Preparation of rhenium-188-tin colloid as a radiation synovectomy agent and comparison with rhenium-188-sulfur colloid

Formulation and In-vivo Characterization of 177Lu-tin-colloid as a Radiosynovectomy Agent

INTRODUCTION

Arthritis is an inflammatory disorder that affects one or more joints of the body for various reasons, including autoimmune disorders, trauma, or infection. In many cases, traditional long-term treatment with various drug combinations (NSAIDs, diseasemodifying antirheumatic drugs, systemic corticosteroids, etc.) can provide relief, but many joints require additional local treatment. Radiosynovectomy (RSV) is an alternative method to current treatment options. Both the global supply shortage of 90Y in recent years and the increasing use of 177Lu-labeled radiopharmaceuticals in the field of nuclear medicine have made it possible to develop 177Lu-labeled microparticles and test them in small groups as RSV agents. This study aimed to develop the 177Lu labeled tin colloid formulation and demonstrate its invivo characterization.

MATERIALS AND METHODS

Particle size, shape, and labelling efficiency of the four formulations developed were determined. The formula with the highest labelling efficiency was selected for further studies. The quality of the formulation was evaluated based on radionuclidic, radiochemical, and microbial purity. In-vitro stability was evaluated by determining the labelling efficiency. In-vitro stability was tested in PBS and synovial fluid. The biological characterization was assessed using SPECT/CT after injecting the formulation into the normal knee joints of the rabbits.

RESULTS

Aggregated colloidal particles were spherical with a particle size of <5 μm. Labelling efficiency and radiochemical purity were >95 and 97.65% (Rf=0.2), respectively. The formulation was stable in vitro for up to 72 hours, both in PBS and synovial fluid. The formulation was homogeneously distributed in the joint at 0 and 1 hour after injection, and radioactivity- related involvement and inguinal lymph node involvement due to possible leakage were not detected in the late period. No pyrogenic/allergic side effects were observed during this period.

CONCLUSION

177Lu-tin-colloid was successfully prepared under optimized reaction conditions with high binding efficiency and radiochemical purity. The radiolabeled colloid was found to be stable in-vitro both in PBS and synovial fluid at room temperature. Serial PCET/CT images revealed that the activity was completely retained within the synovial cavity, with no activity leakage out of the joint until 48 hours after the injection. With the support of the results from further clinical studies, it may be possible for the formulation to enter clinical use.

Recent Development of Rhenium-Based Materials in the Application of Diagnosis and Tumor Therapy

Rhenium (Re) is widely used in the diagnosis and treatment of cancer due to its unique physical and chemical properties. Re has more valence electrons in its outer shell, allowing it to exist in a variety of oxidation states and to form different geometric configurations with many different ligands. The luminescence properties, lipophilicity, and cytotoxicity of complexes can be adjusted by changing the ligand of Re. This article mainly reviews the development of radionuclide 188Re in radiotherapy and some innovative applications of Re as well as the different therapeutic approaches and imaging techniques used in cancer therapy. In addition, the current application and future challenges and opportunities of Re are also discussed.

KSNM60 in Non-thyroidal Radionuclide Therapy: Leaping into the Future

This year, the Korean Society of Nuclear Medicine (KSNM) is celebrating its 60th anniversary. Treatment, as well as diagnosis, has played a very important role in the development of nuclear medicine. Since I-131 was used for thyroid therapy in 1959, other radionuclide therapy is still being used, and attempts to use new radionuclide are increasing. In this review, we briefly summarize and introduce the therapies such as radioimmunotherapy, transarterial radioembolization, radionuclide therapy for neuroendocrine tumors, peptide receptor radionuclide therapy, control of metastatic bone pain, radiation synovectomy, radionuclide brachytherapy, alpha particle therapy, and boron neutron capture therapy, which has been being attempted so far in the field of nuclear medicine.

Formulation and characterization of lutetium-177-labeled stannous (tin) colloid for radiosynovectomy

OBJECTIVE

Easy large-scale production, easy availability, cost-effectiveness, long half-life, and favorable radiation characteristics have made lutetium-177 (Lu) a preferred radionuclide for use in therapy. Lutetium-177-labeled stannous (Lu-Sn) colloid particles were formulated for application in radiosynovectomy, followed by in-vitro and in-vivo characterization.

