The choice of radionuclide—whether an alpha-emitter for targeted alpha therapy, a beta-emitter for radioligand therapy, or a positron/gamma-emitter for molecular imaging—dictates the chelator selection, labeling conditions, and purification strategies required for clinical-grade production. At Protheragen, our radiochemical services platform supports the manipulation of more than 30 diagnostic and therapeutic radionuclides, enabling one-stop radiolabeling solutions from early-stage precursor development through GMP-compliant commercial production for biotech and pharmaceutical partners worldwide.
Radiochemical services encompass the specialized techniques and infrastructure required to attach radioactive isotopes to biologically active molecules—such as small molecules, peptides, antibodies, antibody fragments, and nanoparticles—creating radiopharmaceuticals for diagnostic imaging or targeted therapy. The radiolabeling process is fundamentally governed by the coordination chemistry of the radionuclide: metallic radionuclides (e.g., Lu-177, Ga-68, Ac-225, Zr-89, Cu-64) require bifunctional chelating agents such as DOTA, NOTA, NODAGA, or DTPA derivatives to form stable coordination complexes, while halogen radionuclides (e.g., F-18, I-123, I-124, I-131, At-211) are typically incorporated through electrophilic substitution, nucleophilic substitution, or prosthetic group conjugation.
Fig 1. Schematic representation of radiolabeling. (Núñez-Salinas, Andrés, et al., 2025)
The stability of the radiometal-chelator complex is paramount, as in vivo transchelation or dissociation can lead to off-target radiation exposure, reduced therapeutic efficacy, and compromised imaging quality. Consequently, radiochemical services must integrate chelator design and screening, reaction condition optimization (pH, temperature, buffer composition, scavenger concentration), purification methodologies (solid-phase extraction, HPLC, size-exclusion chromatography), and comprehensive quality control testing including radiochemical purity, radionuclidic purity, specific activity, molar activity, and sterility assessment.
The complexity of radiochemical services extends beyond the benchtop reaction to encompass GMP-compliant production infrastructure, radiation safety protocols, and supply chain management for short-lived isotopes. Automated synthesis modules and cassette-based systems have become standard for clinical-grade production, minimizing human radiation exposure, ensuring batch-to-batch reproducibility, and enabling multi-dose preparation within the constrained timeframe imposed by radionuclide half-lives. For therapeutic radionuclides such as Ac-225 and Pb-212, the challenge is compounded by alpha-particle recoil effects that can destabilize the chelator complex, necessitating advanced chelator architectures and specialized quality control methods including gamma spectrometry for daughter nuclide detection. The field continues to evolve with the development of novel chelators (e.g., macropa for Ac-225, AAZTA5 for versatile radiometal binding), automated platforms for high-throughput screening, and integrated quality control workflows that satisfy both pharmaceutical GMP standards and nuclear medicine regulatory requirements across FDA, EMA, and NMPA jurisdictions.
Protheragen's radiochemical services platform is engineered to address the full spectrum of radionuclide chemistry challenges, from alpha-emitter chelation stability and beta-emitter therapeutic optimization to positron-emitter diagnostic precision and theranostic pair harmonization. With qualified capabilities across more than 30 diagnostic and therapeutic radionuclides, automated GMP synthesis infrastructure, and a dedicated team of radiochemists and quality control specialists, we deliver one-stop radiolabeling solutions that span precursor development, chelator optimization, process validation, and commercial-scale production—empowering our partners to accelerate radiopharmaceutical programs from concept to clinic with confidence and regulatory compliance.
