Radiopharmaceuticals in cardiology

Myocardial perfusion studies are among the most often performedinvestigations in Nuclear Medicine. However, the developmentof radiopharmaceuticals for cardiology is an emergingdiscipline and several other radiotracers have been proven to beuseful. Although the myocardial perfusion studies have a wellestablishedrole in the management of cardiac disorders, stilla number of radiopharmaceuticals are under development fora variety of specific cardiac indications and their eventual clinicalrole remains to be seen. The paper provides a short overviewof currently used radiopharmaceuticals and potential molecularimaging radiotracers applicable in cardiology

Radiopharmaceuticals for somatostatin receptor imaging

The aim of this review is to summarize the developments and briefly characterize the somatostatin analogs which are currently used for somatostatin receptor imaging in clinical routine or in early phase clinical trials. Somatostatin (sst) receptor targeting with radiolabeled peptides has become an integral part in nuclear oncology during the last 20 years. This integration process has been initiated in Europe with the introduction to the market of 111In-DTPA-DPhe1-octreotide [111In-pentetreotide]. Introducing 99mTc in somatostatin receptor targeting radiopeptides resulted in much better image quality, higher sensitivity of tumor detection and lower mean effective dose for the examined patient. The next generation are 68Ga labeled somatostatin analogs. Due to the spatial resolution of PET technique and increasing number of PET scanners, the PET or PET/CT technique became very important in somatostatin receptor imaging. Until up to a couple of years ago the analogs of somatostatin were constructed aiming at their agonistic behavior, expecting that their internalization with the receptor acti­vated by the radiolabeled ligand and its retention within the tumor cell are crucial for efficient imaging and therapy. Recently it has been shown that the antagonists recognize more binding sites at the tumor cell membrane and hence offer an improved diagnostic efficacy, especially when the density of sst receptors is low. This approach may in future improve diagnostic value of somatostatin receptor imaging techniques. The developments in tracer design are followed by the improvements in imaging techniques. The new SPECT scanners offer resolution close to that of PET, which might open a new era for 99mTc and other SPECT radiotracers

Influence of PET/CT 68Ga somatostatin receptor imaging on proceeding with patients, who were previously diagnosed with 99mTc-EDDA/HYNIC-TOC SPECT

BACKGROUND: The aim of this study was the assessment of utility of somatostatin receptor scintigraphy (SRS) by SPECT imaging using 99mTc-EDDA/HYNIC-Tyr3-octreotide (99mTc-EDDA/HYNIC-TOC) in patients with neuroendocrine neoplasm (NEN) or suspected NEN, referred to Nuclear Medicine Dept. of Voivodship Specialty Center in Rzeszow. The selected group of patients was referred also to 68Ga PET/CT. The posed question was the ratio of patients for whom PET/CT with 68Ga would change their management. MATERIAL AND METHODS: The distribution of somatostatin receptors was imaged using 99mTc-EDDA/HYNIC-TOC in 61 planar and SPECT studies between 13/05/2010 and 04/02/2013 in Nuclear Medicine Dept. of Voivodship Specialty Center in Rzeszow. The patient age was within a range of 17–80, with the average age of 57.6. The average age of women (65% of patients over­all) was 55.6 and the average age of men (35% of patients overall) was 61.4. In 46 participants (75% of the study group), that underwent SRS, NEN was documented using pathology tests. Selected patients were referred to PET/CT with 68Ga labeled somatostatin analogs, DOTATATE or DOTANOC. This study group consisted of 14 female and 10 male participants with age range of 35–77 and average age of 55.5 years. Patients were classified into 3 groups, as follows: detection — referral due to clinical symptoms and/or biochemical markers (CgA-Chromogranin A, IAA-indoleacetic acid) with the aim of primary diagnosis, staging — referral with the aim of assessment of tumor spread, and follow-up — assessment of the therapy. RESULTS: Out of 61 patients, 24 underwent both 99mTc-EDDA/HYNIC-Tyr3-octreotide SPECT and 68Ga PET/CT. The result of PET/CT was used as a basis for further evaluation. Therefore, the patients were divided into groups; true positive TP (confirmed presence of tissue somatostatin receptors with 68Ga PET/CT) and TN (68Ga PET/CT did not detect any changes and the results were comparable and had the same influence on treatment protocol). In case of SPECT, the results were assigned as follows: TP, TN (in cases where the results were confirmed by 68Ga PET/CT), FP (patient’s scintigraphy demonstrated focal change by SPECT but not PET/CT) and FN (99mTc-EDDA/HYNIC-Tyr3-octreotide SPECT failed to demonstrate any abnormalities; however, the treatment protocol was changed after PET/CT). CONCLUSIONS: The accuracy of SPECT diagnosis was found to be as high as 91.6%. Only in 8.4% of patients the additional PET/CT with 68Ga-labeled somatostatin analog changed the treatment protocol