METHODS

Stannous chloride (SnCl2) solution and Lu were heated together, the pH was adjusted, and the particles were recovered by centrifugation. The heating time and amount of SnCl2 were varied to optimize the labeling protocol. The labeling efficiency (LE) and radiochemical purity (RCP) of the product were determined. The size and shape of the particles were determined by means of electron microscopy. In-vitro stability was tested in PBS and synovial fluid, and in-vivo stability was tested in humans.

RESULTS

LE and RCP were greater than 95% and ∼99% (Rf=0-0.1), respectively. Aggregated colloidal particles were spherical (mean size: 241±47 nm). The product was stable in vitro for up to 7 days in PBS as well as in synovial fluid. Injection of the product into the infected knee joint of a patient resulted in its homogenous distribution in the intra-articular space, as seen on the scan. No leakage of activity was seen outside the knee joint even 7 days after injection, indicating good tracer binding and in-vivo stability.

CONCLUSION

Lu-Sn colloid was successfully prepared with a high LE (>95%) and high RCP (99%) under optimized reaction conditions. Because of the numerous benefits of Lu and the ease of preparation of tin colloid particles, Lu-Sn colloid particles are significantly superior to its currently available counterparts for use in radiosynovectomy.

Cationic rhenium complexes ligated with N-heterocyclic carbenes – an overview

This review provides an overview of the currently known cationic rhenium NHC complexes.

Radiosynovectomy of Proximal Interphalangeal Joint Synovitis in Rheumatoid Arthritis Treated with Rhenium-188 Labeled Tin-colloid and Imaging with Single-photon Emission Computerized Tomography/Computed Tomography: A First Case Report

Rheumatoid arthritis (RA) is a chronic disease that is mainly characterized by the asymmetric erosive synovitis, particularly affecting peripheral joints. Radiation synovectomy or radiosynovectomy (RSV), also known as radiosynoviorthesis was first described in 1950's as an adjuvant treatment for RA. RSV is based on the irradiation of the joint synovium by the intra-articular administration of various β-emitting radiopharmaceuticals. As a generator-produced β-emitting radionuclide, the importance of rhenium-188 (Re-188) for radionuclide therapy is increasing rapidly. There are previous reports which used Re-188 tin colloid in knee joint synovitis, but use of Re-188 tin colloid in small joint is not yet reported. We describe the use of Re-188 tin colloid in a 45-year-old female who presented with right 4^th proximal interphalangeal joint synovitis due to rheumatoid arthritis.

Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications

A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first (188)Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1'-methylene-bis(3,3'-diisopropylimidazolium-2-ylidene))(188)rhenium(V) hexafluorophosphate ((188)Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the (188)Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new (188)Re-labeled carbene complexes.

90Y-labeled tin fluoride colloid as a promising therapeutic agent: preparation, characterization, and biological study in rats

In this study, tin fluoride colloid (SnF-c) was prepared, labeled with yttrium-90 ((90)Y), and characterized with respect to its physicochemical properties and biological behavior in an animal model. Particle size of SnF-c, at constant concentration of SnF(2), was dependent on pH, concentration of sodium fluoride (NaF), temperature, and time. The particle size of SnF-c decreased with an increase in NaF concentration and a decrease in reaction mixture pH. Radiolabeling yield of (90)Y-SnF-c at higher temperature increased and it was greater than 98% for the preparation at 95 °C. The (90)Y-SnF-c demonstrated high in vitro stability both in human serum and human synovial fluid at 37 °C up to 7 days. In vivo distribution studies in healthy male Wistar rats of (90)Y-SnF-c (particles <1 μm), following intravenous administration, revealed that the localization takes place preferably in the liver. The (90)Y-SnF-c (particles >1 μm) was well retained in the synovial space for 96 h after intra-articular injection, whereas leakage of (90)Y from the joint was 1.96% over this period. Because of high labeling yield and stability, (90)Y-SnF-c might be a promising agent for radiosynovectomy or therapy of liver malignancies.