| Nuclide | Full Name | Decay Mode | Half-Life | Energy | Primary Application | Chelator / Labeling Chemistry | Protheragen Service Scope |
|---|---|---|---|---|---|---|---|
| Ac-225 | Actinium-225 | Alpha | 9.9 days | 5.83 | Targeted Alpha Therapy (TAT) | DOTA, macropa, H2macropa, H4py4pa | Chelator optimization, radiolabeling, QC, stability assessment |
| Pb-212 | Lead-212 | Beta (Bi-212 generator) | 10.6 hours | 0.5685 | Targeted Alpha Therapy (indirect) | DOTA, TCMC | Generator coordination, chelation optimization, daughter nuclide monitoring |
| Th-227 | Thorium-227 | Alpha | 18.7 days | 6.083 | Targeted Alpha Therapy | DOTA, macropa derivatives | Chelator development, radiolabeling, stability validation |
| At-211 | Astatine-211 | Alpha | 7.2 hours | 5.982 | Targeted Alpha Therapy | Prosthetic groups (N-succinimidyl esters), direct electrophilic substitution | Halogenation optimization, purification, QC with gamma spectroscopy |
| Ra-223 | Radium-223 | Alpha | 1.4 days | 5.716 | Bone-Seeking Therapy | Ionic (chloride form) | Formulation, stability, bone uptake validation |
| Lu-177 | Lutetium-177 | Beta + Gamma | 6.7 days | 0.498 | Radioligand Therapy (RLT) | DOTA, NODAGA, AAZTA5 | Automated GMP synthesis, radiochemical purity >95%, specific activity validation |
| Y-90 | Yttrium-90 | Beta | 2.7 days | 2.288 | Radioligand Therapy / Radioembolization | DOTA, DTPA | Chelator screening, radiolabeling, microsphere formulation, QC |
| Tb-161 | Terbium-161 | Beta + Auger | 6.9 days | 0.59 | Radioligand Therapy | DOTA | Chelator optimization, radiolabeling, stability, QC for preclinical/clinical evaluation |
| Ho-166 | Holmium-166 | Beta + Gamma | 1.1 days | 1.8757 | Radioembolization / Therapy | DOTA, resin-based microspheres | Microsphere labeling, formulation, QC, radioembolization validation |
| Re-188 | Rhenium-188 | Beta + Gamma | 0.7 days | 2.128 | Therapy (generators) | HEDP, DTPA, DOTA | Generator coordination, chelation optimization, formulation, QC |
| Re-186 | Rhenium-186 | Beta + Gamma | 3.8 days | 1.076 | Therapy | HEDP, DTPA | Radiolabeling, formulation, stability, QC |
| Sm-153 | Samarium-153 | Beta + Gamma | 1.9 days | 0.81 | Bone Pain Palliation | EDTMP, DOTA | Chelator conjugation, radiolabeling, formulation, QC |
| Cu-67 | Copper-67 | Beta + Gamma | 2.6 days | 0.577 | Radioligand Therapy | DOTA, NOTA, TETA | Chelator optimization, radiolabeling, stability, QC |
| Sc-47 | Scandium-47 | Beta + Gamma | 3.3 days | 0.6 | Radioligand Therapy | DOTA | Chelator development, radiolabeling, QC for preclinical evaluation |
| I-131 | Iodine-131 | Beta + Gamma | 8.0 days | 0.6065 | Therapy / SPECT | Direct iodination (I-), prosthetic groups | Iodination optimization, formulation, QC, stability |
| F-18 | Fluorine-18 | Positron | 1.8 hours | 0.635 | PET Imaging | Direct fluorination (C-F bond), prosthetic groups (N-succinimidyl [18F]fluorobenzoate) | Automated synthesis module development, precursor optimization, QC |
| Ga-68 | Gallium-68 | Positron | 1.1 hours | 1.899 | PET Imaging | DOTA, NOTA, NODAGA, AAZTA5 | Automated synthesis, high radiochemical purity, specific activity validation |
| Cu-64 | Copper-64 | Positron | 12.7 hours | 0.635 | PET Imaging | DOTA, NOTA, TETA | Chelator screening, radiolabeling, purification, QC |
| Zr-89 | Zirconium-89 | Positron | 3.3 days | 0.902 | Immuno-PET | DFO, next-generation chelators | Chelator development, radiolabeling, purification, QC |
| Tb-149 | Terbium-149 | Positron + Alpha | 4.1 hours | / | PET Imaging / Alpha Therapy | DOTA, macropa | Specialized chelator development, automated synthesis, QC |
| Sc-44 | Scandium-44 | Positron | 4.0 hours | 0.635 | PET Imaging | DOTA, NOTA | Chelator optimization, radiolabeling, QC |
| Y-86 | Yttrium-86 | Positron | 14.7 hours | / | PET Imaging (therapy surrogate) | DOTA | Radiolabeling, dosimetry validation, QC |
| Pb-203 | Lead-203 | Positron | 2.2 days | / | PET Imaging | DOTA, TCMC | Chelator development, radiolabeling, QC |
| I-124 | Iodine-124 | Positron | 13.2 hours | 1.533 | PET Imaging / Dosimetry | Direct iodination, prosthetic groups | Iodination optimization, purification, QC for therapy dosimetry |
| Tc-99m | Technetium-99m | Gamma (IT) | 6.0 hours | 0.141 | SPECT Imaging | HYNIC, MAG3, direct reduction, DTPA | Kit formulation, labeling optimization, QC per pharmacopeial standards |
| In-111 | Indium-111 | Gamma | 2.8 days | 0.245 | SPECT Imaging | DTPA, DOTA | Chelator conjugation, radiolabeling, automated synthesis, QC |
| I-123 | Iodine-123 | Gamma | 0.55 days | / | SPECT Imaging | Direct iodination | Iodination optimization, formulation, QC |
| Ga-67 | Gallium-67 | Gamma | 68.3min | 1.899 | SPECT Imaging | Citrate (ionic) | Formulation, QC for established SPECT protocols |
| Tl-201 | Thallium-201 | Gamma | 3.0 days | / | SPECT Imaging | Ionic (chloride) | Formulation, QC for cardiac imaging |
| Pd-103 | Palladium-103 | Auger + X-ray | 17.5 days | / | Brachytherapy | Metallic seed encapsulation | Seed fabrication, quality assessment, brachytherapy support |
The radiochemical services workflow is a systematic, multi-stage process that transforms a targeting vector precursor into a clinical-grade radiopharmaceutical through chelator conjugation, radionuclide incorporation, purification, and quality-controlled release. Each stage demands precise coordination between radiochemistry, analytical science, quality assurance, and regulatory compliance to ensure product safety, efficacy, and batch-to-batch reproducibility.
