Preparation and preclinical evaluation of (66)Ga-DOTA-E(c(RGDfK))2 as a potential theranostic radiopharmaceutical.

INTRODUCTION: Integrin αvß3 plays an important role in angiogenesis and is over-expressed in tumoral endothelial cells and some other tumor cells. RGD (Arg-Gly-Asn) peptides labeled with (68)Ga (t1/2=68min) have showed good characteristics for imaging of αvß3 expression using positron emission tomography (PET). Gallium-66 has been proposed as a PET imaging alternative to (68)Ga and given the unique high energy of its emitted positrons (Emax 4.15MeV) it may also be useful for therapy. The aim of this research is to prepare [(66)Ga]DOTA-E-[c(RGDfK)]2 and evaluate in mice its potential as a new theranostic radiopharmaceutical. METHODS: High specific activity (66)Ga was produced via the (66)Zn(p,n) reaction, and the labelling method of DOTA-E-[c(RGDfK)]2 with (66)Ga was optimized. Radiochemical purity was determined by TLC, and in vitro stability and protein binding were determined. Serial microPET imaging and biodistribution studies were carried out in nude mice bearing C6 xenografts. Radiation absorbed dose estimates were based on the biodistribution studies, where tumor and organs of interest were collected at 0.5, 1, 3, 5 and 24h post-injection of [(66)Ga]DOTA-E-[c(RGDfK)]2. RESULTS: Our results have shown that [(66)Ga]DOTA-E-[c(RGDfK)]2 can be prepared with high radiochemical purity (>97%), specific activity (36-67GBq/µmol), in vitro stability, and moderate protein binding. MicroPET imaging up to 24 post-injection showed contrasting tumors reflecting αvß3-targeted tracer accumulation. Biodistribution studies and dosimetry estimations showed a stable tumor uptake, rapid blood clearance, and favorable tumor-to-tissue ratios. CONCLUSIONS: The peptide conjugated DOTA-E-[c(RGDfK)]2 labeled with (66)Ga may be attractive as a theranostic agent for tumors over-expressing αvß3 integrins.

Click chemistry for [(99m)Tc(CO)(3)] labeling of Lys(3)-bombesin.

(99m)Tc-HYNIC labeled Lys(3)-bombesin has shown specific binding to gastrin-releasing peptide receptors (GRP-r) over-expressed in cancer cells. Click chemistry offers an innovative functionalization strategy for biomolecules such as bombesin. The aim of this research was to apply a click chemistry approach for [(99m)Tc(CO)(3)] labeling of Lys(3)-bombesin and to compare the in vitro MCF7 breast cancer cell uptake and biodistribution profile in mice with that of (99m)Tc-EDDA/HYNIC-Lys(3)-bombesin. The results suggest a higher lipophilicity for (99m)Tc(CO)(3)-triazole-Lys(3)-bombesin which explains its higher in vivo hepatobiliary elimination. Pancreas-to-blood ratio for (99m)Tc(CO)(3)-triazole-Lys(3)-bombesin was 4.46 at 3 h and both bombesin radiopharmaceuticals showed specific recognition for GRP receptors in MCF7 cancer cells. Click chemistry is a reliable approach for [(99m)Tc(CO)(3)] labeling of Lys(3)-bombesin.

Gold nanoparticles conjugated to [Tyr3]octreotide peptide.

A multifunctional system of gold nanoparticles (AuNP) capped by the [Tyr(3)]Octreotide (TOC) peptide was prepared and characterized by transmission electron microscopy (TEM) and UV-Vis, infrared and fluorescence spectroscopy. AuNP and AuNP-TOC fluorescence emission spectra were obtained both in solution and in murine AR42J-tumor tissues. Results suggest that AuNP were functionalized with TOC through interactions with the N-terminal amine of the phenylalanine, the amide groups and possibly with the indole group of the tryptophan residue. The fluorescence analyses in tissue revealed a recognition of the AuNP-TOC conjugate for the neuroendocrine tumor because of the lower energy position of the fluorescence resonance (692 nm) with respect to that of the AuNP in the same tumoral tissue (684 nm). The emission band observed in the near-infrared region (692 nm) opens the possibility for AuNP-TOC use in bioimaging.

