Fundamentals of Rhenium-188 Radiopharmaceutical Chemistry

Protein-functionalized and intrinsically radiolabeled [188Re]ReOx nanoparticles: advancing cancer therapy through concurrent radio-photothermal effects

PURPOSE

Enhancing therapeutic effectiveness is crucial for translating anticancer nanomedicines from laboratory to clinical settings. In this study, we have developed radioactive rhenium oxide nanoparticles encapsulated in human serum albumin ([188Re]ReOx-HSA NPs) for concurrent radiotherapy (RT) and photothermal therapy (PTT), aiming to optimize treatment outcomes.

METHODS

[188Re]ReOx-HSA NPs were synthesized by a controlled reduction of 188ReO4- in HSA medium and extensively characterized. The anticancer effect of [188Re]ReOx-HSA NPs was demonstrated in vitro in murine melanoma (B16F10) cell line. In vivo SPECT/CT imaging, autoradiography and biodistribution studies were performed after intratumoral injection of [188Re]ReOx-HSA NPs in melanoma tumor-bearing C57BL/6 mice. The potential of [188Re]ReOx-HSA NPs for combined RT and PTT treatment was also demonstrated in the aforesaid mice model.

RESULTS

[188Re]ReOx-HSA NPs (size 4-6 nm) were synthesized with high colloidal and radiochemical stability. Upon laser (808 nm) exposure on B16F10 cells incubated with [188Re]ReOx-HSA NPs, only < 20% of cells were alive demonstrating high therapeutic efficacy under in vitro settings. Uniform dose distribution and retention of the radiolabeled NPs in the tumor volume were observed via SPECT/CT imaging and autoradiography studies. Tumor growth in mice model was significantly arrested with ~ 1.85 MBq dose of [188Re]ReOx-HSA NPs and simultaneous laser irradiation, demonstrating synergistic benefit of RT and PTT.

CONCLUSIONS

These results demonstrate that intrinsically radiolabeled [188Re]ReOx-HSA NPs having unique features such as high photothermal effects and favorable nuclear decay characteristics for combined RT/PTT, hold great promise for clinical translation.

Evaluation of maSSS/maSES-PEG2-RM26 for their potential therapeutic use after labeling with Re-188. Could their [99mTc]Tc-labeled counterparts be used to estimate dosimetry?

BACKGROUND

Gastrin releasing peptide receptor (GRPR)-directed radiopharmaceuticals for targeted radionuclide therapy may be a very promising addition in prostate and breast cancer patient management. Aiming to provide a GRPR-targeting theranostic pair, we have utilized the Tc-99m/Re-188 radiometal pair, in combination with two bombesin based antagonists, maSSS-PEG2-RM26 and maSES-PEG2-RM26. The two main aims of the current study were (i) to elucidate the influence of the radiometal-exchange on the biodistribution profile of the two peptides and (ii) to evaluate the feasibility of using the [99mTc]Tc labeled counterparts for the dosimetry estimation for the [188Re]Re-labeled conjugates.

RESULTS

Both peptides were successfully labeled with Re-188 and evaluated both in vitro and in vivo. In GRPR expressing PC-3 cells, both [188Re]Re-labeled peptides displayed high cellular uptake (8.5 ± 0.1% and 5 ± 0.3% of added activity, respectively), heavily GRPR-driven, while retaining the radioantagonistic profile with slow internalization rates. Both agents demonstrated high receptor affinity when loaded with natRe (7.5 nM and 8 nM, respectively). When tested in vivo in GRPR expressing PC-3 xenografts, both radioantagonists demonstrated high tumor accumulation (6.3 ± 0.5%IA/g and 5 ± 1%IA/g at 1 h pi, respectively), with good retention over time (4 ± 2%IA/g and 3.1 ± 0.1%IA/g at 4 h pi, respectively). In addition, their biodistribution profiles were closely mimicking their [99mTc]Tc-labeled counterparts. Statistically significant lower tumor uptake was found for both conjugates labeled with Tc-99m, which may result in underestimation of the dose delivered to the tumor.

CONCLUSIONS

All the results indicate that Tc-99 m could be used for dosimetry evaluation for the two [188Re]Re-labeled radioligands, with minimal alterations in their biodistribution pattern and tumor targeting capabilities.