Studies on the separation of 99mTc from large excess of molybdenum

BACKGROUND: Due to aging and unexpected prolonged shutdown of nuclear reactors producing 99Mo for 99Mo/ 99mTc generators it was necessary to explore the alternative methods of technetium-99m production. The first choice were the accelerators. Three years ago IAEA (International Atomic Energy Agency) initiated the Coordinated Research Project “Accelerator-based Alternatives to Non-HEU production of Mo-99 /Tc-99m” aimed at direct production of 99mTc in proton accelerators using the 100Mo(p,2n)99mTc reaction. POLATOM is participating in this enterprise together with the Heavy Ion Laboratory of Warsaw University and the Institute of Nuclear Chemistry and Technology. MATERIAL AND METHODS: 99Mo/99mTc solutions and pure 99mTc used for generators production or milked from ready to use generators were used in experiments. Commercial chromatographic and laboratory-prepared columns were used for separation. The peristaltic pumps were used for solutions delivery onto the columns. Radioactivity of eluted 99Mo and 99mTc was measured using high resolution gamma spectrometry or ionisation chamber in case of high radioactivity. For separation, three different chromatographic methods were used, one based on ion exchange and two on extraction. RESULTS: Synthetic mixtures simulating the real solutions were used. 99mTc is quantitatively bound in the Dowex-1 × 8 column whereas molybdenum is only slightly retained and totally rinsed with 2M NaOH. 99mTc is eluted with TBAB. The elution yield has been reproducible and amounted to 78%. The AnaLig Tc-02 resin column was used for 99mTc retention. Residual Mo was removed by rinsing with 2M NaOH and 99mTc eluted using small volume of water. The recovery was equal to about 85%. Using C-18 column coated with PEG over 80% of 99mTc was recovered in about 50 mL of water. The reduction of volume was necessary. CONCLUSIONS: The recovery of 99mTc was the highest using AnaLig Tc-02 resin. Time of 99mTc separation is the shortest for AnaLig Tc-02 resin and it is not higher than 100 minutes and it can further be shortened

Oxidation of methionine — is it limiting the diagnostic properties of 99mTc-labeled Exendin-4, a Glucagon-Like Peptide-1 receptor agonist?

BACKGROUND: Preliminary clinical evaluation of 99mTc-EDDA/HYNIC-Met14-Exendin-4 showed that the complex offers new diagnostic possibilities for insulinoma and MTC. Exendin-4 contains methionine at position 14 in the amino acid chain, which may be oxidized to methionine sulfoxide and, from the pharmaceutical point of view, the oxidized moiety becomes an undesired impurity in the final radioactive preparation. Therefore, the aim of this study was to investigate the influence of commonly used methods to eliminate the effect of methionine oxidation in peptides, i.e. the replacement of methionine by norleucine (Nle) and the addition of L-methionine, on the in vitro stability and the biodistribution. MATERIAL AND METHODS: 99mTc-EDDA/HYNIC-Met14-Exendin-4, 99mTc-EDDA/HYNIC-Nle14-Exendin-4, 99mTc-EDDA/HYNIC-Met14-Ex­endin-4 with the addition of L-methionine and an oxidized form of Exendin-4, i.e. 99mTc-EDDA/HYNIC-Met14(ox)-Exendin-4 were compared in vivo with 68Ga-NODAGA-Nle14-Exendin-4 in normal Wistar rats. The stability and lipophilicity were determined in vitro. RESULTS: Biodistribution studies confirmed the specific uptake of all tested complexes in the GLP-1 positive organs: lungs, pancreas and stomach. The uptake of 99mTc-EDDA/HYNIC-Met14-Exendin-4 with the addition of L-methionine and for 68Ga-NODAGA-Nle14-Exendin-4 at 1h p.i. was around 2-fold higher than that of 99mTc-EDDA/HYNIC-Met14-Exendin-4 and 99mTc-EDDA/HYNIC-Nle14-Exendin-4. CONCLUSION: Although the substitution of methionine by norleucine in the HYNIC-Exendin-4 did not result in improved bio­distribution, the use of L-methionine, as the excipient that inhibits the oxidation of methionine in the peptide chain resulted in higher lung/blood and stomach/blood uptake ratios. Our results confirmed that methionine at position 14 of amino acid chain of Exendin-4 plays an important role in the interaction with GLP-1 receptor positive tissue