[166Dy]Dy/166Ho hydroxide macroaggregates: an in vivo generator system for radiation synovectomy.

Radiation synovectomy is an effective treatment in patients suffering from inflammatory-rheumatoid and degenerative joint diseases. The aim of this work was to examine the feasibility of preparing dysprosium-166 (166Dy)/holmium-166(166Ho) hydroxide macroaggregates ([166Dy]Dy/166Ho-HM) as an in vivo generator for radiation synovectomy evaluating whether the stability of 166Dy-HM and 166Ho-HM complexes is maintained when the daughter 166Ho is formed. The Monte Carlo (MCNP4B) theoretical depth dose profile for the in vivo [166Dy]Dy/166Ho generator system in a joint model was calculated and compared with that produced by 90Y, 153Sm and 166Ho. 166Dy was obtained by neutron irradiation of enriched 164Dy2O3 in a Triga Mark III reactor. Macroaggregates were prepared by reaction of [166Dy]DyCl3 with 0.5 M NaOH in an ultrasonic bath. [166Dy]Dy/166Ho-HM was obtained with radiochemical purity >99.5% and with the majority of particles in the 2-5 microm range. In vitro studies demonstrated that the radio-macroaggregates are stable in saline solution and human serum without a significant change in the particle size over 14 d, suggesting that no translocation of the daughter nucleus occurs subsequent to beta- decay of 166Dy. Biological studies in normal rats demonstrated high retention in the knee joint even 7 d after [166Dy]Dy/166Ho-HM administration. The Monte Carlo (MCNP4B) theoretical depth dose profiles in a joint model, showed that the in vivo [166Dy]Dy/166Ho generator system would produce 25% and 50% less radiation dose to the articular cartilage and bone surface, respectively, than that produced by 90Y or pure 166Ho in a treatment with the same therapeutic dose to the synovium surface. Despite that 153Sm showed the best depth dose profile sparing doses to healthy tissues, the use of 166Dy could provide the advantage of being applied in patients that cannot be reached within a few hours from a nuclear reactor and to produce less radiation exposure to the medical personnel during the radiopharmaceutical administration.

Labeling of biotin with [166Dy]Dy/166Ho as a stable in vivo generator system.

The aim of this work was to synthesize [166Dy]Dy/166Ho-DTPA-Biotin to evaluate its potential as a new radiopharmaceutical for targeted radiotherapy. Dysprosium-166 (166Dy) was obtained by neutron irradiation of enriched 164Dy(2)O(3) in a Triga Mark III reactor. The labeling was carried out in aqueous media at pH 8.0 by addition of [166Dy]DyCl(3) to diethylenetriaminepentaacetic-alpha,omega-bis(biocytinamide) (DTPA-Biotin). Radiochemical purity was determined by high-performance liquid chromatography (HPLC) and TLC. The biological integrity of labeled biotin was studied evaluating its avidity for avidin in an agarose column and by size-exclusion HPLC analysis of the radiolabeled DTPA-Biotin with and without the addition of avidin. Stability studies against dilution were carried out by diluting the radiocomplex solution with saline solution and with human serum at 37 degrees C for 24 h. The [166Dy]Dy/166Ho-labeled biotin was obtained with a 99.1+/-0.6% radiochemical purity. In vitro studies demonstrated that [166Dy]Dy/166Ho-DTPA-Biotin is stable after dilution in saline and in human serum and no translocation of the daughter nucleus occurs subsequent to beta(-) decay of 166Dy that could produce release of 166Ho(3+). Avidity of labeled biotin for avidin was not affected by the labeling procedure. Biodistribution studies in normal mice showed that the [166Dy]Dy/166Ho-DTPA-Biotin has a high renal clearance. In conclusion, the radiolabeled biotin prepared in this investigation has adequate properties to work as a stable in vivo generator system for targeted radiotherapy.

99mTc-glucarate for detection of isoproterenol-induced myocardial infarction in rats.

