(175)Yb-TTHMP as a good candidate for bone pain palliation and substitute of other radiopharmaceuticals

Bone metastasis is one of the most frequent causes of pain in cancer patients. Different radioisotopes such as P-32, Sm-153, Ho-166, Lu-177, and Re-186 with several chemical ligands as ethylenediaminetetramethylene phosphonic acid (EDTMP), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene phosphonic acid (DOTMP), and propylenediaminetetramethylene phosphonate (PDTMP) are recommended for bone pain palliation. In this work, (175)Yb-triethylenetetraminehexamethylene phosphonic acid (TTHMP) was produced as a proper alternative to other radiopharmaceuticals. Relatively long half-life (T1/2 = 4.18 days), maximum energy beta particle Eβ =470 keV (86.5%), low abundance gamma emission 396 keV (6.4%), 286 keV (3.01%), 113.8 keV (1.88%) and low cost are considered advantageous of Yb-175 are to wider usage of this isotope; in addition, TTHMP is an ideal carrier moiety for bone metastases. Production, quality control, and biodistribution studies of (175)Yb-TTHMP were targeted. Yb-175 chloride was obtained by thermal neutron bombardment of a natural Yb2O3 sample at Tehran Research Reactor (TRR), radiolabeling was completed in 1 h by the addition of TTHMP at the room temperature and pH was 7.5-8, radiochemical purity was higher than 95%. Biodistribution studies in normal rats were carried out. The results showed favorable biodistribution features of (175)Yb-TTHMP, indicating significant accumulation in bone tissues compared with clinically used bone-seeking radiopharmaceuticals. This research presents (175)Yb-TTHMP can be a good candidate for bone pain palliation and substitute of other radiopharmaceuticals, however, further biological studies in other mammals are still needed.

Imaging biomarkers or biomarker imaging?

Since biomarker imaging is traditionally understood as imaging of molecular probes, we highly recommend to avoid any confusion with the previously defined term "imaging biomarkers" and, therefore, only use "molecular probe imaging (MPI)" in that context. Molecular probes (MPs) comprise all kinds of molecules administered to an organism which inherently carry a signalling moiety. This review highlights the basic concepts and differences of molecular probe imaging using specific biomarkers. In particular, PET radiopharmaceuticals are discussed in more detail. Specific radiochemical and radiopharmacological aspects as well as some legal issues are presented.

Vivid tumor imaging utilizing liposome-carried bimodal radiotracer

By developing a new bimodal radioactive tracer that emits both luminescence and nuclear signals, a trimodal liposome for optical, nuclear, and magnetic resonance imaging is efficiently prepared. Fast clearance of the radiotracer from reticuloendothelial systems enables vivid tumor imaging with minimum background.

Chelators for copper radionuclides in positron emission tomography radiopharmaceuticals

The development of chelating agents for copper radionuclides in positron emission tomography radiopharmaceuticals has been a highly active and important area of study in recent years. The rapid evolution of chelators has resulted in highly specific copper chelators that can be readily conjugated to biomolecules and efficiently radiolabeled to form stable complexes in vivo. Chelators are not only designed for conjugation to monovalent biomolecules but also for incorporation into multivalent targeting ligands such as theranostic nanoparticles. These advancements have strengthened the role of copper radionuclides in the fields of nuclear medicine and molecular imaging. This review emphasizes developments of new copper chelators that have most greatly advanced the field of copper-based radiopharmaceuticals over the past 5 years.

In vitro evaluation of tc-99m radiopharmaceuticals for gastric emptying studies

Objective: Gastrointestinal motility and functional motility disorders causing either delayed or accelerated gastric emptying (GE) may result in similar symptoms including nausea, vomiting, early satiety, fullness, bloating, and abdominal discomfort or pain. Hence, it is important to evaluate patients for both rapid and delayed GE in the same test. The gold standard technique to measure GE is scintigraphy by radiolabeled test meals. The aim of this study was to test alternative Tc-99m agents to label eggs as the solid meal and compare to Tc-99m sulfur colloid (SC) for gastric emptying studies.