The radiometal makes a difference. Synthesis and preliminary characterisation of DOTA-minigastrin analogue complexes with Ga, Lu and Y

BACKGROUND: The minigastrin analogue — CP04: DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 has been developed for CCK2R targeting. This analogue can be radiolabelled with 111In or 68Ga for imaging, or with 90Y and 177Lu for therapy. However, affinity of the chelator-peptide conjugates to the cell membrane receptors may vary depending on the metal incorporated into the complex. So far, there are no such studies for the ligands of gastrin/cholecystokinin receptor CCK2R. It is supposed that the reason for the differentiation of receptor affinity to the respective receptors is in the changes of structure of chelating system and their influence on the bioactive conformations of the metal conjugated peptides. Herein, we report on the radiolabeling of CP04 with 90Y, 177Lu and 68Ga and synthesis of cold CP04 complexes with respective stable metals for further structural and physico-chemical and biological studies. MATERIALS AND METHODS: From 200 to 600 MBq of 90Y, 177Lu or 68Ga were used for radiolabelling of 20 μg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5). Non-radioactive complexes with Lu and Ga were synthesized in milligram amounts starting from 0.5 mg up to 5 mg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5) when using 2-molar excess of the metal ions. Complex formation needed 5 min in microwave oven or 12 min in thermo-block at 95°C. RP-HPLC isocratic method (Kinetex 150/4.6 mm; 25% AcN/0.1% TFA, 1 mL/min) with UV/Vis and radiometric detection was developed for investigation of the radiolabelled and “cold” complexes. For LC-MS investigations, HPLC method was modified replacing TFA by formic acid. RESULTS AND DISCUSSION: Yields of CP04 radiolabelling were greater than 90% for all three radionuclides. The HPLC method enabled identification of these radio-complexes based on comparison to their non-radioactive equivalents. In all cases, chromatograms revealed peaks that could be attributed to the metal-CP04 complexes and to impurities (including methionine oxidation). LC-MS analysis of Ga and Lu complexes revealed conformity of the observed molecular ions to the predicted formulas (m/z 2116 and 2220 Da for Ga and Lu, respectively). Different chromatographic behaviour observed for Ga-CP04 complex comparing to Lu- and Y- labelled peptide (relative retention to CP04: 1.08, 0.86 and 0.85, respectively) suggest different coordination of the metal ions. Therefore, further studies are planned using the non-radioactive complexes in order to assess their structural conformations

Comparison of chromatographic methods for quality control of DMSA complexes with 99mTc and 188Re at (III) and (V) oxidation states