Characterization of Re-188–Sn microparticles used for synovitis treatment

Rhenium-188 labeled tin (Sn) microparticles were developed for pain palliation therapy in the patients suffering from synovitis with acute pain. The rhenium tin microparticles were prepared using stannous chloride and freshly eluted (188)ReO(4)(-) from (188)W/(188)Re generator. The aggregated colloidal particles, packed in a spherical form after boiling for 90-120min were analyzed using electron microscope. The size, surface morphology and stability of microparticles were analyzed by changing temperature and volume conditions. The small colloidal particles clustered and formed spherical microparticles. The 90% of microparticles were in 5-10microm range, after 90min and 120min of boiling. The radiolabeling efficiency was improved to 98% after centrifugation for 10min at 3500rpm. The formulations were stable but the increase in volume had inverse effect on labeling efficiency. No leak was observed from knee area up to 24h with 15-20mCi injection of (188)Re-Sn microparticles. The relief in treated patients, from the pain and inflammation, was observed clinically and by (99m)Tc-MDP perfusion scan.

Radiation synovectomy using 188Re-tin colloid improves knee synovitis as shown by MRI in refractory rheumatoid arthritis

BACKGROUND

Radiation synovectomy is a useful local treatment for patients with refractory synovitis. We previously demonstrated the efficacy and safety of Re-tin colloid for treating rheumatoid arthritis patients with refractory knee synovitis. This open-label, prospective controlled study investigates magnetic resonance imaging (MRI) changes as well as clinical response in knees after receiving different radioactivities of intra-articular Re-tin colloid.

METHODS

Sixteen patients with rheumatoid arthritis refractory to intra-articular corticosteroid therapy were treated with intra-articular injection of Re-tin colloid (555 MBq in six patients, 740 MBq in five, and 925 MBq in five). Contralateral knees were used as controls. Treatment efficacy and safety were evaluated 1, 3 and 6 months later. We compared the changes of synovial thickening and joint effusion between baseline and 6 months. Synovial thickness was measured by gadolinium-enhanced MRI.

RESULTS

Pain intensities on a visual analogue scale were significantly lower (median pain reduction, 78.9%; P=0.0001), joint swelling improved (median, -1.5; P=0.001), range of motion increased (median, 6 degrees , P=0.005), and joint tenderness decreased (median, -1; P=0.005) in treated knees after 6 months. The control knees did not show any significant clinical improvement. At 6 months after therapy, synovial thickening of treated knees improved in 87.5% of patients (P<0.001), and synovial thicknesses were significantly decreased in treated knees (P=0.0067). Furthermore, reduction in synovial thickness was most noticeable in the group treated with 925 MBq (P=0.007). No abnormalities in leukocyte or platelet counts, liver function tests, or urine analysis were observed.

CONCLUSION

Radiation synovectomy using Re-tin colloid in refractory rheumatoid arthritis patients improved MRI findings as well as clinical parameters.

Applied radioactivity in radiation synovectomy with [188Re]rhenium sulfide suspension

BACKGROUND

Early experience demonstrated absorbed dose in radiation synovectomy is about 100 Gy. For reaching this dose, the applied radioactivity should be calculated.

METHOD

Twenty-nine synovitic models of rabbit were treated by intra-articular injection of [(188)Re]rhenium sulfide and histological changes of synovium and cartilage were examined. The applied radioactivity was calculated by method of absorbed dose factor. In clinical, eleven haemophilic patients with haemarthrosis were performed radiation synovectomy with treated [(188)Re]rhenium sulfide. The synovial thickness was evaluated by MR and its value was used to calculate the applied radioactivity. After radiation synovectomy, all patients were followed up by synovial thickness, regional inflammation, and clinical course including bleeding frequency.

RESULTS

In rabbit models, the synovitic membrane can be eliminated by calculated radioactivity as planed without damaging the joint cartilage. In patients study, all patients exhibited significant reductions in synovial thickness and inflammation after radiation synovectomy with the planed radioactivities of [(188)Re]rhenium sulfide. Post-procedure bleeding frequency reduction in excellent and good reached to 63.6% by 18 months. In the cases of joint bleeding, the need for antihaemophilic factor treatment decreased immensely. Most of the recurrent episodes of bleeding were mild, subsiding with local means.

