Comparison of absolute renal uptake by using Tc-99m MAG-3 and Tc-99m DMSA

PURPOSE

The purpose of this study is to compare the value of absolute renal uptake (ARU %) in patients by using Tc-99m MAG-3 and Tc-99m DMSA scan.

MATERIAL AND METHODS

Absolute renal uptake is calculated using Tc-99m MAG-3 and Tc-99m DMSA in renal scintigraphy, Itoh and Tauex kidney depth methods used, respectively. n = 40 adult patients of both genders were included. All patients underwent Tc-99m MAG-3 and Tc-99m DMSA, respectively.

RESULTS

The values of ARU (%) were calculated separately in selected patients n = 40, (left = 17, right = 23 normal functioning kidneys) by MAG-3 and DMSA. Absolute renal uptake (%) of Tc-99m MAG-3 in left kidneys was found to be 15.2 ± 3.4, with spilt renal function 79.2 ± 14.7 and ARU (%) in right kidneys 16.2 ± 3.4 with spilt renal function 77.5 ± 19. Absolute renal uptake of Tc-99m DMSA in left kidneys was 17.5 ± 3.2 and in right kidneys 17.9 ± 4.5 with spilt renal function 81.8 ± 10.7 and 79.3 ± 13.8 for left and right kidney, respectively. Statistical analysis showed strong Pearson correlation.

CONCLUSION

Absolute renal uptake % was found to be more reliable in cases of bilateral compromised kidneys. ARU (%) calculated by Tc-99m MAG-3 solely can be used as predictor of renal function. The use of Tc-99m MAG-3 has more advantages than Tc-99m DMSA alone in renal scintigraphy as dynamic scintigraphy gives less radiation burden to patient, more information regarding renal function, and shorter stay time at hospital in comparison to static renal imaging. SRF % is less reliable than ARU (%).

Preclinical Evaluation of 99mTc-MAG3-5-Fab Targeting TREM2 in Lung Cancer Mouse Models: A Comparison with 99mTc-MAG3-5-F(ab')2

Triggering receptor expressed on myeloid cells-2 (TREM2), which is expressed on the surface of tumor-associated macrophages (TAMs), has been found to play a major role in the diagnosis and treatment of tumors. TREM2 expression is significantly upregulated in tumor tissues, and therefore, targeting TREM2 for tumor imaging may be of value. Previously, we performed TREM2 targeting imaging by using 68Ga-NOTA-COG1410 or a 124I-labeled monoclonal antibody (mAb) and F(ab')2 in mouse models of colon and gastric tumors. However, some of the shortcomings of these probes (i.e., the high uptake of 68Ga-NOTA-COG1410 in the liver, the difficulty of obtaining iodine-124, and the long half-life of iodine-124) have hindered their clinical use. Herein, we sought to synthesize novel molecular probes targeting TREM2 that are more conducive to clinical translation, eliminating the interference of isotope availability and in vivo probe biodistribution issues. Therefore, we established A549 cell lines with negative human TREM2 (hTREM2) expression (GFP tag; hTREM2- A549) or upregulated hTREM2 expression (GFP tag; hTREM2+ A549) using lentiviral transfection and confirmed these with Western blotting and immunocytochemistry. We then prepared a mouse anti-human TREM2 (5-mAb) by immunizing with the hTREM2 antigen. The antibody fragments 5-F(ab')2 and 5-Fab were prepared from 5-mAb, and 99mTc-MAG3-5-F(ab')2 and 99mTc-MAG3-5-Fab were then synthesized with excellent stability and specificity. 99mTc-MAG3-5-F(ab')2 had a slightly higher in vitro affinity than 99mTc-MAG3-5-Fab (Kd = 3.32 ± 0.05 nmol versus 4.62 ± 0.85 nmol). 99mTc-MAG3-5-F(ab')2 and 99mTc-MAG3-5-Fab both showed excellent specificity: after adding a 100-fold precursor, the two probes binding to the cells were almost blocked. In vivo pharmacokinetics showed that the distribution and elimination half-lives of 99mTc-MAG3-5-Fab (T1/2α = 1.25 ± 0.30 min and T1/2β = 21.98 ± 2.80 min, respectively) were significantly reduced compared to those of 99mTc-MAG3-5-F(ab')2 (T1/2α = 2.64 ± 0.37 min and T1/2β = 86.55 ± 26.86 min, respectively). In micro single-photon emission computed tomography/computed tomography (micro-SPECT/CT) imaging, the tumor was clearly displayed at 1 h after 99mTc-MAG3-5-Fab injection, while the blood background was extremely low at 3 h, and the probe was mainly excreted through the kidneys and biliary tract. 99mTc-MAG3-5-F(ab')2 uptake was also detected at the tumor site, although the blood background was consistently high. The biodistribution results were consistent with the micro-SPECT/CT imaging results. 99mTc-MAG3-5-Fab could clearly display hTREM2+ A549 tumors in a short time (1 h) with low uptake in nontumor organs and tissues and thus has clinical application prospects.

