Preparation of (188Re) Re-AEDP and its biodistribution studies

Preparation, Characterization, and Preliminary Imaging Study of [188Re]Re-Ibandronate as a Novel Theranostic Radiopharmaceutical for Bone Metastasis

Background

Bone is a common site of metastasis from a malignant tumor. Several radiopharmaceuticals are available to relieve bone pain in patients with cancer. However, every radiopharmaceutical has its own disadvantages, and there is still a need to investigate easily accessible and high bone affinity radiopharmaceuticals. Ibandronate (IBA) and ¹⁸⁸Re were used for radiolabeling to develop and evaluate a novel type of bone-seeking radiopharmaceutical.

Methods

The preparation conditions of [¹⁸⁸Re]Re-IBA were investigated, and thin-layer chromatography was used to analyze radiochemical purity. The stability, plasma protein binding rate, lipid-water distribution coefficient, safety and biodistribution in normal mice, and bone imaging of [¹⁸⁸Re]Re-IBA in New Zealand rabbits were studied. In addition, the nude mice model of bone metastasis was established, and biodistribution and imaging characteristics of [¹⁸⁸Re]Re-IBA in these nude mice were studied.

Results

[¹⁸⁸Re]Re-IBA was successfully prepared with radiochemical purity >95%. The optimum preparation conditions were as follows: IBA, 0.8–1.4 mg; ascorbic acid, 0.2–0.5 mg; stannous chloride, 0.14–0.18 mg; potassium perrhenate, 0.005 mg; and [¹⁸⁸Re]ReO₄⁻ activity, 18.5–296 MBq, reacted for 30 min at 95°C with pH = 2. [¹⁸⁸Re]Re-IBA demonstrated good stability, high plasma protein binding rate, good hydrophilicity, and low toxicity. The biodistribution and bone imaging in normal animals showed rapid blood clearance, high bone uptake, low uptake in the solid organs and soft tissue, and high contrast during imaging. The biodistribution and imaging of bone metastasis in nude mice showed that [¹⁸⁸Re]Re-IBA has higher uptake in bone metastasis lesions than normal bone.

Conclusions

Our study encompassed the successful preparation of [¹⁸⁸Re]Re-IBA, a novel bone-seeking radiopharmaceutical, and confirmed it has potential in the treatment of bone metastasis and monitoring through imaging.

Analysis of 188Re-EDTMP complexes by HPLC and ultrafiltration

High performance liquid chromatography (anion-exchange, reversed-phase ion-pair and gel permeation chromatography) and ultrafiltration have been employed to analyze 188Re-ethylenediamine-N,N,N´,N´-tetrakis(methylenephosphonic acid) complexes ( 188Re-EDTMP), prepared from the tin chloride reduction or sodium borohydride reduction in the presence or absence of rhenium carrier. The HPLC analysis showed that the 188Re-EDTMP complexes were mixtures of components and the distribution of the components was dependent upon the total amount of rhenium present and the reducing agents (SnCl2, NaBH4). The ultrafiltration analysis showed that the distribution of nominal molecular weight of 188Re-EDTMP was dependent upon the presence of rhenium carrier and the reducing agents. In addition, it was found that the proportion of chemical species with bigger molecular weight in no-carrier-added 188Re(SnCl2)-EDTMP was larger than that in carrier-added 188Re(SnCl2)-EDTMP.

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.

Preparation and biological evaluation of 188Re-ethylenediamine-N,N,N',N'-tetrakis(methylene phosphonic acid) as a potential agent for bone pain palliation

This study was undertaken in order to prepare 188Re labelled ethylenediamine-N,N,N',N'-tetrakis(methylene phosphonic acid) (EDTMP), and to determine its potential as a therapeutic radiopharmaceutical for the palliation of metastatic bone pain. The effects of pH, incubation methods, and concentrations of stannous chloride, EDTMP, and ammonium perrhenate as a carrier on radiochemical yield and stability were evaluated. Biodistribution studies were performed in male Wistar rats after intravenous injection of 188Re-EDTMP and compared with those of hydroxyethylidene diphosphonate (HEDP). Greater than 95% radiochemical yield of 188Re-EDTMP was obtained under the optimal conditions (0.1 mmol x ml(-1) of EDTMP, 0.5 mg x ml(-1) of stannous chloride, and pH 1.0). Heating the reaction mixture (boiling water for 15 min, and microwave heating for 15 s) and the addition of ammonium perrhenate increased the radiochemical stability (>90% at 3 h, and >80% at 48 h). The biodistribution of 188Re-EDTMP showed high bony uptake and rapid clearance from other organs, and high bone-to-soft tissue ratios, which are similar to 188Re-HEDP. In conclusion, 188Re-EDTMP was prepared with high radiochemical yield and stability, and showed favourable biological characteristics. Microwave heating was a convenient and rapid method for the preparation of 188Re-EDTMP. It is considered that 188Re-EDTMP is a potential therapeutic agent for bone metastasis.