CONCLUSION

The applied radioactivity in radiation synovectomy could be calculated according to thickness of inflamed synovium. Further study including comparison therapeutic results from calculated individual activities with results from fixed activities and long-term follow-up is warranted.

99mTc/188Re-labelled lipid nanocapsules as promising radiotracers for imaging and therapy: formulation and biodistribution

PURPOSE

This study focuses on a promising carrier system for imaging and therapeutic purposes using lipid nanocapsules. To assess their potential for clinical use, we labelled nanocapsules with (99m)Tc and (188)Re and analysed some kinetic biodistribution parameters after intravenous injection in rats.

METHODS

Lipophilic complexes [(99m)Tc/(188)Re(S(3)CPh)(2)(S(2)CPh)] ((99m)Tc/(188)Re-SSS) were encapsulated within the nanoparticles during their manufacture with quantitative yield and satisfactory radiochemical purity. Rats were injected intravenously with 3.7 MBq (99m)Tc/(188)Re-labelled nanocapsules and sacrificed at 5, 15 and 30 min and 1, 2, 4, 8, 12, 16, 20 and 24 h.

RESULTS

Dynamic scintigraphic acquisitions showed predominant hepatic uptake, and ex vivo counting indicated a long circulation time of labelled nanocapsules, with a half-life of 21+/-1 min for (99m)Tc and 22+/-2 min for (188)Re. Very weak urinary elimination was observed, indicating good stability of (99m)Tc and (188)Re labelling.

CONCLUSION

(99m)Tc/(188)Re-SSS nanocapsules can be obtained with high yield and satisfactory radiochemical purity. The biodistributions of (99m)Tc/(188)Re-labelled nanocapsules are close to those of classical PEG-coated particles and show good stability of (188)Re/(99m)Tc-SSS labelling.

Radiolabelling of poly(histidine) derivatized biodegradable microspheres with the 188Re tricarbonyl complex [188Re(CO)3(H2O)3]+

OBJECTIVES

Many radiopharmaceuticals have been studied as radiation synovectomy agents. In this study, we developed a new potential agent for radiation synovectomy: poly(lactic acid)-histidine (PLA-his) microspheres radiolabelled with [188Re(CO)3(H2O)3]+.

METHODS

The reaction conditions for the chelation of [188Re(CO)3(H2O)3]+ and the radiolabelling of PLA microspheres were optimized and the stabilities for both steps tested in vitro.

RESULTS

The chelation efficiency of [188Re(CO)3(H2O)3]+ reached 93.12 +/- 1.82% with >95% radiochemical purity once the colloidal and free 188Re were removed by a small Sep-Pak column (Plus QMA). More than 90% of radioactivity stayed in the [188Re(CO)3(H2O)3]+ form over 5 h. The radiolabelling efficiency of PLA-his microspheres with [188Re(CO)3(H2O)3]+ was above 92%. After 3 days incubation at 37 degrees C in calf serum, more than 80% of the radioactivity was still bound to the microspheres.

CONCLUSION

Such microspheres are potentially useful as a radiation synovectomy agent for the treatment of chronically inflamed arthritic joints. Furthermore, they might be valuable in cancer brachytherapy.

Monte Carlo calculation of the sensitivity of a commercial dose calibrator to gamma and beta radiation

The detection process used in a commercial dose calibrator was modeled using the GEANT 3 Monte Carlo code. Dose calibrator efficiency for gamma and beta emitters, and the response to monoenergetic photons and electrons was calculated. The model shows that beta emitters below 2.5 MeV deposit energy indirectly in the detector through bremsstrahlung produced in the chamber wall or in the source itself. Higher energy beta emitters (E > 2.5 MeV) deposit energy directly in the chamber sensitive volume, and dose calibrator sensitivity increases abruptly for these radionuclides. The Monte Carlo calculations were compared with gamma and beta emitter measurements. The calculations show that the variation in dose calibrator efficiency with measuring conditions (source volume, container diameter, container wall thickness and material, position of the source within the calibrator) is relatively small and can be considered insignificant for routine measurement applications. However, dose calibrator efficiency depends strongly on the inner-wall thickness of the detector.