Normal Values of Renal Function measured with 99mTechnetium Mercaptoacetyltriglycine SPECT in Mice with Respect to Age, Sex and Circadian Rhythm

AIM

The aim of this study is to present normal values for ^99mtechnetium mercaptoacetyltriglycine renal uptake kinetics as a function of age, sex and circadian rhythm in mice using multi-pinhole SPECT.

METHODS

Dynamic multi-pinhole SPECT semistationary acquisitions consisting of 10 20 s frames followed by 25 50 s frames began prior to intravenous injection of 50 MBq in 12 female (F) and 12 male (M) C57BL/6N mice. Each mouse had follow-up imaging at 1, 3, 6, 12 and 22 months of age. To assess physiological changes related to circadian rhythm, animals were imaged during light (sleeping phase, SP) and dark conditions (awake phase, AP). Renal excretion time activity curves were analysed to determine maximum time to peak uptake (T_max).

RESULTS

There was an age-related effect on renal T_max. In one-month-old mice median T_max (1.8 min) occurred later than in 3-month-old mice (1.7 min; p = 0.035). Thereafter, mice showed continuously increasing time to renal T_max up to an age of 22 months (2.3 min; p < 0.001). Female mice showed a significantly later renal T_max than males (F 2.1 min, M 1.7 min; p < 0.001) from 3 months onwards. An effect of circadian rhythm on renal uptake was also observed with borderline relevance. Pooled results for all animals showed that renal T_max appeared at a later timepoint after injection during SP (2.0 min) than during AP (1.8 min; p = 0.019), while in age and sex matched animal groups no significant differences were observed.

CONCLUSION

This study showed that kidney function in mice is dependent on age and sex, whereas circadian rhythm does not cause a significant effect. Therefore, age and sex should be considered as important study design considerations for renal scintigraphy in mice, while the impact of circadian rhythm seems negligible. ZIEL:: Ziel dieser Studie war die Erhebung von Normwerten für die Nieren-Uptake-Kinetik von ^99mTechnetium-Mercaptoacetyltriglycin Multipinhole SPECT in Abhängigkeit von Alter, Geschlecht und circadianem Rhythmus bei der Maus.

METHODEN

Bei 12 weiblichen (F) und 12 männlichen (M) C57BL/6N Mäusen wurden unmittelbar vor intravenöser Injektion von 50 MBq ^99mTc-MAG3 dynamische semistationäre Multipinhole-SPECT-Akquisitionen von 10 Frames à 20 s gefolgt von 25 Frames à 50 s gestartet. Jede Maus wurde im Altersverlauf mit 1, 3, 6, 12 und 22 Monaten untersucht. Um physiologische Veränderungen bezüglich des circadianen Rhythmus zu erfassen, wurden die Tiere während der Hellphase (Schlafphase, SP) sowie der Dunkelphase (Wachphase, AP) untersucht. Die Nierenfunktion ist als Zeit-Aktivitäts-Kurve dargestellt und die Zeit bis zum Maximum (T_max) als Median in Minuten aufgeführt.

ERGEBNISSE

Generell zeigte sich ein altersabhängiger Einfluss auf T_max. Bei 1 Mo alten Tieren erfolgte T_max (1,8 min) später als mit 3 Mo (1,7 min; p = 0,035). Im weiteren Altersverlauf zeigten die Mäuse einen kontinuierlich späteren Zeitpunkt von T_max bis 22 Mo (2,3 min; p < 0,001). Weibchen zeigten ein signifikant späteres T_max als Männchen (F = 2,1 min, M = 1,7 min; p < 0,001) ab einem Alter von 3 Monaten. Für den circadianen Rhythmus wurde ein nicht eindeutiger Effekt beobachtet. Wenn alle Tiere zusammengefasst wurden, erfolgte T_max während der SP (2,0 min) später als während der AP (1,8 min; p = 0,019) während sich in den alters- und geschlechtsgetrennten Gruppen keine signifikanten Unterschiede nachweisen ließen.

SCHLUSSFOLGERUNG

Diese Studie zeigte einen deutlichen Einfluss von Alter und Geschlecht auf die Nierenfunktion bei der Maus während der circadiane Rhythmus keinen eindeutigen Effekt aufwies. Deshalb sollten bei Nierenstudien mit Mäusen die Faktoren Alter und Geschlecht berücksichtigt werden, während der circadiane Rhythmus vernachlässigbar erscheint.

New chelation strategy allows for quick and clean 99mTc-labeling of synthetic peptides

Analogues of bombesin have been synthesized in which a N2S2 (bis-mercaptoacetyl functionalized diaminopropionic acid) or a N3S (mercaptoacetyl-Gly-Gly-Gly) radiometal-chelating center has been incorporated that allows radiolabeling of these peptides with 99mTc without the need for conjugation or harsh reaction conditions. A mild radiolabeling is possible by using an acetyl-moiety as sulfur protecting group, which can be removed by mild hydroxylamine-treatment at room temperature before radiolabeling. Retained receptor binding is demonstrated in competitive binding experiments with 99mTc-radiolabeled peptides and PC-3 cells with bombesin receptors.