Methods: In search of alternative agents for gastric emptying studies, we mixed and fried eggs with four different particulate compounds (Tc-99m labeled SC, tin colloid, nanocolloid and MAA), as well as with free pertechnetate and Tc-99m DTPA. We then measured the stability of these compounds in simulated gastric juice.

Results: Our experiments demonstrated that in addition to Tc-99m sulfur colloid;Tc-99m MAA, Tc-99m nanocolloid and Tc-99m tin colloid also appear to make stable complexes with eggs in acidic environment.

Conclusion: Therefore, these agents may be used for gastric emptying studies which could be more practical in routine conditions.

Conflict of interest:None declared.

Recent advances in chelator design and labelling methodology for (68) Ga radiopharmaceuticals

Gallium-68 has the potential to become the technetium-99m of positron emission tomography with ideal decay characteristics and a long-lived parent isotope for generator production. The work in the area of (68) Ga is focused on two key areas: (1) synthesis of a library of bifunctional chelators, which can be quickly radiolabelled to form kinetically inert complexes under mild conditions compatible with biomolecules and (2) development of radiosynthetic methodologies for clinical use and to facilitate radiolabelling of a wide range of chelators under mild conditions. Recent advances in these areas, with particular focus on the past 3 years, are covered herein.

Non-cross-bridged tetraazamacrocyclic chelator for stable (64)cu-based radiopharmaceuticals

N-mono/dimethylated TE2A tetraazamacrocycles (MM-TE2A and DM-TE2A) were synthesized in high yields. Both Cu-MM/DM-TE2A complexes showed increased kinetic stability compared to that of Cu-TE2A, whereas Cu-DM-TE2A showed even higher in vitro stability than that of Cu-ECB-TE2A. MM-TE2A and DM-TE2A were quantitatively radiolabeled with (64)Cu ions and showed rapid clearance from the body to emerge as a potential efficient bifunctional chelator.

Diagnostic use of neuro-spect quantified with 99mTc-ECD a model based on normal data

OBJECTIVE

The purpose of the present study was to prospectively quantify the normal limits of brain perfusion using specific software in a group of asymptomatic young volunteers submitted to single-photon emission tomography (SPECT) with ^99mTc-ethyl cysteinate dimer (^99mTc-ECD).

METHODS

We used 15 MBq/kg of intravenous ^99mTc-ECD in 30 healthy volunteers submitted to brief neuropsychological tests and a clinical questionnaire. These data were normalized relative to the cerebellum (Group 1) and to the brain cortex (Group 2). Statistical analysis was performed with Student's t-test. The average radioactivity was 6.5 million counts/study.

RESULTS

The normalized (Group I) revealed an average value of 78.03%, with standard deviation (SD) of 4.07. Two volunteers in this group had slightly greater than two standard deviations from the mean. When we used (Group II), the average value was 71.01%, with a SD of 4.66. We observed a difference between groups of 9% (P<0.001).

CONCLUSION

The present study suggests normal cortical perfusional values for a group of young asymptomatic volunteers, utilizing ^99mTc-ECD. This allows further quantification of neuro-SPECT data, specifically comparisons across patient populations. Furthermore, this method represents a new tool that can be used to further explore the field of neuroimaging, particularly neuropsychiatry.

Alternative synthesis for the preparation of 16α-[(18) F]fluoroestradiol

We have developed a new precursor, 3,17β-O-bis(methoxymethyl)-16β-O-p-nitrobenzenesulfonylestriol (14c) of 16α-[(18) F]fluoroestradiol ([(18) F]FES). Although we could not selectively protect the C17 alcohol in the presence of the C16 alcohol, we were able to prepare and chromatographically isolate the desired C16 TBDMS, C17,C3-dimethoxymethyl (diMOM) protected estriol derivative and convert into the ultimate fluorination precursor. The MOM protective group proved to be more quickly removed than the cyclic sulfate group. The di-MOM protective precursor at the C3 and C17 alcohols instead of a cyclic sulfate group shortened hydrolysis time. We prepared three different sulfonate precursors at C16 alcohol. After checking their reactivity in the [(18) F]fluorination step and considering the stability of the precursors, we obtained the best results with nosylate precursor 14c.