188Re radiopharmaceuticals for radiosynovectomy: evaluation and comparison of tin colloid, hydroxyapatite and tin-ferric hydroxide macroaggregates

Background

Radiosynovectomy is a therapy used to relieve pain and inflammation from rheumatoid arthritis and related diseases. In this study three ¹⁸⁸Re particulate compounds were characterized according to their physico-chemical properties and their biological behavior in rabbits. The results were compared in order to establish which was the radiopharmaceutical that better fits the requirements of this kind of radiotherapy.

Methods

Three radiopharmaceutical formulations, tin colloid, hydroxyapatite particles (HA) and ferric hydroxide macroaggregates coated with tin colloid (FHMA), were physically characterized (number, volume and surface of the particles). For this purpose laser diffraction methodology was used. To evaluate cavity leakage of activity the following studies in New Zealand rabbits were performed: scintigraphic images for 48 hr after intraarticular injection of each radiopharmaceutical, biodistribution at 48 hr and urine samples collection during the first 24 hr post-radiopharmaceutical administration.

Results

Labeling procedures for ¹⁸⁸Re-HA and ¹⁸⁸Re-Sn-FHMA were labour intensive while ¹⁸⁸Re-Sn was easily prepared. Furthermore, ¹⁸⁸Re-Sn colloid offered the greatest surface area in the 2–10 microm range and was obtained with a radiochemical purity over 95%, while percentage of bound activity for ¹⁸⁸Re-HA and ¹⁸⁸Re-Sn-FHMA were 55% and 92% respectively. Stability was verified for the three radiopharmaceuticals for 24 hr. Scintigraphic studies and biodistribution in rabbits after intraarticular administration of the radiopharmaceuticals showed relevant activity only in the knee, this being over 90% of the residual activity in the whole body at 48 hr in every case. Renal elimination of ¹⁸⁸Re-Sn colloid and ¹⁸⁸Re-Sn-FHMA was detected by activity measurements in urine samples, during the first 12 hr post-radiopharmaceutical injection.

The percentage of activity retained in the knee was 69.1% for ¹⁸⁸Re-Sn colloid, 55.1% for ¹⁸⁸Re-Sn-FHMA and 33.6% for ¹⁸⁸Re-HA.

Conclusion

The ¹⁸⁸Re-Sn colloid was easy to prepare, minimum facilities were required, was stable for 24 hr and showed minimal leakage from the joint after intraarticular injection into the rabbit's knee. Furthermore, ¹⁸⁸Re-Sn colloid has greater retention in the knee when it is compared with the other radiopharmaceuticals, so it could provide the best therapeutic effect/absorbed dose ratio for the patient.

Therapy with 188Re-Labeled Radiopharmaceuticals: An Overview of Promising Results from Initial Clinical Trials

The development of an in-house 188W/188Re-generator has greatly increased the use of 188Re for treating various diseases. 188Re is of widespread interest due to its attractive physical and chemical properties. Many new radiopharmaceuticals labeled with 188Re have been developed and are currently in clinical trials, such as: 188Re-labeled renal excreting agents like 188Re-mercaptoacetylglycylglycylglycine (MAG3) and 188Re-diethylenetriamine pentaacetic acid (DTPA) for prevention of coronary arterial restenosis; 188Re-labeled phosphonates such as 188Re-hydroxyethylidene diphosphonate (HEDP), 188Re-alendronate (ABP), and 188Re-ethylenediamine-N,N,N',N'-tetrakis(methylene phosphoric) acid (EDTMP) for palliation of metastatic bone pain; 188Re-labeled lipiodol such as 188Re-n-hexyldiaminedithiol (HDD)-lipiodol for treatment of liver cancer; and 188Re-labeled colloids and microspheres for treatment of diseases such as rheumatoid arthritis, peritoneal effusion, and other solid tumors. However, there is still a need to develop new 188Re-labeled radiopharmaceuticals that are more specific for target lesions such as cancer-specific monoclonal antibodies and peptides. The availability of 188Re from a generator at a reasonable cost may help increase not only the research activities but also the clinical applications of 188Re-labeled radiopharmaceuticals.

