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The introduction of nanotechnology in nuclear imaging has gained significant interest and could have promising potential for clinical use. Tumor imaging with radiolabeled nanoparticles (NPs) may be used for early detection, characterization, staging of disease, and for monitoring treatment efficacy. In this study we evaluated the biodistribution of porous silicon NPs labeled with positron-emitter gallium-68 in Wistar rats with subcutaneously transplanted cholangioma RS-1. The uptake of 68Ga-NPs in tumor tissue was 0.24±0.02 %ID/g at 5 min postinjection (p.i.) and climbed to 0.87±0.07 %ID/g at 5 h p.i. On the other hand, the amount of free 68Ga injected as 68GaCl3 solution decreased from 0.34±0.07 %ID/g at 5 min p.i. to 0.07±0.01 %ID/g at 5 h p.i. The highest level of radioactivity revealed in liver (8.27–15.79 %ID/g), spleen (0.98–1.27 %ID/g), and lungs (0.98–1.80 %ID/g). 68Ga-NPs were also determined in blood: up to 3.33±0.14 %ID/g at 5 min p.i. The uptake of 68Ga-NPs in other organs and tissues didn’t exceed 1 %ID/g. In conclusion, the obtained results suggest that 68Ga-NPs could be suitable for use as molecular imaging probes.

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Investigation of pharmacokinetic characteristics of the 99m Tc-and 188 Re-labeled monopotassium salt of 1-hydroxyethylidenediphosphonic acid (KHEDP) in rats showed that the level of accumulated activity at 5 min and 1 and 3 h after i.v. injection of 188 Re-KHEDP is higher in most organs and tissues than that after injection of 99m Tc-KHEDP. In the subsequent period (6 and 24 h), the specific activities in the majority of soft organs and tissues equalized due to greater elimination of 188 Re-KHEDP. The dynamics of labeled drug accumulation in bone tissues is characterized by a gradual increase in the activity concentration followed by its slow decrease. The maximum accumulation of 99m Tc-KHEDP in bone was achieved within 3 -6 h whereas the activity of 188 Re-KHEDP was at a maximum 1 h after injection. The activity gradually decreases after reaching the maximum value. The rate of 99m Tc-KHEDP elimination from bone is slower than that for 188 Re-KHEDP. The ratios of the specific activity in organs and tissues upon i.v. injection of 99m Tc-KHEDP and 188 Re-KHEDP are illustrated more clearly by the coefficients of differential accumulation (CDA) of activity in bone (bone of femur, rib, skull, and spine) relative to soft organs and tissues. The dynamics of the change in these values is characterized by a gradual increase over 24 h after injection. The growth is more pronounced for 188 Re-KHEDP than for 99m Tc-KHEDP. These data show that the elimination of activity from bone upon injection of 188 Re-KHEDP is faster than that for 99m Tc-KHEDP. A comparative analysis of the CDA values allows the dynamics of drug accumulation and elimination rates from soft organs and tissues to be evaluated in comparison to bone. Using the CDA values, it is also possible to determine the optimum conditions for carrying out scintigraphy studies of the skeleton using a gamma camera. The results from the study of the pharmacokinetic characteristics of 99m Tc-KHEDP and 188 Re-KHEDP in rats showed that these complexes have similar structures and substantially different biological properties, as indicated by the substantial differences in their in vivo behavior upon i.v. injection.Keywords: 99m Tc-and 188 Re-labeled radiopharmaceuticals, monopotassium salt of 1-hydroxyethylidenediphosphonic acid (KHEDP), pharmacokinetics. 4 -5. The tumor-to-healthy bone activity ratio for 99m Tc-HEDP 4 h after injection was slightly greater (2.45) than that for 99m Tc-MDP (2.20). 3330091-150X/11/4506-0333

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