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

Transarterial Radioembolization (TARE) Agents beyond 90Y-Microspheres

Liver malignancies, either primary tumours (mainly hepatocellular carcinoma and cholangiocarcinoma) or secondary hepatic metastases, are a major cause of death, with an increasing incidence. Among them, hepatocellular carcinoma (HCC) presents with a dark prognosis because of underlying liver diseases and an often late diagnosis. A curative surgical treatment can therefore only be proposed in 20 to 30% of the patients. However, new treatment options for intermediate to advanced stages, such as internal radionuclide therapy, seem particularly attractive. Transarterial radioembolization (TARE), which consists in the use of intra-arterial injection of a radiolabelled embolising agent, has led to very promising results. TARE with 90Y-loaded microspheres is now becoming an established procedure to treat liver tumours, with two commercially available products (namely, SIR-Sphere® and TheraSphere®). However, this technology remains expensive and is thus not available everywhere. The aim of this review is to describe TARE alternative technologies currently developed and investigated in clinical trials, with special emphasis on HCC.

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

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

Novel (188)Re multi-functional bone-seeking compounds: Synthesis, biological and radiotoxic effects in metastatic breast cancer cells

INTRODUCTION

Radiolabeled bisphosphonates (BPs) have been used for bone imaging and delivery of β(-) emitting radionuclides for bone pain palliation. As a β(-) emitter, (188)Re has been considered particularly promising for bone metastases therapy. Aimed at finding innovative bone-seeking agents for systemic radiotherapy of bone metastases, we describe herein novel organometallic compounds of the type fac-[(188)Re(CO)3(k(3)-L)], (L=BP-containing chelator), their in vitro and in vivo stability, and their cellular damage in MDAMB231 cells, a metastatic breast cancer cell line.

METHODS

After synthesis and characterization of the novel organometallic compounds of the type fac-[(188)Re(CO)3(k(3)-L)] their radiochemical purity and in vitro stability was assessed by HPLC. In vivo stability and pharmacokinetic profile were evaluated in mice and the radiocytotoxic activity and DNA damage were assessed by MTT assay and by the cytokinesis-block micronucleus (CBMN) assay, respectively.

RESULTS

Among all complexes, (188)Re3 was obtained with high radiochemical purity (>95%) and high specific activity and presented high in vitro and in vivo stability. Biodistribution studies of (188)Re3 in Balb/c mice showed fast blood clearance, high bone uptake (16.1 ± 3.3% IA/g organ, 1h p.i.) and high bone-to-blood and bone-to-muscle radioactivity ratios, indicating that it is able to deliver radiation to bone in a very selective way. The radiocytotoxic effect elicited by (188)Re3 in the MDAMB231 cells was dependent on its concentration, and was higher than that induced by identical concentrations of [(188)ReO4](-). Additionally, (188)Re3 elicited morphological changes in the cells and induced DNA damage by the increased number of MN observed.

CONCLUSION

Altogether, our results demonstrate that (188)Re3 could be considered an attractive candidate for further preclinical evaluation for systemic radionuclide therapy of bone metastases considering its ability to deliver radiation to bone in a very selective way and to induce radiation damage.

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.

In vivo distribution of (131)I and (125)I dual-labeled gelatin microspheres after implantation into rabbit liver

OBJECTIVE

The purpose of this study was to explore the radionuclide distribution and metabolism of (131)I and (125)I dual-labeled gelatin microspheres ((131)I-(125)I-GMSs) implanted in rabbit liver.

METHODS

The simultaneous radiolabeling of (131)I and (125)I into GMSs was performed by a chloramine-T method to prepare biodegradable dual-labeled radionuclide microspheres. The microspheres were injected into rabbit liver. Radionuclide distribution and metabolism in vivo were examined using single photon emission computed tomography (SPECT) and by blood and urine radioactivity counting.

RESULTS

(131)I and (125)I were labeled into the biodegradable GMSs in accordance with the mixture ratio of batch feeding. After (131)I-(125)I-GMSs had been implanted in rabbit liver, small amounts of (131)I and (125)I were released into the blood along with the degradation of microspheres and excreted via the urine within 24 days. The radionuclides in the rabbit liver injection site could be detected by SPECT until day 48. The microspheres could be observed by histological methods on day 32. No signs of thyroid damage were observed throughout the entire experimental period.