Repetitively dosed docetaxel and ¹⁵³samarium-EDTMP as an antitumor strategy for metastatic castration-resistant prostate cancer

BACKGROUND

β-emitting bone-seeking radiopharmaceuticals have historically been administered for pain palliation whereas docetaxel prolongs life in patients with metastatic castration-resistant prostate cancer (mCRPC). In combination, these agents simultaneously target the bone stroma and cancer cell to optimize antitumor effects. The toxicity and efficacy when each agent is combined at full, recommended doses, in a repetitive fashion is not well established.

METHODS

Patients with progressive mCRPC and ≥ 3 bone lesions received (153) Sm-EDTMP (samarium-153 ethylene diamine tetramethylene phosphonate) at a dose of 1.0 mCi/kg every 9 weeks and docetaxel at a dose of 75 mg/m(2) every 3 weeks. In the absence of unacceptable toxicity, patients were allowed to continue additional cycles, defined by 9 weeks of treatment, until intolerance or biochemical/radiographic disease progression.

RESULTS

Of the 30 patients treated, approximately 50% were considered to be taxane-naive, 36.7% were taxane-refractory, and 13.3% had previously been exposed to taxanes but were not considered refractory. Patients received on average 2.5 cycles of treatment (6.5 doses of docetaxel and 2.5 doses of (153) Sm-EDTMP). Twelve patients (40%) demonstrated a decline in their prostate-specific antigen level of ≥ 50%. The median progression-free survival (biochemical or radiographic) was 7.0 months and the overall survival was 14.3 months. Nine patients (30%) did not recover platelet counts >100 K/mm(3) after a median of 3 cycles to allow for additional treatment, with 4 patients experiencing prolonged thrombocytopenia. The most common reasons for trial discontinuation were progressive disease and hematologic toxicity.

CONCLUSIONS

The results of the current study indicate that (153) Sm-EDTMP can be safely combined with docetaxel at full doses on an ongoing basis in patients with mCRPC. Although thrombocytopenia limited therapy for some patients, preliminary efficacy supports the strategy of combining a radiopharmaceutical with chemotherapy, which is an appealing strategy given the anticipated availability of α emitters that can prolong survival.

A useful EGFR-TK ligand for tumor diagnosis with SPECT: development of radioiodinated 6-(3-morpholinopropoxy)-7-ethoxy-4-(3'-iodophenoxy)quinazoline

OBJECTIVE

Epidermal growth factor receptor tyrosine kinase (EGFR-TK) represents an attractive target for tumor diagnosis agents. Previously, radioiodinated 4-(3-iodophenoxy)-6,7-diethoxyquinazoline (PHY) was reported to possess good characteristics as a tumor imaging agent. We have explored the feasibility of developing tumor diagnosis ligands superior to radioiodinated PHY.

METHODS

New phenoxyquinazoline derivatives were designed with various side chains introduced to the 6th position of PHY. The IC50 values of the new derivatives to interrupt EGFR-TK phosphorylation were evaluated and compared to well-known EGFR-TK inhibitors. Tumor uptake studies of the new (125)I-labeled derivatives were conducted with A431 tumor-bearing mice. Selectivity and binding characteristics were analyzed by in vitro blocking studies and a binding assay. Furthermore, SPECT/CT scans were performed using A431 tumor-bearing mice.

RESULTS

Six quinazoline derivatives were designed and synthesized, and among these, 6a-d were found to have relatively high EGFR-TK inhibitory potency. In tumor uptake studies, [(125)I]6a ([(125)I]PYK) was found to have the highest tumor uptake and longest retention in tumors. In contrast, [(125)I]PYK was rapidly cleared from peripheral tissues, resulting in a high tumor-to-tissue ratio 24 h after injection. Moreover, the EGFR-TK selectivity of [(125)I]PYK was confirmed by pretreatment experiments with specific EGFR-TK inhibitors. Furthermore, [(125)I]PYK provided clear SPECT images of tumors.

CONCLUSIONS

Radioiodinated PYK, one of the newly synthesized quinazoline derivatives, was found to be a desirable ligand for EGFR-TK SPECT imaging. [(125)I]PYK showed high tumor accumulation and selective EGFR-TK binding and also succeeded in delivering high contrast imaging of tumors. These favorable characteristics of [(125)I]PYK suggest that the (123)I-labeled counterpart, [(123)I]PYK, would have great potential for diagnostic SPECT tumor imaging.