BACKGROUND: The reliable method for determination ofidentity and radiochemical purity (RCP) is of great importancein radiopharmaceutical development. This is especially relevantwhen more than one form of radiometal/ligand complex can beformed during radiolabelling, such as complexes of 99mTc or 188Rewith meso-2,3-dimercaptosuccinic acid (DMSA), where dependingon the pH, metal can occur either at +3 or +5 oxidation state.The aim of our study was to evaluate possibilities for optimizationof chromatographic systems leading to specific and reliableanalytical method for determination of the identity and RCP ofDMSA complexes with 99mTc or 188Re.MATERIAL AND METHODS: The commercial DMSA kits(POLATOM) were used for preparation of technetium-99m (III) and (V) complexes with DMSA. 99mTc(V)-DMSA complexeswere prepared by addition of NaHCO3 to the kit vial prior to99mTc-eluate to obtain pH ~8. 188Re(V)-DMSA was prepared eitherdirectly or using intermediate 188Re(III)-EDTA complex addedto DMSA. RCP was evaluated by TLC using: ITLC-SG developedin methylethylketon, SG60 coated plates developed in:n-BuOH/H2O/CH3COOH and n-PrOH/H2O/CH3COOH systems,and in H2O. Comparative biodistribution studies were performedin normal Wistar rats.RESULTS: Using silica gel plates and n-PrOH, H2O and aceticacid in the developing solution, we observed that 99mTc/188Re(III)-DMSA and 99mTc/188Re(V)-DMSA complexes could be wellseparated from each other and from the impurities in the formof free pertechnetate/perrhenate. In vivo studies showed quitedifferent biodistribution of 99mTc(III)- and 99mTc(V)-DMSA. Thetrivalent complex accumulated mainly in kidneys (>40%ID),while 99mTc(V)-DMSA revealed high excretion with urine andrelatively high concentration in osseous tissue (ca. 2 %ID/g).Accumulation of this complex in kidneys was very low (ca.2.5 %ID). Biodistribution pattern of 188Re(V)-DMSA prepareddirectly was almost identical to that of 99mTc(V)-DMSA. Biodistributionresults of the 188Re preparation obtained using 188Re(III)-EDTA intermediate indicated that the preparation contained themixture of penta- and trivalent 188Re complexes. The quite highaccumulation of radioactivity in kidneys (23 %ID) gave evidenceof the presence of 188Re(III)-DMSA in this preparation, what wasalso confirmed by the results of TLC analysis performed usingsilica gel plate and n-propanol/water/acetic acid as developingsystem. CONCLUSIONS: Based on our study, we have made recommendationon the suitable methods for investigations of RCP ofDMSA complexes, i.e.: SG60 plates developed in the mixtureof n-propanol/water/acetic acid, which enable determination of the tri- and pentavalent DMSA complexes, as well as, thepertechnetate/perrhenate impurity, and developed in water fordetermination of the colloidal residue.BACKGROUND: The reliable method for determination ofidentity and radiochemical purity (RCP) is of great importancein radiopharmaceutical development. This is especially relevantwhen more than one form of radiometal/ligand complex can beformed during radiolabelling, such as complexes of 99mTc or 188Rewith meso-2,3-dimercaptosuccinic acid (DMSA), where dependingon the pH, metal can occur either at +3 or +5 oxidation state.The aim of our study was to evaluate possibilities for optimizationof chromatographic systems leading to specific and reliableanalytical method for determination of the identity and RCP ofDMSA complexes with 99mTc or 188Re.MATERIAL AND METHODS: The commercial DMSA kits(POLATOM) were used for preparation of technetium-99m (III) and (V) complexes with DMSA. 99mTc(V)-DMSA complexeswere prepared by addition of NaHCO3 to the kit vial prior to99mTc-eluate to obtain pH ~8. 188Re(V)-DMSA was prepared eitherdirectly or using intermediate 188Re(III)-EDTA complex addedto DMSA. RCP was evaluated by TLC using: ITLC-SG developedin methylethylketon, SG60 coated plates developed in:n-BuOH/H2O/CH3COOH and n-PrOH/H2O/CH3COOH systems,and in H2O. Comparative biodistribution studies were performedin normal Wistar rats.RESULTS: Using silica gel plates and n-PrOH, H2O and aceticacid in the developing solution, we observed that 99mTc/188Re(III)-DMSA and 99mTc/188Re(V)-DMSA complexes could be wellseparated from each other and from the impurities in the formof free pertechnetate/perrhenate. In vivo studies showed quitedifferent biodistribution of 99mTc(III)- and 99mTc(V)-DMSA. Thetrivalent complex accumulated mainly in kidneys (>40%ID),while 99mTc(V)-DMSA revealed high excretion with urine andrelatively high concentration in osseous tissue (ca. 2 %ID/g).Accumulation of this complex in kidneys was very low (ca.2.5 %ID). Biodistribution pattern of 188Re(V)-DMSA prepareddirectly was almost identical to that of 99mTc(V)-DMSA. Biodistributionresults of the 188Re preparation obtained using 188Re(III)-EDTA intermediate indicated that the preparation contained themixture of penta- and trivalent 188Re complexes. The quite highaccumulation of radioactivity in kidneys (23 %ID) gave evidenceof the presence of 188Re(III)-DMSA in this preparation, what wasalso confirmed by the results of TLC analysis performed usingsilica gel plate and n-propanol/water/acetic acid as developingsystem.CONCLUSIONS: Based on our study, we have made recommendationon the suitable methods for investigations of RCP ofDMSA complexes, i.e.: SG60 plates developed in the mixtureof n-propanol/water/acetic acid, which enable determination of the tri- and pentavalent DMSA complexes, as well as, thepertechnetate/perrhenate impurity, and developed in water fordetermination of the colloidal residue

Czy nefrotoksyczność po PRRT jest nadal poważnym problemem klinicznym? Analiza stopnia uszkodzenia nerek po terapii znakowanymi izotopowo analogami somatostatyny z zastosowaniem 90Y-DOTATATE i 90Y/177Lu-DOTATATE