Tissular distributions and kinetics of two renal 99mTc-radiopharmaceuticals in rat

A digital radioimager (RI), conventional radioautography (RA), and tracks microradioautography (MRA) were used to assess the biodistributions and kinetics of 99mTc-dimercaptosuccinic (99mTc-DMSA) and 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) in rat at both macroscopic and microscopic levels. Three groups of male Wistar rats were studied. Using gamma-counting, kidney, liver, spleen and blood kinetics of both tracers were assessed in the three groups. Using RA and RI, renal slices were analyzed in group 1 the animals being sacrified from 2 to 60 min after injection of 99mTc-MAG3, and in group 2 the animals being sacrificed from 0.5 to 24 hr after injection of 99mTc-DMSA. Using MRA, renal slices were analyzed for 99mTc-DMSA (group 3). RA films and RI images displayed the variation with time of the cortical and medullary uptakes of the tracers. No regional heterogeneity within the different structures could be seen neither with RA films nor with MRA. The remaining activity in the blood 24 hr after injection of 99mTc-DMSA was evaluated. The tissular distributions of both tracer being homogenous, mean values of cortical uptake seems to be acceptable for dosimetric studies. Our results incite to use of 99mTc-MAG3 instead of 99mTc-DMSA when both tracers may be indicated.

Effect of protein binding on renal extraction of 131I-OIH and 99mTc-labeled tubular agents

The clearance of 99mTc-mercaptoacetyltriglycine (MAG3) is less than the clearances of o-131I-iodohippurate (OIH) and 99mTc-labeled DD- and LL-ethylenedicysteine (EC). This difference could be associated with the lower affinity of MAG3 for the tubular transport receptor, but MAG3 is more highly protein bound than OIH and the EC isomers; protein binding could also be an important factor governing tubular extraction. To separate the effects of protein binding from tubular receptor affinity, the extraction fractions (EFs) of MAG3, OIH, and the DD, LL, and DL isomers of 99mTc-EC were measured in an isolated perfused rat kidney model using a protein-free perfusate and perfusates containing bovine serum albumin.

METHODS

The right kidney was removed from the rat and perfused with modified Krebs-Henseleit buffers containing 7.5 or 2.5 g/dL bovine serum albumin or a protein-free perfusate. OIH was coinjected into the renal artery with each of the 99mTc-tracers. Protein binding was measured in each of the perfusates, and the venous outflow was collected to determine the EF.

RESULTS

The protein binding of MAG3 in the albumin perfusates ranged from 87% to 95%, significantly higher than the 20%-34% range of protein binding observed with the three EC complexes (P < 0.05). In the 2.5 g/dL albumin perfusate, the EF of MAG3 was 44%, significantly less than the 57%-77% EF of the three EC complexes; in the 7.5 g/dL perfusate, the MAG3 EF fell to 18% versus 39%-45% for the EC complexes (P < 0.05). However, in the protein-free perfusate, the EF of MAG3 was 64%, equal to or higher than the 46%-62% EF of the three EC complexes.

CONCLUSION

Protein binding modulates the tubular extraction of renal tracers. Protein binding and receptor affinity must be considered in the design of future renal radiopharmaceuticals as well as radiopharmaceuticals targeting other receptors.

Evaluation of the hepatobiliary excretion of technetium-99m-MAG3 and reconstitution factors affecting radiochemical purity

Technetium-99-MAG3 is a renal tubular function agent. However, sporadic liver and gallbladder visualization have raised questions about kit stability, impurities and nonrenal routes of excretion. To address these issues, studies were conducted to optimize the labeling efficiency of the TechneScan MAG3 kit and to evaluate the hepatobiliary excretion of the MAG3 complex.

METHODS

Thirty-six vials of the commercial formulation of 99mTc-MAG3 were prepared according to manufacturer's instructions and evaluated for radiochemical purity using two methods: a combination of high-performance liquid chromatography and paper chromatography (HPLC/PC); and the manufacturer's miniature chromatography system (Sep-Pak procedure).

RESULTS

The labeling efficiency was significantly higher when the kit was reconstituted with 10 ml (96.6%) of saline versus 5 ml (91.4%) (p < 0.01). The radiochemical purity of the kits remained stable for up to 6 hr, but the purity determined by Sep-Pak averaged 2.5% higher than that determined by HPLC procedures (p < 0.01). Rat studies to evaluate renal and hepatobiliary elimination of MAG3 showed no difference in the %ID excreted into the urine by 60 min in all groups of animals studied. However, the %ID excreted into the bile was significantly higher for the kit formulation than the HPLC-purified MAG3, 9.9% versus 6.6% (p = 0.0475).

CONCLUSION

The radiochemical purity of the TechneScan MAG3 kit can be improved by reconstituting with larger volumes. In addition, the studies in rats suggest that fasting or kit impurities may be a contributing factor to increased hepatobiliary visualization in patient studies.