Evaluation of 99mTc-succimer dosing in pediatric patients

Balancing image quality with radiation dose is a goal with every diagnostic procedure requiring radiation. Our institution compared the dosing of (99m)Tc-labeled succimer, commonly referred to as dimercaptosuccinic acid ((99m)Tc-DMSA), to pediatric patients using 2 methods of calculation, body surface area (BSA, the method we used from 2009 to 2010) and body weight (BW, the method we used in 2011).

METHODS

A retrospective study was conducted in a 230-bed inpatient, tertiary-care academic pediatric hospital to obtain objective data on patients under the age of 17 y who received a renal nuclear medicine procedure with (99m)Tc-DMSA using a 300,000-count parallel image and four 150,000-count pinhole images. Data collection included patient age, sex, height, weight, calculated activity, assayed activity, administered activity, residual syringe activity, imaging time, and notable patient or equipment factors affecting the procedure.

RESULTS

Calculated activities based on BSA were higher than calculated activities based on BW. (99m)Tc-DMSA adsorption to the plastic syringes was significant, with a range of 3%-82%. Because of the adsorption, an average of 23.7 MBq (SD, ±31 MBq) was added to the patients' calculated dose when the order was placed. Therefore, assayed activities were significantly higher than calculated activities in both groups. Administered activity correlations to BSA and BW calculations were 0.75 and 0.83, respectively. Administered activities from BSA and BW groups were outside the American College of Radiology (ACR)-recommended guidelines 59% and 45% of the time, respectively. Overall, children less than 2 y old were above the ACR recommendations 80% of the time. There was a poor correlation between administered activity and total imaging time (r = 0.23). Average imaging time overall for 5 planar views was 14.8 min (±7.1 min). Patients receiving less than the ACR-recommended administered activities (<1.85 MBq/kg) had an average increase in imaging time of 4.5 min (±3.4 min).

CONCLUSION

The activity administered to patients was significantly affected by the amount of (99m)Tc-DMSA activity adsorbed to the syringe. Syringe residual should be considered when standardizing (99m)Tc-DMSA imaging protocols and calculating patient dose. Although (99m)Tc-DMSA adsorption was variable, the administered activities correlated with calculated activities. In all but one of our patients, the total imaging time was far less than recommended by the ACR and European Association of Nuclear Medicine guidelines. The study indicates that using the BW calculation of 3.7 MBq/kg resulted in a range of administered activity of 1.85-2.59 MBq/kg. (99m)Tc-DMSA dosing of 3.7 MBq/kg for pinhole imaging should be appropriate for most studies.

Targeting bone physiology for the treatment of metastatic prostate cancer

Metastatic prostate cancer has a unique predilection for bone that can lead to significant clinical sequelae, such as fracture and cord compression. This tropism for bone yields not only clinical challenges, but also opportunities to understand the tumor biology in bone and to develop relevant therapeutic strategies. The process by which tumor cells migrate to bone, remain dormant, and then colonize and expand is based on complex interactions between prostate cancer tumor cells and the host microenvironment. This review will provide an overview of these interactions as well as therapies targeting osseous metastases in castration-resistant prostate cancer.

Extended acute toxicity study of (188) Re-liposome in rats

Liposomes can selectively target cancer sites and carry payloads, thereby improving diagnostic and therapeutic effectiveness as well as reducing toxicity. To evaluate therapeutic strategies, it is essential to use animal models reflecting important safety aspects before clinical application. As our previous study found that a high dosage (185 of MBq) of (188) Re-N,N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine-labeled pegylated liposomes ((188) Re-liposome) induced a decrease in white blood cell (WBC) count in Sprague-Dawley rats 7 days postinjection, the objective of the present study was to investigate extended acute radiotoxicity of (188) Re-liposome. Rats were administered via intravenous (i.v.) injection with (188) Re-liposome (185, 55.5 and 18.5 MBq), normal saline as a blank control or non-radioactive liposome as a vehicle control. Mortality, clinical signs, food consumption, body weights, urinary, biochemical and hematological analyzes were examined. In addition, gross necropsy and histopathological examinations were also performed at the end of the follow-up period. None of the rats died and no clinical sign was observed during the 28-day study period. Only male rats receiving (188) Re-liposome at a high dosage (185 MBq) displayed a slight weight loss compared with the control rats. In both male and female rats, the WBC counts of both high-dose and medium-dose (55.5 MBq) groups reduced significantly 7 days postinjection, but recovered to the normal range on Study Day 29. There was no significant difference in urinary analyzes, biochemical parameters and histopathological assessments between the (188) Re-liposome-treated and control groups. The information generated from the present study on extended acute toxicity of (188) Re-liposome will serve as a safety reference for radiopharmaceuticals in early-phase clinical trials.