188Re-tin-colloid as a new therapeutic agent for rheumatoid arthritis

Radiation synovectomy is a useful treatment modality in patients with refractory synovitis. We have developed a 188Re-tin-colloid as a new radiopharmaceutical agent and investigated its efficacy and safety in patients with rheumatoid arthritis. Radiation synovectomy was performed using 188Re-tin-colloid in 22 knees from 21 rheumatoid arthritis patients refractory to intra-articular corticosteroid injection. The efficacy and safety of administration of 370-1110 MBq of 188Re-tin-colloid were evaluated after 1, 3, 6, 9 and 12 months. Pain intensity on a visual analogue scale decreased significantly 12 months after therapy (mean+/-SD: 68.0+/-26.1 mm vs. 25.1+/-23.4 mm; P=0.0001 by the paired t-test). Pain decreased in 19 cases (86.3%), joint tenderness improved in 14 cases (63.6%) and joint swelling was reduced in all cases (100%). 188Re-tin-colloid was safe. The residual activity of 188Re in the blood was 0.077%+/-0.25% of the injected dose. The radioactivity of 188Re in the urine was 0.14%+/-0.13% of the injected dose. Transient reactive synovitis was observed in 18 cases (81.8%). No clinical side-effects or abnormalities in leucocyte count, platelet count, liver function tests or urine analysis were observed in any patient. In conclusion, in this first study of radiation synovectomy using 188Re-tin-colloid for patients with rheumatoid arthritis, the treatment resulted in the improvement of arthritis and was well tolerated.

Preparation of (188) Re-labeled paper for treating skin cancer

For homogeneous delivery of beta radiation to skin cancer, we developed a simple method for preparing (188) Re-labeled nitrocellulose paper. The homogeneity and stability of the labeled paper were investigated. Absorbed dose estimates were calculated using the Monte-Carlo method. A 74-MBq (188) Re-labeled paper with 1-cm diameter delivered 147.2 Gy up to 1-mm depth after 2-h irradiation. Animal experiments on tumor-bearing mice showed that 50 Gy is an adequate dose for treating skin cancer. Tumors disappeared 7 days after irradiation in all the groups irradiated by 50 or 100 Gy. The (188) Re-labeled paper provided a convenient, economical, effective, and non-invasive method of treating skin cancer.

DA-7911, 188Rhenium-tin colloid, as a new therapeutic agent of rheumatoid arthritis

Radiation synovectomy is one of the most useful methods for treating patients with refractory synovitis because of its convenience, long-term effects, repeatability and the avoidance of surgery. In this study, we investigated the toxicity, stability and biodistribution of a rhenium-188 (188Re)-tin colloid to evaluate its suitability as a synovectomy agent. Twenty four hours after injecting the 188Re-tin colloids (74 KBq/0.1 mL) into the tail vein of ICR mice, most of the 188Retin colloidal particles was found in the lungs. In addition, there were no particle size changes at either room temperature or at 37 degrees C after injecting the 188Re-tin colloids in human plasma and synovial fluid. In vitro stability tests showed that the 188Re-tin colloid remained in a colloidal form without a critical size variation over a 2-day period. We investigated the leakage of 188Retin colloids from the intraarticular injection site with gamma counting in New Zealand white rabbits. The 188Re-tin colloids (55.5 MBq/0.15 mL) were injected at the cavum articular and the mean retention percentage of the 188Re-tin colloid was 98.7% for 1 day at the injection site, which suggests that there was neither change in the particle size nor leakage at the injection sites. In the biodistribution study with the SD rats, the liver showed the highest radioactivity (0.0427% ID/organ) except for the injected knees (99.49%). In the SD rats, mild toxicities including the skin or a synovium inflammation were observed as a result of a radioactivity of 15 mCi/kg at the intraarticular injection site. However, there was no systemic toxicity. In the Ovalbumin (OVA)-induced arthritic rabbits, the 188Re-tin colloid improved the macroscopic, the histological score and reduced the knee joint diameter when compared to the arthritic control. In conclusion, a 188Re-tin-colloid is considered as a strong candidate for radiation synovectomy with a superior efficacy and safety.

