A.A. Noujaim

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

Abstract The mechanism of radiogallium uptake into tumor in vivo has been investigated using the canine transmissible venereal tumor (TVT) as a model. The blood clearance and uptake in tumor and in normal tissue were also studied. It appears that the incorporation of this cation in the tumor from gallium-transferrin complex occurred immediately after injection. The uptake pattern is different from that of gallium in the citrate form. While the uptake of transferrin by the tumor remained constant, the radiogallium uptake increased by almost 160% over a 3-h period after administration. These results suggest the existence of a transferrin receptor site on the cell membrane of the tumor with no indication of transferrin endocytosis being detected.

On the role of transferrin in the uptake of gallium by tumor cells.

Abstract Human melanoma cells were incubated with 67 Ga-citrate, a mixture of 67 Ga-citrate and transferrin, 67 Ga-transferrin and 67 Ga-transferrin- 125 I. It was found that there was a greater and more rapid uptake of 67 Ga by the tumor cells when the gallium was complexed to transferrin. It was further noted that when melanoma cells were incubated with 67 Ga-transferrin- 125 I, the 125 I associated with the cell fraction remained constant after 15 min of incubation while the 67 Ga associated with the melanoma cell fraction continued to increase beyond this point. Experiments have indicated the presence of both a passive and active mechanism for the uptake of radiogallium by the human tumor cells. However, it appears that passive diffusion did not play the major role in such uptake and that the transport of 67 Ga into the tumor cells was mediated solely through transferrin of the serum proteins studied. It is further suggested that 67 Ga enters the cell after the gallium-transferrin complex combines with a cell surface receptor and that pinocytosis does not play a role in the uptake of 67 Ga by the tumor cell.

Some aspects of the measurement of 32P Cerenkov radiation in water by a liquid scintillation spectrometer

Abstract The shift of the pulse height spectrum and the relative counting efficiency of 32P Cerenkov radiation in water were examined using a liquid scintillation spectrometer. This shift was related to the spectrophotometric absorbancy of samples containing various dyes. The isotope channels ratio method of producing a counting efficiency correction curve was found to be effective for coloured samples. It was observed that although the addition of some chemicals to the sample caused little change in the counting efficiency, a suspending agent (Cabo-sil∗®) produced a counting efficiency and spectral shift different from those obtained for the samples containing dyes. The absolute counting efficiency for 32P in water was found to be 30·5 per cent.

67Ga and 59Fe uptake in human melanoma cells.

Abstract Human melanoma cells were incubated with 67Ga-transferrin and 59Fe-transferrin in the presence of free unlabeled iron as well as 59Fe and 67Ga and increasing P043− ion concentration. It was observed that factors which influence the uptake of 59Fe by melanoma cells have a similar effect on the uptake of 67Ga by the tumor cells. Furthermore, it was noted that when melanoma cells were incubated with either 125SI-transferrin-59Fe or 125I-transferrin-67Ga the 1251 activity associated with the cells was similar in both cases and remained constant over the various incubation times. However, the rate of uptake of 59Fe and 67Ga by the tumor cells differed. The uptake of 59Fe was very rapid over the first 1 1 2 h . After that time the rate of uptake was reduced, while in the case of gallium the uptake was linear over the time period tested. This would suggest that 125I-transferrin-59Fe has a higher affinity for the cell surface binding site than does 125I-transferrin-67Ga. It may also further suggest that for 59Fe the rate of transferrin receptor complexation is close to, or exceeds, the rate-limiting step which is responsible for transporting the 59Fe across the melanoma cell membrane. This does not appear to be the case with gallium.

Comparative pharmacokinetics of 67Ga and 59Fe in humans

Abstract The comparative pharmacokinetics of 67 Ga-citrate, 59 Fe-citrate and 67 Ga-transferrin was undertaken in three healthy male adults, and was found to differ significantly. Whereas the disappearance of 67 Ga-citrate and 67 Ga-transferrin from the plasma was best described by a three-exponential equation, that of 59 Fe-citrate up to 12 h after injection, best fit a two-exponential function. Statistically significant differences between 59 Fe-citrate and 67 Ga-citrate were observed for the overall elimination rate constant, half-life, volume of distribution and plasma clearance. A marked difference in red blood cell uptake of these two nuclides was also observed. The in vivo organ distribution of 59 Fe was found to be very different from that of 67 Ga in the regions of interest studied. There were no significant differences in the in vivo organ uptake of 67 Ga-citrate, and 67 Ga-transferrin. Thus, the disposition of 67 Ga and 59 Fe in human subjects was not similar despite their common association with transferrin. Other factors must be involved in the uptake of these radionuclides by the various body tissues.