Infarct-avid radiopharmaceuticals are necessary for rapid and timely diagnosis of acute myocardial infarction. The animal model used to produce infarction implies artery ligation but chemical induction can be easily obtained with isoproterenol. A new infarct-avid radiopharmaceutical based on glucaric acid was prepared in the hospital radiopharmacy of the INCMNSZ. 99mTc-glucarate was easy to prepare, stable for 96 h and was used to study its biodistribution in rats with isoproterenol-induced acute myocardial infarction. Histological studies demonstrated that the rats developed an infarct 18 h after isoproterenol administration. The rat biodistribution studies showed a rapid blood clearance via the kidneys. Thirty minutes after 99mTc-glucarate administration the standardised heart uptake value S(h)UV was 4.7 in infarcted rat heart which is six times more than in normal rats. ROIs drawn over the gamma camera images showed a ratio of 4.4. The high image quality suggests that high contrast images can be obtained in humans and the 96 h stability makes it an ideal agent to detect, in patients, early cardiac infarction.

[Radiopharmacokinetic and gammagraphic studies for calculating personalized dosimetry]. / Estudios radiofarmacocinéticos y gammagráficos para cálculos de dosimetría personalizada.

In nuclear medicine radiation absorbed doses are important in the patient's risk/benefit evaluation and are estimated by means of biological and complex mathematical models. The biological model includes radiopharmacokinetic data obtained through blood and urine samples taken at given intervals. A useful mathematical model is the MIRD model and with the value for the time of residence tau the MIRDOSE3 computer program uses several anatomic models and calculates radiation absorbed dose for 25 organs. At the Radiopharmacy Unit of the Nuclear Medicine Department at INCMNSZ two new bone seeking radiopharmaceuticals, 99mTc-ABP and 188Re-ABP, have been designed, characterized and animal-tested. Radiopharmaceutical parameters and sequential scanning were obtained for diagnostic 99mTc-ABP in 10 normal subjects and the aim was to use % 24 hour urine elimination and % bone uptake to calculate radiation absorbed dose and extrapolate the values to 188Re-ABP as the basis for a therapeutic treatment. 99mTc-ABP was eliminated in women's urine 63.2 +/- 7.3%/activity and 70 +/- 11%/activity in men. In women 36.8 +/- 7.3% of the radiopharmaceutical remains on the bone surface and in men 30 +/- 11%. ROIs were drawn on the images and the time-integrated renal cpm/pixel/ROI gave a residence time tau = 0.52 h. Cumulative bone activity A calculated with A = 1.443 (T1/2) A0 was 2358 +/- 469 MBq h for women and 1923 +/- 707 MBq h for men. Residence time tau was 3.19 +/- 0.63 h in women and 2.6 +/- 0.95 h in men. Radiation absorbed dose for the whole body was 0.0020 +/- 0.0004 mGy/MBq for women and 0.0013 +/- 0.0005 mGy/MBq for men. For women's bone marrow it was 0.0063 +/- 0.0013 mGy/MBq and for men 0.0041 +/- 0.0015 mGy/MBq. 188Re-ABP behaves as 99mTc-ABP therefore, the effective dose given by 188Re, a beta emitter, would be for women 0.0936 mSv/MBq and for men 0.0608 mSv/MBq. These characteristics and the radionuclidic characteristics of 188Re indicate that 188Re-ABP might be a good bone metastases pain palliation radiopharmaceutical.

Uptake of (188)Re-beta-naphthyl-peptide in cervical carcinoma tumours in athymic mice.

Radiolabelled somatostatin analogues have been used in diagnostic and therapeutic nuclear medicine to treat cancerous tumours. Lanreotide, a cyclic octapeptide, beta-naphthyl-peptide, with antiproliferative action on human small cell lung carcinoma was (188)Re labelled and characterised, and its biodistribution was studied in mice. Molecular modelling indicates that the lipophilic radiopharmaceutical might be an oxo-rhenium (V) penta-coordinated complex. The implanted human cervical tumour of epidermoid origin was positive for cytokeratins and Vimentin. Uptake of (188)Re-labelled peptide in the implanted tumour in athymic mice was 6.2+/-2.9% and was rapidly cleared via the hepatobiliary system. (188)Re-beta-naphthyl-peptide might be a potential therapeutic agent.

