¹²⁵I-Radiolabeling Service

Due to its unique value on the market, owning its own half-life of 59.4 days, along with the low-energy gamma emissions, the ¹²⁵I radiolabeling is a key tool for extremely sensitive in-vitro and ex-vivo quantitative analysis, pertaining to receptor binding, radioimmunoassays (RIA), and autoradiography, among others. Alfa Cytology offers custom ¹²⁵I-radiolabeling services to supply high-purity and high-specific-activity tracers designed specifically for the precision and reproducibility of your biological assays.

Introduction to ¹²⁵I Isotopes

Iodine-125 (¹²⁵I) is a radioisotope with a half-life of 59.4 days and decays via electron capture, emitting low-energy gamma photons and Auger electrons. Its radiation is not capable of penetrating tissue deep enough, and thus, ¹²⁵I cannot be used for in vivo imaging techniques such as SPECT. However, iodine-125 has a long shelf-life and is highly sensitive, which is why it is the gold standard for in-vitro RIAs and a multitude of other laboratory tests, ex-vivo autoradiography, and other laboratory uses. Its localized energy deposition is also favorable for cancer therapy via sealed brachytherapy seeds, which is why it is an important isotope for cancer therapy.

¹²⁵I -Labeling for SPECT Imaging

In radiopharmaceutical research, iodine-125 (¹²⁵I) is a recognized radionuclide that has a relatively long physical half-life of 59.4 days. Its decay is through electron captures, which release low-energy gamma and X-ray photons. Although low-energy emissions of photons make iodine-125 unsuitable for in-vivo SPECT imaging, but is well-suited for a large array of in-vitro and ex-vivo applications. Stability and long half-life have made iodine-125 a gold standard for RIAs, receptor-ligand binding assays, and autoradiography.

Fig.1 Chemical structures of [¹²⁵I]-labeled chalcone derivatives. (TESSE G, et al., 2024)

¹²⁵I Radiopharmaceutical

Disclaimer: Alfa Cytology focuses on providing preclinical research services. This table is for information exchange purposes only. This table is not a treatment plan recommendation. For guidance on treatment options, please visit a regular hospital.

Common ¹²⁵I Targets

• Tumor Cell Surface Antigens

Monoclonal antibodies or small molecule drugs labeled with iodine-125 are routinely used to target tumor-associated antigens, including HER2, EGFR, and PSMA, present on the surfaces of tumor cells and facilitate specific tumor imaging and targeted therapy.

• Neuroendocrine Receptors

Some somatostatin receptors (SSTR) and other receptors on neuroendocrine tumor cells can be selectively targeted by ¹²⁵I-labeled molecules of peptides. This helps to diagnose and treat neuroendocrine tumors.

• Immune Cell Receptors

¹²⁵I can bind to receptors on immune cells, aiding in the study of immune responses and cell function. ¹²⁵I-labeled antibodies enable quantitative analysis of these immune responses.

• Enzymes

Some ¹²⁵I-labeled molecules serve as substrates or inhibitors for specific enzymes, particularly those involved in key metabolic processes like proteases or kinases.

• Vascular Endothelial Cell Receptors

During the early stage of other diseases like inflammation and cancer, targeted vascular imaging and therapies are possible with the use of ¹²⁵I-labeled molecules, which can bind to receptors on vascular endothelial cells.

Our Services

Alfa Cytology has always focused our efforts on pioneering the development and refinement of ¹²⁵I-labeled conjugations for further improving the accuracy and effectiveness of tumor-targeted therapies. And in the course of pursuing the innovative design of radiopharmaceuticals, our company actively engages in the development of ¹²⁵I radiopharmaceuticals for cancer and molecular imaging to make these procedures safer and more effective.

Custom ¹²⁵I Conjugation Service

The ¹²⁵I conjugation service provides expert chemical labeling of novel research compounds, delivering highly pure and extremely stable radioligands ideal which can be used for the stringent and most sensitive in vitro experiments, including radioimmunoassays and receptor binding studies.

Small-Molecule Radionuclide Conjugate (SMRC)

Antibody-Radionuclide Conjugate (ARC)

Peptide-Radionuclide Conjugate (PRC)

siRNA-Radionuclide Conjugate

Radiolabeling Small Molecules with¹²⁵I for SPECT Imaging

¹²⁵I Custom Radiosynthesis

• Design Labeling Position: Analyze the drug's chemical structure to select a metabolically stable position for the ¹²⁵I label. The goal is to ensure the ¹²⁵I tag remains on the core scaffold after metabolic breakdown, allowing for the tracking of as many metabolites as possible.
• Design Synthesis Route: Choosing the ideal approach for iodination (Direct electrophilic substitution using Chloramine-T, Iodogen, or the indirect labeling using the Bolton-Hunter reagent). Also, optimizing different reaction parameters like the precursor concentration, pH, temperature, and time to maximize yield and purity.
• Custom Radiosynthesis: A dedicated team in radiochemistry executes the ¹²⁵I-labeling synthesis. The synthesis is done in a controlled environment using remote handling techniques in lead-shielded hot cells. The synthesis reaction is closely monitored for consistent and reproducible outcomes.

Purification & Quality Control

The product is thoroughly purified and tested for quality after synthesis to ensure performance and dependability for your research. Proper isotopic labeling as well as the compound's purity and stability are assessed through liquid chromatography (LC), mass spectrometry (MS), and scintillation counting.

In Vitro Evaluation

In vitro tests are performed to evaluate the biological properties of the ¹²⁵I-labeled radiopharmaceutical. This includes studying its interaction with target receptors, cellular uptake, metabolic stability, and other pharmacological properties.

In Vivo Evaluation

This important step begins with carrying out quantitative biodistribution and pharmacokinetic (PK) studies, which aim to assess the extent of accumulation of the agent under study in different organs and the rate at which it is eliminated from the body. Subsequently, SPECT imaging is done in appropriate disease models to assess whether the agent actually engages the given target and to prove the agent's ability to diagnose the disease in vivo through blocking experiments.

Applications of ¹²⁵I-Radiolabeling

With long half-lives and low-energy photon emissions, ¹²⁵ I-radiolabeling applications are focused on its use as the gold standard for highly sensitive in vitro and ex vivo quantitative techniques. Radioimmunoassays, receptor binding assays, and even autoradiography are within this scope.

Why Choose Us?

We offer services that range from molecular design to preclinical testing, such that every stage of development is seamlessly integrated, ensuring efficiency, accuracy, and compliance with regulatory standards.

Experience in ¹²⁵I Chemistry

Full-Service Development

State-of-the-Art Facilities

Application-Specific Tailored Solutions

Alfa Cytology has set up a modern development platform with a unique edge, which allows it to easily conduct diverse ¹²⁵I-labeling, from direct radioiodination to complicated multi-step conjugations. If you have difficulty or a question concerning your project, please reach out to us, and we will provide you with tailored solutions that you may need.

Reference

1. TESSE G, TOLOMEO A, DE FILIPPIS B, et al. Radiolabeled Probes from Derivatives of Natural Compounds Used in Nuclear Medicine [J]. Molecules (Basel, Switzerland), 2024, 29(17).

For research use only. Not intended for any clinical use.