The effects of differing gallium-transferrin-anion complexes on the tumor uptake of gallium-67

Abstract Different gallium-transferrin-anion complexes (nitrilotriacetate, maleate, malonate and oxalate) were investigated to determine the effect of such anion complexes on gallium-67 uptake by tumors. The tumor model used was the canine transmissible venereal tumor (TVT). The activity over the tumor and precordium were monitored. The uptake pattern of gallium by the tumor varied greatly between the anion complexes. Following nitrilotriacetate (NTA) as well as maleate complex administration the radiogallium level in the tumor increased to 181% in both instances over a 3 h period after injection. The rate of tumor uptake of gallium was lower following infusion of Ga-Tf malonate or oxalate complex attaining an increase of 145% and 136% 3 h post-injection. We conclude therefore that different anions, involved in complexing gallium to transferrin do play an important role in the uptake of the radionuclide by tumors.

Toxicity, tissue distribution and excretion of 46ScCl3 and 46Sc-EDTA in mice

Abstract The acute toxicity, differential distribution in tissue, and elimination of ScCl3, 46ScCl3, Sc-EDTA and 46Sc-EDTA, in mice, has been investigated. The LD5024 hr doses for ScCl3 were 440 and 24 mg kg−1 respectively after intraperitioneal and intravenous injection, and 720 and 108 mg kg−1 respectively for Sc-EDTA. 46ScCl3 was extensively deposited in the liver and the spleen. 46Sc-EDTA was rapidly taken up by the kidney with subsequent elimation via the urine. Whole-body desaturation kinetics for 46Sc-EDTA were found to fit a three compartmental model. The fast elimination phase ( T 1 2 = 12.75 min ; K = 0.01722 min −1 ) accounted for 74.6% of the dose; the intermediate phase ( T 1 2 = 40.2 min ; K = 0.01722 min −1 ) for 21.8%, and the slow ( T 1 2 = 5351 min ; K = 0.00013 min −1 ) for 3.6% of the dose.

Investigation of 68Ga-tripolyphosphate as a potential bone-scanning agent

A procedure described for the preparation of carrier-free 68Ga-tripolyphosphate and 68Ga-gallium tripolyphosphate. These radiopharmaceuticals were evaluated and compared as potential bone-imaging agents. A tissue distribution study demonstrated that the respective concentration of these preparations in bone was 43 and 64 per cent of the administered dose four hours after intravenous injection into mice. The toxicity of these chemicals was determined and bone images of rabbits were obtained using a positron camera.

Alterations of gallium-67 uptake in tumors by cis-platinum☆

Abstract Cis -Dichlorodiamine platinum (cis-Pt). a chemotherapeutic agent used for the treatment of a variety of cancers was found to interfere with the normal clinical uptake of radiogallium. Competitive experiments in which cis -Pt and 67 Ga-nitrilotriacetate were incubated with transferrin, demonstrated that no interference of gallium binding to transferrin occurs at this stage. The melanoma tissue culture studies indicated that the uptake of 67 Ga-citrate and 67 Ga-transferrin was affected only after prolonged preincubation of the cells with cis -Pt. This was confirmed in vivo . Tumor-bearing dogs injected with both 67 Ga-transferrin and cis -Pt showed a delayed effect and a reduced uptake of radiogallium in the tumor. These findings suggest that the effect of cis -Pt on gallium uptake is related to the cellular protein synthesis rather than the inhibition of the binding of 67 Ga to transferrin.

Use of Aquasol scintillator micture for liquid scintillation counting of beta radioactivity in biological tissue

Abstract The preparation of biological tissues for liquid scintillation counting, by ultrasonic disruption, decoloration with hydrogen peroxide, and solubilization in Aquasol ® scintillation fluor, has been described. The high tissue-dependent background counts recorded at 25°C were found to decrease to satisfactory levels by cooling and assaying at 2°C. The isotope channels ratio method was found to be a suitable means of quench correction for both tritium and 14 C. External standard channels ratio quench correction was considerd to be unsuitable under these experimental conditions for both tritium and 14 C. Maximum counting efficiencies for tritium and 14 C were 19·5 and 80·4 per cent respectively. Up to 598 mg of tissue, 186 mg of feces and 1·13 ml of urine were radio-assayed using this method.