findings suggest the role of tissue hypoxia with respect to accumulation of 67Ga in tumours, which is likely mediated by transferrin receptors.

Fluorescent chelates for monitoring metal binding with macromolecules

Metals and radionuclides are usually coupled with proteins together with suitable ligands for therapeutic, tumor-imaging, pharmaceuticals, and biocompatibility applications. Several ligands that can strongly coordinate a given nuclide in a specific valency are already known. However, the demand for bifunctionality has limited the applications of these ligands. We hereby report the molecular design of a receptor system based on the linkage of protein to monoazo ligands. By use of basic coordination chemistry, 4-(3-quinolinoazo)hydroxybenzoic acid (QABA) and derivatives were successfully conjugated to ovalbumin, bovine serum albumin, and alkaline phosphatase at a site that was distinct from the metal binding site. The presence of carboxylic acid linkage in the QABA served as a convenient bridge for protein conjugation and may allow the generic application of these ligands for bioconjugate synthesis while ensuring a high in vivo stability. The ligand-protein conjugates were characterized using UV-vis spectroscopy, Fourier transform infrared spectroscopy, thin layer chromatography, NMR, and surface-enhanced laser desorption ionization time-of-flight mass spectrometry. The conjugate was tested for the ability to recognize nonradioactive Ga(3+) at a physiological pH, and a binding constant of 1 x 10(20) was recorded. Also, the in vitro testing results indicated that the fluorescent conjugates exhibited significant selectivity for gallium compared to Pb(2+), Hg(2+), Zn(2+), Cu(2+), Fe(3+), and Co(2+) while no responses were obtained for alkaline and alkaline earth metals. These attributes could allow these conjugates to be used as a model for imaging sensors and for metal detection.

Transferrin is not involved in the entry of 67Ga into hepatocytes from regenerating liver of partially hepatectomized rats

Ever since the first observation of 67Ga accumulation in tumors and inflammatory lesions, 67Ga has been used to detect various tumors and inflammations. The aims of this study were to clarify whether or not transferrin is involved in the uptake of 67Ga by the regenerating liver after partial hepatectomy. The uptake of 67Ga by the liver of rats reached a maximum 2 d after partial hepatectomy. In order to inhibit the binding of 67Ga to transferrin in the blood, FeCl3 was administered 5 min before the injection of 67Ga. The administration of FeCl3 decreased the uptake of 67Ga by the liver of the partially hepatectomized rats, suggesting that transferrin is involved in the uptake by the liver. However, 67Ga was taken up only slightly by hepatocytes obtained from the liver of these rats. We conclude that transferrin is involved in the uptake of 67Ga by the liver tissue of partially hepatectomized rats but is not involved in its entry into the hepatocytes. Only a slight amount of gallium-67 enters the hepatocytes, and may accumulate primarily in the extracellular matrix of the liver tissue of these rats.

A receptor-based bioassay for quantitative detection of gallium

The detection of gallium in biological samples is required due to its role in the diagnosis of tumor and for possible treatment of malignancies. However, the use of purely instrumental techniques is unsuitable for detection of low levels of gallium in biological matrixes. We have synthesized new protein conjugates based on 4-(2-pyridylazo) ligands. The conjugates were successfully employed for the detection of gallium in biological matrixes using a nonantibody-based sandwich assay format. The recovery level obtained was between 97 and 101.3 with a relative standard deviation of less than 5%. The assay resulted in a detection limit of 5 x 10(-8) M and a remarkable selectivity for gallium(III) relative to other metals investigated. The new method provided adequate accuracy for gallium applicable for animal physiology and clinical toxicology.

Studies on 67Ga uptake by mouse granuloma tissues

In connection with the uptake of 67Ga into the inflammatory tissues, such as granuloma tissues produced with turpentine oil, the influence of Fe3+ on the uptake of 67Ga into mouse granuloma and normal tissues and on the uptake of 125I-labeled transferrin and 59Fe were investigated. Fe3+ decreased the uptake of 67Ga into the liver and spleen, but had no influence on the uptake of 67Ga into the granuloma tissues. The uptake patterns of 125I-labeled transferrin and 59Fe in the granuloma tissues were not consistent with that of 67Ga at all. These results show that the uptake of 67Ga into the granuloma tissues occurs in a free, transferrin-unbound form, but into the liver and spleen in a transferrin-bound form.

67Ga in transferrin-unbound form is taken up by inflamed liver of mouse treated with CCl4

In order to investigate whether or not transferrin is involved in the uptake of 67Ga by inflamed liver (acute inflammatory tissues) the uptake of 67Ga by the liver of mice treated with carbon tetrachloride (CCl4) was studied. The serum GPT value reached its maximum on the 1st day after the CCl4 treatment. The uptake of 67Ga by the liver also reached its maximum on the 1st day after the CCl4 treatment and the amount uptaken into inflamed liver was about 6 times that uptaken into normal liver. On the other hand, the uptake of 125I-transferrin into inflamed liver on the 1st day after CCl4 treatment was only about 1.6 times that into normal liver. Moreover, cold Fe3+ decreased the uptake of 67Ga by normal liver but increased the uptake of 67Ga by inflamed liver. These results show that transferrin plays an important role in the uptake of 67Ga by normal liver but not by inflamed liver, i.e. 67Ga in the transferrin-unbound form is preferentially taken up by inflamed liver.

Involvement of transferrin in the uptake of 67Ga in inflammatory and normal tissues

The results from gel chromatography and electrophoresis showed that 67Ga is exclusively bound with transferrin both in vitro and in vivo, but high concentrations of sodium citrate strongly inhibited the binding of 67Ga to transferrin. The influence of sodium citrate on the uptake of 67Ga into inflammatory and normal soft tissues was also investigated. Sodium citrate decreased the uptake of 67Ga into the liver and spleen, but had no influence on the uptake of 67Ga into inflammatory tissue. These results suggest that the uptake of 67Ga into normal soft tissues occurs in a transferrin-bound form but into inflammatory tissue in an unbound form.

The effect of FeCl3 on the accumulation of gallium-67 into inflammatory and normal tissues

The effect of FeCl3 on the uptake of 67Ga by inflammatory and normal tissues was studied to clarify the role of transferrin in 67Ga uptake by inflammatory tissue. The administration of FeCl3 5 min before the injection of 67Ga decreased the uptake of 67Ga by liver and spleen, but had little effect on the uptake of 67Ga by the inflammatory tissue. These results suggest that 67Ga is taken up by normal tissues in a transferrin-bound form but in an unbound form by inflammatory tissue. On the other hand, when FeCl3 was simultaneously injected with 67Ga, the uptake of 67Ga by liver and spleen was markedly increased but the uptake by inflammatory tissue was decreased.