CONCLUSION

(131)I-(125)I-GMS can be retained long term in the injection site. Due to the advantages of combining two radionuclides, (131)I-(125)I-GMS may be a safe and effective choice for cancer brachytherapy.

A study of the radiosynthesis of fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺ and its application in labeling 1,2,3-triazole analogs obtained by click chemistry

OBJECTIVES

To optimize the conditions for the preparation of the organometallic precursor fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺ and to synthesize the radiolabeling compounds of tricarbonyl rhenium. 1,2,3-Triazole analogs were synthesized by click chemistry and labeled with fac-[ReCO₃(H₂O)₃]Br and fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺. The aim was to improve the methods for the synthesis of ¹⁸⁸Re-labeled radiopharmaceuticals for therapy.

METHODS

With potassium boranocarbonate as the CO source and ammonia borane as the reducing agent, fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺ was synthesized, and the click chemistry method was used to prepare the tricarbonyl rhenium complex.

RESULTS

At the optimal reaction condition (the amounts of K₂[H₃BCO₂] and BH₃·NH₃ are 5 and 5 mg, respectively; reaction temperature is 75°C; and reaction time is 15 min), the radiochemical yields were 90%, and the labeling yield of bis(pyridin-2-ylmethyl) amine with fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺ was more than 99% in 1 h at 75°C; the conjugation yields of triazole analog obtained by click chemistry with 'cold' and 'radio' tricarbonyl rhenium were more than 80%.

CONCLUSION

The organometallic precursor fac-[¹⁸⁸ReCO₃(H₂O)₃]⁺ was prepared under optimal reaction conditions with a yield of 90%, and the triazole analogs synthesized by click chemistry were suitable ligands for tricarbonyl rhenium.

Rhenium-188 labeled recombinant human plasminogen kringle5 (rhk5) and preliminary biodistribution. Evaluation in mice bearing A549 tumours

AIM

Angiogenesis plays a critical role in tumour formation and metastasis. Suitable radiolabeled angiogenesis inhibitor can be used for noninvasive imaging of angiogenesis and radionuclide therapy. Here we prepare rhenium-188 labeled recombinant human plasminogen kringle5 (188Re-rhk5) in a convenient manner than evaluate its properties in A549 lung adenocarcinoma.

METHODS

188Re-rhk5 was obtained by conjugating His group at the C end of rhk5 with fac-[188Re(H2O)3(CO)3]+. Chelating efficiency of fac-[188Re(H2O)3(CO)3]+ and radiolabeling efficiency of 188Re-rhk5 were measured by radio thin-layer chromatography (RTLC). In vitro stability of 188Re-rhk5 was determined in human serum at 37°C and analyzed by RTLC. Competition test was also performed to verify the specificity of binding. A biodistribution study was carried out in nude mice bearing A549 lung adenocarcinoma.

RESULTS

188Re-rhk5 was obtained with a radiolabel efficiency of 66.1%, the radiochemical purity (RCP) can reach 95.2% after purification. 188Re-rhk5 showed high stability in human serum, the RCP was more than 80% even 12 h after incubation. Competition test showed a high binding specificity. Furthermore, this radio-complex was excreted mainly through kidneys and showed specific tumour uptake in mice bearing A549 tumours.

CONCLUSION

188Re-rhk5 was prepared by a simple method. Preliminary biodistribution results showed its potential as an agent for possible tumour imaging, therapy and encouraged further investigation.