Labelling of Re-ABP with 188Re for bone pain palliation.

Etidronate and medronate have been labelled with technetium-99m (99mTc-HEDP, 99mTc-MDP) for bone scanning and, with rhenium-188 (188Re-HEDP) to palliate the pain resulting from bone metastases. The objective of this study was to label alendronate, ABP, a new bisphosphonate, with SnF2-reduced-188Re. The reagents for the 5 mg ABP kit were SnF2, KReO4 and gentisic acid at acid pH. The chemical, spectroscopic and microscopic characteristics, quality control, rat bone uptake of [188Re]Re-ABP and similarities with 99mTc-ABP are presented. We conclude that this is a promising new radiopharmaceutical for bone metastases pain palliation.

Preparation, biodistribution, and dosimetry of 188Re-labeled MoAb ior cea1 and its F(ab')2 fragments by avidin-biotin strategy.

The biotinylated monoclonal antibody (MoAb) ior cea1 and its F(ab')2 fragments were labeled with Re-188 by combination of avidin-biotin strategy. 188Re-MoAb, 188Re-MoAb-biotin, 188Re-F(ab')2, and 188Re-F(ab')2-biotin preparations were produced for these studies with specific activities of 1.30+/-0.18 GBq/mg and from instant freeze-dried kit formulations using ethane-1-hydroxy-1,1-diphosphonic acid (EHDP) as a weak competing ligand. There were no significant differences (p > 0.05) between the biodistribution in mice of biotinylated and unbiotinylated 188Re-labeled immunoconjugates. When avidin was injected as a chase after injection of 188Re-MoAb-biotin or 188Re-F(ab')2-biotin, the blood radioactivity level decreased approximately 75% (cumulated activity) and the effective dose decreased almost 25% with respect to that of the radioimmunoconjugates in which the chase effect was not used. Our results suggest that 188Re-labeled biotinylated MoAb ior ceal and its F(ab')2 fragments prepared by this method are stable complexes in vivo.

Radiopharmacokinetics, renal clearance and dosimetry of 99mTc-MAG3.

BACKGROUND: Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) is a radiopharmaceutical for tubular function and can be prepared with 99m-technetium and the ligand Bz-MAG3 (Instituto Nacional de Investigaciones Nucleares, Mexico City). No radiopharmacokinetic parameters have been found for the healthy adult Mexican population with 99mTc-MAG3, prepared with the nationally produced or imported Bz-MAG3 kit. METHODS: The radiopharmacokinetic parameters and the clearance of 99mTc-MAG3 in seven healthy Mexican volunteers were determined by the single- and multi-sample methods. Computer programs were used for the calculations. RESULTS: Using several plasma samples from 0-43 min and the BIEXP program, it was shown that 99mTc-MAG3 follows a two-compartment model of distribution, with an apparent volume in the central compartment Vdcc = 3.8 + 0.7 l, a volume of distribution at steady state Vdss = 6.7 + 1.0 l, T1/2 alpha = 0.07 + 0.02 h-1, T1/2 beta = 0.49 + 0.15 h-1, mean residence time MRT = 0.60 + 0.17 h and clearance = 208 + 57 (ml/min)/1.73 m2. In comparison, the clearance value with a single sample drawn 43 min post-injection and calculated with Tauxe's formula was 193 +/- 59 (ml/min)/m2. CONCLUSIONS: The 15 ml difference between the two methods is neither statistically different (p = 0.11) nor important for routine clinical studies. The single-sample method is recommended because it is reliable and can be done at the same time that the dynamic renal scan is acquired. Estimated absorbed radiation dose was calculated for several organs.

Radiopharmacokinetic data for 99mTc-ABP--a new radiopharmaceutical for bone scanning: comparison with 99mTc-MDP.