The development of copper radiopharmaceuticals for imaging and therapy

The increasing use of positron emission tomography in preclinical and clinical settings has widened the demand for radiopharmaceuticals with high specificity that can image biological phenomena in vivo. While many PET tracers have been developed from small organic molecules labeled with carbon-11 or fluorine-18, the short half-lives of these radionuclides preclude their incorporation into radiotracers, which can be used to image biological processes that are not induced immediately after system perturbation. Additionally, the continuing development of targeted agents, such as antibodies and nanoparticles, which undergo extended circulation, require that radionuclides with half-lives that are complimentary to the biological half-lives of these molecules be developed. Copper radionuclides have received considerable attention since they offer a variety of half-lives and decay energies and because the coordination chemistry of cooper and its role in biology is well understood. However, in addition to the radiometal chelate, a successful copper based radiopharmaceutical depends upon the chemical structure of the entire radiotracer, which may include a biologically important molecule and a chemical linker that can be used to deliver the copper radionuclide to a specific target and modulate its in vivo properties, respectively. This review discusses the development of copper radiopharmaceuticals and the importance of factors such as chemical structure on their pharmacokinetics in vivo.

Nucleophilic radiosynthesis of 2-[18F]fluoro-2-deoxy-D-galactose from Talose triflate and biodistribution in a porcine model

INTRODUCTION

The galactose analogue 2-[(18)F]fluoro-2-deoxy-D-galactose (FDGal) is a promising positron emission tomography (PET) tracer for studies of regional differences in liver metabolic function and for clinical evaluation of patients with liver cirrhosis and patients undergoing treatment of liver diseases. However, there is an unmet need for routine production of FDGal from readily available starting material. In this study, we present the preparation of FDGal with high radiochemical purity and in amounts sufficient for clinical investigations from commercially available Talose triflate (1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl-β-D-talopyranose). In addition, the biodistribution of FDGal in the pig is presented.

METHODS

FDGal was prepared by nucleophilic fluorination of Talose triflate followed by basic hydrolysis. The entire synthesis was performed using the GE TRACERlab MX 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) synthesizer and existing methods for quality control of FDG were applied. Biodistribution of FDGal was studied by successive whole-body PET recordings of two anaesthetized 37-kg pigs.

RESULTS

Up to 3.7 GBq sterile, pyrogen-free and no-carrier-added FDGal was produced with a radiochemical yield of 3.8±1.2% and a radiochemical purity of 98±1% (42 productions; yield is decay corrected). The adopted quality control methods for FDG were directly applicable for FDGal. Biodistribution studies in the pig revealed the liver and the urinary bladder as critical organs in terms of radiation dose.

CONCLUSION

Commercially available Talose triflate is a suitable starting material for routine productions of FDGal. The presented radiosynthesis and quality control methods allow for the production of pure, no-carrier-added FDGal in sufficient amounts for clinical PET-investigations of the liver.

Assessment of disease activity in rheumatoid arthritis using a novel folate targeted radiopharmaceutical Folatescan

OBJECTIVES

Development of a simple and accurate technique for detecting active inflammation in the joints and other tissues of patients with inflammatory disorders is an unmet need in rheumatic diseases. This study is a preliminary assessment of the safety and usage of a radiopharmaceutical, FolateScan (Technetium-99m EC20; 99mTc-EC20), for detecting disease activity in patients with rheumatoid arthritis.

