Rhenium-188 microspheres: a new radiation synovectomy agent

Anticancer and Antibiotic Rhenium Tri- and Dicarbonyl Complexes: Current Research and Future Perspectives

Organometallic compounds are increasingly recognized as promising anticancer and antibiotic drug candidates. Among the transition metal ions investigated for these purposes, rhenium occupies a special role. Its tri- and dicarbonyl complexes, in particular, attract continuous attention due to their relative ease of preparation, stability and unique photophysical and luminescent properties that allow the combination of diagnostic and therapeutic purposes, thereby permitting, e.g., molecules to be tracked within cells. In this review, we discuss the anticancer and antibiotic properties of rhenium tri- and dicarbonyl complexes described in the last seven years, mainly in terms of their structural variations and in vitro efficacy. Given the abundant literature available, the focus is initially directed on tricarbonyl complexes of rhenium. Dicarbonyl species of the metal ion, which are slowly gaining momentum, are discussed in the second part in terms of future perspective for the possible developments in the field.

Rhenium-188 radiosynovectomy for chronic haemophilic synovitis: Evaluation of its safety and efficacy in haemophilic patients

INTRODUCTION

Radiocolloids labelled with less costly and more accessible radionuclides such as rhenium-188 are of interest to developing countries compared with those labelled with rhenium-186 and yttrium-90.

AIM

This study was aimed to evaluate the efficacy and safety of radiosynovectomy using rhenium-188 in patients with chronic haemophilic synovitis and recurrent hemarthrosis.

METHODS

In this quasi-experimental prospective study, 20 haemophilic patients were evaluated at preinjection, and at 1, 3, 6 and 12 months after injection. Magnetic resonance imaging (MRI) was done to measure synovial thickness and to calculate Denver score. Joint radiographs were taken to measure the Pettersson score. The Gilbert questionnaire, Functional Independence Score in Hemophilia (FISH) and visual analogue scale (VAS) for pain were completed, and the number of bleeding episodes and factor consumption were recorded at each follow-up visit.

RESULTS

The number of bleeding episodes, the amount of factor consumption per month, VAS pain scores and synovial thickness decreased significantly over time (P < .05). Gilbert and FISH scores showed significant improvement (P < .001). However, Pettersson score and Denver score showed no significant changes after injection. Minor complications including temporary pain and swelling occurred in 20% of patients, and no major complication was observed after rhenium-188 injection.

CONCLUSION

Our results indicated high clinical impact, efficacy, safety and low invasion of rhenium-188 in radiosynovectomy of haemophilic patients. Considering the availability and relatively low cost of rhenium-188 in developing countries, this can be a good treatment option for haemophilic patients with recurrent hemarthrosis, particularly when the synovial hypertrophy is not massive yet.

Design of Rhenium Compounds in Targeted Anticancer Therapeutics

Background:

Many rhenium (Re) complexes with potential anticancer properties have been synthesized in the recent years with the aim to overcome the clinical limitations of platinum agents. Re(I) tricarbonyl complexes are the most common but Re compounds with higher oxidation states have also been investigated, as well as hetero-metallic complexes and Re-loaded self-assembling devices. Many of these compounds display promising cytotoxic and phototoxic properties against malignant cells but all Re compounds are still at the stage of preclinical studies.

Methods:

The present review focused on the rhenium based cancer drugs that were in preclinical and clinical trials were examined critically. The detailed targeted interactions and experimental evidences of Re compounds reported by the patentable and non-patentable research findings used to write this review.

Results:

In the present review, we described the most recent and promising rhenium compounds focusing on their potential mechanism of action including, phototoxicity, DNA binding, mitochondrial effects, oxidative stress regulation or enzyme inhibition. Many ligands have been described that modulating the lipophilicity, the luminescent properties, the cellular uptake, the biodistribution, and the cytotoxicity, the pharmacological and toxicological profile.

Conclusion:

Re-based anticancer drugs can also be used in targeted therapies by coupling to a variety of biologically relevant targeting molecules. On the other hand, combination with conventional cytotoxic molecules, such as doxorubicin, allowed to take into profit the targeting properties of Re for example toward mitochondria. Through the example of the diseleno-Re complex, we showed that the main target could be the oxidative status, with a down-stream regulation of signaling pathways, and further on selective cell death of cancer cells versus normal cells.

Preparation and imaging of rhenium-188 labeled human serum albumin microsphere in orthotopic hepatoma rats

OBJECTIVE

The present study relates to a method for preparing 188Re-labeled human serum albumin microspheres (HSAM) by 188Re(I)-tricarbonyl ion(188Re(OH2)3(CO)3)+). This radioactive particle can be subjected to radioembolization for liver tumor.

METHODS

The particle sizes and conformations of HSA microspheres were analyzed by Particle sizes-Malvern mastersizer and Scanning Electron Microscope (SEM). For preparing 188Re(I)-tricarbonyl ion, the 188ReO4- was eluted from a 188W/188Re generator with saline. The radio labeling efficiency was analyzed with high-performance liquid chromatography (HPLC). Amino borane-reduced 188ReO4-was interacted with carbon oxide to form (188Re(OH2)3(CO)3]+). For preparing 188Re-HSA microspheres, the 188Re(I)-tricarbonyl ion was added into a vial with HSA microspheres. The in vitro stability was investigated. The rat was injected with 188Re-HSA microspheres via hepatic artery route. Nano-SPECT/CT Imaging was acquired after injection of 188Re-HSA microspheres.