Introduction: The kidneys play an essential role in PRRT. The infusion of amino acids could reduce uptake in the kidney of radiolabelled peptides. The purpose of this study was to determine the extent of kidney damage post PRRT. Material and methods: 53 patients, with disseminated neuroendocrine tumours (NET), received 3–5 cycles of up to a maximum 7.4 GBq/m2 calculated dose of 90Y-DOTATATE (n = 25) and 90Y/177Lu-DOTATATE (n = 28). Creatinine levels were measured and glomerular filtration rates (GFR) were calculated. A mixed amino acid infusion was used for nephroprotection. Results: Patients treated with 90Y-DOTATATE had a mean creatinine level of 0.77 ± 0.19 mg/dL and a mean GFR (mL/min/1.73 m2) of 103.6 ± 30.8. Patients treated with 90Y/177Lu-DOTATATE had a mean creatinine level of 0.92 ± 0.33 mg/dL and a mean GFR of 84.7 ± 26.3. In the follow up, among patients treated with 90Y-DOTATATE and 90Y/177Lu-DOTATATE, the mean GFR level at 12 months was 101.2 ± 31.3 v. 83.9 ± 25.2, at 24 months 80.2 ± 32.7 v. 77.2 ± 31.1, at 36 months 78.9 ± 42.1 v. 67.5 ± 9.7, and 48 months 59.7 ± 15.2 v. 72.6 ± 11.2. The mean yearly decrease in GFR was 4.5 mL in all treated patients; for patients treated with 90Y-DOTATATE and 90Y/177Lu-DOTATATE it was 6.8 v. 3.0, respectively. Conclusions: 90Y/177Lu-DOTATATE treatment induced statistically significantly less change in kidney function compared to 90Y-DOTATATE.Wstęp: Narządem krytycznym w leczeniu guzów neuroendokrynnych z zastosowaniem znakowanych radioizotopowo analogów somatostatyny (PRRT) są nerki. Działanie nefrotoksyczne można ograniczyć, podając roztwór aminokwasów w formie wlewu dożylnego. Celem pracy była analiza stopnia uszkodzenia nerek po PRRT w ciągu pierwszych czterech lat po leczeniu. Materiał i metody: Do badania włączono 53 chorych, z rozpoznanym rozsianym procesem neuroendokrynnym (NET). Chorzy otrzymali 7,4 GBq/m2 90Y-DOTATATE (n = 25) lub 90Y/177Lu-DOTATATE (n = 28) w 3–5 cyklach. Radiofarmaceutyk podawano w trakcie wlewu i.v. roztworu aminokwasów. Oceniano stężenie kreatyniny, na podstawie którego obliczano wartość filtracji kłębuszkowej (GFR). Wyniki: Przed leczeniem w grupie chorych leczonych 90Y-DOTATATE stężenie kreatyniny wynosiło 0,77 ± 0,19 (mg/dl), natomiast GFR 103,6 ± 30,8 (ml/min/1,73 m2). W grupie leczonej 90Y/177Lu-DOTATATE stężenie kreatyniny wynosiło 0,92 ± 0,33 i GFR 84,7 ± 26,3. Nie stwierdzono statystycznie znamiennej różnicy w wartościach badanych parametrów między obydwiema grupami. Po 12 miesiącach wartość GFR w grupie leczonej 90Y-DOTATATE i grupie leczonej 90Y/177Lu-DOTATATE wynosiła odpowiednio: 101 ± 31,3 oraz 83,9 ± 25,2. Po 24 miesiącach odpowiednio: 80,2 ± 32,7 i 77,2 ± 31,1. Po 36 miesiącach odpowiednio 78,9 ± 42,1 i 67,5 ± 9,7. Po 48 miesiącach odpowiednio: 59,7 ± 15,2 i 72,6 ± 11,2. Średni spadek GFR dla wszystkich chorych wynosił 4,5 ml/rok, dla chorych leczonych 90Y-DOTATATE – 6,8 ml/rok, natomiast dla chorych leczonych 90Y/177Lu-DOTATATE — 3,0 ml/rok Wnioski: Leczenie z zastosowaniem 90Y/177Lu-DOTATATE jest związane z istotnie mniejszym statystycznie uszkodzeniem czynności nerek w porównaniu do leczenia z zastosowaniem 90Y-DOTATATE