METHODS

EC20 is a folate-targeted diagnostic radiopharmaceutical which binds to the folate receptor and is preferentially taken up by activated macrophages. In this open-label, cross-sectional study, a total of 40 patients with RA (26 with one or more swollen joints, 14 with clinically quiescent joint disease; 0/66 joint count) as well as 6 patients with osteoarthritis, 12 patients with other inflammatory conditions and 5 healthy subjects received 0.1 mg of EC20 labeled with 20-25mCi of technetium-99m. Disease activity was scored in each joint and other target tissues by a radiologist blinded to the clinical assessment, and results were compared to the rheumatologist's physical examination, which served as the test standard.

RESULTS

The 40 patients (78% female) with RA had a mean age of 56.9 years. Assessment of uptake of 99mTc-EC20 in joints of patients with RA based on image analysis was compared to the clinical examination. FolateScan detected more actively involved joints in 27 patients (68%) than joints recorded as "swollen", and more actively involved joints in 25 patients (63%) than joints recorded as "painful and/or swollen". The number of swollen joints by clinical exam was correlated with ESR (r=0.43; p=0.006) and C-rp (r=0.35; p=0.03). The number of actively involved joints by FolateScan was also correlated with ESR (r=0.47; p=0.002) and C-rp (r=0.36; p=0.02). Joint uptake was also seen in patients with osteoarthritis.

CONCLUSION

FolateScan is a potentially useful tool for detection of disease activity in patients with RA and may be more sensitive than the physical examination.

Assessment of insulin resistance in fructose-fed rats with 125I-6-deoxy-6-iodo-D-glucose, a new tracer of glucose transport

PURPOSE

Insulin resistance, characterised by an insulin-stimulated glucose transport defect, is an important feature of the pre-diabetic state that has been observed in numerous pathological disorders. The purpose of this study was to assess variations in glucose transport in rats using (125)I-6-deoxy-6-iodo-D-glucose (6DIG), a new tracer of glucose transport proposed as an imaging tool to assess insulin resistance in vivo.

METHODS

Two protocols were performed, a hyperinsulinaemic-euglycaemic clamp and a normoinsulinaemic-normoglycaemic protocol, in awake control and insulin-resistant fructose-fed rats. The tracer was injected at steady state, and activity in 11 tissues and the blood was assessed ex vivo at several time points. A multicompartmental mathematical model was developed to obtain fractional transfer coefficients of 6DIG from the blood to the organs.

RESULTS

Insulin sensitivity of fructose-fed rats, estimated by the glucose infusion rate, was reduced by 40% compared with control rats. At steady state, 6DIG uptake was significantly stimulated by insulin in insulin-sensitive tissues of control rats (basal versus insulin: diaphragm, p < 0.01; muscle, p<0.05; heart, p<0.001), whereas insulin did not stimulate 6DIG uptake in insulin-resistant fructose-fed rats. Moreover, in these tissues, the fractional transfer coefficients of entrance were significantly increased with insulin in control rats (basal vs insulin: diaphragm, p<0.001; muscle, p<0.001; heart, p<0.01) whereas no significant changes were observed in fructose-fed rats.

CONCLUSION

This study sets the stage for the future use of 6DIG as a non-invasive means for the evaluation of insulin resistance by nuclear imaging.

Cancer Research UK procedures in manufacture and toxicology of radiotracers intended for pre-phase I positron emission tomography studies in cancer patients

Radiolabelled compounds formulated for injection (radiopharmaceuticals), are increasingly being employed in drug development studies. These can be used in tracer amounts for either pharmacokinetic or pharmacodynamic studies. Such radiotracer studies can also be carried out early in man, even prior to conventional Phase I clinical testing. The aim of this document is to describe procedures for production and safety testing of oncology radiotracers developed for imaging by positron emission tomography in cancer patients. We propose strategies for overcoming the inability to produce compounds in sufficient quantities via the radiosynthetic routes for full chemical characterisation and toxicology testing including (i) independent confirmation as far as possible that the stable compound associated with the radiopharmaceutical is identical to the non-labelled compound, (ii) animal toxicity studies with > or = 10 times (typically 100 times) the intended tracer dose in humans scaled by body surface area, and (iii) patient monitoring during the radiotracer positron emission tomography clinical trial.