Technetium-99m-labeled alendronate is a new radiopharmaceutical for bone scanning developed under strict quality control at the INNSZ. The purpose of this work was to compare the radiopharmacokinetic data and the dosimetry of 99mTc-ABP and 99mTc-MDP in 10 volunteers, after it was tested in laboratory animals. 99mTc-ABP has shorter mean residence time (MRT) and t 1/2 beta; is less protein bound; has a higher renal clearance; smaller Vdss, and similar bone uptake at 1 and 2 h. 99mTc-ABP gives less radiation exposure to the patient with a 740 MBq dose, and the quality of the bone scan is excellent. 99mTc-ABP is a better radiopharmaceutical than 99mTc-MDP for bone scanning.

[99m-Tc alendronate as a new option in bone gammagraphy]. / El 99mTc-alendronato como nueva opción en la gammagrafía ósea.

OBJECTIVE: To compare the quality of bone scans obtained with 99mTc-ABP, a new radiopharmaceutical, and 99mTc-MDP. MATERIAL AND METHODS: A comparative study within subjects was done in nine healthy volunteers, 5 female and 4 male, aged 23 to 39 years. The dose for both radiopharmaceuticals was 740 MBq; radiopharmacokinetic parameters were determined and a whole body bone scan was taken with a MultiSpect 2 gamma camera two hours post administration with a wash-out period of 72 hours between preparations. The images were independently evaluated by three nuclear medicine physicians by drawing of regions of interest (ROIs) on vertebrae, ribs, femur, sternum, joints and skull. Ratios bone/soft tissue were obtained drawing ROIs on several bones. The kappa test and the Wilcoxon rank test were used for statistical comparisons. RESULTS: The agreement on the quality of the images with Tc-ABP and Tc-MDP was fair (kappa 0.4). The femur/soft tissue ratio had a normal distribution and the Wilcoxon test showed no statistical difference between preparations. CONCLUSIONS: Even though bone uptake was higher and faster with Tc-ABP, the quality of the scans obtained with either radiopharmaceutical was similar. We recommend the use of Tc-ABP as a routine bone scan agent because of its less radiation exposure to the patient.

Technetium-99m-alendronate: a new radiopharmaceutical for bone scanning.

The purpose of this paper is to report the preparation of a new technetium-99m-radiopharmaceutical for bone scanning. The chelating agent for 99mTc is a new bisphosphonate, alendronate, 4-amino-1-hydroxy-butylidene-1, 1-bisphosphonate (ABP) used as a treatment for osteoporosis. ABP, because of its amino group, seems to be better suited to form a strong and stable complex with technetium-99m and therefore might be better than 99mTc-etidronate (HEDP) or 99mTc-medronate (MDP) for bone scanning. A sterile dry kit containing APB, a reducing agent and a stabilizer was prepared. The parameters studied were molar concentrations, pH, shelf life, labeling efficiency and radiochemical purity. The oven dried sterile kit was formulated with 5 mg ABP, 0.25 mg stannous fluoride and 0.025 mg gentisic acid at pH 2.5-3.5. The labeling efficiency with 20-1500 MBq of pertechnetate (99mTcO4-) was over 95% at room temperature and was stable for 5 h. Technetium-99m-alendronate was tested in two rabbits and it proved to be a promising new radiopharmaceutical for bone scanning. Work is underway to study 99mTc-ABP biodistribution in a statistically significant number of laboratory animals and, later on, to determine radiopharmacokinetic parameters in normal volunteers.

[Interobserver variation in region-of-interest drawing in computerized gammagraphy]. / Variabilidad interobservadores al delimitar regiones de interés en gamagramas computarizados.