The workflow begins with selection or design of the targeting vector (small molecule, peptide, antibody, or fragment) and identification of the optimal bifunctional chelator or prosthetic group matched to the intended radionuclide. For metallic radionuclides, chelators such as DOTA, NOTA, NODAGA, DTPA, or specialized architectures (macropa for Ac-225, DFO for Zr-89) are evaluated for coordination kinetics, thermodynamic stability, and in vivo inertness. For halogen radionuclides, prosthetic groups or direct labeling strategies are selected based on the vector's chemical reactivity and the radionuclide's incorporation chemistry.
The bifunctional chelator or prosthetic group is conjugated to the targeting vector via standard organic chemistry techniques (amide coupling, thiol-maleimide, click chemistry, etc.), followed by comprehensive characterization using mass spectrometry, HPLC, and NMR to confirm identity, purity, and conjugation efficiency. The resulting precursor is formulated, stored under appropriate conditions, and subjected to stability testing to establish shelf-life before radiolabeling.
The selected radionuclide is procured from cyclotron facilities, reactor sources, or generator systems (e.g., Ge-68/Ga-68, W-188/Re-188, Mo-99/Tc-99m) and subjected to incoming quality control including radionuclidic identity (half-life verification, gamma spectroscopy), radionuclidic purity, specific activity determination, and chemical purity assessment. For short-lived isotopes, just-in-time delivery logistics are coordinated to minimize decay losses.
Radiolabeling conditions are optimized for each radionuclide-precursor pair, including pH adjustment, buffer selection, temperature, reaction time, metal scavenger concentration, and precursor-to-radionuclide molar ratio. For metallic radionuclides, this involves chelation kinetics optimization; for halogen radionuclides, nucleophilic or electrophilic substitution conditions are refined. Downscale models are employed for alpha-emitters to minimize radiation exposure and waste during development.
The crude radiolabeled product is purified using solid-phase extraction (SPE), preparative HPLC, size-exclusion chromatography, or ion-exchange chromatography to remove unbound radionuclide, unreacted precursor, and chemical impurities. The purified product is formulated in an appropriate vehicle (saline, buffer, ethanol/saline mixture) with pH adjustment, filtered for sterility, and dispensed into single-dose or multi-dose vials under aseptic conditions.
Comprehensive quality control testing is performed prior to batch release, including visual inspection, pH measurement, radiochemical purity (radio-TLC, radio-HPLC), radionuclidic purity (gamma spectroscopy, half-life verification), specific activity or molar activity, chemical purity, sterility, endotoxin levels, and stability assessment. For therapeutic radiopharmaceuticals, acceptance limits are typically 95–105% of label claim; for diagnostics, 90–110%.
The formulated radiopharmaceutical is subjected to real-time and accelerated stability studies under simulated clinical storage and use conditions to determine shelf-life, identify degradation pathways, and establish release and expiry specifications. For short-lived isotopes, in-use stability studies validate the timeframe for clinical administration after formulation.
Upon successful optimization, the radiolabeling process is validated for GMP production, including demonstration of batch-to-batch reproducibility, identification of critical process parameters, and establishment of control strategies. Technology transfer to automated synthesis modules or GMP production suites is executed with comprehensive documentation, operator training, and continued process verification to support clinical and commercial manufacturing.
Whether you are developing a novel alpha-emitter therapeutic requiring specialized chelator design, optimizing a beta-emitter radioligand therapy for clinical translation, or seeking a reliable partner for GMP-compliant diagnostic tracer production, Protheragen's radiochemical services team is ready to support your program. Reach out to us today to discuss your radionuclide requirements, explore our chelation chemistry capabilities, and discover how our integrated radiochemical platform can accelerate your radiopharmaceutical from precursor development to clinical supply. Contact us to schedule a consultation and take the next step in bringing your radiopharmaceutical innovation to patients.
Reference