Experimental study on radiational characteristics and nursing care of a novel radioisotope 188Re memory alloy esophageal stent

Radioactive esophageal stent, known for inhibiting tumor growth and delaying restenosis in malignant esophageal tumors, presents challenges due to potent radiation, leading to side effects. This study aims to support the clinical use of 188Re radioactive esophageal stent. The 188Re stent with 128 MBq initial activity was placed in a biomimetic esophageal membrane. Radiation absorption doses were measured by thermoluminescence and calculated using mathematical software. Under simulated positioning, the stent was implanted in the esophagus of an experimental pig, followed by the feeding of Kangfuxin solution and nursing care (KFX-RT). Non-implanted and implanted-only pigs served as normal (CR) and experimental (RT) controls. Blood samples collected on days 7 and 21 were analyzed for inflammatory factors (TGF-β1, TNF-α, IL-6) using enzyme-linked immunosorbent assay. Esophageal tissue cells were assessed for deoxyribonucleic acid index (DI) and subdiploid content through flow cytometry. Absorbed doses at 0.5 mm and 5 mm reference points were 223.91 cGy and 20.55 cGy, respectively, with 92.64% absorbed within a 1 mm thickness. Radiation dose significantly decreased at 6.5 mm, with only 4.72% absorbed at depths ≥6.5 mm. On days 7 and 21, levels of inflammatory factors, DI and subdiploid content were significantly increased in the KFX-RT and RT groups compared to the CR group, while all levels in the KFX-RT group were significantly lower than in the RT group. The 188Re esophageal stent exhibits high radiation absorption in superficial tissues and low absorption in deeper tissues. Kangfuxin solution combined with nursing care alleviates radiation-induced inflammatory damage.

Navigating the landscape of theranostics in nuclear medicine: current practice and future prospects

Theranostics refers to the combination of diagnostic biomarkers with therapeutic agents that share a specific target expressed by diseased cells and tissues. Nuclear medicine is an exciting component explored for its applicability in theranostic concepts in clinical and research investigations. Nuclear theranostics is based on the employment of radioactive compounds delivering ionizing radiation to diagnose and manage certain diseases employing binding with specifically expressed targets. In the realm of personalized medicine, nuclear theranostics stands as a beacon of potential, potentially revolutionizing disease management. Studies exploring the theranostic profile of radioactive compounds have been presented in this review along with a detailed explanation of radioactive compounds and their theranostic applicability in several diseases. It furnishes insights into their applicability across diverse diseases, elucidating the intricate interplay between these compounds and disease pathologies. Light is shed on the important milestones of nuclear theranostics beginning with radioiodine therapy in thyroid carcinomas, MIBG labelled with iodine in neuroblastoma, and several others. Our perspectives have been put forth regarding the most important theranostic agents along with emerging trends and prospects.

Time-series analysis of rhenium(I) organometallic covalent binding to a model protein for drug development

Metal-based complexes with their unique chemical properties, including multiple oxidation states, radio-nuclear capabilities and various coordination geometries yield value as potential pharmaceuticals. Understanding the interactions between metals and biological systems will prove key for site-specific coordination of new metal-based lead compounds. This study merges the concepts of target coordination with fragment-based drug methodologies, supported by varying the anomalous scattering of rhenium along with infrared spectroscopy, and has identified rhenium metal sites bound covalently with two amino acid types within the model protein. A time-based series of lysozyme-rhenium-imidazole (HEWL-Re-Imi) crystals was analysed systematically over a span of 38 weeks. The main rhenium covalent coordination is observed at His15, Asp101 and Asp119. Weak (i.e. noncovalent) interactions are observed at other aspartic, asparagine, proline, tyrosine and tryptophan side chains. Detailed bond distance comparisons, including precision estimates, are reported, utilizing the diffraction precision index supplemented with small-molecule data from the Cambridge Structural Database. Key findings include changes in the protein structure induced at the rhenium metal binding site, not observed in similar metal-free structures. The binding sites are typically found along the solvent-channel-accessible protein surface. The three primary covalent metal binding sites are consistent throughout the time series, whereas binding to neighbouring amino acid residues changes through the time series. Co-crystallization was used, consistently yielding crystals four days after setup. After crystal formation, soaking of the compound into the crystal over 38 weeks is continued and explains these structural adjustments. It is the covalent bond stability at the three sites, their proximity to the solvent channel and the movement of residues to accommodate the metal that are important, and may prove useful for future radiopharmaceutical development including target modification.