RESULTS

The shape of HSA microsphere was rough surfaced sphere or oval-shaped. The particle size was distributed between 20 and 35μm. In the RP-HPLC-UV chromatography, the yield of 188Re(I)-tricarbonyl ion was 75-80%. The labeling efficiency of 188Re-HSA microspheres in this method was more than 85%. After incubation, the 188Re(I)-tricarbonyl ion labeled HSA microspheres were found to be stable in vitro in normal saline and rat plasma. The result of Nano-SPECT/CT Imaging quantification analysis indicated that the percentage of injection dose %ID was maintained at 95% ID-88% ID from 2 to 72h after injection with 188Re- HSA microspheres.

CONCLUSIONS

The method of 188Re(I)-tricarbonyl ion labeled HSA microspheres can proceed with high labeling yield. Furthermore, this method provided a convenient method for radio-labeling of HSA microspheres with 188Re as well as a kit for manufacturing.

Pharmacokinetics and dosimetry of 188 Re-pharmaceuticals

The main objective of this review is to apportion current and new insight into the biodistribution, radiopharmacokinetics, dosimetry and cell targeting of rhenium-188 labeled radiopharmaceuticals used as therapeutic drugs. The emphasis lies on the generator obtained rhenium-188, its physical, therapeutic, dosimetric and coordinated compounds. Its use in radioimmunotherapy for lymphoma and other hematological diseases with monoclonal antibodies is discussed. Radiolabeled peptides to target cell receptors are an important field in nuclear medicine and in some research facilities are already being used, especially, somatostatin, bombesin and other peptides. Small molecules labeled with 188 Re are promising as therapeutic drugs. A review about some of the non-specific targeting molecules with therapeutic or pain palliation effect such as phosphonates, lipiodol, microparticles and other interesting molecules is included. Research on the labeling of biomolecules with the versatile rhenium-188 has contributed to the development of therapeutics with favorable pharmacokinetic and dosimetric properties for cancer treatment.

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.

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.

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.

188Re-labeled hydroxyapatite particles for radiation synovectomy

A new procedure for labeling hydroxyapatite (HA) particles with 188Re for radiation synovectomy is described and standardized. The particles were labeled with 188Re in high yields (99%) in acidic medium. HA particle size remained unaffected by reaction conditions as checked by laser diffraction particle analyzer. 188Re-HA was found to be stable retaining 99% radiochemical purity after 4 days when stored in ascorbic acid solution (10mg/ml, pH 5). Intra-articular injection in rats revealed approximately 98% retention of 188Re-HA in the knee after 48-h pi.

Efficacy of Re-188-labelled sulphur colloid on prolongation of survival time in melanoma-bearing animals

In this study, the effectiveness of a 188Re labeled sulfur colloid with two particle size ranges was used to evaluate the effectiveness of this agent on melanoma tumors in mice in terms of animal lifespan.

METHODS

Two separate group of animals were used for investigating biodistribution and survival time. A total of 188 B16F10-melanoma-bearing BDF(1) mice were injected intraperitoneally with 3.7 MBq (0.1mCi)/2mL of radiolabeled sulfur colloid ten days after intraperitoneal inoculation of 5x10(5) B16F10 melanoma cells/2ml. For group 1, 30 mice were sacrificed at 1, 4, 24, 48 and 72 hours for biodistribution studies. In group 2, 158 mice were divided into 9 groups (n=16 approximately 18/groups)each receiving respectively tumor alone, tumor with normal saline, cold colloid or hot colloid with 16, 23, 31, 46, 62, or 124 MBq activity. Each of these colloid groups was further divided into two groups, one receiving smaller particle sizes (<3 microm:80.4 +/-7.2%, colloid 1) and the other receiving larger particle sizes (<3 microm:12.3+/-1.0%, colloid 2). The animals were checked daily until death and their survival recorded.

RESULTS

Colloid 2 showed higher accumulation in almost all tissues, the highest accumulation organ was tumor ( approximately 40%), then spleen ( approximately 20%), stomach ( approximately 15%), diaphragm ( approximately 3%), and liver ( approximately 2%). There was a significant increase in survival time with increasing amount of the larger-particle-size colloid. Administered levels of 16-31 MBq/mouse were most efficacious and with higher amounts the survival times decreased significantly below that of the controls. There was a significant difference in the dose-response curves for the two preparations. Protection factors (1/Relative-risk) of nearly 5 were achieved using the larger colloid size, and nearly 30 using the smaller colloid size. An amount of 16-31 MBq of the colloid 2 was the optimal activity in these studies. On the one hand, the survival data agreed well with the biodistribution data, where higher accumulation was found in tumor with colloid 2.