Physico-chemical characterisation and biological evaluation of 188-Rhenium colloids for radiosynovectomy

BACKGROUND: Radiosynovectomy is a type of radiotherapy used to relieve pain and inflammation from rheumatoid arthritis. In this study, 188-Rhenium (188Re) colloids were characterized by physical and biological methodologies. This was used to assess which parameters of the kit formulation would be the basis in the development of a more effective radiopharmaceutical for synovectomy. Intraarticular injection in knees of rabbits assessed cavity leakage of activity. METHODS: The physical characteristics of tin (Sn) and sulphur (S) colloids were determined to assess the formulation with suitable properties. Particles were grouped in three ranges for analyzing their distribution according to their number, volume and surface. The ideal particle size range was considered to be from 2 to 10 microns. Membrane filtration and laser diffraction characterization methodologies were used. RESULTS: While membrane filtration could give misleading data, laser diffraction proportions more reliable results. The Sn colloid showed a better distribution of particle volume and surface than S colloid, in the 2 to 10 microns range. The 188Re-Sn colloid was obtained with a radiochemical purity higher than 95% after 30 minutes of autoclaving. While Sn colloid kit stability was verified for 60 days, the 188Re-Sn preparation was stable in the first 24 hrs. No significant intrabatch variability (n = 3) was detected. Biodistribution and scintigraphic studies in rabbits after intraarticular injection showed relevant activity only in knee, being 90% at 48 hours. CONCLUSION: The 188Re-Sn colloid is easy to prepare, is stable for 24 hours and shows minimal cavity leakage after intraarticular injection into rabbit knees, suggesting this radiotherapeutical agent has suitable physical properties for evaluation for joint treatment in humans.

Pharmacokinetics of radioimmunotherapeutic agent of direct labeling mAb 188Re-HAb18

AIM: To label anti-hepatoma monoclonal antibody (mAb) fragment HAb18 F(ab’)₂ was labeled with ¹⁸⁸Re for the pharmacokinetic model of ¹⁸⁸Re-HAb18 F(ab’)₂ and to evaluate its pharmacokinetic parameters in hepatoma-bearing nude mice.

METHODS: HAb18 F(ab’)₂ was directly labeled with ¹⁸⁸Re using 2-mercaptoethanol (2-ME) as reducing agents. Labeling efficiency and immunoreactivity of ¹⁸⁸Re-HAb18 F(ab’)₂ were evaluated by Whatman 3MM paper chromatography and live cell assay, respectively. Biodistribution analysis was also conducted in nude mice bearing human hepatoma in which animals were sacrificed at different time points (1, 4, 18, 24 and 24 h) after ¹⁸⁸Re-HAb18 F (ab’)₂ was injected through tail-vein into hepatoma-bearing nude mice. The blood and radioactivity of organs and mass were measured. The concentrations of ¹⁸⁸Re-HAb18 F(ab’)₂ were evaluated with apharmacokinetic 3P97 software.

RESULTS: The optimum labeling efficiency and immunoreactive fraction were 91.7% and 0.78% respectively. The parameters of ¹⁸⁸Re-HAb18 F(ab’)₂ were: T_1/2, 2.29 h; Vd,1.49 × 10^-9 L·Bq^-1; AUC, 20. 49 × 10⁹ Bq·h·L^-1;CL, 0.45 × 10^-3 L·h^-1. ¹⁸⁸Re-HAb18 F(ab’)₂ could locate specially in hepatoma with high selective reactivity of HAb18 F(ab’)₂. ¹⁸⁸Re-HAb18 F(ab’)₂ was mainly eliminated by kidney. The maximal tumor to blood ratio was at 48 h, and maximal tumor to liver ratio was at 18 h.

CONCLUTION: The pharmacokinetics of ¹⁸⁸Re-HAb18 F (ab’)₂ fital-compartment model.¹⁸⁸Re-HAb18 F(ab’)₂ can be uptaken selectively at the hepatoma site.