Evaluation of biodistribution and antitumor effects of (188)Re-rhk5 in a mouse model of lung cancer

Targeting drugs to receptors involved in tumor angiogenesis is considered to be a novel and promising approach to improve cancer treatment. This study aimed to evaluate the anti-tumor efficacy of (188)Re-labeled recombinant human plasminogen kringle 5 ((188)Re‑rhk5) through [18F]-fluorodeoxyglucose (FDG) micro-positron emission tomography (PET). Radiolabeled rhk5 was obtained by conjugating the hystidine (6 x His) group at the carbon end of rhk5 with fac-[(188)Re(H(2)O)(3)(CO)(3)](+). The biodistribution study of (188)Re-rhk5 showed that (188)Re-rhk5 had a high initial tumor uptake and prolonged tumor retention. The highest tumor uptake of (188)Re-rhk5 (3.65±0.82% ID/g) was found 2 h after injection which decreased to 0.81±0.14% ID/g 12 h after injection. Following therapy, tumor size measurement indicated that (188)Re-rhk5-treated tumors were smaller than (188)Re-, rhk5- and saline-treated controls 6 days after the treatment. In vivo 18F-FDG micro-PET imaging showed significantly reduced tumor metabolism in the (188)Re-rhk5-treated mice vs. those treated with rhk5, (188)Re and saline control, 1 day after treatment. Moreover, the number of microvessels was significantly reduced after (188)Re-rhk5 treatment as determined by CD31 staining. Our results demonstrate that specific delivery of (188)Re-rhk5 allows preferential cytotoxicity to A549 lung cancer cells and tumor vasculature. (18)F-FDG micro-PET is a non-invasive imaging tool that can be utilized to assess early tumor responses to (188)Re-rhk5 therapy.

Radiolabeling RGD peptide and preliminary biodistribution evaluation in mice bearing S180 tumors

OBJECTIVE

To prepare the rhenium-188 (188Re)-arginine-glycine-aspartic acid (RGD) peptide in a convenient manner and to evaluate its potential as an agent for alphavbeta3 integrin receptor-positive tumors.

METHODS

Radiolabeled RGD was obtained by conjugating the His group at the end of peptide with fac-[188Re(H2O)3(CO)3]+. Chelating efficiency of fac-[188Re(H2O)3(CO)3]+ and radiolabeling efficiency of radiolabeled peptide were measured by thin-layer chromatography and high-performance liquid chromatography. In-vitro stability of the radio-complex was determined in phosphate-buffered saline (0.05 mol/l, pH 7.4), new-born calf serum, His or Cys solution at 37 degrees C or room temperature and analyzed by thin-layer chromatography. A biodistribution study was carried out in mice bearing S180 tumors.

RESULTS

188Re-RGD was obtained with a more than 95% of radiolabeling efficiency, and showed high stability in phosphate-buffered saline, new-born calf serum, His and Cys solution. Furthermore, this radio-complex was cleared rapidly from the blood and showed specific tumor uptake in mice bearing S180 tumors.

CONCLUSION

188Re-RGD was prepared by a simple method. Preliminary biodistribution results showed its potential as an agent for cancer therapy and encouraged further investigation.

Fibrin glue system for adjuvant brachytherapy of brain tumors with 188Re and 186Re-labeled microspheres

Brain tumors such as glioblastoma reappear in their original location in almost 50% of cases. To prevent this recurrence, we developed a radiopharmaceutical system that consists of a gel applied immediately after surgical resection of a brain tumor to deliver local radiation booster doses. The gel, which strongly adheres to tissue in the treatment area, consists of fibrin glue containing the beta-emitters rhenium-188 and rhenium-186 in microsphere-bound form. Such microspheres can be prepared by short (2 h or less) neutron activation even in low neutron flux reactors, yielding a mixture of the two beta-emitters rhenium-188 (E(max)=2.1 MeV, half life=17 h) and rhenium-186 (E(max)=1.1 MeV, half life=90.6h). The dosimetry of this rhenium-188/rhenium-186 fibrin glue system was determined using gafchromic film measurements. The treatment efficacy of the radioactive fibrin glue was measured in a 9L-glioblastoma rat model. All animals receiving the non-radioactive fibrin glue died within 17+/-3 days, whereas 60% of the treated animals survived 36 days, the final length of the experiment. Control animals that were treated with the same amount of radioactive fibrin glue, but had not received a previous tumor cell injection, showed no toxic effects over one year. The beta-radiation emitting rhenium-188/rhenium-186-based gel thus provides an effective method of delivering high doses of local radiation to tumor tissue, particularly to wet areas where high adhesive strength and long-term radiation (with or without drug) delivery are needed.