BACKGROUND: Nuclear medicine uses computerized scintillation cameras for scan processing. For the radio-renogram, the main objective is to observe the passage of radionuclides through the kidneys during a given time. The new software automatically provides data of the dynamic studies, but there is one step (the drawing of regions of interest, ROI) handled by an operator. With the ROI drawings the computer integrates their radioactivity and displays it as time/activity curves, and calculates the Tmax (time to achieve maximal activity) and the T1/2 (time to eliminate half of the Tmax) of each kidney. OBJECTIVE: To evaluate inter-observer variability in drawing the ROI on renal scans. MATERIAL AND METHODS: Four observers with at least seven years of experience in the procedure drew independently the ROI of 38 renograms of 20 patients (two transplants) to obtain the Tmax and T1/2. The interobserver CV was calculated for the Tmax and the T1/2 of the 38 scans. RESULTS: Globally the interobserver variability was larger for T1/2 than for Tmax. There were four scans with small differences in Tmax and/or T1/2 but which lead to inter-observer discrepancies in the classification (normal/abnormal). The partition of the scans in three groups (1 = Tmax and T1/2 normal; 2 = only Tmax normal; 3 = both abnormal) showed significant intergroup differences in the interobserver variability (Kruskal-Wallis p = 0.032) which were caused by the larger variability in group 2 (6 of 11 scans with CV > 4%) than in the other groups (none with CV > 4%). CONCLUSIONS: 1. The interobserver discrepancies in classification were observed only in cases with parameters slightly abnormal (8-9 min in Tmax, 15-20 min in T1/2). 2. We have no explanation for the larger interobserver variability of the Tmax in group 2 study of intraobserver variability in these same four observers may help in gaining insight to some of the observations in this study.

[Cost-benefit of the Schilling test using cobalt-57]. / Costo-beneficio de la prueba de Schilling con cobalto-57.

Our purpose in the present publication is to determine the cost-benefit relation of the Schilling test used to measure the intestinal absorption of radioactive vitamin B12. The 60Co-B12 urinary excretion Schilling test was first reported in 1953, and five years later it was being performed at the National Institute of Nutrition (INNSZ) in Mexico City. It was performed in its original version until 1969 and from 1970 to 1980, the direct absorption was measured with a whole-body counter. For the last nine years we have used the Schilling test with 57Co labeled cyanocobalamin. From January 1981 through March 1990, 240 of these tests were carried out in 120 patients. The results were tabulated and compared with their clinical diagnosis. We analyzed our laboratory and labor costs. An oral dose of 0.5 micrograms of vitamin B12 labelled with 18.5 Bq of 57Co is taken by the fasting patients and two hours later one mg of standard B12 vitamin is injected. Urine is collected for 48 hours and the radioactivity is measured in a scintillation counter. Three days later the test is repeated with an additional oral dose of intrinsic factor (IF). The total expense is calculated using the following factors: the cost of the imported radioactive vitamin, IF capsules, parenteral B12 vitamin, syringes, equipment use and its depreciation, laboratory material, and salaries for the professional and administrative personnel.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetic characteristics of a hepatobiliary 99mTc-radiopharmaceutical: comparison of the imported and national kits.

In nuclear medicine, the search for the perfect hepatobiliary agent started in 1955 with the rose bengal dye labeled with 131I. With the advent of technetium-99m, many ligands were labeled and Tc-99m-PG and 99mTc-HIDA were among the best suited for this purpose. Both were synthesized at the radiopharmacy laboratory during 1977-1980 and have been used at INNSZ for clinical studies. For the last three years, a new ligand with a bromine atom and an extra methyl radical has been reported as being one of the best third generation HIDAs. We received the gift of several kits of trimethyl-Br-IDA from Sorin Biomedica, Italy, (A) and of Mebrofenin from ININ, Mexico, (B) to be labeled and tested in order to select one of them for clinical work. For a comparative study on the radiopharmacodynamic characteristics of the two labeled ligands, six healthy women volunteered to undergo two tests with a 72 hour hour rest period to assure complete washout. After the I.V. dose of 111 MBq (3 mCi) the dynamic study was started and a total of 127 16-second images were acquired with a Siemens Digitrac 750 scintillation camera coupled to a Scintiview computer. Static images were taken at the end of the dynamic study and after breakfast. Blood and urine samples were collected for 24 hours and the amount of radioactivity was measured with a well type scintillation detector. The radiopharmacokinetic results are listed in tables 1-4.(ABSTRACT TRUNCATED AT 250 WORDS)