CONCLUSION

Rhenium-188 offers on-site availability, medium half-life, higher beta-particle energy of 2.12 MeV for therapy and emission of 155keV gamma photon suitable for imaging. The present study demonstrated that 188Re-sulfur colloid is an effective agent in controlling tumor cells in the abdominal cavity in animals.

Histologic study of effects of radiation synovectomy with Rhenium-188 microsphere

Rhenium-188 microsphere is a relatively new radiation synovectomy agent developed for the treatment of rheumatoid arthritis. It has been shown that the levels of unwanted extra-articular radiation are negligible with this agent. A histologic study was conducted to assess the effect of radiation synovectomy on synovium and articular cartilage after intra-articular injection of various doses of Re-188 microspheres into the knee joints of rabbits. Intra-articular injection of Re-188 microspheres into rabbit knee joints resulted in mild reactive inflammation and thrombotic occlusion of vessels which subsided rapidly. Sclerosis of subsynovium could be seen 12 weeks after injection. No evidence of damage to articular cartilage was noted. There was no significant difference in the articular pattern after injection of 0.3 or 0.6 mCi Re-188 microspheres. This study suggests that a treatment dose of Re-188 microspheres causes transient inflammation of synovium without any detectable damage to the articular cartilage of knee joint.

On the safety of synoviorthesis in haemophilia

One of the best procedures to prevent haem-arthrosis has been radioactive synovectomy (synoviorthesis). Since the first report of radioactive synovectomy in haemophilia of Ahlberg in 1971 [1], many centres adopted this procedure as the one of choice, through fibrosing the synovial membrane, prevent further haemarthrosis. Since 1976 we have performed 104 such radioactive synoviorthesis in 97 patients, age ranging from 6 to 40 years with a mean of 10 years. Sixty-five of these patients were under 12 years of age. The knees were injected in 61 cases, elbow in 26 cases, ankles in 14 cases and shoulders in three cases. The clinical results of this procedure show 80% of excellent results with no further bleeding. In case of failure, a new injection can be given in the same joint at a 6-month interval, or an injection for the same purpose in other joint. One of the criticisms against this method is the possible chromosomal damage induced by the radioactive material. In our centre, four studies have been carried out in order to see whether these changes, when they occur, are everlasting; all have demonstrated that chromosomal changes are reversible. The radioactive material used in the two first studies was Gold-189 (189Au). In 1978, 354 metaphases were studied with 61 ruptures, 17.23% (nonpremalign) and six structural changes, considered premalign (1.69%). Any number below 2% is considered not to be dangerous. A further study was done in 1982, in the same group of patients with a result of 21 ruptures (3.34%) and no structural changes. This demonstrated that the possible premalign changes disappeared with time. A third study was performed in a series of 13 patients that sustained radioactive synoviorthesis with Rhenium-186 (186Re) in November 1991. For comparison, we carried out a chromosomal study just before and 6 months after the radioactive material injection. The results confirmed that changes that could be linked to the radiation, appeared equally in nonirradiated patients, and those changes due to the radiation disappear with time, never reaching the dangerous zone of 2%. In the group treated with 186Re we studied an additional number of 130 metaphases with identical results and no structural changes. In a study on patients where 90Y was the radiocolloid, no premalign change was found before or after the synoviorthesis. It seems, in view of these results, that radioactive synovectomy is safe and gives great benefits to the haemophilic patients.

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

As a generator-produced beta-emitting radionuclide, the importance of 188Re for radionuclide therapy is increasing rapidly. We prepared 188Re-tin colloid and compared its properties with 188Re-sulfur colloid. Labeling efficiencies reached >98% for tin colloid at 2 h and 89-94% for sulfur colloid at 3 h. All the preparations were stable for 72 h in water, serum, and synovial fluid. If labeled at higher temperature, the particle size of tin colloid increased. The residual radioactivity of 188Re-sulfur colloid in disposable polypropylene syringes after injecting mice was high (62.0+/-7.0%) due to its hydrophobic nature, while that of 188Re-tin colloid was low (2.9+/-1.6%). Although both 188Re-tin colloid and 188Re-sulfur colloid might be useful for radionuclide therapy, we conclude that 188Re tin colloid is more advantageous over 188Re sulfur colloid, due to higher labeling efficiency, control of the particle size, and lower residual activity in the injection syringes.

Preparation and biodistribution of rhenium-188 labeled albumin microspheres B 20: a promising new agent for radiotherapy

Intra-arterial infusion of labeled particles is an effective method for endoradiotherapy of tumors. In this study, we radiolabeled biodegradable HSA microspheres (mean diameter = 25 microm) with the short-lived beta-emitter 188Re available from the aluminia-based 188W/188Re generator system. After 1 h 35-40% of the relative large amount of Sn(II) chloride required for effective reduction of Re(VII) for efficient attachment to the particles is precipitated as an amorphous coat of tin hydroxid colloid on the particle surface. The final 188Re bound to the particles was found to be stable in vitro. The radiolabelling yield was > 90%. The biological half-life was > 250 h and demonstrated sufficient in vivo stability after i.v. injection in Wistar rats. Because of the attractive properties of 188Re and the uniform particle size and stability, in vivo, this new agent is an attractive candidate for endoradiotherapy of tumors after selective catheterization.