Application of fluorocarbon nanoparticles of 131I-fulvestrant as a targeted radiation drug for endocrine therapy on human breast cancer

BACKGROUND

Breast cancer is the most prevalent malignant tumor among women, with hormone receptor-positive cases constituting 70%. Fulvestrant, an antagonist for these receptors, is utilized for advanced metastatic hormone receptor-positive breast cancer. Yet, its inhibitory effect on tumor cells is not strong, and it lacks direct cytotoxicity. Consequently, there's a significant challenge in preventing recurrence and metastasis once cancer cells develop resistance to fulvestrant.

METHOD

To address these challenges, we engineered tumor-targeting nanoparticles termed 131I-fulvestrant-ALA-PFP-FA-NPs. This involved labeling fulvestrant with 131I to create 131I-fulvestrant. Subsequently, we incorporated the 131I-fulvestrant and 5-aminolevulinic acid (ALA) into fluorocarbon nanoparticles with folate as the targeting agent. This design facilitates a tri-modal therapeutic approach-endocrine therapy, radiotherapy, and PDT for estrogen receptor-positive breast cancer.

RESULTS

Our in vivo and in vitro tests showed that the drug-laden nanoparticles effectively zeroed in on tumors. This targeting efficiency was corroborated using SPECT-CT imaging, confocal microscopy, and small animal fluorescence imaging. The 131I-fulvestrant-ALA-PFP-FA-NPs maintained stability and showcased potent antitumor capabilities due to the synergism of endocrine therapy, radiotherapy, and CR-PDT. Throughout the treatment duration, we detected no notable irregularities in hematological, biochemical, or histological evaluations.

CONCLUSION

We've pioneered a nanoparticle system loaded with radioactive isotope 131I, endocrine therapeutic agents, and a photosensitizer precursor. This system offers a combined modality of radiotherapy, endocrine treatment, and PDT for breast cancer.

DNA-Targeted Complexes of Tc and Re for Biomedical Applications

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

Bisphosphonates as Radiopharmaceuticals: Spotlight on the Development and Clinical Use of DOTAZOL in Diagnostics and Palliative Radionuclide Therapy

Bisphosphonates are therapeutic agents that have been used for almost five decades in the treatment of various bone diseases, such as osteoporosis, Paget disease and prevention of osseous complications in cancer patients. In nuclear medicine, simple bisphosphonates such as 99mTc-radiolabelled oxidronate and medronate remain first-line bone scintigraphic imaging agents for both oncology and non-oncology indications. In line with the growing interest in theranostic molecules, bifunctional bisphosphonates bearing a chelating moiety capable of complexing a variety of radiometals were designed. Among them, DOTA-conjugated zoledronate (DOTAZOL) emerged as an ideal derivative for both PET imaging (when radiolabeled with 68Ga) and management of bone metastases from various types of cancer (when radiolabeled with 177Lu). In this context, this report provides an overview of the main medicinal chemistry aspects concerning bisphosphonates, discussing their roles in molecular oncology imaging and targeted radionuclide therapy with a particular focus on bifunctional bisphosphonates. Particular attention is also paid to the development of DOTAZOL, with emphasis on the radiochemistry and quality control aspects of its preparation, before outlining the preclinical and clinical data obtained so far with this radiopharmaceutical candidate.

Nanoparticles based on MIL-101 metal-organic frameworks as efficient carriers of therapeutic188Re radionuclide for nuclear medicine

Nuclear medicine presents one of the most promising modalities for efficient non-invasive treatment of a variety of cancers, but the application of radionuclides in cancer therapy and diagnostics is severely limited by their nonspecific tissue accumulation and poor biocompatibility. Here, we explore the use of nanosized metal-organic frameworks (MOFs) as carriers of radionuclides to order to improve their delivery to tumour. To demonstrate the concept, we prepared polymer-coated MIL-101(Cr)-NH2MOFs and conjugated them with clinically utilized radionuclide188Re. The nanoparticles demonstrated high loading efficacy of radionuclide reaching specific activity of 49 MBq mg-1. Pharmacokinetics of loaded MOFs was investigated in mice bearing colon adenocarcinoma. The biological half-life of the radionuclide in blood was (20.9 ± 1.3) h, and nanoparticles enabled it to passively accumulate and retain in the tumour. The radionuclide delivery with MOFs led to a significant decrease of radioactivity uptake by the thyroid gland and stomach as compared with perrhenate salt injection, which is beneficial for reducing the side toxicity of nuclear therapy. The reported data on the functionalization and pharmacokinetics of MIL-101(Cr)-NH2for radionuclide delivery unveils the promising potential of these MOFs for nuclear medicine.